Spatial Analysis of Water Pollutants: A Case Study on the Nile River in Egypt

Abstract

This study aims to assess and evaluate the water quality along the main stream of the Nile River in Egypt through analyzing and modeling the spatial distributions of the fuctors that influence the water quality, using spatial statistical analysis with the aid of the software "Geographic Information Systems".

The sample frame of the study consists of 78 sampling points located on the main waterway of the Nile River and its two branches Rosetta and Damietta. Values of five variables -Dissolved Oxygen, Acidity, Biological Oxygen Demand, Chemical Oxygen Demand and Total Dissolved Solids- are official measures for each sampling point taken for the period of "February 2008". Additionally, three water quality indices have been constructed as general indicators of the overall water quality of the Nile River, with special emphasis on the drinking water quality.

Exploratory Spatial Data Analysis was carried out on the water quality variables and indices to check the normality assumption and to identify global and local outliers, data trending and spatial autocorrelation. Then, experimental semi-variograms have been plotted and modeled, using theoretical semi-variograms, and spatial interpolation has been performed, using kriging technique. Cross validation was carried out to determine the best fit models. Generated surfaces maps illustrate the spatial distribution of each water quality variable and index along the Nile River. Finally, the resulted levels of each water quality variable have been compared with national and international acceptable limits, concluding the status of the water quality of the Nile River in Egypt. The generated surfaces maps show that the levels of the five water quality variables are generally within their accepted limits, except some polluted areas spotted on the maps. The maps of the three water quality indices show that the quality of water is acceptable along the Nile River except the Rosetta Branch. They also indicate that Upper Egypt has excellent water quality in general, while unfit water for drinking is dominant at Middle and Lower Egypt due to accumulated industrial and agricultural discharges into the r.iver. In fact, intensive physical and chemical treatments with disinfection are becoming pressing options to improve the quality of drinking water.