Linking Sewage Effluent Quality with Salinity-Sodicity Dynamics and Cation Imbalance in Greywater-Irrigated Soils of an Arid Coastal Environment

Abstract

The increasing reuse of greywater for irrigation necessitates a comprehensive understanding of its effects on soil quality and chemical dynamics. This study evaluated the efficiency of a greywater treatment system and its subsequent impact on soil physicochemical properties across multiple urban green spaces. Significant reductions in biochemical oxygen demand, chemical oxygen demand, and total dissolved solids showed limited reduction, indicating the persistence of dissolved salts during treatment.

Soil analyses revealed moderately alkaline conditions (pH 7.43-8.33) and elevated electrical conductivity (0.86-1.27 dS/m), suggesting progressive salinity buildup under greywater irrigation. Nutrient parameters, including soil organic matter (0.49-0.82%), nitrogen, phosphorus, and potassium, exhibited positive interrelationships, reflecting enhanced nutrient retention. In contrast, higher sodium concentrations (130-165 mg/kg), sodium adsorption ratio (10.54-13.33), and magnesium hazard (35.1-44%) indicated increasing sodicity risks. The Ca:Mg ratio (1.27-1.85) showed an inverse relationship with sodicity indicators, highlighting the stabilizing role of calcium in soil structure.

Correlation analysis demonstrated strong positive associations among salinity-related parameters (EC, Na, SAR, MH, and cation balance), while nutrient variables showed negative relationships with salinity indicators, indicating a trade-off between fertility and salinization. Principal component analysis further distinguished salinity-driven processes from nutrient-driven dynamics, with clear clustering of study areas based on soil chemical characteristics.

Overall, the findings suggest that while greywater irrigation enhances soil nutrient status, it simultaneously contributes to salinity and sodicity development. Sustainable management strategies, including controlled irrigation practices and calcium-based amendments, are essential to mitigate long-term soil degradation and ensure the safe reuse of greywater in urban landscapes.