DEGREE OF CONNECTIVITY CAN DRIVE NUTRIENT DYNAMICS IN SMALL AND SHALLOW RESERVOIRS

Aquatic ecosystems, particularly reservoirs, play vital roles in global nutrient cycling and retention along the river continuum. Small, shallow reservoirs (<1000 hectares and <10m deep)  are typically constructed on small and intermittent streams. These flow patterns affect the degree of connectivity between reservoirs and their catchments, as well as the structure of reservoirs over time. This affects nutrient cycling and retention within reservoirs. Our study analysed existing data from the United States Army Corps of Engineers (USACE ) and water quality portal to understand how connectivity changes over time. We evaluated its impact on the absolute and relative concentration of nitrate (NO₃) and phosphate (PO₄) in nine small, shallow reservoirs in southeast Nebraska. Our findings revealed interannual variation in the surface area of reservoirs (proxy of connectivity) with the annual changes ranging from -0.057 to 3.31 hectares per year. Both absolute NO₃ and PO₄ concentrations varied significantly over time in all reservoirs and were strongly influenced by the degree of connectivity.  The relative (N:P) concentration varied across reservoirs and over time in most reservoirs. This study enhanced our understanding of how connectivity shapes nutrient dynamics in small reservoirs. Furthermore, it underscores the importance of investigating how the degree of connectivity influences hydrodynamic functions like mixing dynamics and residence time, which in turn impacts biogeochemical processes in small and shallow reservoirs.

Primary Presenter: Uchechukwu Ogbenna, University of Nebraska-Lincoln (ogbennauchechukwu@gmail.com)

Authors:

Uchechukwu Ogbenna, University of Nebraska-Lincoln  (uogbenna2@huskers.unl.edu)

Daniel Uden, University of Nebraska-Lincoln  (duden2@unl.edu)

Aaron Mittelstet, University of Nebraska-Lincoln  (amittelstet2@unl.edu)

Jessica Corman, University of Nebraska-Lincoln  (jcorman3@unl.edu)