Long-term changes in sediment and nutrient delivery from Conowingo Dam to Chesapeake Bay: Effects of reservoir sedimentation

Environmental Science & Technology
By: , and 

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Abstract

Reduction of suspended sediment (SS), total phosphorus (TP), and total nitrogen is an important focus for Chesapeake Bay watershed management. The Susquehanna River, the bay’s largest tributary, has drawn attention because SS loads from behind Conowingo Dam (near the river’s mouth) have been rising dramatically. To better understand these changes, we evaluated histories of concentration and loading (1986–2013) using data from sites above and below Conowingo Reservoir. First, observed concentration-discharge relationships show that SS and TP concentrations at the reservoir inlet have declined under most discharges in recent decades, but without corresponding declines at the outlet, implying recently diminished reservoir trapping. Second, best estimates of mass balance suggest decreasing net deposition of SS and TP in recent decades over a wide range of discharges, with cumulative mass generally dominated by the 75∼99.5th percentile of daily Conowingo discharges. Finally, stationary models that better accommodate effects of riverflow variability also support the conclusion of diminished trapping of SS and TP under a range of discharges that includes those well below the literature-reported scour threshold. Overall, these findings suggest that decreased net deposition of SS and TP has occurred at subscour levels of discharge, which has significant implications for the Chesapeake Bay ecosystem.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Long-term changes in sediment and nutrient delivery from Conowingo Dam to Chesapeake Bay: Effects of reservoir sedimentation
Series title Environmental Science & Technology
DOI 10.1021/acs.est.5b04073
Volume 50
Issue 4
Year Published 2016
Language English
Publisher American Chemical Society
Contributing office(s) National Research Program - Eastern Branch
Description 10 p.
First page 1877
Last page 1886
Country United States
State Maryland
Other Geospatial Chesapeake Bay, Conowingo Dam, Susquehanna River
Online Only (Y/N) N
Additional Online Files (Y/N) N