| 1. |
- Grasset, Charlotte, et al.
(författare)
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The transformation of macrophyte-derived organic matter to methane relates to plant water and nutrient contents
- 2019
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 64:4, s. 1737-1749
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Tidskriftsartikel (refereegranskat)abstract
- Macrophyte detritus is one of the main sources of organic carbon (OC) in inland waters, and it is potentially available for methane (CH4) production in anoxic bottom waters and sediments. However, the transformation of macrophyte‐derived OC into CH4 has not been studied systematically, thus its extent and relationship with macrophyte characteristics remains uncertain. We performed decomposition experiments of macrophyte detritus from 10 different species at anoxic conditions, in presence and absence of a freshwater sediment, in order to relate the extent and rate of CH4 production to the detritus water content, C/N and C/P ratios. A significant fraction of the macrophyte OC was transformed to CH4 (mean = 7.9%; range = 0–15.0%) during the 59‐d incubation, and the mean total C loss to CO2 and CH4 was 17.3% (range = 1.3–32.7%). The transformation efficiency of macrophyte OC to CH4 was significantly and positively related to the macrophyte water content, and negatively to its C/N and C/P ratios. The presence of sediment increased the transformation efficiency to CH4 from an average of 4.0% (without sediment) to 11.8%, possibly due to physicochemical conditions favorable for CH4 production (low redox potential, buffered pH) or because sediment particles facilitate biofilm formation. The relationship between macrophyte characteristics and CH4 production can be used by future studies to model CH4 emission in systems colonized by macrophytes. Furthermore, this study highlights that the extent to which macrophyte detritus is mixed with sediment also affects CH4 production.
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| 2. |
- Isidorova, Anastasija, et al.
(författare)
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Contribution of aquatic and terrestrial sources to sediment organic carbon of four contrasting tropical reservoirs.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Following construction of a dam, a large amount of sediment is accumulated in the reservoir. The sediment contains organic carbon (OC) that is produced within the reservoir (aquatic) or on land (terrestrial). The origin of the sediment OC can influence the fate of the OC (burial or mineralization) as well as the extent to which the accumulating sediment OC may be accounted as a new carbon sink. In spite of its importance for evaluation of the carbon footprint of reservoirs, however, studies on the sediment OC origin in reservoirs are scarce.We therefore estimated sources of OC to four contrasting tropical reservoir sediments using lipid biomarkers (n-alkanes). The reservoirs ranged in their trophic status from oligotrophic to eutrophic. We used surface sediment to estimate the source of OC to reservoir sediment, and deep sediment to estimate the source of buried OC.We found that terrestrial material (terrestrial plants and soil) was the largest source of sediment OC (61%; a mean of all samples). Terrestrial OC was dominant in river inflows, while aquatic OC increased towards dams. Particularly high aquatic OC in sediment (up to 92%) was found at locations of cyanobacteria blooms. The fraction of aquatic OC in surface sediment increased with reservoir productivity from 31% in oligotrophic reservoir, 45% in mesotrophic, 58% in meso-eutrophic to 66% in eutrophic reservoir. The fraction of aquatic OC was generally lower in deep sediment (33%; a mean of all deep) than in surface sediment (50%). This aquatic OC in deep sediment has a potential to be buried and constitutes an anthropogenic OC sink, thereby decreasing hydropower carbon footprint.
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| 3. |
- Isidorova, Anastasija, et al.
(författare)
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Methane formation in tropical reservoirs predicted from sediment age and nitrogen
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Freshwater reservoirs, in particular tropical ones, are an important source of methane (CH4) to the atmosphere, but current estimates are uncertain. The CH4 emitted from reservoirs is microbially produced in their sediments, but at present, the rate of CH4 formation in reservoir sediments cannot be predicted from sediment characteristics, limiting our understanding of reservoir CH4 emission. Here we show through a long-term incubation experiment that the CH4 formation rate in sediments of widely different tropical reservoirs can be predicted from sediment age and total nitrogen concentration. CH4 formation occurs predominantly in sediment layers younger than 6-12 years and beyond these layers sediment organic carbon may be considered effectively buried. Hence mitigating reservoir CH4 emission via improving nutrient management and thus reducing organic matter supply to sediments is within reach. Our model of sediment CH4 formation represents a first step towards constraining reservoir CH4 emission from sediment characteristics.
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| 4. |
- Isidorova, Anastasija, et al.
(författare)
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Reduced Mineralization of Terrestrial OC in Anoxic Sediment Suggests Enhanced Burial Efficiency in Reservoirs Compared to Other Depositional Environments
- 2019
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 124:3, s. 678-688
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Tidskriftsartikel (refereegranskat)abstract
- Freshwater reservoirs are important sites of organic carbon (OC) burial, but the extent to which reservoir OC burial is a new anthropogenic carbon sink is currently unclear. While burial of aquatic OC (by, e.g., phytoplankton) in reservoirs may count as a new C sink, the burial of terrestrial OC in reservoirs constitutes a new C sink only if the burial is more efficient in reservoirs than in other depositional environments. We carried out incubation experiments that mimicked the environmental conditions of different depositional environments along the land‐sea continuum (oxic and anoxic freshwater, oxic and anoxic seawater, oxic river bedload, and atmosphere‐exposed floodplain) to investigate whether reservoirs bury OC more efficiently compared to other depositional environments. For sediment OC predominantly of terrestrial origin, OC degradation rates were significantly lower, by a factor of 2, at anoxic freshwater and saltwater conditions compared to oxic freshwater and saltwater, river, and floodplain conditions. However, the transformation of predominantly terrestrial OC to methane was one order of magnitude higher in anoxic freshwater than at other conditions. For sediment OC predominantly of aquatic origin, OC degradation rates were uniformly high at all conditions, implying equally low burial efficiency of aquatic OC (76% C loss in 57 days). Since anoxia is more common in reservoirs than in the coastal ocean, these results suggest that reservoirs are a depositional environment in which terrestrial OC is prone to become buried at higher efficiency than in the ocean but where also the terrestrial OC most efficiently is transformed to methane.
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| 5. |
- Kosten, Sarian, et al.
(författare)
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Extreme drought boosts CO2 and CH4 emissions from reservoir drawdown areas
- 2018
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Ingår i: Inland Waters. - : Informa UK Limited. - 2044-2041 .- 2044-205X. ; 8:3, s. 329-340
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Tidskriftsartikel (refereegranskat)abstract
- Although previous studies suggest that greenhouse gas (GHG) emissions from reservoir sediment exposed to the atmosphere during drought may be substantial, this process has not been rigorously quantified. Here we determined carbon dioxide (CO 2) and methane (CH 4) emissions from sediment cores exposed to a drying and rewetting cycle. We found a strong temporal variation in GHG emissions with peaks when the sediment was drained (C emissions from permanently wet sediment and drained sediments were, respectively, 251 and 1646 mg m −2 d −1 for CO 2 and 0.8 and 547.4 mg m −2 d −1 for CH 4) and then again during rewetting (C emissions from permanently wet sediment and rewetted sediments were, respectively, 456 and 1725mg m −2 d −1 for CO 2 and 1.3 and 3.1 mg m −2 d −1 for CH 4). To gain insight into the importance of these emissions at a regional scale, we used Landsat satellite imagery to upscale our results to all Brazilian reservoirs. We found that during the extreme drought of 2014-2015, an additional 1299 km 2 of sediment was exposed, resulting in an estimated emission of 8.5 × 10 11 g of CO 2-eq during the first 15 d after the overlying water disappeared and in the first 33 d after rewetting, the same order of magnitude as the year-round GHG emissions of large (∼mean surface water area 454 km 2) Brazilian reservoirs, excluding the emissions from the draw-down zone. Our estimate, however, has high uncertainty, with actual emissions likely higher. We therefore argue that the effects of drought on reservoir GHG emissions merits further study, especially because climate models indicate an increase in the frequency of severe droughts in the future. We recommend incorporation of emissions during drying and rewetting into GHG budgets of reservoirs to improve regional GHG emission estimates and to enable comparison between GHG emissions from hydroelectric and other electricity sources. We also emphasize that peak emissions at the onset of drought and the later rewetting should be quantified to obtain reliable emission estimates. ARTICLE HISTORY
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| 6. |
- Mendonca, Raquel, 1983-, et al.
(författare)
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Bimodality in stable isotope composition facilitates the tracing of carbon transfer from macrophytes to highertrophic levels
- 2013
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 710:1, s. 205-218
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Tidskriftsartikel (refereegranskat)abstract
- Even though the suitability of macrophytesto act as a carbon source to food webs hasbeen questioned by some studies, some others indicate that macrophyte-derived carbon may play an importantrole in the trophic transfer of organic matter in thefood web of shallow lakes. To evaluate the importanceof macrophytes to food webs, we collected primaryproducers—macrophytes and periphyton—and consumersfrom 19 South American shallow lakes andanalyzed their carbon stable isotopes composition(d13C). Despite the diversity of inorganic carbonsources available in our study lakes, the macrophytes’d13C signatures showed a clear bimodal distribution:13C-depleted and 13C-enriched, averaging at -27.2 and -13.5%, respectively. We argue that the use ofeither CO2 or HCO3- by the macrophytes largelycaused the bimodal pattern in d13C signals. Thecontribution of carbon from macrophytes to the lake’sfood webs was not straightforward in most of the lakesbecause the macrophytes’ isotopic composition wasquite similar to the isotopic composition of periphyton,phytoplankton, and terrestrial carbon. However,in some lakes where the macrophytes had a distinctisotopic signature, our data suggest that macrophytescan represent an important carbon source to shallowlake food webs.
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| 7. |
- Mendonca, Raquel, 1983-, et al.
(författare)
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Carbon Sequestration in a Large Hydroelectric Reservoir : An Integrative Seismic Approach
- 2014
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 17:3, s. 430-441
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Tidskriftsartikel (refereegranskat)abstract
- Artificial reservoirs likely accumulate more carbon than natural lakes due to their unusually high sedimentation rates. Nevertheless, the actual magnitude of carbon accumulating in reservoirs is poorly known due to a lack of whole-system studies of carbon burial. We determined the organic carbon (OC) burial rate and the total OC stock in the sediments of a tropical hydroelectric reservoir by combining a seismic survey with sediment core sampling. Our data suggest that no sediment accumulation occurs along the margins of the reservoir and that irregular bottom morphology leads to irregular sediment deposition. Such heterogeneous sedimentation resulted in high spatial variation in OC burial-from 0 to 209 g C m(-2) y(-1). Based on a regression between sediment accumulation and OC burial rates (R (2) = 0.94), and on the mean reservoir sediment accumulation rate (0.51 cm y(-1), from the seismic survey), the whole-reservoir OC burial rate was estimated at 42.2 g C m(-2) y(-1). This rate was equivalent to 70% of the reported carbon emissions from the reservoir surface to the atmosphere and corresponded to a total sediment OC accumulation of 0.62 Tg C since the reservoir was created. The approach we propose here allows an inexpensive and integrative assessment of OC burial in reservoirs by taking into account the high degree of spatial variability and based on a single assessment. Because burial can be assessed shortly after the survey, the approach combining a seismic survey and coring could, if applied on a larger scale, contribute to a more complete estimate of carbon stocks in freshwater systems in a relatively short period of time.
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| 8. |
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| 9. |
- Mendonca, Raquel, 1983-, et al.
(författare)
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Hydroelectric carbon sequestration
- 2012
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 5, s. 838-840
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Tidskriftsartikel (refereegranskat)
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| 10. |
- Mendonca, Raquel, 1983-, et al.
(författare)
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Organic carbon burial in global lakes and reservoirs
- 2017
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Ingår i: Nature Communications. - : Springer. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Burial in sediments removes organic carbon (OC) from the short-term biosphere-atmosphere carbon (C) cycle, and therefore prevents greenhouse gas production in natural systems. Although OC burial in lakes and reservoirs is faster than in the ocean, the magnitude of inland water OC burial is not well constrained. Here we generate the first global-scale and regionally resolved estimate of modern OC burial in lakes and reservoirs, deriving from a compre- hensive compilation of literature data. We coupled statistical models to inland water area inventories to estimate a yearly OC burial of 0.15 (range, 0.06–0.25) Pg C, of which ~40% is stored in reservoirs. Relatively higher OC burial rates are predicted for warm and dry regions. While we report lower burial than previously estimated, lake and reservoir OC burial cor- responded to ~20% of their C emissions, making them an important C sink that is likely to increase with eutrophication and river damming.
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