Baseline assessment of water quality suitability for irrigation using hydrochemical and heavy metal pollution indices in the Meli gold mining area, Tigray, Ethiopia

Irrigation water quality is a critical determinant of agricultural productivity, soil health, and long-term environmental sustainability, particularly in regions affected by mining activity. In the Meli area of Tigray, Ethiopia, intensified gold mining in recent years has raised concerns that mining-derived contaminants may degrade irrigation water quality. Despite these concerns, no comprehensive assessment has yet quantified irrigation water quality in the study area. This study provides the first baseline assessment of irrigation water quality in the Meli gold mining area using an integrated hydrochemical and heavy metal pollution approach. Water samples were analyzed for physicochemical parameters (pH, electrical conductivity, total dissolved solids, and major ions) and selected heavy metals (Cu, Zn, Pb, and As) following standard analytical procedures. Irrigation suitability was evaluated using the sodium adsorption ratio, sodium percentage, residual sodium carbonate, permeability index, magnesium ratio, Kelly index, potential salinity, and the irrigation water quality index (IWQI), along with the heavy metal pollution index (HPI) and metal index (MI). Results indicate neutral-to-slightly alkaline water (pH 6.9–8.4), with electrical conductivity (0.6–1.89 dS/m) and total dissolved solids (392.6–1227.2 mg/L) indicating low-to-moderate salinity. Hydrochemical indices classified all samples as excellent to good, with IWQI values ranging from 76.8 to 81.7. However, heavy metal contamination is significant: all samples exceeded permissible limits, with HPI (229.5–846.5) and MI (5.5–16.3). This divergence shows that conventional indices alone cannot determine mining-related risks. These findings establish the first integrated baseline for irrigation water quality in Meli, supporting monitoring, pollution mitigation, and sustainable agricultural management in mining-affected regions.