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Since the early twentieth century, the Conowingo Dam has captured a significant portion of the Susquehanna River sediment load bound for the upper Chesapeake Bay. However, the Conowingo Reservoir is nearing its sediment capacity, which has resulted in decreased reservoir sedimentation and increased suspended sediment delivery to the Bay. Additionally, sediment scoured from behind the dam during high flow events contributes to the increased sediment input into the Bay. Sediment-transport models, developed with the aid of sediment budgets, are used to guide management of this excess sediment input; however, these models were calibrated assuming that the Conowingo Reservoir would maintain a constant sediment capacity. Also, recently resurged submersed aquatic vegetation (SAV) beds affect sediment deposition, and their effects were not included in sediment-transport model calibration. The Bay sediment-transport model also needs to take into account the contribution from various sources of sediment (suspended fluvial sediment, Conowingo Reservoir bottom sediments, and sediment from shoreline erosion). Sediment provenance analyses can reveal the different geochemical characteristics between sources, and their relative contribution to the depositional environments.
This research investigates how sediment transport is connected from the lower Susquehanna River into the upper Bay by developing event- and decadal-scale sediment budgets and exploring the potential of sediment provenance techniques to differentiate sediment sources in the upper Bay. This study is driven by the following hypotheses: 1) Highest sediment deposition rates occur on the Susquehanna Flats due to the presence of SAV beds. 2) Recently eroded Susquehanna River sediments will have different geochemical characteristics, such as detectable 7Be activities and greater nutrient bioavailability, than bottom sediments in the Conowingo Reservoir. 3) Coal deposits can be used to distinguish between the coal-rich Susquehanna River sediments and coastal erosion sediments. 4) Sediments deposited in the Susquehanna Flats and upper Bay during lower flow are a mixture of suspended fluvial sediments and sediments from shoreline erosion; during high flow events, Conowingo Reservoir bottom sediments are present as well.
Data from separate research projects on sediment characteristics in the Conowingo Reservoir and Susquehanna Flats will be integrated with sediment data collected from the upper Bay for this project. Decadal- and event-scale accumulation rates will be calculated and compared with sediment load information in order to construct decadal and event sediment budgets. The sediments from the three depositional environments will also be analyzed for the sediment provenance analysis. Radioisotopes, nutrients, and coal signatures in the source sediments will be compared with those in the target sediments to determine the relative sediment contribution from each source.
The results from this study are expected to help improve sediment-transport models and their predictive capabilities, in response to changing reservoir capacity. This study will inform the 2017 Chesapeake Bay Program mid-point assessment, and help guide management decisions that improve water quality. We will directly work with a watershed restoration specialist in order to effectively communicate our results with local governments and agencies, as well as engage the general public to promote coastal resilience.
Russ, E; Palinkas, C. 2020. Evolving sediment dynamics due to anthropogenic processes in upper Chesapeake Bay Estuarine Coastal and Shelf Science235 . doi:10.1016/j.ecss.2020.106596. UM-SG-RS-2019-17.
Russ, ER; Palinkas, CM. 2018. Seasonal-Scale and Decadal-Scale Sediment-Vegetation Interactions on the Subaqueous Susquehanna River Delta, Upper Chesapeake Bay Estuaries and Coasts41(7):2092 -2104. doi:10.1007/s12237-018-0413-8. UM-SG-RS-2018-17.