Saltwater Intrusion and Salinization on Coastal Forests and Farms

Ghost forest (left); farmland impacted by saltwater intrusion (right)

 

Cover of salinization manual

Download the Identification, Mitigation, and Adaptation to Salinization on Working Lands in the U.S. Southeast manual to learn how to identify the stage, cause and likely progression of salinization on working lands, mitigation options if possible, and if not, adaptation strategies that are available.

View this video to learn more about the Identification, Mitigation, and Adaptation to Salinization on Working Lands in the U.S. Southeast manual


We want to hear from you.  To provide the best available guidance, we will update this manual after producers and specialists have had a chance to implement the guidance, assess recommendations, and provide feedback.  Please send all comments and suggestions for improving this manual to Nancy Gibson, USDA Southeast Climate Hub, at Nancy.Gibson@usda.gov.


Key Message

  • Soil salinization in the coastal Southeastern United States is becoming more prevalent as storm surges increase in frequency and sea levels rise.
  • Salinization reduces the productivity of working lands and can prevent crops from growing.
  • Resources are lacking for landowners to understand coastal salinization and how to manage for resilience.
  • Action must be taken if the land is to remain profitable as conditions change.

 


 

Salinity and Salinization Impacts

Coastal Forests in the Southeast are losing habitat due to salt water intrusion and soil salinization.  Photo Courtesy of NC Wetlands.

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.
Chris Miller (left) NRCS Project Liaison to the NE & SE Hubs, and Steve McNulty (right), SE Hub Director, survey farmland in eastern North Carolina that is suspected to have lost productivity due to saltwater intrusion. Photo by Michael Gavazzi, USDA

 

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.

Screenshots from the NOAA Sea Level Rise Viewer showing parts of the east coast, including North Carolina’s Albemarle-Pamlico Peninsula, at the current sea level (left) and with a 3-foot rise in sea level (right).

 

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

Workshop participants discuss options for dealing with soil salinization on working lands in the SE US

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 was used to develop Identification, Mitigation, and Adaptation to Salinization on Working Lands in the U.S. Southeast, 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.

 

Workshop Presentations

Workshop presentations can be viewed by selecting the links below:

Factors Impacting Changing Levels of Coastal Soil Salinity

Forestry Impacts and Adaptation

Agriculture Impacts and Adaptation

Adaptation through Water Control Structures

 

Adaptation Outlook

Salt-tolerant crops, such as seashore mallow have shown promise as non-traditional crops for biofuels and biodegradable absorbents. Photo by Jack Gallagher, University of Delaware.

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.