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EFFECTS OF A RUN OF RIVER RESERVOIR ON DOWNSTREAM WATER QUALITY WITH VARIABLE DISCHARGE

Production of suspended algae within rivers and reservoirs is still not well understood, but could be important for nutrient processing. This study used semi-Lagrangian sampling to measure changes in algal biomass and nutrients downstream of a run-of-river reservoir on the Kalamazoo River (Michigan, USA). Longitudinal surveys showed that the upstream reservoir (Morrow Lake) transformed nitrogen and phosphorus to particulate forms by producing algae (measured as chlorophyll-a). However the algal biomass did not persist for long downstream, and the nutrients it contained were evidently regenerated. The downstream extent of algal biomass transport was dependent on discharge, with algae persisting further downstream in high flow summers than low flow summers, although at the highest discharge flushing limited algal growth in the reservoir. Concentrations of nitrate were reduced within and downstream of the reservoir, particularly during the lowest flow summers, but then returned to upstream concentrations after 30 km downstream. Ammonium did not show such predictable patterns. Understanding how run of river reservoirs affect the movement of nutrients through rivers is important to downstream water quality.

Micaleila Desotelle (Primary Presenter/Author), Michigan State University, desotell@msu.edu;


Stephen K. Hamilton ( Co-Presenter/Co-Author), Michigan State University, hamilton@kbs.msu.edu;