The search for target values of quality indices for bioindicators of the ecological state and environmental factors: Case study of water bodies of the Don river

The possible use of quantitative characteristics of phytoplankton species diversity for water quality bioindication and for the search for ecologically admissible levels of abiotic factors is examined. Retrospective materials on the Don basin obtained from data of state environmental monitoring of freshwater in Russia are used. The effect produced on the characteristics by the diversity of errors in the calculation of the numbers of phytoplankton cells, the procedure used to assess rank distribution parameters, the adequacy of formal models of rank distributions, the relationship between the uniformity of rank distributions and species diversity, sampling season, water body type, and the geographic location of sampling site is analyzed. The obtained diversity characteristics are in agreement with the available monitoring data. Boundaries of the examined characteristics, corresponding to the well-being ranges of phytoplankton communities, were found. The ecologically admissible levels were calculated for the major abiotic factors.