The pit lakes localized in the eastern part of the Muskau Arch (Western Poland) developed as a result of lignite mining at the turn of the 20th century. The formation of the lakes varied over time and was determined by many hydrogeochemical and biological factors, which resulted in very diverse ecosystems. Thirty of these lakes were studied in the vegetation seasons of 2016 and 2017. The aim of the study was to identify the main factors influencing the diversity of macrophyte vegetation growing under very extreme and diversified habitat conditions. Therefore, in each lake the numbers of macrophyte species and communities were determined, and the water was characterized by 26 physico-chemical parameters and Chl a. Additionally, the genesis, age, area and maximum depth of each lake was determined. The results showed high diversity of habitat conditions. Based on the physical and chemical water properties, four different clusters of lakes were distinguished. The multiple statistical comparisons showed that the main factors responsible for lake differentiation were pH, water mineralization and to a lesser extent, nutrient concentration and water transparency. The physico-chemical differentiation was reflected in the significant differences in the number of species, number of communities, maximum vegetation extent and amount of chlorophyll-a per lake. The correlational analyses confirmed significant relationships between habitat conditions and macrophyte flora diversity in the lakes. Some macrophyte species were found in very extreme environments not previously reported in the literature. Our results showed that in addition to natural processes affecting species diversity in the lakes, the negative impact of anthropogenic pressures (neutralization and fertilization of the water), which leads to the degradation of their unique character, is also an important factor.
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