Hydrochemical Assessment and Irrigation Suitability of Groundwater in the Grande Niaye of Pikine (Dakar): Contribution of Multivariate Analysis and Water Quality Indices

Abstract

Groundwater quality is a key concern for sustaining market gardening in peri-urban semi-arid settings where agricultural intensification, urban growth and inadequate sanitation may affect irrigation resources. This study assessed the hydrochemical characteristics and irrigation suitability of groundwater in the Grande Niaye of Pikine (Dakar) using four sampling stations (S1–S4). The investigation combined field and laboratory physicochemical measurements, hydrochemical diagrams, Principal Component Analysis (PCA) and irrigation water quality indices. The analysed waters showed near-neutral pH, with values ranging from 6.7 to 7.5 and a mean of 6.9. Electrical conductivity varied from 668.5 to 1016 µS/cm, with a mean of 840.7 µS/cm, indicating moderate mineralisation and compliance with irrigation guideline values. Major ion concentrations suggested variable enrichment in chloride, bicarbonate, sodium, calcium and magnesium, while nitrate concentrations ranged from 10.6 to 88.5 mg/L, indicating localised nitrogen inputs. PCA accounted for 89.0% of the total variance through the first two components (PC1 = 65.1%; PC2 = 23.9%). PC1 was associated mainly with mineralisation and ionic enrichment, whereas PC2 reflected nitrate-related influence. The irrigation indices indicated generally favourable sodicity conditions: SAR ranged from 2.42 to 3.43, KI from 0.61 to 0.83, SSP from 43.38 to 49.83% and MH from 28.26 to 47.31%. RSC values ranged from -5.74 to 1.85 meq/L, suggesting acceptable carbonate-related risk, whereas potential salinity values of 8.57–14.57 indicated a need for drainage and monitoring. Overall, the groundwater remains broadly suitable for irrigation, but nitrate enrichment, salinity potential and hardness require regular assessment to support sustainable use in this peri-urban agricultural area.