Martyna Bąkowska

We present a unique data set of selected physicochemical parameters characterizing the environment of the Baltic coastal lakes within Polish borders. The peculiarity of the system derives principally from the interaction of the lakes with a sea of relatively low salinity. In contrast to our best understanding of the state of biological knowledge, the abiotic parameters of coastal lakes along the southern Baltic Sea have never previously been so comprehensively supplemented. The database consists of physicochemical properties of 13 coastal lakes based on the analytical assessment of 419 water samples collected seasonally between 2014 and 2019. Water properties were analyzed according to the connection of the lakes to the Baltic Sea using a total of 23 predictors. The lakes were classified as closed, intermittently connected, or open. Based on the physicochemical data, a relationship between the hydrological connection between the lakes and the sea was determined. The data collected could be used to monitor ongoing global climate change at the biosphere level.

Lake Łebsko is the largest and most productive coastal lake of the southern Baltic Sea to which it is permanently connected. The shoreline is well-developed, and the lake is divided into three parts: eastern, central, and western. Seawater intrusion affects most strongly the eastern part, where the Łeba River connects it with the sea. Samples of water and sediments were collected in 2014–2015. In the same places and time interval, bottom fauna was collected to determine the influence of environmental predictors on its qualitative-quantitative structure. Metals Cr (chromium), Pb (lead), Ni (nickel), Cu (copper), and Al (aluminium) in the samples were analyzed using inductively coupled plasma optical emission spectrometry. Most of the analyzed physicochemical variables of water were significantly higher in the eastern part: conductivity, salinity, sulfates (p < 0.0001) and chlorides (p = 0.01). Metal concentrations in water did not differ significantly between the lake parts, but in sediments they were generally higher in the western part. During the study, we detected significant changes in descriptors and abundance of the major groups of benthic fauna (Oligochaeta and Diptera), mostly between the eastern and western parts. BIO-ENV analysis showed that the benthic community of Lake Łebsko is shaped primarily by physicochemical variables of water (42% of the variance), linked with intrusion of seawater. Secondarily, the structure of the benthic community is affected by the amounts of heavy metals in sediments (31%) and water (12%). The findings can help us improve the principles of management of coastal lakes, including modification of hydrological conditions.

The zooplankton community structure and diversity were analysed against the gradient of floodplain lakes connectivity and water level under different flood-pulse dynamics in the Vistula River. The lakes differed in terms of hydrology, among others in the degree/type of their connection with the river (permanent, temporary and no connection). The study was conducted during the growing seasons in the years 2006–2013 and involved the lower Vistula River and three floodplain lakes: isolated, transitional and connected. Water samples were collected biweekly from April to September. Zooplankton was the most diverse and abundant in the transitional lake (the highest Shannon α-diversity index H’ and Pielou’s evenness index J’). The gentle washing of the lakes might have stimulated the development of zooplankton in accordance with the Intermediate Disturbance Hypothesis. The diversity and density of zooplankton were higher in the connected lake compared to the isolated one. We confirmed the hypothesis that zooplankton should be more abundant and diverse in floodplain lakes connected with the river (or transitional) than in isolated ones. Zooplankton analyses indicated that hydrological conditions (flood-pulse regime) contributed most substantially to zooplankton diversity and density in the floodplain lakes of the lower Vistula valley.

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.

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