Saltwater Intrusion and Salinization on Coastal Forests and Farms

Farmland showing areas where crop yield is decreasing or disappearing

Key Message

  • Saltwater intrusion and soil salinization on coastal forests and farms in the Southeast U.S. are primarily caused by sea level rise, storms and tides, drought, water resources management and hydrological connectivity such as canals and ditches.
  • Impacts include coastal forest loss, crop yield declines, nutrient release from the soil, movement of marshes inland, increases in salt tolerant invasive species, and degraded groundwater.
  • Adaptation options include growing alternative crops, planting salt tolerant plant buffers, or applying for a wetland easement. Remediation options have shown varied success and are dependent on site-specific characteristics. For example, applying gypsum and leaching with non-saline freshwater may be able to restore the soil in well-drained areas with sufficient freshwater availability.

 

Salinity and Salinization Impacts

Coastal forests and farmlands in parts of the Southeast are being negatively affected by saltwater intrusion and soil salinization due to sea level rise, storms, tides, droughts, and water resources management. Elevated salinity levels cause crop yield declines, coastal forest loss, increases in salt-tolerant invasive species, eutrophication and marsh migration. Vegetation stressed by salinization is more susceptible to mortality by events such as droughts, hurricanes, and fires. Salinity and salinization can also cause clay dispersion that reduces soil drainage capacity, increases nutrient release that can lead to algal blooms and fish mortality, and degraded groundwater for irrigation.

 

Land Vulnerability and Drivers of Change

Elevation, subsidence (e.g., the sinking of land due to natural and human-caused factors), and drainage all influence the vulnerability of lands to saltwater intrusion and salinization. Coastal forests and farms are particularly vulnerable to salinization due to their low elevation, proximity to oceans, and high rates of soil subsidence. In addition to these factors, the following drivers also contribute to the increased risk of salinization on coastal forests and farms:

  • Sea Level Rise: Rising sea levels increase the reach of tidal influences such as king tides and pushes the salt water/fresh water interface inland.
  • Storms and Tides: Winds and tides can push saltwater far inland. Storm surges inundate land with salt water.
  • Drought: Frequent or extended droughts can push the saltwater-freshwater interface inland and reduce the capacity of soils to leach salts.
  • Water Resources Management: Ground and surface water extraction for human use and reduced freshwater discharge can increase the risk of saltwater intrusion.
  • Hydrological Connectivity: Water control structures (e.g., tide gates, valves, levees, canals, ditches) and tidal creeks influence how water moves within the landscape.

 

Outlook

Salinization is expected to increase in vulnerable areas as sea levels continue to rise. Rising sea levels will inundate lands, increase tide and storm surge levels, and push salt water farther inland through ditches and tidal creeks. Natural leaching of salts from soils is expected to decrease as precipitation patterns change to less frequent, but more intense storms, and longer periods of drought. Working land profitability using traditional management practices is expected to decline with increasing soil salinity.

Predictions of sea level rise are available on the NOAA Sea Level Rise Viewer, which provides visualizations of U.S. coastal areas most vulnerable to salinization and inundation through sea level rise. For example, the North Carolina Albemarle-Pamlico Peninsula has a high rate of sea level rise and is projected to lose about half of its land area to open water with a 3-foot rise in sea level by the end of the century.

 

What are We Doing to Address Salinization Issues in the Southeast U.S.?

The USDA Southeast Climate Hub is working with federal, state, and local public and private groups to better understand the current and projected rate and extent of saltwater intrusion, monitor salinity levels and impacts on crops and forests, and inform producers about adaptation options to improve resilience to saltwater intrusion and soil salinization.

During October 2019 the Southeast Hub hosted a workshop with local and regional subject matter experts to share knowledge and develop plans for addressing salinization issues in the region. The workshop was sponsored by the State Climate Office of North Carolina, and Director Kathie Dello gave the keynote address. Invited speakers gave short talks describing their research, what they know about current and future salinity issues, and management options for improving productivity and resilience of working lands. Group discussions followed each presentation to allow for questions and information sharing.

Information learned during and after the workshop is being used develop a soil salinization mitigation and adaptation manual for farm and forest management. The manual will allow land managers to identify the stage, cause, and likely progression of salinization on their land, mitigation options if possible, and if not, adaptation strategies that are available.

 

Presentations from our Workshops can be viewed by selecting any of following links:

Factors Impacting Changing Levels of Coastal Soil Salinity
Forestry Impacts and Adaptation
Agriculture Impacts and Adaptation
Adaptation through Water Control Structures

 

Adaptation Outlook

Adaptation options include growing alternative crops, developing salt tolerant crops, planting salt tolerant plant buffers, or applying for a wetland easement. Remediation options have shown varied success and are dependent on site-specific characteristics. For example, applying gypsum and leaching with non-saline freshwater may be able to restore the soil in well-drained areas with sufficient freshwater availability.

There is a lack of knowledge on the economic costs and benefits associated with adaptation options. Depending on the region these economic factors can vary, which makes the decision to use new management practices site-specific. Solutions to salt water issues are promising in theory but must be profitable in practice to be useful to farmers and land managers. It will take time to understand how these solutions perform in practice and to identify the regional markets for alternative crops.