The Mid-Atlantic and Northeastern US are experiencing some of the highest rates of sea level rise in the world; particularly affected are the low-lying, shallow sloping coastal lands of the Chesapeake Bay’s Eastern Shore. Sea level rise increases the penetration of saltwater into surface and groundwaters by reducing the elevation difference between land and sea. This phenomenon, known as saltwater intrusion (SWI) reduces crop productivity and mobilizes nutrients. Thus, as sea levels rise, land management (both past and current) interacts with saltwater, crops, and plant communities to affect farm productivity and profitability, as well as nutrient loading in adjacent water bodies. We examined the extent and impact of SWI on soil chemistry, porewater chemistry on Lower Eastern Shore of Maryland in the Choptank River watershed. We collected soil and porewater along a transition from healthy crop to salt-intruded agricultural ditches in four farm fields. Soil and water were analyzed for forms of phosphorus, nitrogen, iron, and other parameters related to the mechanisms of saltwater ion exchange.
Results/Conclusions
Chemical analyses indicate dramatic changes in both soils and porewater along an intrusion transition in farm fields. Salinity levels in farm fields far exceed crop tolerance limits, which increases toward agricultural ditches. Phosphorus concentrations in porewater are highest in salt-intruded fields and marshes (P<0.01), and evidence indicates the transport of phosphorus through the agricultural ditch network to marshes. Similarly, high ammonium concentrations in porewater collected from marshes downstream from salt-intruded agricultural fields suggest that nitrogen may also be mobilized by saltwater intruded and transported to marshes. These marshes may serve as the last line of defense before nutrients are released into the Chesapeake Bay. It is critical to understand their role in nutrient buffering and consider programs that will support marsh migration in this region.