1. Rothamsted Research; Harpenden; Hertfordshire; AL5 2JQ; UK
2. The NERC Centre for Ecology and Hydrology; Lancaster Environment Centre; Library Avenue; Bailrigg; Lancaster; LA1 4AP; UK
3. The NERC Centre for Ecology and Hydrology; Bush Estate; Penicuik; EH26 0QB; UK
4. Porton Down; Salisbury; Wiltshire; SP4 0JQ; UK