Two approaches to lake-naturalness determination - a case study from four mid-forest Polish lakes

This study aimed at evaluate the ecological states of four protected, mid-forest lakes located in mid-western Poland. Two means of evaluation were used and compared: biodiversity (expressed by phytocoe-notic diversity of macrohydrophyte vegetation) and habitat diversity (resulting from abiotic conditions and biota activity). The first method was based on the type and number of plant associations present in the studied lakes. The contribution of naturally and anthropogenically induced plant assemblages to lake vegetation was considered. The other method concerned morphometric, mictic and trophic features of the lakes and their water purity classes. The study results, especially a large number of plant assemblages and natural character of vegetation, evidenced a high degree of naturalness of all the reservoirs. However, re-sults obtained with the use of both methods were to a certain degree inconsistent. With respect to the type of catchment and mid-forest location as well as still limited anthropopressure, the phytocoenotic diversity more clearly differentiated the reservoirs and more accurately reflected their ecological status than the habi-tat diversity whose use - especially as the only or main method - seems to be rather limited.