The Research Behind Salty Soils: What is saltwater intrusion and what are scientists doing about it?
Researchers set-up sampling plots in a salt-damaged corn field.
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.
Saltwater is a particularly tricky invader 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.
Collection of soil samples to be analyzed for salt content.
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.
Soils being processed for sodium content.
Despite nuances and differences, researchers trek on. Tully points out that context is an important aspect in management, contemplating whether continued management, restoration or retreat presents the best opportunity.
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.
This article also ran on UMD’s College of Agriculture and Natural Resources Website.