The “Forgotten” Ecology Behind Ecological Status Evaluation: Re-Assessing the Roles of Aquatic Plants and Benthic Algae in Ecosystem Functioning

Abstract

Aquatic plants and benthic algae have long been used as indicators for nutrient enrichment in lakes and streams. Evaluations of the performance of indices calculated from species assemblages of aquatic plants and algae are generally based on correlations with water nutrient concentrations. We argue that this is a misinterpretation, because water chemistry is both cause and effect: higher nutrient concentrations may cause enhanced plant and algal growth and change their assemblages, but plants and benthic algae also remove nutrients from the water. Additionally, biotic interactions blur water chemistry – aquatic plant relationships. We suggest that indices can be improved by relating biotic responses to quantifiable causal stressors, such as nutrient loading, instead of using water chemistry for performance evaluation of the indices. In addition, a tiered approach, i.e., the use of simpler indices for getting an overview and of sophisticated methods in doubtful cases, could avoid unnecessary costs and efforts while giving important monitoring and management information.