Hydrochemistry and Water Quality Assessment in Freshwater Ecosystems

The Bhavani River Basin acts as a significant socio-ecological link in Southern India, providing critically important water resources and ecosystem services that support biodiversity and communities. Due to increasing anthropogenic pressures, such as irrigation-based farming, industrial effluents, and major nutrient inputs, a robust hydrochemical evaluation is needed to assess the river quality status. A spatial sampling campaign was conducted over 24 months in 15 sampling sites and measured physico-chemical variables such as pH, dissolved oxygen, electrical conductivity, nitrates, phosphates, trace heavy metals, alongside computing water quality indices (WQI). A clear gradient in the degradation was evident, with headwater reaches classified as Good, whilst 40% of the downstream stations obtained 'Poor to Very Poor' quality at certain times of the pre-monsoon. Multivariate analysis highlighted that leaching from agricultural activities and industrial waste was the major driving force of hydrochemical changes in the river, explaining 72.4% of the total variation. Significant accumulation of nitrates and heavy metals from upstream to downstream was identified using the Mann-Kendall trend test with significance at p < 0.05, indicating the increasing pollution loading within the river. These results clearly show that existing water management systems (e.g., check dams, etc.) and their operating procedures cannot prevent the accumulation of pollutants. A radical policy and industrial upgrades, together with the restoration of riverine buffering capacity, are required to ensure the river's health.