Hydrochemical investigations focusing on different iron fractions were conducted in 2007 from January to December on two parts (regulated and restored) of the small lowland Rudnia River in north-eastern Poland. Concentrations of the total iron (TFe) in the water of the Rudnia River ranged from 582 μg dm-3 up to 3646 μg dm-3, and their elevated values are clearly the result of their complex binding with organic matter originating from the peat-mineral catchment of the river. Regardless of the season, in the upper part of the river (regulated channel) higher concentrations of all iron fractions than in the restored river section were observed. All tests on iron fractions showed a clear seasonal variability on both river channel parts. Higher TFe concentrations were typical for the regulated part of the river in autumn or winter, and lower in spring for the restored river channel section. For the whole of the investigated period and regardless of the season, particulate iron fraction (PFe) represented a higher proportion of TFe in the regulated channel than in the restored one. PFe constituted up to 60% TFe, on average, while the other two fractions about 20% of TFe each. However, dissolved reactive iron fraction (DRFe) made up a larger percentage of TFe than organic soluble fraction (DOFe) of iron within the year. The maximum percentage of DOFe fraction outside the growing season was caused by iron release from organic complexes and elevated concentrations of dissolved organic carbon (DOC) derived from wetlands.
This study describes summer phytoplankton communities in 27 lakes in the Suwałki Landscape Park (SLP) using in situ fluorescence methods. Low chlorophyll-a concentrations were noted in most of the studied lakes, particularly in the deepest lakes with highest surface area. Green algae, diatoms and cryptophyta were dominant components of lake phytoplankton. Higher chlorophyll-a concentrations in the shallow or more eutrophicated lakes were connected with an increase of cyanobacteria and cryptophyta concentrations as well as with a decrease in the share of diatoms inphytoplankton structure. Vertical distribution of phytoplankton in stratified lakes revealed the presence of deep chlorophyll layers just below the thermocline where the maximum concentrations of phytoplankton were up to 15 times higher than in the epilimnion zone. The deepest maximum concentration of phytoplankton was noted at a depth of 16.5 metres in Lake Jeglówek. In some lakes two or three significant increases of phytoplankton concentration in the vertical profile were observed, caused by intensive development of different algae groups.
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.