Phytoplankton based assessment of the ecological status of four shallow lakes (Eastern Poland) according to Water Framework Directive – a comparison of approaches

The EU Water Framework Directive includes phytoplankton as one of the four biological elements to be used in the assessment of the ecological status of surface waters. In this work we establish the ecological status of four shallow lakes in the Polesie Region of Eastern Poland on the basis of phytoplankton and physicochemical data from the lake water. A number of recently developed phytoplankton indices, including the Carlson Index, Q index and German PSI were compared. Cyanoprokaryota, chlorophytes and dinophytes dominated in Lakes Głębokie and Sumin, while in the Lakes Rotcze and Maśluchowskie the biggest share belonged to Chlorophyta. On the basis of the Carlson Index, Lake Głębokie had the highest trophic score, while the lowest score was for Lake Rotcze. A similar result was also found with the Q index which indicated a good ecological state for Lake Rotcze (Q=3.5), a bad state for Lake Głębokie (Q=0.9), a poor status for Lake Sumin (Q=1.2) and a moderate status for Lake Maśluchowskie (Q=2.9). Similar results were obtained with the use of the German PSI which classified Lake Głębokie as bad status (PSI=4.7) and Lake Rotcze as good (PSI=2), although differences between the 2 indices appeared between the moderate and poor status lakes (respectively in the case of Lake Sumin – PSI=2.6 and Lake Maśluchowskie – PSI=4.4).