1. Centre for Ecology and Hydrology; Lancaster Environment Centre; Lancaster; LA1 4AP; UK
2. Centre for Ecology and Hydrology; Maclean Building; Benson Lane; Crowmarsh Gifford; Wallingford; Oxfordshire; OX10 8BB; UK
3. Biomedical and Life Sciences Division; Faculty of Health and Medicine; Lancaster University; Lancaster; LA1 4YQ; UK