ASSESSING THE EFFECTS OF LARGE WOOD AND STREAM METABOLISM IN THE ASSABET RIVER, MA

In-stream wood alters hydraulic and geomorphic complexity, which influences stream metabolic processes. Stream metabolism is a measure of gross primary production and ecosystem respiration, which can be assessed by analyzing diel variations in dissolved oxygen (DO). The reduced velocities that wood creates in a channel allows time for increased rates of biogeochemical processing by increasing solute-substrate interactions. Furthermore, wood plays a structural role by increasing habitat diversity, cover, and food resources, which may potentially increase ecosystem respiration. The goal of this study is to assess whether large wood jams significantly alter stream metabolism by examining reach scale changes in water quality parameters from the summer to early winter. A reach is defined as the same bed morphology over a scale of 2 pool-riffle sequences. Field studies were conducted in two reaches, with and without wood, in the 78 km² Assabet River basin in Central Massachusetts. The field site is in a pool riffle, open meadow system with a gradient of 0.002 m/m. Using two YSI 6-Series Multiparameter Water Quality Sondes located upstream near the wood structure and downstream in an open pool, data regarding the temperature, specific conductance, salinity, depth, pH, light intensity, turbidity, and dissolved oxygen concentration was recorded every 15 minutes for the duration of the study. A stage-discharge relationship was developed by measuring velocity with a Marsh-McBirney Flo-Mate meter at a set cross-section once per week and related to each sondes depth readings. The upstream DO surrounding the wood structure ranged from 8.5-8.6 mg/L, while downstream recordings removed from the wood were 9.3-9.6 mg/L, both having a standard deviation of +/- 1.0 mg/L. We expect to see a significant difference in values between the two sondes which will verify that at a reach-scale, stream metabolic functions are affected by in-stream wood. Further analysis will involve correlating changes in DO with water quality and flow hydraulics. This research will further science in river restoration techniques and aid in defining large wood as a key tool in biogeochemical processing at the local scale.