Effects of the addition of nitrogen and sulfate on CH4 and CO2 emissions, soil, and pore water chemistry in a high marsh of the Min River estuary in southeastern China

Exogenous nitrogen (N) and sulfate (SO42 −), resulting from human activity, can strongly influence the emission of CH4 and CO2 from soil ecosystems. Studies have reported the effects of N and SO42 − on CH4 and CO2 emissions from inland peatlands and paddies. However, very few studies have presented year-round data on the effects of the addition of N and SO42 − on CH4 and CO2 emissions in estuarine marshes. The effects of the addition of N and SO42 − on the emission of CH4 and CO2 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 NH4Cl, KNO3, and K2SO4 were applied every month, in doses of 24 g N/SO42 − m− 2·yr− 1. The emission of CH4 and CO2 showed distinct monthly and seasonal variations. Compared with the control, the addition of NH4Cl and NH4NO3 + K2SO4 showed increases in CH4 fluxes (p < 0.05), while the effects of the addition of KNO3 and K2SO4 on CH4 were minor (p > 0.05). NH4Cl had a positive impact on CO2 emissions (p < 0.01), while the addition of KNO3, K2SO4, and NH4NO3 + K2SO4 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 CH4 and CO2 variation. Our findings suggest that CH4 and CO2 emissions were influenced more by ammonium than by nitrate. We propose that the suppressive effect of additional sulfate on CH4 production is insignificant, due to which the inhibition may be overestimated in the estuarine brackish marsh.