Spatiotemporal dynamics of boreal landscapes with ecosystem engineers: beavers influence the biogeochemistry of small lakes

Abstract

It has been suggested that beavers affect biogeochemical processes and the environment on a relatively large scale, thus acting as ecosystem engineers. In this long-term study we evaluated the effects of beavers on water chemistry in small boreal lakes of Southern Finland. We addressed the following three questions; does water chemistry differ between beaver and non-beaver lakes; does water chemistry differ between the flood years in comparison to the antecedent years; and does the flood impact downstream lakes? The results showed that beaver lakes had higher dissolved organic carbon (DOC) concentrations but lower dissolved oxygen (DO) concentrations than non-beaver lakes. DOC concentration increased during the first three beaver-impoundment years when compared to the pre-impoundment situation, and DO concentrations simultaneously decreased. Lake DOC concentrations furthermore declined back to initial levels after the impoundment had lasted for 4–6 years. The opposite occurred with DO. No clear effects caused by beaver impoundments were found in downstream lakes however. Beaver activity had no effect on N and P concentrations in lakes, but our results emphasize that the beaver affects the carbon cycling in the boreal zone. Further research is therefore needed to clarify its effect on the carbon balance at different spatial scales.