Regional-scale lateral carbon transport and CO<sub>2</sub> evasion in temperate stream catchments

Abstract

<p><strong>Abstract.</strong> Inland waters play an important role in regional to global scale carbon cycling by transporting, processing and emitting substantial amounts of carbon, which originate mainly from their catchments. In this study, we analyzed the relationship between terrestrial net primary production (NPP) and the rate at which carbon is exported from the catchments in a temperate stream network. The analysis included more than 200 catchment areas in southwest Germany, ranging in size from 0.8 to 889 km<sup>2</sup> for which CO<sub>2</sub> evasion from stream surfaces and downstream transport with stream discharge were estimated from water quality monitoring data, while NPP in the catchments was obtained from a global data set based on remote sensing. We found that on average 2.7 % of terrestrial NPP (13.9 g C m<sup>2</sup> yr<sup>−1</sup>) are exported from the catchments by streams and rivers, in which both CO<sub>2</sub> evasion and downstream transport contributed about equally to this flux. The average carbon fluxes in the catchments of the study area resembled global and large-scale zonal mean values in many respects, including NPP, stream evasion as well as the catchment-specific total export rate of carbon in the fluvial network. A review of existing studies on aquatic-terrestrial coupling in the carbon cycle suggests that the catchment-specific carbon export varies in a relatively narrow range, despite a broad range of different spatial scales and hydrological characteristics of the study regions.</p>

Large‐Scale Landscape Drivers of CO2, CH4, DOC, and DIC in Boreal River Networks

“…These findings suggest that soil organic C content and NPP act as integrators of broad climate, hydrologic, and biogeochemical regional features, all of which relate one way or another to carbon available for export to the fluvial network, and which could be useful predictors of export in remote areas and with climate change scenarios. DIC did not show any geographical pattern related to NPP or climate, but there a nevertheless clear cross-regional differences in average riverine DIC, which are driven by large-scale patterns in underlying geology, as has been shown before (Giesler et al, 2014;Jantze et al, 2015;Magin et al, 2017;Wallin et al, 2014).…”

“…The consistency between the modeled and measured values with NPP and lack of consistency with soil carbon content ( Figures S3-S5) suggest that NPP is a more effective integrator of climate and environmental factors, and may provide a better index of the active carbon pools that is mobilized into the fluvial network than soil C content. A recent study by Magin et al (2017) found a narrow range of C-export per terrestrial NPP in temperate watersheds and a meta-analysis suggesting that terrestrial-aquatic coupling may be predictive at large scales. Further development of such relationships in the future could be useful for improving global estimates of C-export and emissions which are highly uncertain and still in need of refinement (Drake et al, 2017).…”

“…It is likely that NPP is a proxy for regional climate since NPP is strongly driven by climate (Foley et al, 1996), but it also likely integrates a number of other environmental factors that may indirectly influence the C species in rivers. On the one hand, several recent studies have linked lateral carbon export to fluvial networks to NPP at regional scales (Magin et al, 2017;Stackpoole et al, 2017) and CO 2 emission and NPP in lakes (Maberly et al, 2012), which would suggest a mechanistic link between the two. On the other hand, NPP likely integrates a suite of climatic, hydrologic, and environmental factors that may influence various aspects of C export and processing in fluvial networks, and which are not captured by mean temperature alone.…”

“…). Likewise, riverine dissolved inorganic carbon (DIC) has been shown to be linked to local geologic features, weathering, and pH-related variables (Giesler et al, 2014;Jantze et al, 2015;Magin et al, 2017;Wallin et al, 2014). There have also been studies on the controls of riverine CO 2 , and more recently CH 4 concentrations and fluxes, which have shown that riverine C gas spatial variability is a function of loading of C gas species from land to rivers, as well as factors that influence the in-stream gas production or consumption, such as temperature and organic C (Campeau et al, 2014;Huotari et al, 2013;Teodoru et al, 2009;Wallin et al, 2010;Weyhenmeyer et al, 2012).…”

Fluvial CO2 and CH4 patterns across wildfire‐disturbed ecozones of subarctic Canada: Current status and implications for future change

“…CO 2 supersaturation in streams and rivers is ubiquitous (Raymond et al, ) and in spite of general downstream decline and degassing, CO 2 may never reach equilibrium with the atmosphere because of constant inputs and internal production (Hotchkiss et al, ). Recently, climatic variables (such as NPP) have also been linked to the lateral export of carbon in fluvial networks (Magin, Somlai‐Haase, Schäfer, & Lorke, ; Stackpoole et al, ) as well as directly to fluvial dissolved carbon concentrations at a large scale (Hutchins et al, ).…”