The role of hydropedologic vegetation zones in greenhouse gas emissions for agricultural wetland landscapes

Net greenhouse gas (GHG) source strength for agricultural wetland ecosystems in the Prairie Pothole Region (PPR) is currently unknown. In particular, information is lacking to constrain spatial variability associated with GHG emissions (CH4, CO2, and N2O). GHG fluxes typically vary with edaphic, hydrologic, biologic, and climatic factors. In the PPR, characteristic wetland plant communities integrate hydropedologic factors and may explain some variability associated with trace gas fluxes at ecosystem and landscape scales. We addressed this question for replicate wetland basins located in central North Dakota stratified by hydropedologic vegetation zone on Jul 12 and Aug 3, 2003. Data were collected at the soil-atmosphere interface for six plant zones: deep marsh, shallow marsh, wet meadow, low prairie, pasture, and cropland. Controlling for soil moisture and temperature, CH4 fluxes varied significantly with zone (p<0.05). Highest CH4 emissions were found near the water in the deep marsh (277,800 mu g m(-2) d(-1) CH4), which declined with distance from water to -730 mu g m(-2) d(-1) CH4 in the pasture. Carbon dioxide fluxes also varied significantly with zone. Nitrous oxide variability was greater within zones than between zones, with no significant effects of zone, moisture, or temperature. Data were extrapolated for a 205.6 km(2) landscape using a previously developed synoptic classification for PPR plant communities. For this landscape, we found croplands contributed the greatest proportion to the net GHG source strength on Jul 12 (45,700 kg d(-1) GHG-C equivalents) while deep marsh zones contributed the greatest proportion on Aug 3 (26,145 kg d(-1) GHG-C equivalents). This was driven by a 30-fold reduction in cropland N2O-N emissions between dates. The overall landscape average for each date, weighted by zone, was 462.4 kg km(-2) d(-1) GHG-C equivalents on Jul 12 and 314.3 kg km(-2) d(-1) GHG-C equivalents on Aug 3. Results suggest GHG fluxes vary with hydropedologic soil zone, particularly for CH4, and provide initial estimates of net GHG emissions for heterogeneous agricultural wetland landscapes. (C) 2007 Elsevier B.V All rights reserved.