Methane formation in tropical reservoirs predicted from sediment age and nitrogen

Freshwater reservoirs, in particular tropical ones, are an important source of methane (CH₄) to the atmosphere, but current estimates are uncertain. The CH₄ emitted from reservoirs is microbially produced in their sediments, but at present, the rate of CH₄ formation in reservoir sediments cannot be predicted from sediment characteristics, limiting our understanding of reservoir CH₄ emission. Here we show through a long-term incubation experiment that the CH₄ formation rate in sediments of widely different tropical reservoirs can be predicted from sediment age and total nitrogen concentration. CH₄ formation occurs predominantly in sediment layers younger than 6-12 years and beyond these layers sediment organic carbon may be considered effectively buried. Hence mitigating reservoir CH₄ emission via improving nutrient management and thus reducing organic matter supply to sediments is within reach. Our model of sediment CH₄ formation represents a first step towards constraining reservoir CH₄ emission from sediment characteristics.