Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter

Shumilova, Oleksandra and Zak, Dominik and Datry, Thibault and Schiller, Daniel and Corti, Roland and Foulquier, Arnaud and Obrador, Biel and Tockner, Klement and Allan, Daniel C. and Altermatt, Florian and Arce, María Isabel and Arnon, Shai and Banas, Damien and Banegas‐Medina, Andy and Beller, Erin and Blanchette, Melanie L. and Blanco‐Libreros, Juan F. and Blessing, Joanna and Boëchat, Iola Gonçalves and Boersma, Kate and Bogan, Michael T. and Bonada, Núria and Bond, Nick R. and Brintrup, Kate and Bruder, Andreas and Burrows, Ryan and Cancellario, Tommaso and Carlson, Stephanie M. and Cauvy‐Fraunié, Sophie and Cid, Núria and Danger, Michael and Freitas Terra, Bianca and Girolamo, Anna Maria De and Campo, Ruben and Dyer, Fiona and Elosegi, Arturo and Faye, Emile and Febria, Catherine and Figueroa, Ricardo and Four, Brian and Gessner, Mark O. and Gnohossou, Pierre and Cerezo, Rosa Gómez and Gomez‐Gener, Lluís and Graça, Manuel A.S. and Guareschi, Simone and Gücker, Björn and Hwan, Jason L. and Kubheka, Skhumbuzo and Langhans, Simone Daniela and Leigh, Catherine and Little, Chelsea J. and Lorenz, Stefan and Marshall, Jonathan and McIntosh, Angus and Mendoza‐Lera, Clara and Meyer, Elisabeth Irmgard and Miliša, Marko and Mlambo, Musa C. and Moleón, Marcos and Negus, Peter and Niyogi, Dev and Papatheodoulou, Athina and Pardo, Isabel and Paril, Petr and Pešić, Vladimir and Rodriguez‐Lozano, Pablo and Rolls, Robert J. and Sanchez‐Montoya, Maria Mar and Savić, Ana and Steward, Alisha and Stubbington, Rachel and Taleb, Amina and Vorste, Ross Vander and Waltham, Nathan and Zoppini, Annamaria and Zarfl, Christiane (2019) Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter. Global Change Biology, 25 (5). pp. 1591-1611. ISSN 1354-1013

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Abstract

Climate change and human pressures are changing the global distribution and the extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico-chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56%–98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached OM. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying events.

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