NRE faculty member and students researching effects of salinization on wetlands

Connecticut now has a fraction of the forested wetlands that used to cover the state. Until the middle of the twentieth century, clearing land, constructing roads, building infrastructure and introducing irrigation and drainage systems did not require an assessment or mitigation of potential environmental impacts. Amidst growing concern for wetlands, the US Fish and Wildlife Service conducted a nationwide wetlands inventory in 1954. In the decades that followed, further scientific studies helped raise awareness of the benefits of wetlands for habitat, improving water quality and providing flood protection. The change of public opinion from approving of wetlands use for residential and industrial improvements and landfills towards conservation led to the adoption of legislation throughout the 1960s and ‘70s to safeguard wetlands. The volume of forested wetlands in Connecticut has since remained relatively consistent, with small losses due to natural conversion, typically becoming ponds, and from development projects. The embrace of wetlands research helped ensure the passage of federal and state laws and regulatory controls that stabilized the loss of these important ecosystems.

Beth Lawrence

Forested wetlands are now facing new threats. The application of road salt is salinizing freshwater areas, affecting the ecosystem services these swamps provide. Beth Lawrence, an assistant professor in the Department of Natural Resources and the Environment (NRE) with a joint appointment in UConn’s Center for Environmental Sciences and Engineering, is taking a closer look at the impact of salinization on forested wetlands. Forested wetlands represent over two-thirds of all wetlands in the state.

“The application of road salt and its effects on these swamps are an emerging issue of concern,” says Lawrence.

“The aim of my research is to better understand and quantify the numerous ecosystem services forested wetlands provide. My focus is on how plant community composition, carbon storage and carbon dynamics are affected by salinization. I’m also looking at the effects of experimental road salt applications. We know that wetlands benefit people in a variety of ways, but we do not have a good understanding of the capacity of these ecosystem services and how their functioning may be impacted across environmental gradients,” says Lawrence.

Lawrence has a background in botany and plant-soil interactions. She is concentrating on swamps populated by two tree species: red maple and Atlantic white cedar.

“We wanted to look at red maples because they’re ubiquitous in the region and they can tolerant many different hydrological situations. Atlantic white cedars, on the other hand, are a community of concern. There are only thirty or forty wetlands with Atlantic white cedars remaining across the state. They provide important habitat so this is a conservation issue,” says Lawrence.

Vegetation surveys are already underway. Lawrence aims to collect data from about thirty wetlands, concentrating on eastern Connecticut. Half of the forested wetlands in the state are located in Windham and New London counties.

These initial surveys are examining soil chemistry and composition and abundance of the ground layer, shrubs and trees. Lawrence is assessing and quantifying abiotic factors, including salinity, water temperature, chloride levels, soil, total amounts of carbon and nitrogen and the presence of nitrate, ammonium and phosphate. Electric conductivity and pH will also be assessed. These data will provide information about the relationships between salinity and attributes of the plant community.

“We want to investigate a number of factors to understand exactly how salinity is affecting the diversity, health and growth of the plant community. We also want to examine the relationship between salinity and proximity to roadways,” says Lawrence.

Samples are being extracted at varying distances from roads to assess the impact of road salt application.

Lawrence also plans to research carbon storage and greenhouse gas fluxes. She plans to measure carbon sequestered both above and below ground by measuring tree volume and taking soil samples. Further study of atmospheric levels and decomposing leaves will offer insights into carbon cycling and the release of gases in swamps.

Wetlands store carbon in plants and soil but also release carbon into the atmosphere through the decay of biomass and other natural processes that can contribute to climate change. Measuring the presence of carbon and methane gases is crucial as they are the largest contributors to climate change.

Sammy Walker and Mary Donato
NRE students Sammy Walker (left) and Mary Donato (right) take soil samples.

Several NRE students are assisting Lawrence and completing projects related to the research, supported by grant awards.

Mary Donato and Kayleigh Granville, both NRE undergraduates, were co-recipients of the Dr. Michael Lefor Wetland Science Research Grant provided by the Connecticut Association of Wetland Scientists. Donato’s project is entitled “The Effect of Salt Water Intrusion on Wetland Carbon Emissions.” She also received a Summer Undergraduate Research Fund Award that helps fund her research. Granville’s project is entitled “How Does Sea Level Rise Affect Coastal Wetland Nitrogen Cycling.”

NRE graduate student Samantha Walker is also engaged in the research. She collected eighteen soil samples from each forested wetland site. Using half of those samples sites, Walker defined an herbaceous, shrub and tree plot, identifying all the plants within to assist in the completion of vegetation surveys.

NRE undergraduates, Mary Donato and Alaina Bisson, measure CO2 and methane levels in wetland mesocosms
NRE undergraduates Mary Donato (left) and Alaina Bisson (right) measure CO2 and methane levels in wetland mesocosms.

Walker is currently analyzing the soil samples and data gathered from the vegetation surveys to determine the impact of salinity on vegetation community composition. Her work is partially funded by a field research grant from the Society of Wetland Scientists.

Lawrence also set up an herbaceous mesocosm experiment to conduct further tests for the wetlands research. A mesocosm is an outdoor system that mimics an environment by exposing organisms to natural conditions, but in a controlled setting. The researchers are using the mesocosms to investigate how individual conditions affect certain plant species. She currently has sixty-four one-hundred gallon tanks installed at the Spring Hill Farm in Mansfield, CT. Donato and Granville are collecting samples from these experiments.

The tanks are filled with four different common freshwater plant species: common cattail (Typha latifolia), common reed (Phragmites australis), tussock sedge (Carex stricta) and cordgrass (Spartina pectinata). These plants have three different conditions applied. Treated with a nitrogen enrichment, road salt (sodium chloride) and a saltwater substitute that features the same constituents as seawater, the effects are monitored to determine the impact of each factor on the individual plants.

“This research is about understanding how nitrogen runoff, saltwater intrusion and road salt application are drivers of change in wetlands,” says Lawrence.

Future experiments will involve administering different compositions of road salts to examine fluxes in greenhouse gases. The findings of Lawrence’s study could have implications for policies regarding road salt use and conservation efforts.

“Other states, such as Massachusetts, have low or no salt application zones in areas where drinking water or sensitive habitats may be affected. This work will help us gain a greater understanding of ecosystem services of forested wetlands, potential ways to manage these beneficial natural resources and help inform local and state agencies so they can develop and adopt appropriate policies,” says Lawrence.

Lawrence is also currently conducting research on ecosystem services in coastal wetlands.

By Jason M. Sheldon