Effects of beaver impoundments on dissolved organic matter quality and biodegradability in boreal riverine systems

Beaver impoundments modify the structure of river reaches and lead to changes in ecosystem function and biogeochemical processes. Here, we assessed the changes in dissolved organic matter (DOM) quality and the biodegradation patterns in a set of beaver systems across Sweden. As the effect of beaver impoundments might be transient and local, we compared DOM quality and biodegradability of both pond and upstream sections of differentially aged beaver systems. Newly established dams shifted the sources and DOM biodegradability patterns. In particular, humic-like DOM, most likely leached from surrounding soils, characterized upstream sections of new beaver impoundments. In contrast, autochthonous and processed compounds, with both higher biodegradation rates and a broader spectrum of reactivities, differentiated DOM in ponds. DOM in recently established ponds seemed to be more humic and less processed compared to older ponds, but system idiosyncrasies determined by catchment particularities influenced this ageing effect.