Saltwater Intrusion

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Embarking on a Saltwater Trail

For years, researchers have made progress through scientific discovery and stakeholder outreach

By Carrie Anderson

A long, complex history dating back to the very first agricultural fields on the Eastern Shore can show the inter-tangled story of saltwater’s far-reaching effects. Scientists have stationed their research along the Chesapeake Bay to understand climate and land transformations, looking for clues to help mitigate the impacts.

In 2014, Dr. Kate Tully of the University of Maryland (UMD) met Dr. Keryn Gedan of the George Washington University (GWU), who at the time was researching extensive ghost forests along the Bay and in Blackwater Wildlife Refuge with UMD. One afternoon, Gedan spent time over coffee illustrating to Tully just how far the problem reached, when Tully zooms out on the maps to get a better look at large white rings on the outside of farm fields. 

When Gedan and Tully went out to Somerset County to get a closer look, the Somerset Soil Conservation District knew of the problem and was ready to show a number of fields facing the strange phenomenon. Driving by acres of bleached trees, deserted corn fields and Phragmites australis, an 8-foot tall invasive reed species displayed the extent of the issue, as well as proved salt as the culprit. 

At UMD, Tully’s Agroecology Lab looks to find interconnectivity between agriculture and ecosystem services through different means. Viewing agriculture through the lens of ecology can increase desirable ecosystem services like improving water quality, soil health and adapting to climate change. To see that agriculture systems can be more than food and feed provisioners, and when managed properly, can provide benefits for the environment and people. This vision led to initial seed funding from UMD and the Harry R. Hughes Center for Agro-Ecology to gather basic data and investigate saltwater intrusion.

Since then, researchers have gone on to receive major grants, including from the USDA National Institute of Food and Agriculture. The 2018 grant aimed at preparing coastal farmlands for a future of saltwater intrusion and nutrient loss while developing adaptation methods for agroecosystems to create resilient environments. 

Using methods on three test farms and one control, scientists considered how saltwater intrusion impacted crop productivity, soil health and agriculture profits. Methods included planting experimental salt-tolerant crops on site, helping to match productive planting to future farmland use, along with mapping tools to mark the spatial extent of saltwater intrusion. 

An Extension portfolio was written to convey research outcomes to stakeholders throughout the region. While seeing saltwater intrusion at the source, Extension educators provide information for regional meetings and programs improving a farmer’s toolset against salt stress. Updated factsheets, story maps and a slew of scientific research papers also help researchers grow an informed base of stakeholders ready to adapt to the continuing challenges. 

Through a current Small Watershed Grant from the National Fish and Wildlife Foundation, Tully and colleagues at UMD, GWU and the University of Delaware now look toward restoration-based solutions in the face of saltwater intrusion. By turning to restorative efforts, farmers have options and alternatives that fit the needs of the land and the surrounding ecosystem. Specific goals of the ongoing project include tidal habitat restoration creation on 32 acres of encroached land. By identifying critical areas and informing landowners about restoration practices, this grant offers an environmentally sound solution to saltwater intrusion with a goal of preserving agricultural productivity. This project includes efforts to provide outreach to stakeholders impacted by saltwater intrusion in collaboration with the Hughes Center for Agro-Ecology.

Scientists aim to apply current and past observations to future research and link these findings to other issues agroecosystems face. Farms face a composite of varying issues year to year that can change the way land is used. Increased frequent flooding, for example, can be detrimental to cropland over time, and can increase saltwater inundation, creating two problems in one field. Scientists understand this interrelation of issues, and work to provide multi-faceted solutions to keep land functional and adapt to these drivers of damage.

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The landward movement of seawater into coastal communities is causing salt damage to land along the eastern seaboard of the United States. For coastal communities like on Maryland's rural Lower Eastern Shore, that can mean invasive marsh species, undrinkable water, damaged forests, reduced agricultural crop yields, and salt-stressed soils.

Mapping Saltwater Intrusion on Maryland’s Eastern Shore

By Carrie Anderson and Chelsea Patterson

An invisible tide is actively threatening the future of farms along the Eastern Shore of Maryland. As sea levels continue to rise, saltwater is encroaching inland like never before, leaving sodium deposits detrimental to crop growth.

This phenomenon is called saltwater intrusion and the first of its effects are felt at the Chesapeake Bay’s edge. “Anywhere in this county … around the tide you can see the trees are dying, especially the pine trees, whether that's (from) rising water, salt intrusion or a combination,” said Larry Beauchamp, a farmland manager and Somerset County resident. 

Dying pine trees — prevalent on the Eastern Shore — often indicate the coming of patchy corn, soy or wheat crops. “I just hate to see what was a field go to waste,” said Beauchamp. This is a common concern among those who manage and farm the land like Beauchamp, who has watched local farms end crop planting rotations because of suboptimal yields.  

Despite a consensus that there is a problem, it has been difficult to address because saltwater intrudes underground and is unseen by the eye until it is too late. Researchers at the University of Delaware (UD), George Washington University (GWU), and the University of Maryland (UMD) are working to illustrate this intrusion in the low-lying fields of Somerset and Dorchester counties. 

Brian Moyer, lab technician at UMD’s Agroecology Lab, says that Mapping Salty Soils is a multi-disciplinary project aiming to digitally map the extent of saltwater intrusion and the damage it causes. The Agroecology Lab under the direction of UMD scientist Dr. Kate Tully works collecting soil samples across various field points at different depths to analyze for sodium electrical conductivity (EC). Dr. Keryn Gedan’s Lab at GWU measures plant health data, specifically pertaining to corn crops. At UD, satellite image sensing is used to identify dry and salty patches remotely. 

The Mapping Salty Soils project is funded by the National Fish and Wildlife Foundation partnered with the US Environmental Protection Agency and Chesapeake Bay Program. Through this grant, known as the Chesapeake Bay Stewardship Fund, the Harry R. Hughes Center for Agro-Ecology expands research about restoration options for farmland affected by saltwater intrusion, including increasing tidal wetland habitat for the American black duck. Mapping is specifically detailed in phase one of the grant proposal, identifying at-risk areas for research and restoration. 

“The reason that this project is so cool is that (researchers) are trying to make (saltwater intrusion) as scalable as possible,” said Caitlin Dicara, a Master’s student working out of the Gedan Lab, “We are adding physiological data layered on top of satellite data … to pick out where saltwater intrusion is happening.”

The team's hope is to link salinity to elevation and plant growth, and to later use this data for predictive modeling — creating a comprehensive picture of saltwater’s threat to soil, plants and the overall ecosystem. This modeling has the potential to inform farmers and policymakers on the full scope of the problem, so that management strategies can more effectively address increasing salinity in crop fields.

Projections for sea-level rise have been instrumental in informing decisions, however the impacts of saltwater intrusion are often felt before these fields are lost to the Bay. Mapping Salty Soils is the first step in establishing scientifically supported trajectories that are critical for allowing communities and farmers to plan for the future

Research Funded By Center Aims To Continue Saltwater Intrusion Work

Saltwater intrusion represents the leading edge of coastal climate impacts. Inland movement of seawater can change soil salinity in coastal farmlands, leading to crop yield declines and reduced resilience of coastal lands to climatic events. Current research indicates a 79% rise in salt deposits along the farm fringes in coastal Maryland between 2011 and 2017. However, no dataset exists to determine the annual rate of changes that can be used for better decision-making.

A Hughes Center-funded study led by researchers at the University of Delaware (UD), George Washington University (GWU), and the University of Maryland (UMD) seeks to fill this gap and provide farmers, technical advisors, and policy-makers with information that is needed to promote adaptation and resilience to these sea-level rise and climate-driven changes. The interdisciplinary group will combine satellite data, drone data, crop data, soil data and predictive modeling to calculate the annual rate of change in plant growth due to salt deposit formation and to predict future land or salinity changes.

Dr. Pinki Mondal at UD will lead the satellite remote sensing research where her group will use satellite images and machine learning approaches to identify small patches of salt deposits on an annual basis. Dr. Jarrod Miller at UD will lead drone mapping of these small-scale changes on the ground and in crop health. Dr. Keryn Gedan at GWU will lead research measuring crop health that is tightly connected to soil salinity. Dr. Kate Tully at UMD will lead research on soil salinity. Dr. Rebecca Epanchin-Niell at UMD will bring these components together to develop statistical predictive models of future soil salinity changes. The team will work closely with local partners, including the Eastern Shore Land Conservancy and Lower Shore Land Trust. This research will provide information to agricultural stakeholders regarding at-risk areas and the timing of potential transitions, facilitating timely adaptation. Identifying and predicting transition zones where salinity problems are not yet obvious, but will soon degrade land productivity, may enable farmers to transition at-risk land into easements and allow ecosystem transitions that promote soil and ecosystem health.

This project builds on work that has been ongoing work on saltwater intrusion on Maryland’s Lower Eastern Shore that this team has been performing since 2017. Previous grants funded by the Hughes Center looked into ways to ameliorate salt stress, potential alternative crops, the effectiveness of establishing perennial grasses in the margins of farm fields affected by saltwater intrusion, and the creation of maps to identify priority risk areas.

The Research Behind Salty Soils: What is saltwater intrusion and what are scientists doing about it?

A researcher works in a field

By Carrie Anderson

In coastal communities across the globe, saltwater intrudes into freshwater aquifers, disrupting ecosystems and changing habitats drastically. The Eastern seaboard, particularly land on the Delmarva Peninsula along the Chesapeake Bay, is under threat as high tides, frequent flooding and low water tables fall victim to this sneaky salt. 

The largest estuary in the United States, the Chesapeake Bay boasts miles of complex meandering tributaries. Models of a changing climate warn of sea-level rise and increased flooding frequency, which is coupled with sinking land as a result of ice-sheet retreat in the geologic past. A long history of varied farming practices on low-lying fields also contributes to saltwater’s destruction. Ditches that once drained the land for agricultural uses may now aid in salt and nutrient transport, unfavorable to farm fields that are struggling to stay productive. 

Salt is a particularly difficult nutrient because of the ability to move inland both above and below ground quickly and without initial notice. Low groundwater tables along the Chesapeake Bay are easily intruded and salt can flow through ditches and be propelled into farm soil through plant capillary action. In aboveground transport of saltwater, high tides and storm related flooding are at fault, both of which are projected to worsen in the face of climate change. 

Researchers are rightfully uneasy about saltwater intrusion, studying unique interactions that lead to considerable changes in environments. Inland retreat of forest communities and landward migration of coastal saltwater marshes aids in the decline of agricultural land. While ecosystems like marshes are advantageous in their own right, the loss of varied land use and services raises concern.

Multi-institutional collaboration in a 2019 paper, including Dr. Kate Tully, an Associate Professor of Agroecology at the University of Maryland (UMD), studied the novel geochemical disruption salt can cause in coastal ecosystems along with management decisions in response to such drastic ecosystem changes. Tully and scientists found that biogeochemical properties of salt and how it reacts with other common nutrients make it even more complicated to track. When salinization occurs, the increase in ionic strength, alkalinization, and sulfidation affect how other critical nutrients cycle through plants and soils. 

Researchers present different management and control strategies but these suggestions cannot go beyond basic adaptive measures, all the while the problems faced are layered and unique to each farm and field. 

“Predicting the current and future extent of saltwater intrusion is hard, because it doesn't necessarily move just with sea level rise. So much of it has to do with microtopography and the way that somebody manages their specific field,” said Tully.

Tully points out that context is an important aspect in management, contemplating whether continued management, restoration or retreat presents the best opportunity. 

Dr. Pinki Mondal, a University of Delaware scientist and the principal investigator of the Mapping Salty Soils research, reiterates this, that while options vary, scientists working with land and farm owners are simply “trying to identify if there is something else that we can do.” 

By mapping the path of saltwater intrusion onto lands, researchers like Tully and Mondal provide a timeline and present evidence-based alternatives to the current practices for struggling land on the Delmarva.