UNITED STATES DEPARTMENT OF THE INTERIOR
FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by BUREAU OF GEOLOGY
MAP SERIES NO. 33, August, 1969
_GENERALIZED DISTRIBUTION AND CONCENTRATION
OF ORTHOPHOSPHATE IN FLORIDA STREAMS
Matthew I. Kaufman
Prepared by the
U. S. GEOLOGICAL SURVEY
in cooperation with the
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES
A knowledge of the occurrence of phosphorus in surface waters, from natural
as well as man-influenced sources, is essential to the understanding and
management of the quality aspects of Florida's surface-water resources. Statewide
distributions of orthophosphate in surface waters exist which can be related in
part to naturally-occurring phosphatic-rock formations, wildlife habitats and
streamflow, and in part to cultural influences (industrial, municipal, and
agricultural pollution). The distribution and concentration of orthophosphate,
and to a limited degree total phosphorus, in Florida streams is described herein.
Regional, time, and flow variations of concentrations and loads and their
interrelationships are briefly discussed.
SIGNIFICANCE OF PHOSPHORUS
Phosphorus, one of the major elements required in the synthesis of proteins, is
a primary nutrient in the food chains and as such regulates the extent of plant
growth and ultimately food production within the life cycle. Among
phosphorus-containing compounds the inorganic phosphates are of major
significance, occurring in the orthophosphate form, or as condensed phosphates
which gradually hydrolyze in aqueous solution to the orthophosphate form. (Task
Group Report, 1966.) Orthophosphate includes the three ionized forms of
phosphoric acid, H2PO4-1, HPO4-2, and P04-3, whose relative concentrations in
water are a function of pH (Rainwater and Thatcher, 1960). The combined
orthophosphates are reported in terms of milligrams per liter (mg/1) P04-3.
Orthophosphate values serve as an index of total soluble phosphorus, which must
be determined to permit a comprehensive assessment of the nutrient supply of an
Effects associated with the presence of excessive dissolved phosphates include:
(1) reduced efficiency of the coagulation-flocculation-sedimentation process and
lime-soda ash softening in water treatment, due particularly to the condensed
phosphates (>0.1 mg/1); (2) Over-abundant growth of algae and other aquatic
plants (ie., water hyacinths) in both flowing and non-flowing surface waters, and
the associated problems of objectionable algal blooms, undesirable tastes and
odors, filter clogging, increased color, turbidity, chlorine demand and increased
treatment costs, and (3) a high oxygen demand due to oxidation of organically
derived phosphorus entering an ecosystem, resulting in a reduction of dissolved
oxygen in a lake or stream (Task Group Report, 1966, 1967; FWPCA, 1968;
Sawyer, 1965; McKee and Wolf, 1963). The most serious effects of excess
dissolved phosphate occur downstream from sources of high concentrations of
this nutrient, especially in impoundments or lakes where natural eutrophication
processes can be greatly accelerated. In order to retard some of the associated
effects-i.e., over-abundant growth of algae and other aquatic plants-FWPCA
(1968) suggests that the concentration of total phosphorus should not exceed
0.05 mg/I where streams enter lakes or reservoirs.
SOURCES OF PHOSPHATE
Phosphates are one of the end products of the decomposition of organic matter
and in addition may be derived from leaching of naturally occurring phosphatic
minerals such as fluorapatite (CaS(P04)3sF), an important constituent of
phosphatic sediments in Florida. Phosphates are contributed to water in
significant quantities from several man-made and natural sources, including: (1)
industrial wastes; (2) sewage-treatment plant effluent (human wastes and
detergents); (3) agricultural drainage, including farm-animal wastes and fertilizers;
(4) urban drainage including municipal water-treatment wastes; (5) drainage from
natural phosphatic terranes; (6) rural runoff; and (7) rainfall. Evaluation of the
various sources of phosphorus suggests that the greatest contribution of
phosphorus to water is directly or indirectly a result of the activities of man (Task
Group Report, 1967).
The distribution and concentration of dissolved orthophosphate in Florida
streams is shown on the large nip. The orthophosphate content of streams in
parts of the state can be correlated with phosphatic-rock formations of the
drainage area whereas high values not associated with natural drainage from
phosphatic terranes are due primarily to pollution. These results are consistent
with the earlier work of Odum (1953) who reported on and mapped the
distribution of total dissolved phosphorus in Florida waters. The data and
interpretations herein are based on statewide mass-samplings in May 1966, 1967
(coinciding with periods of low stream-flow and maximum uptake of nutrients by
plants during their growth period), plus sampling at several long-term stations in
west-central peninsular Florida (late 1950's through 1966). Most samples lacked
the addition of a preservative to prevent algae and bacteria from either
assimilating or synthesizing soluble phosphorus. Thus laboratory values may, and
probably in some cases do, vary from field values. As the data are quite limited
over much of the state, regional concentration patterns are of necessity
generalized and local variations may be expected to exist.
Figure 2. Relation between dissolved orthophosphate load
and discharge of selected Florida streams.
ORTHOPHOSPrT COKCENTRATeON. MLLIGMS PER ITER
Figure 3. Relation between dissolved orthophosphate
concentration and discharge of selected Florida streams.
Orthophosphate concentrations greater than 5 mg/1 can be attributed directly
to cultural influences (pollution); however, concentrations in excess of 1 mg/I
(and in some cases 0.5 mg/1), where not associated with phosphatic terranes, may
also be indicative of cultural influences. Exceptiors exist in southernmost Florida,
where high orthophosphate concentrations that o cur during low-flow periods are
attributed to wildlife (ie., bird excrement). Figure 1 shows the dissolved
orthophosphate load in Florida streams in Ma) 1966. The concentration and
dissolved-load maps identify drainage areas control uting significant concentrations
and quantities of orthophosphate to Florida's surface waters and illustrate
Orthophosphate concentrations and loads of 'elected streams and springs are
listed in Table 1, providing an "order of magnitude" estimate for the
contributions from each source. Industrial waste from phosphate-mining areas in
west-central peninsular Florida is the greatest single source of orthophosphate.
The highest orthophosphate concentrations and lads (>200 mg/1 and >100,000
lbs. per day, respectively) are contributed to Tanpa Bay and thence to the Gulf
of Mexico from the Alafia River drainage system (arge map and figure 1).
Major secondary sources include other industrial wastes, sewage effluent, and
drainage from agricultural lands. On a statewide basis, significant quantities of
dissolved orthophosphate in Florida streams occur as the result of drainage from
natural phosphatic terranes. On the basis of data from several springs, the
orthophosphate increment to Florida's surface waters from the Floridan aquifer is
VARIATIONS WITH DISCHARGE AND TIME
The dissolved orthophosphate load and dissolved orthophosphate
concentration/discharge relation in several Florida rivers are shown on figures 2
and 3, respectively. A direct relation is noted between discharge and load, and a
slight inverse relation between discharge and concentration. The latter relation,
however, is poorly defined for natural streams draining non-phosphatic terranes.
Seasonal variations of orthophosphate load ani concentration in west-central
peninsular Florida are portrayed on figures 4 ;md 5. Where streams are not
affected by pollution (Myakka River, fig. 4), here is no consistent relation
between orthophosphate concentration and time of year. However, the loads vary
seasonally, tending to be high in March and again during the period July to
September, coincident with high rates of discharge. Where affected by pollution
(Alafia River, fig. 5), load is directly related and concentration is inversely related
to effluent discharge. Figure 6 illustrates fluctuations of total phosphorus load
and concentration for the Escambia River in western Florida. The highest
concentrations and loads appear to occur in the winter and early spring,
coincident with periods of high discharge.
Frequency curves of dissolved orthophosphite concentration in selected
streams in west-central peninsular Florida are portrayed on figure 7 and show the
range in concentration from relatively uncontaminated streams draining slightly
phosphatic terranes (Myakka River) to highly polluted streams (Alafia River).
Evaluation of orthophosphate data from several steams for the period 1957-58 to
1965-66 utilizing plots of concentration and lo i versus time are inconclusive
with respect to long-term trends. Frequency curves for the Alafia River at Lithia,
however, show that orthophosphate concentrations were considerably higher (at
comparable discharges) during 1965-66 (median concentration: 100 mg/I) than
during 1957-58 (median concentration: 48 nrg/1l). Data are insufficient to
ascertain whether similar increases are occurring m other Florida streams due to
expansion of industry, agriculture, and/or population.
1968 Water quality criteria-Report of Ihe National Technical Advisory
Committee to the Secretary of the Interior, 234 p.
McKee, J. E., and Wolf, H. W.
1963 Water quality criteria, State Water Quality Control Board, pub.
3A, Sacramento, Calif., 548 p.
Odum, H. T.
1953 Dissolved phosphorus in Florida waters, Fla. Geol. Surv. Rept. of
Investigation 9, Part 1, p. 1-40.
Rainwater, F. H., and Thatcher, L. L.
1960 Methods for collection and analysis of water samples, U.S. Geol.
Surv. Water Supply Paper 1454, 301 p.
Sawyer, C. N.
1965 Problems of phosphorus in watei supplies, J. AWWA, V57, p.
Task Group 261 OP Report
1966 Nutrient-associated problems in water quality and treatment, J.
AWWA,.V58, p. 1337-1355.
Task Group 2610 P Report
1967 Sources of nitrogen and phosphorus in water supplies, J. AWWA,
V59, p. 344-366.
U.S. Geological Survey
Quality of surface waters of the U.S. 1957-63, U.S. Geol. Surv.
Water Supply Papers 1571, 1641, 1741, 1881, 1947.
U.S. Geological Survey
Water resources data for Florida, Part 2, Water Quality Records
1964, 1965, 1966.
Figure 4. Seasonal variations of
discharge, dissolved orthophosphate load
and concentration, Myakka River near
Sarasota, 1962-63. 1
I 1 1 7-
Figure 5 Seasonal variations of
discharge, siaolved orthophosphate load
and conemtration, Alafia River at
ORTHOPHOSPHATE LOAD IN LBS PER DAY PER MI2
a <2 >20
>16 ORTHOPHOSPHATE DISCHARGED
TO THE SEA (IN THOUSANDS OF
LBS PER DAY) >16
Figure 1. Dissolved orthophosphate loads of Florida streams, May 1966. 9
TABLE 1. ORTHOPHOSPHATE CONCENTRATIONS AND LOADS OF SELECTED STREAMS AND SPRINGS
Alafia R. at 335
Peace R. at 1367
Fenholloway R. 110
R. nr Chuluota
New R. nr Lake 212
Manatee R. nr 80
Yellow R. nr 1210
Withlacoochee R. 1710
Blue Sptr nr
Silver Spr nr
Lithia Spr nr
Wakulla Spr nr -
*Time weighted average
Figure 6. Monthly discharge, total
sposphorus load and concentration,
Escambia River near Century, 1965-67.
Source Date (cfs)
Ind. Waste 1957-S8 *415
Ortho-PO4 Ortho-PO4 Load
Cone. (mg/1) Lbs./day Lbs./day/mi2 Lbs./yr/mi2 Lbs./yr
1964-65 *843 *6.8
5/16/66 138 46
Sewage Effluent 5/9/66 101
Agric. Drainage 5/10/66 1770
Natural P04 1964/65
Natural, non-PD4 6/2/66
Floridan Aquifer 5/26/66
127,800 382 141,020 47.2 X 106
22 16,400 11.2 X 106
7.7 4,200 18
0.36 3,400 16 -
*1.4 840 10 3,760 0.3 X 106
0.08 660 <2 -
0.06 300 <2
0.39 320 -
5/11/67 854 0.13 600
5/18/67 20.7 0.13 20
5/19/66 380 0.07 140
MAXIMUM ORTHOPHOSPHATE CONCENTRATION
OF FLORIDA STREAMS, MILLIGRAMS PER LITER
F <0.2 5.0-20
1 0.2-0.5 20-100
1 0.5 -1.0 >100
0 SAMPLING SITE
FLORIDAN AQUIFER SPRING c
PERCENT OF TIME CONCENTRTN WA EQUAL TO O GREATER THA A GIVEN VALUE
Figure 7. Frequency curves of dissolved
orthophosphate concentration in selected streams in
west-central peninsular Florida.
F LOR I T)/) SEOLO)3 J C SURVEY ('1~R SERIES S 3931
~ 13 3 c;iA9
0 10 20 30 40 50 MILES
I Color Separation by D. F. Tucker
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