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| 2. |
- Brönmark, Christer, et al.
(författare)
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Decoupling of cascading trophic interactions in a freshwater, benthic food chain
- 1996
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Ingår i: Oecologia. - Heidelberg, Germany : Springer Berlin/Heidelberg. - 0029-8549 .- 1432-1939. ; 108:3, s. 534-541
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Brönmark, Christer, et al.
(författare)
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Indirect effects of fish community structure on submerged vegetation in shallow, eutrophic lakes : an alternative mechanism
- 1992
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Ingår i: Hydrobiologia. - Dordrecht : Springer Netherlands. - 0018-8158 .- 1573-5117. ; 243/244:1, s. 293-301
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Tidskriftsartikel (refereegranskat)abstract
- The loss of submerged macrophytes during eutrophication of shallow takes is a commonly observed phenomenon. The proximate reason for this decline is a reduction of available light due to increasing phytoplankton and/or epiphyton biomass. Here we argue that the ultimate cause for the transition from a macrophyte-dominated state to a phytoplankton-dominated state is a change in fish community structure. A catastrophic disturbance event (e.g. winterkill) acting selectively on piscivores, cascades down food chains, eventually reducing macrophyte growth through shading by epiphyton, an effect that is reinforced by increasing phytoplankton biomass. The transition back from the phytoplankton to the macrophyte state depends on an increase in piscivore standing stock and a reduction of planktivores. A conceptual model of these mechanisms is presented and supported by literature data and preliminary observations from a field experiment. © 1992 Kluwer Academic Publishers.
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| 4. |
- Choudhury, Maidul I., et al.
(författare)
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Enhancing wetland nitrogen removal through macrophyte harvest and installation of woodchips-based floating beds
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Constructed wetlands (CWs) remove nitrogen (N) more efficiently as wetlands age and vegetation establishes. However, when CWs become heavily overgrown and filled with plant litter and root mats, channels form and N removal declines. Here, management may maintain high N removal. We tested two CW management options 1) restoration through macrophyte harvesting including root mat removal, and 2) subsequent installation of woodchips-based floating beds (WFBs) to compensate macrophyte loss. In a field experiment, using 16 heavily overgrown experimental CWs, we applied four treatments: i) macrophyte harvesting, ii) macrophyte harvesting and 5% of the wetland surface covered with WFBs, iii) macrophyte harvesting and 20% WFB cover, and iv) a control treatment (heavily overgrown). WFBs were planted with Glyceria maxima and Filipendula ulmaria before installation. N removal efficiency, removal rate and removal rate coefficient ka were estimated on nine occasions. After the experiment, WFBs were removed and plant biomass accrual, N assimilation, and denitrification gene (nirS, nirK, nosZI and nosZII) abundance on plant roots and woodchips were studied.Macrophyte harvesting significantly improved N removal of heavily overgrown CWs, whereas WFBs installation only improved N removal in harvested treatments on some occasions. Both G. maxima and F. ulmaria grew well on WFBs. Relative biomass production, root length and root surface area were higher for G. maxima than for F. ulmaria whereas biomass N assimilation was higher for F. ulmaria. Denitrification gene abundance was higher on plant roots than on woodchips while G. maxima hosted higher root denitrification gene abundance than F. ulmaria. We conclude that macrophyte harvesting improves N removal in heavily overgrown CWs. Further long-term field studies are needed to precisely evaluate the contribution of WFBs to N removal in CWs.
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| 5. |
- Eriksson, Peder G, et al.
(författare)
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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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Ingår i: 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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Tidskriftsartikel (refereegranskat)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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| 6. |
- Eriksson, Peder G., et al.
(författare)
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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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Ingår i: Freshwater Biology. - Chichester, United Kingdom : Wiley-Blackwell. - 0046-5070 .- 1365-2427. ; 36:3, s. 555-562
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Eriksson, Peder G., et al.
(författare)
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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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Ingår i: Journal of Environmental Quality. - Madison, United States : American Society of Agronomy. - 0047-2425 .- 1537-2537. ; 26:3, s. 905-910
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Graneli, Wilhelm, et al.
(författare)
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Rhizome dynamics and resource storage in Phragmites australis
- 1992
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Ingår i: Wetlands Ecology and Management. - Dordrecht, Netherlands : Springer Netherlands. - 0923-4861 .- 1572-9834. ; 1:4, s. 239-247
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Tidskriftsartikel (refereegranskat)abstract
- Seasonal changes in rhizome concentrations of total nonstructural carbohydrates (TNC), water soluble carbohydrates (WSC), and mineral nutrients (N, P and K) were monitored in two Phragmites australis stands in southern Sweden. Rhizome biomass, rhizome length per unit ground area, and specific weight (weight/ length ratio) of the rhizomes were monitored in one of the stands. Rhizome biomass decreased during spring, increased during summer and decreased during winter. However, changes in spring and summer were small (< 500 g DW m-2) compared to the mean rhizome biomass (approximately 3000 g DW m-2). Winter losses were larger, approximately 1000 g DW m-2, and to a substantial extent involved structural biomass, indicating rhizome mortality. Seasonal changes in rhizome length per unit ground area revealed a rhizome mortality of about 30% during the winter period, and also indicated that an intensive period of formation of new rhizomes occurred in June. Rhizome concentrations of TNC and WSC decreased during the spring, when carbohydrates were translocated to support shoot growth. However, rhizome standing stock of TNC remained large (> 1000 g m-2). Concentrations and standing stocks of mineral nutrients decreased during spring/ early summer and increased during summer/ fall. Only N, however, showed a pattern consistent with a spring depletion caused by translocation to shoots. This pattern indicates sufficient root uptake of P and K to support spring growth, and supports other evidence that N is generally the limiting mineral nutrient for Phragmites. The biomass data, as well as increased rhizome specific weight and TNC concentrations, clearly suggests that "reloading" of rhizomes with energy reserves starts in June, not towards the end of the growing season as has been suggested previously. This resource allocation strategy of Phragmites has consequences for vegetation management. Our data indicate that carbohydrate reserves are much larger than needed to support spring growth. We propose that large stores are needed to ensure establishment of spring shoots when deep water or stochastic environmental events, such as high rhizome mortality in winter or loss of spring shoots due to late season frost, increase the demand for reserves. © 1992 SPB Academic Publishing.
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| 9. |
- Hansson, Anna M., 1984-, et al.
(författare)
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Barriers and drivers for sustainable business model innovation based on a radical farmland change scenario
- 2023
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Ingår i: Environment, Development and Sustainability. - Dordrecht : Springer. - 1387-585X .- 1573-2975. ; 25:8, s. 8083-8106
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Tidskriftsartikel (refereegranskat)abstract
- The agricultural sector has a critical role in creating social and environmental value of natural resources in addition to its traditional role of creating economic value by supplying food to the ever-increasing world population. In fulfilling this dual role, the agricultural sector often faces competing pressures: to operate financially profitable businesses and to create, maintain, and benefit from ecosystem services (ES) in their operations. This paper analyses these pressures in an examination of drivers and barriers to the initiation of the business model innovation process for sustainability (BMIpfS) as perceived by ten agricultural business managers who operate farms in southern Sweden. The paper explores the interplay between managerial cognition and business decisions as revealed in semi-structured interviews. The new ES in focus connect to radical land-use change, paludiculture, as used in the rewetting of farmland intended to reduce the greenhouse gas emissions that drained peat soil causes. The paper contributes to the literature by identifying drivers and barriers that moderates the initiation of the BMIpfS. Although the managers acknowledge the importance of long-term, sustainable social, and environmental value creation, they have grave doubts about the profitability of activities associated with the preservation of peat soils and connected ES. These managers would benefit from taking a more proactive, long-term approach to business model changes for sustainability and from acquiring more knowledge about market demand for sustainability-oriented ES. Successful facilitation and implementation of knowledge transfer and government subsidies that support ES could improve the turning of profits based on sustainable value creation.
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| 10. |
- Johannesson, Karin M., 1982-, et al.
(författare)
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Clay-bound phosphorus retention in wetlands : a catchment comparison
- 2010
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Ingår i: 6th International Phosphorus Workshop (IPW6). ; , s. 127-127
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Ten constructed wetlands, situated in agricultural areas in the south of Sweden, are investigated for phosphorus (P) retention and factors affecting the efficiency. These wetlands are situated in areas dominated by clay or heavy clay soils. National monitoring and estimations have shown that agricultural areas dominated by such clay soils have among the highest phosphorus losses. It has also been shown that a large proportion of P is transported in particulate form; hence, it is expected that sedimentation is the predominant P retention process in the selected wetlands. Sedimentation of clay may, however, be difficult to achieve in wetlands, and the aim of the study is to quantify the function of wetlands as sinks for the P lost from the catchments. Sedimentation and accumulation of particles are measured once a year using sedimentation plates (40×40 cm) placed on the bottom of the wetlands. Additional sedimentation traps (estimating gross sedimentation) have been placed in three of the wetlands, and those are emptied two times per year. This paper presents results for P and soil retention after the first year (in kg P ha-1 year-1), estimated by extrapolating the amount of sediment accumulated on the plates, and the content of total phosphorus (TP), to the whole wetland area. Furthermore, one wetland was selected for a detailed investigation of the effect of a vegetation filter, which in a previous study has been shown to have a positive effect on particle retention. Here, estimates of net and gross sedimentation are measured before, within and after the vegetation filter. To identify some factors of significant importance for wetland P load and retention efficiency, the statistical relationship with different wetland and catchment characteristics is analyzed. The factors included are the ratio wetland area to catchment area, average hydraulic load, and various catchment characteristics, e.g. soil type, topography, fertilization history, and soil P fractions. Since there is some uncertainty regarding sedimentation of fine clay particles (< 0.2 m), the size fractions of the accumulated sediment is determined to see whether or not the finest clay particles from the catchments settle in the wetlands. Previous studies have shown a correlation between particle size and bioavailability, where finer clay particles contain larger proportion of easily available P. Trapping the finest clay particles is therefore of particular ecological importance and needs to be further investigated.
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