UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS
Location: Water Quality and Ecology Research
Title: Pre-restoration Assessment, Big Sunflower River, Mississippi: Where to Begin?
Submitted to: Proceedings of the World Environmental and Water Resources Congress Conference
Publication Type: Proceedings
Publication Acceptance Date: January 20, 2010
Publication Date: May 16, 2010
Citation: Shields Jr, F.D., Knight, S.S. 2010. Pre-restoration assessment, Big Sunflower River, Mississippi: Where to begin? Proceedings, 2010 World Water Congress, American Society of Civil Engineers, Reston, VA. CD-ROM.
Interpretive Summary: Rivers draining the Mississippi Delta and other major floodplains used for agricultural production have great ecological potential, but suffer from extreme degradation due to water pollution, water extraction, channelization and removal of riparian vegetation and large wood. A three-year study was conducted along two reaches of the Big Sunflower River in northwest Mississippi to assess the current status of the ecosystem and provide a basis for ecological restoration and management. Fish congregated below weir structures, but addition of such structures to provide more habitat is likely unwise until water quality issues producing chronic low dissolved oxygen concentrations are addressed. This research is useful to water resource managers working with river systems in intensely cultivated floodplains.
The Big Sunflower River in northwestern Mississippi drains about 8,000 km2, is a low-gradient slowly-moving stream, and has historically provided a valuable ecological, navigational and recreational resource. However, present conditions are characterized by depauperate physical habitat, depressed baseflows linked to falling groundwater levels, elevated turbidity, and chronically low dissolved oxygen levels. Eight 200-m long reaches were sampled biannually (spring and fall) for three years. Two reaches were located downstream from major weirs; three reaches were located in a channelized reach with a trapezoidal cross-section; and three reaches were in a reach with natural morphology. Fish were collected with boat-mounted electroshockers, and bed material types, water depths, and current velocities were sampled using an acoustic Doppler current profiler. Limited water quality data were collected for comparison with data provided by others. Fish populations appear to be primarily limited by degraded water quality. Low-head weirs support relatively dense and diverse fish assemblages and thus provide local habitat enhancement, but may create stagnant zones upstream due to backwater effects that exacerbate low dissolved oxygen problems.