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

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.