Trophic Diatom Index (TDI)

The 1990s saw a new regulatory focus on the problems of nutrients in rivers. New monitoring tools were needed to meet these needs and the Trophic Diatom Index (TDI) was one of these, developed by Martyn Kelly whilst National Rivers Authority (NRA) Research Fellow at the University of Durham.

Designed to be easy to use in the busy environment of a modern water industry laboratory, the TDI provides information on the nutrient status of rivers. The TDI was used first by the NRA and subsequently by the Environment Agency in England and Wales and by the Scottish Environmental Protection Agency, helping biologists to develop robust cases for or against investment in nutrient stripping facilities at sewage works discharging into rivers all over the country.

The first version of the TDI is described in:

Kelly M.G. & Whitton B.A. (1995). A new diatom index for monitoring eutrophication in rivers. Journal of Applied Phycology 7: 433-444.

A revised version was prepared in 2001 and is described in:

M.G Kelly, C Adams, A C Graves, J Jamieson, J Krokowski, E B Lycett, J Murray-Bligh, (2001). The Trophic Diatom Index: A User's Manual Revised Edition. Bristol: Environment Agency. 

This explains how to collect, process and analyse sample as well as how to calculate the TDI and interpret the results. It is available free-of-charge from the Environment Agency's publication catalogue. (Use the search term "Trophic Diatom Index" to find the manual)

Note that the French software program “Omnidia” includes only the first version of the index and uses a different scale for expressing results to that used in the UK.

The latest revision of the TDI was performed in 2006 as part of DARLEQ (see below)

DARLEQ - Diatoms for Assessing River and Lake Ecological Quality

DARLEQ takes the work that started in 1995 with the TDI a step further, providing a tool for estimating ecological status class, as required by the EU’s Water Framework Directive (WFD).

A key requirement of the WFD is that ecological quality is assessed by comparing the actual state of a water body with the state expected in the absence of any human impact. The outcome is expressed as an ‘ecological quality ratio’ or EQR.

DARLEQ is the acronym that describes the outputs of two projects funded by UK environmental regulators – DARES (Diatoms for Assessing River Ecological Status) and DALES (Diatoms for Assessing Lake Ecological Status). Bowburn Consultancy collaborated with the Universities of Bristol, Newcastle and Ulster and with ENSIS Ltd in order to develop the models. Separate models have been developed for lakes and rivers, both based on re-calibrated versions of the TDI. This has now been adopted by the UK and Ireland as part of their standard tool for assessing the health of freshwater ecosystems.

The DARES website has downloadable sampling, preparation and slide analysis protocols along with PowerPoint presentations which include video demonstrations showing how to sample diatoms from different substrata.

The presentations are also available here.

key references:

Kelly, M.G., Juggins, S., Guthrie, R., Pritchard, S., Jamieson, B.J., Rippey, B, Hirst, H & Yallop, M.L. (2008). Assessment of ecological status in UK rivers using diatoms. Freshwater Biology 53: 403-422.

Kelly, M.G., Bennion, H., Burgess, A., Elllis, J., Juggins, S., Guthrie, R., Jamieson, B.J., Adriaenseens, V. and Yallop, M.L. 2009. Uncertainty in ecological status assessments of lakes and rivers using diatoms. Hydrobiologia 633: 5-15.

Bennion, H., Kelly, M.G., Juggins, S., Yallop, M.L., Burgess, A., Jamieson, J. & Krokowski, J. (2014). Assessment of ecological status in UK lakes using benthic diatoms. Freshwater Science 33: 639-654.