As part of an effort to assess the feasibility of applying empirical eutrophication models to reservoirs, relationships among chlorophyll-a, phosphorus, nitrogen, and transparency are empirically examined. The data base is derived from 480 water quality monitoring stations located in 118 U.S. Army Corps of Engineer reservoirs distributed throughout the United States. Existing models assume a direct relationship between seasonally averaged total phosphorus and chlorophyll-a concentrations. It is difficult to identify sets of conditions under which chlorophyll is an exclusive function of total phosphorus in these reservoirs. The phosphorus/chlorophyll relationship derived from stations with average inorganic N/ortho P ratios greater than 10 and non-algal turbidities less than.37#x2002;m#x2212;1 (in units of inverse Secchi depth, corrected for light absorption by chlorophyll-related substances) is found to be similar to phosphorus/chlorophyll relationships derived from P-limited northern lakes. Nitrogen effects on chlorophyll-a are found to be significant in about 22o of the station-years examined, and turbidity effects, in about 69. Modifications of existing empirical models to include nitrogen and turbidity as regulating factors are needed if they are to be valid and useful over the spectrum of physical and chemical environments found in reservoirs.
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