| 1. |
- Bravo, Andrea G., et al.
(författare)
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The interplay between total mercury, methylmercury and dissolved organic matter in fluvial systems : A latitudinal study across Europe
- 2018
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Ingår i: Water Research. - : Elsevier. - 0043-1354 .- 1879-2448. ; 144, s. 172-182
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-mercury (MeHg) concentrations in aquatic ecosystems. Studies attempting to link dissolved organic matter (DOM) to levels of THg or MeHg are few and geographically constrained. Additionally, stream and river systems have been understudied as compared to lakes. Hence, the aim of this study was to examine the influence of DOM concentration and composition, morphological descriptors, land uses and water chemistry on THg and MeHg concentrations and the percentage of THg as MeHg (%MeHg) in 29 streams across Europe spanning from 41°N to 64°N. THg concentrations (0.06–2.78 ng L−1) were highest in streams characterized by DOM with a high terrestrial soil signature and low nutrient content. MeHg concentrations (7.8–159 pg L−1) varied non-systematically across systems. Relationships between DOM bulk characteristics and THg and MeHg suggest that while soil derived DOM inputs control THg concentrations, autochthonous DOM (aquatically produced) and the availability of electron acceptors for Hg methylating microorganisms (e.g. sulfate) drive %MeHg and potentially MeHg concentration. Overall, these results highlight the large spatial variability in THg and MeHg concentrations at the European scale, and underscore the importance of DOM composition on mercury cycling in fluvial systems.
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| 2. |
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| 3. |
- Groeneveld, Marloes M., et al.
(författare)
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The influence of pH on dissolved organic matter fluorescence in inland waters
- 2022
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Ingår i: Analytical Methods. - : Royal Society of Chemistry. - 1759-9660 .- 1759-9679. ; 14:13, s. 1351-1360
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence is an easily available analytical technique used to assess the optical characteristics of dissolved organic matter (DOM). Despite widespread use, there has been some confusion about how robust fluorescence spectroscopy is to differences in solution pH. Here we assess fluorescence characteristics of three natural water samples and one commercially available standard (Nordic Reservoir) by modifying the pH across a range from 3.5 to 9.0 at 0.5 pH increments. We used two statistical approaches to assess if fluorescence intensity shifted significantly across this pH range. We identified that humic-like and protein-like fluorescence was largely stable within the pH range of 5.5 to 7.5, which represents 80% of Swedish lakes and streams. Likewise, we found that the three commonly used fluorescence indices were robust across the full pH range tested with the exception of the humification index, which had a narrower range of stability. The commerical humic substance sample was highly unstable with changes to pH in the regions of protein-like fluorescence being particularly sensitive. One of our conclusions is that differences in fluorescence intensity in the pH range of 5.5 to 7.5, typical for most inland waters, are generally minor. We recommend adjusting the pH when samples fall outside this region and to be especially careful in interpreting results from commercial humic substances.
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| 4. |
- Heffernan, Liam, et al.
(författare)
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Review article : Terrestrial dissolved organic carbon in northern permafrost
- 2024
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Ingår i: The Cryosphere. - : Copernicus Publications. - 1994-0416 .- 1994-0424. ; 18:3, s. 1443-1465
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Forskningsöversikt (refereegranskat)abstract
- As the permafrost region warms and permafrost soils thaw, vast stores of soil organic carbon (C) become vulnerable to enhanced microbial decomposition and lateral transport into aquatic ecosystems as dissolved organic carbon (DOC). The mobilization of permafrost soil C can drastically alter the net northern permafrost C budget. DOC entering aquatic ecosystems becomes biologically available for degradation as well as other types of aquatic processing. However, it currently remains unclear which landscape characteristics are most relevant to consider in terms of predicting DOC concentrations entering aquatic systems from permafrost regions. Here, we conducted a systematic review of 111 studies relating to, or including, concentrations of DOC in terrestrial permafrost ecosystems in the northern circumpolar region published between 2000 and 2022. We present a new permafrost DOC dataset consisting of 2845 DOC concentrations, collected from the top 3 m in permafrost soils across the northern circumpolar region. Concentrations of DOC ranged from 0.1 to 500 mg L−1 (median = 41 mg L−1) across all permafrost zones, ecoregions, soil types, and thermal horizons. Across the permafrost zones, the highest median DOC concentrations were in the sporadic permafrost zone (101 mg L−1), while lower concentrations were found in the discontinuous (60 mg L−1) and continuous (59 mg L−1) permafrost zones. However, median DOC concentrations varied in these zones across ecosystem type, with the highest median DOC concentrations in each ecosystem type of 66 and 63 mg L−1 found in coastal tundra and permafrost bog ecosystems, respectively. Coastal tundra (130 mg L−1), permafrost bogs (78 mg L−1), and permafrost wetlands (57 mg L−1) had the highest median DOC concentrations in the permafrost lens, representing a potentially long-term store of DOC. Other than in Yedoma ecosystems, DOC concentrations were found to increase following permafrost thaw and were highly constrained by total dissolved nitrogen concentrations. This systematic review highlights how DOC concentrations differ between organic- or mineral-rich deposits across the circumpolar permafrost region and identifies coastal tundra regions as areas of potentially important DOC mobilization. The quantity of permafrost-derived DOC exported laterally to aquatic ecosystems is an important step for predicting its vulnerability to decomposition.
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| 5. |
- Kellerman, Anne M., et al.
(författare)
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Chemodiversity of dissolved organic matter in lakes driven by climate and hydrology
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 3804-
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Tidskriftsartikel (refereegranskat)abstract
- Despite the small continental coverage of lakes, they are hotspots of carbon cycling, largely due to the processing of terrestrially derived dissolved organic matter (DOM). As DOM is an amalgam of heterogeneous compounds comprising gradients of microbial and physicochemical reactivity, the factors influencing DOM processing at the molecular level and the resulting patterns in DOM composition are not well understood. Here we show, using ultrahigh-resolution mass spectrometry to unambiguously identify 4,032 molecular formulae in 120 lakes across Sweden, that the molecular composition of DOM is shaped by precipitation, water residence time and temperature. Terrestrially derived DOM is selectively lost as residence time increases, with warmer temperatures enhancing the production of nitrogen-containing compounds. Using biodiversity concepts, we show that the molecular diversity of DOM, or chemodiversity, increases with DOM and nutrient concentrations. The observed molecular-level patterns indicate that terrestrially derived DOM will become more prevalent in lakes as climate gets wetter.
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| 6. |
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| 7. |
- Kellerman, Anne Marie
(författare)
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Molecular-level dissolved organic matter dynamics in lakes : Constraints on reactivity and persistence
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dissolved organic matter (DOM) is a central component of the global carbon cycle. Thus, small changes to the amount of DOM imported, processed and produced within lakes can have a large effect on regional carbon budgets. In addition to being a vital energy source at the base of the aquatic food web, DOM is physico-chemically reactive. However, identifying and understanding the controls of DOM processing has remained challenging due to the complex composition of DOM. DOM comprises a mixture of decomposition by-products of terrestrial origin as well as newly synthesized material from in situ production. DOM compounds form gradients of reactivity to biogeochemical processes, such as photodegradation, biodegradation, and flocculation, and they perform a suite of functions in aquatic systems. The overarching goal of this thesis was to investigate controls of DOM processing in Swedish lakes. We do this in two ways: 1) by characterizing the molecular-level composition of DOM in lakes, and 2) by investigating interactions between very labile and relatively recalcitrant DOM. The first three chapters utilize ultrahigh resolution mass spectrometry to show that the detailed chemical composition of DOM varies along a hydrology gradient, and secondarily along a temperature gradient that co-varies with agriculture and nutrients. Next, we illustrate the coherence between molecular-level characteristics and bulk optical characteristics. Together, these studies suggest that protein-like fluorescence, aliphatic compounds, and N-containing compounds are either resistant to degradation or tightly cycled in the system, and thus persist at long water residence times. The most oxidized compounds, such as vascular plant-derived polyphenolic compounds, are abundant in areas with high precipitation and are lost with increasing water residence time. Vascular plant-derived polyphenolic compounds were most strongly related to DOM with high apparent molecular weight, suggesting that hydrophobic interactions drive aggregate formation. Furthermore, the association of high molecular weight DOM with polyphenolic compounds suggests that aggregates are hotspots of reactivity in aquatic systems. Finally, we find no indication that the addition of labile organic matter enhances the biodegradation of less reactive DOM. Thus, we suggest that in freshwaters, intrinsic molecular properties, such as the basic structural features of compounds, dominate over extrinsic factors.
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| 8. |
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| 9. |
- Kothawala, Dolly N., et al.
(författare)
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Controls of dissolved organic matter quality : evidence from a large-scale boreal lake survey
- 2014
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 20:4, s. 1101-1114
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Tidskriftsartikel (refereegranskat)abstract
- Inland waters transport large amounts of dissolved organic matter (DOM) from terrestrial environments to the oceans, but DOM also reacts en route, with substantial water column losses by mineralization and sedimentation. For DOM transformations along the aquatic continuum, lakes play an important role as they retain waters in the landscape allowing for more time to alter DOM. We know DOM losses are significant at the global scale, yet little is known about how the reactivity of DOM varies across landscapes and climates. DOM reactivity is inherently linked to its chemical composition. We used fluorescence spectroscopy to explore DOM quality from 560 lakes distributed across Sweden and encompassed a wide climatic gradient typical of the boreal ecozone. Six fluorescence components were identified using parallel factor analysis (PARAFAC). The intensity and relative abundance of these components were analyzed in relation to lake chemistry, catchment, and climate characteristics. Land cover, particularly the percentage of water in the catchment, was a primary factor explaining variability in PARAFAC components. Likewise, lake water retention time influenced DOM quality. These results suggest that processes occurring in upstream water bodies, in addition to the lake itself, have a dominant influence on DOM quality. PARAFAC components with longer emission wavelengths, or red-shifted components, were most reactive. In contrast, protein-like components were most persistent within lakes. Generalized characteristics of PARAFAC components based on emission wavelength could ease future interpretation of fluorescence spectra. An important secondary influence on DOM quality was mean annual temperature, which ranged between −6.2 and +7.5 °C. These results suggest that DOM reactivity depends more heavily on the duration of time taken to pass through the landscape, rather than temperature. Projected increases in runoff in the boreal region may force lake DOM toward a higher overall amount and proportion of humic-like substances.
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| 10. |
- Kothawala, Dolly N., et al.
(författare)
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Selective loss and preservation of lake water dissolved organic matter fluorescenceduring long-term dark incubations
- 2012
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 433, s. 238-246
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Tidskriftsartikel (refereegranskat)abstract
- The biogeochemical processing of dissolved organic matter (DOM) in inland waters is inherently related to its molecular structure and ecological function. Controlled bioassays are a valuable tool to analyze these relationships, but are seldom conducted and compared at temporal scales that typically prevail in natural inland waters. Here we incubated water from six boreal lakes in the dark and examined changes to the initial fluorescence and absorbance after 3.5 years. We identified five fluorescence components with parallel factor (PARAFAC) analysis (CC, CM, CA, CX and CT) and found a consistent change in the relative intensity of two dominant PARAFAC components (increase in CA:CC, corresponding to Peak A:Peak C), commonly found in lake water, that represent terrestrially-derived DOM. Surprisingly, we only found minor changes to specific absorbance (SUVA), and did not find any changes to other spectral indexes including the fluorescence index, humification index and freshness index. By incorporating lakes spanning a wide range of initial total organic carbon concentrations (3.7 to 32.5 mg L− 1), water residence times, and spectral characteristics (e.g. SUVA 1.13 to 3.77 L·mg C− 1·m− 1), we found that the relative intensities of two humic-like peaks were the most revealing of changes to DOM structure during dark incubations. We also verified that inner filter effects were adequately corrected within the concentration range of incubated samples. Thus, the processing of DOM under dark conditions, including microbial decomposition and flocculation, may have a greater influence on the humic-like peaks, particularly CC (Peak C), with negligible changes to more commonly used spectral indexes.
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| 11. |
- Kothawala, Dolly N., et al.
(författare)
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The relative influence of land cover, hydrology, and in-stream processing on the composition of dissolved organic matter in boreal streams
- 2015
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 120:8, s. 1491-1505
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Tidskriftsartikel (refereegranskat)abstract
- Low-order boreal streams are particularly sensitive interfaces where dissolved organic matter (DOM) is transported from soils to inland waters. Disentangling the relative influence of key environmental factors suspected to influence stream water DOM composition is highly relevant to predicting the reactivity and fate of terrestrial DOM entering inland waters. Here we examined changes to DOM composition using absorbance and fluorescence, from 17 boreal streams ranging from first to fourth orders, over 14 months, including the rarely studied winter season, and two snowmelt periods (n = 836). We also analyzed soil pore water samples from three forest soil lysimeters to a depth of 70 cm (n = 60). Of five identified fluorescing parallel factor analysis components, two (C4 and C5) expressed a clear mire wetland or forest signature, providing distinct molecular markers of dominant land cover. In fact, land cover alone explained 49% of the variability in DOM composition. In contrast, seasonal fluctuations in hydrology only contributed to minor shifts (8%) in the composition of stream water DOM, while in-stream transformations to DOM composition were undetectable. These findings suggest that low-order boreal streams act as a passive pipe, since in-stream processing of DOM is restricted by short water residence times (6 h to 2 days). In addition, we demonstrated the sensitivity of optical approaches to distinguish between key terrestrial sources of DOM in the boreal landscape. By distinguishing the proportional leverage of key environmental controls on headwater stream DOM composition, we are better equipped to predict where and when key DOM transformations occur in the aquatic conduit.
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| 12. |
- Kutser, Tiit, et al.
(författare)
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Impact of iron associated to organic matter on remote sensing estimates of lake carbon content
- 2015
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Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257 .- 1879-0704. ; 156, s. 109-116
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Tidskriftsartikel (refereegranskat)abstract
- There is a strong need to develop remote sensing methods for mapping lake carbon content on regional to global scales. The use of in situ methods is impractical for monitoring lake water quality over large geographical areas, which is a fundamental requirement to understand the true role of lakes in the global carbon cycle. The coloured component of dissolved organic carbon (DOC), called CDOM, absorbs light strongly in the blue part of the visible spectrum and can be used as a proxy for mapping lake DOC with remote sensing. However, iron associated to organic matter can cause extra browning of waters. Consequently, the remote sensing signal we interpret as DOC may partially be attributed to the presence of iron associated to organic matter, potentially hampering our ability to estimate carbon concentrations. A thorough analysis of biogeochemical parameters was carried out on Lake Malaren on August 23, 2010, and a MERIS full resolution image was acquired simultaneously. MERIS standard, Case 2 Regional, and Boreal processors were used to calculate remote sensing products, which were compared with different lake water characteristics. The carbon to iron ratio was different from the rest of the lake in one of the basins. MERIS standard and Case 2 Regional processors were sensitive to this difference as the correlation between MERIS CDOM product and DOC was low (R-2 = 0.43) for all sampling stations and increased to 0.92 when the one basin was excluded. The Boreal Lakes processor results were less disturbed by the different carbon-iron ratios found in one basin and produced reasonably good results (R-2 = 0.65). We found MERIS products (e.g. total absorption) that provided good correlation (R-2 = 0.80) with DOC-specific absorbance at 254 nm, called SUVA, which is a metric commonly used to assess drinking water treatability. However, none of the MERIS products were suitable for mapping the total organic carbon in Lake Malaren.MERIS total suspended matter product was a good (R-2 = 0.73) proxy for particulate iron, meaning that the particulate iron content in Malaren can be mapped from space. (C) 2014 Elsevier Inc. All rights reserved.
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| 13. |
- Lavonen, Elin, et al.
(författare)
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Tracking changes in the optical properties and molecular composition of dissolved organic matter during drinking water production
- 2015
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 85, s. 286-294
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Tidskriftsartikel (refereegranskat)abstract
- Absorbance, 3D fluorescence and ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) were used to explain patterns in the removal of chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) at the molecular level during drinking water production at four large drinking water treatment plants in Sweden. When dissolved organic carbon (DOC) removal was low, shifts in the dissolved organic matter (DOM) composition could not be detected with commonly used DOG-normalized parameters (e.g. specific UV254 absorbance SUVA), but was clearly observed by using differential absorbance and fluorescence or ESI-FT-ICR-MS. In addition, we took a novel approach by identifying how optical parameters were correlated to the elemental composition of DOM by using rank correlation to connect optical properties to chemical formulas assigned to mass peaks from FT-ICR-MS analyses. Coagulation treatment selectively removed FDOM at longer emission wavelengths (450-600 nm), which significantly correlated with chemical formulas containing oxidized carbon (average carbon oxidation state >= 0), low hydrogen to carbon ratios (H/C: average +/- SD = 0.83 +/- 0.13), and abundant oxygen-containing functional groups (O/C = 0.62 +/- 0.10). Slow sand filtration was less efficient in removing DOM, yet selectively targeted FDOM at shorter emission wavelengths (between 300 and 450 nm), which commonly represents algal rather than terrestrial sources. This shorter wavelength FDOM correlated with chemical formulas containing reduced carbon (average carbon oxidation state <= 0), with relatively few carbon-carbon double bonds (H/C = 1.32 +/- 0.16) and less oxygen per carbon (O/C = 0.43 +/- 0.10) than those removed during coagulation. By coupling optical approaches with FT-ICR-MS to characterize DOM, we were for the first time able to confirm the molecular composition of absorbing and fluorescing DOM selectively targeted during drinking water treatment.
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| 14. |
- Ledesma, Jose, et al.
(författare)
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Stream Dissolved Organic Matter Composition Reflects the Riparian Zone, Not Upslope Soils in Boreal Forest Headwaters
- 2018
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 54:6, s. 3896-3912
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Tidskriftsartikel (refereegranskat)abstract
- Despite the strong quantitative evidence that riparian zones (RZs) are the dominant source of dissolved organic carbon (DOC) to boreal streams, there is still a debate about the potential contribution of upslope areas to fluvial carbon export. To shed new light into this debate, we investigated the molecular composition of dissolved organic matter (DOM) in four upslope-riparian-stream transects in a Northern Swedish forest catchment using absorbance (A(254)/A(365) and SUVA(254)) and fluorescence (fluorescence and freshness indices) metrics. Based on these metrics, our results indicate that stream water DOM molecular composition resembles that of RZs and significantly differs from that of upslope areas. The resemblance between stream and riparian DOM was most apparent for the Dominant Source Layer (DSL), a narrow RZ stratum that, theoretically, contributes the most to solute and water fluxes to streams. Spectroscopic characterization based on traditional interpretations of the metrics suggested that mineral upslope (podzol) DOM is less aromatic, more microbially derived, and more recently produced than organic riparian (histosol) and stream DOM. We conclude that RZs, and specifically DSLs, are the main sources of DOC to boreal headwater streams and potentially to other streams located in low-gradient, organic matter-rich catchments. Plain Language Summary Understanding carbon cycling in natural ecosystems is critical because ongoing climate change can promote the release of previously stored carbon in forest soils to streams and rivers, with the potential to form carbon dioxide, the main greenhouse gas. This is particularly important in boreal ecosystems, which are the largest stores of terrestrial carbon in the world. In this study, we identify the near-stream area, the so-called riparian zone, as the main source of carbon from boreal forest soils to streams. We provide qualitative data to support this, which together with previous quantitative analyses, make up enough evidence to support that the riparian zone is the main source of carbon to streams. As there is still a debate about the potential contribution of other areas in the ecosystem to the fluvial carbon export, our study importantly highlights that the riparian zone should be the focus of scientific assessments and management strategies in relation to carbon exports in surface waters.
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| 15. |
- McCallister, S. L., et al.
(författare)
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Biogeochemical tools for characterizing organic carbon in inland aquatic ecosystems
- 2018
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Ingår i: Limnology and Oceanography Letters. - : Wiley. - 2378-2242. ; 3, s. 444-457
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Tidskriftsartikel (refereegranskat)abstract
- Integration of inland waters into regional and global carbon (C) budgets requires a comprehensive understand- ing of factors regulating organic carbon (OC) delivery and in situ processing. This study reviews advances in optical, molecular, and isotopic approaches to resolve the sources, ages, and transformations of OC in aquatic systems. OC characterization using excitation emission matrix spectra, Fourier transform ion cyclotron mass spectrometry, and nuclear magnetic resonance provides detailed molecular level insight. Radiocarbon isotopic approaches and compound-specific techniques resolve the input, metabolic fate, and turnover time of OC in ecosystems ranging in size from streams to the open ocean. Accumulating evidence suggests that aquatic OC is composed of diverse biogeochemical components. We conclude with enduring and emerging questions that underscore the role of inland systems in the global C cycle and propose unique combinations of approaches to better discern their role in the delivery and transformation of OC from soils to seas.
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| 16. |
- Müller, Roger A., et al.
(författare)
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Hourly, daily, and seasonal variability in the absorption spectra of chromophoric dissolved organic matter in a eutrophic, humic lake
- 2014
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 119:10, s. 1985-1998
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Tidskriftsartikel (refereegranskat)abstract
- The short-term (hourly and daily) variation in chromophoric dissolved organic matter (CDOM) in lakes is largely unknown. We assessed the spectral characteristics of light absorption by CDOM in a eutrophic, humic shallow mixed lake of temperate Sweden at a high-frequency (30 min) interval and during a full growing season (May to October). Physical time series, such as solar radiation, temperature, wind, and partial pressures of carbon dioxide in water and air, were measured synchronously. We identified a strong radiation-induced summer CDOM loss (25 to 50%) that developed over 4 months, which was accompanied by strong changes in CDOM absorption spectral shape. The magnitude of the CDOM loss exceeded subhourly to daily variability by an order of magnitude. Applying Fourier analysis, we demonstrate that variation in CDOM remained largely unaffected by rapid shifts in weather, and no apparent response to in-lake dissolved organic carbon production was found. In autumn, CDOM occasionally showed variation at hourly to daily time scales, reaching a maximum daily coefficient of variation of 15%. We suggest that lake-internal effects on CDOM are quenched in humic lake waters by dominating effects associated with imported CDOM and solar exposure. Since humic lake waters belong to one of the most abundant lake types on Earth, our results have important implications for the understanding of global CDOM cycling.
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| 17. |
- Zhou, Yongqiang, et al.
(författare)
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How hydrology and anthropogenic activity influence the molecular composition and export of dissolved organic matter : Observations along a large river continuum
- 2021
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:5, s. 1730-1742
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Tidskriftsartikel (refereegranskat)abstract
- Large rivers are the main arteries for transportation of carbon to the ocean; yet, how hydrology and anthropogenic disturbances may change the composition and export of dissolved organic matter along large river continuums is largely unknown. The Yangtze River has a watershed area of 1.80 x 10(6) km(2). It originates from the Qinghai-Tibet Plateau and flows 6300 km eastward through the center of China. We collected samples (n = 271) along the river continuum and analyzed weekly samples at the most downstream situated gauging station in 2017-2018 and gathered long-term (2006-2018) water quality data. We found higher gross domestic product, population density, and urban and agricultural land use downstream than upstream of the Three Gorges Dam, coinciding with higher dissolved organic carbon (DOC), UV absorption (a(254)), specific ultraviolet absorbance (SUVA(254)), parallel factor analysis-derived C1-C5, aliphatic compounds, and lower a(250):a(365) and spectral slope (S275-295). Chemical oxygen demand, humic-like C1-C2 and C6, and protein-like C4 and C7 increased, while dissolved oxygen and ammonium decreased with increasing discharge at most of the sites studied, including the intensively monitored downstream site. The annual DOC fluxes were ca. 1.5-1.8 Tg yr(-1), and 12-18% was biodegradable in a 28-d bio-incubation. Our results highlight that urbanization and stormwater periods enhanced the export of both terrestrial organic-rich substances and household effluents from nearshore residential areas. Our study emphasizes the continued need to protect the Yangtze River watershed as increased organic carbon loading or altered composition and bio-lability may change the ecosystem function and carbon cycling.
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| 18. |
- Zhou, Yongqiang, et al.
(författare)
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Selective Exclusion of Aromatic Organic Carbon During Lake Ice Formation
- 2023
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 50:4
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Tidskriftsartikel (refereegranskat)abstract
- Earth's lakes at northern latitudes are mostly ice-covered in winter. When lake water freezes, some organic matter dissolved in the water is excluded from the ice. We performed complementary field sampling and laboratory freeze-up experiments to explore how freeze-up may impact the partitioning and composition of dissolved organic matter (DOM) in boreal lakes. We found that 16.2 ± 4.7% of dissolved organic carbon (DOC) was retained in the overlying ice, 81.3 ± 5.7% of DOC was expelled to underlying unfrozen water, and 1.3 ± 0.7% was expelled as flocs. During ice formation, nitrogen (TDN, total dissolved nitrogen), ions (specific conductance), and oxidized and aromatic DOM were preferentially expelled to the underlying water column. The apparent retention factor DOCIce: DOCBefore decreased from clearwater to brownwater lakes, that is, with increasing allochthonous DOC lost from lake ice, indicating that DOM exclusion from the ice cover will become more prevalent as lakes experience browning.
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