A heron hunts for fish on the Chesapeake Bay in Maryland at sunrise.
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Saltwater Intrusion and Coastal Climate Adaptation: Building Community Resilience

Saltwater intrusion induced by climate change presents an explicit threat to the Earth’s coastal regions. How can communities best adapt to the risks for agriculture and ecosystems?

For coastal areas around the globe, flooding poses well-known and deadly threats. As these regions continue to suffer from floods and incur increasing losses of life and property in the wake of strong storms, society is also grappling with its growing understanding of climate change and the perils associated with sea-level rise and storm surge. Among the hazards, the salinization of waters and soils along coastlines—saltwater intrusion—brings less obvious but distinct risk.

Sea-level rise propels this phenomenon by reducing the difference in elevation between land and sea, making it possible for saltwater to effectively move beyond oceans and seep into surface and groundwater as well as the soil itself. Driving massive changes in coastal ecosystems, increased salinity combined with more frequent inundation causes tree die-off in coastal forests, the loss of freshwater wetlands, and diminished agricultural productivity. Saltwater intrusion can also contaminate critical freshwater sources that people living in coastal watersheds depend on for clean drinking water, reliable irrigation, and other needs. It also alters soil chemistry and mobilizes nutrients—contributing to nutrient loading in adjacent water bodies that reduces water quality and can harm species.

Drought and groundwater extraction (for irrigation and other uses) exacerbate saltwater intrusion because they reduce pressure from freshwater resources that otherwise supports the balance of coastal ecosystems by naturally helping to keep seawater out. Ditches and canals previously built to drain coastal lands to minimize flooding damage in agricultural fields currently complicate the problem, acting as conduits for saltwater and funneling it inland as storms surge locally and sea level rises around the world.

Brown pelicans fly above people fishing in the waters off Tangier Island, Virginia.
Aeriel view of creeks and marshlands along the Chesapeake Bay in Maryland.
A farmhouse and cornfield on Maryland’s Eastern Shore on a foggy day.

Saltwater intrusion induced by climate change presents an explicit threat to the Earth’s coastal regions, and awareness is growing as communities realize the dangers. How can farmers and landowners in coastal areas best adapt to the risks for agriculture and ecosystems? This question and others will remain relevant: because of sea-level rise, there will always be a new edge along coastlines—a new band of land needing to adapt to saltwater intrusion. To both support the well-being of coastal communities and maintain key services provided by these ecosystems, we must have myriad solutions to manage those edges. For example, how will individuals and society weigh trade-offs when making decisions about whether and how to prolong the productivity and profitability of coastal agricultural lands? How will these communities consider those options for land management among others that can facilitate the inland migration of wetlands or improve water quality? In the face of climate change, there is much to gain by exploring how to best transition agricultural lands from current cropping systems that are being harmed by saltwater intrusion to alternative crops or land uses.
 
We’ve assembled a team and are examining the impacts of saltwater intrusion on coastal agroecosystems and the effectiveness of potential management responses for enhancing community resilience in these areas. Achieving socially and environmentally beneficial transitions is more likely with a better understanding of the options for alternative crops and land uses as well as informed policy design that incentivizes sound adaptation strategies. Our work is just beginning and brings together field and laboratory research, hydrologic and remote sensing capabilities, outreach and engagement with agricultural communities, and economic and social analysis. With the broad goal of identifying and evaluating potential approaches for managing the risk of saltwater intrusion induced by climate change, these efforts focus on agricultural lands on the Eastern Shore of the Chesapeake Bay. This region is experiencing some of the highest rates of sea-level rise around the globe, intensified by high rates of land subsidence in already low-lying land (see Figure 1). Sea-level rise and saltwater intrusion will continue to affect more areas of the world over the coming centuries, and the conditions in the Chesapeake Bay area make it an ideal testbed for studying how coastal ecosystems and land-use practices are changing as society adapts. 

Figure 1a. Potential Inundation under Sea-Level Rise in the North American Coastal Plain

Note: A map of the North American Coastal Plain (green) and its inundation (pink) under 3 feet of sea-level rise.
Sources: National Oceanic and Atmospheric Administration. 2017. Sea Level Rise and Coastal Flooding Impacts. Accessed July 6, 2017.
Environmental Protection Agency. 2017. Ecoregions of North America. Accessed July 6, 2017.

Figure 1b. Potential Inundation under Sea-Level Rise in Two Counties on Maryland’s Eastern Shore

Notes: Maps showing primary land covers in Dorchester and Somerset Counties, MD, in 2008. Red shading indicates inundated areas under current sea levels (0 feet of sea-level rise) and scenarios under 1 and 3 feet of net sea-level rise.
Sources: United States Department of Agriculture. 2008. Published crop-specific data layer. Accessed June 23, 2017. USDA-NASS, Washington, DC.
National Oceanic and Atmospheric Administration. 2017. Sea Level Rise and Coastal Flooding Impacts. Accessed July 6, 2017.

Water quality is a long-standing challenge for the Chesapeake Bay region, and Maryland’s Eastern Shore plays an outsized role in the nutrient loading of Bay waters. Farmlands affected by saltwater intrusion sit between developed uplands and tidal creeks and may serve as the last line of defense before water-borne nutrients and sediments reach local waterways. A better understanding of how adaptation strategies may help capture or prevent nutrient runoff in the Bay will benefit both farmers and residents of the Chesapeake as they consider the options.

Adaptation decisions made by farmers are particularly important: these choices affect the mobilization of nutrients into nearby waters and how wetlands can migrate as sea level rises.

Agroecosystems depend heavily on healthy soil for crop productivity, and high salt levels can dramatically alter the soil’s chemical profile by mobilizing nutrients, changing organic matter content, and eroding its acid-neutralizing ability. Further, many traditional crops (including corn and soy, which dominate production on the Eastern Shore) are particularly vulnerable to high soil salinity levels. In fields affected by saltwater intrusion, crop production can drop dramatically, with some areas experiencing 100 percent crop loss.

Farmers and landowners have responded in varying ways to reduced agricultural productivity and new unpredictability in crop yields. Some farmers around the Chesapeake Bay continue to cultivate fields in traditional rotations, and some have begun to switch to more salt-tolerant crops, such as sorghum. Others are simply abandoning fields as they become damaged by salt. Field abandonment can lead to colonization by agricultural weeds and native marsh plants, which could help facilitate ecosystem adaptation. But it also may expose lands to attack by the common reed (Phragmites australis), a noxious invasive species that poses a major threat to valued wildlife in wetlands as well as healthy ecosystem functioning. Landowners are also opting to convert salt-damaged lands to wetlands to restore wildlife habitat and hunting grounds. As saltwater moves inland, the choices made by farmers and landowners about how to adapt will affect future realities for water quality in the Bay, the survival and presence of wetland and migratory birds and other species, and community well-being as a whole.

Egrets flock in a farm pond built to capture runoff next to a cornfield on Maryland’s Eastern Shore.

Adaptation decisions made by farmers, in particular, have important environmental implications: their choices determine how wetlands can migrate as land is lost to sea-level rise. Changes to farmland management, including how to rotate crops and which ones to plant, will also affect the extent to which “legacy” nutrients are released into the Chesapeake Bay. Legacy nutrients are those that have built up in the soil over time—but they are “resurrected” by saltwater intrusion. Heavy nutrient runoff can wreak havoc downstream, causing species to suffer from algal blooms and hypoxic conditions. Farmers also face direct and immediate risk: their resilience to land loss and declining farmland productivity depends on the available options for adaptation. Developing approaches that can help facilitate positive outcomes is especially important for this region, which includes some of the poorest counties in Maryland.

Farmers face direct and immediate risk: their resilience to land loss and declining farmland productivity depends on the available options for adaptation.

Federally subsidized crop insurance also may play several important but conflicting roles as agricultural communities adapt to climate change. On one hand, subsidized insurance may promote resilience for farmers by reducing uncertainty about income as they experience climate-related losses in crop yields. On the other hand, it also may introduce moral hazard if farmers have less incentive to mitigate losses because insurance protects them from the consequences of saltwater intrusion. These issues of resilience and moral hazard also surface in discussions about the federally subsidized National Flood Insurance Program, but there has been little empirical analysis to address them in either context. One study, however, indicates that federal crop insurance disincentivizes farmers to take adaptation measures against extreme heat, translating to higher levels of crop yield losses in the United States than we would see without crop insurance. Similarly, where saltwater intrusion is concerned, farmers may delay shifts away from salt-intolerant crops despite related yield losses because they can rely on subsidized crop insurance to mitigate risk.

Saltwater intrusion is causing dramatic changes along coastlines the world over and pressing communities to tackle complex questions about climate adaptation. We’re embarking on this new research effort in earnest to help inform those discussions. Field studies are underway to examine how alternative crop choices and land-use practices perform in coastal agricultural regions, complemented by laboratory work to test the tolerance of more than a dozen possible crop and transition plant species to increased salinity and flooding. We’re also exploring how different options for land management may affect biogeochemical changes to the soil that accompany saltwater as it moves inland and the related impacts on water quality. Hydrologic studies as part of this effort will help better predict future outcomes by improving understanding of how saltwater intrudes into coastal agricultural lands from below and above ground. Analysis of remote sensing data will enable us to measure current damages and gain perspective on historical land-use transitions that have resulted from saltwater intrusion and ecosystem adaptation. Agricultural extension activities will serve two important purposes: to solicit feedback and input from farmers to ensure that our research findings will be relevant to stakeholders who are most at risk, and to communicate the results of our study through outreach and new educational resources.

Social and economic analyses will help connect the dots across these varying research components. Through interviews and surveys, we will learn more about how farmers in the Chesapeake Bay region are responding to and affected by saltwater intrusion, and how they are making the difficult decisions about necessary trade-offs. We are also assessing the market viability of potential alternative crops for production on farmlands transformed by saltwater, because profitability is key to new crop adoption and the region’s grain markets are driven largely by demand for poultry feed. Over the course of our research, we’ll be able to combine models of agricultural and environmental systems with economic models of land-use decisionmaking to better understand how complex and dynamic conditions interact with policies targeting agriculture and conservation—and how those interactions impact farmers and the environment. Ultimately, this work can be used to inform policies designed with incentives to improve social and ecological outcomes as coastal regions around the world adapt to saltwater intrusion.

About the Author

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Rebecca Epanchin-Niell

Rebecca Epanchin-Niell is a fellow at RFF.

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Keryn Gedan

Keryn Gedan is an assistant professor in the Department of Biological Sciences at George Washington University.

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Jarrod Miller

Jarrod Miller is an assistant professor and extension agronomy specialist in the Department of Plant and Soils Sciences at the University of Delaware.

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Kate Tully

Kate Tully is an assistant professor of agroecology in the Department of Plant Science and Landscape Architecture at the University of Maryland.

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