Based on cartographic material from three time periods during the nineteenth and twentieth centuries, the impact of river capture, which started in the middle of the nineteenth century, on transformations of the watershed and hydrographic network of two Lithuanian rivers, Ula and Katra, is analysed. It has been determined that river capture conditioned marked transformations of water supply and distribution. As a result of the capture, the area of Ula catchment has increased by 62% and its mean discharge by 63%, whereas the area of Katra catchment decreased by 23% and its mean discharge by 27%. The total area of the five largest lakes in the recent Ula catchment has been reduced by 95%. The transformations of water resources in the Ula catchment since the first half of the nineteenth century are the following: Ula runoff volume has increased almost by 100 million m3/yr whereas the water volume of lakes has been reduced by almost 30 million m3.

river ecosystems support a disproportionately large fraction of its biodiversity, while acting also as significant corridors for the movement of plants, animals and nutrients

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