Journal
JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES
Volume 121, Issue 10, Pages 2630-2651Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2016JG003420
Keywords
DOC; CO2; mass balance; water-atmosphere exchange; Riparian flow-concentration Integration Model
Funding
- Bolin Centre for Climate Research
- Carl-Fredrik von Horns fund [H12-0159-CFH]
- Swedish Science Foundation (VR) SITES
- ForWater (Formas)
- Future Forest
- Kempe Foundation
- FOMA
- Swedish Nuclear Fuel and Waste Management Company (SKB)
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Streams and rivers emit large quantities of carbon dioxide (CO2) to the atmosphere. The sources of this CO2 are in-stream mineralization of organic carbon (OC) and CO2 input via groundwater inflow, but their relative importance is largely unknown. In this study, we quantified the role of in-stream OC mineralization as a source of CO2 in a number of nested boreal headwater streams. The results showed that mineralization of stream OC contributed 3% of CO2 supersaturation at time scales comparable to the estimated water travel times in the streams (<24h). Mass balances showed that downstream losses of OC were 3% in low-order streams, whereas up to 16% of the OC was lost in the largest (fourth order) streams. In contrast, 85% of the CO2 was lost along the stream network (longest total stream length=17km). Under the assumption that in-stream OC mineralization was the main source of stream CO2, higher rates of OC mineralization (6% of OC) than those reported across the literature (0.7% of OC) would be required to sustain observed CO2 supersaturation. Further, model results indicated that groundwater inflows were sufficient to sustain observed stream CO2 concentrations. We hence conclude that in-stream OC mineralization was a minor source of CO2 in these boreal headwater systems and that the main source of stream CO2 was inflowing groundwater transporting CO2 originating from soil respiration.
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