Environmental Science and Management
Gold, Arthur, J
Natural Resources Science
Addy, Kelly and Lazar, Julia
Natural Resources Science
Climate change; greenhouse gases; beaver ponds; Rhode Island
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Climate change is one of the largest environmental issues facing humanity today, having the potential to alter fresh water availability, agricultural yields, forest productivity, and global sea levels. As climate change is likely to increase the intensity of extreme weather events, the potential for massive human and financial consequences is of further concern. The Intergovernmental Panel on Climate Change asserts that climate change is due to anthropogenic alterations of the atmosphere’s composition, with additional contributions from natural biochemical processes. In particular, the rapid increase in the concentrations of greenhouse gases (GHGs) in the atmosphere can trigger atmospheric warming as these GHGs absorb the heat radiated from the earth and re-emit it into the atmosphere. Much research has been directed at understanding the sources of GHGs to better assess how to reduce GHG emission rates. The study of biogeochemical cycling, particularly the cycling of carbon (C) and nitrogen (N), underlies our ability to predict GHG generation from natural environments. More scientific research is necessary to accurately derive estimates of GHG emission rates from different landscapes around the globe. These estimates will subsequently inform decisions in GHG management and climate change mitigation.
Research to date has indicated that certain landscape features may function as “hotspots” for GHG emissions. Because it is estimated that natural wetlands account for nearly 30% of total methane emissions (Reddy and DeLaune 2008), it is important to better quantify the fluxes of methane and other GHGs from natural environments into the atmosphere. Studies (Naiman et al. 1994, Soumis et. al 2004) have shown that wetland environments, such as beaver ponds, may be sources of atmospheric carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) – all potent GHGs. Due to the resurgence of the North American beaver (Castor canadensis), there is an increasing interest in investigating beaver ponds as potential hotspots of GHG emission.
Beaver dams impound natural stream flow, creating wetland environments that foster anaerobic conditions, trap sediments and nutrients, and accumulate organic matter. This organic matter serves as a C source for microbial activity to facilitate biogeochemical cycling. With these conditions, beaver ponds alter the cycling of C and N within the riverine environment via the processes of respiration, methanogenesis and denitrification (Naiman et al. 1994) – which generate CO2, CH4 and N2O.
In this study, the diffusive flux of GHGs (CO2,CH4, N2O) from the air-water interface of three beaver ponds in Southern Rhode Island in the fall 2012 and spring 2013 seasons was determined via linear increase in concentration of gases in a static chamber over a defined sampling period (as described in St. Louis et al. 2000). Five floating gas chambers were launched on each beaver pond, sampled in 15-minute intervals over one hour, and the samples were processed on a gas chromatograph. An emission rate was derived for each gas from the linear regression of the change in concentration of the gas over time. Gas chamber sampling occurred three times per season on different dates at each of the three beaver ponds. Across sites, fall mean daily pond emissions ranged from 10 to 600 mg CH4 m-2 d-1 and 4,150 to 23,100 mg CO2 m-2d-1. Spring mean daily pond emissions ranged from 10 to 230 mg CH4 m-2 d-1 and 1,500 to 4,300 mg CO2 m-2 d-1. Emissions of N2O were negligible. Variability in GHG emissions may be due to varying levels of labile C, temperature, photosynthetic activity, and pH. Future research involves investigating environmental parameters, such as subaqueous sediment temperature and reduction-oxidation potential, which may influence GHG emission rates.