Sediment Properties Drive Spatial Variability of Potential Methane Production and Oxidation in Small Streams

Abstract

Emissions of the potent greenhouse gas methane (CH 4 ) from streams and rivers are a significant component of global freshwater methane emissions. The distribution of CH 4 production and oxidation within stream sections and in vertical sediment profiles is not well understood, and the environmental controls on CH 4 production and emission in such systems create a significant challenge for assessing larger-scale dynamics. Here we investigate factors driving the spatial variability of sediment potential methane production (PMP) and potential methane oxidation (PMO) in a temperate stream network in Germany. PMP was highly variable, ranging from 5 × 10 −4 to 28.58 μg CH 4 gDW −1 d −1 and PMO ranged from 0.43 μg CH 4 gDW −1 d −1 to 14.41 μg CH 4 gDW −1 d −1 . Important drivers of spatial variability of PMP and PMO in the sediments of the stream main-stem were related to fine sediment fraction and organic carbon content. At smaller spatial scale, that is, in a sub-catchment stream section, the drivers were more complex and included sediment nitrogen and organic carbon content, as well as porewater dissolved organic carbon, dissolved organic matter quality, and metal concentrations. As with reservoirs and impounded rivers, fine sediment deposition and organic carbon content were found to be key controls on the spatial variability of CH 4 production and oxidation. These findings enhance our understanding of CH 4 dynamics, improve the potential for identifying CH 4 production hotspots in small streams, and provide a potential means for upscaling emission rates in larger-scale assessments.Plain Language Summary Globally, streams and rivers emit a significant amount of the highly potent greenhouse gas methane. The methane emitted from streams is mainly produced in sediments. The distribution of production and consumption in stream sections and sediment profiles is not well understood, which creates a significant challenge for estimating, for example, regional methane emissions from streams and rivers. We investigated possible factors controlling the variability from site to site and different depths of methane production and consumption in sediments of a stream network in south-west Germany. Sediment properties, the amount of fine sediment and organic carbon content, were key drivers of this variability in the main stream. In a smaller side arm of the main stream, the drivers were more complex, including nitrogen and organic carbon content of the sediment, but also porewater dissolved organic carbon, dissolved organic matter quality, and metals. As for reservoirs and dammed rivers, the accumulation of fine sediments and organic carbon content was found to be key controls of sediment methane production and consumption. These findings enhance our understanding of methane dynamics, improve the potential for identifying methane production hotspots in small streams, and provide a potential means for upscaling emission rates in larger-scale assessments.

Integrating Ecosystem Patch Contributions to Stream Corridor Carbon Dioxide and Methane Fluxes

“…The valley and channel gradient of the WS55 subcatchment may be responsible for stream CH 4 undersaturation: with lower organic matter and fewer sources of CH 4 , water flowing over steep gradients remains well oxygenated allowing CH 4 oxidation to use what little CH 4 is available. In reaches of small streams with high spatial variability in CH 4 production and oxidation, sediment nitrogen content was positively correlated with CH 4 production and oxidation (Bodmer et al., 2020). Because stream nitrogen concentrations vary among subwatersheds at Coweeta and over time, with forested streams typically having low stream nitrogen (Knoepp & Swank, 1997; Webster et al., 2016), future work characterizing differences in sediment nutrient contents may provide valuable insights into drivers of CH 4 from our study streams.…”

Spatial and temporal heterogeneity of methane ebullition in lowland headwater streams and the impact on sampling design

“…2c). This variability may be caused by sediment properties that promote CH 4 production at microsites within the sediment (Bodmer et al 2020) or from preferential paths for bubble movement out of the sediment (Delsontro et al 2015), which we did not measure. Relatedly, some studies have found preferential sites for ebullition near aquatic edges (Bastviken et al 2008;Holgerson and Raymond 2016).…”

Abundance and biogeography of methanogenic and methanotrophic microorganisms across European streams

“…Data on potential CH 4 oxidation (PMO) in freshwater ecosystems are also scarce (e.g. Oswald et al., 2015), but it was shown that PMO from river sediments increased with decreasing gravel size (Bodmer et al., 2020). Additional drivers of such distributions and rates in stream sediments have not been identified so far.…”