Stream metabolism controls diel patterns and evasion of CO₂ in Arctic streams

Abstract

Streams play an important role in the global carbon (C) cycle, accounting for a large portion of CO2 evaded from inland waters despite their small areal coverage. However, the relative importance of different terrestrial and aquatic processes driving CO2 production and evasion from streams remains poorly understood. In this study, we measured O2 and CO2 continuously in streams draining tundra‐dominated catchments in northern Sweden, during the summers of 2015 and 2016. From this, we estimated daily metabolic rates and CO2 evasion simultaneously and thus provide insight into the role of stream metabolism as a driver of C dynamics in Arctic streams. Our results show that aquatic biological processes regulate CO2 concentrations and evasion at multiple timescales. Photosynthesis caused CO2 concentrations to decrease by as much as 900 ppm during the day, with the magnitude of this diel variation being strongest at the low‐turbulence streams. Diel patterns in CO2 concentrations in turn influenced evasion, with up to 45% higher rates at night. Throughout the summer, CO2 evasion was sustained by aquatic ecosystem respiration, which was one order of magnitude higher than gross primary production. Furthermore, in most cases, the contribution of stream respiration exceeded CO2 evasion, suggesting that some stream reaches serve as net sources of CO2, thus creating longitudinal heterogeneity in C production and loss within this stream network. Overall, our results provide the first link between stream metabolism and CO2 evasion in the Arctic and demonstrate that stream metabolic processes are key drivers of the transformation and fate of terrestrial organic matter exported from these landscapes.

Carbon dioxide dynamics in an agricultural headwater stream driven by hydrology and primary production

“…In line with findings from similar studies from other environments (arctic tundra, boreal forest, temperate peatlands, alpine) (e.g. Rocher-Ros et al 2019;Riml et al 2019;Crawford et al 2017;Peter et al 2014;Dinsmore et al 2013) we found a mixture of controls on stream CO2 operating at different time-scales generating a highly dynamic stream CO2 pattern. These time-scales covers seasonal patterns to diel cycles, or even shorter scales associated to discharge events.…”

“…Such diel CO2 patterns are commonly observed in stream CO2 time series at base-flow or during receding flow conditions (e.g. Riml et al 2019;Peter et al 2014) and are especially pronounced in amplitude in nutrient-rich streams or in streams without canopy shading (Alberts et al 2017;Crawford et al 2017;Rocher-Ros et al 2019). Initial evaluation of the δ 13 C-DIC data collected during the spring period suggests a relatively steady mixture of geogenic and biogenic DIC although somehow related to variations in discharge ( Figure 11).…”

Metabolism overrides photo‐oxidation in CO2 dynamics of Arctic permafrost streams

“…If photo‐oxidation is the major driver, we predicted that CO 2 concentrations in streams would increase from night to day, when photo‐oxidation rates would be greatest (Cory et al 2014). By contrast, if GPP is the major driver, then CO 2 concentrations would decrease from night to day, when photosynthetic CO 2 fixation is greatest (Rocher‐Ros et al 2020).…”

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

“…Despite this similarity, estimates from stream network modelling were generally higher than for the mass balance. There are several possibilities for this difference; the mass balance does not take into account internal production of CO 2 throughout the stream network which has been observed by others (Hotchkiss et al, 2015;Hutchins et al, 2017;Rocher-Ros, Sponseller, Bergström, Myrstener, & Giesler, 2019) and may therefore underestimate emissions. Another possibility is the stream network emissions were overestimated since the gas exchange was modelled using relationships developed in Sweden (Natchimuthu et al, 2017), and may not reflect the conditions in the western Canadian Taiga.…”