Diatom indices have gained considerable popularity in estimation of the trophic state and degree of pollution in lotic ecosystems. However, their applicability and efficacy have rarely been tested in Indian streams and rivers. In the present study, benthic diatom assemblages were sampled at 27 sites along the Chambal River in Central India. PCA revealed three groups of sites, namely, heavily polluted (HVPL), moderately polluted (MDPL), and least polluted (SANT). A total of 100 diatom taxa belonging to 40 genera were identified. Brachysira vitrea (Grunow) was the most abundant species recorded from the least polluted sites with an average relative abundance of 29.52. Nitzschia amphibia (Grunow) was representative of heavily polluted sites (average relative abundance 31.71) whereas moderately polluted sites displayed a dominance of Achnanthidium minutissimum (Kϋtzing) with an average relative abundance of 26.33. CCA was used to explore the relationship between diatom assemblage composition and environmental variables. Seventeen different diatom indices were calculated using diatom assemblage data. The relationship between measured water quality variables and index scores was also investigated. Most of the diatom indices exhibited strong correlations with water quality variables including BOD, COD, conductivity, and nutrients, particularly phosphate. Best results were obtained for TDI and IPS indices which showed a high level of resolution with respect to discrimination of sites on the basis of pollution gradients. Water quality maps for the Chambal River were hence prepared in accordance with these two indices. However, satisfactory results with respect to water quality evaluation were also obtained by the application of EPI-D and IGD indices. The present study suggests that TDI and IPS are applicable for biomonitoring of rivers of Central India. Diatom indices, which are simpler to use such as IGD, may be considered, at least for a coarser evaluation of water quality.

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This study examines spatial distribution of benthic diatom communities from the rivers Chambal, Ken and Tons in Central India. Their floras consist of total 386 taxa, 110, 206 and 212 taxa in Chambal, Ken and Tons, respectively and are quite similar. Flora is highly similar within each river but varies among their corresponding sections (upper to mouth).Richness decreases gradually from source to mouth because substrate heterogeneity declines. Similarity in richness also declines in each river, but increases mildly amongst their corresponding sections, because substrate differs spatially. Alpha diversity is high and similar for the rivers. Species-rich genera are same. Elements of pristine conditions prevail in the flora. In light of these observations the benthic diatom communities are examined for the spatial distribution of flora and species diversity in the highland -plateau rivers Ken and Tons and Chambal. Studies will be useful to understand the regional patterns of diatom diversity and formulate reference conditions in these and other rivers of this region. The study will serve to assess the impacts of the proposed Ken-Betwa Link and climate change.