Effects of the addition of nitrogen and sulfate on CH and CO emissions, soil, and pore water chemistry in a high marsh of the Min River estuary in southeastern China.

Exogenous nitrogen (N) and sulfate (SO), resulting from human activity, can strongly influence the emission of CH and CO from soil ecosystems. Studies have reported the effects of N and SO on CH and CO emissions from inland peatlands and paddies. However, very few studies have presented year-round data on the effects of the addition of N and SO on CH and CO emissions in estuarine marshes. The effects of the addition of N and SO on the emission of CH and CO were investigated in a Cyperus malaccensis marsh in the high tidal flat of the Min River estuary of southeastern China from September 2014 to August 2015. Dissolved NHCl, KNO, and KSO were applied every month, in doses of 24gN/SOm·yr. The emission of CH and CO showed distinct monthly and seasonal variations. Compared with the control, the addition of NHCl and NHNO+KSO showed increases in CH fluxes (p<0.05), while the effects of the addition of KNO and KSO on CH were minor (p>0.05). NHCl had a positive impact on CO emissions (p<0.01), while the addition of KNO, KSO, and NHNO+KSO had minor positive impacts, compared to the control (p>0.05). Correlation analysis found that soil sulfate concentration, nitrogen availability and enzyme activity were the dominant factors influencing CH and CO variation. Our findings suggest that CH and CO emissions were influenced more by ammonium than by nitrate. We propose that the suppressive effect of additional sulfate on CH production is insignificant, due to which the inhibition may be overestimated in the estuarine brackish marsh.