Impact of Reservoir Sediment Scour on Water Quality in a Downstream Estuary. Issue 3 (1st May 2016)

• Record Type: Journal Article
• Authors: Cerco, Carl F.; Noel, Mark R.
• Is Part Of: Journal of Environmental Quality. Volume 45:Issue 3(2016)
• Page Start: 894
• Page End: 905
• Publication Date: 2016-05-01
• Subjects: Agricultural ecology -- Periodicals; Environmental engineering -- Periodicals; Pollution -- Periodicals; 630
• DOI: 10.2134/jeq2014.10.0425
• Languages: English
• ISSNs: 0047-2425

Abstract

Abstract : The Conowingo Reservoir is situated at the lower terminus of the Susquehanna ‐‐‐River watershed, immediately above Chesapeake Bay. Since construction, the reservoir has been filling with sediment to the point where storage capacity is nearly exhausted. The potential for release of accumulated sediments, organic matter, and nutrients, especially through the action of storm scour, causes concern for water quality in Chesapeake Bay. We used hydrodynamic and eutrophication models to examine the effects of watershed loads and scour loads on bay water quality under total maximum daily load conditions. Results indicate that increased suspended solids loads are not a threat to bay water quality. For most conditions, solids scoured from the reservoir settle out before the season during which light attenuation is critical. The organic matter and nutrients associated with the solids are, however, detrimental. This material settles to the estuary bottom and is mineralized in bed sediments. Carbon diagenesis spurs oxygen consumption in bottom sediments and in the water column via release of chemical oxygen demand. The nutrients are recycled to the water column and stimulate algal production. As a result of a scour event, bottom‐water dissolved oxygen declines up to 0.2 g m −3, although the decline is 0.1 g m −3 or less when averaged over the summer season. Surface chlorophyll increases 0.1 to 0.3 mg m −3 during the summer growing season. Core Ideas: Reservoir sedimentation can adversely impact water quality downstream. Infilling of Conowingo Reservoir results in increased sediments and nutrients passed through to Chesapeake Bay. Sediments are not a threat to water quality in Chesapeake Bay. Nutrients and organic matter associated with sediments contribute to eutrophication in Chesapeake Bay.