Geochemical and isotopic evidence of groundwater salinization processes in the Essaouira region, north-west coast, Morocco

Abstract

The city of Essaouira is located along the north-west coast of Morocco, where groundwater is the main source of drinking, domestic and agricultural water. In recent decades, the salinity of groundwater has increased, which is why geochemical techniques and environmental isotopes have been used to determine the main sources of groundwater recharge and salinization. The hydrochemical study shows that for the years 1995, 2007, 2016 and 2019, the chemical composition of groundwater in the study area consists of HCO3–Ca–Mg, Cl–Ca–Mg, SO4–Ca and Cl–Na chemical facies. The results show that from 1995 to 2019, electrical conductivity increased and that could be explained by a decrease in annual rainfall in relation to climate change and water–rock interaction processes. Geochemical and environmental isotope data show that the main geochemical mechanisms controlling the hydrochemical evolution of groundwater in the Cenomanian–Turonian aquifer are the water–rock interaction and the cation exchange process. The diagram of δ2H = 8 * δ18O + 10 shows that the isotopic contents are close or above to the Global Meteoric Water Line, which suggests that the aquifer is recharged by precipitation of Atlantic origin. In conclusion, groundwater withdrawal should be well controlled to prevent groundwater salinization and further intrusion of seawater due to the lack of annual groundwater recharge in the Essaouira region.

Assessment of Groundwater Quality and the Main Controls on Its Hydrochemistry in a Changing Climate in Morocco (Essaouira Basin)

“…Following the results of the ten years of water quality index, we observed that water quality is deteriorating, particularly on the coast of the aquifers near the Atlantic ocean. The excessive fertilizer used in agriculture seeps into groundwater because the soil surface is close to the water table [10,26]. Therefore, as the hydraulic conductivity is critical, this region is susceptible; another reason is several tourist activities since there is no sanitation network or a water treatment station that generates wastewater infiltration directly onto the water table.…”

“…Isotopic analysis is a useful tool for deciphering the mechanisms that drive an aquifer system's hydrogeological and hydrochemical evolution [26,79,80]. Stable isotopes of oxygen (δ 18 O) and hydrogen (δ 2 H) are thought to be transported conservatively in shallow aquifers, according to Kim [81].…”

“…The reversal of groundwater flow in recent years has resulted in seawater intrusion into the interior along the coastal belt due to heavy pumping of groundwater, especially in summer, making the borehole and the open well unsuitable for agricultural production and consumption [23,24]. Researchers have assessed groundwater quality in several arid and semi-arid countries, notably: Morocco, Tunisia, Egypt, and India [10,23,[25][26][27][28]. Various techniques are used to assess water quality; we cited the following for drinking uses [7,25,[29][30][31].…”

The Assessment of the Groundwater Quality in the Coastal Aquifers of the Essaouira Basin, Southwestern Morocco, Using Hydrogeochemistry and Isotopic Signatures

“…It is considered the most critical and apparent phenomenon that challenges future water use and decreases water quality. Because it limits the amount of water used for agriculture and urban water supply [18][19][20][21][22][23], groundwater salinization is critical to the resilience and sustainability of coastal. Increasing total dissolved solids (TDS) or chloride (Cl − ) content signifies salinization [24].…”