The Effect of Water Levels on Carbon Dioxide Emissions from Soil Microcosms from the Cavalier Wildlife Management Area

Abstract:

Peatlands provide ecosystem services such as pollution filtration, flood control and carbon sequestration. These ecosystems contain 33% to 50% of the global soil carbon pool. Organic matter in the soil provides a substrate for microbial respiration, but soil saturation can alter respiration rate as measured by carbon dioxide emissions. The purpose of this study was to determine rates of soil carbon emissions released from a forested peatland given a set of hydrologic regimes. Soil cores were gathered from Cavalier Wildlife Management Area in Chesapeake, Virginia. Cores were randomly assigned to water level treatments and carbon dioxide emissions were measured using a Licor 6400-XT twice a week. While the water level treatments had the expected effect on volumetric water content, we found that the two soil types responded differently to the treatments. The histosol retained more water and maintained a higher volumetric water content in the same water treatments. After the cores equilibrated for two weeks, both soil type and treatment affected carbon dioxide emissions. The ultisol showed greater emissions at lower water levels. The interaction between the two was also significant, suggesting that soil type affected the relationship between water levels and emissions. The effect of soil type on emissions seems to be driven by the differences in rewetting. Volumetric water content was generally negatively correlated with carbon dioxide emissions in both soils, and the interaction between soil type and vwc was not significant, suggesting that the relationship between co2 emissions and increasing vwc is similar in the two soils. The difference in mean carbon dioxide emissions between the two soil types is likely driven by the water holding capacity of the soil. During the first two weeks, carbon emissions decreased over time, and the decline was greater in the ultisol soils. While bulk density was not statistically different between the two sites, organic matter content was slightly greater on average in the histosol. This difference is potentially driven by a few cores from the ultisol site with low organic matter. These results can help managers set hydrologic targets that support restoration goals.