Geo-environmental impacts of hydrogeological setting and anthropogenic activities on water quality in the Quaternary aquifer southeast of the Nile Delta, Egypt

摘要

Water resources in the Nile Delta have been subjected to ongoing deterioration in quality and quantity as a result of decreasing Nile water flux, poorly managed groundwater abstraction and anthropogenic activities along the course of the Nile branches and drainage canals. Therefore, a proper assessment of water quality is essential to determine the sources of pollution, if present, and to identify measures to mitigate their impact on water quality. In this study, we integrated hydrochemical, bacteriological and land use analyses to assess the natural and anthropogenic impacts on the water quality southeast of the Nile Delta. Urban land use analysis between 1994 and 2018 demonstrated an increase in urban areas, which were almost, tripled increasing from 77.3 km(2) to 198.3 km(2) on the expenses of agricultural areas. This enormous and poorly planned increase in urban areas is expected to affect the water quality in this area. Groundwater samples from the Quaternary Nile aquifer (16 samples) and surface water samples (8 samples) were analyzed for hydrochemical and bacteriological composition. The hydrochemical analysis of groundwater showed anomalously elevated TDS values (up to 3850 mg/l) and high concentrations of NO3, NH4 and PO4 in the northern part of the study area, near Abu Zaabal lake. Bacteriological analyses of surface water and groundwater indicate that most samples are highly polluted by fecal coliform and total bacteria, which are higher than the recommended value (1/100 CFU/ml) indicating a potential mixing between domestic sewage, returned irrigation and groundwater in the shallow Quaternary aquifer. Water quality indices for irrigation purpose indicated that groundwater samples around Abu Zaabal lake range between doubtful to unsuitable water for irrigation. The spatial analysis of TDS, NO3 and PO4 suggested that both natural processes (e.g. groundwater upwelling from the brackish Miocene aquifer) and anthropogenic activities (e.g. point source pollution from industrial waste disposal of phosphate fertilizers and acidic chemicals factories) deteriorate the water quality near Abu Zaabal Lake. Our findings indicate a complex interplay between natural and anthropogenic factors on the water quality east of the Nile Delta and call for further investigation using geostatistical modeling and isotopic analyses to better assess the contaminant distribution and sources in the Nile Delta.