UNITED STATES DEPARTMENT OF THE INTERIOR
MAP SERIES NO. 37 RFVTISED
FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by BUREAU OF GEOLOGY
I I I I I I I I
THE pH OF WATER IN FLORIDA STREAMS
Matthew I. Kaufman
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES
DEPARTMENT OF NATURAL RESOURCES
BUREAU OF GEOLOGY
This public document was promulgated at a total
cost of $299.00 or a per copy cost of $.12 for the
purpose of disseminating hydrologic data.
A knowledge of the distribution and range of the fluctuation of pH in surface
waters, from natural as well as man-influenced sources, is important to the
understanding and management of the quality aspects of Florida's surface-water
According to the Florida Statutes, 1969 (28-5.05 through 28-5.11), for those
waters categorized under classes 1-IV, the pH shall not vary more than one unit
above or below normal; and the lower value shall not be less than 6.0, and the
upper value not more than 8.5. For those waters categorized unders categorized under class V, the
pH shall not be lower than 5.0 nor greater than 9.5 except certain swamp waters
which may be as low as low as 4.5. Recognizing that certain waters of the State, due to
natural causes, may not fall within desired or prescribed limitations, the Statutes
provide for authorized exceptions upon presentation of good and sufficient
This report presents in a succinct and usable form information on the pH of
streams and canals throughout Florida as an aid to water managers, users, and
planners. The variations in pH are related to environmental causes.
The minimum pH of water and the range through which the pH of stream
waters fluctuate in the various geographic areas (large map) is significant with
respect to industrial, municipal, and recreational uses, aquatic productivity, the
State of Florida's water quality standards, corrosivity, and selection of materials
with regard to waterway structures such as culverts, in addition to governing the
toxicity, mobility, and solubility of many compounds.
Florida's surface waters exhibit distinct regional variations in pH extremes,
especially in regard to minimum values. Depending on environmental conditions,
pH values in Florida waters range from less than 4.0 to greater than 8.5.
Environmental controls such as surficial geology, the hydrologic flow system, soil
types and vegetation, proximity to natural swamplands that are flushed by
overland runoff, and industrial and agricultural effluents, among others, govern
the pH. The map shows areas within which the minimum pH values of surface
waters are about the same. The distribution pattern of these values provides
insight into the hydrologic flow system and suggests certain environmental
controls on water quality. This map is one step toward the portrayal of water
quality data for Florida on a regional basis.
DEFINITION OF pIH, SIGNIFICANCE, AND RECOMMENDED LIMITS
The pH of a solution is a measure of the hydrogen-ion activity and is expressed
as the negative logarithm (base 10) of the effective hydrogen-ion concentration.
The range of pH values from strong acids to strong bases is from 0 to 14. The pH
of a neutral aqueous solution is 7. A change of one pH unit indicates a 10-fold
change in the hydrogen-ion activity.
As noted by Mason (1952, p. 158-159), pH exerts a major influence on the
mobility of many elements in the hydrosphere. Such factors as solubility,
hydroxide precipitation, degree of complexation, and sorption of solutes by
particulate matter may depend highly on pH (Lee and Hoadley, 1967). For
example, the solubility of ferrous iron (Fe++) at pH 6 is about 10s times greater
than at pH 8.5. In addition, as discussed by McKee and Wolf (1963, p. 235), the
concentration of H+ ions controls the degree of dissociation of many substances,
and as the undissociated compounds are frequently more toxic than the ionic
forms, pH may be a significant factor in determining limiting or threshold
concentrations. For example, reduction of about 1.5 pH units can cause a
thousand-fold increase in the acute toxicity of a metallocyanide complex, whereas
the addition of strong alkalis may cause the formation of undissociated NH4OH
or un-ionized NH3 in quantities that may be toxic (FWPCA, 1968, p. 41).
Industrial wastes may be strongly acidic or basic and their effect upon the pH of
the receiving waters depends largely on the buffering capacity of the receiving
Waters with a pH below 6.0 can cause excessive corrosion in plumbing systems.
Extremes in pH cannot usually be tolerated by industry; recommended values for
industrial uses (process waters) normally range from 6.0 to 8.3. Recommended
pH values for boiler feedwater range from 8.0 to 9.6, depending on pressure
(McKee and Wolf, 1963, p. 235-236; Rainwater and Thatcher, 1960, p. 237).
The pH of primary contact recreation waters should be within the range of 6.5
to 8.3 except when due to natural causes, and in no case should be less than 5 or
more than 9 (FWPCA, 1968, p. 4). The hydrogen-ion concentration with
co-dependence upon the buffer capacity of the water is of importance in relation
to eye irritation among swimmers.
The availability of many nutrient substances varies markedly with pH, and the
tolerance of fish to low concentrations of dissolved oxygen is greater with higher
pH. The nonlethal limits of pH are narrower for some fish-food organisms than
for fish. From the standpoint of aquatic productivity it is best to maintain the pH
in the range of about 6.5 to 8.2 (McKee and Wolf, 1963, p. 236; FWPCA, 1968,
NATURAL RANGES OF pH, AND ENVIRONMENTAL CONTROLS
The pH of a water results from (1) the balance of a series of chemical reactions,
and (2) equilibria among the ions in solution, the most important of which
involves the hydrolysis of carbonate (C03=) and bicarbonate (HC03) ions (Hem,
1959, p. 44-46). Natural waters commonly contain dissolved carbon dioxide (C02)
and HC03 ions, which form a buffered system with carbonic acid (Davis and
DeWiest, 1966, p. 76). The pH of a solution with high buffer capacity tends to
remain relatively constant when small amounts of acid or base are added, whereas
the pH of a solution of low buffer capacity may be subject to pronounced
changes. Carbonate rocks abound in nature and therefore are a source of
bicarbonate in many terrestrial waters. The resulting buffering system tends to
neutralize acids and bases and thus reduces the range in fluctuations of pH.
In natural environments, pH ranges mostly from 4 to 9. The carbonic system
(C02, HC03 C0s=) is the principal control of the pH of most natural waters and
is effective at pH above about 5. "A saturated solution of C02 at its partial
pressure in the atmosphere has a pH of 5.2, and a solution of calcite in
air-saturated water has a pH near 8" (Mason, 1952, p. 158). The pH of an
organic-rich environment, under aerobic conditions, would be that of a carbonic
acid solution in equilibrium with C02 at one atmosphere, or about 4. In the
presence of decaying vegetation, the pH could be a little lower because of CO2
and organic acids produced during decomposition (Krauskopf, 1967, p. 314).
Lee and Hoadley (1967) note that large populations of aquatic organisms may
markedly influence the pH as well as the buffer capacity of waters as a result of
respiration and photosynthesis (Le., diurnal variations caused by addition and
removal of CO2 from solution).
REGIONAL pH DISTRIBUTIONS, CHEMICAL ASSOCIATIONS, AND
VARIATIONS WITH STREAMFLOW AND TIME
The large map shows the minimum pH of water and the range through which
the pH of stream waters fluctuates in different areas of Florida. The color
patterns show the lower limits of pH that prevail, and delineate areas in which
stream waters exhibit similar ranges in pH. In general, the pH of the principal
streams within the area of a given color fluctuates within the extremes indicated
by that color.
Within each area the range of fluctuation in pH may be related to one or more
environmental controls such as (1) geology (for example, carbonate versus
non-carbonate terrane), (2) significant alkaline ground-water inflow, (3) drainage
from natural swamplands, and (4) industrial and agricultural effluents. These
relations are discussed in more detail below.
The pH values represent laboratory data for 10-day composite samples, plus
daily and intermittent instantaneous samples (early 1940's through 1966, plus
selected 1967 data). Laboratory values may, and probably in some cases do, differ
from field values. Regional distribution patterns and placement of the boundaries
between colored ar areastare of necessity generalized, and local variations may be
expected to exist. Detailed data pertaining to pH values in each of the delineated
areas are on file in the U. S. Geological Survey Water Quality Laboratory, Ocala,
Most natural waters with minimum pH of 4 to 5 (orange and yellow areas on
the large map) are (1) upstream from the influences of significant alkaline
(HC03 -rich) ground-water inflow, (2) drain non-carbonate terranes, or (3) are
affected by drainage from swamps, especially during periods of high flow. In
general, low-pH waters have low specific conductance, low HC03 ion
concentration, are soft, highly colored (except in western Florida), and contain
appreciable iron. They are sodium chloride in type, weakly buffered, potentially
corrosive, and tend to be relatively unstable, exhibiting wide fluctuations in pH.
The low pH is related to the low buffer capacity of these waters, which allows
CO2 and organic acids produced during decomposition of organic matter to have a
The tendency of some waters to fluctuate chemically in response to changes in
discharge is exemplified by data for three north Florida rivers (figs. 1-3). In
general, decreased pH values occur in conjunction with increased discharge.
Figure 4 further illustrates this pH-discharge association. During periods of low
flow, stream pH approaches that of the artesian Floridan Aquifer (median pH 7.7,
with 90 percent of measured values falling between 7.4 and 8.0, for 17 Floridan
Aquifer springs). Duris). During periods of high flow, the pH approaches that of a C02
and organic-acid-rich environment (pH 4) where influence of alkaline
ground-water inflow is negligible. Where alkaline ground-water inflow occurs in
conjunction with high flow, the minimum pH usually stabilizes between 5 and 7.
Natural waters with pH ranging from 6 or 7 to 8.5 or above (blue and green
areas on the larggemap) reflect the presence of areas where limestone crops out or
are influenced by significant alkaline ground-water inflow. These waters have
moderate to high specific conductance, hardness, and bicarbonate concentration,
and are calcium bicarbonate in type. They are well buffered and tend to be
relatively stable, with only minor fluctuations in pH. Diurnal variations in pH
based on field measurements in several southeast Florida canals ranged from 7.3
to 7.8, attesting to the relative stability and high buffer capacity of these waters
(C. B. Sherwood, U. S. Geological Survey, oral common., 1969).
The significance of the carbonic system as the principal control of pH in many
natural waters is illustrated (in part) in figure 5. A direct relation between pH and
HC03 over a wide range is indicated for three weakly buffered streams. The dense
grouping of values for the Miami Canal indicates the relative stability of both pH
and HC03 in well-buffered high-HC03 waters. For comparative purposes, the
median pH vs. the median HC03 concentration for 17 Floridan Aquifer springs is
Downstream variations in pH and associated chemical characteristics (from
orange to yellow to blue areas on the large map) for the Santa Fe River in
north-central peninsular Florida are given in table 1. The downstream increase in
pH, specific conductance and HC03 ion concentration accompanied by decreased
color illustrate the effect of proximity to swamps and of alkaline ground-water
inflow, as discussed earlier.
Waters within the red areas on the large map are affected by acidic industrial or
agricultural effluents. Depending on source, the waters of low pH are
characterized by high specific conductance, sulfate (S04), phosphate (P04), iron
(Fe), fluoride (F) or nitrate (N03). Many are calcium sulfate in type.
Representative chemical characteristics of waters of differing pH are given in table
2, along with remarks concerning environmental influences such as streamflow,
swamp drainage, alkaline ground-water inflow, and discharge of waste.
Curves showing the percentage of time that the pH has remained at or below a
specific value in selected Florida surface waters are portrayed in figure 6. The St.
Marys River typifies waters affected by acidic overland runoff and flushing of
swamps. Analysis of four streams within the orange areas for the period of record
indicates the pH ranged below 5.0 during 33 to 55 percent of the time, and below
4.5 during 7 to 27 percent of the time. The Alafia River, which receives acidic
wastes, was below 5.0 during 27 percent of the time in 1965-66, but only 2
percent of the time in 1964-65. The relatively unstable Suwannee River reflects
the mixture of acidic overland runoff or swamp drainage during high-flow periods
and influent alkaline ground water during low-flow periods. The Yellow and
Escambia Rivers do not receive a significant amount of such input, and thus their
pH values are somewhat more stable. The St. Johns River illustrates the relatively
well-buffered stability of large streams influenced by significant alkaline
ground-water inflow, and the Miami Canal reflects the predominance of
well-buffered alkaline ground water in southeast Florida.
Davis, S. N.
1966 (and Dewiest, R. J. M.) Hydrogeology: New York, John Wiley and
Sons, 463 p.
Federal Water Pollution Control Administration,
1968 Water quality criteria: 234 p.
Hem, J. D.
1959 Study and interpretation of the chemical characteristics of natural
water: U. S. Geol. Survey Water-Supply Paper 1473, 269 p.
Krauskopf, K. B.
1967 Introduction to geochemistry: New York, McGraw-Hill Inc., 721 p.
Lee, G. F.
1967 (and Hoadley, A. W.) Biological activity in relation to the chemical
equilibrium composition of natural waters: in Equilibrium concepts
in natural water systems: Am. Chem. Soc., Advances in Chemistry
Ser. 67, p. 319-338.
1952 Principles of geochemistry: New York, John Wiley and Sons, 310 p.
McKee, J. E.
1963 (and Wolf, H. W.) Water quality criteria: California State Water
Quality Control Board, pub 3-A, 548 p.
Rainwater, F. H.
1960 (and Thatcher, L. L.) Methods for collection and analysis of water
samples: U. S. Geol. Survey Water-Supply Paper 1454, 301 p.
U. S. Geological Survey
Quality of surface waters of the United States, 1940-63: U. S. Geol.
Survey Water-Supply Paper 942, 950, 970, 1022, 1030, 1050, 1132,
1162, 1186, 1197, 1250, 1290, 1350, 1400, 1450, 1520, 1571,
1641, 1741, 1881, 1941, 1947.
U. S. Geological Survey
Water resources data for Florida, pt. 2, Water quality records, 1964,
1965, 1966, 1967.
5 50 1
I I I I 35
S i5 25
Figure I. Relation of
pH to specific
streamow, St. Maas
River aear Macclenny
Figure 2 Variations of pH and
HCO3 ,eih discharge, Su-
wanne River, near Branford.
OCn9 aa 5al~ *
,%4 -670 26 -1)
S n. Mone -,
0i 1o 5 ,oo
DISCHARGE, CUBIC FEET PER SECOND
Figure 4. Relation of pH to discharge in selected Florida
/ / / / EXPLANATION
// /e/ / ,. ,,o,......
/- 2 Suonee Rver 0 .Bronoer
/ 3 St v Ri e'r Cocoo -
-- 7 s, Moys RIv7 neo, Mioccle,
- *11 )
,.0 ,~ii -
/ 1 Ii
8 -4;'" -
,964 1.5 bi
I-igure 3 Fluctuat ons of HCO3 pH,
color and discharge. Sopchoppy River
near Sopchoppy, 1964-67.
.. .. .. ........
9 a 'aC ,
,957.60 UTeos hs)
i 00 l0I
BICARBONATE CONCENTRATION, MILLIGRAMS PER LITER
Figure 5. Relation of pH to HC03 ion
concentration in selected lrd streams
Table 1. Downstream variations in pH and associated chemical characteristics
for the Santa Fe River, in north-central peninsular Florida.
tSpec. Cond. 0Color
Period of pH tHCO3 (unhos per cm. (PtCo
Station record used Median Range (mrg/) at 250 C.) units)
Near Graham 1957-60 5.3
At Worthmgton 1959-60
Near High Springs 1959-60 7 4
t Time-Weighted Average
05 2 5 -0 30 50 70 90 98 995 9 T I *****g* g-- .-
PERCENT OF TIME pH WAS EQUAL TO OR LESS THAN A GIVEN VALUE
Figure 6. Frequency curves of pH in selected Florida streams
Table 2. Representative chemical characteristics of waters of differing pH
Spec. Cond. Color
Discharge Bicarbonate Sulfate (aumhos per cm. (Pt-Co
S.tr .. l iaDate (cf) IPaH (mg/l) (mg/1) at 25C) units) Chemical type
North Prong Alaia 4-26-65
R. at Mulberry
Indian Prairie Canal 11-28-56
Sopchoppy R. nr 8-14-67 734 3.9
Sopchoppy 6-8-65 4.1 7.5
56 4.3 0 432 1,150 15 Ca-SO4
3.7 0 316 777 100 Ca-SO4
4.4-6.4 a5 57 265 Swamp drainage, upper reach of
5.9-7.4 20 77 160 Mostly swamp drainage during high-
flow, alkaline ground-water inflow
6.4-8.3 100 247 100 Lower reach of river, influenced by
alkaline ground-water inflow from
Acidic industrial waste, high in S04,
P04 and F.
Agricultural drainage high in SO4, NO3
0 1.6 43 360 Na-Cl Swamp drainage,high flow.
127 2.4 215 40 Ca-HCO3 Base flow, influenced by alkaline ground
St. Mary's R. 8-17-65 4,210 4.6 0 5.6 30 200 Na-CI. S04 Swamp drainage, high flow.
nr Macclenny 5-9-67 46.1 7.0 36 0.4 80 85 Ca-HCO3 Base flow. influenced by alkaline ground
Suwannee R. nr 6/11-20/57 11960 5.6 17 3.2 47 210 Ca-HCO3 High flow.
Branford 2/11-20/57 1,690 8.1 164 18 301 7 Ca-HCO3 Base flow, influenced by alkaline ground
Silver Springs 2-3-64 681 7.7 200 51 428 5 Ca-HCO3 Floridan Aquifer spring, high SO4
West Palm Beach
Canal at Canal Pt
East of Levee 30
Fenholloway R. at
a Reverse flow
9-19-56 a -824
7.7 148 34 328 10 Ca-HC03
Base flow. influenced by alkaline ground
340 Ca-HCO3 Agricultural drainage laugh in sodium
(Na), S04, ClI, and NO3.
11/1-10/64 331 8.4 232 0 492 60 Ca-HCO3 Influenced by alkaline ground water.
5-16-66 138 8.2
514 104 2,400 1,400 Na-CI, HC03 Alkaline industrial waste high in Na,
HCO3, Cl and SO4.
Generalized areal distribution of minimum
pH values of water in Florida stream. and
Less than 4.0 [ 6.0-7.0
4.0-5.0 greater than 7.0
Maximum pH values in all ateas are
generally 8.0 to 8.5.
() Minimum of 4 yrs. Bimonthly, or at least 20 complete analyses, all flow
Minimum of 2 yrs. Semiannual, or at least 5 complete analyses, all flow
O Annual, 1-4 complete analyses, generally represents low flow
A Daily specific conductance station, minimum eSord 1 yr.
Water Quality Data Stations, Florida ams and canals,' S.
Geological Survey, 1940-1966. OCT 1 2'98
I I I r *
0 to 20 30 40 50
litir orlillri INV. a I nrl v logical Qu it, v x-rrr r -
km /) ..r .
ert am or ana
'%42 la 2- ,.- slo