Hydrology and microtopography control carbon dynamics in wetlands: Implications in partitioning ecosystem respiration in a coastal plain forested wetland
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2017 Elsevier B.V. Wetlands store a disproportionately large fraction of organic carbon relative to their areal coverage, and thus play an important role in global climate mitigation. As destabilization of these stores through land use or environmental change represents a significant climate feedback, it is important to understand the functional regulation of respiratory processes that catabolize them. In this study, we established an eddy covariance flux tower project in a coastal plain forested wetland in North Carolina, USA, and measured total ecosystem respiration (R e ) over three years (20092011). We evaluated the magnitude and variability of three respiration components belowground (R s ), coarse woody debris (R CWD ), and aboveground plant (R agp ) respiration at the ecosystem scale, by accounting microtopographic variation for upscaling and constraining the mass balance with R e . Strong hydrologic control was detected for R s and R CWD , whereas R agp and R e were relatively insensitive to water table fluctuations. In a relatively dry year (2010), this forested wetland respired a total of about 2000 g CO 2 -C m -2 y -1 annually, 51% as Rs, 37% as R agp , and 12% as R CWD . During non-flooded periods R s contributed up to 57% of R e and during flooded periods R agp contributed up to 69%. The contribution of R s to R e increased by 2.4% for every cm of decrease in water level at intermediate water table level, and was nearly constant when flooded or when the water level more than 15 cm below ground. The contrasting sensitivity of different respiration components highlights the need for explicit consideration of this dynamic in ecosystem and Earth System Models.
