Author: Laura Oleniacz
A report by North Carolina Department of Environmental Quality scientists and partners tracked changes in the types of plants growing in wetlands in the outer Coastal Plain of eastern North Carolina, finding gains in salt-tolerant species and losses of shrub and tree cover.
For the project, researchers and their partners tracked changes in plant life at 78 wetland sites that had previously been sampled between 1988 and 2016 through the U.S. Environmental Protection Agency’s National Wetland Condition Assessment and Carolina Vegetation Surveys. Between 2016 and 2022, they resampled 36 sites, and also analyzed data from 42 additional sites that had been resampled by partners. In addition to tracking plant life, they also looked for indicators of saltwater exposure.
In addition to finding gains in the numbers of salt-tolerant plant species, the analysis found that 10 sites were reclassified entirely to a less forested type. For example, a site that was previously classified as a forested wetland would now considered to be a marsh. In addition, they found that 13 out of the 66 sites classified as forested and shrub-covered wetlands lost 50% or more of their tree cover.
“The biggest impacts were to forested wetlands,” said Steve Anderson, wetlands specialist with the NCDEQ Division of Water Resources (DWR). “In forested sites in transitional salinity areas on the edges of brackish marshes, we saw a reduction in tree cover, and also a reduction in new sprouts, or baby trees.”
Environmentally Speaking spoke to Anderson, and Kristie Gianopulos, wetlands scientist with DWR, about the report.
What was the goal of this study?
Gianopulos: After seeing flooded or abandoned fields, areas overtaken by woody salt-tolerant vegetation, and development of ghost forests - which are forests with extensive standing dead trees - one of our former coworkers had the idea of going back to wetlands that we or other scientists had looked at in the past, revisit them and collect data to see how they were doing in terms of their plant life, and in terms of indicators of saltwater intrusion.
So, we combed through our data, and data from the Carolina Vegetation Survey, which is a repository of vegetation plot data where researchers collected data for certain sites on what plant species were there, how many there were, how big there were, and from the US EPA’s National Wetland Condition Assessment. We were looking for wetland sites in the outer Coastal Plain that are within a certain distance of saltwater.
Then, we went back to 36 of those sites to look for information on the vegetation in those same sites that had been tracked in the past. We looked at the plant species that were found at these sites, as well as at their soil and water chemistry.
How did you go about tracking the vegetation in the sites you sampled?
Gianopulos: We visited the sites, set out plots, or defined areas within that location, to write down all the plant species that were there and how much area they were covering. We also collected water samples three feet down in the ground and from the surface if there was standing water anywhere. We collected soil samples to look at the presence of sodium, bromide, chloride and other ions that might indicate saltwater intrusion.
What were some of your findings?
Gianopulos: The majority of the sites did not change in terms of their wetland type, or classification. However, for 10 sites, we saw them change to a completely different type.
Overall, we saw increases in non-native species like the common reed and Japanese honeysuckle, and in plant species that can tolerate brackish water, which is saltier. Examples of plants that can tolerate saltier water are sawgrass, big cordgrass and eastern baccharis. Our transitional salinity forested wetlands in this study had the biggest changes in terms of their plant life, with more non-native plants and loss of cover by tree species.
The species that we saw the most often overall across all sites and all sampling, were Eastern poison ivy, followed by swamp redbay, wax myrtle and red maple.
Anderson: We were also looking for indicators of saltwater in these wetlands intruding into the groundwater, or in the surface water. In this study, our team dug down three feet, and took water samples from whatever water was in the hole, and also on the surface. And almost 70% of sites that we had water data for, they were showing they had been impacted by saltwater in some way based on the chloride concentrations in the water.
What are some of the takeaways from this report?
Anderson: Wetlands of all types can change for a lot of different reasons, including flooding or inundation, land-use changes, extreme temperatures and saltwater exposure. In the Coastal Plain, we know that saltwater, or salt in soil and groundwater, is one of these naturally occurring stressors that can quickly change a natural system. Some of these changes could lead to impacts to our estuaries and fisheries.
Gianopulos: We saw shifts of freshwater wetlands into salt-impacted wetlands. This is important because there are functions and benefits that freshwater wetlands on the coast can provide, like aquifer recharge, water purification and habitat for all kinds of wildlife species. As we see forested wetlands changing into different types, we are most likely losing some of the benefits that freshwater wetlands are providing along the coast.
To learn more, click on the project storymap.