| 1. |
- Campeau, Audrey, et al.
(författare)
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Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen : Implications for peat carbon stock stability
- 2017
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 23:12, s. 5523-5536
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Tidskriftsartikel (refereegranskat)abstract
- The stability of northern peatland's carbon (C) store under changing climate is of major concern for the global C cycle. The aquatic export of C from boreal peatlands is recognized as both a critical pathway for the remobilization of peat C stocks as well as a major component of the net ecosystem C balance (NECB). Here, we present a full year characterization of radiocarbon content (14C) of dissolved organic carbon (DOC), carbon dioxide (CO2), and methane (CH4) exported from a boreal peatland catchment coupled with 14C characterization of the catchment's peat profile of the same C species. The age of aquatic C in runoff varied little throughout the year and appeared to be sustained by recently fixed C from the atmosphere (<60 years), despite stream DOC, CO2, and CH4 primarily being sourced from deep peat horizons (2–4 m) near the mire's outlet. In fact, the 14C content of DOC, CO2, and CH4 across the entire peat profile was considerably enriched with postbomb C compared with the solid peat material. Overall, our results demonstrate little to no mobilization of ancient C stocks from this boreal peatland and a relatively large resilience of the source of aquatic C export to forecasted hydroclimatic changes.
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| 2. |
- Dinsmore, Kerry, et al.
(författare)
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Contrasting CO2 concentration discharge dynamics in headwater streams : a multi-catchment comparison
- 2013
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Ingår i: Journal of Geophysical Research-Biogeosciences. - : American Geophysical Union (AGU). - 2169-8953 .- 2169-8961. ; 118:2, s. 445-461
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Tidskriftsartikel (refereegranskat)abstract
- Aquatic CO2 concentrations are highly variable and strongly linked to discharge, but until recently, measurements have been largely restricted to low-frequency manual sampling. Using new in situ CO2 sensors, we present concurrent, high-frequency (<30 min resolution) CO2 concentration and discharge data collected from five catchments across Canada, UK, and Fennoscandinavia to explore concentration-discharge dynamics; we also consider the relative importance of high flows to lateral aquatic CO2 export. The catchments encompassed a wide range of mean CO2 concentrations (0.73–3.05 mg C L−1) and hydrological flow regimes from flashy peatland streams to muted outflows within a Finnish lake system. In three of the catchments, CO2 concentrations displayed clear bimodal distributions indicating distinct CO2 sources. Concentration-discharge relationships were not consistent across sites with three of the catchments displaying a negative relationship and two catchments displaying a positive relationship. When individual high flow events were considered, we found a strong correlation between both the average magnitude of the hydrological and CO2 response peaks, and the average response lag times. An analysis of lateral CO2 export showed that in three of the catchments, the top 30% of flow (i.e., flow that was exceeded only 30% of the time) had the greatest influence on total annual load. This indicates that an increase in precipitation extremes (greater high-flow contributions) may have a greater influence on the flushing of CO2 from soils to surface waters than a long-term increase in mean annual precipitation, assuming source limitation does not occur.
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| 3. |
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| 4. |
- Johnson, Mark S., et al.
(författare)
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Direct and continuous measurements of dissolved carbon dioxide in freshwater aquatic systems : method and applications
- 2010
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Ingår i: Ecohydrology. - : Wiley. - 1936-0584 .- 1936-0592. ; 3:1, s. 68-78
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Tidskriftsartikel (refereegranskat)abstract
- Understanding of the processes that control CO2 concentrations in the aquatic environment has been hampered by the absence of a direct method to make continuous measurements over both short- and long-term time intervals. We describe an in situ method in which a non-dispersive infrared (NDIR) sensor is enclosed in a water impermeable, gas permeable polytetrafluoroethylene (PTFE) membrane and deployed in a freshwater environment. This allows measurements of CO2 concentration to be made directly at a specific depth in the water column without the need for pumps or reagents. We demonstrate the potential of the method using examples from different aquatic environments characterized by a range of CO2 concentrations (0·5–8·0 mg CO2-C l−1, equivalent to ca 40–650 µmol CO2 l−1). These comprise streams and ponds from tropical, temperate and boreal regions. Data derived from the sensor was compared with direct measurements of CO2 concentrations using headspace analysis. Sensor performance following long-term (>6 months) field deployment conformed to manufacturers' specifications, with no drift detected. We conclude that the sensor-based method is a robust, accurate and responsive method, with a wide range of potential applications, particularly when combined with other in situ sensor-based measurements of related variables.
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| 5. |
- Wallin, Marcus B., et al.
(författare)
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Spatiotemporal variability of the gas transfer coefficient (KCO2) in boreal streams : Implications for large scale estimates of CO2 evasion
- 2011
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Ingår i: Global Biogeochemical Cycles. - : John Wiley & Sons. - 0886-6236 .- 1944-9224. ; 25:3, s. GB3025-
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Tidskriftsartikel (refereegranskat)abstract
- Boreal streams represent potentially important conduits for the exchange of carbon dioxide (CO(2)) between terrestrial ecosystems and the atmosphere. The gas transfer coefficient of CO(2) (K(CO2)) is a key variable in estimating this source strength, but the scarcity of measured values in lotic systems creates a risk of incorrect flux estimates even when stream gas concentrations are well known. This study used 114 independent measurements of K(CO2) from 14 stream reaches in a boreal headwater system to determine and predict spatiotemporal variability in K(CO2). The K(CO2) values ranged from 0.001 to 0.207 min(-1) across the 14 sites. Median K(CO2) for a specific site was positively correlated with the slope of the stream reach, with higher gas transfer coefficients occurring in steeper stream sections. Combining slope with a width/depth index of the stream reach explained 83% of the spatial variability in K(CO2). Temporal variability was more difficult to predict and was strongly site specific. Variation in K(CO2), rather than pCO(2), was the main determinant of stream CO(2) evasion. Applying published generalized gas transfer velocities produced an error of up to 100% in median instantaneous evasion rates compared to the use of actual measured K(CO2) values from our field study. Using the significant relationship to local slope, the median K(CO2) was predicted for 300,000 km of watercourses (ranging in stream order 1-4) in the forested landscape of boreal/nemoral Sweden. The range in modeled stream order specific median K(CO2) was 0.017-0.028 min(-1) and there was a clear gradient of increasing K(CO2) with lower stream order. We conclude that accurate regional scale estimates of CO(2) evasion fluxes from running waters are possible, but require a good understanding of gas exchange at the water surface.
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