Assessment of eutrophication and phytoplankton community impairment in the Buffalo River Area of Concern

A “weight of evidence” approach was used to assess trophic status and phytoplankton community characteristics as a step towards delisting beneficial use impairments in the Buffalo River Area of Concern (AOC). Using a combination of historical data and results of a sampling program conducted in 2006, trophic status was evaluated by considering threshold levels of total phosphorus and chlorophyll a, total phytoplankton abundance, reference-reach comparisons of total phosphorus and nitrate + nitrite, and an ecoregion (percentile) analysis. Microcystin toxin levels were used as an indicator of the presence of undesirable algae. Phytoplankton community characteristics were assessed through consideration of species richness, Shannon–Weaver Index of Diversity, presence of indicator species, centric:pennate diatom ratio, the Trophic Diatom Index (TDI), and the Pollution Tolerance Index (PTI). The weight of evidence suggests that the Buffalo River AOC does not have a eutrophication problem, but nutrient levels are sufficiently high to recommend further implementation of watershed Best Management Practices and continued water quality monitoring. Microcystin was present in all samples but at a level below the World Health Organization guidelines; based on this indicator we conclude that the AOC does not have a problem with undesirable algae. The phytoplankton community exhibits some anthropogenic impact as reflected by the TDI, PTI, and presence of certain indicator species, but these impacts do not indicate extreme stress. Based on the weight of evidence the Buffalo River Remedial Advisory Committee recently concluded that the AOC was not impaired in terms of eutrophication, presence of undesirable algae, and degradation of phytoplankton.