Effect of hydrological conditions on nitrous oxide, methane, and carbon dioxide dynamics in a bottomland hardwood forest and its implication for soil carbon sequestration

Abstract

This study was conducted at three locations in a bottomland hardwood forest with a distinct elevation and hydrological gradient: ridge (high, dry), transition, and swamp (low, wet). At each location, concentrations of soil greenhouse gases (N 2 O, CH 4 , and CO 2 ), their fluxes to the atmosphere, and soil redox potential (Eh) were measured bimonthly, while the water table was monitored every day. Results show that soil Eh was significantly (Po0.001) correlated with water table: a negative correlation at the ridge and transition locations, but a positive correlation at the permanently flooded swamp location. Both soil gas profile analysis and surface gas flux measurements indicated that the ridge and transition locations could be a sink of atmospheric CH 4 , especially in warm seasons, but generally functioned as a minor source of CH 4 in cool seasons. The swamp location was a major source of CH 4 , and the emission rate was higher in the warm seasons (mean 28 and median 23 mg m À2 h À1 ) than in the cool seasons (both mean and median 13 mg m À2 h À1 ). Average CO 2 emission rate was 251, 380 and 52 mg m À2 h À1 for the ridge, transition and swamp location, respectively. At each location, higher CO 2 emission rates were also found in the warm seasons. The lowest CO 2 emission rate was found at the swamp location, where soil C content was the highest, due to less microbial biomass, less CO 2 production in such an anaerobic environment, and greater difficulty of CO 2 diffusion to the atmosphere. Cumulative global warming potential emission from these three greenhouse gases was in an order of swamp4transition4ridge location. The ratio CO 2 /CH 4 production in soil is a critical factor for evaluating the overall benefit of soil C sequestration, which can be greatly offset by CH 4 production and emission.

Spatiotemporal Variations in Nitrous Oxide Emissions from an Open Fen on the Qinghai–Tibetan Plateau: a 3-Year Study

“…Though there was no significant relation between standing water depths and N 2 O emissions, we still considered this related to the temporal dynamics of soil water regime (water tables or standing water depths), which is usually regarded as one of the most important factors controlling N 2 O emissions in variable ecosystems (Mosier et al 1991;Yu et al 2008;Wolf et al 2010). Moreover, temporal dynamics of soil water regime in wetland soils is sensitive to seasonal and inter-annual weather patterns, which will affect the environmental drivers for N-transformation processes (Jørgensen et al 2012).…”

A full greenhouse gases budget of Africa: synthesis, uncertainties, and vulnerabilities

“…Nearly a quarter of the year-to-year variation in the global-scale exchange of CO 2 between land and atmosphere can be attributed to the African continent (Williams et al, 2007). The major source of this variability is gross primary productivity whose variation exceeds that of ecosystem respiration Weber et al, 2009; a EFs from S. Castaldi (personal communication, 2013), Yu et al (2008). b EFs from Castaldi et al (2006).…”

Methane exchange in a boreal forest estimated by gradient method

“…Soil moisture and soil texture influence the soil diffusivity and thus the flux of CH 4 and oxygen from the atmosphere to the soil depths where CH 4 is consumed (Born et al, 1990;Koschorreck and Conrad, 1993;Whalen and Reeburgh, 1996), while water table depth alters the relative extent of anaerobic and aerobic zones in the soil (Whalen and Reeburgh, 1990). Soil moisture and water table depth vary spatially due to, for example, topography, which results in spatial variations of CH 4 exchange (Lessard et al, 1994;Yu K. W. et al, 2008). There is also a temporal variability in CH 4 exchange, mainly due to changes in temperatures and precipitation (Castro et al, 1994;Guckland et al, 2009).…”