An empirical model to predict methane production in inland water sediment from particular organic matter supply and reactivity

The highest CH4 production rates can be found in anoxic inland water surface sediments however no model quantifies CH4 production following fresh particular organic matter (POM) deposition on anoxic sediments. This limits our capability of modeling CH4 emissions from inland waters to the atmosphere. To generate such a model, we quantified how the POM supply rate and POM reactivity control CH4 production in anoxic surface sediment, by amending sediment at different frequencies with different quantities of aquatic and terrestrial POM. From the modeled CH4 production, we derived parameters related to the kinetics and the extent of CH4 production. We show that the extent of CH4 production can be well predicted by the quality (i.e., C/N ratio) and the quantity of POM supplied to an anoxic sediment. In particular, within the range of sedimentation rates that can be found in aquatic systems, we show that CH4 production increases linearly with the quantity of phytoplankton-derived and terrestrially derived POM. A high frequency of POM addition, which is a common situation in natural systems, resulted in higher peaks in CH4 production rates. This suggests that relationships derived from earlier incubation experiments that added POM only once, may result in underestimation of sediment CH4 production. Our results quantitatively couple CH4 production in anoxic surface sediment to POM sedimentation flux, and are therefore useful for the further development of mechanistic models of inland water CH4 emission