Carbon cycling in freshwater lakes; identifying the who, what, where and when.

Algal blooms in freshwaters are happening with increasing frequency due to climate change and input of nutrients. Lake ecosystems may be severely impacted by blooms, particularly the microbial food web. Many of the algae which bloom produce large quantities of photosynthetic fixed carbon which are exudated throughout their growth cycle as dissolved organic carbon (DOC), some of which forms particulate organic carbon (POC).

This carbon is then processed by bacteria and fungi, recycling carbon through the microbial loop. In extreme cases this increased microbial activity depletes oxygen within the lakes.

However, within freshwater lakes little is known about the composition and fate of photosynthetically fixed organic carbon. Many of the bacterial taxa within freshwaters that may breakdown organic carbon are not well characterized. Furthermore, for many microbial groups such as aquatic fungi and heterotrophic protists we know very little about their diversity, distribution and role in breaking down DOC and POC.

Knowledge of this will enable us to gain a greater understanding of carbon cycling in lakes and how this may change in future due to environmental change. The work will be conducted on the lakes of the Lake District UK, with a focus on Lake Windermere, which has received much attention in recent years due to the algal blooms that occur annually.

The aims of this project are:

To assess how the concentration and chemical composition of DOC and POC changes in lakes throughout the lifetime of phytoplankton blooms. To identify the main degrading organisms of DOC and POC, within lake ecosystems both fungal and bacterial. To assess how production and composition of phytoplankton exudates varies in response warming and nutrient inputs

To track the flow of photosynthetically fixed organic carbon into the microbial loop