Publication Date:
2011-06-25
Description:
Emissions of methane (CH 4 ), carbon dioxide (CO 2 ), and nitrous oxide (N 2 O) from a forested watershed (160 ha) in South Carolina, USA, were estimated with a spatially explicit watershed-scale modeling framework that utilizes the spatial variations in physical and biogeochemical characteristics across watersheds. The target watershed (WS80) consisting of wetland (23%) and upland (77%) was divided into 675 grid cells, and each of the cells had unique combination of vegetation, hydrology, soil properties, and topography. Driven by local climate, topography, soil, and vegetation conditions, MIKE SHE was used to generate daily flows as well as water table depth for each grid cell across the watershed. Forest-DNDC was then run for each cell to calculate its biogeochemistry including daily fluxes of the three greenhouse gases (GHGs). The simulated daily average CH 4 , CO 2 and N 2 O flux from the watershed were 17.9 mg C, 1.3 g C and 0.7 mg N m −2 , respectively, during the period from 2003–2007. The average contributions of the wetlands to the CH 4 , CO 2 and N 2 O emissions were about 95%, 20% and 18%, respectively. The spatial and temporal variation in the modeled CH 4 , CO 2 and N 2 O fluxes were large, and closely related to hydrological conditions. To understand the impact of spatial heterogeneity in physical and biogeochemical characteristics of the target watershed on GHG emissions, we used Forest-DNDC in a coarse mode (field scale), in which the entire watershed was set as a single simulated unit, where all hydrological, biogeochemical, and biophysical conditions were considered uniform. The results from the field-scale model differed from those modeled with the watershed-scale model which considered the spatial differences in physical and biogeochemical characteristics of the catchment. This contrast demonstrates that the spatially averaged topographic or biophysical conditions which are inherent with field-scale simulations could mask “hot spots” or small source areas with inherently high GHGs flux rates. The spatial resolution in conjunction with coupled hydrological and biogeochemical models could play a crucial role in reducing uncertainty of modeled GHG emissions from wetland-involved watersheds. Content Type Journal Article Pages 1-13 DOI 10.1007/s11270-011-0855-0 Authors Zhaohua Dai, CSRC, EOS, University of New Hampshire, 8 College Rd., Durham, NH 03824, USA Carl C. Trettin, CFWR, USDA Forest Service, 3734 Highway 402, Cordesville, SC 29434, USA Changsheng Li, CSRC, EOS, University of New Hampshire, 8 College Rd., Durham, NH 03824, USA Harbin Li, CFWR, USDA Forest Service, 3734 Highway 402, Cordesville, SC 29434, USA Ge Sun, EFETAC, SRS, USDA Forest Service, 920 Main Campus Dr., Raleigh, NC 27606, USA Devendra M. Amatya, CFWR, USDA Forest Service, 3734 Highway 402, Cordesville, SC 29434, USA Journal Water, Air, & Soil Pollution Online ISSN 1573-2932 Print ISSN 0049-6979
Print ISSN:
0049-6979
Electronic ISSN:
1573-2932
Topics:
Energy, Environment Protection, Nuclear Power Engineering
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