Abstract: Study of the Cenomanian–Turonian and Plio–Quaternary aquifers of Essaouira basin (Western Morocco), based on the interpretation of geochemical (major elements) and isotopic (18O, 2H, 13C and 14C) data, has aided the understanding of the hydrodynamics of these aquifers, which is greatly affected by tectonics. Hydrochemical characteristics based on the bivariate diagrams of major ions (Cl–, SO42–, NO3–, HCO3–, Na+, Mg2+, K+ and Ca2+) and electrical conductivity and mineral saturation indices indicate that the origins of groundwater mineralisation are the result of: (1) evaporite dissolution; (2) cation exchange reactions; (3) and evaporation processes. Radiogenic isotopes (3H and 14C) have highlighted the presence of significant recent recharge in the eastern part of the basin, with groundwater moving according to the general flow path (south-east to north-west). Stable isotope data from the Essaouira basin plot along the Global Meteoric Water Line and below the Local Meteoric Water Line. This suggests that groundwater has been recharged under several different climate regimes.

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.