Euro-limpacs Deliverables


Report describing a cross comparison study of long-term contemporary data and palaeoecological data from lakes

Climate change has a significant impact upon the structure and functioning of lake ecosystems. However, many lakes that have been affected by climate change in recent years, have also been influenced by changes in nutrient input over the same period. It is, therefore, very difficult to assess the effect of each of these pressures separately. Nevertheless, distinguishing the impacts of each of these pressures on lake ecosystems is crucial for effective management because it affects the setting of realistic targets for restoration. This report compares and contrasts three different approaches to disentangling the combined impacts of climate change and eutrophication in lakes. These approaches are (1) statistical modelling techniques, (2) process−based modelling techniques and (3) palaeolimnological techniques. Each approach is illustrated by one or more case studies.

The choice of approach is, to a large extent, determined by the quality of the available data. Palaeolimnology can be used to reconstruct past events from plant and animal remains preserved in the lake sediments if no long term datasets are available. A statistical technique can be used to look for trends if long−term lake monitoring data exist. The process−based modelling approach can be applied if historical catchment and lake data are available.

The output from each approach varies in terms of temporal resolution and the type of information that is provided. Both the statistical and process−based models have a temporal resolution of less than one year, and in some cases less than one month. The statistical methods provide information on trends within the data and relationships among the variables recorded. The process−based modelling approach provides information on interactions among the variables recorded, although this is restricted only to those relationships that already exist within the model. The palaeolimnological approach is valuable in that it provides temporally integrated data over much longer timescales, thereby reducing noise, but it can provide little information on ecosystem interactions unless multi−proxy studies are undertaken.

Most of the methods investigated have only a limited capacity for predicting the impacts of climate change on water quality in the future. Both the palaeolimnological and statistical methods are especially limited in this respect. The process−based modelling approach has some predictive capability, but these predictions will only be valid if the relationships that are affected by these external changes are represented within the model.

In general, each of the approaches reviewed in this report requires different types of data as input and provides different types of information as output. In practice, the choice of approach for assessing the effects of climate change and eutrophication on any particular lake is more likely to be determined by data availability than by any other criterion. In addition, the type of output will be determined by the approach selected.

During the course of the Euro−limpacs project, multiple approaches will be applied to selected lake sites to allow comparison of the outputs. However, the research undertaken so far suggests that each of these approaches provides different yet complementary information about lake responses to change.

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