Hydrology and microtopography control carbon dynamics in wetlands: Implications in partitioning ecosystem respiration in a coastal plain forested wetland
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 en- vironmental change represents a signi fi cant climate feedback, it is important to understand the functional regulation of respiratory processes that catabolize them. In this study, we established an eddy covariance fl ux tower project in a coastal plain forested wetland in North Carolina, USA, and measured total ecosystem re- spiration (R e ) over three years (2009 – 2011). 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 fl uctuations. 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- fl ooded periods R s contributed up to 57% of R e and during fl ooded 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 fl ooded or when the water level more than 15 cm below ground. The contrasting sensitivity of di ff erent re- spiration components highlights the need for explicit consideration of this dynamic in ecosystem and Earth System Models.
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