Litter per liter - Lakes' morphology and shoreline urbanization index as factors of microplastic pollution: Study of 30 lakes in NE Poland

Human activity and anthropopression play key roles in contaminating aquatic environments with microplastics (MPs). The lakes of northeastern Poland provide a wide range of freshwater ecosystems differing in morphology, hydrology and ecology. In this study, we investigate 30 lakes during summer stagnation, considering their varying levels of anthropogenization of the catchment area and taking into account increased tourist activity. MPs were found in each of the studied lakes in the range from 0.27 MPs/L to 1.57 MPs/L, and the average value was 0.78 ± 0.42 MPs/L. The features of the MPs were evaluated, including size, form and color (most frequent: 4-5 mm (35.0 %); fragments (36.7 %); blue (30.6 %), respectively). Gradual accumulation of MPs has been observed in the lakes that comprise the hydrological sequence. The amount of sewage produced by wastewater treatment plants was considered in the study area. Statistically significant differences were found between lakes with different surface areas and shoreline lengths, where lakes with the highest and smallest values were notably more polluted with MPs than lakes in the medium range (F = 34.64, p < .0001 and F = 5.96, p < .01, respectively). The study presents an easy-to-obtain shoreline urbanization index (SUI) that is particularly useful for lakes with heavily transformed catchments in terms of hydrology. A significant correlation between the MP concentration and SUI, reflecting the degree of direct catchment anthropopression (r = +0.4282; p < .05), was observed. The analysis of the human impact on shoreline conversions and development should also pique the interest of other researchers as a potential indicator of MP pollution.

Top-down and bottom-up control of phytoplankton communities by zebra mussels Dreissena polymorpha (Pallas, 1771)

Zebra mussels (ZM), Dreissena polymorpha (Pallas, 1771), are one of the most aggressive invasive species. ZM have a strong bidirectional impact on phytoplankton because of their high nutrient excretion rates and high grazing pressure. Furthermore, the interactions between excretion and selective grazing are related to the trophic status of a waterbody and could cause unpredictable changes in phytoplankton. We performed three types of experiments: (i) bottom-up where we measured ZM excretion rates; (ii) top-down where we analyzed the effects of ZM on phytoplankton taxonomic structure via grazing in different trophic conditions; (iii) mesocosm experiment where we estimated the combined top-down and bottom-up effects of ZM on phytoplankton assemblages under different trophic conditions. Our first experiment confirmed high excretion rates of dissolved nutrients (PO₄^3- and NH₄⁺) and dissolved organic carbon (DOC) by ZM. The other experiments revealed selective grazing by ZM, where diatoms were mostly selectively rejected, while green algae were preferred. In the top-down experiment, ZM decreased the total biomass of phytoplankton, while in mesocosm experiments where top-down and bottom-up controls acted simultaneously, we observed increased phytoplankton biomass mainly through increases in filamentous green algae. Our experiments show that ZM can influence phytoplankton through a combination of bottom-up and top-down effects that vary with trophic state.

Hydrochemical diversity of semi-natural water system on the background of environmental conditions

Research carried out from 2007 to 2011 showed that a tested semi-natural water system with a diverse catchment (peat, peat-mineral and mineral) has a very varied quality of water, as evidenced by a the large range of conductivity (174-828 μS/cm) and pH (6.34-9.92). Natural lake parts of the semi-natural water system were similar to the artificial parts in terms of physico-chemical parameters, as evidenced by the lack of statistically significant differences between the water quality in both of these ecosystems. Taking into account the quality of various types of water in this semi-natural system, it can be seen that the river waters differed significantly (p < 0.001) in concentrations of biogenic elements (nitrogen, phosphorus) from another type of ecosystems. In addition, rivers poor in organic matter (TOC < 10.0 mg/L) which directly supplied the water system contributed to higher values of many tested parameters (EC, pH, TC, TN, SO4 (2-) or Cl(-)) in waters of the canal. In contrast, rivers with high values of concentrations of organic matter (TOC > 10.0 mg/L) contributed to a decline in values of those parameters. Moreover, lake waters within the tested semi-natural water system showed a "cleansing" function, because they caused a decrease in conductivity, pH or the concentration of carbon, total nitrogen, sulphate(VI) and chloride in waters of the canal.

The trophic status of Suwałki Landscape Park lakes based on selected parameters (NE Poland)

This study describes changes in the trophic status of 12 lakes within Suwałki Landscape Park (SLP). All of the trophic classifications of the lakes were based on the trophic continuum division. Trophic status was determined by means of multiparameter indices using several diverse criteria. In this study, the assessment of the trophic status of lakes included water quality; abundance and biomass of bacterioplankton, phytoplankton, and zooplankton; and primary production of phytoplankton. The Carlson trophic state index (TSI) describes the level of water fertility and indicated the dominance of moderately eutrophic waters. Lakes Perty, Jeglówek, and Hańcza have a trophic status that indicates mesotrophy (TSI <50). The trophic status of the studied lakes was determined based on the bacterial abundance and clearly showed a lack of oligotrophic lakes in SLP. Based on the number of bacteria, only Lake Szurpiły can be classified as β-mesotrophic, whereas Lake Linówek can be characterized as hypertrophic with some features typical for humic waters. The greatest value of gross primary production was observed in Lake Linówek (126.4 mg C/m(3)/h). The phytoplankton trophy index varied from 1.59 to 2.28, and its highest value, which indicated eutrophy, was determined for Lake Udziejek. In the case of Lakes Hańcza, Szurpiły, Perty, Jeglówek, and Kojle, the index ranged from 1.25 to 1.74, which indicated mesotrophy. The majority of the lakes were classified as mesoeutrophic (1.75-2.24). The highest trophic status was assessed for lakes with a marked dominance of cyanobacteria (Lake Przechodnie, Lake Krajwelek, Lake Udziejek, and Lake Pogorzałek), which is commonly recognized as an indicator of high trophic status. Considering all of the indices of trophic status, the analysis of rotifer community structure indicates that the studied group of lakes is mesoeutrophic or eutrophic. The values of crustacean zooplankton indices indicated that the trophic status of the studied lakes was close to that determined using a TSI. The parameters of zooplankton abundance and species structure allowed for the observance of changes in the tropic levels of lakes, which are difficult to detect by a chemical assay alone.

Biomass, abundance and sensitivity to antibiotics and antimycotics of the fungi in the Vistula River with its main tributaries

Mycoplankton of Vistula River and its main tributaries biomass as well as the number and morphotype diversity was studied in summer and autumn 2011. Summer mycoplankton biomass was within the range of 0.2 – 0.5 μg/l, while in the autumn it was two times wider range (0.1 – 1.3μg/l). The number of fungi in river water most often did not exceed 1000 – 2000 CFU/ml. Fungi colonies isolated from rivers water were sensitive to the commonly used amphotericine B (10 μg) and gentamicin (10 μg). It seems to be plausible that aquatic fungi can acquire immunity to drugs as a result of horizontal transfer of a gene responsible for drug resistance or as an effect of antibiotics and antimycotics getting into the aquatic ecosystems from wastewaters.