| 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. |
- Adrian, Rita, et al.
(författare)
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Lakes as sentinels of climate change
- 2009
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 54:6(2), s. 2283-2297
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Tidskriftsartikel (refereegranskat)abstract
- While there is a general sense that lakes can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. We identified the key response variables within a lake that act as indicators of the effects of climate change on both the lake and the catchment. These variables reflect a wide range of physical, chemical, and biological responses to climate. However, the efficacy of the different indicators is affected by regional response to climate change, characteristics of the catchment, and lake mixing regimes. Thus, particular indicators or combinations of indicators are more effective for different lake types and geographic regions. The extraction of climate signals can be further complicated by the influence of other environmental changes, such as eutrophication or acidification, and the equivalent reverse phenomena, in addition to other land-use influences. In many cases, however, confounding factors can be addressed through analytical tools such as detrending or filtering. Lakes are effective sentinels for climate change because they are sensitive to climate, respond rapidly to change, and integrate information about changes in the catchment.
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| 3. |
- Moss, Brian D., et al.
(författare)
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Climate change and the future of freshwater biodiversity in Europe : a primer for policy-makers
- 2009
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Ingår i: Freshwater Reviews. - : Freshwater Biological Association. - 1755-084X. ; 2:2, s. 103-130
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Tidskriftsartikel (refereegranskat)abstract
- Earth's climate is changing, and by the end of the 21st century in Europe, average temperatures are likely to have risen by at least 2 °C, and more likely 4 °C with associated effects on patterns of precipitation and the frequency of extreme weather events. Attention among policy-makers is divided about how to minimise the change, how to mitigate its effects, how to maintain the natural resources on which societies depend and how to adapt human societies to the changes. Natural systems are still seen, through a long tradition of conservation management that is largely species-based, as amenable to adaptive management, and biodiversity, mostly perceived as the richness of plant and vertebrate communities, often forms a focus for planning. We argue that prediction of particular species changes will be possible only in a minority of cases but that prediction of trends in general structure and operation of four generic freshwater ecosystems (erosive rivers, depositional floodplain rivers, shallow lakes and deep lakes) in three broad zones of Europe (Mediterranean, Central and Arctic-Boreal) is practicable. Maintenance and rehabilitation of ecological structures and operations will inevitably and incidentally embrace restoration of appropriate levels of species biodiversity. Using expert judgement, based on an extensive literature, we have outlined, primarily for lay policy makers, the pristine features of these systems, their states under current human impacts, how these states are likely to alter with a warming of 2 °C to 4 °C and what might be done to mitigate this. We have avoided technical terms in the interests of communication, and although we have included full referencing as in academic papers, we have eliminated degrees of detail that could confuse broad policy-making
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| 4. |
- Peeters, E, et al.
(författare)
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Assessing ecological quality of shallow lakes: Does knowledge of transparency suffice?
- 2009
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Ingår i: Basic and Applied Ecology. - : Elsevier BV. - 1618-0089 .- 1439-1791. ; 10, s. 89-96
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Tidskriftsartikel (refereegranskat)abstract
- The European Water Framework Directive (WFD) requires that all aquatic ecosystems in their member states should reach ‘good’ ecological quality by 2015. To assess ecological quality, the WFD requires the definition of reference conditions using biological, physical and chemical indicators and the assignment of each water body to one of five quality classes using these indicators. Elaborate assessment schemes using large sets of variables are now being developed. Here we address the question whether all this is really needed and what the simplest assessment approach would be for the case of shallow lakes. We explore the relationships between the quality class assigned to a lake by experts in shallow lake ecology and a rich set of biological, physical, and chemical data. Multinomial logistic regression analyses were carried out based on data from 86 shallow lakes throughout Europe that were sampled in 2000 and/or 2001. Ecological quality of shallow lakes judged by experts was strongly correlated to physical and chemical variables associated with light regime and nutrients and much less to biological variables. Our regression model showed that ecological quality of this set of shallow lakes judged by experts could be predicted quite well from water transparency expressed as Secchi depth and that other variables did not contribute to it significantly. According to the WFD, lakes should at least have a ‘good’ ecological quality. Quality judged by experts and predicted quality were similar for 78% of the lakes with respect to meeting this standard. As a cautionary note we stress that Secchi depth alone will be a less useful indicator if effects of stressors other than eutrophication (e.g. lake acidification and toxic pollution) are to be considered.
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| 5. |
- Persson, Jonas, 1977-
(författare)
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Food Quality Effects on Zooplankton Growth and Energy Transfer in Pelagic Freshwater Food Webs
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Poor food quality can have large negative effects on zooplankton growth and this can also affect food web interactions. The main aims of this thesis were to study the importance of different food quality aspects in Daphnia, to identify potentially important differences among zooplankton taxa, and to put food quality research into a natural context by identifying the importance of food quality and quantity in lakes of different nutrient content.In the first experiment, the RNA:DNA ratio was positively related to the somatic growth rate of Daphnia, supporting a connection between P content, RNA content, and growth rate. The second experiment showed that EPA was important for Daphnia somatic growth, and 0.9 µg EPA mg C-1 was identified as the threshold below which negative effects on Daphnia growth occurred.A field survey identified patterns in the PUFA content of zooplankton that could be explained by taxonomy and trophic position. Cladocera enriched EPA and ARA relative to seston, and Copepoda primarily enriched DHA. In a whole-lake experiment, gentle fertilization of an oligotrophicated reservoir increased the seston P content and the biomass of high quality phytoplankton (Cryptophyceae, high EPA content). This was followed by increases in zooplankton and fish biomasses.An empirical model based on data from a literature survey predicted that food quantity is most important for zooplankton growth in oligotrophic lakes, and that food quality factors are more important in eutrophic lakes. Thus, zooplankton growth, and energy transfer efficiency in the food web, is predicted to be highest in mesotrophic lakes. The results predict that the strength and nature of food quantity and quality limitation of Daphnia growth varies with lake trophic state, and that some combination of food quantity and/or quality limitation should be expected in nearly all lakes.
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