| 1. |
- Brutemark, Andreas, et al.
(författare)
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Carbon isotope signature variability among cultured microalgae: Influence of species, nutrients and growth
- 2009
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 372:1-2, s. 98-105
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Tidskriftsartikel (refereegranskat)abstract
- In this study we have investigated whether the carbon isotopic signature differs between different groups and species of marine phytoplankton depending on growth phase, nutrient conditions and salinity. The 15 investigated algal species, representing the Bacillariophyceae, Chlorophyceae, Cryptophyceae, Cyanophyceae, Dinophyceae and Haptophyceae classes were grown in batch monocultures and analysed for delta C-13 in both exponential and stationary phase. For all the cultured species, delta C-13 signatures ranged from -23.5 parts per thousand (Imantonia sp.) to - 12.3 parts per thousand (Nodulania spumigena) in the exponential phase and from - 18.8 parts per thousand (Amphidinium carterae) to - 8.0 parts per thousand (Anabaena lemmermannii) in the stationary phase. Three species (Dunaliella tertiolecta, Rhodomonas sp.. Heterocapsa triquetra) were also grown under nutrient sufficient and nitrogen or phosphorus deficient conditions. Nitrogen limitation resulted in a more negative delta C-13 signature, whereas no effect could be observed during phosphorus limitation compared to nutrient sufficient conditions. Growth of Prymnesium parvum in two different salinities resulted in a more negative delta C-13 signature in the 26 parts per thousand-media compared to growth in 7 parts per thousand-media. Our results show that the carbon isotopic signature of phytoplankton may be affected by salinity, differ among different phytoplankton species, between exponential and stationary phase, as well as between nutrient treatments. (C) 2009 Elsevier B.V. All rights reserved.
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| 2. |
- Carlsson, Per, et al.
(författare)
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Bacterial and phytoplankton nutrient limitation in tropical marine waters, and a coastal lake in Brazil
- 2012
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 418, s. 37-45
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Tidskriftsartikel (refereegranskat)abstract
- Bioassay experiments were performed two times (with 2 years in between) in order to investigate if nitrogen (N, ammonium), phosphorus (P, phosphate) and carbon (C, glucose) additions would stimulate the growth of bacteria and phytoplankton differently in three different tropical aquatic environments. The water and their indigenous microbial communities were taken from a freshwater coastal lake (Cabiunas), a coastal (Anjos), and an offshore marine station (Sonar) in the Atlantic outside Cabo Frio, Rio de Janeiro State, Brazil. Ammonium, phosphate and glucose were added alone or in combination to triplicate bottles. In the lake, P seemed to be the primary limiting factor during the first experiment, since both bacterial production and phytoplankton growth was stimulated by the P addition. Two years later, however, addition of P inhibited phytoplankton growth. During both years, C was closely co-limiting for bacteria since CP additions increased the response considerably. For both the coastal and offshore seawater stations, phytoplankton growth was clearly stimulated by N addition in both years and the bacteria responded either to the P, N or C additions (alone or in combination). To conclude, the results from these tropical aquatic systems show that it is possible that phytoplankton and bacteria may compete for a common resource (P) in lakes, but can be limited by different inorganic nutrients in marine waters as well as lakes, suggesting that phytoplankton and bacteria do not necessarily compete for the same growth limiting nutrient in these environments. (C) 2012 Elsevier B.V. All rights reserved.
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| 3. |
- Granéli, Edna, et al.
(författare)
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Nitrogen in Inland Seas
- 2008. - 2nd Edition
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Ingår i: Nitrogen in the Marine Environment. - San Diego : Academic Press. - 9780123725226
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Lindehoff, Elin, et al.
(författare)
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Effect of tertiary sewage effluent additions on Prymnesium parvum cell toxicity and stable isotope ratios
- 2009
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Ingår i: Harmful Algae. - : Elsevier BV. - 1878-1470 .- 1568-9883. ; 8:2, s. 247-253
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the ability of the ichthyotoxic haptophyte Prymnesium parvum to use sewage-originated nutrients applying stable carbon (C) and nitrogen (N) isotope techniques. P. parvum was cultured under N and phosphorus (P) sufficient and deficient conditions in either sewage effluent-based medium or in a nitrate- and phosphate-based control. Cell densities and toxicities were monitored and stable carbon N isotopes signatures (delta C-13 and delta N-15) of P. parvum and the sewage effluent analysed. Nitrogen and P sufficient cultures achieved the highest biomass followed by P and N deficient cultures, regardless of sewage effluent additions. The P deficient cultures with sewage effluent had higher toxicity, estimated as haemolytic activity (9.4 +/- 0 x 10(-5) mg Saponin equiv. cell(-1)) compared to the P deficient control and to all N deficient and NP sufficient cultures. Nutrient deficient conditions had no effect on the cell delta N-15, but a decreasing effect on delta C-13 in the inorganic N deficient treatment. Growth in sewage-based media was followed by a substantial increase in the cell delta N-15 (10.4-16.1.60) compared to the control treatments (2.4-4.9%o), showing that P. parvum is capable of direct use of sewage-originated N, inorganic as well as organic. Uptake of terrestrial derived C in the sewage treatments was confirmed by a decrease in cell delta C-13, implying that P. parvum is able to utilize organic nutrients in sewage effluent. (C) 2008 Elsevier B.V. All rights reserved.
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| 5. |
- Lindell, MJ, et al.
(författare)
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Seasonal photoreactivity of dissolved organic matter from lakes with contrasting humic content
- 2000
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 0706-652X .- 1205-7533. ; 57:5, s. 875-885
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Tidskriftsartikel (refereegranskat)abstract
- We studied seasonal variability in photodegradation of dissolved organic carbon (DOC) resulting from artificial ultraviolet-A (UV-A) and UV-B irradiation. Water samples were taken approximately monthly from the surface layers of two oligotrophic lakes with contrasting humic content, situated in southern Sweden. Lake water was filter-sterilized (0.2 mum) and exposed to artificial UV radiation in quartz tubes. Potential DOC photodegradation, measured as a photoproduction of dissolved inorganic carbon (DIC) and oxalic, malonic, formic, and acetic acid in irradiated samples, was observed throughout the sampling period. In addition, exposure to UV radiation resulted in a decrease in DOC, absorbance, and humic substance fluorescence. The photoproduction of DIC and the low molecular weight (LMW) organic acids varied seasonally, being generally higher in winter and spring (December-May), while DOC appeared to become less photoreactive after the extensive exposure to solar radiation during summer. Production rates of both DIC and LMW organic acids were approximately eight times higher in the humic lake despite that the DOC concentration was only two times higher than in the clearwater lake. This is most probably due to the high input of allochthonous DOC and the resulting higher absorbance to DOC ratio in the humic system. Furthermore, the longer hydraulic residence time in the clearwater system could have resulted in an accumulation of residual DOC, recalcitrant to further photodegradation.
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| 6. |
- Abreu, Paulo Cesar, et al.
(författare)
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Importance of biofilm as food source for shrimps (Farafantepenaeus paulensis) evaluated by stable isotopes (∂13C and ∂15N)
- 2007
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981. ; 347:1-2, s. 88-96
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The contribution of biofilm and artificial feeds for the growth of the pink shrimp Farfantepenaeus paulensis reared in tanks and net cages were evaluated by using stable isotope (δ13C and δ15N) analysis. In the net cage experiment, mass balance and mixing equations showed that the biofilm contribution to shrimp growth was over 49% of carbon and 70% of nitrogen. These data suggest that the artificial feed offered in this experiment, although ingested, was not properly incorporated in the shrimp tissue. In contrast, biofilm growing in tanks contributed little to the nitrogen incorporated by the shrimp (maximum of 29%). In this experiment, shrimp presented an unusually large isotope fractionation. These results imply that the shrimp are selectively ingesting some items from the biofilm, or differentially assimilate specific items of the artificial feed, due to differential digestibility. The hypothesis of selective feeding of biofilm microorganisms was corroborated in the experiment with net cages, where shrimp preferentially consumed centric diatoms. This study also demonstrated that shrimp biofilm consumption and the presence of artificial feed largely influenced biofilm formation. The consumption of centric diatoms by shrimp seem to stimulate biofilm chlorophyll-a, while biofilm δ15N values measured in tanks indicate that microorganisms present in the biofilm absorbs nitrogen released by artificial feed after its decomposition.
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| 7. |
- Abreu, PC, et al.
(författare)
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Eutrophication processes and trophic interactions in a shallow estuary: Preliminary results based on stable isotope analysis (delta C-13 and delta N-15)
- 2006
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Ingår i: Estuaries and Coasts. - 1559-2731. ; 29:2, s. 277-285
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Tidskriftsartikel (refereegranskat)abstract
- Stable isotopes ratios (delta C-13 and delta N-15) were measured in primary producers and consumers of two bays with contrasting eutrophic conditions in the pains Lagoon estuary, southern Brazil: the Justino bay, a more pristine ecosystem, and the Mangueira bay, a heavily polluted region that receives the Rio Grande city sewage and effluents of several industries. delta C-13 values of organisms collected in both subsystems were not different, but delta N-15 values had significant statistical differences, ca. 3.5 parts per thousand higher in the Mangueira bay. It is likely that primary producers and consumers in this subsystem are greatly influenced by higher nitrogen input due to domestic and industrial sewages. The stable isotope analysis also corroborated several trophic interactions previously established by gut content analysis, and due to its higher sensitivity, it was possible to better determine the contributions of different primary producers and detrital fractions to the consumers' diets. It was confirmed that plant detritus represents the main food source for most organisms. The stable isotope analysis also demonstrated that detritivorous benthic organisms in the same habitat have distinct diet compositions, with differential consumption of C3 and C4 plants. This technique showed that some consumers that eat detritus do not have in their stable isotopic signature any relationship with that of plants. It is likely that these consumers assimilate their carbon and nitrogen from other sources like microalgae or microorganisms that colonize decaying plants.
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| 8. |
- Anesio, Alexandre Magno, et al.
(författare)
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Bacterial growth on photochemically transformed leachates from aquatic and terrestrial primary producers
- 2000
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Ingår i: Microbial Ecology. - : Springer Science and Business Media LLC. - 1432-184X .- 0095-3628. ; 40:3, s. 200-208
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Tidskriftsartikel (refereegranskat)abstract
- We measured bacterial growth on phototransformed dissolved organic matter (DOM) leached from eight different primary producers. Leachates (10 mg C liter(-1)) were exposed to artificial UVA + UVB radiation, or kept in darkness, for 20 h. DOM solutions were subsequently inoculated with lake water bacteria. Photoproduction of dissolved inorganic carbon (DIC), ranging from 3 to 16 mug C liter(-1) h(-1), and changes in the absorptive characteristics of the DOM were observed for all leachates upon UV irradiation. The effects of irradiation exposure on DOM bioavailability varied greatly, depending on leachate and type of bacterial growth criterion. Bacterial carbon utilization (biomass production plus respiration) over the entire incubation period (120 h) was enhanced by UV radiation of leachate from the terrestrial leaves, relative to carbon utilization in non-irradiated leachates. Conversely, carbon utilization was reduced by radiation of the leachates from aquatic macrophytes. In a separate experiment, the stable C and N isotope composition of bacteria grown on irradiated and non-irradiated DOM was estimated. Bacterial growth on UV-irradiated DOM was enriched in C-13 relative to the bacteria in the non-irradiated treatments; this result may be explained by selective assimilation of photochemically produced, isotopically enriched labile compounds.
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| 9. |
- Anesio, Alexandre M, et al.
(författare)
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Decreased bacterial growth on vascular plant detritus due to photochemical modification
- 1999
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Ingår i: AQUATIC MICROBIAL ECOLOGY. - 0948-3055. ; 17:2, s. 159-165
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the effects of UV radiation on abiotic decomposition and dissolution of leaf Litter from the aquatic macrophyte Phragmites australis. Dead leaves were autoclaved and incubated in quartz tubes with autoclaved Milli-Q water, in darkness, und
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| 10. |
- Anesio, Alexandre Magno, et al.
(författare)
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Effect of Humic Substance Photodegradation on Bacterial Growth and Respiration in Lake Water
- 2005
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 71:10, s. 6267-6275
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This study addresses how humic substance (HS) chemical composition and photoreactivity affect bacterial growth, respiration, and growth efficiency (BGE) in lake water. Aqueous solutions of HSs from diverse aquatic environments representing different dissolved organic matter sources (autochthonous and allochthonous) were exposed to artificial solar UV radiation. These solutions were added to lake water passed through a 0.7-µm-pore-size filter (containing grazer-free lake bacteria) followed by dark incubation for 5, 43, and 65 h. For the 5-h incubation, several irradiated HSs inhibited bacterial carbon production (BCP) and this inhibition was highly correlated with H2O2 photoproduction. The H2O2 decayed in the dark, and after 43 h, nearly all irradiated HSs enhanced BCP (average 39% increase relative to nonirradiated controls, standard error = 7.5%, n = 16). UV exposure of HSs also increased bacterial respiration (by 18%, standard error = 5%, n = 4), but less than BCP, resulting in an average increase in BGE of 32% (standard error = 10%, n = 4). Photoenhancement of BCP did not correlate to HS bulk properties (i.e., elemental and chemical composition). However, when the photoenhancement of BCP was normalized to absorbance, several trends with HS origin and extraction method emerged. Absorbance-normalized hydrophilic acid and humic acid samples showed greater enhancement of BCP than hydrophobic acid and fulvic acid samples. Furthermore, absorbance-normalized autochthonous samples showed 10-fold greater enhancement of BCP than allochthonous-dominated samples, indicating that the former are more efficient photoproducers of biological substrates.
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| 11. |
- Anesio, Alexandre Magno, et al.
(författare)
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Increased photoreactivity of DOC by acidification: Implications for the carbon cycle in humic lakes
- 2003
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 48:2, s. 735-744
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Tidskriftsartikel (refereegranskat)abstract
- Effects of ultraviolet (UV)-B radiation and acidification on pelagic carbon flux in a humic lake (dissolved organic carbon [DOC] similar to15 mg C L-1) were studied in a mesocosm experiment during the summer of 2000. Triplicate tanks (107 liters volume, 1 m high) were exposed to natural solar radiation, a daily extra dose of UV-B radiation, or kept dark. One set of tanks was submitted to a decrease in pH (from 5.7 to 4.7), and one set was kept at the natural pH level. During 70 d, water samples were taken regularly from the mesocosms for measurements of DOC, absorbance, dissolved inorganic carbon (DIC), and pH. Additionally, we regularly incubated samples to measure photooxidation rates, primary production, and community respiration. We found an increase in the photooxidation rates in the acidified mesocosms relative to ambient pH. The greater abiotic production of DIC (i.e., photooxidation) in acidified conditions could explain similar to27% of the decline in DOC in the same conditions. Laboratory experiments were done to test the effects of pH on the dissolved organic matter (DOM) photoreactivity. At lower pH values, we found both higher abiotic DIC production and specific absorbance fading, relative to neutral pH values in water from a humic lake. In a separate experiment, samples were exposed to prolonged irradiation under laboratory conditions, resulting in complete loss of absorptivity in the wavelengths between 290 and 400 nm. Decreases in DOC in the long-term exposure caused by photochemical mineralization were similar to45 and 55% of the initial pool for natural pH and acidified samples, respectively, at the end of the experiment. An increase in the dissolved organic matter photoreactivity by acidification could be an important mechanism to explain the increased water transparency and in-lake DOC removal in acid lakes found in several previous studies.
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| 12. |
- Anesio, Alexandre Magno, et al.
(författare)
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Influence of humic substances on bacterial and viral dynamics in freshwaters
- 2004
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 70:8, s. 4848-4854
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial and viral abundances were measured in 24 lakes with dissolved organic carbon (DOC) concentrations ranging from 3 to 19 mg of C liter(-1). In addition, a laboratory experiment was performed to test the effects of different sources of carbon (i.e., glucose and fulvic acids) and nutrients on the dynamics of viruses and bacteria. In the lake survey, no correlation was found between virus abundance and DOC concentration, yet there was a significant positive correlation between bacterial abundance and DOC concentration. A negative correlation was found between the virus-to-bacteria ratio and DOC level. These results are in agreement with our findings in the laboratory, where virus counts were significantly lower in treatments with fulvic acid additions than in a control (mean, 67.4% +/- 6.5% of the control). Virus counts did not differ significantly among the control and treatments with glucose, indicating that it was the type of organic carbon and not quantity which had an impact on viruses. Results from this study suggest that the way viruses control bacterial assemblages in humic lakes is different from the mechanism in clear water systems.
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| 13. |
- Anesio, Alexandre Magno, et al.
(författare)
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Photochemical mineralization of dissolved organic carbon in lakes of differing pH and humic content
- 2004
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 160:1, s. 105-116
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Tidskriftsartikel (refereegranskat)abstract
- Photochemical mineralization of dissolved organic carbon (DOC) to dissolved inorganic carbon (DIC) was studied in surface water from 10 oligotrophic lakes in Southern Sweden differing in DOC, pH, and iron content. In addition, we studied the effects of acidification on the DOC photoreactivity. Samples from each lake were filtered through 0.2 mum-filters, acidified by one pH unit or kept under ambient pH conditions, and incubated in quartz tubes, in situ and in the laboratory. We found a positive relationship between photochemical DIC production at the surface and DOC concentration or absorbed dose of UV radiation. On average, lake water treated with acid showed higher rates of photooxidation than lake water with ambient pH. However, the difference in rates of photooxidation between acidified and non-acidified treatments was only evident for lake water with high DOC and iron content (i.e. lakes with DOC concentration > 10 mg C/l, and iron concentration > 400 mug/l). Results from this study indicate that acidification may increase photochemical mineralization, especially in humic lakes. Finally, we showed that a substantial increase in UV-B radiation (e. g. a doubling) would influence the rates of photochemical mineralization of DOC in humic lakes (DOC > 10 mg C/l) substantially less than a rather moderate decrease in pH of one unit. In clear lakes an increased UV-B radiation would have a stronger impact on areal DIC-production than a decrease in pH.
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| 14. |
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| 15. |
- Bergman, Eva, et al.
(författare)
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Synthesis of theoretical and empirical experineces from nutrient and cyprinid reductions in Lake Ringsjön
- 1999
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Ingår i: Hydrobiologia. - 0018-8158. ; 404, s. 145-156
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Tidskriftsartikel (refereegranskat)abstract
- The reduction in external phosphorus load to Lake Ringsjön during the 1980s, did not result in improved water transparency during the following ten-year period. Furthermore, a fish-kill in the Eastern Basin of the lake, in addition to a cyprinid reduction programme (biomanipulation; 1988–1992), in contrast to theory, did not lead to any increase in zooplankton biomass or size. This absence of response in the pelagic food chain may have been attributed to the increase in abundance of YOY (0+) fish, following the fish reduction programme. Despite the lack of effect on zooplankton, there was a decrease in phytoplankton biomass, a change in species composition and an increase in water transparency following biomanipulation. In 1989, one year after the fish-kill in Eastern Basin, the Secchi depth (summer mean) increased from 60 cm to 110 cm. In the following years, water transparency increased further, despite an increase in phosphorus loading. An unexpected effect of the biomanipulation was an increase in benthic invertebrate and staging waterfowl abundances, which occurred 2–4 years after fish reduction. Hence, the response in the benthic community following biomanipulation was considerably stronger than in the pelagic community. A likely explanation is that reduction in abundance of the benthic feeding fish species bream (Abramis brama), strongly affected the benthic invertebrate fauna. In this paper, we present what we believe happened in Lake Ringsjön, and which processes are likely to have been important at various stages of the restoration process.
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| 16. |
- Bertilsson, Stefan, et al.
(författare)
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Influence of solar radiation on the availability of dissolved organic matter to bacteria in the Southern Ocean
- 2004
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Ingår i: Deep-Sea Research II: Topical Studies in Oceanography. - : Elsevier BV. ; 51, s. 2557-2568
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Tidskriftsartikel (refereegranskat)abstract
- The influence of solar radiation on the ability of dissolved organic matter (DOM) to support bacterial growth, was studied in the eastern Atlantic sector of the Southern Ocean during the SWEDARP 1997/1998 cruise with SA Agulhas December 1997–February 1998. Vertical profiles of water samples (2–3000 m) were obtained from the Spring Ice Edge (SIE, 60°S, high chlorophyll-a) and from the Winter Ice Edge (WIE, 56°S, low chlorophyll-a) areas. Filter-sterilized water from each area and depth was incubated under natural solar radiation and in the dark for comparison. Photobleaching of humic substance fluorescence occurred in all studied water samples. The bleaching was typically larger in the initially more fluorescent deep waters, compared to the low-fluorescent surface waters. Both the irradiated water and the dark controls were re-inoculated with a mixed bacterial inoculum from the initially sampled water. Bacterial growth (accumulating cells) and bacterial production (protein synthesis) were monitored during a 16–19 day incubation of these cultures at near in situ temperature (2 °C). Bacterial growth in cultures prepared from SIE water was largest at the surface (2–25 m), while the growth in corresponding cultures from the WIE did not vary much over depth. In contrast to the observed photobleaching, no clear effects of the irradiation on the ability of the DOM to support bacterial growth could be observed in either of the experiments. Hence, the degradation of fluorescent structures and other photochemical alterations of the organic matter did not have a major effect on the total pool of biodegradable organic substrates. The lack of effects of photoreactions on bacterial growth potential in the present study disagrees with the short-term bacterial growth response observed in other oceanic environments. This could be due to the different experimental approaches employed (short-vs. long-term incubations) or may indicate that the impact of photoreactions on bacterial growth in the Southern Ocean differ substantially from aquatic systems that are more influenced by terrestrial environments, as well as the warmer oligotrophic oceanic environments.
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| 17. |
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| 18. |
- Bertilsson, Stefan, et al.
(författare)
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Photochemically induced changes in bioavailable carbon and nitrogen pools in a boreal watershed
- 1999
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Ingår i: Aquatic Microbial Ecology. - Oldendorf : Inter-Research. - 0948-3055 .- 1616-1564. ; 19:1, s. 47-56
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Tidskriftsartikel (refereegranskat)abstract
- In several recent studies, a net stimulation of bacterial growth has been demonstrated after exposing humic surface waters to solar radiation or artificial ultraviolet radiation. This stimulation has been attributed to a photochemical release of bioavailable carbon or nitrogen compounds (ammonium). In a synoptic experiment, we exposed 0.2 mu m filtered water from 12 different habitats in a river system, dominated by allochthonous carbon input, to mild artificial UV radiation. A significant photochemical release of carboxylic acids of low molecular weight occurred. Furthermore, the exposure increased carbon-limited bacterial yield on average by a factor of 1.7. No photochemical production of free ammonium could be detected, which was in accordance with the lack of effects of radiation on bacterial growth yield under nitrogen-limited conditions. We conclude that, in boreal systems dominated by allochthonous carbon input, photochemical production of bioavailable carbon rather than nitrogen compounds is likely to positively influence the total substrate pool available for bacterial utilization.
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| 19. |
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| 20. |
- Bertilsson, S, et al.
(författare)
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Size-selective predation on pelagic microorganisms in Arctic freshwaters
- 2003
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 25:6, s. 621-631
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Tidskriftsartikel (refereegranskat)abstract
- Herbivorous zooplankton may have a pronounced influence on pelagic microorganisms in Arctic freshwaters. We quantified experimentally the size-selective feeding of several zooplankton groups on pelagic microorganisms in high Arctic tundra systems. Our experiments and field study focused on dominant herbivores in Arctic freshwaters, including the cladoceran Dophnia, the copepod Diaptomus and the anostracan Branchinecta, and their effects on prey ranging in size from bacteria to large phytoplankton. Grazing experiments showed that Dophnia were effective predators on all types of prey, whereas Diaptomus grazed preferentially on larger phytoplankton with low clearance rates for bacterial cells. Further analysis by flow cytometry indicated that Diaptomus grazed selectively on the largest bacteria. In contrast to the results obtained in the controlled experiments, Arctic lakes and ponds with a zooplankton community dominated by Dophnia had a higher bacterial production and abundance than systems not dominated by this grazer. This may indicate that the stimulatory effect of grazers on bacterial growth is more pronounced in natural systems, or that factors other than zooplankton grazing are more important in regulating bacterial abundance and production in natural systems. Although Arctic waters differ considerably from temperate systems with respect to temperature and light regime, herbivore-prey dynamics as well as the bacterial response to temperature appear to be similar between the climatic regions.
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| 21. |
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| 22. |
- Bragée, Petra, et al.
(författare)
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Historical TOC concentration minima during peak sulfur deposition in two Swedish lakes
- 2015
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 12:2, s. 307-322
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Tidskriftsartikel (refereegranskat)abstract
- Decadal-scale variations in total organic carbon (TOC) concentration in lake water since AD1200 in two small lakes in southern Sweden were reconstructed based on visible-near-infrared spectroscopy (VNIRS) of their recent sediment successions. In order to assess the impacts of local land-use changes, regional variations in sulfur, and nitrogen deposition and climate variations on the inferred changes in TOC concentration, the same sediment records were subjected to multi-proxy palaeolimnological analyses. Changes in lake-water pH were inferred from diatom analysis, whereas pollen-based land-use reconstructions (Landscape Reconstruction Algorithm) together with geochemical records provided information on catchment-scale environmental changes, and comparisons were made with available records of climate and population density. Our long-term reconstructions reveal that inferred lake-water TOC concentrations were generally high prior to AD1900, with additional variability coupled mainly to changes in forest cover and agricultural land-use intensity. The last century showed significant changes, and unusually low TOC concentrations were inferred at AD1930-1990, followed by a recent increase, largely consistent with monitoring data. Variations in sulfur emissions, with an increase in the early 1900s to a peak around AD1980 and a subsequent decrease, were identified as an important driver of these dynamics at both sites, while processes related to the introduction of modern forestry and recent increases in precipitation and temperature may have contributed, but the effects differed between the sites. The increase in lake-water TOC concentration from around AD1980 may therefore reflect a recovery process. Given that the effects of sulfur deposition now subside and that the recovery of lake-water TOC concentrations has reached pre-industrial levels, other forcing mechanisms related to land management and climate change may become the main drivers of TOC concentration changes in boreal lake waters in the future.
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| 23. |
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| 24. |
- Daniel, Cesar Bolivar, et al.
(författare)
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Stimulation of metazooplankton by photochemically modified dissolved organic matter
- 2006
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 51:1, s. 101-108
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Tidskriftsartikel (refereegranskat)abstract
- We examined the response of bacteria and proto- and metazooplankton to photomodified dissolved organic matter (DOM). Sterile filtered water from a eutrophic and a humic lake, that was either exposed to artificial ultraviolet (UV) radiation or kept dark, was added to semicontinuous laboratory microcosms that lasted for 7 weeks. Bacterial production responded positively to photochemical modification of DOM regardless of lake type. Final heterotrophic biomass (bacteria + proto + metazooplankton) was 47 +/- 5 and 37 +/- 5 mu g carbon (C) L-1 in microcosms with UV-exposed and unaltered eutrophic water DOM and 15 +/- 4 and 11 +/- 2 mu g C L-1 in microcosms with UV-exposed and unaltered humic water DOM, respectively. For the eutrophic water, there were no significant differences in proto- or metazooplankton biomasses between microcosms receiving UV-exposed or nonexposed DOM. Differences between eutrophic water microcosms were not significant when flagellates, ciliates, cladocerans, and copepods were examined separately. In microcosms with UV-exposed humic water, biomasses of heterotrophic flagellates, rotifers, nauplii, and cladocerans were higher than in those with nonexposed DOM. Higher final metazooplankton biomass following addition of UV-exposed humic water indicates that photochemically modified DOM can be effectively transferred through the microbial loop.
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| 25. |
- Daniel, C, et al.
(författare)
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Microbial food webs in the dark: independence of Lake Plankton from recent algal production
- 2005
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Ingår i: Aquatic Microbial Ecology. - 0948-3055. ; 38:2, s. 113-123
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the development of a heterotrophic plankton food web with or without phytoplankton primary production in a long-term (>1 yr) laboratory experiment. Water from 3 Swedish lakes (humic, oligotrophic clearwater, eutrophic) was exposed to low light or kept in total darkness in triplicate 100 1 cylinders. Dissolved organic carbon (DOC) dynamics, bacterial growth and biomass of protozoans, rotifers and microcrustaceans were followed over 18 mo. In the dark treatments, no primary production was detected and DOC concentrations decreased by between 19 and 27% (1.3 to 3.2 mg C l(-1)). There was bacterial and protozoan growth in the dark during the whole experimental period. However, numbers and production of bacteria, as well as protozoan biomass, were significantly lower in darkness. Dissolved (DOM) and particulate organic matter (POM) initially present in the water (i.e. 18 mo old at the end of the experiment) helped to support substantial metazoan biomasses in dark treatments in the humic and eutrophic waters, but not in the oligotrophic clearwater lake. DOM in the humic water, thus largely of allochthonous origin, gave the highest and most prolonged support to zooplankton living in darkness. Our study indicates that a microbial food web, based on allochthonous organic matter and developing independently from phytoplankton, can act as a link to metazoan zooplankton, especially in oligotrophic humic lakes. These results confirm studies using stable C isotopes, showing a substantial incorporation of terrestrial carbon into zooplankton.
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