A simple method for assessing and monitoring hydrochemical baselines and variability in snow-dominated mountain...

The definition of natural geochemical baselines is fundamental for water quality assessment, yet long-term hydrochemical monitoring records in river systems are often sparse or discontinuous. This study explores the use of total basin snow water equivalent (SWE) volume for characterizing and eventually reconstructing streamflow geochemistry in snow-dominated catchments. We analyzed five river basins in the Coquimbo Region of north-central Chile using SWE estimates derived from a data-assimilation framework and historical hydrochemical records (2000-2024) from the Chilean Water Authority. Discharge-weighted concentrations of major ions (Na, K, Ca, Mg, Cl, SO₄), Fe, specific conductance (SC), and pH were evaluated against SWE at annual and sub-annual scales, considering potential hydrological memory effects and time lags. Statistically significant relationships were identified for most constituents. Major ions and SC exhibited strong negative correlations with SWE (often |r|> 0.7), consistent with dilution during high snowmelt periods, whereas Fe shows positive correlations, likely reflecting sediment mobilization under increased discharge. No significant relationship was found for pH. The strongest correlations generally occur within the same hydrological year or with lags of up to one year, with some spatial differences between northern and southern basins within the study area. Despite the influence of additional hydrogeochemical and anthropogenic controls (beyond the scope of this work), the results demonstrate that estimates of the basin SWE volume emerge as a simple but robust and novel basis for estimating expected baseline concentrations, infilling incomplete hydrochemical time series, and potentially detecting hydrochemical anomalies in snow-fed river systems.