| 1. |
- Becares, Eloy, et al.
(författare)
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Effects of nutrients and fish on periphyton and plant biomass across a European latitudinal gradient
- 2008
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Ingår i: Aquatic Ecology. - : Springer Science and Business Media LLC. - 1386-2588 .- 1573-5125. ; 42:4, s. 561-574
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Tidskriftsartikel (refereegranskat)abstract
- Replicated, factorial mesocosm experiments were conducted across Europe to study the effects of nutrient enrichment and fish density on macrophytes and on periphyton chlorophyll a (chl-a) with regard to latitude. Periphyton chl-a densities and plant decline were significantly related to nutrient loading in all countries. Fish effects were significant in a few sites only, mostly because of their contribution to the nutrient pool. A saturation-response type curve in periphyton chl-a with nutrients was found, and northern lakes achieved higher densities than southern lakes. Nutrient concentration and phytoplankton chl-a necessary for a 50% plant reduction followed a latitudinal gradient. Total phosphorus values for 50% plant disappearance were similar from Sweden (0.27 mg L-1) to northern Spain (0.35 mg L-1), but with a sharp increase in southern Spain (0.9 mg L-1). Planktonic chl-a values for 50% plant reduction increased monotonically from Sweden (30 mu g L-1s) to Valencia (150 mu g L-1). Longer plant growing-season, higher light intensities and temperature, and strong water-level fluctuations characteristic of southern latitudes can lead to greater persistence of macrophyte biomass at higher turbidities and nutrient concentration than in northern lakes. Results support the evidence that latitudinal differences in the functioning of shallow lakes should be considered in lake management and conservation policies.
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| 2. |
- Collentine, D., et al.
(författare)
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Catch : Decision support for stakeholders in catchment areas
- 2002
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Ingår i: Water Policy. - 1366-7017 .- 1996-9759. ; 4:5, s. 447-463
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Forskningsöversikt (refereegranskat)abstract
- Policy proposals for the management of water resources need to take into account two emerging themes: public involvement in the development of resource use policy and water management on a catchment level. The CATCH-model, a decision support system for catchment-based water management, builds on the use of 'discourse and deliberation' within stakeholder groups to define relevant socio-economic parameters and the relationships between these parameters. The sets of matrices that describe these parameters and their interrelation serve as the basis for evaluation of alternative management strategies and evaluation of specific measures for improving water quality. © 2002 Elsevier Science Ltd. All rights reserved.
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| 5. |
- Hansson, Lars-Anders, et al.
(författare)
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Responses to fish predation and nutrients by plankton at different levels of taxonomic resolution
- 2004
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:12, s. 1538-1550
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Tidskriftsartikel (refereegranskat)abstract
- 1. To improve mechanistic understanding of plankton responses to eutrophication, a mesocosm experiment was performed in the shallow littoral zone of a south Swedish lake, in which nutrient and fish gradients were crossed in a fully factorial design. 2. Food chain theory accurately predicted total biomass development of both phyto- and zooplankton. However, separating zooplankton and algae into finer taxonomic groups revealed a variety of responses to both nutrient and fish gradients. 3. That both nutrients and fish are important for phytoplankton dynamics was seen more clearly when viewing each algal group separately, than drawing conclusions only from broad system variables such as chlorophyll a concentration or total phytoplankton biovolume. 4. In some taxa, physiological constraints (e.g. sensitivity to high pH and low concentrations of free CO2) and differences in competitive ability may be more important for the biomass development than fish predation, grazing by herbivorous zooplankton, and nutrient availability. 5. We conclude that food chain theory accurately predicted responses in system variables, such as total zooplankton or algal biomass, which are shaped by the dynamics of certain strong interactors ('keystone species'), such as large cladocerans, cyanobacteria and edible algae (<50 mum), whereas responses at finer taxonomic levels cannot be predicted from current theory.
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| 6. |
- Moss, B, et al.
(författare)
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Continental-scale patterns of nutrient and fish effects on shallow lakes: synthesis of a pan-European mesocosm experiment
- 2004
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:12, s. 1633-1649
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Tidskriftsartikel (refereegranskat)abstract
- 1. Results are analysed from 11 experiments in which effects of fish addition and nutrient loading on shallow lakes were studied in mesocosms. The experiments, five in 1998, six in 1999, were carried out in six lakes, distributed from Finland to southern Spain, according to a standard protocol. 2. Effects of the treatments on 29 standard chemical, phytoplankton and zooplankton variables are examined to assess the relative importance of bottom-up (nutrient enrichment) and top-down (fish predation) effects. For each year, the experiments in different locations are treated as replicates in a meta-analysis. Results of individual experiments are then compared in terms of the patterns of significant influences of nutrient addition and fish predation with these overall results (the baseline), and between years in the same location. 3. The overall meta-analysis gave consistent results across the 2 years, with nutrient loading influencing all of the chemical variables, and on average 31% of primary producer and 39% of zooplankton variables. In contrast, fish influenced none of the chemical variables, 11% of the primary producer and 44% of the zooplankton variables. Nutrient effects on the system were thus about three times greater than fish effects, although fish effects were not inconsiderable. 4. The relative importance of nutrients and fish in individual experiments often differed between years at the same location and effects deviated to varying degrees from the baseline. These deviations were treated as measures of consistency (predictability) of conclusions in repeat experiments. Consistency increased southwards and this is interpreted as a consequence of more variable annual weather northwards. 5. The influence of nutrient loading was greater southwards and this was probably manifested through naturally greater annual macrophyte abundance in warmer locations in consequence of the longer plant growing-season. There was no trend in the relative importance of fish effects with latitude but this may partly be an artefact of the simple fish community used. These findings suggest that nutrient control should be a greater priority than biomanipulation in the restoration of eutrophicated shallow lakes in warm temperate regions. 6. Starting conditions affected the outcome of experiments. High initial concentrations of total phosphorus and planktonic chlorophyll a concentration (created by local conditions prior to the experiment) led to de-emphasis of the importance of nutrient loading in the experiment.
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| 7. |
- Rengefors, Karin, et al.
(författare)
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Factors regulating the recruitment of cyanobacterial and eukaryotic phytoplankton from littoral and profundal sediments
- 2004
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Ingår i: Aquatic Microbial Ecology. - 0948-3055. ; 36:3, s. 213-226
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Tidskriftsartikel (refereegranskat)abstract
- Many phytoplankton species produce resting cysts, forming 'seed banks' on lake sediments until they germinate and provide inocula (recruitment) for future pelagic populations. We have addressed the question of whether the littoral or the profundal zone provides the inoculum for planktonic populations in a eutrophic and dimictic lake (Lake Erken, Sweden). Our hypotheses were that high temperature, light, and sediment mixing would enhance recruitment. Also, we hypothesized that recruitment from littoral sediments would be greater than from profundal sediments. In situ recruitment traps were utilized to compare littoral and profundal recruitment, while laboratory experiments were performed to analyze which factors were most important. Seven common taxa were investigated: Asterionella formosa (Bacillariophyceae), Ceratium hirundinella (Dinophyceae), Microcystis botrys, M. wesenbergii, Anabaena sp., A. solitaria, and A. lemmermannii (Cyanobacteria). Our main findings were that light and sediment mixing were the most important factors in triggering and enhancing recruitment in the laboratory. Temperature and sediment origin (littoral/profundal) had a significant effect on recruitment only for A. lemmermannii and C. hirundinella, respectively. The field experiments showed that recruitment at the littoral site was much higher than at the profundal site, where little or no recruitment occurred. Together, these results strongly suggest that littoral sediments in temperate lakes provide inocula for most phytoplankton populations, likely due to favorable light conditions and high sediment mixing.
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| 8. |
- Stephen, D, et al.
(författare)
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Continental-scale patterns of nutrient and fish effects on shallow lakes: introduction to a pan-European mesocosm experiment
- 2004
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:12, s. 1517-1524
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Tidskriftsartikel (refereegranskat)abstract
- 1. Shallow lake ecosystems are normally dominated by submerged and emergent plants. Biological stabilising mechanisms help preserve this dominance. The systems may switch to dominance by phytoplankton, however, with loss of submerged plants. This process usually takes place against a background of increasing nutrient loadings but also requires additional switch mechanisms, which damage the plants or interfere with their stabilising mechanisms. 2. The extent to which the details or even major features of this general model may change with geographical location are not clear. Manipulation of the fish community (biomanipulation) has often been used to clear the water of algae and restore the aquatic plants in northerly locations, but it is again not clear whether this is equally appropriate at lower latitudes. 3. Eleven parallel experiments (collectively the International Mesocosm Experiment, IME) were carried out in six lakes in Finland, Sweden, England, the Netherlands and Spain in 1998 and 1999 to investigate the between-year and large-scale spatial variation in relationships between nutrient loading and zooplanktivorous fish on submerged plant and plankton communities in shallow lakes. 4. Comparability of experiments in different locations was achieved to a high degree. Cross-laboratory comparisons of chemical analyses revealed some systematic differences between laboratories. These are unlikely to lead to major misinterpretations. 5. Nutrient addition, overall, had its greatest effect on water chemistry then substantial effects on phytoplankton and zooplankton. Fish addition had its major effect on zooplankton and did not systematically change the water chemistry. There was no trend in the relative importance of fish effects with latitude, but nutrient addition affected more variables with decreasing latitude. 6. The relative importance of top-down and bottom-up influences on the plankton differed in different locations and between years at the same location. The outcome of the experiments in different years was more predictable with decreasing latitude and this was attributed to more variable weather at higher latitudes that created more variable starting conditions for the experiments.
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| 9. |
- Ståhl-Delbanco, Annika, et al.
(författare)
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Effects of bioturbation on recruitment of algal cells from the "seed bank" of lake sediments
- 2002
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 47:6, s. 1836-1843
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Tidskriftsartikel (refereegranskat)abstract
- Effects of different bioturbators on recruitment of several nuisance algae, Anaboena spp. (Cyanophyta), Microcystis spp. (Cyanophyta), and Gonvostomum semen (Raphidophyta), from sediment to water were studied in a long-term laboratory experiment. Natural sediment, where macrofauna larger than 1 mm had been removed, was added to 18 aquaria. To each of six aquaria, individuals of Asellus aquaticus (Isopoda) or Chironomus plumosus (Arthropoda) larvae were added, and six aquaria were left as bioturbation-free controls. Recruitment of Anabaena, Microcystis, and G. semen from the sediment was detected using inverted traps that were sampled once a week during 8 weeks. The activities of the isopod A. aquaticus increased recruitment rates of all algal groups investigated, whereas chironomids had a less pronounced effect. With respect to Anabaena, increased recruitment rate was expressed as a promotion of growth in the pelagic habitat. To our knowledge, these results are the first to demonstrate that bioturbating invertebrates affect the recruitment of phytoplankton resting stages. Moreover, our results suggest that recruitment rate might be more pronounced in littoral areas, which are often dominated by A. aquaticus, rather than in profundal areas of a lake, generally dominated by chironomids. Hence, with respect to algal dynamics, the strength of the coupling between the benthic and pelagic zones might vary both spatially and temporally, depending on composition of the benthic invertebrate community and the ontogenetic development of the individuals within it.
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| 10. |
- Ståhl-Delbanco, Annika
(författare)
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Recruitment from resting stages among bloom-forming cyanobacteria
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cyanobacteria are known to form heavy blooms in eutrophicated freshwaters and also form resting stages, associated with the sediments, during harsh growth conditions. These resting stages can serve as inoculum for pelagic populations and function as a potential source for bloom formations. However, the factors involved in initiating recruitment from resting stage to the pelagic phase are not fully understood. In my thesis, I have been studying several potential triggers. I found that elevated temperatures and increased light availability were important. In addition, sediment mixing, e.g. from bioturbating animals, also played a significant role in increasing recruitment rates of cyanobacteria from the sediments. Hence, the littoral-zone, where these factors have substantial impact, should be the major recruitment site, which was also confirmed in my studies. Cyanobacteria has a low internal N:P ratio and in eutrophic freshwaters, cyanobacterial dominance is often correlated with low N:P ratios. Accordingly, I found that recruitment rates of cyanobacterial resting stages were increased at declining N:P ratios. A plausible explanation to my result is that a declining N:P ratio signals improving nutrient conditions for cyanobacteria and is therefore a suitable trigger for recruitment to the water column. This implies that a declining N:P ratio could be an important mechanism behind, and an early warning of cyanobacterial blooms.
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