Proposing biologically-based nutrient thresholds for Greek Lakes

Abstract

According to WFD, the composition and abundance of biological communities guide the assessment of lake ecological status; physicochemical parameters, such as nutrients, are supportive elements in this process. In this context, the thresholds of Good-Moderate (GM) status for Total Phosphorus concentrations (TP) in two high alkalinity lake types in Greece have been proposed using a European toolkit. Our objective was to investigate the conformity of GM thresholds for TP with changes in biological communities of two types of lake ecosystems, shallow polymictic and warm monomictic, in Greece. We examined pressure response relationships using data collated from the National Monitoring Network. We plotted parameters of phytoplankton, aquatic macrophytes and water transparency across TP concentrations in the two types of natural lakes. In TP threshold values of 20-40 μg/l changes in biological communities and water transparency were observed in both lake types. These nutrient thresholds seem comparable with the ones proposed with the application of a standard toolkit. Changes in the composition and abundance of biological communities, as well as in water transparency, appear to be explained by TP concentrations in two types of natural lakes in Greece. Efforts should focus in minimizing phosphorus loading in lake waters.