Abstract:We evaluated the influence of habitat connectivity and local environmental factors on the distribution and abundance of functional fish groups in 10 floodplain lakes in the Biebrza River, northeastern Poland. Fish were sampled by electrofishing, and 15 physico-chemical parameters were recorded at three sampling sites at each lake in the period of 2011-2013. A total of 18,399 specimens, belonging to 23 species and six families, were captured. The relationships between environmental factors and fish communities were explored with the use of canonical correspondence analysis (CCA). Sampling sites were grouped based on fish communities using a hierarchical cluster analysis (HCA). Along a lateral connectivity gradient from lotic to lentic habitats (parapotamic-plesiopotamic-paleopotamic), the proportions of rheophilic species were determined as 10:5:1, whereas the proportion of limnophilic species was determined as 1:2:5. The predominant species were the roach (Rutilus rutilus), and pike (Esox lucius) in parapotamic lakes, rudd (Scardinius erythropthalmus) and pike in plesiopotamic lakes, and sunbleak (Leucaspius delineates) and Prussian carp (Carassius auratus gibelio) in paleopotamic lakes. The findings indicated that the composition and abundance of fish communities are determined by lake isolation gradient, physico-chemical parameters and water stage. Although intact riverine ecosystems may promote fish biodiversity, our findings suggest that lateral connectivity between the main channel and floodplain lakes is of utmost importance. Thus, the conservation of fish biodiversity requires the preservation of this connectivity.

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River restoration projects rely on environmental engineering solutions to improve the health of riparian ecosystems and restore their natural characteristics. The Kwacza River, the left tributary of the Słupia River in northern Poland, and the recipient of nutrients from an agriculturally used catchment area, was restored in 2007. The ecological status of the river’s biotope was improved with the use of various hydraulic structures, including palisades, groynes and stone islands, by protecting the banks with trunks, exposing a fragment of the river channel, and building a by-pass near a defunct culvert. The effects of restoration treatments were evaluated by comparing the physicochemical parameters of river water along the 2.5 km restored section between the source and the mouth to the Słupia, before restoration and 6 years after hydrotechnical treatments. A total of 18 physicochemical parameters were analyzed at 10 cross-sections along the river. The greatest changes were observed in the concentrations of NO3−-N and NH4+-N, which decreased by 70% and 50%, respectively. Dissolved oxygen concentration increased by 65%. Chloride values increased by 44%, and chlorophyll-a concentration increased by 30% after the project. The cut-off channel (by-pass), semi-palisades, and single groynes were the treatments that contributed most to water quality improvement. The results of this study indicate that river restoration projects can substantially reduce nitrogen pollution, which is particularly important in agricultural areas. Such measures can effectively reinstate natural conditions in river ecosystems. Hydrochemical monitoring is required to control the parameters of restored rivers.

The paper presents the research results on the relation between the contents of total zinc and its bioavailable form (Zn a) and physicochemical properties of soil carried out along three catenas in the postglacial valley of the middle Łyna River, in NE Poland. We focused on topographical factors to determine the amount of Zn in the soil in relation to specific geochemical landscape types. The analyzed soil showed a relatively low level of soil pollution with Zn and did not exceed the threshold values for soil contamination with Zn. The average Zn content amounted to 45.75 mg kg-1 d.m. and ranged from 8.80 to 176.26 mg kg-1 d.m. The heavy metal content in the soil was related to organic matter and clay fraction, while it was inversely proportional to the share of sandy fraction. Distribution of zinc showed variability due to factors derived from topography, soil heterogeneity in the river valley as well as fluvial processes taking place within the floodplain. Different geochemical landscapes showed depressive trends in both Zn and Zn a contents along the catenas. It diminished from eluvial to transeluvial landscapes and increased again to superaqual landscape. Depressions after former river channel were favorable for the Zn a accumulation. The most abundant in Zn a were upper horizons of Fluvisols in superaqual landscape (45.12 mg kg-1) filling overgrown and terrestialized floodplain lakes. The share of Zn a was the highest in organic horizons of Fluvisols and achieved 51.4% of total Zn. The nature and power of functional links between the heavy metal mobility and the soil properties were determined with multivariate statistics and GAM models. Applied ordination statistics confirmed its usefulness in soil factor analyses.

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