Everglades Wetland Research Park Research

Ecosystem Services of Coastal Mangrove Wetlands

We are beginning measurements of methane emissions and carbon sequestration in mangrove coastal wetlands. Early results show that methane emissions are essentially zero but carbon sequestration rates are comparable to nearby freshwater wetlands. These measurements validate the renewed interest in the concept of coastal saltwater wetlands such as salt marshes and mangroves being carbon sinks; in fact that concept has a now accepted term of “blue carbon.”  The EWRP has also done some research on the importance of mangrove wetlands serving as buffers for coastal storms and tsunamis in tropical regions around the world (Marois and Mitsch, in press). 

Long-term Patterns of Methane Emissions and Nutrient Retention in Created Wetlands

Created wetlands may or may not contribute to climate change because they both sequester carbon but also emit the greenhouse gas methane. Studies of methane emissions, began by our lab in 2003 at the Olentangy River Wetland Research Park in Columbus, Ohio, including large-scale methane emission estimates from an eddy covariance tower created at this site. Support from the National Science Foundation allowed us to compare two different chamber techniques that we have used for methane emission measurements (Waletzko and Mitsch, 2014). That paper is being published in a new special issue (Mitsch et al., 2014a) along with a re-evaluation of the nutrient retention trends of the experimental wetlands at the Olentangy River site in Ohio (Mitsch et al., 2014b). We found that after about 10 years, there are signs that retention of nitrogen and phosphorus are starting to increase from year to year, something counter to the conventional wisdom of many previous studies of created wetlands. EWRP is also involved in an international (organized in Sweden) meta-analysis of the literature on nutrient retention in created and restored wetlands (Land et al., 2013). 

Nutrient Removal Efficacy of Wetland Plant Communities in the Florida Everglades

This 3-year, 18-mesocosm study focused on estimating the efficacy of different wetland plant communities for reducing phosphorus input into the Florida Everglades. This project was part of the overall Everglades Restoration where 23,000 ha of wetlands, called Stormwater Treatment Areas (STAs), have been created on former agricultural land that had, in turn, replaced wetlands decades ago. The study investigated if certain types of wetland communities are better than others in reducing phosphorus inputs to the Florida Everglades, thus reducing the invasion of plants such as Typha (cattails) from taking over the native Cladium (sawgrass) in the Everglades “river of grass.”  Our study (Mitsch et al. 2015) found that by the end of the study, the Nymphaea, control/Chara, and Typha vegetation communities had lower outflow phosphorus concentration than the inflow (p < 0.05) with average outflow concentration of 11 ± 1, 15 ± 3 and 16  ± 1 ppb respectively. We conclude that any treatment wetland constructed with local Florida soils and designed to achieve low (~10–15 ppb P) concentrations would probably take a minimum of 2 years to become sinks of phosphorus. We also conclude that wetlands can be created to achieve these low thresholds if low TP loading and self-design strategies are incorporated into the project design (Mitsch et al., 2015). Two companion studies on this project are also published.  Villa and Mitsch (2014) investigated the contribution of the different wetland plant species to exported DOC (and by inference to DOP) by using carbon stable isotope techniques.  Marois et al. (in press) investigated the relative importance of aquatic metabolism on the retention of phosphorus in these vegetation communities and found that plant communities without emergent macrophytes may perform best in the retention of phosphorus in low inflow concentration conditions.  

Carbon Fluxes in Subtropical Wetland Ecosystems

Corkscrew Swamp near Naples Florida— considered by some to be one of the world’s most majestic forested wetlands in the USA —was chosen as a convenient site for comparing different wetland ecosystems in the Everglades: sawgrass wet prairies, bald cypress swamps, pond cypress swamps, and pine flatwoods—for their ability to sequester carbon into permanent soil storage as well as for their emissions of the greenhouse gas methane. These measurements will ultimately help to estimate the net effect of wetland ecosystems such as those found at Corkscrew in the cooling or warming of the planet. The results, published in two recent papers, illustrate that seasonality in methane emissions was positively correlated with water levels but not with soil temperature (Villa and Mitsch, 2014) and that carbon sequestration was not necessarily enhanced by prolonged saturated conditions but may be affected more by the quantity and chemical composition of the organic material reaching the soil (Villa and Mitsch, 2015). These studies are continuing by comparing methane emissions from these pristine wetlands with more heavily impacted forested and herbaceous wetlands on FGCU’s campus.