Responses of CH4 emissions to nitrogen addition and Spartina alterniflora invasion in Minjiang River estuary, southeast of China

Abstract

Abstract:The nitrogen (N) input and Spartina alterniflora invasion in the tidal marsh of the southeast of China are increasingly serious. To evaluate CH 4 emissions in the tidal marsh as affected by the N inputs and S. alterniflora invasion, we measured CH 4 emissions from plots with vegetated S. alterniflora and native Cyperus malaccensis, and fertilized with exogenous N at the rate of 0 (N0), 21 (N1) and 42 (N2) g N/(m 2 ·yr), respectively, in the Shanyutan marsh in the Minjiang River estuary, the southeast of China. The average CH 4 fluxes during the experiment in the C. malaccensis and S. alterniflora plots without N addition were 3.67 mg CH 4 /(m 2 ·h) and 7.79 mg CH 4 /(m 2 ·h), respectively, suggesting that the invasion of S. alterniflora into the Minjiang River estuary stimulated CH 4 emission.Exogenous N had positive effects on CH 4 fluxes both in native and in invaded tidal marsh. The mean CH 4 fluxes of N1 and N2 treatments increased by 31.05% and 123.50% in the C. malaccensis marsh, and 63.88% and 7.55% in the S. alterniflora marsh, respectively, compared to that of N0 treatment. The CH 4 fluxes in the two marshes were positively correlated with temperature and pH, and negatively correlated with electrical conductivity and redox potential (Eh) at different N addition treatments. While the relationships between CH 4 fluxes and environmental variables (especially soil temperature, pH and Eh at different depths) tended to decrease with N additions. Significant temporal variability in CH 4 fluxes were observed as the N was gradually added to the native and invaded marshes. In order to better assess the global climatic role of tidal marshes as affected by N addition, much more attention should be paid to the short-term temporal variability in CH 4 emission.

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

“…The average salinity of the tidal water was 4.2 ± 2.5 (Tong et al, 2014). The dominant type of soil was coastal saline soil (Mou et al, 2014). The main vegetation types include the native species Cyperus malaccensis, Phragmites australis, and the invasive species Spartina alterniflora .…”

“…The doses of N and SO 4 2applied in this study were 5-and 3-times higher than the natural deposition, respectively. Such large amounts of N and SO 4 2were applied to evaluate GHG emissions due to N-and SO 4 2--saturated conditions that may occur in the future (Zhang et al, 2007;Mou et al, 2014). N and SO 4 2powders were dissolved in 600 mL of deionized water and evenly sprayed over the plots once a month for a total of 12 equal applications throughout the year.…”

“…Control plots were watered with the same quantity (600 mL) of deionized water. In order to maximize the retention of the treatment solution in the experimental plots, irrigation was carried out after the ebb of the neap tide (Moseman-Valtierra et al, 2011;Mou et al, 2014). Furthermore, to minimize the disturbance to the measurement sites during sampling, a wooden access boardwalk was constructed adjacent to the experimental blocks.…”

“…Coastal estuarine marshes, located along the intersection between sea and land, can sequester C at higher rates compared to other ecosystems (Moseman-Valtierra et al, 2011). In recent years, the increasing intensity of human activities has caused the enrichment of N and SO 4 2in near-shore waters, becoming a key factor in changing the biogeochemical cycle of these environments (Thang et al, 2013;Mou et al, 2014).…”

“…According to a recent report, the subtropical Shanyutan estuarine tidal marsh in the Min River estuary has been receiving a large amount of N and SO 4 2due to upstream and tidal action (Fujian Provincial Oceanic and Fishery Administration, 2016). Studies on the influence of high N and SO 4 2loading on CH 4 and CO 2 emissions in natural subtropical estuarine tidal marshes can enhance the current GHG emissions inventory, especially for China, where little previous work has been carried out (Moseman-Valtierra et al, 2011;Mou et al, 2014). The goals of the present work were to: (1) quantify the individual and combined effects of the addition of N and SO 4 2on CH 4 and CO 2 emissions; (2) determine the effects of the addition of N and SO 4 2-on soil and pore water chemistry; and (3) investigate the factors responsible for changes in CH 4 and CO 2 emission induced by the addition of N and SO 4 2-.…”