Coastal farmland is losing ground to saltwater faster than expected

On both sides of the Atlantic, researchers are documenting how rising seas and shrinking groundwater are letting salt water reach farmland. In eastern England, the eastern English Fens produce 11% of the UK's agri-food economy from just 4% of the country's agricultural land, according to the University of Lincoln (source 3). In the US Mid-Atlantic, a study led by William & Mary's Batten School and the Virginia Institute of Marine Science found that about 25,000 acres of farmland in the Chesapeake and Delaware Bay watersheds were lost to sea level rise between 1984 and 2022 (source 4).

In the Fens, a team from the University of Lincoln mapped the shallow groundwater beneath the region for the first time, using electrical soundings to find how deep salt water sits below the surface. Even six miles from the coast, they found salty groundwater only a few metres down (source 3). A separate but related effort, Project Groundwater, run by Lincolnshire County Council with the University of Lincoln, is now collecting soil salt data and building models of how salt water might spread through the soil in the future (source 2).

In the Fens, the threat comes from underground. The Lincolnshire aquifer, an underground layer of rock and sediment that holds water, has historically stayed full enough to keep nearby sea water from pushing in. But climate change is drying up that groundwater, and Lincolnshire County Council says salt water is now moving into the space left behind, seeping into the soil and threatening the food supply (source 2). Dr Daniel Magnone of the University of Lincoln said the groundwater could become "a pathway to salinisation" of the Fens through either sea-level rise or excessive pumping of water from the ground, known as over-abstraction (source 3).

In the Mid-Atlantic, the process looks different but reaches the same end point. As sea levels rise, salt water pushes farther inland through groundwater, tidal creeks, and storm surges, a process the VIMS-led study calls saltwater intrusion. It kills off freshwater plants and lets salt-tolerant marsh grasses take their place, and researchers track this change by measuring how far the boundary between dry land and marsh has shifted, called retreat (source 4). The study's authors also tracked the elevation of that boundary rather than just its distance inland, which let them compare farmland and forest more directly regardless of how flat or steep the land was.

The Mid-Atlantic study's central finding challenges an assumption that farmers can protect valuable land from the sea. "There's this assumption that we'll never let sea level rise consume farmland, that people will protect valuable land. And it's just wrong," said Matt Kirwan, a co-author and professor at the Batten School & VIMS (source 4). The team found that marsh encroachment happens up to seven times more often on agricultural land than on forestland in the Mid-Atlantic, and that regionally, farmland appears to speed up the effects of saltwater intrusion rather than resist them.

This runs against the researchers' own expectation. "We hypothesized, and most people would intuitively expect, that marshes would migrate slower into farmland, that forests are more vulnerable than farmland. But we found the opposite," Kirwan said (source 4). Crops live for less than a year, while trees can take decades to die, which the study points to as one reason farmland gives way faster. Farmers have built small levees and earthen berms to hold back the water, and field surveys found these structures did slow marsh encroachment locally, bringing it in line with forest rates — but regionally, farmland remained more vulnerable than forest, and the study notes that few new structures have been built since Virginia and Maryland protected tidal wetlands from development in the 1970s.

In the Fens, the economic stakes are already partly measured. Previous University of Lincoln research found that salinisation could cost farming businesses up to £5,000 per hectare for every saline flood, due to falling yields of the high-value crops grown in the region (source 3). Lincolnshire County Council's Project Groundwater team is now working to quantify these economic consequences more broadly as part of its ongoing modelling work (source 2).

Both projects describe work that is still in progress rather than finished. Project Groundwater has only begun collecting present-day salt level data in the Fens and building the modelling software needed to project how salt water might move through the soil in the future (source 2). Dr Magnone said the next task for the Lincoln team is to predict how climate change will affect salinisation and to work out what level of groundwater pumping the area can sustain (source 3).

The VIMS-led study also stops short of offering solutions. Its authors note that marsh migration onto farmland, while damaging to farmers, could at the same time help marshes keep pace with rising seas and support broader coastal resilience, since marshes need to move to higher ground if they cannot build soil fast enough to outrun the tide (source 4). Lead author Grace Molino said she hopes science can find a path that serves both farmers and coastal ecosystems, but the study frames this as an open problem rather than one it has resolved. Separately, reporting on North Carolina's Coastal Plain describes farmers there already grappling with saltwater intrusion and repeated flooding in low-lying areas such as Hyde County, though the account of what follows from that trouble is incomplete (source 5).