Use of the trophic diatom index to monitor eutrophication in rivers

The performance of the trophic diatom index (TDI), a new index of trophic status in rivers, was evaluated at sites above and below major sewage works where nutrient removal is being considered. Some modifications to the index are proposed as a result. These include changing the scale from I (low nutrients) to 5 (high nutrients) to 0-100, the removal of taxa that are predominately planktonic from the index, and some minor adjustments to taxa sensitivities and indicator values. More detailed guidelines on the choice of sample site are also proposed. In particular, it is important that sites in the "recovery zone" downstream of sewage works are chosen so that the influence of the gross effects of organic pollution on the index is minimised. A "look-up" chart to aid data interpretation is also described, The revised TDI is now recommended to regulatory organisations as a tool for assessing eutrophication in rivers. (C) 1998 Elsevier Science Ltd. All rights reserved.