Tanya Vasileva
This study presents a comprehensive regional-scale assessment of groundwater suitability for agricultural irrigation across Bulgaria. The escalating pressure on water resources enforce the precise evaluation of alternative water sources, with groundwater playing a pivotal role. A major ion chemistry data (Ca2+, Mg2+, Na+, K+, HCO3-) from a national monitoring network (2015–2019) was analyzed by applying established irrigation water quality indices: Soluble Sodium Percentage (SSP), Kelly’s Ratio (KR), Permeability Index (PI), and Residual Sodium Bicarbonate (RSBC). Statistical analysis and spatial 2D modeling revealed distinct spatial patterns of groundwater quality. The results indicate that most of the groundwater in Bulgaria is of ‘excellent’ to ‘good’ quality for irrigation. Specifically, 97.8% of samples fall in the ‘excellent’ to ‘good’ SSP categories, 99.2% have a KR < 1 (suitable), and 98.8% exhibit safe RSBC levels (less than 1.25 mEq/L). The PI index classifies 98.9% of groundwater as ‘slightly good’ (class II), indicating generally acceptable permeability characteristics. Principal Component Analysis distilled the indices into two independent risk dimensions explaining 87.9% of variance: sodium hazard (PC1, 52.1%) and permeability-alkalinity hazard (PC2, 35.7%). This enabled identification of three spatial risk clusters (A, B, C) and statistical outliers (Yambol District for sodium hazard, p = 0.041; Smolyan District for unique hydrochemical profile, p = 0.019). The macro-level assessment provides an important tool for supporting water resource management and agricultural planning in Bulgaria by identifying regional vulnerabilities and guiding more detailed, local studies.