The Past and Future Responses of Salinity in the Delaware Estuary to Sea-level Rise and River Discharge Variability

We use a combination of long historical records (1950s-present) and statistical, idealized, and 3D numerical models to explore the response of salinity in the Delaware Estuary to sea-level rise and changing river discharge. Over the historical period, salinity generally shows negligible or downwards trends, mostly as a result of increasing river discharge. However, after removing the influence of river discharge using the observations and a statistical model, there is a positive sea-level rise signal at several locations. The salinity increase as a result of sea-level rise determined by the statistical models closely matches the values simulated by the idealized and 3D numerical models. Under a scenario of 0.55 m of additional sea-level rise, all three models project salinity increases of up to 1.5-2.5 psu. Allowing sea level to rise by 1 meter will increase salinity by about 2.5-4.5 psu. All three models also show that although increasing river discharge has moderated salinity trends in the past, future increases in river discharge are unlikely to be able to offset the salinity increase caused by sea-level rise. In addition, the spatial distribution of these changes and potential consequences for the estuarine ecosystem are discussed.