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| 2. |
- Berggren, Martin, et al.
(författare)
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Unified understanding of intrinsic and extrinsic controls of dissolved organic carbon reactivity in aquatic ecosystems
- 2022
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 103:9
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Tidskriftsartikel (refereegranskat)abstract
- Despite our growing understanding of the global carbon cycle, scientific consensus on the drivers and mechanisms that control dissolved organic carbon (DOC) turnover in aquatic systems is lacking, hampered by the mismatch between research that approaches DOC reactivity from either intrinsic (inherent chemical properties) or extrinsic (environmental context) perspectives. Here we propose a conceptual view of DOC reactivity in which the combination of intrinsic and extrinsic factors controls turnover rates and determines which reactions will occur. We review three major types of reactions (biological, photochemical, and flocculation) from an intrinsic chemical perspective and further define the environmental features that modulate the expression of chemically inherent reactivity potential. Finally, we propose hypotheses of how extrinsic and intrinsic factors together shape patterns in DOC turnover across the land-to-ocean continuum, underscoring that there is no intrinsic DOC reactivity without environmental context. By acknowledging the intrinsic–extrinsic control duality, our framework intends to foster improved modeling of DOC reactivity and its impact on ecosystem services.
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| 3. |
- Lapierre, Jean-Francois, et al.
(författare)
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Increases in terrestrially derived carbon stimulate organic carbon processing and CO2 emissions in boreal aquatic ecosystems
- 2013
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The concentrations of terrestrially derived dissolved organic carbon have been increasing throughout northern aquatic ecosystems in recent decades, but whether these shifts have an impact on aquatic carbon emissions at the continental scale depends on the potential for this terrestrial carbon to be converted into carbon dioxide. Here, via the analysis of hundreds of boreal lakes, rivers and wetlands in Canada, we show that, contrary to conventional assumptions, the proportion of biologically degradable dissolved organic carbon remains constant and the photochemical degradability increases with terrestrial influence. Thus, degradation potential increases with increasing amounts of terrestrial carbon. Our results provide empirical evidence of a strong causal link between dissolved organic carbon concentrations and aquatic fluxes of carbon dioxide, mediated by the degradation of land-derived organic carbon in aquatic ecosystems. Future shifts in the patterns of terrestrial dissolved organic carbon in inland waters thus have the potential to significantly increase aquatic carbon emissions across northern landscapes.
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- Panneer Selvam, Balathandayuthabani, et al.
(författare)
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Degradation potentials of dissolved organic carbon (DOC) from thawed permafrost peat
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Global warming can substantially affect the export of dissolved organic carbon (DOC) from peat-permafrost to aquatic systems. The direct degradability of such peat-derived DOC, however, is poorly constrained because previous permafrost thaw studies have mainly addressed mineral soil catchments or DOC pools that have already been processed in surface waters. We incubated peat cores from a palsa mire to compare an active layer and an experimentally thawed permafrost layer with regard to DOC composition and degradation potentials of pore water DOC. Our results show that DOC from the thawed permafrost layer had high initial degradation potentials compared with DOC from the active layer. In fact, the DOC that showed the highest bio- and photo-degradability, respectively, originated in the thawed permafrost layer. Our study sheds new light on the DOC composition of peat-permafrost directly upon thaw and suggests that past estimates of carbon-dioxide emissions from thawed peat permafrost may be biased as they have overlooked the initial mineralization potential of the exported DOC.
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| 6. |
- Panneer Selvam, Balathandayuthabani, et al.
(författare)
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Effect of permafrost thaw on labile dissolved organic carbon in a northern palsa mire
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Permafrost thaw can substantially increase the total export of dissolved organic carbon (DOC) to aquatic systems. The effects for bio- and photo-degradable DOC, however, are poorly known, because previous studies have mainly targeted lakes and streams which are indirectly affected by permafrost, while direct experimental work on permafrost thaw is lacking. We thus incubated permafrost cores from a northern palsa mire in a climate chamber to directly compare active layer and the effect of thaw on 1) DOC composition (using fluorescence analyses and PARAFAC modeling) and 2) DOC bioavailability and photo-degradability. Our results show that compared with DOC from the active layer, the permafrost-thaw DOC was more bioavailable, coherent with its optical characteristics indicating higher protein content and lower molecular weight DOC. This biolabile DOC, however, does not appear to contribute to photo-oxidation as we found no difference in photo-degradation between the active layer and permafrost DOC. Our study suggests that permafrost thaw results in the export of both bio- and photo-degradable DOC, indicating that an increase in permafrost thaw could positively affect the carbon cycling of aquatic ecosystems.
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| 7. |
- 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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| 8. |
- Lapierre, Jean-Francois, et al.
(författare)
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Climate and landscape influence on indicators of lake carbon cycling through spatial patterns in dissolved organic carbon
- 2015
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 21:12, s. 4425-4435
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Tidskriftsartikel (refereegranskat)abstract
- Freshwater ecosystems are strongly influenced by both climate and the surrounding landscape, yet the specific pathways connecting climatic and landscape drivers to the functioning of lake ecosystems are poorly understood. Here, we hypothesize that the links that exist between spatial patterns in climate and landscape properties and the spatial variation in lake carbon (C) cycling at regional scales are at least partly mediated by the movement of terrestrial dissolved organic carbon (DOC) in the aquatic component of the landscape. We assembled a set of indicators of lake C cycling (bacterial respiration and production, chlorophyll a, production to respiration ratio, and partial pressure of CO2), DOC concentration and composition, and landscape and climate characteristics for 239 temperate and boreal lakes spanning large environmental and geographic gradients across seven regions. There were various degrees of spatial structure in climate and landscape features that were coherent with the regionally structured patterns observed in lake DOC and indicators of C cycling. These different regions aligned well, albeit nonlinearly along a mean annual temperature gradient; whereas there was a considerable statistical effect of climate and landscape properties on lake C cycling, the direct effect was small and the overall effect was almost entirely overlapping with that of DOC concentration and composition. Our results suggest that key climatic and landscape signals are conveyed to lakes in part via the movement of terrestrial DOC to lakes and that DOC acts both as a driver of lake C cycling and as a proxy for other external signals.
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| 9. |
- Lapierre, Jean-Francois, et al.
(författare)
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Continental-scale variation in controls of summer CO2 in United States lakes
- 2017
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : AMER GEOPHYSICL UNION. - 2169-8953 .- 2169-8961. ; 122:4, s. 875-885
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the broad-scale response of lake CO2 dynamics to global change is challenging because the relative importance of different controls of surface water CO2 is not known across broad geographic extents. Using geostatistical analyses of 1080 lakes in the conterminous United States, we found that lake partial pressure of CO2 (pCO(2)) was controlled by different chemical and biological factors related to inputs and losses of CO2 along climate, topography, geomorphology, and land use gradients. Despite weak spatial patterns in pCO(2) across the study extent, there were strong regional patterns in the pCO(2) driver-response relationships, i.e., in pCO(2) regulation. Because relationships between lake CO2 and its predictors varied spatially, global models performed poorly in explaining the variability in CO2 for U.S. lakes. The geographically varying driver-response relationships of lake pCO(2) reflected major landscape gradients across the study extent and pointed to the importance of regional-scale variation in pCO(2) regulation. These results indicate a higher level of organization for these physically disconnected systems than previously thought and suggest that changes in climate and land use could induce shifts in the main pathways that determine the role of lakes as sources and sinks of atmospheric CO2. Plain Language Summary In this study we show that changes in climate and terrestrial landscapes could affect which are the main mechanisms responsible for the widespread emissions of CO2 by lakes. Although mechanisms such as aquatic primary production, respiration by microorganisms, or terrestrial loadings of carbon have been studied extensively, their relative importance across broad geographic extents with different climate or land use remains unknown. Based on an analysis of 1080 lakes distributed across the continental U.S., we show that lake CO2 dynamics depend on the climate and landscape context where these lakes are found, such as precipitation, elevation, percent agriculture, or wetlands in the lakes catchments. We observed a widespread effect of in-lake primary production, while the color of water, which has often been identified as one of the main controls of lake CO2 in northern lakes, was important in only a small fraction of the lakes studied. Our results show that controls on lake CO2 dynamics vary geographically and that considering that variation will be important for creating accurate global carbon models.
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| 10. |
- Lapierre, Jean-Francois, et al.
(författare)
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Similarity in spatial structure constrains ecosystem relationships : Building a macroscale understanding of lakes
- 2018
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Ingår i: Global Ecology and Biogeography. - : John Wiley & Sons. - 1466-822X .- 1466-8238. ; 27:10, s. 1251-1263
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Tidskriftsartikel (refereegranskat)abstract
- Aim: We aimed to measure the dominant spatial patterns in ecosystem properties (such as nutrients and measures of primary production) and the multi‐scaled geographical driver variables of these properties and to quantify how the spatial structure of pattern in all of these variables influences the strength of relationships among them.Location and time period: We studied > 8,500 lakes in a 1.8 million km2 area of Northeast U.S.A. Data comprised 10‐year medians (2002–2011) for measured ecosystem properties, long‐term climate averages and recent land use/land cover variables.Major taxa studied: We focused on ecosystem properties at the base of aquatic food webs, including concentrations of nutrients and algal pigments that are proxies of pri -mary productivity.Methods: We quantified spatial structure in ecosystem properties and their geograph-ical driver variables using distance‐based Moran eigenvector maps (dbMEMs). We then compared the similarity in spatial structure for all pairs of variables with the cor -relation between variables to illustrate how spatial structure constrains relationships among ecosystem properties.Results: The strength of spatial structure decreased in order for climate, land cover/use, lake ecosystem properties and lake and landscape morphometry. Having a compa -rable spatial structure is a necessary condition to observe a strong relationship be -tween a pair of variables, but not a sufficient one; variables with very different spatial structure are never strongly correlated. Lake ecosystem properties tended to have an intermediary spatial structure compared with that of their main drivers, probably be -cause climate and landscape variables with known ecological links induce spatial patterns.Main conclusions: Our empirical results describe inherent spatial constraints that dic -tate the expected relationships between ecosystem properties and their geographical drivers at macroscales. Our results also suggest that understanding the spatial scales at which ecological processes operate is necessary to predict the effects of multi‐scaled environmental changes on ecosystem properties.
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