Title Page
 Table of Contents
 List of Tables
 Literature review
 Materials and methods
 Results and discussion
 Summary and recommendations
 Biographical Sketch

Title: The nature of phosphorus uptake and release by organic soils under laboratory conditions
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00086021/00001
 Material Information
Title: The nature of phosphorus uptake and release by organic soils under laboratory conditions
Physical Description: x, 310 leaves : ill. ; 28 cm.
Language: English
Creator: Mestan, Richard John, 1952-
Publication Date: 1986
Subject: Histosols   ( lcsh )
Soils -- Phosphorus content   ( lcsh )
Phosphorus   ( lcsh )
Environmental Engineering Sciences thesis Ph. D
Dissertations, Academic -- Environmental Engineering Sciences -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Thesis: Thesis (Ph. D.)--University of Florida, 1986.
Bibliography: Bibliography: leaves 298-309.
Statement of Responsibility: by Richard John Mestan.
General Note: Typescript.
General Note: Vita.
 Record Information
Bibliographic ID: UF00086021
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000893983
oclc - 15300516
notis - AEK2510

Table of Contents
    Title Page
        Page i
        Page ii
        Page iii
    Table of Contents
        Page iv
        Page v
    List of Tables
        Page vi
        Page vii
        Page viii
        Page ix
        Page x
        Page 1
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        Page 3
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    Literature review
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    Materials and methods
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    Results and discussion
        Page 122
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    Summary and recommendations
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    Biographical Sketch
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Full Text








The following people are hereby acknowledged in regard

to my completion of this work and their respective roles are


1. My parents Mr. & Mrs. John G. Mestan for their love

in addition to moral and financial support which brought me

the opportunity to do this in the first place.

2. The federal government Guaranteed Student Loan

(GSL) program and its participating bank, Florida Federal

Savings of St. Petersburg for lending me the extra money

needed to complete this work.

3. The members (old and new) of my supervisory

committee; John Zoltek, Jr. (Chairman), Joseph Delfino, Bob

Volk, Ben Koopman, John McCreary, Del Bottcher and Barry

Baldwin for their support and advice.

4. Frank Sodek, Larry Schwartz, Mark Brenner and Ray

Bienert for their assistance at various stages of this work.

5. Shirley Jordan for her assistance and advice in

technical aspects and construction of the many items needed

for laboratory experiments.

6. Katherine Williams (Professional Typing) and her

staff for their excellent work in typing and putting

together this document. Also to Hoa Dang-Vu for her

patience and effort in organizing and typing an earlier


7. Jim Heaney in Water Resources for his patience in

regard to completion of the EPA project report which

comprised an earlier version of this dissertation.

8. The music station ROCK 104 and staff for providing

the ample amounts of Rock n Roll that made many hours of

tedious laboratory work more bearable.






ABSTRACT . . . . .



Global Distribution and Abundance of
Phosphorus . . . .
The Need for Phosphorus and Man's Impact on
the Global Cycle . . .
The Role of Soils in Phosphorus Control .
Objective . .. . .
Note . . . . .


Soil Phosphorus Retention . . .
Laboratory Studies . .. .
Fate of Phosphorus in Wetlands Treated with
Wastewater . . . .
Notes . . . .


Digestion Methods Used to Determine Total
Phosphorus . . . .
Collection of Soil Samples . .
Determination of Measurable Soil Properties
Phosphorus Uptake by Clermont Marsh Peat .
Phosphorus Uptake by 13 Organic Soils (Batch
Test A) .. . . .. .
Phosphorus Uptake by 18 Organic Soils (Batch
Test B) . . .
Phosphorus Uptake and Release of 20 Soils
(Batch Test C) . . .


. ii

. vi

* ix

S. xi

S. .78
. 84
S. .87
. 100

. 103

. 106

. 107

. .



Phosphorus Uptake and Release of 10 Peat Soils
(Column Test I) . . . 111
Phosphorus Uptake and Release of 10 Peat Soils
(Column Test II) . . ... 116
Note . . . . . 121


Total Phosphorus Content of Clermont Peat Using
Four Digestion Methods . . .. 123
Evaluation of Ignition Digestion Method with
EPA Sludge . . . . 128
Sand Content of Organic Soils . .. 132
Phosphorus Uptake Capacity of Soil Sands .. 136
Measurable Soil Properties of Organic Soils 146
Phosphorus Uptake by Organic Soils . .. 172
Interpretation and Discussion (Batch Tests A
and B) . . . . 198
Phosphorus Uptake and Release Using 20 Soils
(Batch Test C) . . . 213
Phosphorus Uptake and Release (Column Test I) 230
Phosphorus Uptake and Release (Column Test II) 249
Notes . . . . .. .. 274

V CONCLUSIONS . . . . 276


A Method to Evaluate a Wetland Soil for
Wastewater Treatment . . . 282
Notes . . . . 296

BIBLIOGRAPHY . . . . . 298



Table Table Title or Short Form Thereof Page

2-1 Natural Wetlands Used for Wastewater
Treatment . . . ... .66

2-2 Artificial Wetlands Used for Wastewater
Treatment . . . ... .76

3-1 Identification and Locations of Organic
Soils and Sediments . . .. 85

3-2 Summary of Phosphorus Uptake Parameters
Used for Batch Tests A and B . .. 104

3-3 Summary of Phosphorus Uptake and Release
Parameters--Column Test I . .. .. 112

3-4 Summary of Phosphorus Uptake and Release
Parameters--Column Test II . ... .120

4-1 Total Phosphorus Content of Clermont Peat-
Auto Analyzer Analysis. . ... 123

4-2 Total Phosphorus Content of Clermont Peat-
Spectrophotometer Analysis . .. .. 124

4-3 Total Phosphorus Content of EPA Sludge 131

4-4 Total Iron Content of EPA Sludge . .. .131

4-5 Total Aluminum Content of EPA Sludge . 133

4-6 Comparison of Sand Obtained Between Washing
and Ignition Methods . . .. 139

4-7 Phosphorus Uptake by Soil Sands Under Batch
Conditions . . . . 140

4-8 Assessment of Sand Contribution to Sorption
of Phosphorus by Whole Soils . .. 143

4-9 Relationships Between Ash Contents and Total
Phosphorus, Iron and Aluminum ...... 152

Table Table Title or Short Form Thereof Page

4-10 Linear Correlations Between Measurable
Soil Properties . . . 152

4-11 Solution pH Comparison Between Initial pH
Values and Those Obtained from Maximum
KH2PO4 Addition and Batch Mixing . 170

4-12 Comparison of the Freundlich and Langmuir
Models to Fit the Equilibrium Sorption of
Phosphorus (Batch Run A) . . 199

4-13 Comparison of the Freundlich and Langmuir
Models to Fit the Equilibrium Sorption of
Phosphorus (Batch Run B) . .. .. 200

4-14 Linear Correlations Between Phosphorus
Uptake at 5 ppm P-Batch Test A . 203

4-15 Linear Correlations Between Phosphorus
Uptake at 10 ppm P-Batch Test A . 204

4-16 Linear Correlations Between Phosphorus
Uptake and Freundlich K Values-
Batch Test A . . . .. 205

4-17 Linear Correlations Between Phosphorus
Uptake at 5 ppm P-Batch Test B . .. 210

4-18 Linear Correlations Between Phosphorus
Uptake at 10 ppm P-Batch Test B . 211

4-19 Linear Correlations Between Phosphorus
Uptake and Freundlich K Values-
Batch Test B . . . .212

4-20 Summary of Sequential Batch Tests Cl, C2
and C3 Phosphorus Uptake and Release . 214

4-21 Phosphorus Uptake-Comparison of Tests A, B
and C . . . . 217

4-22 Correlations of Phosphorus Uptake with
Measurable Soil Properties-Batch Test C 219

4-23 Summary of Phosphorus Uptake and Release-
Column Test I . . . . 244

4-24 Summary of Phosphorus Uptake and Release-
Column Test II .. . . .. 261

4-25 Comparison of Phosphorus Uptake and Release
Between Column Tests I and II ... 263


4-26 Effluent pH Values Measured for Column
Test II During Phosphorus Dosing and
Leaching . . . . 265

4-27 Comparison of Phosphorus Uptake Values
Between Column Tests I, II & Batch Test C .267



Table Title or Short Form Thereof


Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy



Richard John Mestan

August, 1986

Chairman: John Zoltek, Jr.
Major Department: Environmental Engineering

Results of past field studies involving the treatment

of domestic wastewater using wetlands have demonstrated a

poor understanding of the role that soils play in regard to

uptake and release of phosphorus. The main objective of

this laboratory study was to investigate the phosphorus

uptake characteristics of wetland organic soils to aid in

future predictions concerning the fate of phosphorus using

wetland treatment.

The initial phase of this study was devoted to finding

a suitable procedure for determining the total phosphorus

content of organic soils. A number of different techniques

were compared using marsh peat and EPA sludge. The second

phase of the study was devoted to determining the phosphorus

uptake capabilities of various organic soils under batch

laboratory conditions. An attempt was made to identify soil

components responsible for phosphorus uptake by statisti-

cally correlating uptake with measurable properties that

included pH, ash content, native phosphorus, total iron and

aluminum as well as extractable iron and aluminum. The

third phase of the study was devoted to organic soil phos-

phorus uptake and retention under leaching conditions. This

was accomplished by performing batch laboratory and column

tests using artificial wastewater spiked with inorganic


Results of the initial phase of this work showed that a

slightly modified version of the ignition digestion method

to be the best of four methods compared when considering

factors such as accuracy, precision, simplicity and safety.

Results of the second phase of this work showed the phos-

phorus uptake characteristics of organic soils were related

to their mineral contents but the correlations between

uptake and extractable iron and aluminum were not signifi-

cantly higher than those obtained with total iron and

aluminum. Results of the third phase of this work demon-

strated that low ash organic soils had small phosphorus

uptake capacities and could not retain phosphorus under

leaching conditions. Higher ash peat soils could fix and

retain more phosphorus, but significant amounts could be

still leached using rainwater. It also appeared that the

phosphorus uptake capacities of the organic soils were

positively related to temperature and pH within the acid




Global Distribution and Abundance of Phosphorus

Phosphorus ranks about tenth in abundance of the

elements in the earth's upper crust. Brinck (1978) reported

that the average concentration of phosphorus in the environ-

ment is about 0.1% by weight. Although widely distributed

in nature, phosphorus is never found in a free or uncombined

state because of its affinity for oxygen. When the molten

surface of the earth solidified over four billion years ago,

its fixed quantity of phosphorus became bound in igneous

rock in the form of orthophosphate. With the advent of the

first rainstorms, the gradual process of liberation and

redistribution of phosphorus began and continued for about

three billion years. This event marked the beginning of

redistribution of phosphorus in the form of sedimentary

deposits. The oceans deposited excess phosphorus in both

chemical and biological form as they inundated land masses.

This geological accumulation has converted slightly over

half of the earth's phosphorus from igneous rock to sedimen-

tary deposits, which account for 85% of the phosphate rock

that is currently mined (Griffith, 1978). The remaining 15%

of igneous origin comes mostly from the Kola peninsula in

the USSR. Based on the size and growth rate of annual

production, Brinck also reported the global phosphorus

reserves to be approximately 20 x 10 metric tons

(22 x 10 tons). On a broader basis, the total amount of

phosphorus resources have been estimated to be between

40 x 10 and 500 x 10 metric tons. In the absolute sense,

the global supply of phosphorus is considered to be very

large in that the current reserves alone are estimated to

satisfy current consumption for many hundreds of years.

The Need for Phosphorus and Man's
Impact on the Global Cycle

Despite the abundance of global reserves, phosphorus is

naturally present as a minor constituent in soils ranging

from 0.02 to 0.5 percent with an average of only

0.05 percent. The only natural pathway of phosphorus to the

soil solution pool is from gradual mineral weathering.

Unfortunately this does not meet the existing demand for

phosphorus to grow crops which feed the world's population.

Therefore, large amounts of phosphorus are needed to supple-

ment this deficiency which ranks second only to nitrogen as

the major soil fertility problem in the world (Lindsay and

Vlek, 1977).

Phosphorus is an important mineral in the human diet.

It is contained in the major food groups and the RDA for

adults is 800 mg. In addition to using phosphorus directly

in food, mankind utilizes large quantities of phosphorus in

detergents of which it is a primary ingredient.

The impact of man on the global phosphorus cycle,

therefore, is a result of the need to supplement agricul-

tural, domestic and to a certain extent, industrial demands.

This is illustrated in Figure 1-1 which shows the natural

pathways of phosphorus in addition to the pathways due to

man's activities. Griffith (1978) reported the phosphate

rock that has been mined in the history of the earth at

about two billion tons. As far as the global phosphorus is

concerned, this is only about 0.15 percent of the total

phosphorus reserves and less than 5 x 10-5 percent of the

earth's total phosphorus! However, this relatively small

amount of phosphorus has had a significant effect on both

man and his environment. The world's population has quad-

rupled as a consequence of using phosphorus to increase food

production. Figure 1-1 also shows that the phosphorus that

man has injected into the cycle has a major effect on the

freshwater component. In the same way that phosphorus has

increased crop production, it also has caused overproduction

eutrophicationn) in freshwaters where it is not desired.

The Role of Soils in Phosphorus Control

Mankind's use of phosphorus results in a unique para-

dox. On one hand, it desired to obtain the highest possible

crop production by maximizing the availability of phosphorus

to plants. Conversely, it is also desired to minimize the

amount of phosphorus which reaches freshwaters and causes

pollution. The contradiction arises from the fact that



1. Precipitation and deposition
from seawater . ..

2. Biological collection and
deposition . .
3. Precipitation/adsorption .
4. Mining and processing by man
5. Weathering and biological use
6. Runoff of soluble phosphorus.




* Billions of Tons
. 5.5 x 105 Tons/yr (birds)
* 2.0 x 106 Tons/yr
. 1.5 x 106 Tons/yr
* 2.0 x 106 Tons/yr
* 3.3 x 10 Tons/yr

At least a 100 million years before mankind exerted
any influence on the phosphorus cycle a natural pattern
had already been established. Basically, the sedimentary
phosphorus that is deposited on land by the seas eventually
returns to the sea as a consequence of biological use and
weathering. The estimated turnover time of phosphorus in
the oceans is 50,000 years, which is much shorter than the
three billion years required to saturate the oceans with
phosphorus for the first time. Until the 19th century
mankind caused no significant influence on the natural
phosphorus cycle. At present, modern man has only slightly
influenced the phosphorus cycle on a global scale.
(Griffith, 1978)

Figure 1-1. Global Phosphorus Cycle and Mankind's Influ-

achieving success in either one of those goals can lead to

failure in the other. Only about 15 percent of the phos-

phorus that is mined annually reaches freshwater. This is

because the majority of mined phosphorus that is used in

fertilizer becomes tied up with the soil. From an agricul-

tural standpoint, this is not good because a significant

portion of the phosphorus fixed by soils is irreversible and

unavailable to plants. From an environmental standpoint,

this is good because the soils have played a role in pre-

venting the majority of phosphorus from reaching freshwaters

where it is usually detrimental. Bailey (1968) pointed out

that for agricultural purposes, land having high phosphorus

fixation power poses a problem. However, for use as a

wastewater soil treatment system, these types of soils are



The objective of this work was to assess the phosphorus

uptake potential (fixation power) of organic soils (histo-

sols) that are native to wetland environments. This was

accomplished by measuring phosphorus uptake and retention of

organic soil samples under laboratory conditions and relat-

ing it to predetermined soil properties.


The term resources is used to represent reserves plus
all such materials which might become economically recover-
able in more favorable conditions.



Soil Phosphorus Retention


Since Way (1850) demonstrated that soils retained

soluble phosphate, scientists have strived to learn more

about their phosphorus fixing capacities. This knowledge

was first desired because of the need to determine the

fertilizer requirements which maximized the amount of

available phosphorus for crops and forests. In more recent

times, environmental scientists have studied the importance

of knowing how soils react with phosphorus contained in

wastewaters. and agricultural runoff. Numerous efforts have

been undertaken to describe the mechanisms and factors that

govern soil phosphorus retention. Despite the voluminous

amount of work that has been done, the exact mechanisms and

factors are still not fully understood. Syers and Iskandar

(1981) point out that comparing results in the literature is

difficult because of the widely different experimental

conditions that have been employed. It appears that the

results of phosphorus retention studies are very dependent

upon the conditions under which phosphorus retention is

measured and by the methods used to express it. The follow-

ing sections present some of the fundamental schools of

thought concerning phosphorus retention mechanisms and the

important factors which affect phosphorus uptake by soils.

It should be noted that the word "retention" is used as a

general term here to describe how soils react with phos-

phorus without implying any particular mechanism. In

addition, other terms such as "uptake" or "fixation" will

also be used interchangeably to refer to phosphorus reten-

tion in a general sense.

Phosphorus Retention Mechanisms--Reviews

Larsen (1967) was a proponent of the precipitation/dis-

solution theory of phosphorus interaction with soils. He

felt that the upper limit of phosphorus concentration in

solution is set by the heterogeneous equilibria in which it

takes part. The two main reaction types involved are the

dissolution and precipitation of sparingly soluble salts and

the adsorption of phosphorus on the surface of soil parti-

cles. The relevant sparingly soluble salts are those of Mg,

Ca, Al and Fe. Larsen felt that any lack of agreement

between phosphorus concentrations and that predicted by

solubility products did not exclude them as controlling

factors. Larsen attributed these discrepancies to incom-

plete understanding of solubility products and complications

of impurities. He felt that for neutral and calcareous

soils, hydroxyapatite was the principal solid phase which

controlled phosphorus equilibria. Conversely, at pH values

of 5 and below the solubility of Al phosphate (variscite) is

the controlling factor. Even in the absence of precipitat-

ing ions, phosphorus will still be removed from solution by

adsorption onto the surface of soil particles such as clay

or calcium carbonate. As the adsorption system becomes more

saturated with phosphorus, the concentration of phosphorus

in solution will increase to a point when precipitation of a

sparingly soluble phosphorus compound will occur. If the

phosphorus concentration is lowered, sparingly soluble

phosphate will dissolve until the adsorption complex has

been saturated to a degree which corresponds to the solu-

bility of the least stable phosphorus compound present.

Larsen felt that other influences that distorted solubility

predictions included lack of equilibrium (i.e., kinetics),

microbial activity, influence of soil:solution ratio and

formation of soluble complexes.

Bailey (1968) stated that the adsorption complex of a

soil consisted mainly of colloidal substances which could be

either organic or inorganic in nature. The noncolloidal

materials such as silt and sand are not significant. The

active inorganic fractions consist of clays and Fe and Al

sesquioxides1 while the organic counterparts are the humic

components of soil organic matter. Adsorption has been

suggested as one of the mechanisms responsible for the

fixation of phosphorus by soils, but the mechanism has not

been clearly defined or described. In many cases,

investigators have called the uptake of phosphorus by the

soil "adsorption" whereas no direct evidence has substanti-

ated this. Bailey pointed out the argument that observed

agreements between soil phosphorus uptake data and Langmuir

or Freundlich isotherms are not sufficient proof of adsorp-

tion. To ascertain unequivocally whether true adsorption

occurs, the problem would have to be studied by infared

and/or NMR spectroscopy.

Bailey (1968) maintained that research has verified

phosphorus fixation by acid soils to be a result of the

formation of Al and Fe compounds. Results indicate that Al

is more important than Fe in phosphorus fixation. Some

investigators are proponents of the theory that phosphorus

fixation can occur by isomorphic replacement (specific anion

adsorption). This reaction is characterized by the substi-

tution of phosphate ions for hydroxyl ions in clay minerals

or hydrated oxides of Al and Fe. Regardless of the sorption

mechanism, the increased population of phosphorus anions on

the soil surface favors structural breakdown and recrystal-

lization of phosphorus compounds. Although the same results

can occur by direct precipitation, the different pathways

are a function of environmental conditions.

Parfitt (1978) noted that reactive sites for anion

adsorption in pure systems consist of the singly coordinated

A1'OH and Fe'OH groups which are exposed at surfaces. These

groups exist at the edge of clay minerals and on the sur-

faces of hydrous oxides and therefore are present in most

soils. Many workers have correlated extractable Fe and Al

in soils with adsorption data. The Tamm acid oxalate

reagent introduced by Tamm in 1932 has been widely used to

extract Fe and Al from soils and is described by Saunders

(1965). This reagent is thought to cause dissolution of

amorphous Fe and Al compounds which are believed to be

responsible for phosphorus adsorption. Parfitt noted the

arguments between the adsorption versus the precipitation

mechanisms in soil phosphorus uptake. Although there had

been a general consensus that crystalline Fe and Al phos-

phates do not persist in acid soils, recent work suggested

that basic Al phosphates may form in acid soils even at low

phosphorus concentrations. In regard to organic components

of soils, Parfitt noted that humic and fulvic acids form

complexes with Fe and Al ions. It has been reported that

part of the Al which reacted with humic acid was exchange-

able and could adsorb phosphate and other anions. In

addition, Fe is also strongly completed by humic and fulvic

acids and has been shown to react with phosphorus by adsorp-

tion onto these complexes. Significant correlations

obtained between soil organic matter and phosphorus uptake

have verified that phosphorus is adsorbed by Fe or Al ions

that are chelated to large organic molecules. However,

Parfitt also noted reports that phosphorus is sometimes

weakly held on organic soils and can be removed by leaching.

Ryden and Pratt (1980) noted that schools of thought

concerning the nature of phosphorus retention2 have

oscillated from those implying the dominance of sorption

reactions to those which have relied exclusively on solu-

bility and precipitation principles. On the basis that Al

and Fe phosphates could be formed and identified from

solutions of similar composition to the soil solution, and

from consideration of solubility equilibria of phosphorus

compounds, various investigators postulated that retention

involved a precipitation reaction. However attempts to

correlate phosphorus concentrations in aqueous soil extracts

with the solubility isotherms3 of various Al, Fe and Ca

phosphates were unsuccessful. For example, it was shown

that hydrous oxides of Fe and Al actually maintained much

lower phosphorus concentrations by a sorption reaction than

would be predicted by the solubilities of variscite and
strengite. Similarly, investigators found that various

discrete minerals of Fe, Al and Ca formed from soil fertili-

zation did not appear stable enough to persist in soils.

Ryden and Pratt noted evidence showing that fertilizer

reaction products, formed in soils, would unlikely control

the chemical mobility of phosphorus in the soil as a whole.

More recently, sorption models have been favored as a basis

for understanding chemical mobility in soils.

Syers and Iskandar (1981) noted that in land treatment

of wastewater phosphorus is applied in smaller more frequent

amounts when compared to agriculture. This alone is

believed to cause significant differences in the chemical

reactions of phosphorus between the two systems. In land

treatment of liquid wastes, phosphorus is always applied at

rates far in excess of crop uptake and therefore the extent

of removal depends largely on the soil.

According to Syers and Iskandar, the three most impor-

tant reactions in regard to phosphorus removal by soils are

precipitation-dissolution, sorption-desorption and immobil-

ization-mineralization reactions. These processes are

mediated by chemical, physio-chemical and biological pro-

cesses respectively. It has been suggested that amorphous

ferric and aluminum phosphates are important initial reac-

tion products in soils receiving fertilizer. These com-

pounds are considered to crystallize slowly to strengite and

variscite. It was noted that the conditions which occur in

the immediate vicinity of phosphate fertilizer granules in

soils are unique to the initial formation of short range

order phosphates. These conditions of strong acidity

(pH 1.5) combined with high solution concentration of

phosphorus (4.0 moles per liter), would be highly unlikely

to occur at a slow infiltration wastewater application site.

Another point of view was that impure hydroxyapatite

controlled the chemical mobility of phosphorus in soils even

when the soil pH level was as low as four. This approach

was not widely accepted due to lack of evidence in several

studies that the solubility of phosphorus compounds

accounted for the concentration of phosphorus in solution.

Syers and Iskandar (1981) noted that phosphorus has

been shown to be highly adsorbed onto hydrous oxides of Fe

and Al as well as amorphous aluminosilicates allophanee).

Differences in phosphorus uptake among soils is largely

attributed to the number of sites available for adsorption.

The amount of phosphorus maintained in solution is higher if

the sorption complex is more saturated. The two most common

models used to describe adsorption by soils are the Langmuir

and Freundlich isotherms. The Langmuir equation has been

used more extensively but the assumptions associated with it

are limited. These assumptions include a constant heat of

adsorption, no interaction of adsorbed species, and nonlayer

sites dictating the maximum adsorption possible. Deviations

of phosphorus uptake from the Langmuir equation are thought

to be a result of these limitations. Most of the criticism

of the Langmuir equation has been due to its failure to

consider changes in surface charge during phosphorus adsorp-

tion. It has been shown that modifications of the Langmuir

equation which consider two or three adsorption regions

(population sites) for soils, have been more realistic in

describing actual soil phosphorus uptake data.

The simple mechanism of exchange adsorption whereby the

sorption of phosphorus involved the exchange of a phosphate

ion with a hydroxyl group (OH-) on edge MOH sites (M = Fe or

Al), was generally favored until the mid-1960's. The

exchange mechanism theory was advanced to where phosphorus

was thought-to be specifically adsorbed by ligand exchange

leading to an increase in negative charge of the soil

surface. More advanced equations of phosphorus sorption

have shown the formation of mononuclear complexes whereby

phosphorus ions replace OH and H20 molecules, or binuclear

bridging whereby phosphorus coordinates with two surface

groups (M O) in exchange for H20, OH- or even H+ ions.

Syers and Iskandar conceded that a shift from adsorption to

precipitation can occur in certain cases, but the extent to

which this would take place under field conditions is not


Syers and Iskandar also pointed out that previous

reviews regarding land treatment of wastewater neglected to

consider the role of phosphorus in organic form. They

considered the amount of organic phosphorus in soil to be a

reflection of the balance between immobilization and decom-

position reactions that were mediated by microbes. Various

investigators had shown evidence that appreciable amounts of

fertilizer phosphorus could accumulate in the organic form

when applied to soil. Therefore, it was reasonable to

expect that when wastewater phosphorus is added to soils,

organic phosphorus would accumulate up to a certain level

when the rate of immobilization balanced the rate of decom-

position. The extent to which the regular addition of

wastewater having a pH of seven to eight influences these

microbial processes needed further evaluation.

Factors Affecting Soil Phosphorus Retention

Berkheiser et al. (1980) pointed out that investigators

have correlated soil chemical properties with phosphorus

sorption. The various properties have included extractable

iron (Fe) and aluminum (Al), pH, CaCO3 content, particle

size distribution and organic carbon. Most emphasis has

been placed on the effect of Fe and Al constituents in the

soil, which form relatively insoluble complexes and precipi-

tates with phosphate. Organic matter appears to affect

phosphorus adsorption indirectly in that organically com-

plexed Fe and Al are the most likely sites for adsorption on

organic matter surfaces.

Berkheiser et al. (1980) and Syers and Iskandar (1981)

stated that the failure of various researchers to obtain

consistent results in regard to phosphorus retention is

because of the widely differing techniques and experimental

conditions employed. Important factors reviewed by Berk-

heiser et al. (1980) include temperature, pH, electrolyte,

time, aeration, concentration range (i.e., of phosphorus)

solid-to-solution ratio (soil:solution ratio) and previous

phosphate addition. Syers and Iskandar (1981) noted that in

evaluating factors which affect phosphorus retention, it is

useful to distinguish between those that influence the

kinetics of reactions from those which appear to have an

absolute effect.

In addition to the amount and nature of soil compon-

ents, Syers and Iskandar (1981) discussed the effects of

pH, other ions, kinetics and degree of saturation of the

sorption complex. Heatwole (1984) noted the reviews of

other investigators who have defined factors affecting

phosphorus retention. Soil components including clay

minerology, clay content, x-ray amorphous colloid content,

exchangeable Al and soil organic matter were defined as

being very important. In addition to these soil components,

factors such as pH (lime addition), microorganism activity,

and flooding were mentioned and/or discussed.

Bailey (1964) stressed that the pH of a soil system is a

dominating factor in phosphorus fixation. In an acid

environment (considering solubility product), a predominance

of Al and Fe phosphates would be expected; while in an

alkaline environment, Ca phosphates would be expected to

predominate. The general rule is that a minimum of phos-

phorus fixation occurs when the soil pH is close to

neutrality (i.e., pH 6-7) (Bailey, 1964; Buckman and Brady,

1969). In regard to acid soils, Buckman and Brady (1969)

have noted that phosphorus fixation most likely occurs as a

result of precipitation with Fe or Al or adsorption onto

their hydrous oxide surfaces. The basic Fe and Al phos-

phates such as strengite and variscite would be expected to

form at pH levels between three and four where they have

minimum solubility. As the pH is increased, the phosphate

in solution (particularly H2PO4 ions) would be more likely

to react with insoluble hydrous oxides of Fe and Al.

Although the end products of both pathways were expected to

be similar, Buckman and Brady (1969) felt that the quantity

of phosphorus fixed by adsorption quite likely exceeds that

of precipitation.

Laboratory Studies


The sections to follow contain a review of significant

laboratory studies which have been conducted to gain better

understanding of the nature of phosphorus retention. It

should be noted that much more work in the area of soil

phosphorus retention has been done with mineral soils. The

uptake of phosphorus by organic soils has received consider-

ably less attention. Although the focus of this disserta-

tion is on organic soils, the abundance of work done with

mineral soils cannot be ignored and is therefore also


Many of the studies reviewed in the reactions to follow

are characterized by a common empirical approach to reveal-

ing the nature of phosphorus uptake. This approach consists

of measuring the magnitudes of phosphorus retention by

different soils and correlating the resulting uptake values

with various measurable soil properties. The results of

these studies have contributed to understanding which soil

components take part in phosphorus uptake, in addition to

indirectly revealing the mechanisms involved.

Batch Laboratory Studies--Organic Soils

Of the many laboratory studies of soil phosphorus

retention, few have been done using organic soils. Organic

Soils belong to one of ten soil orders called histosols

(from the Greek word histos, meaning tissue). According to

the United States system of classification, histosols must

contain 12 to 18% organic carbon, depending upon the clay

content of the mineral fraction. Andrejko et al. (1983)

outlined the Organic Sediments Research Center (OSRC)

definition of peat, a type of histosol, as having 25% or

less inorganic material (ash) on a dry weight basis. McCool

(1921) noted the capacity of peat and muck soils for

retaining phosphorus increased with mineral content and

degree of decomposition. Doughty (1930) performed a

detailed study of phosphorus retention by organic soils and

concluded that iron, aluminum and calcium accounted for

phosphorus retention under field conditions. Kasakow (1934)

found that the maximum retention of phosphorus by fen peats

occurred at pH values between two and three due to their

higher content of iron, aluminum and calcium. The fen peats

were observed to retain more phosphorus than bog peats which

contained lesser amounts of these minerals. Verhoeven

(1946) maintained that phosphorus retention by irreversibly

shrinking peat soils was primarily dependant upon their

mobile iron content. Mobile iron refers to iron oxides in

the colloidal form or in true solution that are capable of

being transported within the soil profile.

Larsen (1957) found a positive correlation between

aluminum and iron compounds (sesquioxides) of organic soils

and their phosphorus retention capacity. Kaila (1959)

measured the phosphorus retention capacity of 134 peat

samples representing six types of peat at various depths.

The magnitude of phosphorus retention capacity sorptionn

index) obtained for each soil sample was expressed in terms

of the K value of the Freundlich sorption equation. The K

values were then statistically correlated with five soil

parameters that were thought to play a significant role in

phosphorus uptake. The parameters included degree of

humification, acidity of the peat, sampling depth, and

extractable calcium, iron and aluminum. When soils and/or

sediments are treated with reagents that extract limited

amounts of minerals such as iron or aluminum, these amounts

are referred to as extractable amounts. The results showed

that phosphorus retention correlated most significantly with

acid soluble aluminum and to some degree with iron and

degree of decomposition. Phosphorus retention of the

samples was observed to differ quite markedly, even with the

same peat soil at different depths. The association between

aluminum, iron and degree of decomposition was further

analyzed by statistically isolating the effect of one

variable from the others. It appeared that the aluminum

effect was entirely independent, the iron effect was

slightly lower without aluminum and the decomposition effect

disappeared by eliminating aluminum. Lopez-Hernandez and

Burnham (1974a) studied the phosphorus retention character-

istics of British organic soils. Results showed that the

type of peat was important in predicting phosphorus

retention capacity. It was observed that moss peats and

decomposed acid basin peats (isolated basins) exhibited

lower phosphorus retention capacities. On the other hand,

fen peats and high mineral content valley bog peats

exhibited higher phosphorus retention capacities. Multiple

statistical correlations of phosphorus retention with

various soil parameters indicated that retention was sig-

nificantly associated with extractable iron, aluminum,

manganese and total mineral matter. Total mineral matter

was estimated by measuring the weight loss upon ignition at

9000C for at least three hours. Correlations were also made

of the various soil parameters with each other. Surpris-

ingly, the correlations between total mineral matter and

each of iron, aluminum and manganese were not significant.

Because of this, it was speculated that a nonsesquioxide

mineral component such as clay had an independent role in

phosphorus retention. Lopez-Hernandez and Burnham (1974a)

also made a comparison between the phosphorus retention

capacity of dried peats to those in their natural state. It

was found that dried peats with high iron and/or manganese

content exhibited significantly more phosphorus retention

than that of their unaltered counterparts. For peats that

contained lesser amounts of these elements, there was no

significant difference in phosphorus retention capacity

observed between dried peats and unaltered peats. The

higher retention capacity of dried peats containing iron and

manganese was attributed to the oxidation of these elements

caused by the drying process. It was concluded the higher

oxidation states of iron (Fe3+) and manganese (Mn3+) gave

the soil a higher net positive charge which in turn retained

more negatively charged phosphate anions. Pereverzev and

Alekseyeva (1965) ascribed phosphorus retention to the

aluminum and iron compounds contained in bog soils of the

U.S.S.R. Phosphorus retention was observed to be higher in

cultivated bog soils as opposed to virgin bog soils.

The irreversible drying property of these peats was likewise

attributed to their sesquioxide content. Wondrausch (1969)

studied phosphorus retention of four peat soils in Poland

that were different in regard to chemical composition.

Results showed that two acid peats containing significant

amounts of iron in the form of mobile compounds had high

phosphorus retention capacity. Mobile refers to oxides or

hydroxides of iron and/or aluminum in soils which are more

soluble and therefore more "active." Phosphorus frac-

tionation of these soils showed 70 to 90% of the phosphorus

was associated with iron. Phosphorus in soils can be

fractionated by procedures such as that of Chang and Jackson

(1957). A third acid peat which was low in iron content but

high in aluminum content, exhibited lower phosphorus reten-

tion capacity. It was speculated that because the aluminum

did not exist in an active form (as measured by selective

extraction), it did not play a significant role in

phosphorus retention. The extractant used to measure active

forms of iron and aluminum was the acid-oxalate mixture

referred to by Saunders (1965). The phosphorus retention

capacity of a more alkaline peat containing calcium was

found to be moderately high. Although it was expected that

phosphorus would be primarily bound with calcium compounds,

39% of phosphorus binding was found to be with iron. It was

not clear in this work if the phosphorus fractionation

procedure was performed on the soil samples after treating

with phosphorus. It was concluded that acid-oxalate

extracted iron was the best index of phosphorus retention

and that it accounted for 70 to 90% of bound phosphorus in

acid soils. In addition, the ratio of Fe203 to P205

extracted by acid-oxalate procedure was also found to be an

index of phosphorus retention. It was found that when this

ratio was greater than ten, phosphorus retention was high

even if the soil iron quantity was low. Wondraush (1969)

also found that phosphorus retention capacity of the soils

could be decreased by adding completing agents such as

citrate, versenate and oxalate. It was believed that these

compounds interfered with phosphorus retention by competing

with multivalent metals such as iron, aluminum and calcium.

Bloom (1981) studied the retention of phosphorus by a peat

soil which was modified by supplementing it with additional

aluminum. This was accomplished by substituting aluminum

ions for hydronium ions (H ) onto the organic matter

exchange sites. The aluminum-substituted peat demonstrated

high phosphorus retention in the pH range of 3 to 6.

Interpretation of both the sorption and solubility data led

to the conclusion that retention of phosphorus by the peat

was occurring by precipitation and complexation. Bloom

(1981) concluded that the precipitant being formed was an

amorphous Al-phosphate product, A1H2PO4(OH)2. The complexes

that were being formed were aluminum peat complexes. It was

speculated that a significant amount of extractable alum-

inum, which had been shown to correlate with phosphorus

retention by all types of soils, was derived from organic

matter completed with aluminum. In contrast to the works of

Kaila (1959) and Kasakow (1934), Bloom (1981) also found

that phosphorus retention of the Al-peat increased with

higher pH. Based on surface charge, phosphorus retention

should increase with lower pH due to negatively charged

phosphate ions being attracted to the protonated surface of

the substrate. Overall, Bloom concluded that Al-organic

matter complexes may play a major role in phosphorus reten-

tion in acid surface soils, particularly with soils high in

organic matter content. John (1971) conducted a comprehen-

sive laboratory study to investigate which soil properties

affect the retention of phosphorus from wastewater effluent.

Altogether over 300 soils were tested, the majority being

from interior and coastal areas in British Columbia, Canada.

Although most of the soils were mineral soils, there were a

few organic soils tested. Results showed that the wet

coastal soils removed an average of 85% phosphorus from the

effluent, contrasting with only 31% phosphorus removal by

the dry interior soils. However, organic soils removed the

least amount of phosphorus compared to other soils types

from the coastal region. Fox and Kamprath (1971) conducted

a study of acid organic soil samples and those of high

organic-matter sand. The soils which were collected from an

agricultural tidewater area in North Carolina were used for

growing corn, soybeans, and blueberries. Both types of

soils were characterized by their lack of inorganic colloid

content. One of the objectives of the study was to test the

theory that the poor phosphorus retention capacity exhibited

by the organic soils under field conditions was attributed

to their lack of mineral colloids. As predicted, the

results showed that the organic soil samples exhibited very

poor retention capacity of water soluble phosphorus. This

theory was further supported by observing a significant

increase in phosphorus retention by the soils after being

supplemented with aluminum in the form of A1Cl3. In addi-

tion, results showed that the retention of phosphorus by the

muck soil was considerably higher for surface samples at a

pH of 4.6 than for subsurface samples at a pH of 3.3.

White and Thomas (1981) studied the adsorption of

phosphorus onto peats and humic acid cation exchange resin

which were treated with Al. It was desired to learn more

about the relationship between the hydrolysis of Al adsorbed

onto organic matter and its capacity to retain phosphorus.

Such knowledge was considered to be of practical value since

the leaching of phosphorus from acid peat soils caused

economic loss to farmers and also increased the potential of

eutrophication in surface waters receiving drainage.

Phosphorus uptake was considered to be a result of adsorp-

tion, the magnitude of which depended on the amount of Al

held on exchange sites and the degree of hydrolysis of the

adsorbed Al. White and Thomas (1981) estimated the degree

of hydrolysis of adsorbed Al ions by using a procedure to

measure their surface charge. This was accomplished by

comparing titration curves of the organic soils with the

quantity of Al they adsorbed. The degree of hydrolysis of

the adsorbed Al directly affected the net positive charge

per Al species. This was expressed in terms of the

basicity, which was defined as the OH/Al ratio of adsorbed

Al species. The basicity of adsorbed Al is defined as OH/Al

ratio and has a minimum value of zero in the absence of

attached hydroxyl groups. In contrast the maximum value is

three for fully hydrolyzed Al. Results showed that Al was

extensively hydrolyzed on the organic matter surfaces in the

pH range of 3.0 to 4.5. This is in contrast to that of

clays which contain exchangeable Al predominantly in the

form of A(H20)63+ within that pH range. White and Thomas

attributed this phenomenon to weakly acid carboxyl groups

which act as sinks for protons produced by hydrolysis and

polymerization of Al(H20)6 ions. Thus, the Al contained

in adsorption systems which possessed weak acid groups was

easily hydrolyzed and would not be as effective in adsorbing

phosphorus. It was suggested that highly acidic virgin

peats retain little phosphorus against leaching because

their Al contents were low and that which is present is of

high basicity. Furthermore, the greater tendency of Fe

(III) compared to Al to hydrolyze at a given pH might

explain why additions of Fe (III) to organic matter are

found to be less effective than Al in retaining phosphorus.

Batch Laboratory Studies--Mineral Soils

The majority of laboratory studies of soil phosphorus

retention have been conducted with mineral soils of various

types. A mineral soil is one consisting predominantly of,

and having its properties determined predominantly by,

mineral matter. It usually contains less than 20% organic

matter, but this depends on other factors such as the clay

content of the mineral fraction. One cannot ignore the

literature dealing with mineral soils even though the

emphasis of this report is on organic soils. This is

supported by the evidence that phosphorus retention capacity

of organic soils is dependent upon the components which make

up the mineral fraction. Likewise, many mineral soil

studies have shown that phosphorus retention has correlated

highly with organic matter content. This section is a

review of the significant studies which have attempted to

empirically correlate phosphorus retention with various

measurable soil properties.

Many different methods have been used to determine and

express the phosphorus retention capacity of various soils.

There is little doubt that results of these various studies

have been dependant upon which phosphorus retention index

was used. A good evaluation of phosphorus retention indexes

is contained in the work of Bache and Williams (1971).

Williams et al. (1958) studied phosphorus retention of acid

mineral soils in Scotland. The capacity of the soils to

retain phosphorus was evaluated using two methods. The

first method, which was developed by Piper (1942), was

considered to be a measurement of the soils' anion exchange

capacity (AEC). The second method, described by Bache and

Williams (1971) has been referred to as the single-point

sorption method. The magnitudes of phosphorus retention

sorptionn indexes), as measured by both these methods, were

correlated with soil properties that included extractable

iron and aluminum, loss on ignition, organic carbon, pH and

clay content. Results indicated that phosphorus retention

by three out of four parent soil groups was most highly

related to aluminum extracted by the acid-oxalate method.

Phosphorus retention by the fourth soil group correlated

most significantly with loss on ignition. Loss on ignition

is an estimation of organic matter content as measured by

igniting the soil at 5000C and above. The loss that is

referred to is the weight loss due to release of carbon

dioxide. In addition, aluminum extracted by dithionite-HCl

treatment and dilute acetic acid also gave significant

correlation with phosphorus retention. For iron, the

quantity extracted by the acid-oxalate method gave the only

significant correlation with phosphorus retention. Multiple

correlations between phosphorus retention and iron and

aluminum together were lower than for aluminum alone.

Phosphorus retention also appeared to correlate signifi-

cantly with organic carbon and loss on ignition. However,

since both loss on ignition and organic carbon also correl-

ated highly with acid-oxalate aluminum, it was felt that the

aluminum and iron associated with organic matter was most

responsible for phosphorus retention. The iron and aluminum

associated with organic matter was referred to as active and

was considered to be present in the form of humate com-

plexes. The term active was used to indicate that the iron

and aluminum of this nature was directly involved in the

retention of phosphorus by some sort of physio-chemical

combination. Phosphorus retention did not correlate well

with clay content, although it was not clear as to whether

the clays were separated prior to the retention tests. It

should be noted that residues from each soil group after

acid-oxalate extraction were also tested for phosphorus

retention capacity. In each case the phosphorus sorption

values were only five to 20% of those exhibited by the

original soils, the average being 10%. Williams (1971)

concluded there was no doubt phosphorus sorption was due

mainly to iron and aluminum that was removed by the Tamm

extraction. The clay minerals which apparently remained

were not important in phosphorus sorption. The word sorp-

tion will be sometimes used interchangeably with retention.

Sorption appears to be a general term for indicating physi-

cal or chemical retention. This may include adsorption

which specifically refers to the attraction of ions or

compounds to the surface of a solid. Although sorption may

involve penetration of the surface, it does not refer to


Saunders (1965) studied the phosphorus retention of New

Zealand topsoils and subsoils. The method of testing

phosphorus retention by utilizing a single dosage (single

point index) was favored over the AEC method. Phosphorus

retention was statistically correlated with various soil

properties that included aluminum, iron and silica extracted

by the acid-oxalate and CDB methods, pH, organic matter,

organic phosphorus, total nitrogen, clay content and

exchangeable calcium (Ca). (CDB is short for citrate-

dithionite-bicarbonate). Extractants are sodium citrate

(Na3C6H507'2H20) and sodium dithionite (Na2S204). Sodium

bicarbonate (NaHCO3) is a buffer. The results indicated

that phosphorus retention by topsoils correlated closely

with organic carbon, total nitrogen, loss on ignition,

organic phosphorus, acid-oxalate Al and Fe and CDB iron.

Saunders (1965) felt that the soil organic matter was not

directly related to phosphorus retention because the organic

matter also correlated highly with acid-oxalate aluminum and

iron. For high organic matter soils that exhibited low

phosphorus retention, the correlation between organic matter

and Tamm iron and aluminum was insignificant. Overall

results showed that phosphorus retention increased to a

maximum with moderately weathered soils of silt texture, but

decreased with strongly weathered soils of clay texture.

The only soil properties which correlated with phosphorus

retention were those of soil organic matter or free

sesquioxides, which refer to oxides of iron and aluminum

that exist in soils as discrete particles and coatings on

soil minerals and/or as cement between mineral particles.

Other properties such as soil pH, percent base saturation,

exchangeable calcium and clay content showed little or no

correlation. Percent base saturation represents the portion

of soil exchangeable cations other than hydrogen or

aluminum. Whereas exchangeable hydrogen and aluminum

contribute to the acidity of a soil, the exchangeable base

cations increase soil alkalinity.

Saini and MacLean (1965) examined the phosphorus

retention of two-dozen New Brunswick (Canada) soils and

correlated it with soil properties. The soils treated were

thought to have high retention capacity because of the high

demand for phosphorus in crop production. Using the AEC

method discussed by Bache and Williams (1971), as a

phosphorus retention index, Saini and MacLean (1965) showed

the phosphorus retention capacities of the soils tested were

very substantial. The retention capacities ranged from

2,200-17,600 pg phosphorus per gram of soil, with an average

value of 7,700 pg per gram. The phosphorus retention

capacities as measured by Piper's method were understandably

higher than for any other given method because this method

involved saturation of the soil in regard to phosphorus.

Results of simple correlation between phosphorus retention

and soil properties indicated that retention was highly

related to aluminum and organic matter content but not to

clay or iron. The strong relationship between phosphorus

retention and aluminum content was expected and supported

similar results obtained by Williams et al. (1958) and

Bromfield (1964). The significant correlation between

organic matter and phosphorus retention agreed with studies

such as Williams et al. (1958), but the exact role of the

organic matter was not clear. Although Saini and MacLean

(1965) did not rule out the possibility of phosphorus

directly combining with organic matter, its association with

aluminum was thought to be a more plausible explanation of

organic matter significance. This was supported by the

significant cross correlation obtained between organic

matter and aluminum. Although iron content did not corre-

late with phosphorus retention, it was not ruled out as

being insignificant considering the evidence of other

studies such as Williams et al. (1958) and Weir and Soper

(1963). Saini and MacLean (1965) concluded the particular

method used to measure active iron may not have been effec-

tive. It was also concluded that clay was not directly

involved in phosphorus retention and that indications of

this were only due to active aluminum and/or iron associated

with the clay.

Yuan and Breland (1969) studied various Florida soils

by correlating their capacities for retaining added phos-

phorus with aluminum and iron extracted by five different

methods. Previous studies by Bromfield (1965), Saini and

MacLean (1965), Williams et al. (1958), Ahenkorah (1968),

and Sree Ramulu et al. (1967) indicated that there was a

significant relationship between phosphorus retention and

aluminum but the relationship with iron seemed to differ

with soils and extractants. For this reason, Yuan and

Breland (1969) focused solely on extractable iron and

aluminum by methods which included ammonium acetate

(NH4OAc), dilute hydrochloric acid (HC1), ammonium oxalate

(NH4)2C204 (acid-oxalate method), buffered sodium dithionite

(Na2S204) (CDB method) and dilute sodium hydroxide (NaOH).

The Florida soils that were used were classified scientifi-

cally according to their orders and great groups. A new

system of soil classification was adopted for use in the

United States on January 1, 1965. Soils are grouped toge-

ther according to similar physical, morphological and

chemical properties. The system of classification starts

with the soil orders and progresses down with suborders,

great groups, subgroups, families and series. Altogether,

forty-three virgin soil samples representing twenty-four

soil types classified under four soil orders and eight great

groups were studied. Yuan and Breland (1969) placed empha-

sis on retention of added phosphorus rather than the total

phosphorus retention capacities of the soils. Therefore the

index used for measuring phosphorus retention was the amount

of phosphorus retained from a 100 ppm solution instead of

Piper's AEC method. Results showed that, regardless of the

extractant use, extractable aluminum correlated signifi-

cantly with phosphorus retention. The highest correlations

between phosphorus retention and extractable aluminum were

obtained with the acid-oxalate and CDB methods. Correla-

tions between phosphorus retention and extractable iron were

not as good, but significant relations were obtained with

some of the soils using NaOH, acid-oxalate and CDB methods.

In addition to determining simple correlations between phos-

phorus retention and iron and aluminum, Yuan and Breland

(1969) also investigated the relationship between phosphorus

retention and iron and aluminum combined. This interpreta-

tion showed that although the significance of correlation

was the same as for aluminum alone, some higher correlation

coefficients were obtained by combining the two elements.

Yuan and Breland (1969) speculated that aluminum and iron of

amorphous nature were responsible for soil phosphorus

retention because higher combined correlations were obtained

from acid-oxalate, CDB and NaOH methods. These extractants

were considered to obtain more of the amorphous forms of

iron and aluminum from the soils. Overall, it was concluded

that extractable aluminum and iron could be used to predict

phosphorus retention by soils if they could be grouped to

contain similar aluminum and iron compounds.

Harter (1969) studied the phosphorus retention capaci-

ties of acid mineral soils of Connecticut and correlated

them with soil properties which included extractable alumi-

num, percent organic matter, percent clay, percent free iron

oxides and pH. A unique feature of this experiment was the

attempt to directly ascertain the fate of phosphorus

retained by the soil. This was accomplished by re-

extracting the phosphorus which was adsorbed onto the soils

during the retention tests according to the procedure of

Chang and Jackson (1957). Initially developed for use in

soil fertility and genesis studies, this method was employed

extensively to fractionate inorganic soil phosphates. In

this method ammonium fluoride (NH4F) is used to extract

aluminum phosphate and sodium hydroxide (NaOH) is used to

extract iron phosphate. Thus, the amount of phosphorus

adsorbed into both the NH4F and NaOH fractions was desired.

Results showed that the soil characteristics measured

accounted for 85% of the variability in phosphorus adsorbed

into the NH4F fraction and 90% of the variability in phos-

phorus adsorbed into the NaOH fraction. Although the

correlation between aluminum extracted by NH4F and phos-

phorus adsorbed into this fraction was significant, it was

lower than expected. This, along with the higher

correlation obtained for percent organic matter, led Harter

(1969) to believe the organic matter was most important in

the initial bonding of phosphorus with the soil.

John (1971) measured the phosphorus retention from

domestic wastewater effluent by soils collected from

376 sites in British Columbia and six from New Zealand. The

soils, which represented both interior and coastal regions,

were predominantly mineral soils but a few were organic.

The phosphorus retention of the soils was correlated with a

total of 22 different soil properties. Overall, the results

showed that phosphorus retention was higher with the more

weathered acid soils of the coastal regions and lower with

the less weathered soils of the interior. Extractable iron

and aluminum, pH and degree of phosphorus saturation all

correlated significantly with phosphorus retention. Extrac-

tion methods that correlated best with phosphorus retention

were dependant upon the particular region or soil group the

samples were from. The soil parameter which accounted for

the most variation in phosphorus removal was base satura-

tion. John (1972) did a follow up study on phosphorus

retention of the British Columbia soils from solutions of

radioactivity labelled potassium dihydrogen phosphate
(32 P-KH2PO4). Lindsay and Stephenson (1959) had pointed out

that extremely high concentration of phosphorus in the

environment could only develop around fertilizer granules.

Therefore, high dosage phosphorus retention tests were

basically unrealistic in comparison with the concentrations

of phosphorus in the soil solution. However, John (1972)

felt that problems concerning the sensitivity and interfer-

ence of other ions associated with the colorimetric phos-

phorus test discouraged the use of low dosage retention

studies. The use of labelled phosphorus was considered to

be an advantage because it eliminated these problems and

also allowed specific identification in regard to source of

measured phosphorus. Soil samples of surface horizons from

virgin sites, as well as A horizons from cultivated sites

throughout British Columbia, were air dried and passed

through a screen to remove stones and roots. Any given soil

is made up of distinct horizontal layers called horizons.

The combination of soil horizons make up the soil profile.

Although very few if any soils consist of all major soil

horizons, all soils possess some of them. The A horizons

are characterized by significant leaching. John (1972)

shook one gram of soil overnight with 100 ml of a dilute

labelled KH2PO4 solution (0.2 ppm P) and the uptake of

phosphorus was measured using a Geiger-Muller counter.

Results confirmed that the phosphorus retained by the soils

was specifically that from solution. In a similar fashion

to this 1971 report, John (1972) correlated phosphorus

retention with 16 soil properties using simple and multiple

regression techniques. Results indicated that soil pH,

calcium, phosphorus, aluminum, iron, organic matter and

particle size all significantly influenced the amount of

phosphorus adsorbed by the soils. Overall, the more highly

weathered and relatively acidic soils of the humid coastal

region adsorbed more phosphorus than the dry interior soils.

Syers et al. (1973) studied the phosphorus retention of

three different Brazilian mineral soils. The index of

phosphorus retention utilized to compare the soils was the

amount of phosphorus uptake for the highest single phos-

phorus dosage. Soil properties that were measured included

pH, clay content and extractable iron and aluminum.

Although correlation coefficients were not determined

between phosphorus uptake and the various soil properties,

the results showed that phosphorus retention by the most

weathered soil was highest and phosphorus retention by the

least weathered soil was the lowest. The ability of the

three soils to sorb added phosphorus increased with an

increase in clay content, exchangeable aluminum, CDB iron

and aluminum and the amorphous material content of the clay

fraction. As expected, phosphorus retention appeared to be

higher for a lower soil pH but this may have been due to

coincidence. Because the soil components thought to be

related to phosphorus retention were also known to be

interrelated among themselves (Syers et al., 1971), it was

felt that pinpointing the most significant components would

be difficult. Ballard and Fiskell (1974) studied the

phosphorus retention characteristics of forest soils from

the southeastern United States coastal plains. An unique

feature to this study was that the correlation between soil

phosphorus retention and extractable aluminum was examined

for different applied phosphorus dosages. The results

showed that the correlation coefficient between phosphorus

retention and extractable aluminum became increasingly

higher with higher applied phosphorus. This dependency on

phosphorus dosage level was attributed to the need for

saturating all possible phosphorus retention sites of a soil

in order to get a true relationship. It was found that for

the soils used in this study a dosage of 2,500 ug P per gram

of soil was adequate to insure true linear relationships.

Other soil properties which were found to correlate signifi-

cantly with phosphorus retention included soil pH, clay,

silt and loss on ignition. The correlation between phos-

phorus retention and pH was positive, which was of interest

due to its contradiction with previous reports (Udo and Uzu,

1972). Soil properties which did not correlate with phos-

phorus retention included exchangeable calcium and cation

exchange capacity (CEC), which is defined as the sum total

of exchangeable cations that a soil can adsorb. It is

expressed in terms of milliequivalents per 100 grams of

soil. Ballard and Fiskell (1974) further interpreted the

results by taking into consideration that soil properties

such as clay, silt, pH and organic matter may only be

related to soil phosphorus retention because of their

interrelationships to iron and aluminum. This was accom-

plished by determining the partial correlation coefficients

for each soil property, thus eliminating the indirect effect

of extractable aluminum. This resulted in a significant

reduction of all correlations except for pH. Extractable

aluminum and iron values were determined by seven different

methods and these values were correlated with phosphorus

retention. Results showed that extractable soil aluminum

provided the single best index of soil phosphorus retention

over a range of soils. Also, the correlation coefficients

between phosphorus retention and extractable aluminum were

all very similar despite large differences in the amounts of

aluminum extracted. It was felt the form of aluminum being

extracted that related to phosphorus retention was an

amorphous form. In contrast, the correlations between

phosphorus retention and amounts of extractable iron dif-

fered markedly. Unlike the aluminum correlations which

appeared to be independent of amounts extracted, the iron

correlations increased with the amount of iron extracted up

to a point and then decreased. The optimum iron quantity

appeared to be that extracted by oxalate, which was also

considered to be an amorphous form of iron. Overall, it was

concluded that the order of activity of aluminum and iron

per unit weight in phosphorus retention was exchangeable >

amorphous > crystalline. Although various extractants of

aluminum provided the best single index of phosphorus

retention, multiple regression data suggested that the

contribution of active forms of iron was significant.

Lopez-Hernandez and Burnham (1974b) studied the phos-

phorus retention of temperate acid soils from Great Britain

as well as tropical acid soils from Malaya, Venezuela and

Ghana. The retention of phosphorus was examined by two dif-

ferent methods. One of the methods was the AEC method

developed by Piper (1942). A second method used was the

Bache and Williams (1971) index. In addition, partial

correlation coefficients of phosphorus retention and soil

properties were determined to take into account the fact

that the relevant soil properties were themselves inter-

related. For the tropical soils, the highest correlations

between phosphorus retention and soil properties were

obtained with extractable aluminum and free iron oxides.

Percent organic carbon correlated significantly with the

Piper sorption index, but not with the Bache and Williams

index. A low level of significance between phosphorus

retention and clay content was observed, but it was felt

that this was due to a relation between clay and aluminum.

For the tropical soils there was no significant relationship

observed between pH and phosphorus retention. In addition,

there was not a significant correlation between organic

matter and extractable aluminum and iron as was expected.

For the temperate British soils, phosphorus retention was

found to correlate highly with iron oxides and extractable

aluminum. Although organic matter was found only to be

significantly correlated by using the partial coefficient,

it was still regarded as significant in phosphorus reten-

tion. Overall, it was found that the deeper subsoils of

both tropical and temperate soils retained more phosphorus

than the topsoils. The higher phosphorus retention

exhibited by the subsoils also coincided with their higher

content of phosphorus retaining soil properties.

Vijayachandran and Harter (1975) studied phosphorus

retention of various different United States and Puerto

Rican mineral soils. The purpose of the study was to

observe the phosphorus retention ability of contrasting

soils because it was felt that too many previous studies

were performed using similar soils. Two indexes of phos-

phorus retention that were used included a single dosage

(single point) index and the Langmuir sorption maximum

value. The Langmuir maximum value is obtained from the

Langmuir adsorption model, which was originally developed to

describe the adsorption of gases onto solids. The Langmuir

model was first applied to phosphate and soils by Olsen and

Watanabe (1957). A sorption maximum is determined by

adapting the Langmuir equation to soil phosphorus retention

data consisting of a series of increasing phosphorus doses.

Vijayachandran and Harter (1975) showed that both phosphorus

retention indexes correlated with aluminum extracted by

ammonium acetate and hydrochloric acid/sodium hydroxide

treatment. Phosphorus retention according to the single

dosage index correlated with aluminum extracted by the CDB

method. Multiple regression analysis demonstrated that each

combination of significant correlations, including organic

matter content, improved the overall correlation with

phosphorus retention. However, even though the addition of

organic matter to the regression improved the correlation,

the cross correlation between organic matter and extractable

iron and aluminum was not significant. In contrast to other

reports, this indicated that the iron and aluminum related

to phosphorus retention was not associated with organic

matter. Vijayachandran and Harter (1975) also examined the

phosphorus retention capacities of soils after stripping

them of extractable iron and aluminum. The results showed a

general decrease in phosphorus retention following this

treatment. It appeared that the organic fraction remaining

after HCl-NaOH treatment was not active in phosphorus

retention. It was concluded that only a portion of soil

organic matter was effective in initial phosphorus reten-


Khalid et al. (1977) studied the phosphorus retention

characteristics of Louisiana rice growing soils. The

phosphorus retention capacities were evaluated by examining

the sorption patterns of pretreated soil suspensions under

both aerobic and anerobic conditions. Results showed that

the difference in phosphorus retained between oxidized or

reduced conditions was negligible for low dosages of phos-

phate. However, the phosphorus retention behavior at higher

dosages was highly influenced by redox conditions. For the

majority of the soil samples tested, considerably more

phosphorus was retained under reduced (anerobic) conditions.

This was attributed at least in part to an increase in

oxalate extractable iron and higher pH associated with the

anerobic conditions. This was supported by a higher

correlation between phosphorus retention and oxalate

extractable iron for reduced conditions. In addition,

phosphorus retention data relating to various soil

properties were subjected to multiple regression analysis.

Phosphorus retention data for both oxidized and reduced

conditions were analyzed using a single dosage of 500 ug P

per gram of soil as the index of phosphorus retention. The

results for oxidized conditions showed that total carbon,

oxalate extractable iron, extractable phosphorus, and

phosphate potential accounted for 85% of the variation in

phosphorus retention. It should be noted that various

studies such as this have shown that the capacity for a soil

to retain phosphorus is related to various forms of

phosphate initially present in the soil. Larsen (1967)

noted the equilibrium between phosphorus in solution and the

solid phase has been described by principles of physical

chemistry. The concept of "phosphate potential" was

proposed by investigators to be an index of soil phosphate

availability. Clay content, pH and phosphorus extracted by

calcium chloride were excluded from the regression. For

reduced conditions, all soil properties minus phosphate

potential contributed to account for 80% of the variation in

phosphorus retention.

McCallister and Logan (1978) studied phosphorus reten-

tion characteristics of agricultural mineral soils (surface

soils) and stream sediments. One objective was to compare

the phosphorus retention of both types of substrates in

regard to correlation with various soil properties. One

index of phosphorus retention utilized was the Langmuir

sorption maximum obtained by a series of phosphorus dosages.

Results for surface soils showed that phosphorus retention

significantly correlated with initial total phosphorus,

inorganic phosphorus and fine clay content. There was no

significant correlation between phosphorus retention and

extractable phosphorus. For the stream sediments, phos-

phorus retention correlated very highly with extractable

iron, aluminum and silica. This was a contrast to the

surface soils in which none of these properties strongly

correlated to the sorption maximum. High correlation was

also obtained with total and inorganic phosphorus, and clay

content. In addition, the stream sediments also exhibited a

significant negative correlation with pH and carbonate

content. The higher phosphorus retention for lower pH soils

was expected from a surface charge theory, but the relation-

ship to carbonate content was less obvious. It was specu-

lated that the carbonate content was only superficially

related to phosphorus retention because its presence merely

diluted out iron and aluminum content.

A unique feature in the work of McCallister and Logan

(1978) was that three properties related to the stability of

the bond formed between phosphorus and the soil were exam-

ined. The three properties, which could be considered as

phosphorus release (desorption) indexes, were adsorption

energy, EPC and sequentially desorbed phosphorus. The

adsorption energy is equivalent to the heat released during

adsorption. All adsorption reactions are exothermic.

McCallister and Logan (1978) estimated the adsorption energy

indirectly from one of the constants obtained by the Lang-

miur equations. Although the letters EPC were not specifi-

cally defined, it appears that they stood for "equilibrium

phosphate concentration." The EPC was defined as the

solution concentration in which phosphorus is neither

adsorbed nor desorbed from a soil. Sequentially desorbed

phosphorus was determined by summing the total phosphorus

desorbed per unit mass of soil or sediment after 10 succes-

sive 6-hour desorptions into 0.01 Molar calcium chloride

(CaC12) at a 1:10 soil/solution ratio. Results for the

surface soils showed a negative correlation between extrac-

table phosphorus and adsorption energy. This supported the

theory that more phosphorus would be available for release

from a soil that had lower bonding energy. Further inter-

pretation of correlation data indicated that the source of

phosphorus released by washing or extraction appeared to be

the inorganic fraction. For the stream sediments the only

significant correlation between phosphorus desorption

indexes and soil properties occurred between sequentially

desorbed phosphorus and extractable phosphorus. Overall,

the phosphorus retention capacities of the stream sediments

were an order of magnitude greater than those of the surface

soils. The sorption maxima of the stream sediments ranged

from 1930 to 4550 ug phosphorus per gram of soil, while

those of the surface soils ranged from 199 to 287 pg phos-

phorus per gram. One stream sediment had a value of only

222 ug phosphorus per gram but it was felt this may have

been an anomaly due to the high sand content of the sample.

If the weight of the sand was incorporated into the deter-

mination of the sorption capacity, then the active fraction

would be, in effect, diluted out. Since clays were consid-

ered to be highly reactive by the nature of their large

surface area, the surface soil clay fractions were tested

independently in regard to their phosphorus retention and

release properties. Results showed that the sorption maxima

of the total clay fractions were slightly higher than those

of the whole soils, but still an order of magnitude less

than the stream sediments. McCallister and Logan (1978)

concluded that the eroded and transported clay fractions

could not account for all the phosphorus retention by bottom

sediments or even by the whole soils. It was speculated

that the higher phosphorus retention exhibited by stream

sediments was due to changes in the chemical structure of

the eroded soil material after deposition in the stream. It

was possible that a significant amount of the original

crystalline structure was converted to amorphous form. This

was supported by the fact that for the stream sediments, the

quantity of oxalate extractable iron was about twice that of

the CDB extractable iron. The significance of this was that

normally the CDB extraction was assumed to remove both

crystalline and amorphous sesquioxides, while oxalate

removes the amorphous fraction only. Assuming this was

true, the stream sediments evidently consisted of consider-

able amorphous material that even the CDB method did not

reveal. This phenomena had also been reported by Williams

et al. (1971) for lake sediments. McCallister and Logan

(1978) felt that the absolute quantity of amorphous mater-

ial, especially that of iron, could account for the high

phosphorus retention capability of the sediments as compared

to the surface soils. However, it should be noted that the

absolute quantities of oxalate extractable sesquioxides of

the stream sediments were not significantly higher than

those of the surface soils. In regard to absolute quanti-

ties, the only constituent that the surface soils and their

clay fractions appeared to lack compared to the stream

sediments was free carbonate. Indeed, the fact that oxalate

iron was higher than CDB iron could be explained by the

possibility that oxalate was extracting various forms of

iron carbonate. McCallister and Logan (1978) speculated

that oxalate may have been extracting iron in the sediments

from such forms as siderite or magnetite. Gamble and

Daniels (1972) had reported that, while magnetite had

appreciable solubility in oxalate, it was only sparingly

soluble in CDB. However, the fact that the stream sediments

showed a negative correlation between phosphorus retention

and carbonate content did not support the possibility that

it could be responsible for their high phosphorus

capacities. It was concluded that the stream sediments were

significantly undersaturated with respect to phosphorus and

that they acted as phosphate "sponges." However, because

the stream sediment adsorption energies were considered to

be low, McCallister and Logan (1978) predicted significant

phosphorus release could occur when the sediments become


Stuanes (1984) studied the sorption of phosphorus by

soils in Norway and Sweden which were to be used to treat

wastewater. Previous studies for measuring the phosphorus

sorption capacity of soils used the maximum value obtained

by the Langmuir equation. The Langmuir maximum however, was

found to be lower than actual amounts of phosphorus retained

over time in various column and field studies. Stuanes

(1984) therefore attempted to realistically simulate seepage

bed conditions by repeatedly adding phosphorus to the soil

samples. Results showed that the sorption capacities of

soils receiving repeated additions of phosphorus were twice

as high as the Langmuir maximum values for the same soils.

However, the two measurements were well correlated to each

other. Stuanes (1984) noted from the results that the

uptake of phosphorus by soils equilibrated with the same

phosphorus solution over long periods of time was not the

same as for repeated additions of fresh solution. The

results showed that even after 10 additions of fresh solu-

tion, equilibrium was not reached and the soils continued to

retain added phosphorus. To test the stability of the bond

between the soils and fresh additions of phosphorus, Stuanes

(1984) subjected them to 10 subsequent extractions using

0.01 Molar calcium chloride (CaCl2). The results appeared

to indicate that bonding was fairly irreversible, as only an

average of 20% of the sorbed phosphorus became desorbed.

Stuanes (1984) felt this to be an important observation,

because phosphorus sorbed in a soil renovation system would

only be desorbed to a small extent if the input phosphorus

decreased as a result of surface water leakage into the

system. Correlations were made between phosphorus retention

and soil properties by utilizing a stepwise multiple regres-

sion technique. Results indicated that CDB extractable

aluminum correlated the best with phosphorus retention as

expressed by the Langmuir maximum and by multiple additions.

For phosphorus retention after only one addition (single

point index), a significant correlation was obtained with

pH. Stuanes (1984) noted that although numerous studies

have shown correlation between phosphorus retention and

iron, aluminum and other soil properties, the correlation

deteriorated when data from several others were pooled

together. A similar result was reported by Berkheiser et

al. (1980). It was felt that phosphorus retention capacity

of soils could not be measured indirectly, e.g. by extract-

able iron and aluminum. It was concluded that repeated

additions of fresh phosphorus solution gave a more realistic

estimate of the long term retention capacity of a given

soil. However, since the correlations between the Langmuir

sorption maxima and the multiple addition values were high,

the sorption maximum could be a useful measure if the

conversion factor was known.

Column Studies

Larsen et al. (1958) studied phosphorus retention and

leaching by organic and mineral soils using soil columns.

phosphorus retention appeared to closely correlate to the

sesquioxide content and degree of decomposition. The virgin

muck with the lowest sesquioxide content retained the least

amount of applied fertilizer phosphorus. In contrast, the

mineral soil possessing the highest sesquioxide content

retained all of the phosphorus. For the mineral soil,

phosphorus was only detected in the upper 1.5 inches of the

soil core.

Farnham and Brown (1972) studied phosphorus uptake

using plastic cylinders which contained various combinations

of peat soils over sand as filtering media. These experi-

ments were conducted along with those using peat-filter beds

(lysimeters)5 already in progress. Both secondary sewage

effluent and solution spiked with phosphorus were applied.

It was not clearly specified just how much phosphorus was

removed by the cylinders, but it was stated that they

satisfactorily removed phosphorus even with additions as

high as 700 inches. Systems where quackgrass (Agropyron

repens) was seeded on the peat consistently removed more

phosphorus than those without grass cover. The systems that

contained only bare peat over sand were erratic in regard to

phosphorus removal. It was felt that vegetative cover

reduced the moisture content thus permitting a more uniform

distribution of influent and microbial activity.

A surprising result of this study was that the physical

condition of the peats improved with time during the appli-

cation period rather than deteriorate due to loss of struc-

ture. Infiltration capacities of the peats were observed to

improve with time.

Rock et al. (1984) used columns to determine the

capacity of sphagnum peat at various hydraulic and organic

loadings. Results showed that the peat was incapable of

removing substantial amounts of phosphorus. The limited

phosphorus removal of 10% was attributed to microbial

assimilation rather than adsorption. It was felt that soil

Fe and Al in concentrations of 0.076 and 0.069% respectively

were too low to be a factor in phosphorus uptake. Nichols

and Boelter (1982) reported higher phosphorus removal in

peat-soil filter beds and attributed this to its higher Fe

and Al contents of 0.46 and 0.51% respectively.

Sawhney (1977) studied phosphorus removal by two acid

mineral soils under saturated conditions. The soils were

treated with solution containing 6 ppm P, but no mention of

electrolytes was made. Results showed that the amount of

phosphorus retained by fine sandy loam (fsl) and silt loam

(sil), before the occurrence of breakthrough, was about

equal to the sorption capacities determined from isotherms

obtained over a long reaction time of 200 hours. Break-

through occurred for fsl and sil soils after 50 and 60 pore

volumes of phosphorus solution were respectively applied.

This was equivalent to approximately 2,500 ml of influent

solution. The amount of phosphorus uptake by the fsl soil

at the time of breakthrough was 65 micrograms per gram. It

was felt that phosphorus removal over an extended period of

time involved a faster adsorption reaction onto mineral sur-

faces in addition to a slower precipitation reaction. The

slow reaction was speculated to be due to the precipitation

of Al and Fe phosphates. It was concluded that although

phosphorus is readily adsorbed by the soil, the concentra-

tion of phosphorus in the effluent will be increasingly

large after breakthrough.

Lance (1977) studied phosphorus removal from secondary

sewage effluent by columns containing calcareous sand.7 The

columns were flooded periodically for nine days with a

five day drying period in between. This schedule was

maintained for a period of two years prior to the experi-

ments conducted in the report! The concentration of phos-

phorus was reduced from 12 ppm to below 1.0 ppm P for over

200 days before increasing and levelling off at various

equilibrium values depending on the infiltration rate. The

amount of phosphorus removal increased as the infiltration

rate decreased. Evidently phosphorus was initially adsorbed

by a reaction independent of flow velocity or contact time,

but when this adsorption capacity was exhausted, the amount

removed was determined by a time dependant adsorption or

precipitation reaction. Overall, the results indicated that

tremendous quantities of orthophosphate can be stored in a

calcareous sand and that even when the adsorption capacity

is exhausted, 75 to 80% of phosphorus can be removed at

loading rates below 15 cm per day. An interesting aspect of

this report was that the presence of bermudagrass greatly

increased the levels of phosphorus in the column effluents!

It appeared that plant root exudates were responsible for

maintaining a higher solution phosphorus concentration.

Digestion Methods Used to Determine Total Phosphorus In

The objective of this analytical experiment was to

investigate and compare the reliability of methods for

measuring total phosphorus content in soils. The total

phosphorus amount was needed for the purpose of evaluating

future mass balance experiments. The following section

contains a review of different methods employed to digest

total phosphorus from substrates prior to analysis. In this

work digestion is defined as the conversion of condensed and

organic forms of phosphorus to the ortho form which can be

analyzed. Substrate includes bottom materials such as

soils, sediments and sludges or biological materials such as

plant tissues. The extraction of phosphorus from a given

amount of substrate by any method, followed by analysis,

constitutes measurement of phosphorus content. When the

term digestion is employed, it is assumed that total

phosphorus is being extracted for analysis. A number of

different methods have been used for extracting total

phosphorus. Two methods which have been considered most

reliable for total phosphorus include fusion with sodium

carbonate (Na2CO3) and digestion using perchloric acid

(HC104). These procedures are outlined by Jackson (1958)

and the American Society of Agronomy (ASA) No. 9 monographs,

part 2 (1965). The Na2CO3 fusion method, although tedious

and expensive (platinum crucibles are needed) is regarded as

a method that will recover quantities of phosphorus equal to

or greater than other methods. The perchloric acid method

has been shown to recover almost as much phosphorus as

Na2CO3 fusion in most cases. However, the perchloric acid

method also has its disadvantages. These include the need

for a special hood apparatus for safely removing HCIO4

fumes, and the necessity for pre-oxidizing soil organic

matter to prevent violent reaction upon contact with the

HC14. Because of the disadvantages with the Na2CO3 fusion

and HCIO4 methods, other digestion procedures for extracting

total phosphorus have been investigated.

Anderson (1976) compared phosphorus recovery from lake

sediments by two different methods. The first method used

was the perchloric acid digestion. The other method studied

was the ignition method. Because of the organic matter

present in the sediment, the perchloric acid digestion had

to be supplemented with pre-nitric acid treatment due to the

violent reaction possible between perchloric acid and

organic matter. The ignition method utilized a muffle

furnace at 5500C followed by boiling in dilute hydrochloric

acid (HC1). Results showed that the ignition method gave

only slightly lower recovery values compared to the per-

chloric acid digestion (i.e., 94.4 to 100.5% phosphorus

recovery) for four sediment samples and one sample of dried

leaves. The reproducibility of the ignition method was also

only slightly less than that of the perchloric acid method.

In addition, the ignition method was further evaluated by

testing recovery of phosphorus from sediments spiked with

known amounts of hydroxyapatite Ca5(PO4)30H. The recovery

of phosphorus for spiked sediments ranged from 98.5 to

102.6%. Anderson noted that the ignition method did not

seem to be as suited for substrates with a high content of

humic matter. However, even though the percent recovery of

phosphorus was lowest for the humic matter (i.e., dried

leaves), recovery was still 97.3% of that obtained for

perchloric digestion. Dick and Tabatabai (1977) developed

an alkaline oxidation method for total soil phosphorus

determination. They pointed out that the two most widely

used methods of perchloric acid and Na2CO3 fusion both had

disadvantages. The perchloric acid digestion for phosphorus

was noted to give low results if the soils contained sili-

cated minerals of phosphorus. This would have to be

accounted for by adding hydrofloric acid (HF) to the list of

undesirable reagents. The Na2CO3 fusion method was felt to

be too tedious and expensive. Using the alkaline oxidation

method, which involved boiling the soil with sodium hypo-

bromite in a sand bath, the amount of phosphorus recovered

was in close agreement to that obtained by the perchloric

acid and Na2CO3 fusion methods. The substrates measured

included a diverse group of mineral soils, lake sediments

and sewage sludge. The average phosphorus recovery from

mineral soils by alkaline oxidation was about 4% lower than

Na2CO3 fusion, but 1% higher than perchloric acid digestion.

It was observed that for soils containing high amounts of

iron, the alkaline oxidation method did not recover as much

phosphorus if the soil solution ration was greater than

0.004. The overall precision for the alkaline oxidation

method was observed to be high. Although the phosphorus

content of substrates ranged from 162-34,200 ppm, the

coefficient of variation of sample replicates was never

above 2.6%. Wilken and Bowman (1982) modified a block

digestion procedure originally used to measure total phos-

phorus and total Kjeldahl nitrogen in natural water samples.

The procedure employed a mixture of sulfuric acid (H2S04),

potassium sulfate (K2SO4) and mercuric oxide (HgO) as the

digestion reagent. The modifications included increasing

the digestion acid volume, the length of digestion time and

the volume of diluent. These changes were employed to test

if the block digestion procedure could be used for measuring

the total nitrogen and phosphorus of sediments and sludges.

Evaluation of the methods' precision was conducted by

spiking sediments and sludges with known quantities of

nitrogen and phosphorus prior to digestion. Evaluation of

accuracy was accomplished by digesting reference sediments

and sludges along with organic nitrogen compounds. Results

showed the mean phosphorus recovery of samples spiked with

monobasic potassium phosphate (KH2PO4) was 100% for sludge

samples and 101% for sediment samples. The modifications of

the block digestion procedure gave results that indicated it

would be useful for determining total phosphorus and total

Kjeldahl nitrogen in both sediments and sludge.

Fate of Phosphorus in Wetlands Treated with Wastewater


J. Zoltek (Prof. of Environmental Eng., Univ. of Fla.,

personal communication, 1979) noted the problem of ultimate

disposal of secondarily treated sewage in the state of

Florida in addition to other sections of the country.

Although low in organic content, secondary effluent contains

relatively high concentrations of nitrogen and phosphorus

which cause eutrophication of lakes and streams. In Florida

the problem is magnified because of the presence of many

warm and shallow lakes which are easily eutrophied by small

additions of nutrients, particularly phosphorus. Removal of

nutrients in wastewater by the use of advanced waste treat-

ment (AWT) has proved to be a very costly solution to the

problem. An alternative to AWT is the disposal of effluent

in freshwater wetlands where the nutrients are removed

and/or diluted before reaching open lakes or streams.
Recently in Florida, a new rule has been adopted which

will allow more extensive use of wetlands for the disposal

and treatment of domestic wastewater effluent. Prior to the

new rule, wetlands could only be used for sewage disposal if

all water quality standards were met in the wetlands or if

special approval was granted for limited experimental use.

Three new categories of wetlands that have been added as a

result of the new rule include

(1) All man-made or created wetlands.

(2) All hydrologically altered wetlands.10

(3) Woody or non-herbacious unaltered wetlands.

The sections to follow review studies which have been

conducted using both natural and artificial wetlands to

treat wastewaters with emphasis on soil phosphorus removal.

Natural Wetlands

Zoltek and Bayley (1979) conducted a field study of a

peat marsh used for treating effluent wastewater in

Clermont, Florida. Small areas were isolated to achieve a

quantitative estimate of the nutrient balance in the

ecosystem. All major components of the system were moni-

tored for a 24-month period. The results showed that most

of the nitrogen could be accounted for, but the same mass

balance could not be achieved for phosphorus. Effluent

sampling from the treated areas showed that removal of

phosphorus was very high (97-99%), but the amount of phos-

phorus stored in the system did not verify the high phos-

phorus removal. It was not known if the techniques for

measuring total phosphorus in the system were inaccurate, or

whether phosphorus had been flushed out of the system unde-

tected. McKim (1982) studied the treatment of secondary

effluent using natural wetlands for Disney World in central

Florida. It was observed that significant reduction of

phosphorus did not occur. The organic soils of the system

were considered to have poor ability to adsorb phosphorus

and it was speculated that nutrients from stormwater may

have overloaded the system. Boyt et al. (1977) studied the

fate of nutrients by a well established wetland treatment

system in Wildwood, Florida. Phosphorus reduction in this

hardwood swamp was reported to be as high as 98%. However,

total phosphorus measured in sediment core samples was not

higher than the total phosphorus content of control sedi-

ments. The high reduction of phosphorus through the treat-

ment area was attributed to the dilution factor caused by

all combined inputs to the swamp. Dierburg and Brezonik

(1983) summarized the results of a long term field study of

cypress domes treating wastewater effluent in Gainesville,

Florida. It was concluded that 92% of the phosphorus

entering the treated dome was removed by plant uptake or

sediment deposition. The phosphorus assimilative capacity

was not found to be diminished over a three-year period.

Kadlec (1981) reported that despite 90% nutrient removal

from wastewater in a Michigan freshwater marsh, no signifi-

cant change in soil content was observed. A nutrient

concentration increase was observed in the surface water

surrounding the wastewater discharge point which gradually

decreased away from the site. The decrease was attributed

to luxury uptake of nutrients by plants surrounding the

discharge site. However, it was found that nutrients were

only temporarily immobilized by vegetation, because signifi-

cant quantities were observed to be released by seasonal

decomposition and leaching of dead plants. Kadlec and

Hammer (1981) reported, in a summary of the Houghton Lake

(Michigan) site, that a quantitative estimate of the phos-

phorus pathways in the entire marsh could not be made. This

was because the background content of phosphorus in soil and

vegetation was too high compared to the amount of phosphorus

added by effluent wastewater. Tilton and Kadlec (1979)

conducted a pilot study at the Houghton Lake site prior to

full scale disposal of wastewater. It was observed that the

efficiency of phosphorus removal by the marsh was higher

when the surface water depth was 6 cm compared to 30 cm. In

addition, the phosphorus content of peat soil samples

obtained close to the discharge point was found to be higher

than background levels. This suggested the possibility that

the wastewater phosphorus was taken up by the peat despite

the fact that a clay layer underneath the peat minimized

downward flow through it. It was also observed that the

phosphorus content of vegetation increased at the same time

that increased phosphorus was noticed in the marsh peat.

Fetter et al. (1978) sampled a Wisconsin cattail marsh

intensively with the goal of obtaining an accurate mass

balance of nutrients. The marsh, located downstream from

the city of Brillion, received significant pollution loading

from domestic and industrial treatment plants plus agricul-

tural runoff. Removal of phosphorus through the entire

system over a 15-month period was estimated to be about 32%.

The phosphorus content of the organic marsh sediment

appeared to remain uniform throughout the study period,

ranging from 1.2 to 2.4 mg phosphorus per gram of soil.

However, the phosphorus content of the sediments in the

two channels leading to the marsh were 9.0 and 21.0 mg phos-

phorus per gram of soil, respectively. It was thought that

significant phosphorus was being uptaken by the clay and/or

silt fractions of the channel sediment. Phosphorus removal

was also suspected to be occurring as a result of coprecip-

itation by aquatic plants aided by existing hardwater

conditions. Lee et al. (1975) studied four marsh areas in

Wisconsin which received nutrient loading from agricultural

runoff and domestic wastewater effluents. The complex

hydrology of these areas prevented an accurate quantitative

assessment of the overall nutrient budgets. Two of the

marshes appeared to be precipitating calcium carbonate in

the summer months and the coprecipitation of phosphorus was

also believed to be occurring. However, there appeared to

be more evidence that the marsh systems were exporting

phosphorus instead of removing it. Even during the growing

season when net uptake of phosphorus was expected, export of

phosphorus was observed to occur during periods of high

flows. It was felt that phosphorus was being dissolved from

decomposing vegetation and then leached out during the high

flow periods. It was also observed that an unusually high

fraction of the phosphorus exported from the marshes was in

organic form. Simpson et al. (1983) studied the nutrient

budgets of two freshwater tidal marshes in Delaware that

received significant non-point source pollution. Results

indicated little evidence that phosphorus was accumulating

in the soil, although one of the marshes showed higher soil

phosphorus content during the fall season. Steward and

Ornes (1975a and b), studied the nutrient distribution of

fertilizer enriched plots of an everglades marsh in South

Florida. The phosphorus content of the organic soil was

measured to be four times higher in treated plots than in

control plots. However, 125 days after treatment ceased the

phosphorus content of the soil dropped 50%. This indicated

that phosphorus was being utilized by plants or being

removed by some other pathway such as leaching. One possi-

bility was that the phosphorus could have changed its form

and subsequently was not detected by the measurement tech-

nique used. Kitchens et al. (1975) studied a hardwood swamp

in South Carolina that received a significant nutrient load

from upstream civilization. Intensive sampling was done in

all regions of the swamp to obtain a "nutrient-map" of the

ecosystem. Results indicated that net uptake of nutrients

was occurring, especially for phosphorus. The flow pattern

within the swamp was sheet flow with no additional hydrolo-

gical inputs that could account for dilution. It was felt

that phosphorus uptake was occurring as a result of demands

by aquatic and epiphytic vegetation. The possibility that

phosphorus was being adsorbed by suspended silts and clays

which settled out in the swamp was not ruled out.

Nichols (1983) supported the theory that phosphorus

uptake by soils under acid conditions occurs by combining

with iron and aluminum. Similarly, phosphorus is thought to

combine with calcium under neutral to alkaline conditions.

However, it was felt that retention of phosphorus by wetland

environments receiving wastewater would decrease with time

because the soils would become phosphorus saturated.

Nichols (1983) believed this phenomenon occurred in Dundas,

Ontario (Cootes Paradise), where a net release of soil

phosphorus appeared to be occurring in the effluent canal

leading to the marsh. The canal was eventually dredged,

thus exposing fresh soil to the flow. After the dredging a

net decrease in phosphorus concentration was observed to

occur in the effluent passing through the channel. It was

felt that the marsh soils were also saturated with phos-

phorus that was released when the soils were exposed to

solution low in phosphorus concentration. In his review of

different wetland treatment sites, Nichols (1983) felt that

the overall nitrogen and phosphorus removal was most effi-

cient at low loading rates. Kadlec (1981) concluded sedi-

ments were an important factor in phosphorus removal. The

sediments were considered unique in that they originated

from wastewater and/or runoff, thus becoming a new component

of the ecosystem. During their mobile phase, the sediments

were thought to react with and remove solution phosphorus as

they gradually settled out in the ecosystem. Kadlec (1981)

pointed out that the soil was the only ultimate sink for

phosphorus in the natural wetland ecosystems he reviewed.

Phosphorus release from soils was considered to be occurring

at a much slower rate than soil phosphorus uptake. However,

only a relatively shallow layer of the substrate (soils and

sediments) was considered to be involved in phosphorus

uptake. Van der Valk et al. (1979) reviewed a number of

different wetlands utilized for treating wastewaters. Of

the seventeen sites presented, sixteen demonstrated net

phosphorus uptake at least during the growing season.

However, because of the evidence showing seasonal releases

of phosphorus, many of these ecosystems ended up releasing

more phosphorus on a yearly basis than they retained. Stumm

and Morgan (1970) and Wetzel (1975) stated that orthophos-

phate forms insoluble complexes with various metals such as

iron under aerobic conditions. In anerobic conditions

however, phosphorus can diffuse from the substrate into the

water column. The various wetland studies presented by Van

der Valk et al. (1979) showed different results as to

whether the primary phosphorus uptake took place in the soil

or by plants and algae. It was concluded that because of

the different conditions encountered by the wetland treat-

ment sites reviewed, it was impossible to make realistic

comparisons in regard to nutrient removal. Steward and

Ornes (1975) also showed evidence that phosphorus can be

quickly transferred from soil to plants, but the phosphorus

is later released during litter decay. Whigham (1982)

reviewed various wetland treatment sites and observed that

peat based systems and cypress domes appeared to be best

suited for wastewater treatment. The difficulty in evalu-

ating such ecosystems, however, appears to be the accounting

for phosphorus in the soil. Spangler et al. (1976), Fetter

et al. (1978) and Simpson et al. (1978) found that phos-

phorus was only retained seasonly in non-peat based wetland

systems. This was attributed to marginal uptake by the soil

and significant seasonal release patterns. Whigham (1980)

observed that phosphorus in a non-peat ecosystem was tempor-

arily immobilized in the litter component. Klopatek (1978),

Prentki et al. (1978) and Kitchens et al. (1975) pointed out

that harvesting vegetation in natural wetland systems will

not guarantee increased nutrient removal by the system.

The wetland studies discussed above are summarized in

Table 2.1. These and many other wetland studies are also

Table 2-1. Natural Wetlands Used for Wastewater Treatment.

Investigators) Year Location Wetland Type

Zoltek et al.
Dierburg &
Kadlec &
Fetter et al.
Lee et al.
Simpson et al.
& Ornes
Kitchens et al.
Boyt et al.



a & b

Clermont, Florida
Disney World, Florida
Gainesville, Florida

Bellaire, Michigan
Houghton Lake, Michigan

Calumet County, Wisconsin
Dane County, Wisconsin
-- Delaware
South Florida

South Carolina
Wildwood, Florida

freshwater marsh
freshwater marsh
cypress domes

northern peatlands
northern peatlands

freshwater marsh
freshwater marsh
freshwater tidal marsh
everglades sawgrass
hardwood swamp
hardwood swamp

Above classification scheme is general. Refer to discussion by CTA Environmental, Inc.
et al. (1983) for more extensive and detailed versions. This source also contains more
information regarding wetland treatment sites in southeast USA.

summarized in reviews by Tchobanoglous and Culp (1980),

Whigham (1982) and Nichols (1983).

Artificial Wetlands

Tchobanoglous and Culp (1980) defined artificial

wetlands as those constructed in locations where none

previously existed. Brinson and Westall (1983) defined

three categories of artificial wetlands

(1) Aquaculture systems--artificial wetlands which

treat wastewater for the purpose of harvesting

biomass as a food, fiber or fertilizer resource.

(2) Designed wetlands--wetlands designed specifically

for wastewater treatment. The field is open in

creative efforts to design systems which mimic

natural ecosystems.

(3) Volunteer wetlands--conventional land treatment

systems which are hydraulically overloaded either

intentionally or non-intentionally.

The studies reviewed in this section consist mainly of those

in the designed wetlands category. In addition, some of the

studies reviewed are of natural wetlands which have been

modified by man-made controls. The purpose of modifying

natural ecosystems usually is to enhance the efficiency of

wastewater treatment.

Seidel (1976), along with coworkers in Europe, pio-

neered artificial wetlands for wastewater treatment. The

systems utilized specific vegetation planted in gravel

substrates and have been used in Holland, Hungary, Poland

and Yugoslavia. A similar system was eventually patented in

the United States. Seidel (1976) emphasized that vegetation

"should not be allowed to feed from nutritious soils, but

should have to rely on nutrients available in the water that

is applied to the planting bed. For this reason, vegetation

must stand in inert material, i.e. gravel or sand, which has

been washed." However, Spangler et al. (1976) found that

66% of the phosphorus retained by a gravel bed wetland was

associated with the gravel. De Jong (1976) reported that

the vegetation in such a system merely provided attachment

sites for a phosphorus sorbing microbial population. Small

(1978) discussed the use of artificial wetland systems used

to treat sewage in New York, as a basis for similar systems

in Florida. One system consisted of a meadow-marsh-pond in

series and the other a marsh-pond in series. Phosphorus

removal was measured for each system component so that

comparisons of removal efficiency could be made on indi-

vidual sections. The results showed that individual com-

ponents of the multiple ecosystem had higher phosphorus

removal efficiency. The individual components of both

systems were able to retain shock loads of phosphorus. It

was postulated the removal of phosphorus occurred as a

result of its combination with sediments that were being

deposited in the wetland systems. Sediments containing iron

and/or aluminum were thought to provide the primary sites

for which phosphorus was being completed and/or

precipitated. The data accumulated in a period of

four years in Brookhaven showed that phosphorus levels in

domestic wastewater could be consistently reduced to between

1 and 2 ppm. This level was satisfactory for discharge to

the Long Island aquifer. Wile et al. (1981) studied the

treatment of municipal wastewater by an artificial wetland

systems in Listowel, Ontario. Different types of wetland

systems were examined for their capability of handling both

raw domestic wastewater and wastewater effluent. The

different systems included component ponds, marshes and

channelled marshes individually and in combinations. Except

for the pond, all components were constructed by first

compacting and backfilling the underlayer with a mixture of

subsoil, topsoil and peat. Then vegetation was planted in

the form of cattails. Results indicated that phosphorus

removal was significant in all wetland systems during the

growing season. It was also observed that phosphorus

removal efficiency was better in systems which received the

raw wastewater. During the winter the uptake of phosphorus

in all systems was reduced, but the artificial wetland

receiving raw wastewater continued to remove a significant

amount of phosphorus. Farnham and Brown (1972) studied the

removal of phosphorus in secondary wastewater effluent using

outdoor peat filter beds (lysimeters). The study was

conducted in Minnesota for two consecutive years including

winters. Results showed that the peat-sand filter beds

operated most efficiently with the water level slightly

below the surface of the peat. This condition was accom-

plished by underlying the peat with a sand/soil mixture.

This mixture allowed just enough drainage to lower the water

content of the peat surface. Measurements taken for a

12 week period from September through December showed

consistent phosphorus reduction from 7 ppm to 0.05 ppm.

Similarly the BOD was reduced from 110 ppm to 2 ppm. After

a period of time, it was evident that the peat filters

planted with vegetation were more effective in removing

phosphorus than filters which contained soil only. Phos-

phorus removal efficiency was reduced in winter but remained

significant. Severely cold weather caused freezing prob-

lems. The rate of wastewater application to the peat

filters was 10 cm per day but rates as high as 20 cm per day

for short periods did not cause overloads. Farnham and

Brown studied filters that consisted of both reed sedge peat

as well as sphagnum moss peat. Both types of peat filters

were highly efficient in removing phosphorus from wastewater

during the growing season. The uptake of phosphorus was

attributed to microbial assimilation and adsorption within

the aerobic surface layer of the filters. It was speculated

that the high carbon content of the peat plus the additional

carbon from wastewater was responsible for stimulating

microbial activity. The microbes were thought to be assim-

ilating inorganic phosphorus, thus converting it to organic

form. Evidence of microbial activity was further supported

by the increased percolation capacity of the filters with

time. This was attributed to the microbes consuming excess

organic matter that would otherwise clog the filters.

Chemical uptake (adsorption/precipitation) by the soil was

thought to be occurring because iron, aluminum and calcium

were present in sufficient amounts. Farnham (1974) reported

continued results of outdoor peat filter beds used for

treating secondary wastewater effluent. Peat soils com-

prised of different degrees of decomposition were compared.

All peat soil types proved to be suitable for nutrient

removal using an underlayer of sand/soil, but the best media

for growing grasses was the moderately decomposed hemic peat

soil. Results of a hemic filter bed treating wastewater for

a 12-week period showed that phosphorus removal was very

high. The removal of phosphorus was attributed to the

combined effects of soil, microbes and vegetation. As

expected, the high BOD removal that also occurred was

evidence of significant microbial activity within the

filters. In regard to phosphorus removal efficiency,

optimum ratios of carbon (C), nitrogen (N) and phosphorus

(P) were determined. It was found that the best C/P ratio

was 500/1 and the best N/P ratio was 4/1. To test the

phosphorus loading capacity, a peat filter bed was dosed

with a synthetic phosphorus solution of 40 to 50 ppm. The

filter bed soon became overloaded with this continual

dosage. Upon subsequent reduction of the phosphorus concen-

tration to 5 to 10 ppm, the filter system was able to reduce

phosphorus efficiently again. In separate experiments

Farnham tested various grasses in regard to their ability to

enhance the nutrient uptake of the filter beds. The spe-

cific results were not published, but it appeared that

vegetation increased the lifespan of the filter in regard to

nutrient uptake. In his summary, Farnham attributed more

phosphorus removal by microbial activity than by sorption to

the peat soil. Vegetation was highly recommended if effi-

cient wastewater treatment was desired for a long time span.

Nichols and Boelter (1982) studied the treatment of secon-

dary effluent wastewater using a unique peat-sand filter

bed. The system was located at the North Star Campground in

Minnesota and was operated five months per year for

eight years. The peat used in the filter bed was a moder-

ately decomposed reed-sedge acid peat. From 1973 to 1980

the filter removed phosphorus in the wastewater from an

average of 8.63 ppm to 0.07 ppm. The main ecosystem com-

ponents were tested for their phosphorus content in an

attempt to account for the nutrients removed by the system.

Results showed that 88% of the phosphorus applied from 1979

could be accounted for in harvested vegetation and within

the filter bed to a depth of 40 cm. A breakdown of that

88% showed that 37% was removed in grass cuttings, 37% was

in the peat to a depth of 12 cm and the remainder was

measured in the lower peat-sand layers. Phosphorus uptake

in the soil was attributed to adsorption and/or precipita-

tion as a result of the relatively high soil iron and

aluminum content. In order to test if phosphorus was

leaching from the filter during late fall and early spring,

sampling was conducted during these times for two consecu-

tive years. No evidence of phosphorus leaching was detected

from seasonal turnover. The peat filter bed continued to

effectively remove both nitrogen and phosphorus from secon-

dary wastewater after eight years. In regard to nutrient

removal, the filter was estimated to have a life of 12 years

with wastewater loading averaging 7 cm per week. It was

thought that the filter lifetime could be significantly

increased by applying the wastewater more evenly and by

supplementing the peat soil with additional iron and alum-

inum. Kamppi (1972), Surakka and Kamppi (1971), Farnham and

Brown (1972) and McKay (1980) each reported modified wet-

lands utilized for treating raw wastewater in Finland. The

systems consisted of peatland infiltration ditches that were

drained down to appropriate levels in order for sewage to be

pumped into them. The wastewater then percolated horizon-

tally through the peat soil until it reached smaller inter-

cept ditches. This process accomplished average removals of

35% phosphorus, 62% nitrogen, 80% BOD and 90-95% bacteria.

One such system, located at the village of Kesalahti, has

been achieving 82% phosphorus removal and 90% nitrogen

removal since 1957. Overall, about 20 ditched peat systems

were in operation in 1976, most being operated to treat raw

wastewater from small villages. However, two of these

systems were being used to treat dairy and potato processing


Forsee and Neller (1942) studied phosphorus leaching in

everglades peat used for growing crops under lysimeter

conditions. The loss of phosphorus by leaching was measured

to be small for all time periods, but this may have been a

result of the fact that 59 to 84% was being removed by

crops. Thus the phosphorus fertilizer added had been

utilized very efficiently by the growing crops with little

lose due to leaching.

Wapora Inc. (1983) reported the treatment of screened

raw sewage in narrow marsh trenches using subsurface flow

and underdrains. Because of limited pretreatment the system

became clogged and there was a difficulty in establishing

stands of planted vegetation. Treatment efficiency remained

poor despite efforts to maintain flow control by raking the

sludge buildup on the marsh surface. Wapora Inc. (1983)

also reported phosphorus removal efficiency as high as

98 percent in the Listowel system described earlier (Wile et

al., 1981). However, it was felt that phosphorus removal

efficiency would eventually decline because substrate

sorption sites would be used up. The substrate consisted of

a mixture of subsoil, top soil and peat. Phosphorus removal

by chemical addition was therefore recommended during


Overall, artificial wetlands have been reported to be

more efficient in removing phosphorus, nitrogen and COD from

wastewater than natural wetlands (CTA Environmental, Inc. et

al. 1985). Wapora, Inc. (1983) report that in most

instances, the primary purpose of a constructed wetland

system is nutrient removal. Although phosphorus can be

permanently fixed onto soils, there does not exist a removal

pathway equivalent to denitrification for nitrogen.

Harvesting vegetation would be the only phosphorus removal

pathway from the system. There has been no comparison

conducted to determine the long term adsorption capacity of

different types of soil. The artificial wetlands discussed

in this chapter are summarized in Table 2-2.

Table 2-2. Artificial Wetlands Used for Wastewater Treatment.

Investigators(s) Year Location Configuration Waste+

Seidel 1976 Europe vegetation in gravel substrate
Wagner 1974 U.S.A. vegetation in gravel substrate
Spangler et al. 1976 Seymour, Wisconsin vegetation in gravel substrate 1, 2
De Jong 1976 Europe ponds with rushes or reeds 1
Wile et al. 1981 Listowel, Ontario artificial marsh-pond system 4, 5
Farnham & Brown 1972 St. Paul, Minnesota peat filter beds 1
Farnham 1974 St. Paul, Minnesota peat filter beds 1
Nichols & Boelter 1982 Marcell, Minnesota peat/sand filter bed 1
Kamppi 1971 Finland peat infiltration ditches 1, 2
Surakka & Kampi 1971 Kesalahti, Finland peat infiltration ditches 1, 2, 5
Small 1978 Brookhaven, N.Y. marsh and pond 5
Pope 1981 Laguna Miguel, Cal marsh trenches 5
Gersburg 1982 Santee, California marsh trenches 1
Water & Wastes Int. 1982 Neshamjay Falls, N.Y. marsh-pond-meadow system 5
Brooks et al. 1984 Orono, Maine peat filter fields 3

+Wastewater effluents-(1) secondary (2) primary (3) septic tank (4) stabilization pond
(5) raw wastewater. Others- (6) slaughterhouse (7) crop irrigation (8) agricultural


"Sesquioxides"--general term referring to oxides and
hydroxides of iron and aluminum.

Retention is used here to loosely describe phosphorus
removal from solution implying no distinct reaction type or

Refer to the work of Lindsay and Moreno (1960).

Variscite and strengite are Al and Fe phosphates

A "lysimeter" is a device for measuring percolation
and leaching losses from a column of soil under controlled

"Breakthrough" is defined as the point where phos-
phorus is first detected in the column effluent.

In contrast to the silica sand (contained in some of
the soils in this study), calcareous sand is made up of
calcium and/or magnesium carbonate and has been shown to
react with phosphates.
Refer to amendments to Chapter 17-6, Florida Adminis-
trative Code (FAC), Wastewater to Wetlands Rule, effective
April 27, 1986.

9Man-made treatment wetland--Refer to 17-6.030 (FAC).

10Hydrologically altered wetland--Refer to 17-6.030



Digestion Methods Used to Determine total Phosphorus


Four different methods for digesting soils were

evaluated in regard to their ability to extract total

phosphorus from a soil. The methods studied were:

1. Perchloric acid digestion method

2. Persulfate/sulfuric acid method

3. Ignition method

4. Alkaline oxidation method.

The soil used to evaluate the four methods was a

histosol collected from a peat marsh in Clermont, Florida.

Ten samples of peat soil were digested by each method.

Perchloric Acid Digestion

Three preliminary soil samples were digested prior to

proceed with the test on 10 soil samples. The purpose was

to troubleshoot the method and eliminate any unforeseen

problems. The sizes of the preliminary samples were one,

two and three grams, respectively. The peat soils were

weighed out and digested in their natural wet state without

any kind of pretreatment or drying. The preliminary samples

were initially placed in beakers to which 10 ml of

concentrated nitric acid and about 25 ml of deionized water

were added. The purpose of the nitric acid was to oxidize

the organic matter in the peat to prevent the possibility of

an explosion that could result from direct mixing with

perchloric acid. The mixtures were heated using a hot plate

until about half the initial volumes were evaporated off.

It is noted that the procedure was carried out using a

special hood apparatus designed to handle perchloric acid

(HC104) fumes. At this time, 15 ml of HC104 was added

slowly to each sample. About six high purity alundum

boiling granules were also added. The mixtures were

evaporated slowly by gentle boiling until dense white fumes

appeared. The samples were then allowed to cool before

preparing them for phosphorus analysis.

The digestates were prepared for phosphorus analysis by

dilution, neutralization and filtration. The digestates

were defined as the final solution obtained from a method

used to extract total phosphorus (or other element) from a

soil. The solution is assumed to contain the total amount

of the element originally present in the soil. Each sample

was diluted with deionized water and neutralized with drops

of 11 N NaOH. Several backdrops of 11 N H2S04 were added to

redissolve any precipitates formed during neutralization.

Filtration was accomplished with the use of syringe-operated

easy-pressure holders and glass fiber filters. All

dilutions and additions were recorded in order to make the

proper back calculations for original phosphorus content.

The samples were then set aside for phosphorus analysis. To

avoid confusion, phosphorus analysis will be referred to in

this work as analysis of phosphorus in the ortho form.

Since it is assumed that digestion of the soil converts all

phosphorus to the ortho form, the analysis is equivalent to

total phosphorus.

The procedure described above was repeated with ten

additional samples of Clermont peat, but with a few

modifications. A portion of the peat was blended before

weighing out the samples for digestion in order to obtain

better homogeniety. Also, instead of using small beakers to

start the digestion procedure, 125 ml erlenmeyer flasks were

substituted for the entire procedure. In addition, the new

digestates were filtered prior to NaOH neutralization

instead of after this step. Filtration was performed

initially because it was found that neutralizing the

solutions in the presence of the soil substrate resulted in

a loss of phosphorus. However, it should be noted that the

perchloric/nitric solutions eroded the plastic

easy-pressure filter holders. Phosphorus analysis was

performed twice on all samples using different instruments

as a check on each other. This quality control step was

adopted for all digestion methods. The first instrument

used was a Technicon Auto-Analyzer II (automated) system and

the alternate instrument used was a Perkin Elmer 552


Persulfate Digestion

The persulfate digestion was originally developed for

determination of total phosphorus in wastewater and natural

water samples. The procedure is outlined in Standard

Methods for the Examination of Water and Wastewater (1980).

However, in this case it was adapted for determining the

total phosphorus content of soil samples. Ten samples of

blended marsh peat were weighed into 125 ml erlenmeyer

flasks. Except for blending, the peat was not subject to

any pretreatment or drying. The wet weights of the peat

samples ranged between two and three grams. Each sample was

mixed with 50 ml of deionized water, 7.5 ml of 1.19 M

Potassium persulfate (K2S208) and five ml of 11 N sulfuric

acid. The samples were then heated at 1200C in an autoclave

for one hour at a pressure of 20 to 25 psig. After cooling,

an aliquot of each sample was filtered using easy-pressure

holders and glass fibre filters and then neutralized with

drops of 11 N NaOH. A pH meter was used to monitor the

neutralization. The samples were then analyzed twice for

total phosphorus by the ascorbic acid method. The first

analysis was done using a Technicon II Auto Analyzer and the

second analysis was performed using a Perkin Elmer 552


Ignition Method

This procedure was used to determine the total

phosphorus content of lake sediments as outlined by Anderson

(1976). Three preliminary samples of blended wet peat were

weighed into small porcelain crucibles. The wet weights of

the samples ranged from one to four grams. The samples were

then dried at about 500C for 19 hours. After cooling and

reweighing, the samples were ignited in a muffle furnace by

bringing the temperature up slowly to 5500C and maintaining

that temperature for 1.0 to 1.5 hours. The ignited samples

were allowed to cool overnight inside the furnace after

shutting off the heat. After cooling, the ash residues were

transferred into erlenmeyer flasks using a combination of

1.0 N HC1 and deionized water for rinsing. The transfer

technique was facilitated by using a small glass funnel and

a rubber policeman. The mixtures were then boiled on a hot

plate for 15 minutes using glass beads to aid in gentle

boiling. Aliquots from each sample were filtered and

neutralized using drops of 11 N NaOH prior to total

phosphorus analysis. In addition, other aliquots of the

samples that were not neutralized were also analyzed so that

a comparison could be made. At this point 10 additional

samples of peat were prepared for ignition in a similar

fashion. However, the oven drying temperature was raised

from 500C to 1000C with a drying time of 6.5 hours. The new

samples were similarly ignited, cooled, boiled and diluted

before neutralization and subsequent total phosphorus

analysis. All necessary back calculations were made to

account for additions, transfers and/or dilutions made with

the samples. Analysis of the samples for total phosphorus

were made by both the Technicon II Auto-Analyzer system and

Perkin Elmer spectrophotometer using the ascorbic acid


Alkaline Oxidation Method

This method for extracting total phosphorus from soils

was outlined by Dick and Tabatabai (1977). Three samples of

blended wet marsh peat weighing 1.8 to 2.3 grams were

weighed into to 50 ml erlenmeyer flasks and one 125 ml

erlenmeyer flask. Each sample was then mixed with 3.0 ml of

sodium hypobromite solution. This solution was prepared by

slowly adding 3.0 ml of liquid bromine with constant

stirring to 100 ml of 2.0 M NaOH. After swirling the

mixtures and allowing them to stand five minutes, the flasks

were inserted in a sand bath at a temperature of 2550C.

The sand bath was prepared by placing three to four cm of

silica sand inside a rectangular mold made of aluminum foil.

The aluminum foil was initially molded and placed on a large

hot plate prior to being filled with sand. The temperature

of the sand was monitored using a high temperature

thermometer and the entire procedure was carried out inside a

fume hood. The sand temperature was raised to about 2700C

and the flasks were heated to dryness in 10 to 15 minutes

followed by 30 minutes of additional heating time. After

cooling, each sample was mixed with deionized water, 90%

formic acid and 1.0 N H2SO4 and allowed to sit overnight.

An aliquot from each digestate was filtered and neutralized

with drops of NaOH and backdrops of H2SO4 to adjust the pH

prior to phosphorus analysis. The neutralization procedure

was monitored with a pH meter. The above procedure was

repeated in the same way for 10 additional samples of marsh

peat with the exception that only the small 50 ml flasks

were used to contain the mixtures. After filtration and

neutralization, the samples were analyzed twice for total

phosphorus using a Technicon II Auto-Analyzer System

followed by Perkin Elmer 552 spectrophotometer.

Digestion Results Conclusion

The digestion procedure chosen from the results

obtained from the evaluation tests was the ignition method.

Full details are presented in the results section. An

experiment was also conducted using EPA quality control

samples to further evaluate the ignition digestion before

utilizing it in the remainder of this study. The

description and results of this quality control test are

also included in the results section.

Collection of Soil Samples

Seventeen organic soils and one mineral sediment were

collected in Florida at locations identified in Table 3-1.

The peats were obtained by visiting peat mine sites and

Table 3-1. Identification and Locations of Organic Soils and Sediments.


Peace River Peat

Reliable Peat Co.

Peace River Peat

Traxlers Peat Co.

Florida Potting

Anderson Peat Co.

Greenleaf Prod-
ucts Inc.

Delta Soils Inc.

Disney World

Disney World

F.E. Stearns Peat













Florida Town







Haines City


Lake Buena Vista

Lake Buena Vista





Polk r

Putnam h


Lake r


Hillsborough r


OrangeHillsborough r
Hillsborough r

Soil Classification
US Dept.
of Int. OSRC System

low-ash peat

low-ash peat

*eed-sedge low-ash peat

lumus peat low-ash peat

low-ash peat

eed-sedge low/medium-ash
peat peat


eed-sedge medium-ash peat

medium-ash peat

high-ash peat

*eed-sedge medium-ash peat


Table 3-1. Continued.

Text Soil Classification
Refer- Nearest Florida US Dept.
Source ence Florida Town County of Int. OSRC System

12 Townson Peat TOW Eaton Park Polk medium-ash peat
& Soil

13 Superior Peat SUP Sebring Highlands humus high-ash peat
& Soil

14 Clermont Marsh CLE Clermont Lake high-ash peat

15 Lake Apopka APO1 Orange low-ash carbona-
Muck Farms ceous sediment

16 Paynes Prairie PAY Gainesville Alachua high-ash carbon-
Preserve aceous sediment

17 North Central JAS Jasper Hamilton high-ash carbona-
Florida Wetland ceous sediment

18 Abandoned borrow- TER Gainesville Alachua mineral sediment
pit (Terwilliger

collecting the samples from freshly excavated mounds of

peat. The remainder of soils were collected by hand-digging

them directly from their marsh environments. Two

classification schemes are also shown in Table 3-1. The

first scheme, labelled "soil type," is the classification

assigned to the soil by the United States Department of The

Interior. The second scheme is that assigned to each soil

according to the system adopted by the Organic Sediments

Research Center (OSRC), located at the University of South

Carolina. All soils were collected into five gallon buckets

with tight fitting lids and brought back to the laboratory

for subsequent experimentation. The buckets were initially

stored at room temperature for a short period and thereafter

at 170C in a walk-in constant-temperature room.

Determination of Measurable Soil Properties


To prepare the soils for laboratory measurement they

were mixed thoroughly inside their respective storage

buckets. This was accomplished with the use of a strong

wood stick or metal spatula. Samples from each bucket were

transferred to smaller plastic bottles with screw caps for

easier handling. The sample bottles were stored at room

temperature. Aliquoting samples of the organic soils for

testing was accomplished by using a small metal spatula for

the drier soils and a cutoff syringe for the muckier soils.

The techniques used to handle these organic soils in their

natural states had to be refined several times in order to

dispense and weigh them accurately. Aliquot weights for

soil property measurements ranged between two and six grams

on a wet weight basis.

Soil Sand, Moisture and Ash Contents

The ignition digestion method was also used to

determine sand, moisture and ash content of the soils in

addition to total phosphorus, iron and aluminum. The

moisture content of each soil was determined by measuring

the weight loss of samples as a result of over drying.

Triplicate samples of each soil were weighed into porcelain

crucibles and dried for 24 hours at 100 to 1100C. The

sample sizes were sufficiently small to assure that constant

weight had been achieved after the 24 hour time period. The

samples were allowed to cool to room temperature before

reweighing. All weight measurements were made using an

analytical balance. Although knowledge of individual soil

moisture contents was useful in predicting dry weight values

of soil samples, the moisture content value had no

scientific significance. This is because the actual "field"

moisture values were most likely not preserved during the

collection of the soil samples themselves. The moisture

content values of the soil samples are presented in later

sections only for comparative purposes. To determine ash

content, the over dried soil samples were placed inside a

muffle furnace and ignited at a sustained temperature of

5500C for about two hours. The time required to accomplish

complete ashing depended upon sample size, but two hours was

usually sufficient. After removal and cooling, the sample

crucibles were reweighed again. The ash content of each

soil was determined from the weight loss from the oven dried

samples as a result of ignition.

It was desired to classify the soils in regard to their

organic matter content according to the system by the

Organic Sediments Research Center. Using this system, any

soil with an ash content of 25% or less on a dry weight

basis is considered to be a peat soil. Soils with ash

contents between 25 to 75% are referred to as carbonaceous

sediments. Any soil with an ash content greater than 75% is

considered a mineral sediment A particular difficulty

encountered was caused by the presence of sand in the peat

soils. It was felt that the layers of sand, which

frequently underlie the peat soils in a natural marsh, were

disturbed during excavation of the peat by the mining

companies. Thus, the peat samples collected from these

mining sites contained some sand which was not originally

associated with the peat layer. Similar sand contamination

took place with the samples of organic sediments which were

collected directly by on-site digging. This especially

occurred where the layer of organic matter was shallow, thus

making it impossible to avoid some of the sand directly

beneath. Therefore, it was decided that in order to

properly compare the organic soils in regard to their ash

contents, the weight of the sand would have to be subtracted

out. Thus it became necessary to determine the sand content

of each soil so that an appropriate correction factor could

be applied.

The sand content of each soil sample was determined in

conjunction with preparing the ignited ash residues for

total phosphorus, iron and aluminum measurement. The

procedure was initiated by gently adding 1.0 N HC1 directly

to the ash material in each crucible using a plastic squeeze

bottle. Care was taken with this step not to blow light ash

material out of the crucible. Except for the sand, the

resulting mixtures were then transferred from the crucibles

into 100 ml volumetric flasks. This transfer was

facilitated by using a funnel and a rubber policeman. The

rinsing procedure was repeated until the solutions were

clear and all visible particles (i.e. clays) other than sand

were removed. An attempt was made to minimize the rinsing

volume because of the boiling step to follow. A final rinse

was made with deionized water. The crucibles and their

remaining sand were then allowed to air dry at room

temperature for 24 hours before reweighing for determination

of sand content.

Total Phosphorus, Iron and Aluminum Contents

The procedure for determining total phosphorus, iron

and aluminum was continued by boiling the HC1-ash mixture

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