Heavy Metal Dynamics in the Giri S tream: Linking Water Quality to Fish Community Structure

Abstract

The Giri stream, a major perennial tributary of the Yamuna River originating in the Himalayan foothills of Himachal Pradesh, serves as a vital freshwater resource supporting local fisheries, irrigation, and biodiversity. This study systematically evaluated heavy metal contamination and ichthyofaunal diversity along longitudinal gradients of the Giri stream, encompassing three representative reaches: the upstream reach at Kharapathar (Shimla), the midstream reach at Giri Pul (Solan), and the downstream reach at Nawada Bridge (Sirmaur), over during 2025–2026.Twelve heavy metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Hg, Pb) were quantified using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). All metal concentrations were well within the permissible limits prescribed by the World Health Organization (WHO, 2017) and Bureau of Indian Standards (BIS, 2012).  A total of 10 fish species belonging to 4 orders and 5 families were recorded, with lowest species richness upstream (1 species) and highest downstream (8 species). Pearson's correlation analysis revealed strong relationship between heavy metals and fish diversity indices. However, this relationship is not causal; instead, it represents a common downstream spatial trend, where both metal concentrations and fish diversity increase along the upstream-to-downstream gradient due to separate ecological and geochemical processes. Overall, the findings suggest that the Giri stream maintains good ecological integrity, characterized by low heavy metal contamination and satisfactory water quality. Nevertheless, periodic monitoring is recommended to ensure the sustained health of the aquatic ecosystem.