Review of Nutrient Dynamics, Physico-Chemical Controls and Cyanobacterial Risk in Indian Lakes

Abstract

Indian lakes—ranging from Himalayan basins and floodplain wetlands to coastal backwaters and dense urban waterbodies—are increasingly exposed to nutrient enrichment, altered hydrology, and warming, creating conditions that favor recurrent cyanobacterial blooms and associated health risks. This review synthesizes how external nutrient inputs from wastewater, agriculture, and land-use change interact with internal nutrient recycling and physico-chemical controls to shape bloom hazard across diverse Indian lake types. We highlight three coupled mechanisms: (i) monsoon-driven variability in flushing and residence time that governs nutrient retention and seasonal accumulation; (ii) sediment–water exchanges that regenerate bioavailable phosphorus and sustain eutrophication under warm, low-oxygen conditions even when external loads fluctuate; and (iii) physical habitat filtering by temperature, stratification, light climate, alkalinity, and episodic mixing that promotes buoyant, bloom-forming cyanobacteria and surface scum formation. We further discuss how nutrient form and stoichiometry influence community composition, including shifts between nitrogen-fixing and non-fixing taxa under seasonally changing limitation patterns. Evidence across representative Indian systems indicates that cyanobacterial risk is an emergent outcome of nutrient loads, nutrient speciation, oxygen regime, and seasonal hydrodynamics rather than a simple function of total nutrient concentrations. The review concludes by outlining a risk-focused framework linking catchment management, in-lake feedback control, and tiered monitoring (including early-warning indicators) to reduce bloom frequency, toxin exposure potential, and ecological degradation in Indian lakes.