Greenhouse Gas Emissions Over a Tidal Cycle in a Freshwater Wetland

摘要

Tidal freshwater wetlands are located at the interface of non-tidal freshwater riverine systems and estuarine tidal systems. These habitats experience freshwater tides, creating unique redoximorphic soil characteristics while simultaneously presenting an opportunity for hydrologic nutrient transport into the system. Because of this periodic flooding and draining, tidal freshwater wetlands are systems of intense biogeochemical transformations, which are microbially mediated. Several microbial transformations (e.g., methanogenesis, incomplete denitrification, and nitrification) result in the production of greenhouse gases (CO2, CH4, and N2O) at globally-significant levels. For example, wetlands are one of the greatest sources of methane on Earth, accounting for 20-33% of the global methane budget (Schlesinger and Bernhardt, 2013).Compared to global methane emission estimates, the global nitrous oxide budget remains largely uncertain (Tian et al. 2015), and the contribution of wetlands is currently unknown (Schlesinger and Bernhardt, 2013). However, given that recent work by Liengaard et al. (2012) estimated that nitrous oxide emissions from the Pantanal wetland system in South America alone represent ~2% of global emissions, it is reasonable to expect wetlands to be major contributors to atmospheric concentrations of this potent greenhouse gas. Despite the growing recognition that wetlands are important sources of greenhouse gases, little research has examined how flux rates vary in response to basic environmental drivers such as tidal cyclingObjectives: The main objective of this study is to assess rates of CO2, CH4, and N2O production at high and low tides in a tidal freshwater wetlands. In addition, we sought to determine if pore water ion concentrations and edaphic characteristics fluctuate over a tidal cycle.