During the period of summer rivers are intensively used for leisure activities such as kayaking. The most noticeable impact of such water transport is a mechanical disturbance of aquatic plants (cut off the flowers and fruits) and their habitats (causing the erosion of riverbed and accumulation of sediments in river onshore). Water courses with Ranunculion fluitantis and Callitricho-Batrachion vegetation – habitat type (HT) of European importance 3260 is one of the habitat types that is sensitive to kayaking caused disturbances. It requires special attention, because its sustainability related not only with support of typical environmental conditions (fast course, low temperatures, coarse bottom sediments), but also with the influence of anthropogenic activity. The Ranunculus sect. Batrachium as a key vegetation component of these habitats are at risk by reason of increasing human activities, environmental pollution, and recreation.
The study investigated the impact of disturbance due to kayaking in 5 Lithuanian rivers of 15 experimental fields and 5 control fields. In each field, the species composition of the plants and their cover (according to the Braun-Blanquet scale) and the total cover of all plants (%) were assessed.
The study showed that kayaking is most intense in the months of July and August when Ranunculus species are flowering or producing the achenes. We could also find a negative correlation between the number of kayaks and the abundance of Ranunculus plants in our experimental plots. In addition, kayaking moves sediments that accumulate along the river's banks, facilitating the establishment of shade-tolerant plants, like invasive Elodea canadensis.