Coastal farmland in the U.S. Mid-Atlantic is being swallowed up by rising sea levels at an alarming rate and being replaced by tidal marshes significantly faster than coastal forests, a new study shows, exposing a long-neglected rural frontline in the context of climate change. The study, based on decades of satellite observations and the latest field measurements, focused on the Chesapeake Bay and Delaware Bay watersheds and found that about 25,000 acres of farmland were lost to sea level rise between 1984 and 2022, even as local farmers implemented a variety of engineering measures to try to hold on to the land.
“Ghost forests”—large expanses of dead trees after being invaded by salt water—have long been viewed as the most visible sign of rising sea levels along the Mid-Atlantic coast. But new research led by the College of William and Mary's Batten School of Coastal and Marine Sciences and the Virginia Institute of Marine Science (VIMS) points out that the reality is more severe than imagined: as tidal marshes push inland, the frequency of "cannibalization" of farmland can be up to seven times that of forests in many areas, and farmland as a whole is more vulnerable to loss of saltwater pressure. The research team said that this result subverted many people's intuition - people often believe that due to higher economic value, farmland will be more protected and thus more "erosion-resistant" than forests, but the data gives the opposite picture.
The study characterized the effects of sea level rise by tracking long-term changes in the boundary between dry land and marsh, and using boundary elevation rather than just horizontal position measurements to circumvent errors caused by terrain slope, allowing for a more precise comparison of marsh migration across farmland and forest. The rate of sea level rise in the Mid-Atlantic coastal region is about twice the global average, making it a classic "frontier laboratory" for observing saltwater intrusion and landscape transformation.
Co-author Matt Kirwan, a professor of marine sciences at Batten College and VIMS, said the study found a large number of fields where small embankments have been built to block salt water, but these protections often only slow, rather than prevent, the conversion of farmland into marshes. On farmland, signs of saltwater intrusion are often more subtle: Maybe just a row or two at the edge of a field turning from green to yellow, but cumulatively across an entire area, it means a loss of productivity for thousands of acres of agricultural land. After combining regional-scale data, the team found that farmland often "amplifies" the land conversion effects of saltwater intrusion.
The study also examines the economic and policy context of coastal farmland vulnerability. Virginia and Maryland began protecting tidal wetlands as early as the 1970s, severely limiting the space for new large hard defense structures. This means that many of the earthen embankments, bunds and drainage ditches constructed in the past have been abandoned over time and are now surrounded by the surrounding expanding marshes. Grace Molino, the first author of the paper and a doctoral graduate of Batten College, pointed out that during field visits to six farms on the east coast, the team found that although existing levees and earthen embankments can indeed reduce local saltwater intrusion and reduce the "vertical retreat rate" of farmland boundaries to the level of nearby forests, from the perspective of the entire region, farmland is still significantly more susceptible to saltwater transformation than forests.
Scientists explain that this is not just because farmland is flatter, but more due to biological differences. A tree can live for hundreds of years, and it often takes decades for trees to die due to rising salinity. Crops are usually annuals and are extremely sensitive to salt and stagnant water. An abnormality in one growing season is enough to make farming lose economic significance. In addition, the complex licensing and approval procedures have objectively raised the threshold for farmers to reinforce or build new protective facilities, causing many farmlands to gradually be "taken over" by swamps due to institutional inertia and financial pressure.
The research also highlights that coastal farmland has long been undervalued in climate adaptation and resilience discussions. Current policy and scientific research attention tend to focus on urban coastal defenses, such as breakwaters, seawalls, and hardened coastlines. These engineering facilities will indeed block the migration of wetlands inland, thus weakening the buffering effect of wetlands on sea level rise. However, in the United States, heavily developed areas make up less than 15 percent of coastal watersheds, and much of the coastline is in rural areas, where human activities and their impact on wetland migration have rarely entered decision-making in the past.
In rural coastal areas of the Mid-Atlantic, the future of coastal landscapes is being profoundly shaped by the everyday choices of farmers and landowners. Since research is usually prioritized on public land, the team had to adopt the traditional "house-to-house" method this time, contacting farmers directly and applying for access to private land for measurements. Molino said that many landowners have lived in the area for generations and are well aware of the changes in surrounding fields and wetlands over decades. Their experiential information is extremely valuable for scientific analysis.
At one site in Maryland, a property owner who uses his land as a weekend waterfowl hunting ground showed researchers two large water storage projects he had built on saline land that was no longer farmable, one of which was partially funded by a USDA-related program to create wildlife habitat. For this owner, in the face of saltwater intrusion, he chose not to "hardly fight" against sea level rise, but to completely change the land use and convert farmland into a wetland space that is both ecological and recreational. In another case, Molino specifically called a farmer after returning to inform him of the precise location of the breach in the bank identified in the drone images so that the other party could repair the defense line. This also reflects the direct help of scientific research at the specific individual level.
The study points out that tidal marshes themselves are also threatened by rising sea levels. If their peat accumulation and surface elevation cannot keep up with the rise in water levels, they will have to retreat to higher ground. From an ecological perspective, the conversion of farmland to wetland to swamp provides a more convenient migration channel and helps to enhance the overall coastal protection capability; however, for farmers, this process means the continuous loss of productive land and income. Therefore, how to find a balance between maintaining the functions of coastal ecosystems and ensuring the livelihood of landowners has become a difficult problem that future policy design must respond to.
Molino believes science can play a key role in this balance, by providing data and tools to help identify land use options that would benefit wetland relocation while creating alternative benefits for farmers. She emphasized that truly understanding the driving factors behind coastal landscape changes is inseparable from an in-depth understanding of the decision-making logic of individual landowners, and this requires researchers to go out of the laboratory, into farmhouses and fields, and to establish long-term mutual trust with local people.
The research, funded by the National Science Foundation, was published in the journal Nature Sustainability on May 18, 2026. The authors point out that the rapid conversion of farmland to wetlands along the Mid-Atlantic coast indicates that in a world where sea levels continue to rise, more coastal agricultural areas around the world may face a similar fate, which will require policymakers to invest as serious adaptation planning and resources in rural areas as in cities.