Hydrogeochemical dynamics and seasonal variability of water sources in the Munnar CZO, Southern Western Ghats, India: unveiling chemostatic behaviour

Abstract

This study quantifies hydrochemical dynamics, silicate/carbonate weathering rates, CO₂ consumption, and concentration-discharge (C-Q) relationships across intermittent streams (IS), the Amaravathi River, and groundwater (GW) in the Munnar Critical Zone Observatory (CZO), Southern Western Ghats, India. Dominance of Na⁺, Ca²⁺, and HCO₃⁻ across all water sources reflects active silicate (SW) and carbonate (CW) weathering. Discharge-weighted SW rates peak during monsoon in IS (6.77 t km^− 2 yr^− 1) and the river (8.17 t km^− 2 yr^− 1), while CW dominates IS in pre-monsoon (2.89 t km^− 2 yr^− 1 vs. river: 0.23 t km^− 2 yr^− 1). Silicate weathering drives CO₂ consumption in IS (1.65 × 10⁵ mol km^− 2 yr^− 1) and the river (2.01 × 10⁵ mol km^− 2 yr^− 1), with CW contributing 0.40 × 10⁵ and 0.15 × 10⁵ mol km^− 2 yr^− 1, respectively. Forward geochemical modeling identifies SW as the primary solute source in IS (40%) and GW (34.3%), whereas atmospheric deposition dominates river solutes (46%), followed by SW (41.6%). Carbonate dissolution contributes 23% to GW and 16.2% to IS. Hydrologically, IS exhibit chemostatic behaviour (stable solute concentrations across discharge), contrasting with the river’s chemodynamic responses (seasonal dilution/enrichment linked to monsoon-driven runoff). These results underscore the role of lateritic regolith in buffering IS hydrochemistry and highlight monsoon-driven surface processes controlling river solute variability. By bridging weathering fluxes, CO₂ budgets, and hydrological controls, this work provides critical implications for sustainable water management and climate resilience in tropical critical zones.