The effect of beaver ponds on water physico-chemical composition in the Carpathians (Poland and Slovakia)

Abstract. In recent decades, the population of the Eurasian beaver (Castor fiber) has undergone a rapid recovery from near extinction to abundance across vast areas of Europe. The ability of this species to build dams makes its reintroduction an important environmental factor in the recolonised areas. This study investigated nine beaver-inhabited streams distributed across the Western Carpathians to assess the effects of geomorphic type, age of beaver pond sequence and seasonality on the physico-chemical changes to water in and below beaver ponds.

In general, greater reductions in NO₃^- and SO₄^2- were observed with increasing temperatures during the warm period (spring–summer). A comparison of two distinct types of beaver ponds revealed that there was a greater decrease in NO₃^- and Ca²⁺ in overflowing ponds and a greater decrease in pH downstream to these ponds compared to in-channel reservoirs. Beaver pond sequence age was positively related to decrease in dissolved oxygen, SO₄^2- and pH. Biogeochemical processes involving organic matter accumulated in beaver ponds, that include decomposition, aerobic/anaerobic oxidation and CaCO₃ precipitation, are responsible for changes of these physico-chemical parameters in stream water. The natural development of extensive beaver ponds and their persistence may be crucial for sustaining water purification processes. Further research based on a more frequent sampling strategy should aim to identify the biogeochemical processes that occur in beaver ponds under specific hydro-meteorological conditions: during low flow periods, snowmelt and rainfall events.