Funded External Research in Support of Numeric Nutrient Criteria Development in Florida
Through receipt of EPA Region IV Nutrient Criteria Development funds, DEP has been able to sponsor several research projects to aid in the determination of appropriate numeric nutrient criteria for Florida's waters. Descriptions of each of these efforts follow.
Historical water-quality changes in Lakes Conine, Haines, and May in Polk County, Florida were assessed using diatom assemblages in sediment cores. Preliminary diatom evidence suggested eutrophication but lacked the resolution to adequately define pre-disturbance water-quality conditions or document trends. The present study uses six diatom-based predictive models to infer past limnetic total P, averaged trophic state index, and limnetic chlorophyll a values. All indicators demonstrate that cultural eutrophication occurred in Lake Conine. Pre-disturbance limnetic chlorophyll a concentrations of approximately 8-17 ug/L, TSIAVG values of 53-55, and limnetic total P concentrations of 35-40 ug/L. Productivity decreased somewhat during recent decades, probably because of the removal of point-source nutrient supplies. In Lakes Haines and May, limnetic total P was approximately 40-42 ug/L, TSIAVG was 58-59, and limnetic chlorophyll a was approximately 16-19 ug/L. Data suggest that a very slight recovery in trophic state might have occurred in both lakes during recent decades. Paleolimnological evidence suggests that the lowest practical restoration target for Lake Haines, and perhaps other lakes in region 75-36, is approximately 42 ug/L limnetic total P. Attempts to manage lakes at limnetic nutrient concentrations that are less than pre-disturbance values are likely to prove ineffective because pre-disturbance water-quality is determined by the natural edaphic supply of nutrients to lakes.
Researchers at the Michigan State University Department of Zoology's Ecology, Evolutionary Biology and Behavior Program (R. Jan Stevenson and Bruce Wang, P.I.s) undertook analyses to develop algal indicators of trophic status for Florida streams. Testing the hypothesis that nutrients affected valued ecological attributes of streams (including algal biomass and algal growth potential), MSU researchers evaluated FDEP datasets to determine the significance of relationships between algal species indicators and nutrient conditions. Species response measures were found to best correlate with a multimetric index describing nutrient concentrations, incorporating values for five water chemistry parameters (NH3, NOx, TN, PO4, and TP) and three measures of algal biomass response (periphyton and plankton chlorophyll a and assays of algal growth potential).
Sedimentary concentrations of algal pigments are considered proportional to productivity of lakes at the time of their deposition. Total carotenoid pigments are good indicators of primary production in freshwater. Thus total carotenoids along with the cyanobacterial pigments oscillaxanthin and myxoxanthophyll were extracted from sediment cores from Lakes Conine, Haines and May in Polk County and Lake Wauberg in Alachua County. Percent native chlorophylls were also analyzed to evaluate pigment preservation quality. Algal pigment profiles were compared with preliminary sedimented-diatom analyses. Lake Conine showed abrupt increases in total carotenoid, oscillaxanthin, and myxoxanthophyll pigments in upper sediments, which indicates eutrophication. Diatoms and sedimented pigments suggest that nutrient mitigation efforts, such as removal of the wastewater plant around 1990, might have reduced the lake’s trophic state somewhat during recent decades. Pigment profiles in Lake Haines show clear evidence of recent eutrophication that is consistent with cultural activities. Diatom and algal-pigment data suggest that eutrophication has been pronounced and more recent in Lake Haines than in the other study lakes. In Lake May, total carotenoids and preliminary diatom data suggest that eutrophication began after a period of shoreline disturbance in the lower 1/3 of the core. In Lake Wauberg, algal pigments were high throughout the core. Algal pigments and diatom evidence both support the conclusion that trophic state has been high historically in Lake Wauberg and has fluctuated over time.
DEP contracted with researchers at the University of Florida's Department of Fisheries and Aquatic Sciences (Thomas Whitmore and Mark Brenner, P.I.s) to determine pre-disturbance water quality conditions for eight Florida lakes believed to have undergone cultural eutrophication. UF researchers conducted simplified paleolimnological analyses of sediment cores to infer historic limnetic water quality through the use of statistical models based on sedimented diatoms, calibrated with data from a large set of Florida lakes.
Analyses were undertaken to approach numeric nutrient criteria recommendations for five classes of Florida lakes, defined by water color, pH, and geographic region - Acid Clear Lakes in EPA Level II Ecoregion 65, Acid Clear Lakes in Ecoregion 75, Acid Color Lakes, Alkaline Clear Lakes, and Alkaline Color Lakes. DEP contractors (TetraTech, Inc., Jeroen Gerritsen, P.I.) identified six (6) potential approaches to define numeric nutrient criteria for Florida lakes. The first three approaches focused on methods to identify least impacted background nutrient concentrations, whereas the second three were designed to identify nutrient concentrations protective of biological condition. These analyses yielded the several recommendations for provisional nutrient criteria, which should be recognized to be only recommendations at this point.
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Last updated: September 29, 2011
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