| 1. |
- Al-Kharusi, Enass Said, et al.
(författare)
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Drought Offsets the Controls on Colored Dissolved Organic Matter in Lakes
- 2024
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Ingår i: Remote Sensing. - 2072-4292. ; 16:8
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Tidskriftsartikel (refereegranskat)abstract
- The concentration of colored dissolved organic matter (CDOM) in lakes is strongly influenced by climate, land cover, and topographic settings, but it is not known how drought may affect the relative importance of these controls. Here, we evaluate the controls of CDOM during two summers with strongly contrasting values of the Palmer drought index (PDI), indicating wet vs. dry conditions. We hypothesized that lake CDOM during a wet summer season is regulated mainly by the surrounding land cover to which the lakes are hydrologically connected, while, during drought, the lakes are disconnected from the catchment and CDOM is regulated by climatic and morphometric factors that govern the internal turnover of CDOM in the lakes. A suite of climate, land cover, and morphometric variables was assembled and used to explain remotely sensed CDOM values for 255 boreal lakes distributed across broad environmental and geographic gradients in Sweden and Norway. We found that PDI explained the variability in CDOM among lakes in a dry year, but not in a wet year, and that severe drought strongly decreased CDOM during the dry year. Large lakes, especially, with a presumed high degree of catchment uncoupling, showed low CDOM during the dry year. However, in disagreement with our hypothesis, climate, land cover, and morphometry all showed a stronger impact on lake CDOM in wet vs. dry years. Thus, drought systematically weakened the predictability of CDOM variations at the same time as CDOM was offset toward lower values. Our results show that drought not only has a direct effect on CDOM, but also acts indirectly by changing the spatial regulation of CDOM in boreal lakes.
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| 2. |
- Al-kharusi, Enass Said., et al.
(författare)
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Large-Scale Retrieval of Coloured Dissolved Organic Matter in Northern Lakes Using Sentinel-2 Data
- 2020
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 12:1, s. 157-157
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Tidskriftsartikel (refereegranskat)abstract
- Owing to the significant societal value of inland water resources, there is a need for cost-effective monitoring of water quality on large scales. We tested the suitability of the recently launched Sentinel-2A to monitor a key water quality parameter, coloured dissolved organic matter (CDOM), in various types of lakes in northern Sweden. Values of a(420)CDOM (CDOM absorption at 420 nm wavelength) were obtained by analyzing water samples from 46 lakes in five districts across Sweden within an area of approximately 800 km2. We evaluated the relationships between a(420)CDOM and band ratios derived from Sentinel-2A Level-1C and Level-2A products. The band ratios B2/B3 (460 nm/560 nm) and B3/B5 (560 nm/705 nm) showed poor relationships with a(420)CDOM in Level-1C and 2A data both before and after the removal of outliers. However, there was a slightly stronger power relationship between the atmospherically-corrected B3/B4 ratio and a(420)CDOM (R2 = 0.28, n = 46), and this relationship was further improved (R2 = 0.65, n = 41) by removing observations affected by light haze and cirrus clouds. This study covered a wide range of lakes in different landscape settings and demonstrates the broad applicability of a(420)CDOM retrieval algorithms based on the B3/B4 ratio derived from Sentinel-2A. View Full-Text
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| 3. |
- Berggren, Martin, et al.
(författare)
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Allochthony in major groups of crustacean zooplankton in boreal lakes – strongly contrasting patterns across space and time
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The role of terrestrial organic carbon for recipient aquatic ecosystems is intensively researched. A multitude of studies now show that terrestrially-derived carbon supports a significant share (allochthony) of consumer biomass in many freshwaters. However, little is known about the mechanisms by which terrestrially-derived carbon is transferred to the level of metazoan zooplankton, and whether these pathways vary among taxonomic and functional groups. Here we present stable isotope-inferred allochthony in three major groups of crustacean zooplankton – Cladocera, Calanoida and Cyclopoida – measured both seasonally and across wide ranges of environmental gradients in boreal areas of Canada and Sweden. Our data show strongly contrasting patterns between taxa in the allochthony regulation. Whereas allochthony in calanoids was regulated by shortage of phytoplankton particles per se, both across space and time, allochthony in cyclopoids was related to food chains supported by dissolved organic carbon. Cladocerans showed the highest allochthony, but a more complex regulation. Terrestrial organic matter can be an important resource for cyclopoids and cladocerans on an annual basis, but it can also sustain otherwise herbivorous calanoids during low productivity conditions, e.g. in winter.
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| 4. |
- Berggren, Martin, et al.
(författare)
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Intraspecific autochthonous and allochthonous resource use by zooplankton in a humic lake during the transitions between winter, summer and fall
- 2015
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- Seasonal patterns in assimilation of externally produced, allochthonous, organic matter into aquatic food webs are poorly understood, especially in brown-water lakes. We studied the allochthony (share biomass of terrestrial origin) in cladoceran, calanoid and cyclopoid micro-crustacean zooplankton from late winter to fall during two years in a small humic lake (Sweden). The use of allochthonous resources was important for sustaining a small population of calanoids in the water column during late winter. However, in summer the calanoids shifted to 100% herbivory, increasing their biomass several-fold by making efficient use of the pelagic primary production. In contrast, the cyclopoids and cladocerans remained at high levels of allochthony throughout the seasons, both groups showing the mean allochthony of 0.56 (range in mean 0.17-0.79 and 0.34-0.75, for the respective group, depending on model parameters). Our study shows that terrestrial organic matter can be an important resource for cyclopoids and cladocerans on an annual basis, forming a significant link between terrestrial organic matter and the higher trophic levels of the food web, but it can also be important for sustaining otherwise herbivorous calanoids during periods of low primary production in late winter.
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| 5. |
- Berggren, Martin, et al.
(författare)
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Lake secondary production fueled by rapid transfer of low molecular weight organic carbon from terrestrial sources to aquatic consumers
- 2010
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 13:7, s. 870-880
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Tidskriftsartikel (refereegranskat)abstract
- P>Carbon of terrestrial origin often makes up a significant share of consumer biomass in unproductive lake ecosystems. However, the mechanisms for terrestrial support of lake secondary production are largely unclear. By using a modelling approach, we show that terrestrial export of dissolved labile low molecular weight carbon (LMWC) compounds supported 80% (34-95%), 54% (19-90%) and 23% (7-45%) of the secondary production by bacteria, protozoa and metazoa, respectively, in a 7-km2 boreal lake (conservative to liberal estimates in brackets). Bacterial growth on LMWC was of similar magnitude as that of primary production (PP), and grazing on bacteria effectively channelled the LMWC carbon to higher trophic levels. We suggest that rapid turnover of forest LMWC pools enables continuous export of fresh photosynthates and other labile metabolites to aquatic systems, and that substantial transfer of LMWC from terrestrial sources to lake consumers can occur within a few days. Sequestration of LMWC of terrestrial origin, thus, helps explain high shares of terrestrial carbon in lake organisms and implies that lake food webs can be closely dependent on recent terrestrial PP.
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| 6. |
- Berggren, Martin, et al.
(författare)
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Nutrient limitation masks the dissolved organic matter composition effects on bacterial metabolism in unproductive freshwaters
- 2023
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 68:9, s. 2059-2069
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Tidskriftsartikel (refereegranskat)abstract
- Aquatic microbial responses to changes in the amount and composition of dissolved organic carbon (DOC) are of fundamental ecological and biogeochemical importance. Parallel factor (PARAFAC) analysis of excitation–emission fluorescence spectra is a common tool to characterize DOC, yet its ability to predict bacterial production (BP), bacterial respiration (BR), and bacterial growth efficiency (BGE) vary widely, potentially because inorganic nutrient limitation decouples microbial processes from their dependence on DOC composition. We used 28-d bioassays with water from 19 lakes, streams, and rivers in northern Sweden to test how much the links between bacterial metabolism and fluorescence PARAFAC components depend on experimental additions of inorganic nutrients. We found a significant interaction effect between nutrient addition and fluorescence on carbon-specific BP, and weak evidence for influence on BGE by the same interaction (p = 0.1), but no corresponding interaction effect on BR. A practical implication of this interaction was that fluorescence components could explain more than twice as much of the variability in carbon-specific BP (R2 = 0.90) and BGE (R2 = 0.70) after nitrogen and phosphorus addition, compared with control incubations. Our results suggest that an increased supply of labile DOC relative to ambient phosphorus and nitrogen induces gradually larger degrees of nutrient limitation of BP, which in turn decouple BP and BGE from fluorescence signals. Thus, while fluorescence does contain precise information about the degree to which DOC can support microbial processes, this information may be hidden in field studies due to nutrient limitation of bacterial metabolism.
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| 7. |
- Berggren, Martin, et al.
(författare)
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Quality transformation of dissolved organic carbon during water transit through lakes : contrasting controls by photochemical and biological processes
- 2018
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Ingår i: Biogeosciences. - : European Geosciences Union (EGU). - 1726-4170 .- 1726-4189. ; 15:2, s. 457-470
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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.
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| 8. |
- Berggren, Martin, et al.
(författare)
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Systematic microbial production of optically active dissolved organic matter in subarctic lake water
- 2020
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Ingår i: Limnology and Oceanography. - : Association for the Sciences of Limnology and Oceanography (ASLO). - 0024-3590 .- 1939-5590. ; 65:5
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Tidskriftsartikel (refereegranskat)abstract
- The ecology and biogeochemistry of lakes in the subarctic region are particularly sensitive to changes in the abundance and optical properties of dissolved organic matter (DOM). External input of colored DOM to these lakes is an extensively researched topic, but little is known about potential reciprocal feedbacks between the optical properties of DOM and internal microbial processes in the water. We performed 28-day dark laboratory incubation trials on water from 101 subarctic tundra lakes in northern Sweden, measuring the microbial decay of DOM and the resulting dynamics in colored (CDOM) and fluorescent (FDOM) DOM components. While losses in dissolved oxygen during the incubations corresponded to a 20% decrease in mean DOM, conversely the mean CDOM and total FDOM increased by 22% and 30%, respectively. However, the patterns in microbial transformation of the DOM were not the same in all lakes. Notably, along the gradient of increasing ambient CDOM (water brownness), the lakes showed decreased microbial production of protein-like fluorescence, lowered DOM turnover rates and decreasing bacterial growth per unit of DOM. These trends indicate that browning of subarctic lakes systematically change the way that bacteria interact with the ambient DOM pool. Our study underscores that there is no unidirectional causal link between microbial processes and DOM optical properties, but rather reciprocal dependence between the two.
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| 9. |
- Berggren, Martin, et al.
(författare)
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Terrestrial support of zooplankton biomass in northern rivers (invited)
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The contribution of terrestrially-derived carbon to micro-crustacean zooplankton biomass (i.e. allochthony) has been previously studied in lakes and reservoirs, but little is known about allochthony in rivers. We hypothesized that restricted selective grazing in turbulent environments such as rivers would decouple zooplankton from specific microbial and algal food resources, such that their allochthony would mirror the allochthonous contribution to the bulk particle pool. Allochthony was analyzed in 13 widely distributed Swedish rivers, using a dual-isotope mixing model. Zooplankton biomasses were generally low, and allochthony in different micro-crustacean groups (Cladocera, Cyclopoida, Calanoida) varied from 2% to 77%. As predicted, there were no correlations between allochthony and variables such as Chlorophyll-a or bacterial production. Instead, allochthony was similar to the terrestrial contribution in the particulate organic matter, with relationships close to 1:1. The total zooplankton community allochthony was strongly related to the ecosystem metabolic balance between production and respiration, which in turn was dependent upon the ratio between total autochthonous organic carbon concentrations and water color. Our study suggests that micro-crustacean allochthony is regulated differently in rivers compared to in lacustrine systems.
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| 10. |
- Creed, Irena F., et al.
(författare)
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Global change-driven effects on dissolved organic matter composition : Implications for food webs of northern lakes
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:8, s. 3692-3714
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Forskningsöversikt (refereegranskat)abstract
- Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.
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