Sediment methane production within eutrophic reservoirs: The importance of sedimenting organic matter

Abstract

While temperate reservoirs can be a significant source of atmospheric methane (CH₄), knowledge of the role they play in global emissions of the gas remains limited in line with extreme temporal and spatial variability noted both within and between reservoirs. There is also still no clear identification of the environmental factors influencing the emission of this gas to the atmosphere. This article presents the results of research into the influence of sedimenting matter on CH₄ emission from the surface of different zones of reservoirs. The research were conducted in 2018-2019 within Maziarnia and Nielisz Reservoirs - two artificial bodies of water of eutrophic status both located in SE Poland. Their diffusive CH₄ fluxes at the water-air interface were measured using the "static chamber" method, while sediment traps monitored the rate of accumulation of sedimenting matter in bottom sediments (U_S). The CH₄ fluxes noted at the reservoirs proved highly variable, both temporally and spatially, ranging from 0.02 to over 2500 mmol/m²·d. Determined accumulation indexes were in turn in the 13.61-618.49 g/m²·d range. Nevertheless, CH₄ flux was found to correlate significantly with sedimentation index (U_S), with highest observed values for both reservoirs noted in river zone, while the lowest characterise the lacustrine zone. On this basis, it was hypothesised that sedimentation index may prove a useful tool in estimating CH₄ emissions from reservoirs, with the reverse relationship also likely to apply. Furthermore, the key factor found to be responsible for the aforementioned temporal and spatial variations in CH₄ emissions is primary production, whose subsequent sedimentation supplies sediments with easily-degradable organic matter. The results presented here contribute to an understanding of environmental factors that may influence spatial variation in CH₄ production and can be useful to serve determinate of potential methods by which to reduce emissions this gas from managed systems such as reservoirs.

Keywords: Methane; Reservoir; Sedimenting organic matter; Sediments.