Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → Japon → Impact of Surface Development on Subsurface Environment in an Arid Climate : Consideration Based on Groundwater Quality and Isotopic Signals at the New Reclaimed Land, Eastern Nile Delta, Egypt

Tokyo University (2016)

Impact of Surface Development on Subsurface Environment in an Arid Climate : Consideration Based on Groundwater Quality and Isotopic Signals at the New Reclaimed Land, Eastern Nile Delta, Egypt

Mahmoud Mostafa Abd Elrahim Mohamed Khalil

Titre : Impact of Surface Development on Subsurface Environment in an Arid Climate : Consideration Based on Groundwater Quality and Isotopic Signals at the New Reclaimed Land, Eastern Nile Delta, Egypt

Auteur : Mahmoud Mostafa Abd Elrahim Mohamed Khalil

Université de soutenance : Tokyo University

Grade : Doctoral Thesis 2016

Résumé
Groundwater is increasingly recognized as a main factor in arid land development, i.e., desert reclamation, in many arid countries where the surface water resources are limited or scarce. Throughout the rapid urban and agricultural development, changes of groundwater quantity and quality commonly occur by the increase of groundwater abstraction and the introduction of new sources of recharge. Therefore, understanding the contribution and the changes of various recharge sources, natural and anthropogenic, to aquifer systems will provide important knowledge to develop water resources management and environmental conservation plans, and to assess pollution mechanisms. This study highlights these aspects for the Quaternary aquifer system underlying the new reclaimed lands in the eastern fringes of the Nile Delta, Egypt, through the identification of groundwater end-members and their sources. Using a set of chemical and isotopic (δ2H, δ18O, δ13C and 14C) data in tandem with multivariate data analysis, source components in groundwater of the Quaternary aquifer system were estimated. Electric conductivity (EC) and stable isotopic characteristics of water varied widely and were used to group the samples into four clusters by applying hierarchical cluster analysis (HCA). The water groups were then examined through principal component analysis (PCA) together with the information on the groundwater from the Miocene aquifer, the water from the Ismailia canal, the old Nile water, and wastewater. The overlap of clusters 1 and 2, i.e., low EC groundwater, with the old Nile water and the water from the Ismailia canal in PCA space indicated that groundwater in the northern parts of the Quaternary aquifer are hydraulically connected with the water in the Ismailia canal. Depletion of stable isotopes of water of subcluster 1.3 suggested a different source other than the Nile water. Clusters 3 and 4, i.e., high EC groundwater, were grouped with the groundwater of the Miocene aquifer in PCA space to infer the hydraulic connection with the groundwater in the Miocene aquifer, mainly in the southern part of the study area. Cluster 4 samples were stable-isotopically enriched and showed high nitrate concentrations. Also, the cluster 4 samples were distributed in the agricultural area where treated/untreated wastewater has been supplied for irrigation. The information obtained from the analysis of city water balance and recent geophysical data suggested the possibility of wastewater infiltration, which may explain the characteristics of the cluster 4 samples. Northward increasing trend of 14C and the lowest 14C values reported in the southern portion, i.e., cluster 3, of the Quaternary aquifer confirmed the stated mixing processes. Subcluster 1.3 was interpreted to be the “native” groundwater component of the Quaternary aquifer from their plotted zones in PCA space, δ2H-δ18O plots, and δ18O-Cl- plots. Overall, five different sources were introduced to the Quaternary aquifer in the area. Salinization, overexploitation and contamination from wastewater infiltration are found to be the main negative environmental impacts of land development as estimated from the end-members analysis while some irrigation practices, i.e., freshwater ponds, might have the positive ones. From a broader point of view, these results confirm that an understanding of the mixing processes in heavily development lands of arid/semi-arid region is vital for the continued groundwater resource management in similar settings.

Présentation

Version intégrale (15,9 Mb)

Page publiée le 22 avril 2020