| 1. |
|
|
| 2. |
|
|
| 3. |
- Berggren, Martin, et al.
(författare)
-
Quality transformation of dissolved organic carbon during water transit through lakes : contrasting controls by photochemical and biological processes
- 2018
-
Ingår i: Biogeosciences. - : European Geosciences Union (EGU). - 1726-4170 .- 1726-4189. ; 15:2, s. 457-470
-
Tidskriftsartikel (refereegranskat)abstract
- Dissolved organic carbon (DOC) may be removed, transformed, or added during water transit through lakes, resulting in changes in DOC composition and pigmentation (color). However, the process-based understanding of these changes is incomplete, especially for headwater lakes. We hypothesized that because heterotrophic bacteria preferentially consume noncolored DOC, while photochemical processing removes colored fractions, the overall changes in DOC color upon water passage through a lake depend on the relative importance of these two processes, accordingly. To test this hypothesis we combined laboratory experiments with field studies in nine boreal lakes, assessing both the relative importance of different DOC decay processes (biological or photochemical) and the loss of color during water transit time (WTT) through the lakes. We found that influence from photo-decay dominated changes in DOC quality in the epilimnia of relatively clear headwater lakes, resulting in systematic and selective net losses of colored DOC. However, in highly pigmented brown-water lakes (absorbance at 420 nm > 7 m(-1)) biological processes dominated, and there was no systematic relationship between color loss and WTT. Moreover, in situ data and dark experiments supported our hypothesis on the selective microbial removal of nonpigmented DOC, mainly of low molecular weight, leading to persistent water color in these highly colored lakes. Our study shows that brown headwater lakes may not conform to the commonly reported pattern of the selective removal of colored constituents in freshwaters, as DOC can show a sustained degree of pigmentation upon transit through these lakes.
|
|
| 4. |
- Erhagen, Björn, et al.
(författare)
-
Bioavailability of stream dissolved organic carbon (DOC) during spring flood and base flow in high-latitude streams
- 2015
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An important component of the carbon cycle is the lateral flow of dissolved organic carbon (DOC) from terrestrial ecosystems to streams and rivers. The fate of this carbon depends very much on the bioavailability of DOC (BDOC), which may determine whether DOC is returned to the atmosphere as CO2 or deposited in sediments. This study focuses on the linkages between stream DOC composition, optical characteristics and bioavailability along vegetation gradients in subarctic Sweden. We sampled streams from tundra, birch forest, and boreal forest ecoregions, which encompass large differences in C:N ratios (6.4-30.1) and spectroscopic characteristics, all related to variation in landscape properties. The DOC bioavailability was determined through laboratory bioassays carried out twice during the year (spring-flood and base flow). During spring flood, DOC concentration varied between 0.5 - 6.7 mg L-1 and the BDOC ranged between 3- 24 %, with the highest BDOC from birch forest/tundra and tundra streams. Results suggest that broad-scale transitions in vegetation structure across sub-arctic landscapes have important implications for the quantity and quality of DOC delivered to aquatic ecosystems.
|
|
| 5. |
- Natchimuthu, Sivakiruthika, et al.
(författare)
-
Influence of weather variables on methane and carbon dioxide flux from a shallow pond
- 2014
-
Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 1573-515X .- 0168-2563. ; 119:1-3, s. 403-413
-
Tidskriftsartikel (refereegranskat)abstract
- Freshwaters are important sources of the greenhouse gases methane (CH4) and carbon dioxide (CO2) to the atmosphere. Knowledge about temporal variability in these fluxes is very limited, yet critical for proper study design and evaluating flux data. Further, to understand the reasons for the variability and allow predictive modeling, the temporal variability has to be related to relevant environmental variables. Here we analyzed the effect of weather variables on CH4 and CO2 flux from a small shallow pond during a period of 4 months. Mean CH4 flux and surface water CH4 concentration were 8.0 [3.3-15.1] +/- A 3.1 mmol m(-2) day(-1) (mean [range] +/- A 1 SD) and 1.3 [0.3-3.5] +/- A 0.9 A mu M respectively. Mean CO2 flux was 1.1 [-9.8 to 16.0] +/- A 6.9 mmol m(-2) day(-1). Substantial diel changes in CO2 flux and surface water CH4 concentration were observed during detailed measurements over a 24 h cycle. Thus diel patterns need to be accounted for in future measurements. Significant positive correlations of CH4 emissions with temperature were found and could include both direct temperature effects as well as indirect effects (e.g. related to the growth season and macrophyte primary productivity providing organic substrates). CO2 flux on the other hand was negatively correlated to temperature and solar radiation, presumably because CO2 consumption by plants was higher relative to CO2 production by respiration during warm sunny days. Interestingly, CH4 fluxes were comparable to ponds with similar morphometry and macrophyte abundance in the tropics. We therefore hypothesize that CH4 and CO2 summer emissions from ponds could be more related to the morphometry and dominating primary producers rather than latitude per se. Data indicate that CH4 emissions, given the system characteristic frameworks, is positively affected by increased temperatures or prolonged growth seasons.
|
|
| 6. |
|
|
| 7. |
- Panneer Selvam, Balathandayuthabani, et al.
(författare)
-
Degradation potentials of dissolved organic carbon (DOC) from thawed permafrost peat
- 2017
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
-
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.
|
|
| 8. |
- Panneer Selvam, Balathandayuthabani, et al.
(författare)
-
Effect of permafrost thaw on labile dissolved organic carbon in a northern palsa mire
- 2015
-
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.
|
|
| 9. |
- Panneer Selvam, Balathandayuthabani, et al.
(författare)
-
Influence of soil frost on the character and degradability of dissolved organic carbon in boreal forest soils
- 2016
-
Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8961 .- 2169-8953. ; 121:3, s. 829-840
-
Tidskriftsartikel (refereegranskat)abstract
- Recent studies suggest that increases in extent and duration of winter soil frost increases dissolved organic carbon (DOC) concentrations in boreal riparian soils and connected aquatic systems during the subsequent spring and summer. However, little is known about the impact of frost on DOC character and its degradability. We applied three experimental treatments to riparian soils in northern Sweden—shallow soil frost (insulated), deep soil frost (snow removed) and control plots—to test the effect of different soil frost regimes on the chemical characteristics and degradability of soil DOC. Soil pore water samples were analyzed using excitation-emission fluorescence (parallel factor analysis) combined with biological and photochemical degradation experiments. We found that the absolute bacterial metabolic rates were significantly lower in samples from the shallow soil frost treatments, compared with the other treatments. Explorative multivariate analyses indicate that increasing soil frost is contributing to increased protein-like fluorescence and to increased biological degradability of the DOC. Our study shows that decreases in riparian soil frost due to climate warming may not only contribute to decreased riparian DOC concentrations but also lead to shifts in the DOC composition, resulting in decreased biodegradability (yet similar photodegradability) of the DOC that is exported from riparian soils to streams.
|
|
| 10. |
- Panneer Selvam, Balathandayuthabani, et al.
(författare)
-
Methane and carbon dioxide emissions from inland waters in India - implications for large scale greenhouse gas balances
- 2014
-
Ingår i: Global Change Biology. - : Wiley: 12 months. - 1354-1013 .- 1365-2486. ; 20:11, s. 3397-3407
-
Tidskriftsartikel (refereegranskat)abstract
- Inland waters were recently recognized to be important sources of methane (CH4) and carbon dioxide (CO2) to the atmosphere, and including inland water emissions in large scale greenhouse gas (GHG) budgets may potentially offset the estimated carbon sink in many areas. However, the lack of GHG flux measurements and well-defined inland water areas for extrapolation, make the magnitude of the potential offset unclear. This study presents coordinated flux measurements of CH4 and CO2 in multiple lakes, ponds, rivers, open wells, reservoirs, springs, and canals in India. All these inland water types, representative of common aquatic ecosystems in India, emitted substantial amounts of CH4 and a major fraction also emitted CO2. The total CH4 flux (including ebullition and diffusion) from all the 45 systems ranged from 0.01 to 52.1mmolm(-2)d(-1), with a mean of 7.8 +/- 12.7 (mean +/- 1 SD) mmolm(-2)d(-1). The mean surface water CH4 concentration was 3.8 +/- 14.5m (range 0.03-92.1m). The CO2 fluxes ranged from -28.2 to 262.4mmolm(-2)d(-1) and the mean flux was 51.9 +/- 71.1mmolm(-2)d(-1). The mean partial pressure of CO2 was 2927 +/- 3269atm (range: 400-11467atm). Conservative extrapolation to whole India, considering the specific area of the different water types studied, yielded average emissions of 2.1 Tg CH(4)yr(-1) and 22.0 Tg CO(2)yr(-1) from Indias inland waters. When expressed as CO2 equivalents, this amounts to 75 Tg CO2 equivalentsyr(-1) (53-98 Tg CO2 equivalentsyr(-1); +/- 1 SD)(,) with CH4 contributing 71%. Hence, average inland water GHG emissions, which were not previously considered, correspond to 42% (30-55%) of the estimated land carbon sink of India. Thereby this study illustrates the importance of considering inland water GHG exchange in large scale assessments.
|
|
