Title: Effects of reclamation on net ecosystem CO_2 exchange in wetland in the Yellow River Delta, China
Abstract: Aims Wetland ecosystems are an obvious carbon sink, but with constant land reclamation, many wetlands disappeared and degenerated, and reclamation also influences the carbon-cycle between wetland ecosystems and the atmosphere. Cropland is a dominant use of reed (Phragmites australis) wetland in the Yellow River Delta, but the CO2 flux of wetland ecosystems under escalating human influences remains unclear. Our objective was to investigate the impact of wetland reclamation on net ecosystem CO2 exchange (NEE) dynamics and quantify CO2 exchange of the two ecosystems’ response to environmental and biological factors. Methods Based on eddy covariance technique, we measured CO2 fluxes over the reed wetland and cropland ecosystems and monitored environmental and biological factors in 2011. Important findings The averaged diurnal variation of NEE showed the U-type curve in different months of the growing season over wetland and cropland ecosystems. In the non-growing season, NEE lacked a diurnal pattern and the range of NEE was very small as the result of soil microbial activity. Analyses of NEE showed that the wetland was a net sink for each month from April to September 2011 and a source of CO2 to the atmosphere for the fall and winter months of November to March. In contrast, the cropland was calculated to be a significant net sink for CO2 in the growing season (May to October), while significant net losses of CO2 occurred in the non-growing season (November to April). During the growing season, the maximum daily CO2 uptake and release rates were 16.04 (August 17) and 14.95 (August 9) g CO2·m–2·d–1 and 18.99 (August 22) and 12.23 (July 29) g CO2·m–2·d–1 over wetland and cropland, respectively. Daytime NEE values were strongly correlated with photosynthetic activeradiation (PAR) in the growing season. The CO2 flux was mainly affected by temperature of soil (Ts) in the non-growing season. Soil water content (SWC) and T s were the main factors that influenced nighttime NEE in the growing season. The two ecosystem respiration quotient (Q10) were 2.30 (wetland) and 3.78 (cropland) during the growing season. The wetland and cropland ecosystems were both carbon sinks during the growing season as they absorbed 780.95 and 647.35 g CO2·m-2 , respectively, which means wetland reclamation can reduce its carbon sequestration ability. During the non-growing season, the two ecosystems were carbon sources, releasing 181.90 (wetland ecosystem) and 111.55 (cropland ecosystem) g CO2·m–2 . Over all of 2011, the wetland and cropland ecosystems both were obvious carbon sinks with absorption of 599.05 and 535.80 g CO2·m–2, respectively.
Publication Year: 2013
Publication Date: 2013-01-01
Language: en
Type: article
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