Comparisons of trophic state measurements

Abstract

Twenty-nine methods commonly used to measure trophic state were compared with respect to their ability to rank 44 test lakes against two standards: total phosphorus, a nutrient or driving force standard and chlorophyll a, an eutrophication response standard. The phosphorus loading models had high rank correlations with phosphorus; however, they did not rank the lakes well against chlorophyll. The relative trophic ranking of many lakes differed depending upon whether primary nutrients or biological manifestations were used as the ranking mechanism. Secchi disk was very effective in ranking the lakes against phosphorus but was relatively ineffective in ranking them against chlorophyll. Total Kjeldahl nitrogen was effective in ranking the lakes against phosphorus and had the highest rank correlation of all the methods tested against chlorophyll. Methods based upon phytoplankton community structure were especially ineffective in ranking the test lakes. Algal assay control yield gave disappointing results when compared against the chlorophyll standard. Most methods were much more effective in ranking the lakes against the total phosphorus standard than the chlorophyll a standard.