Effect of environmental improvements on the diatoms of the River Axe, southern England.

The River Axe, a lowland river in South-west England is used as a model system for describing how ecological status assessments can be applied in practice. Seasonal sampling over a three-year period established a strong baseline against which future changes could be assessed. These indicated that the river was enriched with nutrients and that ecological status was significantly below the good/moderate status boundary, implying the need for a Programme of Measures to be implemented. Reductions in both point and diffuse sources of nutrients led to changes in the diatom assemblage, reflected by increasing EQRs at monitored sites. An understanding of the uncertainty inherent in diatom-based ecological status assessments allows the success of control measures to be assessed. In the case of the River Axe, diatom-based assessments suggest that the river is now close to good status at many monitored sites, although there is still evidence of some nutrient enrichment.