The Effect of Beaver Dams on Macroinvertebrate Communities

Impacts of habitat alterations caused by beaver presence on the composition and disturbance tolerance of local macroinvertebrate communities were studied. Beavers act as ecosystem engineers by altering water flow, temperature, nutrient, organic carbon and groundwater storage, and by increasing the overall geomorphic complexity of river systems through dam construction. Macroinvertebrates are widespread across freshwater habitats, they act as primary processers of organic materials serve as a food source for various freshwater species. Samples of macroinvertebrate communities were collected in the streams within the Methow River Watershed in North-Central Washington. Streams with known beaver presence (n= 4) and without beaver activity (n=4) were included in the study. On beaver impacted streams collections were taken above (n=3) and below (n=6) the beaver dams. Additionally, aquatic and terrestrial plants and macroinvertebrates were collected from all streams for stable isotope analysis. Macroinvertebrate species known to be sensitive to water quality were more abundant (lower HBI score) below beaver dams than above dams across all streams. One measure of community diversity (lower Percent Dominance) was greater below beaver dams than above dams. Furthermore, highly pollutant tolerant taxa (Diptera) were less abundant below beaver dams than above dams. These results demonstrate a relationship between beaver dams and a greater diversity of local macroinvertebrate communities as well as an improvement in overall stream health