The realisation that the effects of land-use changes in the Thames catchment take more than 30 years to show themselves fully has profound implications for policies to monitor and manage the river's water quality.

BBC: Thames archive reveals long nitrate rise

The scheme is an agri-environment scheme, which provides funding for farmers to manage their land in a way designed to benefit biodiversity and landscape features and improve the quality of water and soil.

BBC: Environment and Sustainability Committee