ASSESSING THE EFFECTS OF BEAVER DAMS AND ARTIFICIAL DAMS ON DISSOLVED OXYGEN AND AMMONIUM CONCENTRATIONS IN MASSACHUSETTS STREAMS

Stream discontinuities, including artificial dams and beaver dams, can alter the overall water quality of streams by modifying the cycling of nutrients and organic material. This study was performed to determine how these stream discontinuities influence the movement and biogeochemical cycling of materials in small streams in Massachusetts by measuring dissolved oxygen (DO) and ammonium (NH₄) concentrations. Comparisons were made between DO and NH₄ in streams obstructed by beaver dams and streams that were obstructed by artificial dams, thus giving an indication of how these structures affect the biogeochemical processing of material. Using a YSI handheld Professional Series probe, DO was measured along the longitudinal profile in four different watersheds both upstream and downstream of discontinuities. DO, NH4, light intensity, temperature, longitudinal bed elevations, water depth, in-channel wood were surveyed in 10 reaches. Geomorphic elements such as the existence of pools and riffles and the appearance of wood were considered as potential explanations for DO and NH₄ variability. We expected to see results that showed positive correlation between light intensity and DO, and results that showed a larger average amount of NH₄ concentrations downstream of the beaver dams than downstream of the artificial dams. Our preliminary data showed that there were high NH₄ and DO concentrations downstream of one of our beaver dam sites, but there was not a significantly higher level of NH₄ and DO concentrations at our second beaver dam site. The results of this study can help determine if certain water quality alterations are specific areas with beaver activity.