Interrelationships between macrophytes (including charophytes) and phytoplankton and the ecological state of lakes

Multidisciplinary investigations of 30 lakes (mid-Western Poland) were carried out in the years 2001–2004. Micro- and macrophyte vegetation was studied against the background of abiotic conditions. Significantly higher biomass of phytoplankton was found in nutrient rich shallow lakes without both charophyte and vascular submersed vegetation as well as in lakes with only poorly developed vascular communities. Visibly better abiotic conditions and the lowest phytoplankton biomass were observed in deeper lakes with diverse macrophyte (and particularly charophyte) vegetation. Lakes with poorly developed charophyte vegetation represented transitional conditions and biomass. Nevertheless, in some (mostly shallow) lakes, where submersed vegetation and particularly charophyte communities were well developed, phytoplankton biomass was rather low and the transparency was high despite eutrophic conditions. Additionally, in those lakes macrophyte vegetation was not only abundant but also diverse with rare, valuable or even unexpected communities of high bioindicator value. Interestingly, an opposing situation with abundant phytoplankton and bad light conditions was also documented in shallow lakes with submersed vegetation. In those lakes, however, only vascular macrophytes developed dense but homogeneous (monospecific) beds. The results are discussed regarding interrelationships between macrophyte vegetation and phytoplankton assemblages.