Hydraulic linkages to ecosystem integrity: Determining metrics for evaluating in-stream flow conditions and relative shifts in stream ecosystem structure and function
Blersch, Stacey Sloan
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An investigation was made into the connections between ecosystem function and hydraulic conditions in a stream ecosystem impacted by degradation and affected by restoration activities. Stream ecosystem function was measured on multiple reaches of a characteristic stream in western New York using net ecosystem metabolism metrics. Measurements were taken at a variety of scales ranging from the sub-meter scale, using tile deployment for periphyton sampling and metabolic chamber methods, to the decameter scale, using one- and two-point oxygen diurnal methods over multiple seasons. Coincident measurements of stream geomorphic characteristics, such as width, depth, and average pebble size, and hydraulic measurements, such as average flow velocity and stage measurements, were taken at multiple cross sections of the stream in multiple reaches. Geomorphic and flow characteristics were used to calculate and model flow descriptors using standard flow modeling computation programming. Also, observations of stream reach geomorphic condition were recorded using standard rapid assessment techniques, pebble counts, and geomorphic cross sectional surveys. Biotic structure of the stream macroinvertebrate community was quantified in multiple reaches using standard sampling and counting procedures as well as analysis of fish surveys conducted by NYDEC in Elton Creek. Following this data collection, ecosystem metabolism measures were correlated to stream geomorphic descriptors, flow descriptors, and geomorphic assessment criteria. Results showed that ecosystem metabolism at the macroscale varied as a function of geomorphic condition, showing trends towards higher primary production and respiration for reaches observed to be geomorphically unstable. These results were confirmed by correlations at the microscale investigations, where periphyton samples from the disturbed reach exhibited higher metabolic characteristics than those from stable or restored reaches. The results suggest the possibility of defining characteristic metabolic signatures to represent the stage of development of an evolving stream reach trending towards geomorphic dynamic equilibrium. Additionally, these metabolic signatures at the reach scale are related to a set of geomorphic and flow indicators that might be characterized as the reach hydraulic signature, which might be defined as the average set of flow and geomorphic characteristics for a reach that are incident upon and define the biological response of the resident periphyton community of that reach. These signatures share a specific relationship between them that might be verified through future repeated measures on evolving streams in multiple landscapes. These results imply that a set of analyses on stream ecosystem metabolism can be developed as tools for informing the stage of ecosystem development for practitioners of stream restoration engineering and provide direct link of shifts in geomorphic and hydraulic structure to metabolic function.