THE IMPACT OF STREAM RESTORATION PROJECTS ON ECOSYSTEM FUNCTION THROUGH CHANGES IN NUTRIENT SPIRALING DYNAMICS

Millions of dollars have been spent on stream restoration and habitat improvement projects in the Lake Superior watershed. The effectiveness of these projects in providing lift to ecological function of a stream reach is not well measured or understood. This knowledge gap is echoed within restoration work worldwide. This project seeks to begin to fill this knowledge gap by evaluating the “functional lift” from 4 full channel realignment stream restoration projects conducted on north shore streams from 2017-2019 using nutrient spiraling dynamics as a process-based measure of stream health and function. Nutrient spiraling dynamics describe the level of benthic microbial activity and hyporheic processes within the stream as well as the ability of the stream to increase uptake rates in response to increased nutrient loading. The stream’s “resilience”, the ability to adapt uptake rates, governs nutrient export within a reach, which impacts catchment-scale water quality concerns such as basin eutrophication. Thus changes in spiraling dynamics have implications for both stream health in situ as well as for the catchment at large.

Nutrient spiraling and physical habitat metrics are compared in four restored treatment reaches with unrestored, control reaches on the same stream, with reaches matched for similar physical habitat characteristics. Nutrient dynamics were characterized at each reach through Tracer Additions for Spiraling Curve Characterization analysis. Habitat characterization surveys were conducted at each reach using standardized methods from the National Rivers and Streams Assessment and the Minnesota Stream Quantification Tool to enable comparison with existing datasets. Physical habitat metrics, such as channel slope, planform, and presence of bedrock were compared between treatment and control to assess the quality of their match. Nutrient dynamics were compared between matched control and treatment reaches to evaluate the effect of full-channel realignment on nutrient dynamics. The influence of habitat characteristics altered by restoration activities(such as pool-riffle spacing, grain size, canopy cover, and riparian vegetation assemblage) on nutrient dynamics were also compared to further elucidate the mechanisms by which stream restoration affects nutrient dynamics.