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

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.

Dynamic stream network intermittence explains emergent dissolved organic carbon chemostasis in headwaters

“…Understanding the controls on DOC is critical to accurately estimating terrestrial C balance (Butman et al, ). Most studies do not include intermittent reaches, which is an important gap because intermittent streams are pervasive globally across stream networks (Shumilova et al, ). Because network context is so important, intermittence is important even for understanding patterns in perennial reaches and during high flows, when most DOC is exported.…”

“…Understanding the controls on DOC is critical to accurately estimating terrestrial C balance (Butman et al, 2016). Most studies do not include intermittent reaches, which is an important gap because intermittent streams are pervasive globally across stream networks (Shumilova et al, 2019).…”

“…Although streamflow intermittence can occur throughout stream networks (González-Ferreras & Barquín, 2017), headwater streams are more likely to experience periodic drying (Fritz et al, 2013;González-Ferreras & Barquín, 2017;Jaeger et al, 2019). Streamflow intermittence varies across headwaters (e.g., Godsey & Kirchner, 2014;Jensen, McGuire, & Prince, 2017) and reach-scale patterns of stream drying have been linked to variation in carbon cycling and transport (e.g., Acuña, Giorgi, Muñoz, Sabater, & Sabater, 2007;Shumilova et al, 2019). DOC sources and transformation rates vary within intermittent reaches through wetting and drying (Acuña et al, 2005, Acuña et al, 2007Datry, Corti, Claret, & Philippe, 2011;Dieter et al, 2011;Abril, Muñoz, & Menéndez, 2016;Harjung, Sabater, & Butturini, 2017), and legacies of drying can impact C cycling through the accumulation of organic matter and drying impacts on biotic communities (von Schiller et al, 2015).…”

“…Models with a spatial component (i.e., either spatial or spatio-temporal metrics) do not replace but instead complement temporal dimensions of intermittence, which have been well studied. At a point, there is strong evidence that temporal legacies of intermittence strongly affect C cycling through material accumulation (Acuña et al, 2007;von Schiller et al, 2015;Shumilova et al, 2019) and altered rates of processes such as decomposition (Feminella, 1996;Bonada et al, 2007;Arscott et al, 2010;Bogan et al, 2013;Datry et al, 2016;D'Ambrosio et al, 2017;Figure 1). A key gap in our understanding of intermittency effects on C cycling is how spatial and temporal aspects of intermittence interact to control biogeochemical patterns and processes.…”

Accounting for flow intermittency in environmental flows design

“…Although local (alpha) biodiversity may increase with increasing permanence, spatial and temporal regional (gamma) diversity are likely to decline due to reduced hydrological habitat diversity (Larned, Datry, Arscott, & Tockner, ). In terms of ecosystem function, losing the characteristic alternation of wet and dry phases in temporary waterways will change their unique ‘biogeochemical heartbeat’, with pulsed temporal and spatial variations in nutrient and organic matter inputs, instream processing and downstream transport (Acuña, Giorgi, Muñoz, Uehlinger, & Sabater, ; Jacobson & Jacobson, ; Shumilova et al, ).…”