Beaver dam effect on phytoplankton and periphyton composition and hydrology in streams from Tierra del Fuego (Argentina)

There is practically no stream or river without non-native beaver impact, past or current, in Tierra del Fuego (TDF), Argentina. In this study, we evaluated the effect of beaver activity on water quality and algal composition in forested streams and rivers from TDF. We sampled five streams and rivers with current beaver activity during the austral summers of 2016 and 2017. Also, three streams which have had beaver activity in the past but with no activity since several years ago (ca. 10 years) were included in the study. Sampling was performed in a paired design upstream and downstream the beaver dam or the site where it used to be located. Physical and chemical variables as well as phytoplankton and epilithon chlorophyll-a and algal composition were monitored. Results show a decrease in dissolved organic carbon concentration and an increase in both phytoplankton abundance and periphyton taxa richness downstream the dam. The diatom Hannaea arcus was present in both communities only in impacted sites, thus influencing the clustering. In this study, we show that beaver activity influences periphyton richness and composition, and phytoplankton abundance in impacted streams and rivers, though it exerted a minor influence on water physical and chemical variables.