Project Description

Our overall hypothesis, based on analysis of unique long-term datasets of up to 70 years duration, is that the documented warming of water in the two basins of Windermere has facilitated the expansion of a non-indigenous species, the roach and caused a trophic cascade that has changed the water quality in the lake.

Specifically, we aim to test the following five interlinked hypotheses (shown in Fig. 1), that:

1. roach populations have increased as a result of warming surface water;

2. the recent reduction in summer zooplankton is causally linked to increased predation pressure by planktivorous fish;

3. the increased abudance of summer phytoplankton, and associated changes in the lake such as increased ratio of phytoplankton chlorophyll a to total phosphorus, is causally linked to the reduction in grazing pressure;

4. the decline in Arctic charr in the lake is causally linked to competition for food with other planktivorous fish, particularly the introduced roach in recent years;

5. invasion by a generalist consumer (roach) has also affected the top predator in the lake (the pike) by shortening the food chain, further influencing food-web interactions.

Fig. 1. Echoes in the Ecosystem: the hypotheses that will be tested in this project.

This work will exploit the unique long-term data on Windermere maintained by CEH and also spatial data from the database and atlas of freshwater fish also held by CEH as a component of the Biological Records Centre. We will complement detailed, targeted analysis of the unique long-term records with analysis of automatic monitoring data, collection of new data on fish diet, analysis of hydroacoustic data, stable isotope analysis of new and archived fish and zooplankton samples (see below) and modelling.

Analysis of the rare archived samples extending over more than 60 years, initially collected by the Freshwater Biological Association and subsequently by CEH, provides a unique ability to trace the history of change though taxonomic and stable isotope analysis. Most data are available for the two linked, but differently-responding basins of Windermere.

This will allow us to compare the response of lake basins experiencing similar patterns of climate change. The different complementary approaches will be reviewed and synthesised to produce a holistic understanding of the factors responsible for the observed changes in the two lake basins.

Further details of the proposed work can be found in the documents section on the right.