Site-dependent species composition, structure and environmental conditions of Chara tomentosa L. meadows, western Poland

• Seasonal study of Chara tomentosa meadows and the associated water chemistry in 4 lakes.
• Among 15 macrophytes, 8 charophytes were recorded in the studied stands.
• Nutrient concentration determined species distribution and abundance.
• PVI correlated with temperature, pH and solute content in the water.
• The interactions of charophytes and water chemistry are discussed.

In this study we investigated the relationships between charophyte abundance and water chemistry in four well vegetated lakes in western Poland differing in morphometry, catchment basin characteristics, and intensity of human pressure. Species composition and abundance (expressed as cover and, additionally, as PVI values, defined as per cent volume of water infested by plants) of vegetation patches dominated by Chara tomentosa L. were determined along with water physicochemical characteristics at nine permanent study sites monthly from spring through autumn. We hypothesised that the species composition of C. tomentosa meadows is lake-specific whereas the abundant growth is the cause rather than a response to water quality of the studied lakes. C. tomentosa formed dense swards in every studied vegetation patch, irrespective of water depth, with negligible contributions of vascular plants to species richness and abundance. Although 15 macrophyte species were identified in the studied meadows, including eight charophytes, C. tomentosa dominated throughout the growing season. Heterogeneity observed in the species composition and cover was site-specific rather than related to physicochemical differences among the lakes. PVI values were positively correlated with water temperature and pH, and negatively correlated with water conductivity, hardness and Ca2+ concentrations. The results indicate a preference for high water clarity by most charophyte species found in the studied patches and highlight the possible influence of charophyte meadows on water quality, primarily on solute content, hardness and, thereby, as a positive feedback, on water clarity.