| 1. |
- Bastviken, David, et al.
(författare)
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Degradation of dissolved organic matter in oxic and anoxic lake water
- 2004
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 49:1, s. 109–116-
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Tidskriftsartikel (refereegranskat)abstract
- Decades of conflicting results have fueled a debate about how O-2 affects organic matter (OM) degradation and carbon cycling. In a laboratory study, using both OM taken directly from a humic lake and chemically isolated fulvic acid, we monitored the mineralization of dissolved OM in freshwater under purely oxic and anoxic conditions, under oxic then anoxic conditions, and under anoxic then oxic conditions, for 426 d. Between 5% and 24% of the initial OM was mineralized, with most extensive mineralization occurring under purely oxic and anoxic-oxic conditions. A sequential change in the O-2 regime did not result in greater overall degradation, but initially anoxic conditions favored subsequent oxic mineralization. A substantially greater fraction of the OM was degraded than in previous shorter studies, with as much as 50% of the total OM degradation occurring after 147 d into the experiment. Three fractions of the degradable OM were identified: OM degraded only under oxic conditions (68-78%), OM degraded more rapidly under anoxic conditions than under oxic conditions (16-18%), and OM degraded at equal rates under both oxic and anoxic conditions (6-14%). The degradation patterns of natural dissolved OM from a humic lake and chemically isolated fulvic acid were very similar, which indicates a similar level of bioavailability. The difference between anoxic and oxic degradation was greater in our long-term studies than in previous short-term experiments, which indicates that the oxic and anoxic degradation potentials vary with increasing overall OM recalcitrance and that similar oxic and anoxic degradation rates can be expected in short-term experiments in which <30% of the long-term degradable OM is allowed to decompose.
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| 2. |
- Bertilsson, S, et al.
(författare)
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Photochemical transformation of dissolved organic matter in lakes
- 2000
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 45:4, s. 753-762
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Tidskriftsartikel (refereegranskat)abstract
- In a survey of photochemical transformation of dissolved organic matter (DOM) in lake water, we found photochemical production of dissolved inorganic carbon (DIC) and low molecular weight carboxylic acids (oxalic, malonic, formic, and acetic acid), upon simulated solar ultraviolet (UV) radiation exposure of filter-sterilized surface water from 38 investigated lakes. Given the large variability in water chemistry of the studied systems, we suggest that these photoproducts are universally produced in sunlight exposed lake water. The measured production of carboxylic acid carbon corresponded to 34.4% (median) of the produced DIC. The production of DIC and carboxylic acids during 8 h of mild UV irradiation corresponded to an average of 4.7% (SD 2.9) of the total dissolved organic carbon pool. Hence, photochemical degradation could be a major sink for DOM in the surface layer of lakes. All photoreaction rates were strongly correlated to the total radiation absorbed during UV exposure (r(2) > 0.8), which depends mainly on amount of colored DOM in the water. The variability in DIC production after normalizing for absorbed radiation energy could partly be attributed to general water chemistry parameters (e.g., pH, iron concentration, conductivity).
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| 3. |
- Bianchi, Thomas S, et al.
(författare)
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Cyanobacterial blooms in the Baltic Sea : Natural or human-induced?
- 2000
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 45:3, s. 716-726
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Tidskriftsartikel (refereegranskat)abstract
- Massive summer blooms of nitrogen-fixing cyanobacteria have been documented in the Baltic Sea since the 19th century, but are reported to have increased in frequency, biomass, and duration in recent decades-presumably in response to the well-documented anthropogenic eutrophication of the Baltic. Here, we present an 8,000-yr record of fossil cyanobacterial pigments, diatom microfossil assemblages, and delta(15)N variations in sediment cores from the Baltic proper. This record indicates that nitrogen-living cyanobacterial blooms are nearly as old as the present brackish water phase of the Baltic Sea, starting as far back as ca. 7000 B.P.-soon after the former freshwater Ancylus Lake turned into the brackish Litorina Sea. Demonstration of cyanobacterial blooms in the Baltic prior to the greatly increased anthropogenic nutrient inputs of the 20th century is important for setting realistic goals when trying to reduce the magnitude of present brooms. Our results suggest that the presently predominating nitrogen (N) limitation of phytoplankton in the Baltic Sea proper is not man-induced, but a natural phenomenon, which has endured for some 7,000 yr. These cyanobacterial blooms were possibly initiated by increased availability of phosphorus (P)-from inflow of P-rich seawater and increased P release from sediments-during periods of deep-water anoxia, caused by the establishment of salinity stratification. Efforts to restore the Baltic proper to a more oligotrophic and natural condition should take into account that nitrogen-fixing cyanobacterial blooms are a characteristic, natural feature of this sea.
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| 4. |
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| 5. |
- Humborg, Christoph, et al.
(författare)
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Nutrient variations in boreal and subarctic Swedish rivers : Landscape control of land–sea fluxes
- 2004
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 49:5, s. 1871-1883
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Tidskriftsartikel (refereegranskat)abstract
- We examined the hypothesis that the extent of vegetation cover governs the fluxes of nutrients from boreal and subarctic river catchments to the sea. Fluxes of total organic carbon (TOC) and dissolved inorganic nitrogen, phosphorus, and dissolved silicate (DIN, DIP, and DSi, respectively) are described from 19 river catchments and subcatchments (ranging in size from 34 to 40,000 km2) in northern Sweden with a detailed analysis of the rivers Lulea¨lven and Kalixa¨lven. Fluxes of TOC, DIP, and DSi increase by an order of magnitude with increasing proportion of forest and wetland area, whereas DIN did not follow this pattern but remained constantly low. Principal component analysis on landscape variables showed the importance of almost all land cover and soil type variables associated with vegetation, periglacial environment, soil and bedrock with slow weathering rates, boundary of upper tree line, and percentage of lake area. A cluster analysis of the principal components showed that the river systems could be separated into mountainous headwaters and forest and wetland catchments. This clustering was also valid in relation to river chemistry (TOC, DIP, and DSi) and was confirmed with a redundancy analysis, including river chemistry and principal components as environmental variables. The first axis explains 89% of the variance in river chemistry and almost 100% of the variance in the relation between river chemistry and landscape variables. These results suggest that vegetation change during interglacial periods is likely to have had a major effect on inputs of TOC, DIP, and DSi into the past ocean.
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| 6. |
- Jansson, Mats, et al.
(författare)
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Allochthonous organic carbon decreases pelagic energy mobilization in lakes
- 2003
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 48:4, s. 1711-1716
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Tidskriftsartikel (refereegranskat)abstract
- Over the past decade, it has been Shown that unproductive lakes worldwide are net heterotrophic because bacterial respiration of allochthonous. organic carbon (AOC) makes community respiration exceed primary production. Net heterotrophy means that aquatic systems are net sources of CO2 to the atmosphere but also that bacterial utilization of AOC increases bacterioplankton production (BP) and bacterial uptake of limiting inorganic nutrients at the expense of phytoplankton production (PP). We studied 15 unproductive lakes in northern Sweden with dissolved organic carbon concentrations between 3 and 22 mg L-1. We found a highly significant negative relationship between the degree of heterotrophy and total pelagic energy mobilization (PP + BP based on AOC) per unit of limiting nutrient. We suggest that this is because the high cell phosphorous (P) requirement of bacteria makes energy mobilization per P unit considerably lower in bacterioplankton than in phytoplankton. We also suggest that the productivity of the entire pelagic ecosystem is determined by the availability of inorganic nutrients and AOC and by whether nutrients are allocated to BP or PP.
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| 7. |
- Jonsson, Anders, et al.
(författare)
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Whole-lake mineralization of allochthonous and autochthonous organic carbon in a large humic lake (Örträsket, N. Sweden)
- 2001
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 46:7, s. 1691-1700
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Tidskriftsartikel (refereegranskat)abstract
- Organic carbon mineralization was studied. in a large humic lake (Lake Örträsket) in northern Sweden during a well-defined summer stratification period following high water flow during snowmelt. Several independent methods including plankton counts, measurements of bacterioplankton and phytoplankton production, stable isotope monitoring, sediment trapping, and mass balance calculations were used. Total organic carbon mineralization showed a summer mean of 0.3 g C m(-2) d(-1) and was partitioned about equally between water and sediment. In the water column, organic matter was mineralized by bacteria (60%) and protozoan and metazoan zooplankton (30%), as well as by photooxidation (10%). Most of the mineralized organic carbon was of allochthonous origin. Primary production in the lake contributed at most 5% of the total organic carbon input and about 20% of the total organic carbon mineralization. Total carbon mineralization in. the epilimnion and metalimnion agreed well with an estimate of CO2 evasion from the stratified lake, while CO2 accumulation in the hypolimnion matched the O-2 consumption and resulted in a very negative delta C-13 of DIC before autumn overturn (-23 parts per thousand). Isotopic compositions of DIC and POC confirmed the dominant influence of terrestrial organic input on the cycling of both organic and inorganic carbon in the lake.
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| 8. |
- Karlsson, Jan, et al.
(författare)
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Control of zooplankton dependence on allochthonous organic carbon in humic and clear-water lakes in northern Sweden
- 2003
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 48:1, s. 269-276
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Tidskriftsartikel (refereegranskat)abstract
- We compared the stable carbon isotopic composition (delta(13)C) of crustacean zooplankton with that of potential carbon sources in 15 lakes in northern Sweden with different dissolved organic carbon (DOC) concentrations (2-9 mg L-1) to test the hypothesis that zooplankton depended more on allochthonous carbon in humic lakes than in clear-water lakes. Based on delta(13)C signature, we found that the pool of organic matter in the lakes was dominated by carbon of allochthonous origin over the whole DOC gradient. Zooplankton were generally depleted in C-13 compared to organic matter in the catchment, particulate organic matter in the lake water, and shallow surface sediment. However, the isotopic composition of zooplankton could not be explained without a significant contribution from both allochthonous and autochthonous carbon sources in all lakes. The relative importance of these two carbon sources did not relate to the concentration of, or proportion between, allochthonous and autochthonous organic carbon in the water. Instead, the proportion between allochthonous and autochthonous carbon in the crustacean zooplankton was consistent with a rather conservative use of the energy mobilized by bacterioplankton and phytoplankton in the lakes.
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| 9. |
- Legrand, Catherine, et al.
(författare)
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Phagotrophy and toxicity variation in the mixotrophic Prymnesium patelliferum (Haptophyceae)
- 2001
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 46:5, s. 1208-1214
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Tidskriftsartikel (refereegranskat)abstract
- Phagotrophy was investigated in the photosynthetic and ichthyotoxic Prymnesium patelliferum (Haptophyceae) using fluorescent microspheres, fluorescently labeled bacteria, and live bacteria cells. Ingestion rates were estimated both from prey uptake and disappearance experiments in phosphorus (P)-limited and -replete algal cultures. Prymnesium patelliferum was feeding preferentially on bacteria (bact) compared to fluorescent microspheres (FM). Large fluorescent microspheres (1.6 and 3 mum) were ingested at very low rates (< 0.1 FM alga(-1) h(-1)), and small microspheres (0.5 mum) were not ingested. Ingestion of bacteria (mean size 2 mum) was highest in P-limited P. patelliferum cultures (up to four bact alga(-1) h(-1)) compared to P-replete cultures (0-1.2 bact alga(-1) h(-1)). In addition, cellular P content of P-limited cells fed with bacteria became similar to those of P-replete cultures after 48 h, indicating a close relation between cellular P content and feeding behavior. Hemolytic activity of P. patelliferum was up to four times higher in P-limited cultures compared to P-replete cultures. During the transition from P-limiting to P-replete conditions, the addition of bacteria and/or the corresponding bacterial filtrate (< 0.2 mum) and/or PO43- to P-limited cultures resulted in a decrease (50%) of the hemolytic activity after 24 h in relation to controls (no addition of bacteria, filtrate. or P). No PO43- was detectable as a result of enriching cultures with bacterial cells or bacterial filtrates. These results indicate that P. patelliferum can use different sources of P (inorganic and dissolved, organic and particulate) and adapt its mode of nutrition in a short time. Furthermore, the decrease of hemolytic activity in the highly toxic P-limited cells also occurred rapidly following a recovery in cellular P status through mixotrophic feeding or uptake of inorganic phosphate, suggesting that toxicity in P. patelliferum cells can be minimized by nutrient manipulation.
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| 10. |
- Logue, Jürg Brendan, et al.
(författare)
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Relationship between sediment organic matter, bacteria composition, and the ecosystem metabolism of alpine streams
- 2004
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 49:6, s. 2001-2010
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Tidskriftsartikel (refereegranskat)abstract
- We tested whether sediment bacteria abundance (4´,6-diamidino-2-phenylindole–stained cell counts) were related to sediment organic content (ash-free dry mass [AFDM]) in 11 nonforested streams of three different Alpine catchments during summer 2003. We used terminal restriction fragment–length polymorphism (T-RLFP, a moleculargenetic technique) to test for seasonal and spatial differences in bacterial composition in these same streams. We then related the above parameters, in conjunction with periphyton biomass and hyporheic respiration, to whole stream estimates of gross primary production (GPP) and ecosystem respiration (ER) in a glacial and nonglacial stream, representing environmental extremes, in one of the catchments. The percentage of organic matter of sediments was 4–14% (0.01–0.04 g AFDM ml sediment-1), and counts of bacteria cells per millimeter of sediment averaged 2x10^6–4x10^6. Bacteria counts correlated with sediment AFDM only for streams in the catchment with highest sediment AFDM levels. Bacteria composition (based on the presence and absence of terminal restriction fragments from T-RFLP analysis) changed seasonally in the different streams and differed between glacial- and groundwater-fed streams. In the one catchment, hyporheic respiration averaged 0.0004 and 0.0003 g O2 h-1 kg sediment-1 and was positively correlated with AFDM (r2=0.23). Ecosystem metabolism displayed a strong seasonality, with GPP averaging 4.5 and 8.4 and ER averaging 5.4 and 9.9 g O2 m-2 d-1 for the two sites, respectively, thus indicating a predominance of heterotrophy (P:R<1) in these high-elevation, open-canopied systems. Bacteria play a strong role in the trophic dynamics of alpine streams.
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