Effects of methyl halide flux characteristics following Spartina alterniflora invasion in a seaward direction in a temperate salt marsh, China.

In this study, we explored the source-sink characteristics of methyl halide (CHX; X = Cl, Br, I) in coastal wetlands located in temperate regions, and identified key factors affecting the spatio-temporal variation of CHX during the invasion of Spartina alterniflora. We used static chamber-gas chromatography to monitor CHX fluxes in the S. alterniflora area and bare flat area of the Jiaozhou Bay salt marsh for a long time from August 2015 to May 2017. Our results indicated that CHX emissions showed obvious seasonal and diurnal variations. The S. alterniflora area was a source of CHX, with higher fluxes in the spring and autumn seasons. CHX fluxes were higher during the daytime than at night, and the diurnal difference in CHBr was the most significant (4.51 times). The bare flat area was mainly a sink for CHX, and the maximum absorption flux occurred in summer. At this time, the microbial activity was greater, and the consumption rate during the day was higher than that at night. Extreme linear correlations existed between the fluxes of CHCl, CHBr, and CHI (P < 0.01), indicating that the production and consumption of the three gases were likely to have similar mechanisms and were affected by the same factors. S. alterniflora invasion increased CHX emissions and shifted the original bare flat area from a sink to a source of CHX. The biomass of S. alterniflora, especially the leaf, significantly affects CHX fluxes. Additionally, S. alterniflora increased the content of total organic carbon, total sulfur, available sulfur, and iron (III) in the soil, which were the main factors promoting the source-sink transformation of CHX. Based on the current invasive area of S. alterniflora in China, we estimated that the annual emissions of CHCl, CHBr, and CHI from S. alterniflora into the troposphere were 9.04 × 10, 2.42 × 10 and 2.06 × 10 mol, respectively.