Diel and seasonal variability of methane emissions from a shallow and eutrophic pond

Abstract. Ponds play a critical role in biogeochemical carbon cycling and have been identified as hot spots of methane (CH₄) emission. Yet, most existing studies focused on ponds in the boreal zone and current estimates of the relevance of ponds in global CH₄ budgets as well as knowledge of the environmental factors regulating their emissions are poorly constrained. Both nutrient concentration and temperature can potentially alter CH₄ dynamics in shallow ponds, but there are still few investigations into the response of CH₄ emission to nutrient enrichment and rising temperatures. Here we studied the magnitude and regulation of two CH₄ pathways (diffusion and ebullition) from a shallow and eutrophic pond located in the subtropical zone in Central China. Ebullitive fluxes were on average 96.4 mg CH₄ m⁻² d⁻¹ and contributed 88.6 % to the total (diffusive + ebullition) CH₄ emissions. Daily CH₄ fluxes were related to daily mean water temperature, with ebullition having a stronger temperature dependence than diffusion (Q₁₀ of 5.52 vs. 2.05). Relationships between temperature and CH₄ emission were affected by seasonal variation of the concentration of total phosphorus. The temperature dependence of both ebullitive and diffusive fluxes increased with increasing phosphorous concentration. Our study highlights that increasing eutrophication by anthropogenic impacts and climate warming will increase CH₄ emissions from ponds, thus representing a positive feedback mechanism to global warming.