Intermittent rivers and ephemeral streams (IRES) may represent over half the global stream network, but their contribution to respiration and carbon dioxide (CO2) emissions is largely undetermined. In particular, little is known about the variability and drivers of respiration in IRES sediments upon rewetting, which could result in large pulses of CO2. We present a global study examining sediments from 200 dry IRES reaches spanning multiple biomes. Results from standardized assays show that mean respiration increased 32‐fold to 66‐fold upon sediment rewetting. Structural equation modeling indicates that this response was driven by sediment texture and organic matter quantity and quality, which, in turn, were influenced by climate, land use, and riparian plant cover. Our estimates suggest that respiration pulses resulting from rewetting of IRES sediments could contribute significantly to annual CO2 emissions from the global stream network, with a single respiration pulse potentially increasing emission by 0.2–0.7%. As the spatial and temporal extent of IRES increases globally, our results highlight the importance of recognizing the influence of wetting‐drying cycles on respiration and CO2 emissions in stream networks.
In a global change context, the intensity and the frequency of drastic low flow periods or drought events will most likely increase to a substantial extent over the coming decades, leading to a modification in the abiotic characteristics of wetlands. This change in environmental parameters may induce severe shifts in plant and animal communities and the functioning of ecosystems. In this study, we experimentally estimated the effect of drought and the accumulation of ammonia (NH3 ) on the feeding activities of three generalist macroinvertebrates (i.e. Gammarus pulex, Gammarus roeselii and Asellus aquaticus) on three types of organic matter: leaves of Berula erecta growing in submerged conditions, leaves of the same species growing in emerged conditions and dead leaves of Alnus glutinosa. We observed a modification in the biomechanical and stoichiometric characteristics of the plants as a result of the emersion of the aquatic plants. This shift produced a substantial decrease in organic matter recycling by invertebrates and in their associated physiological ability (i.e. the energy stores of the animals) to face conditions associated with environmental change. Moreover, the accumulation of NH3 amplified the negative effect of emersion. This snowball effect on invertebrates may profoundly modify the functioning of ecosystems, particularly in terms of organic matter production/degradation and carbon mineralization.
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