Principal Investigator: 
Raymond Najjar (
Penn State University
The success of efforts to restore the Chesapeake and Delaware Bays, two large, degraded estuaries in the Eastern United States, will depend on the future climate of the watersheds of these estuaries. The loads of sediment, nutrients, and organic matter from the land surface to these estuaries, which are strongly influenced by climate variability, have been—and are expected to be—the main drivers of water quality in these estuaries. To date, there has been no systematic analysis of projected changes in these loads, which is hampering the development of effective management strategies.
In this project, we synthesized the output of climate and hydrological models of the Susquehanna and Delaware River basins, the main sources of terrestrial inputs to the Chesapeake and Delaware Bays, respectively, for two time periods: 1971–2000 and 2041–2070. The future simulations were created by various researchers running the models under levels of atmospheric carbon dioxide expected under business-as-usual scenarios (the A2 and RCP8.5 scenarios used by the Intergovernmental Panel on Climate Change). 45 simulations were considered for the Susquehanna River Basin and 39 simulations were considered for the Delaware River Basin. Projections of sediment and nutrient inputs were available for six simulations of the Susquehanna River basin. Statistical models of sediment and nutrient loads as a function of streamflow were developed using historical data for the Susquehanna River. These models were then applied to all of the Susquehanna streamflow projections. In summary, we developed distributions of projected changes in streamflow and loadings of total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) from the Susquehanna to the Chesapeake Bay and projected changes in streamflow from the Delaware River to the Delaware Bay based on dozens of individual climate projections.
The main finding is a likelihood of increased winter streamflow in both river basins, with median projected increases of 30–40%. Fewer than 25% of the models projected flow declines in December, January, February, or March. Sediment and nutrient loads were found to be highly correlated with streamflow with a nearly exponential dependency. Hence, projected increases in winter TSS, TN, and TP loads were found to be considerable, with median increases of 60–100%, 20–40%, and 60–80%, respectively. Projected changes in flow, sediment, and nutrients were more equivocal in other seasons, with projected median changes not significantly different from zero from April to November, except for a few months of reduced flow in the Susquehanna River basin. Uncertainty in projected loads is large, particularly during the summer and fall. The main uncertainty stems from the wide range in projected precipitation, which was the main determinant of changes in fresh water, sediment, and nutrient loads among the models.
This research has implications for management of the Chesapeake and Delaware Bays. Planning should incorporate the likelihood of increased winter loads while being mindful of large potential increases or decreases in other seasons. Future research should focus on improvements in predicting the response of precipitation in the Mid-Atlantic region of the United States to increases in greenhouse gases.
Research Year: 
Funding Amount: 
Current or Past research?: 
Past Research

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