Abstract
Aquatic macrophytes in shallow lakes emit high levels of methane. We hypothesize that the presence of emergent aquatic macrophytes in an artificial shallow lake promotes important input of autochthonous organic matter (OM) in sediment and higher levels of methane emission via bubbles. Samplings were performed at three sites in a small, shallow subtropical lake: (1) one station in the limnetic region and (2) - (3) two stations in the littoral region ((2) inside and (3) outside aquatic macrophyte stands). A higher concentration of OM was observed at the macrophyte station, and within this site, a higher methane concentration was observed in the sediment. These results could explain the methane ebullition values at macrophyte sites. At the macrophyte station, methane emission via bubbles contributed 17% to 56% of the total methane emission; however, at the other stations, its contribution via bubbles, was lower than 1%. This research confirmed the importance of emergent macrophytes at Polegar Lake as a source of OM in sediment and methane emission via bubbles. Further, we could confirm the positive effects of temperature on methane emission, mainly by bubbles.
Highlights
Methane emissions from global freshwater systems represent a significant contribution to the global balance of greenhouse gases [1]
Studies on methane dynamics in shallow lakes in southern Brazil have shown that a variation of almost 10 ̊C between sampling periods was positively related to the concentration of methane, indicating the importance of seasonality, mainly in an oligo-mesotrophic environment [10]
The hypothesis of this study is that the presence of emergent aquatic macrophytes in an artificial shallow lake promotes important input of autochthonous organic matter (OM) for sediment and higher methane emission via bubbles
Summary
Methane emissions from global freshwater systems represent a significant contribution to the global balance of greenhouse gases [1]. Recent estimates of the global number of lakes [13] indicate the great importance of small lakes for methane emission These ecosystems present higher methane fluxes per unit area than larger lakes [14]. The presence of macrophytes can modify sediment composition via the accumulation of detritus [16], which is refractory in nature [17] These plants are morphologically adapted to grow in anoxic sediments; for example, they develop aerenchyma tissue that supplies their roots with O2. The hypothesis of this study is that the presence of emergent aquatic macrophytes in an artificial shallow lake promotes important input of autochthonous organic matter (OM) for sediment and higher methane emission via bubbles
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