Abstract: Groundwater is an important water resource for agricultural irrigation and urban and industrial utilization in the coastal regions of northern China. In the past 5 decades, coastal groundwater salinization in the Yang–Dai river plain has become increasingly serious under the influence of anthropogenic activities and climatic change. It is pivotal for the scientific management of coastal water resources to accurately understand groundwater salinization processes and their causative factors. Hydrochemical (major ion and trace element) and stable isotopic (δ18O and δ2H) analysis of different water bodies (surface water, groundwater, geothermal water and seawater) were conducted to improve understanding of groundwater salinization processes in the plain's Quaternary aquifer. Saltwater intrusion due to intensive groundwater pumping is a major process, either by vertical infiltration along riverbeds which convey saline surface water inland, and/or direct subsurface lateral inflow. Trends in salinity with depth indicate that the former may be more important than previously assumed. The proportion of seawater in groundwater is estimated to have reached up to 13 % in shallow groundwater of a local well field. End-member mixing calculations also indicate that the geothermal water with high total dissolved solids (up to 10.6 g L−1) with depleted stable isotope compositions and elevated strontium concentrations (> 10 mg L−1) also mixes locally with water in the overlying Quaternary aquifers. This is particularly evident in samples with elevated Sr ∕ Cl ratios (> 0.005 mass ratio). Deterioration of groundwater quality by salinization is also clearly exacerbated by anthropogenic pollution. Nitrate contamination via intrusion of heavily polluted marine water is evident locally (e.g., in the Zaoyuan well field); however, more widespread nitrate contamination due to other local sources such as fertilizers and/or domestic wastewater is evident on the basis of NO3 ∕ Cl ratios. This study provides an example of how multiple geochemical indicators can delineate different salinization processes and guide future water management practices in a densely populated water-stressed coastal region.

Abstract: Hydrogeological and geochemical data, in conjunction with the results of an electrical imaging tomographic survey, were examined to determine the main factors and mechanisms controlling the groundwater chemistry and salinity of the unconfined aquifer of Bou-Areg, on the Mediterranean coast of NE Morocco. In addition, statistical and geochemical interpretation methods were used to identify the distribution of the salinity. Multivariate statistical analysis (cluster and principal component factors) revealed the main sources of contamination. Groups A, B, and C in the cluster analysis and Factors 1–3 (Factor 1: CE, Cl−, K+, SO42-, and Mg2+; Factor 2: Ca2+, HCO3-, and pH; Factor 3: NO3-) represent the ‘signature’ of seawater intrusion in the coastal zone, the influence of marly-gypsum outcrops in the upstream zone, and anthropogenic sources, respectively. The ionic delta, the ionic ratio, the saturation index, and Stuyfzand’s method were applied to evaluate geochemical processes. The results obtained indicate, on the one hand, the phenomenon of salinization in both the coastal and the upstream zones, and on the other, the dilution of groundwater by recharge. Cation exchange is shown to modify the concentration of ions in groundwater. Locally, with respect to salinization processes in the coastal zone, the results of electrical imaging tomography show that salinity increases both with depth and laterally inland from the coastline, due to seawater intrusion.