Comparison of Eutrophication Indexes for Delaware Lakes

Abstract

ABSTRACT A total of 30 lakes were sampled and classified according to trophic conditions. There was a poor correlation between summertime chlorophyll a and total phosphorus concentrations and between total phosphorus concentrations and secchi disc transparency. None of these three parameters could be used as a single parameter trophic index for describing aquatic weed problems in Delaware lakes. There was a divergence in the Carlson indexes for chlorophyll a, total phosphorus and secchi disc transparency. None of the Carlson indexes could be used to determine the trophic conditions, based on aquatic weed problems, for each of the lakes. Critical phosphorus loading rates calculated by the Vollenweider model for highly eutrophic conditions were much lower than actual phosphorus loading rates for all of the lakes. A five parameter trophic state index composed of total phosphorus, chlorophyll a, secchi disc transparency, total nitrogen and dissolved oxygen did not adequately describe the trophic state of all the lakes in Delaware. The five parameter index was better for describing the trophic conditions, based on aquatic weed problems, than the Carlson indexes or Vollenweider model.