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 used 2015 NAIP imagery (1m resolution) with a combination of machine learning and visual inspection to determine the spatial extent of SWI in Somerset county, Maryland. 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:
Geospatial analysis shows that 41% of agricultural lands in Somerset county, MD in 2010 that were located within 0.6 meters above sea-level transitioned to natural lands (including wetlands, shrub and forest lands, and barren) by 2016. Further, we determined that ~2,075 hectares of farmland (4.6% of total agricultural land) are currently experiencing SWI in Somerset county. Chemical analysis indicate dramatic changes in both soils and porewater along an intrusion transition in farm fields. Salinity, chloride, and sulfate in porewater increased along the intrusion transition from the center of farm fields to agricultural ditches (P<0.0001). In addition, porewater phosphate and ammonium were positively correlated with increased salinity along SWI transitions (P<0.05). Soil organic matter, organic phosphorus species, and non-crystalline iron are all significantly higher near agricultural ditches (P<0.02) due to a combination of anaerobic conditions and chemical exchange. Although SWI may affect relatively small portions of the landscape, these farm fields may have an outsized impact on the health of the Chesapeake Bay. Our data can inform farm management and conservation practices in regions experiencing SWI due to human-induced sea-level rise.