UMD researchers and colleagues found 19,000 acres of farmland converted to marsh in 6 years
A patch of light, crusty soil in a corn field reveals saltwater intrusion.
Image Credit: Rebecca Epanchin-Niell / UMD
Researchers from UMD, University of Delaware and George Washington University mapped the spread of saltwater intrusion on farmland in Delaware, Maryland and Virginia, and found that land area covered by visible salt patches almost doubled from 2011 to 2017, and over 19,000 acres converted to marsh due to intrusion.
Potential economic losses from the salt patches totaled over $427,000, with Sussex County, Delaware, experiencing the highest potential losses, estimated at $84,431. The researchers also estimated potential economic losses of between $39-70 million annually due to the reduced yield in farmland within 200 meters of salt patches.
The research paper was published July 20, 2023, in the journal Nature Sustainability.
Across the globe, sea level is rising, and in the mid-Atlantic region, land is also sinking due to large geological shifts and climate change. The result is that saltwater intrudes into surface and groundwaters in low-lying areas, making the soils too salty for farming.
“Saltwater intrusion often happens in advance of sea level rise, which is why we call it the invisible flood,” said Kate Tully, an associate professor in the Department of Plant Science and Landscape Architecture at UMD and a co-author of the study. “This research is the first visualization of this often invisible symptom of climate change.”
The findings in the study present the first fine-scale mapping of salt patches across the DelMarVa region, a low-lying region that is facing increasing effects of salt water intrusion and sea level rise.
“This spatial information can help identify high risk areas and better target resources and support to regions where transitions are occurring,” said Rebecca Epanchin-Niell, an associate professor in the Department of Agriculture and Resource Economics at UMD and co-author of the study.
Using aerial and satellite images, the researchers leading the remote sensing analyses trained and tested a machine-learning algorithm by inputting 94,240 reference points from 14 coastal counties in Delaware, Maryland and Virginia. These reference points taught the algorithm how to identify photos by land-type, such as a forest, marsh or salt patch, and tested the accuracy of the algorithm outputs. The research team then analyzed the results to see how those landscapes have changed over the years.
Their results show that the effect of salt patches on agricultural production extends far beyond what is currently mappable. While in some cases, the acreage of land with visible salt patches may be small, its presence denotes that the entire field is at risk of conversion to saline soil that is unsuitable for traditional farming. Additionally, soil salinity in nearby areas of the field may be high enough to reduce crop yield but not enough to leave bare patches.
“From the datasets we developed, what we’re noticing is quite alarming because we see that the salt patches are accruing quite fast,” said Pinki Mondal, lead author of the study from the University of Delaware. “The area of farmland with salt patches has almost doubled in the six years we studied.”
The researchers also sampled soils in their study area to make sure that the salt patches seen on the photos were indicative of actual salty soil, and to understand the salinity content of surrounding soils. The researchers found high salinity levels hundreds of meters away from a visible salt patch.
This is an especially acute problem for corn farmers, because corn is not very salt tolerant, yet it makes up a substantial portion of the crops grown in the DelMarVa region. In the short term, farmers could switch to growing more salt tolerant crops such as sorghum to keep profit loss at a minimum. But in the long run, increasing salinity will eventually render the fields unfarmable even for salt-tolerant crops.
One possible long-term solution is to proactively convert some farmland into marsh, which would provide wildlife habitat and act as a natural barrier to slow the saltwater encroachment. Such actions would require public policy changes and support for farmers, and the researchers hope their datasets can help stakeholders identify priority areas for various interventions. Because the datasets are so detailed, individual farmers and land-owners can see how they are being impacted by saltwater intrusion.
-This story was adapted from the original, written by Adam Thomas, University of Delaware.
Co-authors of this study from the University of Maryland include: Associate Professor of Agricultural and Resource Economics Rebecca Epanchin-Niell, Associate Professor of Plant Sciences and Landscape Architecture Kate Tully.
The UMD portion of this research was supported by Financial Acknowledgements: USDA National Institute for Food and Agriculture (Award No. 12451226), U.S. Environmental Protection Agency (Assistance Agreement No. CB96358101), USDA’s Natural Resources Conservation Service (Assistance Agreement No. NR193A750007C005) and the National Fish and Wildlife Foundation’s Chesapeake Bay Stewardship Fund (Award No. 0603.20.071142), as well as the State of Maryland, and Harry R. Hughes Center for Agro-Ecology. The views expressed in this article do not necessarily reflect the views of these organizations.
