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The aim of this study was to characterize the spatial and temporal variability of total organic carbon concentrations in a shallow, eutrophic lake (Lake Jaroslawieckie,the Wielkopolski National Park, mid-western Poland) against the background of lake habitat heterogeneity. The interrelations between TOC and chlorophyll a in different studied sites (in macrophyte communities as well as in open water sections) were also taken into account. In November 2000, March, May, June and July 2001, water samples were collected in two transects along and across the lake traversing macrophyte communities of the phytolittoral zonation (7 sites) and reaching the open water zone (mid-lake, 3 sites) and, additionally, in a site close to a beach attracting local inhabitants and tourists. Statistical analyses revealed significant temporal differentiation and reverse patterns of changes of both TOC and chlorophyll a concentrations in the studied lake, whereas the spatial one was not significant. No correlations between both parameters were found. The results of cluster analyses suggest macrophyte vegetation and its seasonal changes in development as the main factor to influence TOC concentrations. [ABSTRACT FROM AUTHOR]

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 phytocoenotic 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,results 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 habitat diversity whose use -especially as the only or main method -seems to be rather limited. [ABSTRACT FROM AUTHOR]