Anaerobic Oxidation of Methane in Freshwater Sediments of Rzeszów Reservoir

Dorota Szal,Renata Gruca-Rokosz

doi:10.3390/w12020398

Abstract

The anaerobic oxidation of methane (AOM) is an important sink of methane that plays a significant role in global warming. However, evidence for the AOM in freshwater habitats is rare, especially in dam and weir (small-scale dam) reservoirs. Here, the AOM process was examined in freshwater sediments of a small-scale dam reservoir located in Rzeszów, SE Poland. The AOM rate was determined in the main experiment with the addition of the 13CH4 isotope marker (He+13CH4). Sediments were collected three times: in spring (in May, 15 °C), in summer (in July, 20 °C) and in autumn (in September, 10 °C). Further analysis considers the impact on AOM rate of potential electron acceptors present in pore-water (NO2−, NO3−, SO42−, and Fe3+ ions). The work suggests that an AOM process does take place in the studied reservoir sediments, with this evidenced by the presence in the headspace of an increased 13CO2 concentration deemed to derive from 13CH4 oxidation. Rates of AOM noted were of 0.36–1.42 nmol·g−1·h−1, with the most intensive oxidation in each sediment layer occurring at 20 °C. While none of the potential electron acceptors considered individually were found to have had a statistically significant influence on the AOM rate, their significance to the dynamics of the AOM process was not precluded.

Highlights

Methane (CH4 ) is an important gaseous atmospheric pollutant contributing to the greenhouse effect through its capacity to capture heat 23 times more effectively than carbon dioxide (CO2 ), as the best-known greenhouse gas
It is possible that the combination of electron acceptors and their pathways for CH4 oxidation may be present in the sediments from Rzeszów Reservoir
Anaerobic oxidation of methane (AOM) is a process occurring in freshwater sediments, i.e., at Rzeszów, given that a 13 CH4 isotopic marker added in the course of incubation trials underwent systematic oxidation to 13 CO2

Summary

Introduction

Methane (CH4 ) is an important gaseous atmospheric pollutant contributing to the greenhouse effect through its capacity to capture heat 23 times more effectively than carbon dioxide (CO2 ), as the best-known greenhouse gas. There is strong evidence that inland waters (especially dam reservoirs) can play a role in the global dynamics of greenhouse gases that is disproportionate, given the way these cover just 3.6% of the Earth’s surface [2,3], yet may well account for 16% of total CH4 emissions to the atmosphere [4,5,6]. Organic matter is the most frequent electron donor in the natural environment, but recent studies have shown how CH4 may affect the growth of microorganisms under anaerobic conditions significantly [12]. This suggests a role for methane itself as an electron donor, with the acceptors being nitrates (NO3 − ), manganese (Mn4+ ), iron (Fe3+ ), or sulphates (SO4 2− ).

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Conclusion