Benthic Diatoms as indicators of water quality in Sharda (Kali), a Transboundary Himalayan River

Abstract Bioassessment studies in river systems of India are rather scarce and most of the monitoring programmes still rely on the traditional physical and chemical analysis. We explored the biomonitoring potential of benthic diatoms from the Sharda (Kali) river in the Himalayas, which is due interlinking with the Yamuna River under the National River Linking Programme (NRLP) in India. Seventeen sites along the Sharda were sampled in November 2022 for the analysis of 14 physical and chemical variables and benthic diatoms. Hierarchical agglomerative cluster analysis (HACA) and Principal Component analysis (PCA) of the physico-chemical data set revealed two major groups of sites; the majorly unpolluted sites at higher elevations of Kumaun Himalayas (KH) and the low or moderately polluted sites of Terai Plains (TP) at lower elevations. Application of WQI assigned a good water quality class (B) to all selected sites. A total of 107 diatom taxa were recorded during the present study. Achnanthes pseudoswazi, Achnanthes minutissima, Achnanthidium pusillum, Geissleria decussis, Reimeria sinuata were the most abundant forms from KH whereas Gomphonema acuminatum, Cymbella excisa, Cocconeis pediculus, Nitzschia linearis, Navicula angusta were the dominant forms recorded from TP. A decrease in diatom diversity was observed from KH to TP sites. Significant differences (p < 0.05 & p < 0.01) between diatom diversity index scores was observed between KH and TP sites. Diversity indices correlated significantly with important water quality variables. The results of the TDI, IPS, IDG and IDSE diatom biotic indices corroborated well with the recorded physico-chemical variables and WQI values. IPS diatom index exhibited better resolution than WQI with reference to categorization of sites and subsequent establishment of ecological status. IPS was found to be the most suitable index and could be utilized for a pre-linkage ecological status establishment for the Sharda River. However, weak correlations of diatom indices and water quality variables along with low percentage of taxa included for computation of diatom indices reiterates the importance of establishment of region specific autecological preferences of diatoms and subsequent formulation of a customized diatom index for the Sharda River system.