Development of tools for ecological quality assessment in polish marine areas according to the Water Framework Directive. Part III — Secchi depth

The implementation of the EU Water Framework Directive (WFD) requires ecological status quantification on the basis of biological and physico-chemical parameters, and an assessment of reference conditions and relevant environmental pressures for the construction of response curves. In this study the linking of water transparency, a proposed eutrophication indicator, to environmental pressure parameters was examined in the Polish sector of the Baltic Sea. Statistically significant linear correlations were detected between nutrient concentrations in sea water and Secchi depth, and between nutrient riverine loads and Secchi depth. The magnitude of acceptable deviation from reference conditions is also discussed.