Chemical and Mineral Components

Spatiotemporal distribution of some chemical and minerals components in an Egyptian lake connected to Mediterranean Sea: In relation to different pollutant inputs

Ghada F. El-Said, Manal M. El-Sadaawy, Nayrah A. Shaltout, Abeer A. Moneer

Marine Environment Division, National Institute of Oceanography and Fisheries, Kayet Bay, El-Anfoushy, Alexandria, Egypt

Abstract

Lake Edku is one of Egyptian delta lakes locating along the Mediterranean Sea and suffering from intensive anthropogenic activities and ecological degradation due to societal development. The seasonal variation of some physicochemical variables of T, S‰, Cl‰, pH, DO, P, Si, HCO3, CO3, Ca, Mg, Na, K, B, F, and SO4 were measured along Lake Edku as well as in the drains.

The saturation index (SI) of anhydrite, gypsum, calcium phosphate, magnesium phosphate, calcite, aragonite, dolomite, magnesite, fluoroapatite (FAP), hydroxyapatite (HAP), octacalciumphosphate (OCP), and carbonate-fluorapatite (CFAP) was calculated.

In addition, the multivariate analyses using the correlation matrix, multiple stepwise linear regression, and cluster analyses were applied. The dissolving salts modeling using Palmer-Roger’s diagram and piper ternary diagram were estimated.

The statistical analyses, mineral formation, and the dissolving salts modeling confirmed the significant relation between the chlorinity, and the determined parameters indicating the impact of seawater, and the drainage waters. Generally, apatite, and phosphate minerals including FAP (SI: 30.63-65.65), CFAP (SI: 28.14-40.02), HAP (SI: 24.83-31.81), Ca3(PO4)2 (SI: 23.99-25.95), OCP, (Si: 19.96-25.47) and Mg3(PO4)2(SI: 15.80-17.46) gave high SI values. In contrast, carbonate, and sulfate minerals represented by dolomite, calcite, aragonite, and gypsum revealed limited distribution along the lake.

Magnesite had negative SI values along all the lake, and in all the seasons, except in the location affected by the entering of seawater through El-Maadiya inlet.

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Interestingly, the investigation of the chemical and mineral components in Lake Edku not only shows a wide view about their contribution in solving the state of pollution but also in making better decisions towards the pollution levels.

Keywords: Seawater. Physicochemical parameters. Minerals, Dissolved salts. Multivariate analysis. Lake Edku. Egypt

 Introduction

Mediterranean Sea is considered as a semi-closed area subjected to huge amounts of highly populated industrial, agricultural and sewage wastewaters. The low water interchange between the Atlantic Ocean and Mediterranean Sea lead to the contamination of this area by the extensive human activity byproducts along the coastal seawater zone. The industrial field in Egypt uses 0.638 km3 a-1 of water, however, about 0.549 km3 a-1 of which is discharged into the delta lakes (Edku, Mariut, Manzala, and Burullus) through the drains (Gu et al. 2013). The brackish Lake Edku is one of five northern hosting Egyptian lakes along the Mediterranean Sea that represent about 25% of total wetland region (Emam et al. 2013).

The configuration and the chemical constituents of the lake are changing rapidly due to mankind activities including urbanization, industrialization and socio-economic activities beside the supplying water sources. The lake is affected by two water supplies; seawater comes from through El-Maadiya inlet at the eastern north region from Abu Qir bay along Mediterranean Sea and fresh water containing agricultural drains entering from the southern (Berzik drain) and the western north (El-Khairy and Edku drains) sides.

According to the salinity, the lake can be divided into eastern, central and western basins. The maximum drainage water entering the lake is always recorded duringsummer due the extensive use of water irrigation needed for some crops, whereas, the minimum one is obtained in winter (El-Said 1999). The wind direction is the main factor that forces seawater to enter into the northern position of lake. The dramatic anthropogenic impacts in Abu Qir bay due to the human activities affect the east and center regions of the lake through the opening of El-Maadiya inlet.

The chemical equilibriums in the heterogonous aquatic systems control the solubility and precipitation of the different salts and minerals (Somasundaran et al. 1985). The characterization and formation of various soluble and the sparingly soluble minerals and the intra interactions in the ecosystems are affected by the physicochemical factors including, temperature, pH, salinity, chlorinity, ions contents, atmospheric CO2, etc. (Somasundaran et al. 1985). The behavior of the soluble species in the ecosystems impresses the mineral productions. The stability ofinteractions among the minerals is controlled by the product of the molar concentrations of ions and the equilibrium solubility of mineral constants.

The demineralization and remineralization in mixed mineral systems were studiedby many investigations (Heslop et al. 2005; PatiñoDouce et al. 2011; Tanaka et al. 2013; Raj and Shaji 2017; Takashima et al. 2017). The earth’s crust contains about 3413 mineral species including, silicates, carbonates, phosphates, and sulfates classes (Marfunin 1994). Earth’s crust is dominated by eight major elements (O, Si, Al, Fe, Mg, Ca, Na and K) and four minor elements (Ti, Mn, P and H), while all otherelements are present only in trace quantities.

For example, apatites are derived from the class of phosphate minerals that are used in many natural and industrial processes such as: fertilizer production and the remediation of polluted soils (Cegla et al. 2014). Pure apatites exist in aquatic environment in the three forms of fluorapatite [Ca5(PO4)3F], chlorapatite [Ca5(PO4)3Cl], and hydroxyapatite [Ca5(PO4)3OH] with wide range of compositions (Bengtsson 2007). It was suggested that the composition of pure apatites in the surface layer of aquatic media were with non-stoichiometric structure and differ from those in the bulk.

However, calcium can be substituted by different cations, whereas, phosphate can be replaced by some anions. Apatites can also, dissolve in the formation of surface complexes, however, their surface sites can contribute in surface complexation reactions. These reactions are controlled by several environmental conditions such as pH, ionic activity, lattice energy of an ionic crystal, as well as calcium, phosphate, fluoride, organic and carboxylic acidsconcentrations.

The mechanism of apatites precipitation is difficult to study in aquatic systems due to the change in the different constituents, especially in the polluted coastal zones (Gunnars et al. 2004). Furthermore, the dominant determination methods of the mineral composition are dependent on the procedure of equilibria, stoichiometry and selective extraction.

For example, the saturation index (SI) for each mineral species can be computed from the division of the product of the ion activity of the element components by the mineral equilibrium solubility constant. The use of saturation index can assess in the evaluation of the existed mineral components in different coastal areas as well as help in the prediction of the pollution status (El-Said et al. 2016a).

There are major concerns on the effect of environmental pollution on humankind, other animals, ecosystems, and also on the built environment. The formation of sparingly soluble minerals in aquatic media can service the pollution problems. To the best of our knowledge there are few studies on the minerals evaluation in Egyptian lakes and the mineralogical aspects controlling the pollution operation are usually neglected (El-Said et al. 2015; Strakhovenko et al. 2015). The objective of this investigation is to study the seasonal distribution of some physicochemical parameters of Lake Water and to investigate mineral compositions in Lake Edku according to the entering water sources quality.

Material and methods

Investigated area

Lake Edku is considered as one of the Egyptian lagoons opened to the Mediterranean Sea locating in the Nile Delta, west of Rashid branch. This lake is subjected to drastic constructions and anthropogenic activates, accordingly, its area was diminished from 336.4 km2 to 17.1 km2 during 1800 – 2010 (EEAA 2010). The diminishing of the lake area has many economic influences especially on the fishing process due to its contamination by the untreated drainage wastes. The lake extents between, latitudes 31º10ʹ, and 31º18ʹ N and longitudes 30º8ʹ and 30º22ʹ E. Its northern edge is bordered by Abu Qir Bay along Mediterranean Sea which is which linked to the lake through El-Maadiya inlet. The Lake comprises an approximate area of 126 km2; whereas, most of this area, especially the eastern and southern sides are heavily vegetated with aquatic plantsthat make the navigation very difficult through these sides (El-Sarraf et al. 2001).

Generally, it is a shallow lake with a depth ranges between 0.4 and 1.5 m. The lake is influenced by the entering drainage waters coming from the two main drains at the eastern and southern sides that include high amounts of sewage, domestic, and agricultural and industrial wastes beside the untreated waste waters of more than 300 fish farms which drainages from El-Khairy drain (El-Said et al. 2014).

One of the two drains is known by Kom Belag lies at the eastern area. It obtains its discharged waters from the three sub-drains namely Bosily, Edku and El-Khairy. The other main drain, Berzik locates at the southern region of the lake, supplies the lake with agricultural drainage water (El-Said et al. 2015).The documented amount of the annual drainage water entering the lake in 2010 was 142 X106 m3 (Moneer et al. 2012). The lake can be considered as aeutrophic area due to the high nutrients supply coming from the two feeding drains (Soliman 2005).

Sampling and sampling analyses

The fifty six water samples were seasonally sampled from fourteen sites along Lake Edku during January-November 2017 (Figure 1 and Table 1). The surface water samples were collected by motor boat using Niskin bottle. About one litter of each sample was preserved in a white plastic bottle in the ice box and then was frozen at less than 20 °C in the National Institute of Oceanography for the studied parameters measurements. Dissolved oxygen was fixed in dark bottles in the field and evaluatedin the laboratory by the Winkler titration method (Strickland and Parsons 1968). pH was determined by the calibrated digital pH-meter (model 607).

Salinity (S‰) was calculated by Beckman model RS10 Salinometer. Chlorinity (Cl‰) was computed from the equation based on the salinity values (Strickland and Parsons, 1965). However, fluoride was determined using the alizarin red S and zirconyl chloride solutions (Courtenary and Rex 1951; Masoud et al. 2004). Calcium and magnesium were determined by the titration of ethylenediaminetetraacetic acid disodium solution in presence of murexide and eriochrome black T indicators, respectively (APHA 1999). Sodium and potassium were measured by Flame Photometer JENWAY PEP7. Boron was obtained by curcumin colorimetric procedure (APHA 1999).

Phosphate and silicate were determined based on the reaction with an acidified molybdate reagent to yield phosphomolybdate and silicomolybdate complexes (Strickland and Parsons 1965). Sulfate was calculated turbidmetrically using barium chloride salt (APHA 1999). Carbonate and bicarbonate concentration (CO3-2 and HCO3-) were calculated by applying the software package CO2SYS to inorganic carbon system parameters (Dickson et al. 2007). All blanks were prepared using the same procedure and all the determined parameters were triplicateanalyzed.

Mineral composition

The saturation index (SI) of twelve mineral structures namely anhydrite (CaSO4), gypsum (CaSO4.2H2O), calcium phosphate (Ca3(PO4)2), magnesium phosphate (Mg3(PO4)2), calcite (CaCO3), aragonite (CaCO3), dolomite (CaMg(CO3)2), magnesite (MgCO3), fluoroapatite (FAP; Ca5(PO4)3F), hydroxyapatite (HAP; Ca5(PO4)3OH), octacalciumphosphate (OCP; Ca4H(PO4)3.2.5H2O), carbonate-fluorapatite, (CFAP; Ca10(PO4)5(CO3)F2.72(OH)0.28) with Ksp values of 4.93[image: image2.png]10-5, 3.14, 2.07[image: image6.png]10-33, 1.04[image: image8.png]10-24, 3.36[image: image10.png]10-9, 6.010-9, 1.0[image: image14.png]10-11, 6.82[image: image16.png]10-6, 1.0[image: image18.png]10-60.15, 1.0[image: image20.png]10-57.5, 1.0 10-47and 1.0[image: image24.png]10-103, respectively were computed (Gunnars et al. 2004; El-Said et al. 2016a).

Dissolved salts modeling

Palmer’s method is used to represent the hypothetical salt combinations of water samples (Masoud et al. 2005). However, the graphical representation of Palmer’s characteristics was developed to the Palmer-Roger’s diagram (bar-graph) using the milliequivalent percentage of the major anions (Cl-, SO4-2 and HCO3-) and cations (K+, Na+, Ca+2 and Mg+2). Also, the hydrochemical components are evaluated by using the piper ternary diagram (Gao et al. 2017).

Multivariate analysis

The relationships among the different studied parameters in Edku lake water and the saturation indices of the precipitated materials were examined by the correlation matrix, multiple stepwise linear regression and cluster analyses with coefficient constants of r and R, respectively at significance of P ≤ 0.05 using the program of STATISTICA version 5.

 Results and discussion

 Distribution of the studied physicochemical parameters

The measured parameters show variable distributions along the sampling locations in Lake Edku. Water temperature (T), S‰, Cl‰, pH, DO, P, Si, HCO3, and CO3 showed a wide seasonal variations of 18.90-31.5 °C, 0.60-27.90, 0.32-15.44 g/Kg, 7.10-8.80, 0.34-7.00 mg/l, 0.02-1.03 mg/l, 0.00-1.89 mg/l, 89.70-611.99 mg/l, and 1.00-46.82 mg/l, respectively (Table 2). The salinity and chlorinity in the lake was strongly related to variation in the hydrochemical levels along the lake in addition to the amount of discharged water from different drains (Branchu and Bergonzini 2004). The seasonal ranges and average of the chlorinity ratio of Ca, Mg, Na, K, B, F, and SO4 along the lake are presented (Table 3). The effect of the drainage waters on the change of physicochemical composition of the lake is observed during of each season. For example, the Cl‰, pH, Ca, Mg, Na, K, B, and SO4 during summer indicate the influence of Berzik El-Khairy and Edku drains in the southern and eastern regions as well as the entering seawater from the northern area (Figure 2). However, Ca and Mg have opposite trends with both Cl‰ and pH distribution, whereas, Na, K, B and SO4 give a direct relation with both Cl‰ and pH variations.

The correlation matrix of the annual variation of the determined parameters and the computed formed minerals confirm their strong correlations with each other in the lake ecosystem.

The high correlation of salinity with dissolved oxygen (r= 0.744, p=0.002) refers to the respiration and photosynthesis processes of flora and fauna species beside the effects of the water quality and quantity of discharged water from different drains into the lake (Jack et al. 2009). Also, the moderate negative correlations between S‰ & Si (r= -0.6491, p= 0.012, S‰ &HCO3 (r= -0.5396, p=0.046), and the high positive correlations among S‰&Ca (r= 0.8330, p = 0.000), S‰ & Mg (r= 0.8470, p= 0.000), S‰ & K (r= 0.7475, p=0.002), S‰ B (r= 0.7251, r= 0.003), and S‰ &SO4 (r= 0.6656, p= 0.009) indicate their high composition in the discharged waters, beside the precipitation of silicate and phosphate compounds.

The strong correlation between pH & CO3 (r= 0.9186, p= 0.000), reflects the direct relationship between them (El-Said et al. 2016a). The relations between DO&HCO3 (r= -0.71890, p= 0.004), DO&Si (r = -0.6223, p= 0.017), DO&Ca (r= 0.6724, p= 0.008), DO & Mg (r= 0.6716, p= 0.009) and DO & K(r= 0.7175, p= 0.004) may relate to the formation of the phosphate apatites, siliceous frustules of aquatic organisms as well as the dissolution of calcium and magnesium minerals in the presence of high K (Manasrah et al. 2006; El-Said et al. 2016a). The Si/P ratio that relates to the presence of some aquatic organisms such as diatoms and some algal species may be responsible for the correlation between (P&Si; r= 0.847, p= 0.000) (Stauffer 1986).

The moderate negative correlation between P & CO3 (r= -0.6443, p=0.013) reflects the release of exchangeable P from calcium carbonate minerals and/or and the decaying bacterial and phytodetritus aggregators. Whereas, the moderate negative relations between Si & CO3 (r= -0.6545, p= 0.011), Si &Ca (r= -0.5630, p= 0.036) and Si & Mg (r = -0.6327, p= 0.015) probably relate to the uptake of the dissolved SiO2 formed during the precipitation of calcite and/or recrystallization of aragonite and Mg-calcite (Klein and Walter 1995). In addition, the moderate negative correlation between Si & Na (r = -0.5977, p= 0.024) and Si & SO4 (r=-0.6299, p= 0.016) may accompany with the precipitation of high amounts of sodium and sulfate compounds of the agricultural wastes onto the clay minerals of the lake.

The moderate negative correlations between HCO3&Ca (r= -0.5991, p= 0.024), HCO3& Mg (r= -0.6107, p= 0.020) and HCO3& K(r= -0.6177, p= 0.019) reflects the relationship involving the equilibrium of CO2–HCO3- –CO3-2 equilibrium. However this equilibrium is influenced by phototropic species and the shifting of the equilibrium due to the formation of carbonate minerals, i.e. the decreasing of CO3 and increasing of HCO3 which is negatively correlated with Ca, Mg, and K (El-Said et al. 2016a). The good correlations between Ca& Mg (r= 0.9735, p= 0.000), Ca& Na (r = 0.6418, p=0.013), Ca& K (r= 0.8525, p=0.000), Ca& B (r= 0.8366, p=0.000), Ca, F (r = 0.6044, p=0.022), Ca& SO4 (r= 0.7693, p=0.001), Mg & Na (r= 0.6289, p=0.016) and Mg & K (r = 0.8286, p=0.000) may relate to the formation of calcite and aragonite that are influenced by the presence of the amounts of Mg , Na, K as well as fluoride minerals, beside the effect of the discharged waters (El-Said et al. 2016a,b).

The dissolution or the formation of epsomite (MgSO4.7H2O) and sellaïte (MgF2) as well as the presence of its ion pairs (MgF+, MgB(OH)4+, and MgOH+) probably accompany with the high correlations obtained between Mg & B (r= 0.8161, p=0.000), Mg & F (r= 0.642, p=0.013) and Mg &SO4(r= 0.8184, p=0.000) (Cole1979). The correlations between Na & K (r= 0.6579, p=0.011), K & B (r= 0.7596, p=0.002) , SO4& B (r =0.6901, p=0.006) and F & SO4 (r = 0.5369, p=0.048) possibly reflect to the effect of the discharged waters containing agricultural wastes on the chemical composition of the lake beside the formation of sodium, potash feldspar minerals and fluoride minerals (El-Said 2005; El-Said et al. 2010; El-Said 2013).

Distribution of the precipitated minerals

The saturation index (SI) of the twelve mineral structures (anhydrite, gypsum, calcium phosphate, magnesium phosphate, calcite, aragonite, dolomite, magnesite, fluoroapatite (FAP), hydroxyapatite (HAP), octacalciumphosphate (OCP); and carbonate-fluorapatite (CFAP) are calculated (Table 4). Owing to the SI values,theformationof the minerals takes the orders of FAP> CFAP> HAP> Ca3(PO4)2> OCP>Mg3(PO4)2> dolomite> calcite> aragonite> gypsum> magnesite, CFAP> FAP> HAP> Ca3(PO4)2> OCP> Mg3(PO4)2> dolomite> calcite>n aragonite> gypsum, CFAP> FAP> HAP> Ca3(PO4)2> OCP> nMg3(PO4)2> dolomite> calcite>n aragonite> gypsum, CFAP> FAP> HAP> Ca3(PO4)2> OCP> Mg3(PO4)2> dolomite> calcite> aragonite> gypsum> anhydrite> magnesite during winter, spring, summer and autumn, respectively.

Accordingly, the SI values of these minerals in the different seasons in indicate formation of fluoride apatites (FAP and CFAP), hydroxyapatites (HAP and OCP) and phosphate minerals (Ca3(PO4)2 and Mg3(PO4)2) in great amounts (Table 4). In contrast, dolomite, calcite, aragonite, gypsum, and anhydrite precipitate in minor amounts. In contrast, magnesite can be observed in location 2 during winter due to the high volume of sea water entering the lake through El-Maadiya inlet.

The horizontal contours of the carbonate, phosphate, sulfate and apatite minerals along Lake Edku indicate the effect of the untreated discharged waters on their distribution (Figures3-5). It seems that, calcite, aragonite, and dolomite beside gypsum minerals deposit in great extent along the eastern and southern regions of the lake. This observation is related to the effect of the agricultural wastes transporting through the Berzik drain and the pH values. It was recorded that fertilizers contain calcium, magnesium, sulfate, fluoride, phosphate, etc. (Mukherjee 2011, Guet al. 2013).

However, it was stated that the carbonate precipitation is directly influenced by the alkalinity of water (Nezli et al. 2009). In contrast, the western side of the lake shows lower deposition to the four previously mentioned minerals. Phosphate and apatite minerals show opposite trends along Lake Edku. However, the high SI values recorded along the western side may accompany with the low values of pH that are related to the industrial, domestic, sewage, and agricultural wastes discharging from El-Khairy drain. Wherever, the concentration of P is high enough so hydroxyapatite could be formed (Mukherjee 2011). Interestingly, the studied minerals in the other seasons show similar horizontal distributions along the lake and this could indicate that the lake is well mixing during these seasons.

The physicochemical parameters of lake water affect in great extent the precipitation and/or the release of the minerals. However, T is highly related to the formation or dissolution of calcium phosphate (r= 0.7004, p= n0.005). Also, the S‰ shows high correlation with dolomite deposition (r=0.6986, p=0.005), and moderate effect with mgnesite precipitation (r=0.5901, p=0.026), beside its weak influence on both gypsum (r= 0.5544, p= 0.040) and anhydrite compositions (r= 0.5544, p= 0.040). Additionally, the moderate correlation of dolomite & B (r=0.5823, p=0.029) indicates the adsorption of B on dolomite (Pentecost 2005).

The results agrees with the previous presented results that referred to the declination of phosphorus contents during the carbonate minerals formation, however, P amount decreases by the formation of calcite (r= n-0.6933, p=n 0.006), aragonite (r= -0.7088, p= 0.005), dolomite (r= -0.7744, p=0.001), and magnesite (r=-0.76, p=0.002)(Pentecost 2005).In contrast, in the same manner the dissolved P contents increases during the precipitation of gypsum (r= -0.6608, p=0.010) and anhydrite (r=-0.6608, p=0.010). In contrast, the P level in lake water is directly correlated with the deposition of Ca3(PO4)2 (r= 0.7279, p= 0.003), Mg3(PO4)2 (r= 0.6098, p= 0.021), OCP (r= 0.8657, p= 0.000) and CFAP (r= 0.669, p= 0.009).

The direct relation between gypsum & pH (r= 0.6953, p= 0.006), and anhydrite & pH (r= 0.6953, p= 0.006) agrees with the previous study (Shukla et al. 2008). pH is correlated with the formation of Ca3(PO4)2 (r= -0.6503, p= 0.012), Mg3(PO4)2 (r= -0.5988, p= 0.024), calcite (r= 0.8462, p= 0.000), aragonite (r= 0.8689, p=0.000), dolomite (r= 0.8018, p=0.001), magnesite (r= 0.8796, p= 0.000), OCP (r= -0.7162, p= 0.004) and CFAP (r= -0.6018, p= 0.023). Also, the deposition of Ca3(PO4)2 (r= -0.6055, p= 0.022), Mg3(PO4)2 (r= -0.7122, p= 0.004), calcite (r= 0.9142, p= 0.000), aragonite (r= 0.9136, p= 0.000), magnesite (r= 0.888, p= 0.000) and OCP (r= -0.7314, p= 0.003) are influenced by CO3 content in lake water.

Fluorapatite (FAP), shows a negative correlation with Mg (r= -0.5642, p= 0.036) and negative correlations with F (r= -0.7321, p= 0.003) and SO4 (r= -0.5352, p= 0.049). CFAP is highly correlated with other formed phosphate minerals. However, there are high direct relation between CFAP&Ca3(PO4)2 (r= 0.8478, p= 0.000), Mg3(PO4)2 (r= 0.8161, p= 0.000), HAP (r= 0.7391, p= 0.003) and OCP (r= 0.8896, p= 0.000). Recalling that, the dissolution of the minerals is affected by different factors such as: pH, ionic strength beside the amount of water components (Taiet al. 2006). However, during the operation of nucleation process in supersaturation waters, the components of wastewater may mix with minerals (Taiet al., 2006). I was stated that crystal growth rate was affected by the supersaturation, pollutant type, ion activity and temperature (Taiet al. 2006).

The presented data indicate that the existence of gypsum and anhydrite arehighly related to SO4 (r= 0.6687, p= 0.009), Si (r= -0.738, p= 0.003), moderately related to CO3 (r= 0.5998, p= 0.023), Na (r= 0.5828, p= 0.029) and B (r=0.5916, p= 0.026), whereas, they are weakly correlated to Ca (r= 0.553, p= 0.040) and Mg (r= 0.5479, p= 0.043). However, it was reported that the dissolution of gypsum is influenced by Ca, Mg, and Na (Sun et al. 2015). Additionally, the association of sulfur during the deposition of calcite was estimated (Pentecost 2005).

The very high correlations of calcite & aragonite (r=0.9900, p=0.000), calcite & dolomite (r= 0.9332, p= 0.000), and calcite&magnesite (r= 0.9665, p= 0.000) reflect the calcite precipitates witharagonite beside the formation of magnesite. However, the properties of calcite are similar to magnesite (Warren 2000; El-Said et al. 2016a). The moderate negative correlations between calcite & OCP (r= -0.6160, p= 0.019), aragonite& OCP (r= -0.6178, p= 0.019), dolomite & OCP (r= -0.5815, p= 0.029) and magnesite&OCP (r= -0.6251, p= 0.017) reflect the OCP deposition affects the precipitation of calcite, aragonite, dolomite and magnesite in the lake.

The multiple regression equations of the highly correlated minerals with the annual determined parameters reflect the effect of the physicochemical composition of the drainage waters and the entering seawater from El-Maadiya intent beside the biological activates of the plants (Table 5). Consequently, the mineral composition and deposition and/or dissolution along the lake are strongly associated with type of feeding waters. This conclusion is confirmed by the cluster analysis that shows five main clusters corresponding to sites 2&11, 3&4, 5&6, 7&10, and 12&13 (Figure 6). However, the clusters of sites 2&11 and 3&4 represent the effect of the entering seawater from Abu Qir Bay along the Mediterranean Sea. Whereas, the clusters of 5&6 and 7&10 relate to the mixed waters corresponding to seawater and discharged drainage. The cluster of sites 12&13 refers to the physicochemical similarity of the outside drainage waters of Edku and El-Khairy drains.

 Distribution of dissolved salts

The dissolved salts during autumn, spring, summer and winter along Lake Edku are presented by Palmer’s method and piper diagram (Table 4 and Figure 7). Amongst the constructed piper diagrams of lake water in all seasons, Na is the most abundant cation, follows by Mg, Ca, and K, except in winter, Mg shows inverse trend with Na in the other seasons. Generally, Cl is the most anion dominates along thelake.

Furthermore, these diagrams mention to the huge presence of NaCl in water in all seasons. In the same manner, Palmer’s method shows a high NaCl abundance in winter, spring, summer, and autumn of 30, 40, 46 and 75 %, respectively (Table 4). Moreover, MgCl2 can be considered as the second most abundant dissolved species formed in the lake water, with a percentage range of 45-25 %. In autumn, NaCl is appeared to be the most existence chloride species along the lake, with a percentage of 75 % due to the entering of seawater to the lake through El-Maadiya intent. Also, Na2SO4, CaCl2, Ca(HCO3)2, CaSO4, MgCl2, Mg(HCO3)2, Mg2SO4 and KCl are formed with different proportions in the varies seasons.

 Conclusions

The Delta lakes in Egypt are serving as a collection basin for agricultural, industrial, sewage, domestic wastewater. Lake Edku is one of the Delta lakes that interexchange its water by the contaminated seawater of Abu Qir Bay along Mediterranean Sea through the El-Maadiya, especially, in winter. In the other seasons, this lake is extensively affected by huge amounts of pollutants transported from three main drains in its southern and the eastern sides, namely Berzik, El-Khairy and Edku drains.

The presented study was directed to the seasonal measurement of some physicochemical parameters (T, S‰, Cl‰, pH, DO, P, Si, HCO3, CO3, Ca, Mg, Na, K, B, F, and SO4) in Lake Edku, Egypt. The results indicated the great effect of the discharged water from different drains inside the lake and seawater on the chemical composition and the minerals formation along the lake.

Also, the minerals composition that was computed by the saturation index (SI) assured the effect of the drainage waters on the mineral composition of the lake. Twelve mineral species including anhydrite, gypsum, calcium phosphate, magnesium phosphate, calcite, aragonite, dolomite, magnesite, fluoroapatite, hydroxyapatite, octacalciumphosphate, and carbonate-fluorapatite were evaluated. The data referred that the lake was over saturated by the fluorapatite minerals (FAP and CFAP). The saturation indices values of calcite, aragonite, dolomite and gypsum reflected their supersaturation along the eastern and southern region of the lake due to the effect of agricultural wastes discharge. Whereas, phosphate and apatite minerals showedthis observation along the western side of Lake Edku due to the low values of pH that was relating to the industrial, domestic, sewage, and agricultural wastes discharging from El-Khiery drain. The depositing of stable minerals decrease the presence of the excess ions (such as: Ca, Mg, Na, K, SO4, F, B, P, etc.) transforming from the drains into the lake area.

The performed statistical analyses using, correlation matrix, multiple regression equation, and cluster for the determined and calculated parameters confirmed the interactions between the physicochemical parameters of lake water and the formed mineral species.

Piper ternary diagrams mentioned the abundance of Na and Cl ions along the lake during the period of investigation. Also, Palmer-Roger’s method reflected the high NaCl existence followed by MgCl2 beside the formation of Na2SO4, CaCl2, Ca(HCO3)2, CaSO4, Mg(HCO3)2, Mg2SO4 and KCl salts with different t percentages.

Recalling to the low water interchange between the Atlantic Ocean and Mediterranean Sea and the extensive byproducts produced by the anthropogenic activities, the coastal zone of Mediterranean Sea in the long run may considered as a contaminated area. Fortunately, the production of the minerals can solve the problem of pollution by metal and other pollutants along Lake Edku. Accordingly, this study constitutes a good basis for further studies about the minerals and other components in Lake Edku which might help policy makers to take effective decisions for proper management of the pollution status in this lake.

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