| 1. |
- Bade, Darren L., et al.
(författare)
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Sources and fates of dissolved organic carbon in lakes as determined by whole-lake carbon isotope additions
- 2007
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 1573-515X .- 0168-2563. ; 84:2, s. 115-129
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Tidskriftsartikel (refereegranskat)abstract
- Four whole- lake inorganic C-13 addition experiments were conducted in lakes of differing trophic status. Inorganic C-13 addition enriched algal carbon in C-13 and changed the delta C-13- DOC by + 1.5 parts per thousand to + 9.5 parts per thousand, depending on the specific lake. This change in delta C-13- DOC represented a significant input of algal DOC that was not completely consumed by bacteria. We modeled the dynamics in delta C-13- DOC to estimate the fluxes of algal and terrestrial carbon to and from the DOC pool, and determine the composition of the standing stock. Two experiments in lightly stained, oligotrophic lakes indicated that algal production was the source of about 20% of the DOC pool. In the following year, the experiment was repeated in one of these lakes under conditions of nutrient enrichment, and in a third, more humic lake. Algal contributions to the DOC pool were 40% in the nutrient enriched lake and 5% in the more humic lake. Spectroscopic and elemental analyses corroborated the presence of increased algal DOC in the nutrient enriched lake. Natural abundance measurements of the delta C-13 of DOC in 32 lakes also revealed the dual contributions of both terrestrial and algal carbon to DOC. From these results, we suggest an approach for inferring the contribution of algal and terrestrial DOC using easily measurable parameters.
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| 2. |
- Carpenter, Stephen R., et al.
(författare)
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Ecosystem subsidies : Terrestrial support of aquatic food webs from C-13 addition to contrasting lakes
- 2005
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Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 86:10, s. 2737-2750
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Tidskriftsartikel (refereegranskat)abstract
- Whole-lake additions of dissolved inorganic C-13 were used to measure allochthony (the terrestrial contribution of organic carbon to aquatic consumers) in two unproductive lakes (Paul and Peter Lakes in 2001), a nutrient-enriched lake (Peter Lake in 2002), and a dystrophic lake (Tuesday Lake in 2002). Three kinds of dynamic models were used to estimate allochthony: a process-rich, dual-isotope flow model based on mass balances of two carbon isotopes in 12 carbon pools; simple univariate time-series models driven by observed time courses of delta(13)CO(2); and multivariate autoregression models that combined information from time series of delta(13)C in several interacting carbon pools. All three models gave similar estimates of allochthony. In the three experiments without nutrient enrichment, flows of terrestrial carbon to dissolved and particulate organic carbon, zooplankton, Chaoborus, and fishes were substantial. For example, terrestrial sources accounted for more than half the carbon flow to juvenile and adult largemouth bass, pumpkinseed sunfish, golden shiners, brook sticklebacks, and fathead minnows in the unenriched experiments. Allochthony was highest in the dystrophic lake and lowest in the nutrient-enriched lake. Nutrient enrichment of Peter Lake decreased allochthony of zooplankton from 0.34-0.48 to 0-0.12, and of fishes from 0.51-0.80 to 0.25-0.55. These experiments show that lake ecosystem carbon cycles, including carbon flows to consumers, are heavily subsidized by organic carbon from the surrounding landscape.
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| 3. |
- 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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| 4. |
- Kritzberg, Emma
(författare)
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Allochthonous and autochthonous carbon sources of lake bacterioplankton
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic substrates for pelagic bacteria are derived from dissolved organic carbon (DOC) in the water column that originates either from primary production from within the lake itself (autochthonous), or import of organic matter from the terrestrial watershed (allochthonous production). This thesis addresses the utilization of allochthonous versus autochthonous carbon (C) sources by lake bacterioplankton. In addition, I examine the connection between the source of the organic matter and the structure and function of the bacterial community. In spite of low allochthonous C inputs, high respiration:primary production and bacterial:primary production suggested that five oligotrophic clear-water lakes on the Faroe Islands were net heterotrophic (respiration exceeded primary production) and that the heterotrophic plankton were subsidized by allochthonous organic C. While the occurence of net heterotrophy does not reveal anything about the fate of the allochthonous C, the importance of autochthonous versus allochthonous DOC in supporting bacterial production was examined by whole-lake additions of 13C (Forest lakes in Northern Wisconsin), and tracing its subsequent uptake by phytoplankton and on to bacteria. Bacterial production in lakes ranging from eutrophic and low-humic to oligotrophic and humic, consisted of 40 ? 80 % allochthonous C, confirming the often stated hypothesis that autochthonous carbon alone does not support bacterial production. Yet, autochthonous DOC was preferentially utilized relative to terrestrial DOC, although the preference for autochthonous C was not complete. Furthermore, based on a correlative study of ten lakes in the same area, bacteria seemed to grow more efficiently on autochthonous C, suggesting that this C is more effectively transferred to higher organisms. The results of the lake survey and the whole-lake isotope additions were simulated by a simple steady state model of bacterial utilization of autochthonous and allochthonous dissolved organic C. This showed that a higher preference and greater growth efficiency of bacteria on autochthonous C could explain why bacterial production was coupled to autochthonous production also in net heterotrophic ecosystems where the use of allochthonous C by bacteria was high. Finally, the source of the organic substrate (autochthonous and allochthonous) appeared to influence the bacterial community composition as well as general bacterial functions (production, respiration, growth yield and substrate utilization). Hence, bacterial sub-populations growing at different rates on substrates of differing origin, might explain why we observe a selective utilization of autochthonous C by the total bacterial community.
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| 5. |
- Kritzberg, Emma, et al.
(författare)
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Bacterial growth on allochthonous carbon in humic and nutrient-enriched lakes: Results from whole-lake C-13 addition experiments
- 2006
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 9:3, s. 489-499
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Tidskriftsartikel (refereegranskat)abstract
- Organic carbon (C) in lakes originates from two distinct sources-primary production from within the lake itself (autochthonous supply) and importation of organic matter from the terrestrial watershed (allochthonous supply). By manipulating the C-13 of dissolved inorganic C, thereby labeling within-lake primary production, we examined the relative importance of autochthonous and allochthonous C in supporting bacterial production. For 35 days, (NaHCO3)-C-13 was added daily to two small, forested lakes. One of the lakes (Peter) was fertilized so that primary production exceeded total respiration in the epilimnion. The other lake (Tuesday), in contrast, was low in productivity and had high levels of colored dissolved organic C (DOC). To obtain bacterial C isotopes, bacteria were regrown in situ in particle-free lake water in dialysis tubes. The contribution of allochthonous C to bacterial biomass was calculated by applying a two-member mixing model. In the absence of a direct measurement, the isotopic signature of the autochthonous end-member was estimated indirectly by three different approaches. Although there was excess primary production in Peter Lake, bacterial biomass consisted of 43-46% allochthonous C. In Tuesday Lake more than 75% of bacterial growth was supported by allochthonous C. Although bacteria used autochthonous C preferentially over allochthonous C, DOC from the watershed contributed significantly to bacterial production. In combination with results from similar experiments in different lakes, our findings suggest that the contribution of allochthonous C to bacterial production can be predicted from ratios of chromophoric dissolved organic matter (a surrogate for allochthonous supply) and chlorophyll a (a surrogate for autochthonous supply).
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| 6. |
- Kritzberg, Emma, et al.
(författare)
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Does autochthonous primary production drive variability in bacterial metabolism and growth efficiency in lakes dominated by terrestrial C inputs?
- 2005
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Ingår i: Aquatic Microbial Ecology. - 0948-3055. ; 38:2, s. 103-111
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Tidskriftsartikel (refereegranskat)abstract
- During the past 20 yr, aquatic microbiologists have reported 2 strong patterns which initially appear contradictory. In pelagic systems, bacterial growth and biomass is well correlated with the growth and biomass of primary producers. However, bacterial respiration often exceeds net primary production, which suggests that bacteria are subsidized by external inputs of organic matter. We hypothesize that bacterial growth efficiency (BGE) varies systematically between autochthonous and allochthonous carbon (C) sources and that this variation resolves the above conundrum. To test these ideas, we examined the ecological regulation of bacterial secondary production (BP), bacterial respiration (BR) and BGE in a series of lakes dominated by terrestrial (allochthonous) C inputs. BP was correlated with autochthonous C sources (chlorophyll a) even though the lakes were net heterotrophic (i.e. heterotrophic respiration consistently exceeded primary production). The results were simulated by a simple steady-state model of bacterial utilization of autochthonous and allochthonous dissolved organic C. A higher preference and greater growth efficiency of bacteria on autochthonous C may explain why BP is coupled to autochthonous production also in net heterotrophic ecosystems where the use of allochthonous C by bacteria is high. These results suggest that little of the allochthonous C assimilated by bacteria is likely to reach higher consumers.
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| 7. |
- Kritzberg, Emma, et al.
(författare)
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Influence of dissolved organic matter source on lake bacterioplankton structure and function - implications for seasonal dynamics of community composition
- 2006
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Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 56:3, s. 406-417
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that autochthonous (internally produced) organic carbon and allochthonous (externally produced) organic carbon are utilized by phylogenetically different bacterioplankton. We examined the relationship between the source of organic matter and the structure and function of lake bacterial communities. Differences and seasonal changes in bacterial community composition in two lakes differing in their source of organic matter were followed in relation to environmental variables. We also performed batch culture experiments with amendments of various organic substrates, namely fulvic acids, leachates from algae, and birch and maple leaves. Differences in bacterial community composition between the lakes, analysed by terminal restriction fragment length polymorphism, correlated with variables related to the relative loading of autochthonous and allochthonous carbon (water colour, dissolved organic carbon, nutrients, and pH). Seasonal changes correlated with temperature, chlorophyll and dissolved organic carbon in both lakes. The substrate amendments led to differences in both structure and function, i.e. production, respiration and growth yield, of the bacterial community. In conclusion, our results suggest that the source of organic matter influences community composition both within and among lakes and that there may be a coupling between the structure and function of the bacterial community.
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| 8. |
- Kritzberg, Emma S., et al.
(författare)
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Influence of dissolved organic matter source on lake bacterioplankton community structure and function : implications for seasonal dynamics of community structure.
- 2006
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Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 56:3, s. 406-417
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that autochthonous (internally produced) organic carbon and allochthonous (externally produced) organic carbon are utilized by phylogenetically different bacterioplankton. We examined the relationship between the source of organic matter and the structure and function of lake bacterial communities. Differences and seasonal changes in bacterial community composition in two lakes differing in their source of organic matter were followed in relation to environmental variables. We also performed batch culture experiments with amendments of various organic substrates, namely fulvic acids, leachates from algae, and birch and maple leaves. Differences in bacterial community composition between the lakes, analysed by terminal restriction fragment length polymorphism, correlated with variables related to the relative loading of autochthonous and allochthonous carbon (water colour, dissolved organic carbon, nutrients, and pH). Seasonal changes correlated with temperature, chlorophyll and dissolved organic carbon in both lakes. The substrate amendments led to differences in both structure and function, i.e. production, respiration and growth yield, of the bacterial community. In conclusion, our results suggest that the source of organic matter influences community composition both within and among lakes and that there may be a coupling between the structure and function of the bacterial community.
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| 9. |
- Pålsson, Carina, et al.
(författare)
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Net heterotrophy in Faroe Islands clear-water lakes: causes and consequences for bacterioplankton and phytoplankton
- 2005
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 50:12, s. 2011-2020
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Tidskriftsartikel (refereegranskat)abstract
- 1. Five oligotrophic clear-water lakes on the Faroe Islands were studied during August 2000. Algal and bacterial production rates, community respiration, and CO2 saturation were determined. In addition, we examined the plankton community composition (phytoplankton and heterotrophic nanoflagellates) and measured the grazing pressure exerted by common mixotrophic species on bacteria. 2. High respiration to primary production (6.6–33.2) and supersaturation of CO2 (830–2140 μatm) implied that the lakes were net heterotrophic and that the pelagic heterotrophic plankton were subsidised by allochthonous organic carbon. However, in spite of the apparent high level of net heterotrophy, primary production exceeded bacterial production and the food base for higher trophic levels appeared to be mainly autotrophic. 3. We suggest that the observed net heterotrophy in these lakes was a result of the oligotrophic conditions and hence low primary production in combination with an input of allochthonous C with a relatively high availability. 4. Mixotrophic phytoplankton (Cryptomonas spp., Dinobryon spp. and flagellates cf. Ochromonas spp.) constituted a large percentage of the plankton community (17–83%), possibly as a result of their capacity to exploit bacteria as a means of acquiring nutrients in these nutrient poor systems.
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