Habitat requirements of Elodea canadensis Michx. in Polish rivers

The main objectives of this work were to investigate the range of habitat conditions (in terms of water chemistry and hydromorphological parameters) at sites colonized by Elodea canadensis and to analyze the species composition of communities with this plant species. We analyzed physicochemical, hydromorphological and biological data from 1135 sites located in Polish rivers to identify environmental factors that determine the occurrence of Elodea canadensis. Canadian waterweed was present at 18.1% of the analyzed river sites, located mainly in the lowlands (26.2% of all lowland sites).The results show that Elodea canadensis prefers moderately mineralized water (545 ± 329 μS cm⁻¹), rich in calcium and magnesium carbonates (174 ± 63 mg CaCO₃ l⁻¹, 84.1 ± 31.4 mg Ca²⁺ l⁻¹ and 11.1 ± 6.4 mg Mg²⁺ l⁻¹), with moderate concentrations of chlorides and sulfates (38.9 ± 59.1 mg Cl^- l⁻¹ and 62.3 ± 50.9 mg SO₄²⁻ l⁻¹) and in terms of nutrients, it prefers water from moderately rich to mesotrophic and eutrophic. This plant has high light requirements and grows mainly in unshaded sections of shallow rivers. The studied species avoids sections of rivers strongly transformed and those with reinforced banks and bottoms. Canadian waterweed occurs mostly in the company of vascular macrophytes associated with slow-flowing rivers with sandy bottom material, indicating mesotrophic and eutrophic water.