Spatiotemporal variation in water quality and its association with cyanobacterial diversity in the Hirakud Reservoir, Sambalpur, Odisha, India

ABSTRACT The present study evaluates the impact of seasonal variation on the water quality and the cyanobacterial diversity in the Hirakud Reservoir. Different physicochemical water quality parameters were determined using standard methods as prescribed by American Public Health Association (APHA). Morphometric identification of cyanobacterial species and their diversity in reservoir water were assessed during three different seasons. The Trophic State Index (TSI) of the reservoir was calculated based on the depth of the water and the phosphate and chlorophyll-a contents. The physicochemical parameters of the water samples revealed a minimum of 3.8 mg/L of dissolved oxygen during the pre-monsoon season, and a maximum of 6.2 mg/L during the monsoon season. Nitrate content in water was found to be maximum (12.7 mg/L) in the post-monsoon season, whereas total phosphate concentration was recorded to be maximum (4.17 mg/L) during the pre-monsoon period. Higher cyanobacterial diversity was observed during pre-monsoon and was mostly dominated by Microcystis species. Cyanobacterial species such as Anabaena, Calothrix, Oscillatoria, Chroococcus, Phormidium, Cylindrospermum, Nostoc, Spirulina, and Phormidium were recorded in the reservoir. The TSI analysis indicated that the reservoir is in transition from the mesotrophic state to the eutrophic state. Principal Component Analysis indicated that increased anthropogenic activities upstream and around the reservoir contributed significantly to nutrient enrichment and subsequent deterioration of water quality.