| 1. |
- Olid, Carolina, 1981-, et al.
(author)
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The Role of Methane Transport From the Active Layer in Sustaining Methane Emissions and Food Chains in Subarctic Ponds
- 2021
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In: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 126:3
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Journal article (peer-reviewed)abstract
- Groundwater discharge from the seasonally thawed active layer is increasingly recognized as an important pathway for delivering methane (CH4) into Arctic lakes and streams, but its contribution to CH4 emissions from thaw ponds and its influence on the trophic support and nutritional quality of pond food chains remains unexplored. We quantified the transport of CH4 from the active layer through groundwater discharge into thaw ponds in a subarctic catchment in northern Sweden, using radon (222Rn) as groundwater tracer. We analyzed stable isotopes and fatty acids of pond macroinvertebrates to evaluate the potential effects of groundwater-mediated CH4 inputs on the aquatic food chains. Our results indicate that active layer groundwater discharge flows are nontrivial (range 6%–46% of pond volume per day) and the associated CH4 fluxes (median 339 mg C m−2day−1, interquartile range [IQR]: 179–419 mg C m−2 day−1) can sustain the diffusive CH4 emissions from most of the ponds (155 mg C m−2 day−1, IQR: 55–234 mg C m−2 day−1). Consumers in ponds receiving greater CH4 inputs from the active layer had lower stable carbon (C) isotope signatures that indicates a greater trophic reliance on methane oxidizing bacteria (MOB), and they had lower nutritional quality as indicated by their lower tissue concentrations of polyunsaturated fatty acids. Overall, this work links physical (CH4 transport from the active layer), biogeochemical (CH4 emission), and ecological (MOB-consumer interaction) processes to provide direct evidence for the role of active layer groundwater discharge in CH4 cycling of subarctic thaw ponds.
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| 2. |
- Serk, Henrik, 1980-, et al.
(author)
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Global CO2 fertilization of Sphagnum peat mosses via suppression of photorespiration during the twentieth century
- 2021
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In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 11:1
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Journal article (peer-reviewed)abstract
- Natural peatlands contribute significantly to global carbon sequestration and storage of biomass, most of which derives from Sphagnum peat mosses. Atmospheric CO2 levels have increased dramatically during the twentieth century, from 280 to > 400 ppm, which has affected plant carbon dynamics. Net carbon assimilation is strongly reduced by photorespiration, a process that depends on the CO2 to O2 ratio. Here we investigate the response of the photorespiration to photosynthesis ratio in Sphagnum mosses to recent CO2 increases by comparing deuterium isotopomers of historical and contemporary Sphagnum tissues collected from 36 peat cores from five continents. Rising CO2 levels generally suppressed photorespiration relative to photosynthesis but the magnitude of suppression depended on the current water table depth. By estimating the changes in water table depth, temperature, and precipitation during the twentieth century, we excluded potential effects of these climate parameters on the observed isotopomer responses. Further, we showed that the photorespiration to photosynthesis ratio varied between Sphagnum subgenera, indicating differences in their photosynthetic capacity. The global suppression of photorespiration in Sphagnum suggests an increased net primary production potential in response to the ongoing rise in atmospheric CO2, in particular for mire structures with intermediate water table depths.
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| 3. |
- Zahajská, Petra, et al.
(author)
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Modern silicon dynamics of a small high-latitude subarctic lake
- 2021
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In: Biogeosciences. - : European Geosciences Union (EGU). - 1726-4170 .- 1726-4189. ; 18:7, s. 2325-2345
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Journal article (peer-reviewed)abstract
- High biogenic silica (BSi) concentrations occur sporadically in lake sediments throughout the world; however, the processes leading to high BSi concentrations vary. We explored the factors responsible for the high BSi concentration in sediments of a small, high-latitude subarctic lake (Lake 850). The Si budget of this lake had not been fully characterized before to establish the drivers of BSi accumulation in this environment. To do this, we combined measurements of variations in stream discharge, dissolved silica (DSi) concentrations, and stable Si isotopes in both lake and stream water with measurements of BSi content in lake sediments. Water, radon, and Si mass balances revealed the importance of groundwater discharge as a main source of DSi to the lake, with groundwater-derived DSi inputs 3 times higher than those from ephemeral stream inlets. After including all external DSi sources (i.e., inlets and groundwater discharge) and estimating the total BSi accumulation in the sediment, we show that diatom production consumes up to 79 % of total DSi input. Additionally, low sediment accumulation rates were observed based on the dated gravity core. Our findings thus demonstrate that groundwater discharge and low mass accumulation rate can account for the high BSi accumulation during the last 150 cal yr BP. Globally, lakes have been estimated to retain one-fifth of the annual DSi terrestrial weathering flux that would otherwise be delivered to the ocean. Well-constrained lake mass balances, such as presented here, bring clarity to those estimates of the terrestrial Si cycle sinks.
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