Binfeng Sun

Surface methane emissions from different land use types during various water levels in three major drawdown areas of the Three Gorges Reservoir

Methane (CH4) emissions from the drawdown area of the Three Gorges Reservoir (TGR) have not been thoroughly investigated even though the drawdown area encompasses one third of the reservoir surface. In this study, CH4 emissions from different land uses were measured in the TGR drawdown area. The average diffusive CH4 emissions were 2.61, 0.19, 0.18, and 0.12 mg CH4 m(-2) h(-1) in rice paddies, fallow lands, deforested lands, and croplands, respectively, and were positively related to the duration of the inundated season among the latter three land uses. On average the drawdown areas studied here (except rice paddies) were sources in the inundated season (0.22 +/- 0.26 mg CH4 m(-2) h(-1)) and a sink in the drained season (-0.008 +/- 0.035 mg CH4 m(-2) h(-1)). The water level was the dominant factor that controlled whether the drawdown area was either inundated or drained, which in turn determined whether the drawdown area was a source or sink of CH4 emissions. The average diffusive CH4 emissions from the fallow lands, croplands, and deforested lands increased as the distance from the dam increased from Zigui (0.10 +/- 0.15 mg CH4 m(-2) h(-1)) to Wushan (0.15 +/- 0.29 mg CH4 m(-2) h(-1)) to Yunyang (0.24 +/- 0.27 mg CH4 m(-2) h(-1)), which could reflect different sediment characteristics and water velocities. The total CH4 emission from the drawdown area was estimated to range from 1033.5 to 1333.9 Mg CH4 yr(-1), which would account for 42-54% of the total CH4 emissions from the water surface of TGR.

The effects of nitrogen fertilizer application on methane and nitrous oxide emission/uptake in Chinese croplands

Abstract The application of nitrogen (N) fertilizer to increase crop yields has a significant influence on soil methane (CH 4 ) and nitrous oxide (N 2 O) emission/uptake. A meta-analysis was carried out on the effect of N application on (i) CH 4 emissions in rice paddies, (ii) CH 4 uptake in upland fields and (iii) N 2 O emissions. The responses of CH 4 emissions to N application in rice paddies were highly variable and overall no effects were found. CH 4 emissions were stimulated at low N application rates ( −1 ) but inhibited at high N rates (>200 kg N ha −1 ) as compared to no N fertilizer (control). The response of CH 4 uptake to N application in upland fields was 15% lower than control, with a mean CH 4 uptake factor of −0.001 kg CH 4 -C kg −1 N. The mean N 2 O emission factors were 1.00 and 0.94% for maize ( Zea mays ) and wheat ( Triticum aestivum ), respectively, but significantly lower for the rice ( Oryza sativa ) (0.51%). Compared with controls, N addition overall increased global warming potential of CH 4 and N 2 O emissions by 78%. Our result revealed that response of CH 4 emission to N input might depend on the CH 4 concentration in rice paddy. The critical factors that affected CH 4 uptake and N 2 O emission were N fertilizer application rate and the controls of CH 4 uptake and N 2 O emission. The influences of application times, cropping systems and measurement frequency should all be considered when assessing CH 4 and N 2 O emissions/uptake induced by N fertilizer.

Effects of drought on net primary productivity: Roles of temperature, drought intensity, and duration

Northeast China has experienced frequent droughts over the past fifteen years. However, the effects of droughts on net primary productivity (NPP) in Northeast China remain unclear. In this paper, the droughts that occurred in Northeast China between 1999 and 2013 were identified using the Standardized Precipitation Evapotranspiration Index (SPEI). The NPP standardized anomaly index (NPP-SAI) was used to evaluate NPP anomalies. The years of 1999, 2000, 2001, and 2007 were further investigated in order to explore the influence of droughts on NPP at different time scales (3, 6, and 12 months). Based on the NPP-SAI of normal areas, we found droughts overall decreased NPP by 112.06 Tg C between 1999 and 2013. Lower temperatures at the beginning of the growing season could cause declines in NPP by shortening the length of the growing season. Mild drought or short-term drought with higher temperatures might increase NPP, and weak intensity droughts intensified the lag effects of droughts on NPP.