Biological indices such as the IBI for fish (Karr, 1981), BIBI
for macroinvertebrates (Kerans and Karr, 1994) and TDI for
diatoms (Kelly and Whitton, 1995) simplify the complicated
ecology of streams and rivers into a form that permits rapid
assessment of the overall condition of a stream in a manner
that is easily understood by non-technical resource managers.
Diatom indices can be used in; gaining support and recognition
for diatom-based approaches to water quality monitoring;
providing an indication of water quality and allowing for the
dissemination of simplified useful information to resource
managers, conservationists and the general public; and allowing
for sample and data collection which can then be used later
in the formulation of diatom index (Taylor et al., 2007). The
TDI is one of a number of diatom-based tools developed to