Abstract
Globally, rivers and streams are important sources of carbon dioxide and methane, with small rivers contributing disproportionately relative to their size. Previous research on greenhouse gas (GHG) emissions from surface water lacks mechanistic understanding of contributions from streambed sediments. We hypothesise that streambeds, as known biogeochemical hotspots, significantly contribute to the production of GHGs. With global climate change, there is a pressing need to understand how increasing streambed temperatures will affect current and future GHG production. Current global estimates assume linear relationships between temperature and GHG emissions from surface water. Here we show non-linearity and threshold responses of streambed GHG production to warming. We reveal that temperature sensitivity varies with substrate (of variable grain size), organic matter (OM) content and geological origin. Our results confirm that streambeds, with their non-linear response to projected warming, are integral to estimating freshwater ecosystem contributions to current and future global GHG emissions.
Highlights
Sami Ullah[1], Nicholas Kettridge[1], Globally, rivers and streams are important sources of carbon dioxide and methane, with small rivers contributing disproportionately relative to their size
Increased temperature generally led to a rise in sediment respiration and greenhouse gas (GHG) production in the investigated streambed sediments
We found the temperature sensitivity of streambed sediment respiration and GHG production to be dependent on substrate, organic matter (OM) content and geological origin, with the greatest reactivity, and largest responses to increased temperature, found in the fine, high OM content sediments
Summary
Sami Ullah[1], Nicholas Kettridge[1], Globally, rivers and streams are important sources of carbon dioxide and methane, with small rivers contributing disproportionately relative to their size. Previous research on greenhouse gas (GHG) emissions from surface water lacks mechanistic understanding of contributions from streambed sediments. Current global estimates assume linear relationships between temperature and GHG emissions from surface water. Our results confirm that streambeds, with their non-linear response to projected warming, are integral to estimating freshwater ecosystem contributions to current and future global GHG emissions. Previous research has mainly quantified surface water contributions[8,9,10,11] estimating global fluxes from streams and rivers to be 1.8 Pg CO2-C yr−1 8, and 26.8 Tg CH4-C yr−1 12. Despite recent advances in analysing freshwater carbon cycling, the spatially and temporally variable drivers of enhanced GHG production in streambed sediments, CH4:CO2 ratios and the relative importance of sediment GHG to overall C emissions[2,5,7,28,29] remain insufficiently understood[1,5,7]
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