The impact of fluctuation of the Nile River level on water composition

The River Nile is considered the longest river in the world and it is the main source of life to millions of people. The Nile flows through many countries, reaching to ten countries, which are the Democratic Republic of the Congo, Burundi, Egypt, Eritrea, Kenya, Ethiopia, the Sudan, Rwanda, Tanzania and Uganda make up the Nile River basin (Mohamoda 2003). The Nile is considered the donor of life to Egypt and represents the main freshwater resource for the country. The River Nile is meeting most of the demands for drinking water, industry and irrigation (Mohamed et al. 1998). The main source of the River Nile water is rainfall generating of two rivers, namely the White Nile and the Blue Nile, coming from two major areas: the mountainous hinterland of the Great Lakes in Uganda and the Ethiopian Plateau, respectively. At Khartoum, the Blue Nile and the White Nile merge into the single river. From downstream Khartoum, the river is called River Nile (Jonsson 2007).

Water pollution is one of the principal reason of public health and environmental problems which Nile River is facing. Water pollution is any chemical, physical or biological change in the quality of water that has a harmful effect on any living thing drinks, uses or lives (in) it (Anwar 2003; Gad & Osman 2007). The Nile River pollution sources are chemical and industrial pollution, oil pollution, organic pollution, biological waste and agricultural pollution (Lenntech 2004; Wahaab & Badawy 2004; Khalil et al. 2007; Woodford 2015). Water pollution has been a source of interest for the focus of many studies (Mapfumo et al. 2002; Carr & Neary 2008; Safe Drinking Water Foundation 2009; Abdo & El-Nasharty 2010; El Bouraie et al. 2010; UNEP 2010; Woodford 2015).

The aim of the present study is to assess the impact of fluctuation of the Nile River level on the concentration of water pollutants during the year. The Nile River has four periods during the year; the periods are Flood, intermediate, drought and intermediate. The assessment was made by measuring impurities concentration, whether physical, chemical or biological, in Nile River at different periods and by studying the relationship between impurities concentration and the Nile level.

To ensure the validity of the obtained results, a comprehensive survey of all the results of the laboratory of potable water station in some parts of Egypt will be made.

The temperature (°C) was measured by using an ordinary dry mercury thermometer.

Enumeration of phytoplankton concentration was measured by Microscope (Model Leica CM-E). The analysis was carried out according to the American Public Health Association for the Examination of Water and Wastewater (APHA 2005).

The hydrogen ion concentration (pH) was measured by using PH meter, (Model Jenway 3510). Total solids (TS), volatile suspended solids (VSS), total dissolved solids (TDS), total suspended solids (TSS) and oil and grease were measured by gravimetric methods. Electrical conductivity (EC) was measured by using Conductivity meter, (Model Jenway 3110). Turbidity was measured by using turbidity meter, (Model Turbo Direct). Color was measured by using U.V-VIS spectrophotometer, (Model Gary 100 U.V-Vis). The analysis of and was carried out using titrimetric methods. Analysis of Cl⁻, ⁠, Ca²⁺, Mg²⁺, Na⁺, K⁺, ⁠, ⁠, total phosphorus (TP) and F⁻ was carried out by using Ion chromatography, (Model Dionex-ICS-5000). Analysis of Mn, Zn, Al, Fe, Cu, Pb, Cd, As, Co, Cr, Ni, Sn, Hg, Ti and B was made by using inductively coupled plasma optical emission spectrometry (ICP), (Model Agilent ICP-OES 5100). Analysis of N-NH₄ was carried out by using Gerhardt Digestion and Distillation apparatus, (Model Vapodest 20S). All the analyses, unless otherwise specified, were carried out according to the American Public Health Association for the Examination of Water and Wastewater (APHA 2005).

Temperature was the water quality indicator that exhibited big variance between the periods. The values ranged from 39–36 °C to 8–5 °C for air and water respectively (Table 1).

Nile river water showed various phytoplankton structures belonging to three main groups, namely, Chlorophyceae (Green Algae), Cyanophyceae (Blue-Green Algae) and Bacillariophyceae (Diatoms). It was observed that diatoms represent the most abundant group in all samples (Table 1). This is in agreement with the findings of (Shehata et al. 2008).

The chemical results showed a different behavior in comparison to the biological results during the different periods.

As for EC, the ions in solution are formed by dissociation of inorganic compounds. For this reason, the measurement of conductivity gives a good indicator of the concentration of dissolved salts in water. In the present study, EC values ranged from 339 to 370 μs/cm during the year (Table 2). The variation in EC averages depends on the presence of the ions and their total conductivity, mobility, relative concentration and the temperature of measurement. The results of EC were matching with (Gupta & Paul 2013).

The pH of Nile water has slightly changed during the year (Table 2), which is in confirmation with the results obtained by (Niles et al. 2014). The values of TS, TDS, TSS, VSS and turbidity decreased at flood period and increased at drought period (Table 2). This was attributed mainly to the influence of Nile level, which affected concentration. The results are in agreement with similar finding by (Rawway et al. 2016).

The values of Na, Cl and Mg, also decreased at flood period and increased at drought period (Table 2). Similar results of Na were obtained by (Goher et al. 2014). The results of Cl and Mg are in agreement with similar finding obtained by (Rawway et al. 2016).

The values of Carbonate, Fe, F, NO₂, NO₃, NH₄, TP, Ca and K changed slightly during the year (Table 2) which can be attributed to the influence of Nile level. The change in their concentration during the year is not significant when compared to the previous biological change. The results of Carbonate, NO₂, NO₃, NH₄, Ca and K are in confirmation with (Hassanein et al. 2013). The results related to both of Ca and K are in line with (Ollivier et al. 2010), whereas the results of K and TP are similar to those obtained by (Goher et al. 2014). There are no contradiction between our results related to Fe, F⁻, NO₂, NH₄ and TP and the results obtained by (Ali et al. 2014) for Fe, (Salem et al. 2001) for F⁻ and NO₂, and (Niles et al. 2014) for NH₄.

The values of Bicarbonate, SO₄, oil and grease mg/l took a different behavior during all periods (Table 2). The concentration increased at flood period and decreased at drought period. This may be attributed to the industrial effect in the area under study. The results of (SO₄) are similar to those obtained by (Abdo 2010; Goher et al. 2014). The result of Bicarbonate is in line with (Hassanein et al. 2013).

The values of heavy metals have undetected values during all periods. The concentration is smaller than 0.01 mg/l during all periods (Table 2). The results of Heavy Metal are in agreement with the finding of (Salem et al. 2001; Abdo 2010; Goher et al. 2014).

The comprehensive survey which was made for laboratory results of potable water station in some parts of Egypt validated the above results. The survey showed that the change in the level of the River Nile has markedly affected the concentration of phytoplankton compared to chemical elements.

The algae can effectively remove metals from multi-metal solutions. Dead cells absorbs more metal than live cells, Algal periphyton have great potential for removing metals from wastewaters (Mehta & Gaur 2005). The presence of algae in marine surface water sources and freshwater may cause serious challenges in industrial and drinking water production (Villacorte et al. 2015). The different pollutants and environmental parameters are the main factors which are controlling the biochemical contents of phytoplankton (El-Hady 2014).

Some algae and cyanobacteria produce ligands to tie up heavy metals, specifically zinc and copper, thereby keeping them at non-toxic levels in the ocean. Nutrients and essential elements have a high effect on algae growth. Nutrients change according to algae type. There are essential elements required by all algae which are nitrogen (N), phosphorus (P), magnesium, iron, manganese, copper, zinc, molybdenum, … etc (Hardiman 1993). Nitrogen is an essential element for the growth of microalgae. Nitrogen has a wide source; some species of microalgae can fix the nitrogen gas in the air through nitrogen fixation process for their own use. The increased amount of nitrogen content in growing conditions will increase the growth of microalgae (Ren 2014).

Yang et al. (2014) studied the effects of nitrogen, phosphorus, iron and silicon concentration on growth of five species of benthic diatoms. When the nitrogen concentration was 0 mg/L, diatoms did not grow; with the concentration going up, diatoms grew better and better. When the phosphorus concentration was 0 mg/L, diatoms did not grow; with the concentration going up, diatoms grew better and better. When the iron concentration was 0 mg/L, diatoms could grow normally; with the concentration going up, diatoms grew better and better. When the silicon concentration was 0 mg/L, diatoms could just grow slowly; with the concentration going up, diatoms grew better and better. Optimal phosphorus concentration is conducive to the growth of microalgae. When TP ≤ 0.045 mg/L, the microalgae growth will be prohibited. High concentration of phosphorus TP ≥ 1.65 mg/L also cannot significantly promote microalgae growth rate (Ren 2014).

Diatoms are the major players in the biochemical cycles of carbon, nitrogen, phosphorus, and silicon with a strong impact on global climate, not only in the ocean but also in the freshwater environment. In the ocean, they tend to dominate the phytoplankton assemblage under nutrient-rich conditions; whereas, in freshwater ecosystems, high turbulence and the combination of low temperature/high nutrients favor diatom blooming. Therefore, the diatoms can be considered as one of the most successful taxonomic groups with respect to evolution and ecology. However, the genetic and physiological basis why diatoms became so ecologically successful is still a matter of debate (Wilhelm et al. 2006). The eventual decline of cell concentration cultures may be attributed to depletion of nutrients in the medium (e.g., inorganic carbon, nitrogen, phosphorus, silicon and other trace metals) (Villacorte et al. 2015).

During growth, phytoplankton takes up trace metals thus continuously reducing their concentrations in the medium. Phytoplankton takes up major nutrients and trace elements from the culture medium (Price et al. 1989). Some trace metals such as Fe, Ni, Cu, and Zn are essential for the growth of phytoplankton. Trace element uptake is ultimately limited by the kinetics of reaction with transport ligands or by diffusion to the cell. The uptake of all necessary trace metals by phytoplankton occurs via binding to a surface ligand and subsequent transfer across the cell membrane (Morel et al. 1991). The accumulation of heavy metals in algae involves two processes: an initial rapid (passive) uptake followed by a much slower (active) uptake (Jahan et al. 2004). During the passive uptake, metal ions adsorb onto the cell surface within a relatively short span of time, and the process is metabolism- independent. Active uptake is metabolism-dependent, causing the transport of metal ions across the cell membrane into the cytoplasm. In some instances, the transport of metal ions may also occur through passive diffusion owing to a metal-induced increase in permeability of the cell membrane (Jahan et al. 2004). Cobalt is an essential element for Blue-Green Algae (Holm-Hansen et al. 1954). Brown algal biomass has proven to be highly effective as well as reliable and predictable in the removal of, for example, Pb2+, Cu2+, Cd2+, and Zn2+ from aqueous solutions (Davis et al. 2003).

Many algae have immense capability to sorb metals. Metal sorption involves binding on the cell surface and to intracellular ligands (Mehta & Gaur 2005). Algae accumulate high concentrations of metals depending on their concentration in the external environment. The concentration factor for heavy metals varies greatly in different algal species, but it increases as the metal concentration in the water decreases (Sharma & Azeez 1988). The amount of metal accumulated by algae is related with the concentration of metal in water. It may be possible to use the metal content of indigenous algae for biomonitoring of metal pollution in a water body (De Filippis & Pallaghy 1994).

The findings of the present study clearly demonstrate the relation between pollution, whether physical, chemical or biological, and Nile level. The inverse relationship strongly manifests at biological pollution but not at chemical, which could be due to the phytoplankton or other microorganisms eating the chemical element which leads to balancing the chemical composition of The Nile.

The fluctuation of the Nile River level had a significant impact on its biological nature rather than chemical nature. The fluctuation increases the algae count at drought period. The stability of chemical elements in the Nile during the year could be attributed to the presence of algae. The Nile algae work as a biological treatment for the Nile chemical pollution.

We are grateful to the National Research Centre, water pollution control department and El-Minia laboratory of the Holding Company for Potable Water and Sanitary Drainage for useful suggestions.