| 1. |
- Chmiel, Hannah Elisa, 1983-, et al.
(författare)
-
The role of sediments in the carbon budget of a small boreal lake
- 2016
-
Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 61:5, s. 1814-1825
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the role of lake sediments as carbon (C) source and sink in the annual C budget of a small (0.07 km2), shallow (mean depth 3.4 m), and humic lake (mean DOC concentration 17 mg L-1) in boreal Sweden. Organic carbon (OC) burial and mineralization in sediments were quantified from 210Pb-dated sediment and laboratory sediment incubation experiments, respectively, and upscaled to the entire basin and to one whole year, by using sediment thickness derived sub-bottom profiling, basin morphometry, and water column monitoring data of temperature and oxygen concentration. Furthermore, catchment C import, open water metabolism, photochemical mineralization as well as carbon dioxide (CO2) and methane (CH4) emissions to the atmosphere, were quantified to relate sediment processes to other lake C fluxes. We found that on a whole-basin and annual scale, sediment OC mineralization was three times larger than OC burial, and contributed about 16% to the annual CO2 emission from the lake to the atmosphere. Remaining contributions to the CO2 emission were attributed to water column metabolism (31%), photochemical mineralization (6%), and catchment imports via inlet streams and inflow of shallow groundwater (47%). We conclude that on an annual and whole-basin scale 1) sediment OC mineralization dominated over OC burial, 2) water column OC mineralization contributed more than sediments to lake CO2 emission, and 3) catchment import of C to the lake was greater than lake-internal C cycling.
|
|
| 2. |
- Denfeld, Blaize A., et al.
(författare)
-
Constraints on methane oxidation in ice-covered boreal lakes
- 2016
-
Ingår i: Journal of Geophysical Research - Biogeosciences. - : AMER GEOPHYSICAL UNION. - 2169-8953 .- 2169-8961. ; 121:7, s. 1924-1933
-
Tidskriftsartikel (refereegranskat)abstract
- Boreal lakes can be ice covered for a substantial portion of the year at which time methane (CH4) can accumulate below ice. The amount of CH4 emitted at ice melt is partially determined by the interplay between CH4 production and CH4 oxidation, performed by methane-oxidizing bacteria (MOB). Yet the balance between oxidation and emission and the potential for CH4 oxidation in various lakes during winter is largely unknown. To address this, we performed incubations at 2 degrees C to screen for wintertime CH4 oxidation potential in seven lakes. Results showed that CH4 oxidation was restricted to three lakes, where the phosphate concentrations were highest. Molecular analyses revealed that MOB were initially detected in all lakes, although an increase in type I MOB only occurred in the three lake water incubations where oxidation could be observed. Accordingly, the increase in CO2 was on average 5 times higher in these three lake water incubations. For one lake where no oxidation was measured, we tested if temperature and CH4 availability could trigger CH4 oxidation. However, regardless of incubation temperatures and CH4 concentrations, ranging from 2 to 20 degrees C and 1-500M, respectively, no oxidation was observed. Our study indicates that some lakes with active wintertime CH4 oxidation may have low emissions during ice melt, while other and particularly nutrient poor lakes may accumulate large amounts of CH4 below ice that, in the absence of CH4 oxidation, will be emitted following ice melt. This variability in CH4 oxidation rates between lakes needs to be accounted for in large-scale CH4 emission estimates.
|
|
| 3. |
- Denfeld, Blaize Amber, 1988-
(författare)
-
Greenhouse Gas Dynamics in Ice-covered Lakes Across Spatial and Temporal Scales
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lakes play a major role in the global carbon (C) cycle, despite making up a small area of earth’s surface. Lakes receive, transport and process sizable amounts of C, emitting a substantial amount of the greenhouse gases, carbon dioxide (CO2) and methane (CH4), into the atmosphere. Ice-covered lakes are particularly sensitive to climate change, as future reductions to the duration of lake ice cover will have profound effects on the biogeochemical cycling of C in lakes. It is still largely unknown how reduced ice cover duration will affect CO2 and CH4 emissions from ice-covered lakes. Thus, the primary aim of this thesis was to fill this knowledge gap by monitoring the spatial and temporal dynamics of CO2 and CH4 in ice-covered lakes. The results of this thesis demonstrate that below ice CO2 and CH4 were spatially and temporally variable. Nutrients were strongly linked to below ice CO2 and CH4 oxidation variations across lakes. In addition, below ice CO2 was generally highest in small shallow lakes, and in bottom waters. Whilst below ice CH4 was elevated in surface waters near where bubbles from anoxic lake sediment were trapped. During the ice-cover period, CO2 accumulation below ice was not linear, and at ice-melt incomplete mixing of lake waters resulted in a continued CO2 storage in bottom waters. Further, CO2 transported from the catchment and bottom waters contributed to high CO2 emissions. The collective findings of this thesis indicate that CO2 and CH4 emissions from ice-covered lakes will likely increase in the future. The strong relationship between nutrients and C processes below ice, imply that future changes to nutrient fluxes within lakes will influence the biogeochemical cycling of C in lakes. Since catchment and lake sediment C fluxes play a considerable role in below ice CO2 and CH4 dynamics, changes to hydrology and thermal stability of lakes will undoubtedly alter CO2 and CH4 emissions. Nevertheless, ice-covered lakes constitute a significant component of the global C cycle, and as such, should be carefully monitored and accounted for when addressing the impacts of global climate change.
|
|
| 4. |
- Denfeld, Blaize, et al.
(författare)
-
Regional Variability and Drivers of Below Ice CO2 in Boreal and Subarctic Lakes
- 2016
-
Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 19:3, s. 461-476
-
Tidskriftsartikel (refereegranskat)abstract
- Northern lakes are ice-covered for considerable portions of the year, where carbon dioxide (CO2) can accumulate below ice, subsequently leading to high CO2 emissions at ice-melt. Current knowledge on the regional control and variability of below ice partial pressure of carbon dioxide (pCO(2)) is lacking, creating a gap in our understanding of how ice cover dynamics affect the CO2 accumulation below ice and therefore CO2 emissions from inland waters during the ice-melt period. To narrow this gap, we identified the drivers of below ice pCO(2) variation across 506 Swedish and Finnish lakes using water chemistry, lake morphometry, catchment characteristics, lake position, and climate variables. We found that lake depth and trophic status were the most important variables explaining variations in below ice pCO(2) across the 506 lakes(.) Together, lake morphometry and water chemistry explained 53% of the site-to-site variation in below ice pCO(2). Regional climate (including ice cover duration) and latitude only explained 7% of the variation in below ice pCO(2). Thus, our results suggest that on a regional scale a shortening of the ice cover period on lakes may not directly affect the accumulation of CO2 below ice but rather indirectly through increased mobility of nutrients and carbon loading to lakes. Thus, given that climate-induced changes are most evident in northern ecosystems, adequately predicting the consequences of a changing climate on future CO2 emission estimates from northern lakes involves monitoring changes not only to ice cover but also to changes in the trophic status of lakes.
|
|
| 5. |
- Ricão Canelhas, Monica, et al.
(författare)
-
Methane oxidation at the water-ice interface of an ice-covered lake
- 2016
-
Ingår i: Limnology and Oceanography. - : WILEY-BLACKWELL. - 0024-3590 .- 1939-5590. ; 61, s. S78-S90
-
Tidskriftsartikel (refereegranskat)abstract
- Lakes are important components of the global methane (CH4) cycle. In seasonally ice-covered lakes, CH4 transported by ebullition (bubbling) from anoxic sediments gets trapped at the water-ice interface. If not oxidized by methane-oxidizing bacteria (MOB), this can potentially lead to high episodic CH4 emissions at ice-melt. To understand the fate of CH4 trapped below ice, we measured depth-distributions of CH4 concentrations in the water column near bubbles trapped below ice in Lake Erken. We also performed a 21 d incubation experiment at low temperature (2.3 +/- 0.2 degrees C) to investigate the potential for CH4 oxidation. During most sampling occasions, we found steep CH4 concentration gradients just below the ice with a 13-fold decrease from the surface to a depth of 20 cm. In vitro incubations revealed that CH4 oxidation can occur at low temperatures typical for the water-ice interface. CH4 oxidation was observed as a significant decrease in CH4 concentration, a significant increase in stable isotope C-13 signature, and an increase in MOB during the incubation. Thus, CH4 accumulating in the top 20 cm of the water column, fed by diffusion from CH4 in trapped bubbles, may fuel significant CH4 oxidation. Since northern latitude lakes can be ice-covered for many months of the year and significant amounts of CH4 accumulate below the ice, the extent of CH4 oxidation under these low temperature-conditions is important for understanding the potential CH4 emissions to the atmosphere during ice-melt.
|
|
