The goal of this project is to measure Greenhouse Gas (GHG) emissions from wetlands and quantify the effects of weather, vegetation structure, and water level dynamics on components of the GHG budget of the wetland systems. To do this a combination of experimental and modeling tasks will be employed. Two distinct urban temperate wetland ecosystems, one in Ohio, a freshwater wetland, and one in New Jersey, a tidal salt marsh, will be studied. Methods combine direct measurements of CO2 and CH4 in the air over the two wetland systems, measurements of CH4 emissions in chambers, and measurements of wetland vegetation structure and ecophysiology in the context of an existing biosphere-atmosphere model. As the two wetlands to be investigated have been constructed or restored, all aspects of ecological engineering will be assessed for their effects on GHG emissions. The data collected in the wetlands will be used to parameterize the GHG emission module in the ecosystem model. This can be used as a planning tool to predict GHG budgets in different climates, wetland designs, and management practices. In addition to two Ph.D. candidates, two undergraduate students participating in the Louis Stokes Alliances for Minority Participation (LSAMP) will be trained in climate change science through this project.
Bruce K. Hamilton 6/29/10
Wetlands contribute to the global warming potential by releasing the more potent greenhouse gas (GHG) methane (CH4). Current estimates of carbon (C) uptake strengths of wetlands have an uncertainty of more than 100% associated with it, thus predictions for conditions under altered climatic conditions are even more difficult. Therefore, it is crucial to determine current C sink strengths, dynamics and factors influencing it, to be able to predict future C sink potential. Especially in urban areas, not only climatic and edaphic factors determine C uptake strengths but also previous land use, air pollution and the biophysical environment. In this study, net ecosystem exchange of CH4 fluxes of an urban tidal salt marsh was investigated at the Marsh Resource Meadowlands Mitigation Bank, located in Carlstadt, Bergen County, New Jersey. The marsh was populated with the indigenous Spartina alterniflora and invasive Phragmites australis. Monthly methane flux rate was estimated using chamber-based gas measurements from June 2011 to November 2012. Sampling was done in three replicates along four transects paralleled to the marsh front (mud flat, transect-marsh front, transect-middle, transect-road) at the intertidal wetland (Figure 1). The transect immediately paralleled to the front end of the marsh, transect-marsh front, experienced the longest inundation. The transect-road was located as far away from the marsh front as possible and experienced the shortest inundation. The transect-middle situated between the two transect lines. Thirty mL of air were drawn from the chamber and placed into pre-evacuated 10-mL glass vials. After the initial sample, five additional samples spaced at five-minute intervals were collected in the morning during low tide. Gas samples were stored at 4°C for no longer than 7 days until analysis on a Shimadzu gas chromatograph (GC) using flame ionization detection. Matheson methane standards, balanced with N2 gas, were used to perform four-point calibration curves. Methane flux rates (mg CH4-C m-2 h-1) were calculated from trend regressions of methane concentrations from the GC. Regressions for each set of samples plotted vs. time will be used to determine linearity of emission. Regressions with R2 < 0.9 will be considered non-linear and corresponding samples will be rejected; only linear positive and negative regressions will be used. In 2011, the dominant vegetation along transect-road was invasive Phragmites australis. The dominant vegetation along transect-marsh front was Spartina alterniflora. The vegetation found along transect-middle was a mixture of the two species. Therefore, the results of the methane fluxes not only was impacted by the duration of inundation but also by the plant species. In 2011, chamber measurements show variability of methane fluxes between wetland patches with various dominant vegetations at the landscape scale (Figure 4). The unvegetated mud flat was found to have the lowest flux rate among the four types of wetland patches. The Phragmites australis dominant transect experienced the least inundation and was found to have the greatest flux rate among the four. At the end of fall 2011, the study site was unfortunately affected by the invasive plant management activities. The management activities were a part of the mitigation wetland maintenance. Unfortunately, for this project, Phragmites australis patches were eradicated. The area along two transects (transect-road and transect-middle) was severely disturbed by heavy machinery. Therefore, in 2012, the three vegetated transects experienced various duration of inundation and various degrees of recovering from disturbance. In 2012, chamber measurements show variability of methane fluxes between wetland patches at the landscape scale. The un-vegetated mud flat was found to have the lowest flux rate late compared to the vegetation with exception during the hot summer months in 2012. We found that methane emissions are strongly correlated with soil temperature. The highest methane flux rates were found in July 2012. The flux rate declined throughout the fall (Figure 5) This project provided valuable learning opportunities for four undergraduate students and five graduate students from Montclair State University. The study site and the chamber-based methane measurements were used in both graduate and undergraduate classes for student groups to gain field experience in the ecological services of the wetland through water quality of GHG sequestration. This project also provided learning opportunities for participants of a NSF REU program at Montclair State University on multidiscipline environmental science research. The background of this study and the content of this project were used as environmental education materials for environmental outreach activities to k-12 students and science educators.
