Anthropogenic Effects on Fluxes of Ecosystem Respiration and Methane in the Yellow River Estuary, China

To evaluate the influence of human activities on ecosystem respiration (CO2) and CH4 fluxes and determine the seasonal and spatial variations, we measured CO2 and CH4 fluxes at four sampling sites (west side of the seawall, WSS; oilfield, OF; Spartina alterniflora coastal marsh, SCM; aquaculture pond, ACP) in the Yellow River estuary from June to December in 2013. Both CO2 and CH4 fluxes showed seasonal and spatial variations in the Yellow River estuary. The average CO2 fluxes from WSS, OF, SCM and ACP were 125.36, 111.03, 241.97 and -39.49 mg CO2 m(-2) h(-1), while CH4 fluxes were -0.0110, -0.0165, 0.2012 and 0.0034 mg CH4 m(-2) h(-1), respectively. Spatial variations of CO2 and CH4 fluxes were mainly affected by vegetation and soil moisture. There were significant relationships between both CO2 fluxes in WSS and SCM and CH4 flux in SCM with temperature. CO2 and CH4 fluxes were mainly affected by the interactions of thermal conditions and other abiotic factors in OF and ACP. Human activities have great effect on greenhouse gas emission, especially in the area where exotic-species S. alterniflora invaded. The construction of seawall blocked sea water transporting into the study area leading to low soil moisture which accelerated CO2 emission. Aquaculture ponds act as an emission of CH4 and consumption of CO2.