Soil greenhouse gas emissions and carbon budgeting in a short-hydroperiod floodplain wetland

• Published in: Journal of geophysical research. Biogeosciences 2015-01, Vol.120 (1), p.77-95
• Main Authors: Batson, Jackie, Noe, Gregory B., Hupp, Cliff R., Krauss, Ken W., Rybicki, Nancy B., Schenk, Edward R.
• Format: Article
• Language: English
• Subjects: Air pollution; Anaerobic respiration; Aquatic ecosystems; Budgeting; Carbon; Carbon dioxide; Carbon dioxide emissions; Drying; Emissions; floodplain; Floodplains; Floods; geomorphology; Greenhouse gases; hydrologic connectivity; Levees; Methane; Moisture content; Nitrous oxide; Nitrous oxides; Respiration; riparian; Rivers; Sedimentation; Sedimentation & deposition; Soil (material); Soil gases; Soil water; Texture; Urbanization; Vegetation; Watersheds
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1002/2014JG002817

Understanding the controls on floodplain carbon (C) cycling is important for assessing greenhouse gas emissions and the potential for C sequestration in river‐floodplain ecosystems. We hypothesized that greater hydrologic connectivity would increase C inputs to floodplains that would not only stimulate soil C gas emissions but also sequester more C in soils. In an urban Piedmont river (151 km2 watershed) with a floodplain that is dry most of the year, we quantified soil CO2, CH4, and N2O net emissions along gradients of floodplain hydrologic connectivity, identified controls on soil aerobic and anaerobic respiration, and developed a floodplain soil C budget. Sites were chosen along a longitudinal river gradient and across lateral floodplain geomorphic units (levee, backswamp, and toe slope). CO2 emissions decreased downstream in backswamps and toe slopes and were high on the levees. CH4 and N2O fluxes were near zero; however, CH4 emissions were highest in the backswamp. Annual CO2 emissions correlated negatively with soil water‐filled pore space and positively with variables related to drier, coarser soil. Conversely, annual CH4 emissions had the opposite pattern of CO2. Spatial variation in aerobic and anaerobic respiration was thus controlled by oxygen availability but was not related to C inputs from sedimentation or vegetation. The annual mean soil CO2 emission rate was 1091 g C m−2 yr−1, the net sedimentation rate was 111 g C m−2 yr−1, and the vegetation production rate was 240 g C m−2 yr−1, with a soil C balance (loss) of −338 g C m−2 yr−1. This floodplain is losing C likely due to long‐term drying from watershed urbanization. Key Points Soil CO2, CH4, and N2O emissions were independent of C inputs CO2 and CH4 fluxes varied along gradients in soil wetness and texture This floodplain is losing C likely due to long‐term drying from urbanization