| 1. |
- Brönmark, Christer, et al.
(author)
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Decoupling of cascading trophic interactions in a freshwater, benthic food chain
- 1996
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In: Oecologia. - Heidelberg, Germany : Springer Berlin/Heidelberg. - 0029-8549 .- 1432-1939. ; 108:3, s. 534-541
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Journal article (peer-reviewed)abstract
- Food chain theory provides explicit predictions for equilibrium biomasses among trophic levels in food chains of different lengths. Empirical studies on freshwater benthic food chains have typically been performed on chains with up to three levels and in field experiments with limited spatial and temporal scale. Here we use a ‘’natural snapshot experiment” approach to study equilibrium biomass and abundance among trophic levels in natural ponds differing only with respect to fish assemblage structure. Forty-four ponds were surveyed for their density and biomass of fish, snails and periphyton. Ponds were divided into three categories based on fish assemblage: ponds with no fish (two trophic levels), ponds with molluscivorous fish (three trophic levels), ponds with molluscivorous fish (three trophic levels) and ponds that also had piscivorous fish (four trophic levels). Ponds without fish had a high density and biomass of snails and a low biomass of periphyton, whereas snails with molluscivorous fish. In the presence of piscivores, molluscivore populations consisted of low numbers of large individuals. Snail assemblages in piscivore ponds were characterised by relatively high densities of small-bodied detritivorous species and periphyton biomass was not significantly different from ponds with three trophic levels. Thus, predictions from classic food chain theory were upheld in ponds with up to three trophic levels. In ponds with four trophic levels, however, there was a decoupling of the trophic cascade at the piscivore-molluscivore level. Gape-limited piscivory, predation on snails by molluscivores that have reached an absolute size refuge from predation, and changes in food preferences of the dominant snails are suggested to explain the observed patterns.
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| 2. |
- Eriksson, Peder G, et al.
(author)
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An experimental study on effects of submersed macrophytes on nitrification and denitrification in ammonium-rich aquatic systems
- 1999
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In: Limnology and Oceanography. - Waco, United States : American Society of Limnology and Oceanography, Inc.. - 0024-3590 .- 1939-5590. ; 44:8, s. 1993-1999
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Journal article (peer-reviewed)abstract
- We have examined the role of microbial communities on the surface of submersed macrophytes and in the underlying sediment for nitrification and denitrification in light and dark in NH(4)(+)-enriched microcosm systems using isotope pairing and dilution techniques. Potamogeton pectinatus L. and intact sediment cores were collected in a shallow reservoir receiving treated municipal wastewater and containing dense submersed vegetation. Chambers containing P. pectinatus shoots, sediment, or both P. pectinatus shoots and sediment were exposed to 6 h of darkness, 6 h of light, and 6 h of darkness. (14)NH(4)(+) and (15)NO(3)(-) were added at ambient concentrations of 15 and 5 mg N liter(-1), respectively. NH(4)(+) was primarily nitrified in the epiphytic microbial communities, and NO; was denitrified in the underlying sediment. In chambers containing macrophytes, there was a net production of O(2) and NO(3)(-) in light and a net consumption in dark, and nitrification was higher in light than in dark. In chambers with only sediment, there was always a net consumption of NO(3)(-), and nitrification was similar in light and dark. The results show that submersed macrophytes can be important for the N metabolism in NH(4)(+)-rich freshwaters (e.g., wastewater treatment systems) by stimulating nitrification through providing surfaces for attached nitrifying bacteria and possibly also through diurnal changes in the water chemistry.
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| 3. |
- Eriksson, Peder G., et al.
(author)
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Functional differences in epiphytic microbial communities in nutrient-rich freshwater ecosystems : An assay of denitrifying capacity
- 1996
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In: Freshwater Biology. - Chichester, United Kingdom : Wiley-Blackwell. - 0046-5070 .- 1365-2427. ; 36:3, s. 555-562
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Journal article (peer-reviewed)abstract
- 1. The denitrifying capacity of epiphyton was used to evaluate differences in the function of epiphytic microbial communities on submersed macrophytes in nutrient-rich freshwater ecosystems. The denitrifying capacity of epiphyton on Patamogeton perfoliatus shoots of different age and with different epiphytic abundances from a eutrophic lake was investigated in laboratory microcosms in the Light and dark. Additionally, differences between epiphyton on shoots of Potamogeton pectinatus grown under different in Situ nutrient and hydraulic conditions were investigated by examining their denitrifying capacity. 2. Denitrification was registered in well-developed epiphytic layers on both mature and senescent shoots in the dark, with activities 3- to 10-fold higher in the epiphytic communities of senescent shoots. No activity was detected on young shoots with sparse epiphyton or on shoots from which loosely attached epiphyton had been removed. Denitrification never occurred during illumination. 3. Even though the epiphytic abundance was similar in magnitude, the denitrifying capacity of epiphyton adapted to high nutrient loadings was about a hundred times higher than that of epiphyton adapted to lower nutrient levels. Additionally, epiphytic abundance and denitrifying capacity were higher at sites less exposed to wave turbulence or water currents, than at sites with more water turbulence. 4. The results illustrate how the hydraulic and nutrient conditions of the surrounding water affect both the quantity and function of epiphytic microbial communities in nutrient-rich freshwater ecosystems.
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| 4. |
- Eriksson, Peder G., et al.
(author)
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Nitrogen removal in a wastewater reservoir : The importance of denitrification by epiphytic biofilms on submersed vegetation
- 1997
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In: Journal of Environmental Quality. - Madison, United States : American Society of Agronomy. - 0047-2425 .- 1537-2537. ; 26:3, s. 905-910
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Journal article (peer-reviewed)abstract
- The aim of this study was to examine the importance of epiphytic denitrifying bacteria on submersed vegetation in removing N from a shallow nutrient-enriched freshwater ecosystem. The investigation was conducted during the summer of 1994 in a surface now reservoir receiving municipal tertiary-treated wastewater. The submersed vegetation in the reservoir was dominated by Potamogeton pectinatus L. and filamentous green algae (FGA). The N loading was 2300 mg N h(-1) m(-2) and the N removal, calculated as the mean difference between influent and effluent N, was 190 mg N h(-1) m(-2) (8%). The majority of influent N consisted of NH4+, but the main part of the N removal was due to the removal of NO3- whereas no net retention of NH4+ was found. Mean total soluble solids and BOD7 retention was 69 and 38%, respectively, Denitrification measurements were conducted in darkness at in situ temperature in microcosms with P. pectinatus, FGA, or infect sediment cores. Epiphytic denitrification ranged between 0.21 to 7.0 mg N h(-1) m(-2) reservoir surface area depending on the abundance of the submersed vegetation (5-140 g DW m(-2)). Sediment denitrification was 4.7 mg N h(-1) m-L reservoir surface area. The mean assimilative N uptake of the submersed vegetation and epiphyton was 3.4 and 1.6 mg N h(-1) m(-2) reservoir surface area, respectively. Measured N removal rates through plant uptake and denitrification could only account for a minor part of the N removal observed by mass balance. However, microcosm denitrification measurements underestimate actual denitrification. Thus, the major part of the N removal was most likely due to denitrification. In conclusion, this study indicates that denitrification in epiphytic microbial communities on submersed vegetation can be of significant importance for the N removal in nutrient-enriched freshwater ecosystems.
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| 5. |
- Strand, John A., et al.
(author)
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Wave exposure related growth of epiphyton : Implications for the distribution of submerged macrophytes in eutrophic lakes
- 1996
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In: Hydrobiologia. - Dordrecht : Kluwer Academic Publishers. - 0018-8158 .- 1573-5117. ; 325:2, s. 113-119
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Journal article (peer-reviewed)abstract
- The distribution of submerged macrophytes in eutrophic lakes has been found to be skewed towards sites with intermediate exposure to waves. Low submerged macrophyte biomass at exposed sites has been explained by, for instance, physical damage from waves. The aim of this study was to investigate if lower biomass at sheltered sites compared to sites with intermediate exposure to waves can be caused by competition from epiphyton. Investigations were performed in eutrophic lakes in southern Sweden. Samples of submerged macrophytes and epiphytic algae on the macrophytes were taken along a wave exposure gradient. The amount of epiphyton (AFDW) per macrophyte biomass decreased with increased exposure. Biomass of submerged macrophytes, on the other hand, increased with increased exposure until a relatively abrupt disappearance of submerged vegetation occurred at high exposures. Production of epiphytic algae was monitored on artificial substrates from June to September at a sheltered and an exposed site in three lakes. It was higher at sheltered sites compared with exposed sites. We suggest that epiphytic algae may be an important factor in limiting the distribution of submerged macrophytes at sheltered sites in eutrophic lakes.
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| 6. |
- Weisner, Stefan E.B. 1954-
(author)
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Effects of an organic sediment on performance of young Phragmites australis clones at different water depth treatments
- 1996
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In: Hydrobiologia. - Dordrecht, Netherlands : Springer Netherlands. - 0018-8158 .- 1573-5117. ; 330:3, s. 189-194
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Journal article (peer-reviewed)abstract
- Performance of young Phragmites australis plants was examined after 7 weeks on an artificial nutrient-enriched inorganic substrate and on the same substrate to which an organic sediment from a eutrophic lake was added, at three different water depth treatments. Growth decreased, and proportional allocation of biomass to roots increased, with the addition of sediment. These differences were significant in shallow and deep water, but not at a medium depth. Concentrations of phosphorus and nitrogen in plant biomass decreased, and concentration of iron increased, with addition of sediment. The effects of sediment addition may have resulted from a decreased availability of nutrients in the substrate or from an impaired root functioning. Nutrient exhaustion in the substrate, due to a fast plant growth, can explain the relatively strong effects in shallow water. Deep water, on the other hand, probably restricted oxygen transport to the roots, resulting in an impaired root functioning in the low-redox sediment environment. The results show that, especially in relatively deep water, growth of undisturbed plants of P. australis may be inhibited by eutrophication of sediments, probably because of an impaired root functioning in sediments containing reduced toxic compounds (e.g. ferrous iron).
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| 7. |
- Weisner, Stefan E.B. 1954-, et al.
(author)
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Mechanisms regulating abundance of submerged vegetation in shallow eutrophic lakes
- 1997
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In: Oecologia. - Heidelberg,Germany : Springer Berlin/Heidelberg. - 0029-8549 .- 1432-1939. ; 109:4, s. 592-599
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Journal article (peer-reviewed)abstract
- Shallow eutrophic lakes tend to be either in a turbid state dominated by phytoplankton or in a clear-water state dominated by submerged macrovegetation. Recent studies suggest that the low water turbidity in the clear-water state is maintained through direct and in-direct effects of the submerged vegetation. This study examined what mechanisms may cause a recession of the submerged vegetation in the clear-water state, and thereby a switch to the turbid state. The spatial distribution of submerged vegetation biomass was investigated in two shallow eutrophic lakes in the clear-water state in southern Sweden. Biomass of submerged vegetation was positively correlated with water depth and wave exposure, which also were mutually correlated, suggesting that mechanisms hampering submerged vegetation were strongest at shallow and/or sheltered locations. The growth of Myriophyllum spicatum, planted in the same substrate and at the same water depth, was compared between sheltered and wave exposed sites in two lakes. After 6 weeks the plants were significantly smaller at the sheltered sites, where periphyton production was about 5 times higher than at the exposed sites. Exclosure experiments were conducted to evaluate the effects of waterfowl grazing on macrophyte biomass. Potamogeton pectinatus growth was decreased by grazing, whereas M. spicatum was not affected. The effects were greater at a sheltered than at a wave-exposed site, and also negatively related to distance from the reed belt. These results suggest that competition from epiphytes and waterfowl grazing hamper the development of submerged vegetation at sheltered and/or shallow locations. An increased strength of these mechanisms may cause a recession of submerged vegetation in shallow eutrophic lakes in the clear-water state and thereby a switch to the turbid state.
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| 8. |
- Weisner, Stefan, 1954-, et al.
(author)
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Rhizome architecture in Phragmites australis in relation to water depth : Implications for within-plant oxygen transport distances
- 1996
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In: Folia Geobotanica. - Dordrecht : Springer Netherlands. - 1211-9520 .- 1874-9348. ; 31:1, s. 91-97
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Journal article (peer-reviewed)abstract
- Phragmites australis (CAV.) TRlN. ex STEUD. is a perennial plant, largely relying on its rhizomes for resource storage, spreading and anchorage in the substrate. Vertical distribution and length of horizontal rhizomes of Phragmites australis were investigated at the reed bed edge in a lake in southern Sweden. In deep water, horizontal rhizomes were relatively short and superficially situated in the substrate. It is hypothesised that this is an adaptation to water depth by keeping O-2-transport distances through shoots and rhizomes as short as possible. In shallow water, P. australis rhizomes generally penetrated deeply into the substrate, probably improving anchorage and nutrient uptake possibilities. Further, horizontal rhizomes were longer in shallow water, which may increase the rate of vegetative spread. Because of these changes in rhizome architecture, "critical within-plant oxygen transport distances" did not change with water depth. This indicates that P. australis maximises the extension of its rhizomes in relation to spatial differences in water depth. This may limit the ability of P. australis to tolerate sudden temporal increases in water depth or eutrophication.
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| 9. |
- Wertz, Ingrid, et al.
(author)
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Potamogeton pectinatus and Myriophyllum spicatum response to sediments from a calcareous, shallow, eutrophic lake
- 1997
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In: Journal of freshwater ecology. - Philadelphia, United States : Taylor & Francis. - 0270-5060 .- 2156-6941. ; 12:1, s. 1-10
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Journal article (peer-reviewed)abstract
- The effect of sediment composition on the growth of Potamogeton pectinatus and Myriophyllum spicatum was evaluated by a greenhouse experiment in which segments of both species were grown on 37 sediments, which ranged from highly flocculent to sandy, collected from the calcareous, shallow eutrophic Lake Krankesjon. The two species responded similarly to the 37 sediment types; there was a strong correlation between the find biomass of M. spicatum and the find biomass of P. pectinatus for a given sediment type. Our results indicated that in these sediments, organic matter and density were not effective predictors of macrophyte growth. Root:shoot ratios of both P. pectinatus and M. spicatum were inversely related to the final biomass, and phosphorus and nitrogen concentrations of M. spicatum shoots were inversely related to root:shoot ratios. This suggests that plants were responding to sediment infertility by allocating proportionately more growth to root formation. Tissue analysis indicated that M. spicatum growth was phosphorus limited on some sediments, and this may have been a result of reduced phosphorus availability due to binding with calcium.
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