| 1. |
- 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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| 2. |
- 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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| 3. |
- Van de Bund, WJ, et al.
(författare)
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Responses of phytoplankton to fish predation and nutrient loading in shallow lakes: a pan-European mesocosm experiment
- 2004
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:12, s. 1608-1618
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Tidskriftsartikel (refereegranskat)abstract
- 1. The impacts of nutrients (phosphorus and nitrogen) and planktivorous fish on phytoplankton composition and biomass were studied in six shallow, macrophyte-dominated lakes across Europe using mesocosm experiments. 2. Phytoplankton biomass was more influenced by nutrients than by densities of planktivorous fish. Nutrient addition resulted in increased algal biomass at all locations. In some experiments, a decrease was noted at the highest nutrient loadings, corresponding to added concentrations of 1 mg L-1 P and 10 mg L-1 N. 3. Chlorophyll a was a more precise parameter to quantify phytoplankton biomass than algal biovolume, with lower within-treatment variability. 4. Higher densities of planktivorous fish shifted phytoplankton composition toward smaller algae (GALD < 50 mum). High nutrient loadings selected in favour of chlorophytes and cyanobacteria, while biovolumes of diatoms and dinophytes decreased. High temperatures also may increase the contribution of cyanobacteria to total phytoplankton biovolume in shallow lakes.
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| 4. |
- 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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| 5. |
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| 6. |
- Goma, C., et al.
(författare)
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Spencer-Attix water/medium stopping-power ratios for the dosimetry of proton pencil beams
- 2013
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 58:8, s. 2509-2522
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Tidskriftsartikel (refereegranskat)abstract
- This paper uses Monte Carlo simulations to calculate the Spencer-Attix water/medium stopping-power ratios (s(w, med)) for the dosimetry of scanned proton pencil beams. It includes proton energies from 30 to 350 MeV and typical detection materials such as air (ionization chambers), radiochromic film, gadolinium oxysulfide (scintillating screens), silicon and lithium fluoride. Track-ends and particles heavier than protons were found to have a negligible effect on the water/air stopping-power ratios (s(w, air)), whereas the mean excitation energy values were found to carry the largest source of uncertainty. The initial energy spread of the beam was found to have a minor influence on the s(w, air) values in depth. The water/medium stopping-power ratios as a function of depth in water were found to be quite constant for air and radiochromic film-within 2.5%. Also, the s(w, med) values were found to have no clinically relevant dependence on the radial distance-except for the case of gadolinium oxysulfide and proton radiography beams. In conclusion, the most suitable detection materials for depth-dose measurements in water were found to be air and radiochromic film active layer, although a small correction is still needed to compensate for the different s(w, med) values between the plateau and the Bragg peak region. Also, all the detection materials studied in this work-except for gadolinium oxysulfide-were found to be suitable for lateral dose profiles and field-specific dose distribution measurements in water.
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