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Sediment dynamics and implications for management: State of the science from long‐term research in the Chesapeake Bay watershed, USA

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Abstract This review aims to synthesize the current knowledge of sediment dynamics using insights from long‐term research conducted in the watershed draining to the Chesapeake Bay, the largest estuary in the U.S., to inform management actions to restore the estuary and its watershed. The sediment dynamics of the Chesapeake are typical of many impaired watersheds and estuaries around the world, and this synthesis is intended to be relevant and transferable to other sediment‐impaired systems. The watershed's sediment sources, transport, delivery, and impacts are discussed with implications for effectively implementing best management practices (BMPs) to mitigate sediment issues. This synthesis revealed three key issues to consider when planning actions to reduce sediment loading: Scale, time, and land use. Geology and historical land use generated a template that current land use and climate, in addition to management, are acting upon to control sediment delivery. Important sediment sources in the Chesapeake include the Piedmont physiographic region, urban, and agricultural land use, and streambank erosion of headwater streams, whereas floodplain trapping is important along larger streams and rivers. Implementation of BMPs is widespread and is predicted to lead to decreased sediment loading; however, reworking of legacy sediment stored in stream valleys, with potentially long residence times in storage, can delay and complicate detection of the effects of BMPs on sediment loads. In conclusion, the improved understanding of sediment sources, storage areas, and transport lag times reviewed here can help target choices of BMP types and locations to better manage sediment problems—for both local streams and receiving waters. This article is categorized under: Science of Water > Water Quality Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness
Three of the eras of sediment in the Chesapeake watershed, with inferred or measured relative rates of sediment input, storage, and export
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(a) Map of the Chesapeake Bay and its watershed. Red colors indicate urban/developed areas and tan color indicates agricultural areas (i.e., cultivated crops and pasture/hay) from the 2016 National Land Cover Database; (b) Satellite image of sediment plume entering the Chesapeake Bay after Tropical Storm Lee in 2011 (image courtesy of NASA); (c) Deer Creek, Maryland, with high concentrations of suspended sediment after a storm (image courtesy of USGS)
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(a) Cumulative annual suspended sediment load and the trendline of flow‐normalized load at the nine River Input Monitoring stations discharging to the Chesapeake Bay, from 1985 to 2016 (Moyer, Langland, Blomquist, & Yang, 2017); (b) trends in flow‐normalized suspended sediment load across the Chesapeake watershed from 2007 to 2016 relative to the TMDL target of 20% reduction in loading to the Chesapeake Bay (dashed vertical line; Moyer et al., 2017); and (c) directionality of flow‐normalized trends at each station (green down arrows indicate decreasing load, gray circles indicate no trend, and orange up arrows indicate increasing load, Moyer et al., 2017) overlaid on estimated suspended sediment yield by SPARROW modeling (Brakebill et al., 2010)
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Examples of some potential pathways of transport, storage, erosion, and export of sediment within a stream valley of a watershed
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Summarized sediment mass balances derived from sediment budgets of Chesapeake small watersheds. Inputs and outputs may not balance because of unmeasured processes or measurement and extrapolation errors. Units are in mg km−2 year−1
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Estimates of the contribution of different upland land uses to the load of stream sediment that is transported to the outlet of individual tributaries of the Chesapeake Bay watershed (accounting for both sediment generated in the watershed of that tributary and retained during transport), derived from SPARROW modeling (Brakebill et al., 2019)
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Water and Life > Conservation, Management, and Awareness
Water and Life > Stresses and Pressures on Ecosystems
Science of Water > Water Quality

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