Final Report Summary - CLIMBING (Climate and nutrient impacts on lake biodiversity and ecosystem functioning)
CLIMBING: Climate and nutrient impacts on lake biodiversity and ecosystem functioning.
Freshwater biodiversity is declining at an alarming and unprecedented rate due to the concomitant impact of several anthropogenic pressures. Recent studies indicate that climate change will markedly exacerbate eutrophication problems through a complex set of mechanisms yet to be clarified. The additive effects of climate change and eutrophication may further deteriorate freshwater biodiversity and induce a major shift in ecosystem processes. Thus, the objective of the project was to gain much needed insight into how a changing climate interacts with nutrient supply to alter the relationship between biodiversity and ecosystem functioning in lakes. The project employed and integrated multifaceted approaches at a range of spatial and temporal scales: a) the world’s longest running freshwater ecosystem mesocosm experiment; b) spatial and time-series analysis of data; and c) empirical modelling.
Overview of results:
The project has provided evidence that climate change impacts different components of biodiversity (taxonomic and functional) at continental and local scale. The combined effects of nutrients, water level changes and increased salinity may exacerbate the negative effects of warming and cause changes in ecosystem functioning.
Specifically:
- The results using artificial shallow lake mesocomos showed that there is a positive effect of increase nutrients concentration on turbidity, phytoplankton and zooplankton biomass and a negative effect on zooplankton taxonomic and functional diversity and macrophytes coverage. The temperature effects were minor compared to nutrient effects.
- Large scale data showed that climate- and nutrient-related shifts in predator (i.e. fish) size structure may affect the size distribution of lower trophic levels with negative implications for lake ecosystem functioning and ecological state. They also provide evidence that the changes in functional diversity related to warming may affect the trophic food web and the lake ecosystem processes.
- Fish assemblages in colder regions (i.e. central and northern European lakes) are relatively more functionally redundant compared with the fish assemblages in warmer regions (Mediterranean lakes). This suggests that fish assemblages in cold lakes may withstand better extinctions because one functional trait is represented by different species. Thus, the higher functional redundancy may render them more resilient to environmental change. In contrast, our results suggest that fish assemblages in warmer lakes are more vulnerable if extinctions occur because the removal of one species could result in the removal of a whole functional trait.
- Altogether, these results show that increased warming has negative effects on shallow lakes biodiversity and ecosystem processes and it diminishes the chances of maintaining clear water state conditions.
Conclusions and the socio-economic impacts:
The European freshwater ecosystems have an increased fragility resulting from the concomitant action of several anthropogenic pressures. In this project I have shown that climate change is leading to further changes, and potentially counteracting the efforts to reach good ecological status. I have also provided evidence of the negative effects of the combined increased temperature, nutrient and hydrological changes on the food web and biodiversity of aquatic ecosystems. Additionally, I showed that lakes in warmer regions (e.g. Mediterranean) are particularly vulnerable to species extinctions because the removal of one species is likely to result in the removal of an ecological trait and thus lead to changes in the whole ecosystem functioning. All these results will likely have an impact on the Water Framework Directive Strategy and the EU Biodiversity Strategy to 2020.
The societal implications which arise from the findings are the need to apply measures to mitigate climate change effects and to reduce even more the nutrient loads on lakes. These measures should be aimed mainly at increasing the natural resilience of ecosystems against external perturbations. For instance, measures taken to reduce the nutrient input to freshwaters, beyond those already implemented or planned. This may include: i) application of fertilisers as determined by soil retention capacity and crop needs, leading to less intensive land use in catchments with sensitive freshwaters in order to reduce diffuse nutrient inputs; ii) (re)-establishment of riparian vegetation to buffer nutrient transfers to water bodies, iii) re-meandering of channelised streams to increase retention, decomposition and loss of organic matter and nutrients; iv) improvement of land management and agricultural practices to reduce sediment and particulate and dissolved nutrient export from catchments; v) more effective reduction of nutrient loading from point sources by proper sewage water treatments and from the atmosphere, the latter by reducing emissions from industry and agriculture; vii) in warmer regions, application of restrictions on alterations of natural hydrological cycles and water use, in particular for irrigated crop farming so as to reduce the risk of severe eutrophication and salinisation. Some of these adaptation measures have been integrated in the River Basin Management Plans required under the European Water Framework Directive, but since they are largely qualitative they will certainly stir a heated debate among different stakeholders.
Freshwater biodiversity is declining at an alarming and unprecedented rate due to the concomitant impact of several anthropogenic pressures. Recent studies indicate that climate change will markedly exacerbate eutrophication problems through a complex set of mechanisms yet to be clarified. The additive effects of climate change and eutrophication may further deteriorate freshwater biodiversity and induce a major shift in ecosystem processes. Thus, the objective of the project was to gain much needed insight into how a changing climate interacts with nutrient supply to alter the relationship between biodiversity and ecosystem functioning in lakes. The project employed and integrated multifaceted approaches at a range of spatial and temporal scales: a) the world’s longest running freshwater ecosystem mesocosm experiment; b) spatial and time-series analysis of data; and c) empirical modelling.
Overview of results:
The project has provided evidence that climate change impacts different components of biodiversity (taxonomic and functional) at continental and local scale. The combined effects of nutrients, water level changes and increased salinity may exacerbate the negative effects of warming and cause changes in ecosystem functioning.
Specifically:
- The results using artificial shallow lake mesocomos showed that there is a positive effect of increase nutrients concentration on turbidity, phytoplankton and zooplankton biomass and a negative effect on zooplankton taxonomic and functional diversity and macrophytes coverage. The temperature effects were minor compared to nutrient effects.
- Large scale data showed that climate- and nutrient-related shifts in predator (i.e. fish) size structure may affect the size distribution of lower trophic levels with negative implications for lake ecosystem functioning and ecological state. They also provide evidence that the changes in functional diversity related to warming may affect the trophic food web and the lake ecosystem processes.
- Fish assemblages in colder regions (i.e. central and northern European lakes) are relatively more functionally redundant compared with the fish assemblages in warmer regions (Mediterranean lakes). This suggests that fish assemblages in cold lakes may withstand better extinctions because one functional trait is represented by different species. Thus, the higher functional redundancy may render them more resilient to environmental change. In contrast, our results suggest that fish assemblages in warmer lakes are more vulnerable if extinctions occur because the removal of one species could result in the removal of a whole functional trait.
- Altogether, these results show that increased warming has negative effects on shallow lakes biodiversity and ecosystem processes and it diminishes the chances of maintaining clear water state conditions.
Conclusions and the socio-economic impacts:
The European freshwater ecosystems have an increased fragility resulting from the concomitant action of several anthropogenic pressures. In this project I have shown that climate change is leading to further changes, and potentially counteracting the efforts to reach good ecological status. I have also provided evidence of the negative effects of the combined increased temperature, nutrient and hydrological changes on the food web and biodiversity of aquatic ecosystems. Additionally, I showed that lakes in warmer regions (e.g. Mediterranean) are particularly vulnerable to species extinctions because the removal of one species is likely to result in the removal of an ecological trait and thus lead to changes in the whole ecosystem functioning. All these results will likely have an impact on the Water Framework Directive Strategy and the EU Biodiversity Strategy to 2020.
The societal implications which arise from the findings are the need to apply measures to mitigate climate change effects and to reduce even more the nutrient loads on lakes. These measures should be aimed mainly at increasing the natural resilience of ecosystems against external perturbations. For instance, measures taken to reduce the nutrient input to freshwaters, beyond those already implemented or planned. This may include: i) application of fertilisers as determined by soil retention capacity and crop needs, leading to less intensive land use in catchments with sensitive freshwaters in order to reduce diffuse nutrient inputs; ii) (re)-establishment of riparian vegetation to buffer nutrient transfers to water bodies, iii) re-meandering of channelised streams to increase retention, decomposition and loss of organic matter and nutrients; iv) improvement of land management and agricultural practices to reduce sediment and particulate and dissolved nutrient export from catchments; v) more effective reduction of nutrient loading from point sources by proper sewage water treatments and from the atmosphere, the latter by reducing emissions from industry and agriculture; vii) in warmer regions, application of restrictions on alterations of natural hydrological cycles and water use, in particular for irrigated crop farming so as to reduce the risk of severe eutrophication and salinisation. Some of these adaptation measures have been integrated in the River Basin Management Plans required under the European Water Framework Directive, but since they are largely qualitative they will certainly stir a heated debate among different stakeholders.