Saltwater intrusion (SWI) is typically located along field edges that border tidal creeks, saltwater marshes, or field drainage ditches. Our current knowledge for agricultural fields points towards salinity from surface flooding, which can occur due to storm surges as well as sunny day flooding. As our fields have gentle gradients towards wetland edges, flooding and the depositing of salts can easily occur, and then transition into upland portions of the field with normal salt concentrations.
Wetland Edges: Fields that border tidal wetlands may experience occasional flooding. Unlike the adjacent wetland, which is constantly flushed by the tide, deposits of salts will remain and build up in the soil. Due to the reduced leaching that can occur at these low elevations, these salts are difficult, if not impossible to remove from the soil. Eventually these portions of the field may be abandoned or converted to conservation easements.
Field Ditches: Farmers originally installed ditches to allow for drainage of their fields. As sea level rises and flooding can occur at greater elevations, salinity can move up these ditches and deposit along the edges. Although these edges are sometimes at slightly higher elevations and may leach salts easier, they remain as conduits further into the field. Farmers and landowners can place tide gates at the mouth of a ditch, which can prevent lesser flooding events from entering the field.
Soil sampling across six coastal Delmarva farms confirmed that salt-affected soils are most common near tidal wetlands and along field ditches, highlighting how flooding and drainage influence salinity. Saline soils (green), with high levels of soluble salts, can limit crop growth by reducing water uptake, while sodic soils (black), dominated by sodium, can degrade soil structure and lower fertility. Many low-lying areas near wetlands accumulated these salts, which are difficult to leach, and ditch edges often contained saline-sodic soils (blue) extending further into the field. These patterns help explain why crop damage can occur beyond visibly affected areas and emphasize the importance of management practices—such as installing tide gates or monitoring low-elevation zones—to maintain soil health and protect crop productivity.
FACTSHEET: Salt Effects on Crops of the Delmarva Peninsula
FACTSHEET: Delmarva Soils and Potential Salinity Effects
Flooding Events and Field Elevations
In this graph red lines represent electrical conductivity, a proxy for salinity. The blue lines are soil moisture, revealing rainfall or potential flooding events. While some flooding occurs over the summer, the fall hurricane and nor’easter season along Delmarva brings excess salinity, which gradually falls over the winter months. This will certainly vary annually and by field type.
In this graph we measured sodium (Na) concentrations along field gradients, extending from about 2 feet above sea level to 13 feet. Salinity quickly drops as you rise in elevation to almost normal soil levels (<60ppm by Mehlich3). This can better be described by observing the height above the mean high higher water level, which will vary along the coastline.
