Spatial and Seasonal Variation of Dissolved Nitrous Oxide in Wetland Groundwater

Understanding the spatial and temporal pattern of dissolved nitrous oxide (N 2 O) in groundwater is essential to estimate the N 2 O emissions from groundwater to the unsaturated zone and to the atmosphere. In order to study the spatial distribution and seasonal change of dissolved N 2 O in wetland, a headwater wetland in Ichikawa, Chiba Prefecture, Japan, was chosen. Variations of nitrate (NO 3 - ), dissolved N 2 O and ? 15 N-NO 3 - indicated that the dissolved N 2 O in the groundwater of study wetland consists of two parts, one from denitrification within the wetland, and another from nitrification at upland. Principal component analysis (PCA) was used to assess the shallow groundwater parameters in the wetland. And t-test was conducted to find statistically significant differences of the variables between the ASW and NS, warm season and cool season. The concentrations of dissolved N 2 O increased from the upland to the zone of adjacent area between slope and wetland (ASW) and then decreased at the zone near the stream (NS). In sight of dissolved N 2 O associated nitrogen migration, groundwater in the study area can be divided into three stages: upland as the stage 1, ASW as the stage 2, and NS as the stage 3. Higher temperature results in higher denitrification rate, lower dissolved oxygen (DO) and oxidation-redox potential (ORP), yielding higher concentration of N 2 O in the warm season. Therefore, the seasonal change of dissolved N 2 O in study wetland can be mainly interpreted by the variation of temperatures of groundwater.