| 1. |
- Bogard, Matthew J., et al.
(författare)
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Patterns of Spring/Summer Open-Water Metabolism Across Boreal Lakes
- 2020
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Ingår i: Ecosystems (New York. Print). - : Springer Science+Business Media B.V.. - 1432-9840 .- 1435-0629. ; 23, s. 1581-1597
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Tidskriftsartikel (refereegranskat)abstract
- Northern regions host the greatest density of surface water globally, but knowledge of lake metabolism in this vast yet remote landscape is limited. Here, we used an oxygen stable isotope approach to quantify patterns and drivers of surface layer metabolism in lakes throughout an approximately 10(6) km(2) tract of boreal Canada. Ecosystem gross primary production (GPP) and respiration rates (R) were much higher than previously assumed for spring and summer months. Both rates were strongly linked to nitrogen (N) concentrations, not light availability, despite earlier work showing community-level light effects. Net ecosystem production (NEP = GPP - R) was negative for most lakes. Hierarchical modeling revealed that although NEP is strongly stabilized via similar effects of N on both GPP and R, NEP decreases with increasing dissolved organic carbon (DOC). These interactive controls on NEP were not predictable from bivariate regressions linking NEP to physical, chemical or habitat-specific drivers. In contrast to expectations, NEP was higher in warmer waters due to increased temperature dependency of GPP, not R. Temperature and DOC content had opposing effects on NEP in all but the most dystrophic lakes, possibly implying a muted response of metabolic balances to future shifts in both regional climate and OC delivery.
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| 2. |
- Campeau, Audrey, et al.
(författare)
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Autumn destabilization of deep porewater CO2 store in a northern peatland driven by turbulent diffusion
- 2021
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The deep porewater of northern peatlands stores large amounts of carbon dioxide (CO2). This store is viewed as a stable feature in the peatland CO2 cycle. Here, we report large and rapid fluctuations in deep porewater CO2 concentration recurring every autumn over four consecutive years in a boreal peatland. Estimates of the vertical diffusion of heat indicate that CO2 diffusion occurs at the turbulent rather than molecular rate. The weakening of porewater thermal stratification in autumn likely increases turbulent diffusion, thus fostering a rapid diffusion of deeper porewater CO2 towards the surface where net losses occur. This phenomenon periodically decreases the peat porewater CO2 store by between 29 and 90 g C m−2 throughout autumn, which is comparable to the peatland’s annual C-sink. Our results establish the need to consider the role of turbulent diffusion in regularly destabilizing the CO2 store in peat porewater.
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| 3. |
- Campeau, Audrey, et al.
(författare)
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Regional contribution of CO2 and CH4 fluxes from the fluvial network in a lowland boreal landscape of Quebec
- 2014
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 28:1, s. 57-69
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Tidskriftsartikel (refereegranskat)abstract
- Boreal rivers and streams are known as hot spots of CO2 emissions, yet their contribution to CH4 emissions has traditionally been assumed to be negligible, due to the spatially fragmented data and lack of regional studies addressing both gases simultaneously. Here we explore the regional patterns in river CO2 and CH4 concentrations (pCO(2) and pCH(4)), gas exchange coefficient (k), and the resulting emissions in a lowland boreal region of Northern Quebec. Rivers and streams were systematically supersaturated in both gases, with both pCO(2) and pCH(4) declining along the river continuum. The k was on average low and increased with stream order, consistent with the hydrology of this flat landscape. The smallest streams (order 1), which represent <20% of the total river surface, contributed over 35% of the total fluvial greenhouse gas (GHG) emissions. The end of winter and the spring thaw periods, which are rarely included in annual emission budgets, contributed on average 21% of the annual GHG emissions. As a whole, the fluvial network acted as significant source of both CO2 and CH4, releasing on average 1.5 tons of C (CO2 eq) yr(-1)km(-2) of landscape, of which CH4 emissions contributed approximately 34%. We estimate that fluvial CH4 emissions represent 41% of the regional aquatic (lakes, reservoirs, and rivers) CH4 emissions, despite the relatively small riverine surface (4.3% of the total aquatic surface). We conclude that these fluvial networks in boreal lowlands play a disproportionately large role as hot spots for CO2 and more unexpectedly for CH4 emissions. Key Points pCO(2) and pCH(4) decrease, whereas the k600 increases with increasing stream order Small streams and spring thaw period play a large role in regional C balance Rivers are significant sources of CO2 and unexpectedly large sources of CH4
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| 4. |
- Donis, Daphne, et al.
(författare)
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Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer
- 2021
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:12, s. 4314-4333
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Tidskriftsartikel (refereegranskat)abstract
- To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L-1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4 degrees C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature.
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| 5. |
- Grosbois, Guillaume, et al.
(författare)
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Efficiency of crustacean zooplankton in transferring allochthonous carbon in a boreal lake
- 2020
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Ingår i: Ecology. - : Wiley-Blackwell. - 0012-9658 .- 1939-9170. ; 101:6
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Tidskriftsartikel (refereegranskat)abstract
- Increased incorporation of terrestrial organic matter (t-OM) into consumer biomass (allochthony) is believed to reduce growth capacity. In this study, we examined the relationship between crustacean zooplankton allochthony and production in a boreal lake that displays strong seasonal variability in t-OM inputs. Contrary to our hypotheses, we found no effect of allochthony on production at the community and the species levels. The high-frequency seasonal sampling (time-for-space) allowed for estimating the efficiency of zooplankton in converting this external carbon source to growth. From the daily t-OM inputs in the lake (57-3,027 kg C/d), the zooplankton community transferred 0.2% into biomass (0.01-2.36 kg C/d); this level was of the same magnitude as the carbon transfer efficiency for algal-derived carbon (0.4%). In the context of the boundless carbon cycle, which integrates inland waters as a biologically active component of the terrestrial landscape, the use of the time-for-space approach for the quantifying of t-OM trophic transfer efficiency by zooplankton is a critical step toward a better understanding of the effects of increasing external carbon fluxes on pelagic food webs.
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| 6. |
- Karlsson, Jan, 1974-, et al.
(författare)
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Ice-melt period dominates annual carbon dioxide evasion from clear-water Arctic lakes
- 2024
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Ingår i: Limnology and Oceanography Letters. - : John Wiley & Sons. - 2378-2242. ; 9:2, s. 112-118
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Tidskriftsartikel (refereegranskat)abstract
- Current estimates of carbon dioxide (CO2) evasion from Arctic lakes are highly uncertain because few studies integrate seasonal variability, specifically evasion during spring ice-melt. We quantified annual CO2 evasion for 14 clear-water Arctic lakes in Northern Sweden through mass balance (ice-melt period) and high-frequency loggers (open-water period). On average, 80% (SD: ± 18) of annual CO2 evasion occurred within 10 d following ice-melt. The contribution of the ice-melt period to annual CO2 evasion was high compared to earlier studies of Arctic lakes (47% ± 32%). Across all lakes, the proportion of ice-melt : annual CO2 evasion was negatively related to the dissolved organic carbon concentration and positively related to the mean depth of the lakes. The results emphasize the need for measurements of CO2 exchange at ice-melt to accurately quantify CO2 evasion from Arctic lakes.
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| 7. |
- Klaus, Marcus, et al.
(författare)
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Challenges of predicting gas transfer velocity from wind measurements over global lakes
- 2020
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Ingår i: Aquatic Sciences. - : Springer. - 1015-1621 .- 1420-9055. ; 82:3
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Tidskriftsartikel (refereegranskat)abstract
- Estimating air-water gas transfer velocities (k) is integral to understand biogeochemical and ecological processes in aquatic systems. In lakes, k is commonly predicted using wind-based empirical models, however, their predictive performance under conditions that differ from their original calibration remains largely unassessed. Here, we collected 2222 published k estimates derived from various methods in 46 globally distributed lakes to (1) evaluate the predictions of a selection of six available wind-speed based k models for lakes and (2) explore and develop new empirical models to predict k over global lakes. We found that selected k models generally performed poorly in predicting k in lakes. Model predictions were more accurate than simply assuming a mean k in only 2-39% of all lakes, however, we could not identify with confidence the specific conditions in which some models outperformed others. We developed new wind-based models in which additional variables describing the spatial coverage of k estimates and the lake size and shape had a significant effect on the wind speed-k relationship. Although these new models did not fit the global dataset significantly better than previous k models, they generate overall less biased predictions for global lakes. We further provide explicit estimates of prediction errors that integrate methodological and lake-specific uncertainties. Our results highlight the potential limits when using wind-based models to predict k across lakes and urge scientists to properly account for prediction errors, or measure k directly in the field whenever possible.
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| 8. |
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| 9. |
- Kokic, Jovana, et al.
(författare)
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High spatial variability of gas transfer velocity in streams revealed by turbulence measurements
- 2018
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Ingår i: Inland Waters. - : Taylor & Francis. - 2044-2041 .- 2044-205X. ; 8:4, s. 461-473
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Tidskriftsartikel (refereegranskat)abstract
- Streams are major sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere, but current large-scale estimates are associated with high uncertainties because knowledge concerning the spatiotemporal control on stream emissions is limited. One of the largest uncertainties derives from the choice of gas transfer velocity (k(600)), which describes the physical efficiency of gas exchange across the water-atmosphere interface. This study therefore explored the variability in k(600 )and subsequent CO2 and CH4 emission rates within and across streams of different stream order (SO). We conducted, for the first time in streams, direct turbulence measurements using an acoustic Doppler velocimeter (ADV) to determine the spatial variability in k(600) across a variety of scales with a consistent methodology. The results show high spatial variability in k(600) and corresponding CO2 and CH4 emissions at small spatial scales, both within stream reaches and across SO, especially during high discharge. The k(600) was positively related to current velocity and Reynolds number. By contrast, no clear relationship was found between k(600) and specific stream characteristics such as width and depth, which are parameters often used in empirical models of k(600). Improved understanding of the small-scale variability in the physical properties along streams, especially during high discharge, is therefore an important step to reduce the uncertainty in existing gas transfer models and emissions for stream systems. The ADV method was a useful tool for revealing spatial variability in this work, but it needs further development. We recommend that future studies conduct measurements over shorter time periods (e.g., 10-15 min instead of 40 min) and at more sites across the reach of interest, and thereby derive more reliable mean-reach k(600) as well as more information about controls on the spatial variability in k(600).
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| 10. |
- Prairie, Yves T., et al.
(författare)
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Greenhouse Gas Emissions from Freshwater Reservoirs : What Does the Atmosphere See?
- 2018
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 21:5, s. 1058-1071
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Tidskriftsartikel (refereegranskat)abstract
- Freshwater reservoirs are a known source of greenhouse gas (GHG) to the atmosphere, but their quantitative significance is still only loosely constrained. Although part of this uncertainty can be attributed to the difficulties in measuring highly variable fluxes, it is also the result of a lack of a clear accounting methodology, particularly about what constitutes new emissions and potential new sinks. In this paper, we review the main processes involved in the generation of GHG in reservoir systems and propose a simple approach to quantify the reservoir GHG footprint in terms of the net changes in GHG fluxes to the atmosphere induced by damming, that is, ´€˜what the atmosphere sees’. The approach takes into account the pre-impoundment GHG balance of the landscape, the temporal evolution of reservoir GHG emission profile as well as the natural emissions that are displaced to or away from the reservoir site resulting from hydrological and other changes. It also clarifies the portion of the reservoir carbon burial that can potentially be considered an offset to GHG emissions.
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