Seasonal Variations in the Physico-Chemical Characteristics of Freshwaters of India: A Narrative Review

The quality of water is one of the crucial concerns nowadays. The quality of water in a region is influenced by both natural processes such as precipitation, weathering and soil erosion as well as by the anthropogenic effects like discharge of waste and wastewater by municipal, agricultural, and industrial activities. India's freshwater ecosystems, encompassing rivers, lakes, reservoirs, and wetlands, are characterised by pronounced seasonal variation in their physico-chemical properties, driven primarily by the monsoon-dominated climate of the subcontinent. This narrative review synthesises the published literature on seasonal dynamics of key physico-chemical parameters — including water temperature, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), turbidity, total dissolved solids (TDS), electrical conductivity (EC), hardness, alkalinity, and nutrients — across the diverse freshwater bodies of India. A comprehensive literature search was conducted using the electronic databases Web of Science, Scopus, Google Scholar, and PubMed. Evidence drawn from studies spanning Himalayan rivers, peninsular river systems, Indo-Gangetic plains, lakes, and wetlands consistently demonstrates that seasonal transitions between pre-monsoon (summer), monsoon (rainy), and post-monsoon (winter) periods exert profound and measurable effects on water quality. During the monsoon, dilution of ionic constituents reduces TDS and EC, whilst increased surface run-off elevates turbidity and nutrient loads; conversely, the pre-monsoon period is associated with elevated temperatures, reduced DO, and concentrated dissolved solids. Post-monsoon and winter conditions generally favour water quality improvement due to temperature-driven oxygen saturation and reduced anthropogenic pressure. The review further examines how lithology, land use, population density, and industrial activities modulate and superimpose upon these natural seasonal cycles. The emerging influence of climate change on seasonal hydrological patterns, and its cascading effects on water quality, is also addressed. The review identifies significant gaps in long-term monitoring, standardised methodologies, and data availability, particularly for under-researched regions of north-eastern India and the Western Ghats. Strengthened regulatory frameworks and integrated freshwater monitoring strategies are recommended.