Methane formation in tropical reservoirs predicted from sediment age and nitrogen

Anastasija Isidorova,Raquel Mendonça,Charlotte Grasset,Sebastian Sobek

doi:10.1038/s41598-019-47346-7

Anastasija Isidorova, Raquel Mendonça + Show 2 more

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https://doi.org/10.1038/s41598-019-47346-7

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Abstract

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.

Highlights

Methane (CH4) is a potent greenhouse gas that contributes to climate change with a global warming potential 34 times greater than carbon dioxide (CO2) at a 100 year time scale[1]
We suggest that the importance of total N (TN) may be related to the amount, source and diagenetic state of the sediment organic matter (OM)
The TN concentration in the sediment is representative of the OM source[37]: autochthonous OM is comparatively rich in protein and poor in cellulose, while allochthonous OM is protein-poor and rich in lignocellulose

Summary

Introduction

Methane (CH4) is a potent greenhouse gas that contributes to climate change with a global warming potential 34 times greater than carbon dioxide (CO2) at a 100 year time scale[1]. At an estimated global organic carbon (OC) burial rate of 0.06 Pg C year−1 in reservoir sediments[7], there is apparently a large supply of organic substrate to the methanogenic microbes that live in anoxic sediments of reservoirs. At timescales relevant in sediments (years), the effect of decreasing reactivity during OM decomposition on sediment CH4 formation is currently not clear. Sediment CH4 formation can at present not be predicted at environmentally relevant timescales (years), severely limiting our understanding of the globally important function of reservoir sediments as both sinks of OC and sources of atmospheric CH4. We investigate the impact of OM source, characteristics and age on CH4 formation rates in sediment of three widely different tropical reservoirs. Www.nature.com/scientificreports sediment varying in age between 1 and 48 years, in order to understand CH4 formation in reservoir sediments over the typical lifetime of reservoirs. We expected a decrease of CH4 formation potential with increasing sediment age, and lower CH4 formation in the sediment of a reservoir with little autochthonous OM production than in a reservoir with high autochthonous OM production

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