REDUCTION IN PHOSPHORUS LOADING
Principal Author: Dan Scheidt, USEPA Region 4. Reviewers/Participants/Information provided by: Dr.Gary Goforth, SFWMD; Paul Whalen, SFWMD, Alan Hall, SFWMD; Dr. Tom Fontaine, SFWMD; Frank Nearhoof, FDEP; Dr. William Walker; Suggestions by Science Sub-Group members; Suggestions received by the Technical Oversight Committee (SFWMD, FDEP, USACE, USFWS, NPS) after presentation of this topic at their October 1995 meeting.
In recent decades anthropogenic phosphorus enrichment of the Everglades has resulted in systemic ecological changes in public Everglades wetlands. Scores of scientific publications dating from the 1970s, 1980s and 1990s document Everglades phosphorus enrichment and its ecological consequences. The public areas receiving the highest phosphorus concentrations and loadings with the greatest eutrophic impacts are portions of Loxahatchee National Wildlife Refuge and WCA2A. Lesser impacts have been observed within WCA3 and Everglades National Park. Scientific publications documenting these impacts have been authored by scientists from SFWMD, NPS, Duke University, Florida International University, University of Florida, USGS, USEPA, and other entities. Nearhoof (1992 ) summarizes some of the relevant Everglades scientific literature on this issue. Numerous related journal publications have come out since Nearhoof's summary. Other historic summary information is contained in the Surface Water Improvement and Management Plan for the Everglades (SFWMD, 1992). Various phosphorus control strategies for treating water discharged from the Everglades Agricultural Area (EAA) are under implementation as a result of the 1991 Settlement Agreement/1992 federal court Consent Decree for the Everglades water quality lawsuit and Florida's 1994 Everglades Forever Act.
The stated precursor success index for phosphorus is "reduction of phosphorus loading". Much of what is proposed below is mandated by either Florida law, the federal court Consent Decree, or both. As such, the success index for reduction of Everglades phosphorus loading is already dictated.
Phosphorus Loading Reduction by the Everglades Nutrient Removal Project
Statement of the success criteria. "Maintain a long-term ENR Project effluent flow weighted mean water total phosphorus effluent concentration of 50 ppb or less". The Everglades Nutrient Removal (ENR) Project is a 3700 acre prototype Stormwater Treatment Area (STA) designed and operated to maximize phosphorus removal of EAA drainage water prior to its discharge into Loxahatchee National Wildlife Refuge. The Project was designed beginning in 1989 and completed in 1993, with discharge commencing in August of 1994. The Everglades Forever Act requires that about 44,000 acres of STAs be constructed to remove phosphorus from EAA drainage water prior to discharge into the Everglades. The Act also requires that the STAs discharge their design rate of 50 ppb total phosphorus on a long-term average basis.
Reference Baseline. Not relevant. Success for the ENR project is based on attaining the long-term effluent concentration of 50 ppb or less.
Historic condition. Not relevant. The ENR Project was designed to obtain a long-term effluent of 50 ppb total phosphorus, as compared to background Everglades marsh total phosphorus concentrations of less than 10 ppb.
Expectation from restoration. The long-term expectation from restoration is providing water to the receiving Everglades wetlands that is adequate for protection the designated use of the water body - recreation, protection and maintenance of a well-balanced population of fish and wildlife (class III waters). In addition, Loxahatchee National Wildlife Refuge and Everglades National Park are afforded nondegradation water quality protection as Outstanding Florida Waters (OFW). Ultimately the concern is for protection of the ecological resources and avoiding nutrient-induced biological changes, not a concern for phosphorus in and of itself.
Scores and scoring methodology. Not relevant. Success for the ENR project is based on attaining the long-term effluent concentration of 50 ppb or less. SFWMD reports (SFWMD, 1995a) that during its first year of operation the ENR Project: treated about 120,000 acre-feet of water (20% of the S-5A flow), removed 18 metric tons of phosphorus; achieved an 83% load reduction based on a 12-month rolling flow-weighted mean, received inflow water averaging over 100 ppb phosphorus and discharged water consistently less than 50 ppb, with 70% of samples less than 30 ppb and 90% of samples less than 40 ppb.
Reduction in phosphorus loading from the EAA by Agricultural Best Management Practices.
Statement of the success criteria. "Attain a 25% phosphorus load reduction in waters discharged from the EAA into the Everglades Protection Area". This is the load reduction mandated by the SFWMD's regulatory program.
Reference Baseline. Primary compliance with the Everglades Regulatory Program is determined by monitoring EAA basin surface water discharges to the Everglades. Total phosphorus loads are monitored by SFWMD at S-5A, S-6, S-7, S-8 and S-150. Compliance with the 25% annual reduction goal will be determined by comparing a current year's total phosphorus load with the average annual total phosphorus load predicted from the October 1, 1978 through September 30, 1988 base period. The prediction takes into consideration the hydrologic conditions of the current year as compared to the hydrologic conditions observed during the 1O-year base period and load is accordingly adjusted. The SFWMD regulatory compliance year is set to be May 1 through April 30. The first year of compliance determination will be May 1, 1995 to April 30, 1996.
Historic condition. Unknown. Prior to the presence of agricultural operations in the EAA (circa 1900) this basin was largely sawgrass marsh. There were no canals traversing the area, and water flowed slowly from the northern portions of the present EAA as sheetflow southward through the vast Everglades system to what is now the Water Conservation Areas and Everglades National Park. It can be inferred that in this historic condition the phosphorus concentrations in this marsh water were comparable to present background marsh concentrations at oligotrophic interior marsh locations - less than 10 ppb.
Expectation from restoration. The long-term expectation from restoration is providing water to the receiving Everglades wetlands that is adequate for protection the designated use of the water body - recreation, protection and maintenance of a well-balanced population of fish and wildlife (class III waters).
Scores and scoring methodology. See section B above. Although the rule is not effective yet, SFWMD reports a 17% load reduction due to BMPs in the 1994 year and a 30% reduction in the 1995 year (adjusted for rainfall).
Reduction in phosphorus loading from the EAA to the Everglades as measured at S-150, S-5A, S-6. S-7 and S-8.
Statement of the success criteria. "Attain an 80% reduction of phosphorus load from the EAA to the Everglades Protection Area as measured at S-150, S-5A, S-6, S-7 and S-8".
Reference Baseline. The reference baseline is the annual average load adjusted for hydrologic conditions from 1978 to 1988.
Historic condition. The historic condition is not known. A hundred years ago there were no canals and no water control structures within what is now the EAA.
Expectation from restoration. The expectation from restoration is a reduction in the phosphorus load from the EAA such that the quality of water delivered from the EAA to the receiving wetlands of the Everglades Protection Area is adequate for preventing imbalances in natural populations of aquatic flora and fauna, and for preservation intact of the ecological resources of the Everglades over the long-term.
According to the 1992 Consent Decree, Appendix C, implementation of the STA program and the EAA BMP program together are to reduce the combined flow-weighted mean phosphorus concentration in discharges from S-150, S-5A, S-6, S-7, and S-8 from 168 ppb to 50 ppb. The STAs are to deliver a long term annual mean flow-weighted effluent of 50 ppb. This would translate to an overall load reduction of about 80% from the EAA into the EPA and a load reduction of at least 85% from the EAA into Loxahatchee National Wildlife Refuge. This assumes that the EAA BMP program results in a 25% phosphorus load reduction.
Scores and scoring methodology. As above in item 2.
Attaining phosphorus limits at structures discharging into Everglades National Park.
Statement of the success criteria This success criterion has already been developed. Long-term discharge limits have been developed to meet the OFW water quality criteria for structures that discharge into Everglades National Park. The adequacy of these OFW criteria to meet the State water quality Class III standard (prevent an imbalance in natural populations of aquatic flora or fauna) will be verified by long-term monitoring and research in downstream marshes. Phosphorus limits apply to flow-weighted mean concentrations computed on an annual water year (October to September) with data reported and calculated on a monthly basis. To account for observed hydrologic variations at Shark Slough structures (S-12A, S-12B, S-12C, S-12D, S-333 and any new structures that discharge from WCA3 into the Park) the limits vary with the previous 12 month's total discharge. The limits represent the 10% rejection level (this allows for a degree of natural variation in phosphorus concentration) of the observed flow-weighted mean concentration at a given annual total flow adjusted to a baseline period of March 1, 1978 to March 1, 1979 (the Park's OFW baseline).
This criteria and the relationship for structures discharging phosphorus to the Park is defined in the Consent Decree (Appendix A) and in the 1992 Everglades SWIM Plan. Compliance with these concentration limits is expected to provide a long-term annual average flow-weighted mean inflow concentration of about 8 ppb for the Shark River Slough basin. The interim limits for Shark Slough (effective 1997) vary from about 14 ppb (dry year) to about 9 ppb (wet year). The long-term limits for Shark Slough (effective 2002) vary from about 13 ppb (dry year) to about 8 ppb (wet year). The limit for the Taylor Slough (S-332 and S-175) and Coastal Basins (S-18C) does not vary with flow. It is fixed at a long-term limit (allowable maximum) of 11 ppb which if attained is expected to provide a long-term average flow-weighted mean inflow concentration to these basins of about 6 ppb.
Reference Baseline. March 1,1978 to March 1,1979, based upon SFWMD phosphorus data. This timeframe is based upon the Park's OFW designation and Florida's requirement that the quality of water that existed in the year prior to date of the OFW designation be maintained. Data from 1978 to 1988 were used to derive the discharge - phosphorus relationship (the relationship is inverse), with an observed trend adjusted (detrended) to the 1978 to 1979 OFW reference baseline.
Historic condition. Unknown. The Tamiami Canal was completed in 1928, although at this time numerous unobstructed culverts still allowed free flow of water from what is now WCA3A to what would become Everglades National Park. The southern levee of WCA3 was completed in 1962, along with the S-12 structures, resulting in a physical barrier to the sheetflow of water to the Park. A hundred years ago, surface water inflow to the Park was marsh sheetflow that originated from rainfall. There were no canals that could influence the quality of water delivered to the Park, or deliver water that differed from marsh background quality. It can be presumed that historic marsh water phosphorus concentrations would have been what present concentrations are at interior marsh locations that are not influenced by nutrient-rich discharges - less than 10 ppb. The median marsh , surface water concentration from 1986 to 1993 at Park marsh stations P-34, NP-207, NP- 201 and EP was 5 ppb. The total phosphorus detection limit for the SFWMD lab is 4 ppb.
Expectation from restoration. Water quality that is adequate for the long-term maintenance of natural populations of aquatic flora and fauna. No further nutrient-induced systemic ecological impacts, and perhaps a reversal of the nutrient impacts that have already been observed in the Park immediately downstream of the S-12 structures (see Raschke, 1993; Doren, et al., in press).
Scores and scoring methodology. See section A above. SFWMD's Everglades 1995 annual report states that: phosphorus concentrations of 9.8 ppb in Shark Slough at the end of September 1994 were below the calculated interim limit (10.1 ppb) but exceeded the long-term limit (8.6 ppb); frequency of Shark Slough samples greater than 10 ppb exceeded the allowable frequency in 1992, 1993, and 1994; phosphorus concentrations of 10.1, 11.0, and 12.3 ppb at the end of September 1992, 1993 and 1994 in the Taylor Slough and Coastal Basins met the 11.0 ppb limit in two of the three years; frequency of samples greater than 10 ppb in Taylor Slough and the Coastal basins met the allowable limit in 1992, 1993 and 1994.
Statement of the success criteria. This success criterion has already been developed. A relationship between surface water phosphorus concentration at 14 interior Refuge marsh stations and water elevations measured at 3 stage gages within the Refuge is defined in the Consent Decree (Appendix B) and in the Everglades SWIM Plan. Compliance with these concentration levels is intended to limit mean phosphorus concentrations in water samples collected monthly at the 14 interior marsh stations to values between 8 and 22 ppb when water elevations in the Refuge are between 17.14 and 15.42 feet msl. The focus of this index is measuring the surface water phosphorus concentration within the receiving resource (in this case Loxahatchee). This is in contrast to the other above indices which either measure phosphorus concentration or load upstream of the receiving water or discharge to the receiving water, but not within the receiving natural resource itself.
Reference Baseline. June 1978 to June 1979, based upon SFWMD marsh phosphorus data. This timeframe is based upon the Refuge's OFW designation and Florida's requirement that the quality of water that existed in the year prior to date of the OFW designation be maintained. Data from 1978 to 1983 were used to derive the marsh phosphorus - stage relationship, with an observed trend adjusted (detrended) to the June 1978 to June 1979 reference baseline.
Historic condition. Unknown. The Loxahatchee marsh differs from the rest of the Everglades in that it is a parched, soft-water, slightly acidic system. Presumably the historic marsh water within what is presently the Refuge would have been largely derived from rainfall, and there were no external sources of surface water nutrient loading such as the present day EAA or the S-5A structure. It can be presumed that historic marsh water phosphorus concentrations would have been what present concentrations are at interior marsh locations that are not influenced by nutrient-rich discharges - less than 10 ppb.
Expectation from restoration. Water quality that is adequate for the long-term maintenance of natural populations of aquatic flora and fauna. No further nutrient-induced systemic ecological impacts, and perhaps a reversal of the impacts that have already been observed in the Refuge.
Scores and scoring methodology. Compliance with these interim concentration levels is expected to provide a long-term mean 14 station interior marsh concentration of approximately 10 ppb. Interim values for the 14 station geometric mean concentration levels can be calculated from a given mean daily stage using the equation found in Appendix B page 6. These interim levels become effective in 1997. In addition, effective 2002 the long-term total phosphorus concentration levels for the refuge will be the 10% rejection level (allows for natural variability) of stations CA1-5, CA 1-6, and CA 1-16 at a given mean daily stage. These three stations had the lowest geometric mean total phosphorus concentrations during the 1978 - 1983 baseline period. These long-term levels will apply to all 14 marsh stations, and compliance with these levels is expected to provide a long-term average 14 station interior marsh concentration of approximately 7 ppb.
SFWMD states in their Everglades 1995 annual report that from June 1, 1994 through May 31, 1995 the interim marsh surface water phosphorus concentration was met in 9 of the 12 months while the long-term level was met in 7 of 12 months.
None identified. It appears that all of the necessary water quality and discharge data for determining if Everglades phosphorus loading is decreasing has already been identified and is being collected.
Attaining several of the other proposed ecological success criteria is dependent upon the successfulness in attaining the present criteria for reduction of phosphorus loading. Some of these other success criteria include: increase in landscape diversity; reduction in expanses of nutrient-tolerant plant species; and presence of periphyton community taxonomic composition characteristic of oligotrophic, natural hydroperiod systems.
No new support identified.
Reducing phosphorus loading to the Everglades and the specific success criteria proposed above are to a large extent either mandated by the Everglades Forever Act of the lawsuit Consent Decree, or both. Therefore much of the Phase I phosphorus control efforts (those efforts intended to attain 50 ppb or less phosphorus in waters discharged into the Everglades) relevant to reducing phosphorus loading are already underway.
The effluent phosphorus concentration needed for Phase II of the phosphorus control program will be determined by the ongoing research program to numerically interpret the narrative Everglades nutrient criterion. The present water quality criteria for nutrients that applies to the Everglades is the Class III narrative criteria- "in no case shall nutrient concentrations of a body of water be altered so as to cause an imbalance in natural population of aquatic flora or fauna". The Everglades Forever Act requires FDEP to numerically interpret for phosphorus the Class III narrative nutrient criterion necessary to meet all water quality standards in the Everglades Protection Area (EPA). By December 31, 2001 FDEP is to file a notice of rule making to establish a phosphorus criterion in the EPA. In no case shall the phosphorus criterion allow waters in the EPA to be altered so as to cause an imbalance in the natural populations of aquatic flora or fauna. The default criterion shall be 10 ppb in the EPA in the event FDEP does not adopt such criterion by December 31, 2003. What all of this means is that the numeric interpretation of the Class III narrative criterion for the Everglades will result in a total phosphorus standard somewhere between 10 ppb and 50 ppb. The Phase II phosphorus control effort will then have to attain a phosphorus effluent that meets the new numeric phosphorus criterion for waters discharged into the Everglades. At that time the success criteria for reduction of phosphorus into the Everglades will have to be reevaluated for adequacy.
Some of the many references relevant to reducing phosphorus loading to the Everglades follow. Not all have been specifically cited in the above text.
Abtew, Wossenu, and Nagendra Khanal. 1994. Water Budget Analysis for the Everglades Agricultural Area Drainage Basin. Water Resources Bulletin 30:429-439.
Belanger, T. V., D. J. Scheidt, and J.R. Platko II. 1989. Effects of Nutrient Enrichment on the Florida Everglades. Lake and Reservoir Management 5: 101-111.
Coale, F. J., F. T. Izuno, and A. B. Bottcher. 1994. Phosphorus in Drainage Water from Sugarcane in the Everglades Agricultural Area as Affected by Drainage Rate. J. Environ. Qual. 23:121-126.
Craft, C. B., and C. J. Richardson. 1993. Peat Accretion and Phosphorus Accumulation along a Eutrophication Gradient in the Northern Everglades. Biogeochemistry 22: 133 156.
Davis, Steven M. 1991. Growth, Decomposition, and Nutrient Retention of Cladium jamaicense Crantz and Typha domingensis Pers. in the Florida Everglades. Aquatic Botany 40:203-224.
Davis, S. M. 1994. Phosphorus inputs and Vegetation Sensitivity in the Everglades. pp. 357-378 in "Everglades: The Ecosystem and its Restoration." S. M. Davis and J. C. Ogden, editors. St. Lucie Press, Delray Beach, Florida.
DeBusk, W. F., K. R. Reddy, M. S. Koch, and Y. Wang. 1994. Spatial Distribution of Soil Nutrients in a Northern Everglades Marsh: Water Conservation Area 2A. Soil Sci. Soc. Am. J: 58:543-552.
Doren, Robert F., Thomas V. Armentano, Louis D. Whiteaker, and Ronald D. Jones. In press. Marsh vegetation patterns and soil phosphorus gradients in the Everglades ecosystem.
Fleming, D. M., W. W. Wolff, and D. L. DeAngelis. 1994. Importance of Landscape Heterogeneity to Wood Storks in Florida Everglades. Environmental Management 18(5):743-757
Florida Department of Environmental Regulation. 1987. Water Quality Data Assessment of South Florida Water Conservation Areas. Florida Department of Environmental Regulation. Tallahassee, Florida.
Grimshaw, Herbert J., Morris Rosen, David R. Swi`ft, Kevin Rodberg, and Jill M Noel. 1993. Marsh Phosphorus Concentrations, Phosphorus Content and Species Composition of Everglades Periphyton Communities. Arch. Hydrobiol. 128:257-276.
Gunderson, Lance H., and William F. Loftus. 1993. The Everglades. pp. 199-255 (Chapter 6) in Biodiversity of the Southeastern United States: Lowland . John Wiley & Sons, Inc.
Hoffman, W., G. T. Bancroft and R. J. Sawicki. 1994. Foraging Habitat of Wading Birds in the Water Conservation Areas of the Everglades. pp. 585-614 in Everglades: The Ecosystem and its Restoration. S. M. Davis and J. C. Ogden, editors. St. Lucie Press, Delray Beach, Florida.
Jensen, J. R., K. Rutchey, M. S. Koch and S. Narumalani. 1995. Inland Wetland Change Detection in the Everglades Water Conservation Area 2A Using a Time Series of Normalized Remotely Sensed Data. Photogrammatic Engineering and Remote Sensing 61(2):199-209.
Izuno, F. T., C. A. Sanchez, F. J. Coale, A. B. Bottcher, and D. B. Jones. 1991. Phosphorus Concentrations in Drainage Water in the Everglades Agricultural Area. J. Environ. Qual. 20:608-619.
Koch, Marguerite S. 1991. Soil and Surface Water Nutrients in the Everglades Nutrient Removal Project. Technical Publication 91-04, DRE 302. South Florida Water Management District, West Palm Beach, Florida. 57 pp.
Koch, M. S., and K. R. Reddy. 1992. Distribution of Soil and Plant Nutrients along a Trophic Gradient in the Florida Everglades. Soil Sci Soc. Am. J: 56:1492-1499.
Mattraw, Harold C., Daniel J. Scheidt, and Anthony C. Federico. 1987. Analysis of Trends in Water-Quality Data for Water Conservation Area 3A, the Everglades, Florida. U.S. Geological Survey, Water-Resources Investigations Report 87-4142. USGS, Tallahassee, Florida. 52 pp.
McPherson, B. F., B. G. Waller and H. C. Mattraw. 1976. Nitrogen and Phosphorus Uptake in the Everglades Conservation Areas, Florida, with Special Reference to the Effects of Backpumping Runoff. USGS Water Resources Investigation 76-29. Tallahassee, Florida 120 pp.
Nearhoof, Frank L. 1992. Nutrient-Induced Impacts and Water Quality Violations in the Florida Everglades. September 1992 Draft. Florida Department of Environmental Regulation Water Quality Technical Series, Vol. 3, Num. 24. Florida Department of Environmental Regulation, Tallahassee, Florida. Raschke, R. L. 1993. Diatom (Bacillariophyta) Community Response to Phosphorus in the Everglades National Park, USA. Phycologia 32:48-58.
Scheidt, Daniel J., David R. Walker, Ramona G. Rice and Mark D. Flora. Diel Dissolved Oxygen levels under Experimental Nutrient Loading Conditions in Shark Slough, Everglades National Park, Florida. Abstract. Florida Scientist Volume 48 Supplement 1:36.
Scheidt, D.J., M.D. Flora, and D.R.Walker. 1989. Water Quality Management for Everglades National Park. pp. 377-390. In "Wetlands: Concerns and Successes." American Water Resources Association, Bethesda, MD. USA.
South Florida Water Management District. 1992. Surface Water Improvement and Management Plan for the Everglades. South Florida Water Management District, West Palm Beach, Florida.
South Florida Water Management District. 1995a. Everglades Nutrient Removal Project: Year 1 Synopsis. West Palm Beach, Florida. 4 pp.
South Florida Water Management District. 1995b. Everglades 1995 Annual Report. West Palm Beach, Florida. 40 pp.
Steward, Kerry K., and W. Harold Ornes. 1975. Assessing a Marsh Environment for Wastewater Renovation. Journal Water Pollution Control Federation 47:1880- 1891.
Stober, Q. J., R. D. Jones and D. J. Scheidt. 1995. Ultra trace level mercury in the Everglades Ecosystem, a multi-media canal pilot study. Water, Air and Soil Pollution 80: 991-1001.
Urban, N. H., S. M. Davis, and N. G. Aumen. 1993. Fluctuations in Sawgrass and Cattail Densities in Everglades Water Conservation Area 2A Under Varying Nutrient, Hydrologic and Fire Regimes. Aquatic Botany 46:203-223.
Walker, David R., Mark D. Flora, Ramona G. Rice, and Daniel J. Scheidt. 1988. The Response of the Everglades Marsh to Increased Nitrogen and Phosphorus Loading, Part II: Macrophyte Community Structure and Chemical Composition. Report to the Superintendent. Everglades National Park, Homestead, FL. 34 pp.
Walker, W. W. In press. Design Basis for Everglades Stormwater Treatment Areas. Water Resources Bulletin, 1995 Manuscript Number 94139.
Walker, W. W. 1991. Water Quality Trends at Inflows to Everglades National Park Water Resources Bulletin 27:59-72.