Nutrient loading caused by human activities can drive changes in methane (CH₄) production pathways, yet the mechanisms and magnitudes of estuary CH₄ emissions remain poorly understood. Here we investigated CH₄ fluxes and δ¹³C-CH₄ values in wet and dry seasons from five subtropical estuaries with varying human activity intensity and hydrologic conditions. Water dissolved CH₄ concentrations varied from 0.19 to 0.51 µmol CH₄ L^–1 in these studied estuaries, resulting in coincident water–air CH₄ fluxes ranging from 5.46 to 29.6 µg CH₄ m^–2h⁻¹. Water CH₄ concentrations and fluxes were significantly lower in the wet than dry season, and were higher in the high human-impacted estuaries, indicating that large discharge and water flow could slow down areal CH₄ emissions. The ratios of C-CH₄ to organic carbon (OC) were much higher and showed a positive response to increasing nitrogen concentrations in high human-impacted estuaries, suggesting that eutrophic estuaries trigger high CH₄ emissions. In addition, an increase in δ¹³C-CH₄ and a declining in fractionation factor (α_app) from the low to high human-impacted estuaries were accompanied by a switch of CH₄ production from hydrogenotrophic to acetoclastic pathways. These results suggest that human activity intensity can drive the alterations in the pathways and magnitudes of CH₄ production and that hydrologic conditions can modify CH₄ emissions, which have important implications for estimates of CH₄ emissions from global estuaries under increasing human activity intensity.

人类活动引起的营养负荷可以推动甲烷 (CH ₄ ) 生产途径的变化，但对河口 CH ₄排放的机制和量级仍知之甚少。在这里，我们调查了人类活动强度和水文条件不同的五个亚热带河口在湿季和旱季的 CH ₄通量和δ ¹³ C-CH _4值。在这些研究的河口，水中溶解的 CH ₄浓度从 0.19 到 0.51 µmol CH ₄ L ^–1不等，导致水-空气 CH ₄通量一致，范围从 5.46 到 29.6 µg CH ₄ m ^–2 h^-1。湿季水体 CH ₄浓度和通量显着低于旱季，而在人为影响高的河口则更高，表明大流量和水流可以减缓区域 CH ₄排放。C-CH ₄与有机碳 (OC) 的比率要高得多，并且对人为影响高的河口中氮浓度的增加表现出积极的反应，这表明富营养化的河口会引发高 CH ₄排放。此外，从低人类影响河口到高人类影响河口，δ ¹³ C-CH ₄的增加和分馏因子 ( α _app ) 的下降伴随着 CH 的转换₄从氢营养到乙酸分解途径的生产。这些结果表明，人类活动强度可以驱动 CH ₄产生的路径和量级的改变，并且水文条件可以改变 CH ₄排放，这对于在人类活动强度增加的情况下估算全球河口的 CH _{4排放具有重要意义。}