Morphological forms of two macrophytes (yellow water-lily and arrowhead) along velocity gradient

We investigated morphological response of yellow water-lily and arrowhead to water velocity gradient in the lowland We?na river (Western Poland). Percentage cover of floating and submerged forms of yellow water-lily and arrowhead had been measured in randomly selected sites of 16 m². We analyzed 62 stands of Nuphar lutea and 80 stands of Sagittaria sagittifolia using 13 environmental variables. Redundancy analysis (RDA), the Monte Carlo permutation test, ranges of chemical and hydrological data, Generalized Additive Models (GAMs) and transfer function were used to describe reaction of investigated species to water velocity. Among the analyzed parameters of microhabitats with the floating and submerged forms of investigated species, velocity, pH, water colour, hydration and organic matter in bottom sediments were statistically significant. In S. sagittifolia case, the velocity was the most important parameter, while in N. lutea — both velocity and content of organic matter in river substrate were statistically significant.