What's happening to these forests?

The story of saltwater intrusion on North Carolina's coasts

Image source:  Jessie Baker Heim 

Documenting Change: A Coast Tour of NC

“We know sea level rise is happening, and we have confidence it will continue to keep happening. [...] These swamps are bellwethers of change.” -Gregory Noe, USGS

Emily Ury

Modeling Saltwater Intrusion

This photo was taken in 2009. The red line shows where the same shoreline was in 1984. Section "B" used to be swamp forest and is now shrub land. Source: Alligator River National Wildlife Refuge,  Coastal Review 


Warning Signs of Saltwater Intrusion

Researchers aim to determine early warning signs of saltwater intrusion. Early detection may help improve outcomes of management strategies employed to reduce or mitigate the effects of saltwater intrusion and sea level rise. Scientists use vegetation stress, such as reflectance in the infra-red band (see below), to detect areas experiencing inundation by saltwater ( Shiklomanov  et. al 2019).

Thermography, and infrared thermography, tell us about the temperature differences in vegetation. Pictured above is the thermography of a sunflower. Temperature differences are associated with plant cooling mechanisms and stomatal density, indicating potential water loss (Shiklomanov et. al 2019).

1984 (left) vs. 2015 (right). Source: Joy Reeves, Google Earth Engine

Saltwater Intrusion Research

This educational story map is only a small part of an ongoing project to research saltwater intrusion in North Carolina. Scientists are working collaboratively to answer complex questions about coastal salinization: How are plants and microbial communities responding to saltwater intrusion? To what extent is salt-resistant vegetation continuing to grow productively in salty environments? What other factors are working alongside saltwater intrusion to alter ecosystems and kill off trees?

The team that put together this story map is focused on understanding large-scale geospatial patterns. Because there are so many other factors responsible for landscape change in the Ablemarle-Pamlico Peninsula, a 2019  Duke University Data+ Project  took on the challenge of modeling and comparing a variety of datasets from Google Earth Engine layers (Landsat, MODIS) and from the Alligator River National Wildlife Refuge to export informative layer-maps like these:

Elevation (Duke Data+)

Classification (Duke Data+)

Shoreline Loss (Duke Data+)

One current goal of researchers is to develop a comprehensive "vulnerability index" gauging a region's susceptibility to saltwater intrusion (by elevation, tree loss, rate of tree loss, vegetation type change, reflectance data, etc.) and host the finalized index in the form of an interactive and user-friendly map tool, applicable to refuges across the coast. Existing data visualization models like those pictured above are promising tools for land managers in the future, as they will continue to face difficult conservation decisions due to persisting sea level rise.


An International Phenomenon

There are regions all across the world experiencing saltwater intrusion. Explore the map below to find a few examples. Can you zoom in and use satellite imagery to look for potential aerial "warning signs" of the landscape changing?

Source: Climate.gov, Herbert et. al. 2015

Raising Awareness and Building Resiliency

“It matters how people are willing to adapt or willing to fight against what may be kind of a permanent change in the landscape." -Todd Bendor

What can we do to raise awareness and build landscape resiliency in the face of saltwater intrusion? We may not be able to stop sea level rise, unless we make major changes in the next 10 years. So, we must begin to think about "pre-storation" strategies. This could mean incentivizing landowners to let healthy wetlands migrate in towards their property, or fostering habitats for salt-resistant plants (like  phragmites !) that begin to fill the roles of previously lost vegetation. Assuming an attitude of forward-thinking, prioritization, adaptation, and prevention will help land managers and coastal residents prepare for changing coastlines. Stakeholders and local community members provide  valuable insights  into the conversations around saltwater intrusion.

Spread awareness by informing others on the reality of "what's happening to these forests."

Or, check out some of the links below to get involved in citizen science programs for monitoring and responding to coastal salinization.

“The big question is, how do we respond to [the] change? Is it business as usual as long as possible? Or, are there proactive decisions that can be made in the coming years and decades that can maintain quality of life in the region’s communities and conserve its natural resources for future generations?” -Ryan Emanuel, N.C. State University


Want to learn more?

Check out the saltwater intrusion  Science Friday Podcast !


References

Herbert, Ellen R., et. al. "A global perspective on wetland salinization: ecological consequences of a growing threat to freshwater wetlands." Ecosphere, vol. 6, no. 10, pp. 5-7. The Ecological Society of America. Accessed 15 July 2019.

Shiklomanov, Alexey N., et al. "Enhancing global change experiments through integration of remote‐sensing techniques." Frontiers in Ecology and the Environment, vol. 17, no. 4, May 2019, pp. 215-24. The Ecological Society of America. Accessed 22 July 2019.

Tully, Kate, et. al. "The Invisible Flood: The Chemistry, Ecology, and Social Implications of Coastal Saltwater Intrusion." BioScience, vol. 69, no. 5, May 2019, pp. 368–378. Oxford Academic. https://doi.org/10.1093/biosci/biz027. Accessed 20 July 2019.

Xiao, Han, et. al: "Assessing sea-level rise impact on saltwater intrusion into the root zone of a geo-typical area in coastal east-central Florida."Science of The Total Environment, vol. 630, 2018. pp. 211-221, ScienceDirect. https://doi.org/10.1016/j.scitotenv.2018.02.184. Accessed 22 July 2019.

Emily Ury

This photo was taken in 2009. The red line shows where the same shoreline was in 1984. Section "B" used to be swamp forest and is now shrub land. Source: Alligator River National Wildlife Refuge,  Coastal Review 

Thermography, and infrared thermography, tell us about the temperature differences in vegetation. Pictured above is the thermography of a sunflower. Temperature differences are associated with plant cooling mechanisms and stomatal density, indicating potential water loss (Shiklomanov et. al 2019).

1984 (left) vs. 2015 (right). Source: Joy Reeves, Google Earth Engine

Elevation (Duke Data+)

Classification (Duke Data+)

Shoreline Loss (Duke Data+)