Continuous measurement of CO2, CH4 and H2O fluxes from restored marl fen and inland salt marsh communities overlaying chemical-byproduct settling basins

There is a legacy problem of chemical process byproducts being stored in settling basins with no liners. Awareness of the transport of these compounds as leachate has led to modern day efforts to prevent leachate formation and transport to nearby water bodies. For large sites, impermeable liners over the basin may be prohibitively expensive and have a large greenhouse gas impact. The use of vegetative covers that transpire otherwise percolating water may be a more cost-effective option and can sequester carbon. However, overland flow of contaminants may be significant in these cases and so wetlands often serve as sediment basins. The water fluxes associated with these wetlands are not well understood but are important for determining the residence time of water in the basins, which may in turn serve as important design criteria. Similarly, the carbon budgets associated with these wetlands have only scarcely been studied. The residence time of carbon in these systems may be indicative of ecosystem health and may indicate the status of sorbable carbon molecules in the system. Wetlands have anoxic soil conditions, though, which reduce microbial decomposition rates and promote methanogenesis. Although wetlands in general are the single largest natural source of CH4 worldwide, the ecological drivers of the carbon budget of constructed wetlands are still uncertain and vary by site, and the carbon residence times of the wetland may be affected by CH4 emissions to the atmosphere. We measured continuous CO2, CH4 and H2O fluxes associated with an inland salt marsh planted in 2009 on the Solvay wastes in Camillus, New York using the eddy covariance method over the 2019 and 2020 growing seasons and compared our results to data gathered between 2011 and 2013. We quantified the biogeochemical cycling associated with an alkaline, infertile soil (pH and total N approximately 8.5 and 0.5%, respectively) and combined the fluxes with a host of meteorological data to better understand the water and carbon budgets associated with the site. In a composite year we found that there was greater evapotranspiration than precipitation nearly continuously. We also found that the site was a slight carbon and warming sink. Carbon fluxes and water fluxes were highly correlated, indicating that the water fluxes were largely driven by vegetative processes.