A new Trophic Diatom Index for Tropical Reservoirs (TDIR).

We developed the Trophic Diatom Index for Reservoirs (TDIR), the first index proposal for water trophic quality assessment of tropical reservoirs in Brazil. Furthermore, we applied four borrowed diatom indices to compare their performances with TDIR. The proposal development considered a calibration set from surface sediment diatoms (n = 113) from reservoirs ranging from ultraoligotrophic to hypereutrophic. Weighted averaging methods were applied to infer optimum (values) and tolerances for total phosphorous for each diatom species. Indicative values were categorized within the trophic classification for tropical reservoirs, and sensitivity values were classified according to the range of tolerances of diatom species. The TDIR index scores ranged from 1 (ultraoligotrophic) to 6 (hypereutrophic). The TDIR showed good performance for the trophic classification of reservoirs. In contrast, the borrowed diatom indices developed in subtropical rivers underestimated the water quality, whereas the diatom index developed for lakes in temperate regions overestimated the water quality of our reservoirs. Moreover, we calculated new records of indicative values, and some well-cited species had different optimum and tolerances values concerning other well-known studies. TDIR provides an applicable index and contributes as a reliable tool for assessing the water quality and ecological status of tropical reservoirs. [ABSTRACT FROM AUTHOR]