Recharge and Hydro-geochemical Evolution Groundwater in Semi-Arid Zone (Essaouira Basin, Morocco)

Abstract

Arid and semi-arid areas are threatened by desertification, and thus the degradation due to various factors, including drought, of course, but also the exploitation of resources. They are, in fact, already in a state of stress (resources less than 500 m³ per year per capita) with important disorders induced by climate change. These make an impact on the hydrological cycle, with longer droughts and increased flooding. These disorders will strengthen the already observed degradation of ecosystems, which are often overexploited. Essaouira synclinal area is part of the semi-arid areas of Morocco that are subject to the impact of climatic and human pressures. In the case of this coastal area, which includes two main aquifers superimposed; the Plio-Quaternary and Turonian, the resulting vulnerability is compounded by the risk of infiltration navy. The Rainfall in the area does not exceed 300 mm year^-1, the average temperature hovers around 20 °C, the piezometric map of Essaouira synclinal basin was made, different water samples have been collected from October 2009 after exceptional rainfall, all waters are sodium-chloride facies, interpretation of mineralization indicates power by the Ksob Wadi in the northeast and increasing levels of chlorides in the central part generated by the Essaouira diaper hidden. Excessive levels of nitrates have been identified, as well as chlorides after rains of winter 2009. The electrical conductivity and concentrations of ¹⁸O and ²H were measured, a local meteoric water line was determined according to the Atlantic origin of precipitation.

However, the water Turonian, characterized by significant resources, demonstrates a very low charging current; its vulnerability would be more related to human pressure than changes in climatic conditions.

The Essaouira Basin is more vulnerable to drought because its climate is entirely dependent on recharge meteoric waters.

Keywords : Basin of Essaouira; Aquifer; Semi-Arid Regions; Drought; Hydro-geochemistry;  Stable Isotopes; Recharge.