Adam Cudowski, Andrzej Stefan Górniak and Marta Hryniewicka
Physicochemical studies in four dystrophic lakes (Suchar Wielki, Suchar II, Suchar IV, and Wądołek) were carried out in Wigry National Park, NE Poland. Total manganese concentrations oscillated within the range of 386.6-647.5 μg Mn dm-3, while those of soluble reactive manganese, 112.5-328.2 μg Mn dm-3. Fairly high boron contents were recorded in the studied lakes, which amounted to 0.09-2.20 mg B dm-3. The increase in dissolved reactive manganese (DRMn) and decrease in dissolved boron concentration with the lake depth were observed. Almost half (47%) of the total manganese pool was composed of dissolved reactive soluble fraction (DRMn), then dissolved organic form (DOMn, 41%), whereas the particulate fraction (PMn) made up the smallest share (12%). Microbial decomposition of lake organic matter disappears and requirements of authotrophic plankton for Mn2+ decreases when the water temperature drops, thus the fraction prevails. The following regularity was recorded in all analysed dystrophic lakes: iron concentration decreases along with the depth, hence boron content can also be observed due to precipitated borates to bottom sediments, where they are accumulated.