WRS MS Defense

Channel Realignment Restoration Impacts on Flow and Microbial Activity in the Hyporheic Zone

Nationwide, over a billion dollars is spent each year on stream restoration projects (Bernhardt et al., 2005). These projects are performed for a variety of reasons including erosion reduction, nutrient retention, and habitat creation, particularly for charismatic fish species such as trout. A commonly employed method of restoration is channel realignment. Channel realignment projects can have profound impacts on stream channel structure and function, yet few studies have been conducted to understand the impacts of channel realignment on basic functional processes like hyporheic exchange.  To better understand how channel realignment impacts shallow hyporheic exchange, we ran tracer experiments with the reactive resazurin-resorufin tracer system in control and restored reaches on three full channel realignment stream projects and two streams before restoration had started in Duluth, MN. Resazurin is a weakly fluorescent dye that converts to the strongly fluorescent compound resorufin in the presence of aerobic respiration by the removal of an oxygen. It has been shown that the conversion mostly occurs in stream bed sediments, typically the top 5 cm, and not the water column. Thus, the processing rate of resazurin is a function of hyporheic exchange and aerobic respiration rates. We found no statistical difference of resazurin processing rates between control and restored reaches however, each restored reach had slightly higher resazurin processing rates than its paired control reach. Resazurin processing rates were compared to various geomorphic parameters and results highlight the complex relationships between geomorphology, grain sizes, and resazurin processing rates as only sinuosity had a moderate correlation with processing rates. Bromide was found to be a better conservative tracer than chloride for tracer experiments in north shore streams due to high background concentrations of chloride and non-conservative behavior of chloride. This study is part of a larger project to understand the impacts of channel realignment restoration on stream function and ecology, focused on streams in northeastern Minnesota.