Composition and origin of the sabkha brines, and their environmental impact on infrastructure in Jizan area, Red Sea Coast, Saudi Arabia

Transcription

1 Environ Earth Sci (2016)75:105 DOI /s ORIGINAL ARTICLE Composition and origin of the sabkha brines, and their environmental impact on infrastructure in Jizan area, Red Sea Coast, Saudi Arabia Mohammed H. Basyoni 1 Mahmoud A. Aref 1,2 Received: 2 March 2015 / Accepted: 8 August 2015 Springer-Verlag Berlin Heidelberg 2015 Abstract The sulfate evaporite minerals (gypsum and anhydrite) and brines of Jizan sabkha cause corrosion of the steel reinforcement and deterioration of the concrete, and consequently hinder the development activity for building new urban communities and industrial zones in Jizan area, Red Sea coastal plain of Saudi Arabia. The sabkha evaporite minerals below the sediment surface are represented by displacive and inclusive growth of lenticular and rosette gypsum, and nodular anhydrite. In small saline pans, halite precipitates form rafts, chevrons and cornets. The salinity (TDS) of the groundwater in the sabkha area is highly variable, and ranges from 12,900 to 495,000 mg/l, compared to the average value of the Red Sea water of 40,366 mg/l. The low salinity values of the sabkha brines are most probably caused by localized influx of groundwater of meteoric origin from direct rain fall and/or temporary floods, in addition to seepage of sewage water from septic tanks. The electric conductivity (EC) values range from 20,000 to 199,100 ls/ cm which are conformable to the salinity values of the brine. The dominant cation concentration order in seawater and brines of the sabkha is Na? [ Mg 2? [ Ca 2? [ K?,or Na? [ Mg 2? [ K? [ Ca 2?. The dominant anion concentration order is Cl - [ SO 2-4 [ HCO - 3. The dominant brine type for most samples is sodium chloride, with variable proportions of the major cations Ca 2? and Mg 2? and the major anion SO 2-4. Most brine samples indicate their source & Mahmoud A. Aref m1aref@yahoo.com 1 2 Department of Petroleum Geology and Sedimentology, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia Geology Department, Faculty of Science, Cairo University, Giza, Egypt is of modified marine water having an elevated CaCl 2 content, which may be derived from dissolution of mixed salt from the Miocene salt dome in Jizan area. The chemical composition and origin of the brines, and mineralogy and textures of the evaporite minerals in Jizan sabkha help in understanding the nature of the corrosive factors to the foundations in Jizan area. Keywords Brine chemistry Genesis Gypsum Corrosion Infrastructure Sabkha Saudi Arabia Introduction Sabkhas are ubiquitous geomorphic features in arid and semiarid regions where evapotranspiration potentials are very high and the hydrological inputs are conducive to the development of endoreic (internal) drainage systems (Goudie and Wells 1995; Shaw and Thomas 1997). They represent flat and barren surfaces that are in dynamic equilibrium with eolian deflation and sedimentation controlled by local water table level. Major geotechnical and constructional problems, namely, strength loss, differential settlement, concrete deterioration, and steel corrosion may emerge due to the presence of sabkha (Abou Al-Heija and Shehata 1989; Shehata et al. 1990; Youssef et al. 2012; Youssef and Maerz 2013). In addition, salt crystallization usually occurs in the concrete pores above the water table leading to their slow disintegration due to the high crystallization pressure that is enhanced by evaporation (Al-Amoudi and Abduljauwad 1994; Al-Amoudi et al. 1995). There are three different models that explain the sources of the groundwater and solutes in sabkhas. These are the seawater flooding model that was proposed by Kinsman (1969), Butler (1969), and Patterson and Kinsman

2 105 Page 2 of 17 Environ Earth Sci (2016)75:105 (1977, 1981). The evaporative pumping model was proposed by Hsü and Siegenthaler (1969); Hsü and Schneider (1973), and McKenzie et al. (1980). The recent model of ascending brine or conceptual model was proposed by Wood and Sanford (2002), Yechieli and Wood (2002), Wood et al. (2005), and Tyler et al. (2006) for the recent sabkha and most coastal-sabkha environments. In this model, capillary forces bring solutes and water to the surface, where the water evaporates and halite and other soluble minerals are precipitated. Retrograde minerals, sensu Wood et al. (2005), such as gypsum, anhydrite, calcite, and dolomite precipitate and accumulate in the capillary zone beneath the surface of the coastal sabkha. Sabkha sediments in Jizan area have a negative impact on infrastructure causing problems to buildings. The degree of damage depends on the characteristics of the sabkha, the amount of subsidence and the bearing capacity of the sabkha (Shabel 2007). In addition, salt domes offer some problems related to underground dissolution in the Jizan area, especially in the old city of Jizan. These include surface collapse, building failure, fractures, tilting, cracked roads, undulating ground surface, tilting of posts and electricity poles or even damage of the old buildings and infrastructure (Erol 1989; Al-Mhaidib 2002; Youssef et al. 2012; Youssef and Maerz 2013). Most studies carried out on Jizan sabkha are related to the geotechnical properties of the sabkha soil and the problems related to construction on the sabkha (Dhowian et al. 1987; Dhowian 1990; Erol 1989; Al-Shamrani and Dhowian 1997; Al-Mhaidib 2002; Shabel 2007; Youssef et al. 2012; Youssef and Maerz 2013). Erol and Dhowian (1988) found severe and widespread damage in the settlements of Jizan city, which is related to sinkholes and to linear depressions associated with solution channels in the salt dome. The regional composition of the sediments in the Jizan sabkha is the interest of Al-Shamrani and Dhowian (1995, 1997), Youssef et al. (2012), and Youssef and Maerz (2013). The objectives of the present paper are: (1) identification of the evaporite mineral composition and textures of the sabkha sediments, (2) understanding the hydrochemistry, brine evolution and genesis of Jizan sabkha, and (3) understanding the effect of brine and evaporite minerals to building failure in Jizan sabkha. The results can be used to interpret the chemistry and source of the brines, formation and textures of gypsum, anhydrite and halite in ancient sabkha deposits. Materials and methods The present paper is based on the results of 10 days of field work and excavation of several shallow trenches down to the groundwater table ( cm in depth) in the area of Jizan sabkha. The water and brine samples were taken in this area from seawater, groundwater, surface shallow pan or surface excavations in Jizan sabkha (Fig. 1; Tables 1, 2). During the field work, the salinity, temperature and ph value of the brine in trenches dug in the sabkha were measured. The salinity was determined by glass hydrometers taking into account the measuring of standard sea water. The hydrometer measures the mass % NaCl in the brine up to 250 %. Temperatures were measured at the surface by mercury thermometer ranging from 0 to 100 C in 0.1 C divisions. The density of the brine samples was measured by using two portable glass hydrometers, the first measures density from 1.00 to 1.10 g/cm 3, and the second measures density from 1.10 to 1.2 g/cm 3. The ph value of the brine was measured in the field by these portable phmeters. Thirteen (13) samples (10 samples from sabkha brines and 3 samples from the Red Sea water) were chemically analyzed at the Geochemistry Lab, Saudi Geological Survey, following the procedures given by Clesceri et al. (1998). The chemical analyses were carried out for the major cations Na?,K?,Ca 2?, and Mg 2? and the major anions HCO 3 -,CO 3 2-,SO 4 2- and Cl -. Total dissolved solids (TDS) were measured by sample evaporation techniques. Calcium (Ca 2? ) and magnesium (Mg 2? ) are determined by compleximetric titration using standard EDTA solution. Chloride (Cl - ) is determined by titration with standard (0.05 N) AgNO 3. Bicarbonate ions (HCO 3 - ) are determined by titration with standard (0.1 N) HCl. Sodium (Na? ) and potassium (K?) are measured by flame photometry. Sulfate ions (SO 4 2- ) are determined colorimetrically using spectrophotometer technique. The analytical precision of the ions is determined by calculating the absolute error in ionic balance in terms of equivalents per milligram (meq/l), which is found in all samples within a standard limit of ±5 %. All concentration values were expressed in milligram per liter (mg/l) unless otherwise indicated. The chemical data on the major cations and anions were displayed in graphical forms of the Trilinear Piper and Sulin diagrams to delineate the composition and origin of the brines in the sabkha. Previous studies In the Red Sea coastal plain of Saudi Arabia, most of the hydrochemical works are concerned with coastal pollution that resulted from sewage plants and other human inference (Turki 2007; Badr et al. 2009; Basaham et al. 2009). Some works are concerned also with the hydrochemistry of coastal lagoons and supratidal sabkhas in the Red Sea and Arabian Gulf coasts (e.g., Bahafzullah et al. 1993; Basyoni 1997; Basyoni and Mousa 2009; Al-Shaibani 2013; Taj and Aref 2015). Bahafzullah et al. (1993) classified the sabkha

3 Environ Earth Sci (2016)75:105 Page 3 of a 13 b Jizan 1 Duba NORTH 12 EGYPT SUDAN SUDI ARABIA Jeddah RED SEA RED SEA SAUDI ARABIA km Jizan YEMEN 9 Quaternary surficial deposits 8 Pleistocene basalt RED SEA 2 7 Mesozoic & Paleozoic sedimentary rocks Hijaz-Asir complex 6 Granite pluton Proterozoic rocks Seawater sample Brine sample Wet mudflat/sandflat 0 3km 5 Sample number Dry mudflat/sandflat Miocene salt dome Fig. 1 Surface sediments in Jizan sabkha and geologic setting of Jizan area. (a) Surface sediments and location of seawater and brine samples in Jizan sabkha, (b) Geology of Jizan area (After Blank et al. 1986) development around Sulaymaniya lagoon area into four stages; these are: (1) incipient; (2) slightly developed; (3) moderately developed; and (4) well developed. They found that the salinities of the water samples in incipient and slightly developed sabkhas are very saline and slightly hypersaline waters, whereas the moderately to well-developed sabkhas are moderately to highly hypersaline. Basyoni (1997) found that the groundwater in Al-Lith sabkha is moderately hypersaline and highly hypersaline, whereas slightly hypersaline and very saline water exist south of Al-Lith sabkha. He found positive correlations between TDS, and Na? and CI -. The TDS values, cations and anions, except SO 4 2- of the pore water decrease with depth. The ph values of the groundwater of Al Lith sabkha range from 6.8 to 7.9, in contrast to the ph values of the Red Sea water. Serhan and Sabtan (1999) measured a salinity range of % in the groundwater in Al- Nekhaila sabkha, south Jeddah. This water has a high content of sulfate and chloride that cause corrosive action on reinforced concrete. Banat et al. (2005) studied numerous water samples from coastal sabkhas between Jeddah and Yanbu Al-Bahar, Red Sea coast. They assumed that the climatic conditions over the Red Sea sabkhas lead to the formation of marine brines of magnesium-sodic to chloride type with neutral ph value. Al-Harbi et al. (2008) studied the hydrogeochemical processes and the isotopic characteristics of Al-Awshaziyah inland sabkha in Al-Qaseem region, central Saudi Arabia, as well as the waters from shallow and deep wells. They compared the salinity, cations and anions concentrations, and found that the water types of the sabkha are sodium-magnesium chloride, magnesium-sodium-chloride and sodium-chloride, and of meteoric origin. Alsaaran (2008) studied the brine chemistry of Jayb Uwayyid sabkha, eastern Saudi Arabia, and found that the average total dissolved solids in the sabkha brines is 243 %, and the order of cation dominance is Na? [ Mg 2? [ Ca 2? [ K?, and the anion dominance is Cl - [ SO 4 2- [ HCO 3 -. He concluded that sabkha brines have evolved from deep groundwater rather than from other near surface sources (i.e., direct rainfall, runoff from the surroundings, or inflow of shallow groundwater). Al-Dakheel et al. (2009) interpreted the major hydrodynamic process in Al Asfar Lake, Al Hassa area, Saudi Arabia, as possibly due to the upward migration of subsurface brines from groundwater by capillary action due to evaporation, that precipitate salt on the surface. Basyoni and Mousa (2009) interpreted the brines of Murayr sabkha, Arabian Gulf as belonging to chloride type (MgCl 2

4 105 Page 4 of 17 Environ Earth Sci (2016)75:105 Table 1 Concentration values of the major cations and anions in the seawater of Jizan area NH 4 F NO 2 PO 4 TDS PH Mg/Ca Brine type SO 4 2- S. no. Unit Ca 2? Mg 2? Na? K? Cl - HCO 3-1 mg/l Mg, Ca, sodium, SO 4, chloride epm mg/l , Mg, sodium, SO 4, chloride epm mg/l , Ca, Mg, sodium, chloride epm Maximum , Minimum , , , Average , Location of samples is in Fig. 1a and CaCl 2 ) that recharged mainly from seepage of recent marine water from the Gulf side and from marine and meteoric waters reacted with the surrounding carbonates. They assumed that the capillary rise of these waters from the shallow water table to the surface is a consequence of surface evaporation that led to deposition of evaporite minerals in the sabkha. Hussein and Loni (2011) studied the Jizan thermal springs that flowed through fractures within the Precambrian- Cambrian Arabian Shield rocks. The thermal springs are characterized by having a lower (Cl -? SO )/HCO 3 ratio ( ), higher (Na?? K? )/(Ca 2?? Mg 2? ) ratio ([4) and Cl - [ SO 2-4. Al-Shaibani (2013) estimated the concentrations and total masses of magnesium, potassium, calcium, and sodium from 20 shallow wells in Jayb Uwayyid sabkha, eastern Saudi Arabia. His results showed that Jayb Uwayyid sabkha contains about 1.4, 0.4, 0.9, and 9.9 million metric tons of magnesium, potassium, calcium and sodium, respectively. In the south Jeddah area, Taj and Aref (2015) found that the supratidal saline pans increase in salinity from 80 to 140, and % during deposition of gypsum and halite, respectively. The dominant cations and anions concentration order in the saline pans is Na? [ Mg 2? [ - K? [ Ca 2?, and Cl - [ SO 2-4 [ HCO - 3, respectively. They indicated that the brines were derived mainly from recent and old marine waters of MgCl 2 and CaCl 2 characters, with minor contribution of meteoric water. Study area Geologic setting and location of Jizan sabkha Three topographic zones exist in the Jizan area, which run for 1800 km parallel to each other in a northwest-southeast direction (Blank et al. 1986; Hussein and Loni 2011), these are (Fig. 1b): (1) the dissected highland of Hijaz-Asir escarpment that forms a narrow belt of strongly eroded terrain of Precambrian basement complex; (2) the central plateau is a west-east gently sloping peneplain that penetrated by west-east trending wadis which drain the western highlands. It consists of the Cambro-Ordovician Wajid Sandstone that rests unconformably on peneplain Precambrian basement rocks and below Permian rocks (Powers et al. 1966); and (3) the Tihama, low-elevation and gently sloping coastal plain that forms a strip of land that consists of the Quaternary eolian sands to alluvial terrace deposits. A Miocene salt dome forms a prominent high land (\50 m) that intersects the monotonous flat coastal plain area. Recent moist, sabkha sediments are widespread near the shore of the Red Sea, whereas loess and sand dunes exist in the dry land to the east of the coastal plain. The Jizan sabkha is present in- and around Jizan city at the

5 Environ Earth Sci (2016)75:105 Page 5 of Table 2 Concentration values of the major cations and anions in the brines of Jizan sabkha S. no. Brine nature unit Ca 2? Mg 2? Na? K? Cl - HCO 3 - SO 4 2- NH 4 F NO 2 PO 4 TDS PH Mg/ Ca Brine type 4 Water table; depth 36 cm mg/l , Ca, Mg, sodium, epm chloride 5 Halite pond mg/l , Mg, sodium, chloride epm Water table; depth 150 cm 7 Water table; depth 150 cm 8 Artificial excavation 9 Water table; depth 120 cm 10 Water table; depth 150 cm 11 Water table; depth 70 cm 12 Artificial excavation mg/l , Mg, Na, calcium, epm chloride mg/l , Ca, Mg, sodium epm chloride mg/l , Mg, sodium, SO 4, epm chloride mg/l , Ca, Mg, sodium, SO 4, epm chloride mg/l , Sodium, chloride epm mg/l , Ca, Na, magnesium epm chloride mg/l , Mg, sodium chloride epm Water table; depth mg/l , Sodium chloride 80 cm epm Maximum 18,100 15, ,700 16, , , Minimum , Average , , , Location of samples is in Fig. 1a

6 105 Page 6 of 17 Environ Earth Sci (2016)75:105 southwestern sector of Saudi Arabia, between latitudes and N and longitudes and E (Fig. 1a). Climate The Jizan area has a subtropical desert climate, where several ephemeral wadi systems drain to the Red Sea, such as Jizan, al Khums, Mais, Bish and others (Abdelrahman and Ahmad 1995). Jizan city is characterized by sparse rain storms which vary in intensity and duration. The southern part of the city is sometimes exposed to the risk of flash floods due to the heavy rain intensity, and the wadis flow from the east towards west (Elsebaie et al. 2013). Abdelrahman (1997) reported that the average temperature in Jizan area is 23 C, the annual precipitation is 1.3 cm, and the average relative humidity varies between 45 and 65 % in winter, and 25 and 40 % in summer. The mean rate of evaporation at Jizan was estimated as 156 cm/year by Abdelrahman and Ahmad (1995), and cm/year by Al-Subhi (2012). The prevailing winds at Jizan blow from the west during summer and southwest during winter, with wind speeds ranging between 2 and 50 km/h. Elsebaie et al. (2013), in their study on the mangroves of Jizan city, stated that the average surface temperature of the Red Sea water in Jizan area ranges between 26 C in winter and 32 C in summer. The seawater at the southern part of the Jizan area has a lower salinity (36 37 %) than the northern part ( %). Sediment characteristics of the sabkha area The coastal plain of Jizan area extends approximately 10 km inland to the foothills of the Red Sea escarpment, and is covered by Quaternary eolian sand, alluvial sand and gravel, loess and flood plain silt deposits. The prominent elevated relief on the coastal plain is a salt dome at Jizan city (Fig. 1a). The recent sediments are represented by sabkha deposits on the wet, coastal plain of Jizan area, in addition to sand dunes and loess deposits in the dry land. The old city of Jizan is situated at an elevated terrain, 5 50 m (above sea level) underlain by the Miocene salt dome covering an area of 4 km 2. The salt dome is covered by cap rocks of brecciated gypsum, anhydrite, dolomite, shale and sandstone layers. Several dissolution sinkholes of a diameter\4 m and depth exceeding 6 m are observed on the floor of the abandoned salt quarries (Fig. 2). Loess sediment is distributed over the eastern side of Jizan city. Loess form small hills, \5 m in height, and is composed of well-sorted, silt to fine sand-sized quartz, feldspar, and mica grains. Sand dunes (barchan) and sand sheets form most of the eastern part of the coastal plain. Youssef et al. (2012) measured the highest point of the barchan dunes as about 4 m with a slope angle reaching 40. The high slope angle of the dunes may be related to the occurrence of efflorescent gypsum and/or halite cements between the sand grains at/or near their sediment surface. Three areas are distinguished in the sabkha that vary in the composition and mechanism of formation of the evaporite minerals, and the nature and depth of the brine that precipitates the evaporite minerals; these are the halite pan, wet sabkha, and dry sabkha. Few, small halite pans (\25 m 2 in diameter, and cm deep) exist in the lowest topographic depressions in the sabkha (Fig. 3a). They are filled with high salinity brine ([250 %, and density 1.26 g/cm 3 ). Halite crystallizes in these pans at the brine surface as thin rafts and pyramidal hoppers, and on the floor of the pan as aggregates of chevrons and cornets (Fig. 3b). The wet sabkha is represented by wet mudflat and sandflat areas, where the water table ranges from 36 to 150 cm below the surface (Fig. 3c). The sabkha sediments are composed mainly of moist, loose sand and silt that form adhesion ripples, in addition to a variable abundance of gypsum, anhydrite and halite minerals (Basyoni and Aref, 2015). The surface of the wet sabkha is composed of buckling petee crusts (Fig. 3d). The petee structure is composed of black and green microbial mats and gypsum layers that form elongated, hollow, twisted ridges (Fig. 3d). The dry sabkha is composed of \1 cm thick halite crusts that form inverted, V-shaped, polygonal tepee structures (Fig. 3e). The subsurface sediments in all sabkha areas are composed of interbedded brown, sand and grey, mud layers. Scattered lenticular and rosette gypsum crystals (Fig. 3f) are aggregated and form thin layers at the depths of 10, 40 and 90 (Fig. 3c). Nodular mosaic and enterolithic folds of milky white, soft anhydrite are recorded at the depth of 15 cm (Fig. 3g). Fig. 2 A funnel-shaped sinkhole forms due to recent dissolution of halite and its partial filling with clastic sediments

7 Environ Earth Sci (2016)75:105 Page 7 of a b c d e f g Fig. 3 Evaporite deposition in the sabkha area. (a) Shallow, desiccated pan encrusted with white halite rafts and skeletal crystals. (b) Bedding plane view showing the variable size of halite cubes that form the rafts. (c) A general sand mud layering, with gypsum crystallization at several levels (arrows). (d) Elongated, wavy, ridges with smooth upper surface form the petee structure. (e) Inverted, V-shaped, polygonal ridges (\5 cm in height) of tepee halite crusts, partially covered with eolian sand. (f) Aggregates of lenticular and rosette gypsum grow inclusively in brownish silt. (g) Milky white anhydrite nodules grow displacively at a certain level in the wet sand of the sabkha

8 105 Page 8 of 17 Environ Earth Sci (2016)75:105 Results and discussion Chemical composition of seawater and the brines The distribution of the concentrations of the cations Na?, K?,Ca 2? and Mg 2?, the anions Cl -,SO 2-4, and HCO - 3, NH 4, TDS and ph are presented in Figs. 4 and 5. The statistical parameters, such as maximum, minimum and mean of the chemical composition of the brines in Jizan sabkha are also presented in Tables 1 and 2. Generally, the concentrations of cations and anions in the seawater are lower than the concentration values of the sabkha brines in most samples, except samples Nos. 4 and 7 (Fig. 4), which have also lower salinity values due to recharge from rain water, temporary floods and seepage of sewage water from septic tanks. Na? has the highest concentration with respect to the cations K?,Mg 2? and Ca 2? in the brines of the sabkha (Fig. 4a). Mg 2? concentration is next in abundance, followed by Ca 2? in most samples, whereas K? concentration value is the lowest, except in samples Nos. 12 and 13 (Fig. 4a). For the anions, the Cl - concentration is the highest among all samples, SO 2-4 concentration is very low, whereas the HCO - 3 is the lowest (Fig. 4b). The Cl - concentration in the seawater of Jizan area ranges from 19,466 to 21,619 mg/l, with an average value of 20,497 mg/l, whereas the Na? concentration ranges from 12,206 to 14,727 mg/l, with the average of 13,431.1 mg/l (Table 1). The dominant anion in the brines of Jizan sabkha is Cl - where its concentration ranges from 5367 to 226,789 mg/l, and the average is 104,424 mg/l, which accounts for more than 50 % of the charge balance in the brines. The dominant cation is Na?, where its concentration ranges from 2292 to 251,700 mg/l, with the average concentration value of 70,023 mg/l. Such concentrations of Cl - and Na? in the brines of Jizan sabkha are several times higher than their concentration in seawater of Jizan area. They are also slightly higher than the average concentration values of chloride (96,851 mg/l) and sodium (45,239 mg/l), measured in the groundwater of Dahaban sabkha by Banat et al. (2005). The Ca 2? concentration in seawater of Jizan area ranges from 680 to 824 mg/l, with the average of 748 mg/l, and the Mg 2? concentration ranges from 2000 to 4000 mg/l, with the average of 2694 mg/l (Table 1). In the brines of Jizan sabkha, the Ca 2? concentration ranges from 1024 to 18,100 mg/l, with the average of 8516 mg/l, and the Mg 2? concentration ranges from 830 to 15,500 mg/l, with the average of 8248 mg/l (Table 2). The average concentrations of Ca 2? and Mg 2? in the brines of Jizan sabkha greatly exceed the values measured from the seawater of Jizan area. They are also higher than the average concentrations of Ca 2? (2832 mg/l) and Mg 2? (4314 mg/l), a b Seawater Brine sample Seawater Brine sample c d ph Seawater Brine sample Seawater Brine sample Fig. 4 Histograms representing the concentration of the cations (Ca 2?,Mg 2?,Na? and K? ), anions (Cl -, HCO 3 2- and SO 4 2- ) and TDS, and ph values in seawater and brine samples of Jizan sabkha

9 Environ Earth Sci (2016)75:105 Page 9 of measured by Banat et al. (2005) for Dahaban sabkha, north Jeddah. K? ions have a narrow range of mg/l in seawater of Jizan area, with the average of 437 mg/l (Table 1). The concentration of K? in the brines of Jizan sabkha ranges from 132 to 16,050 mg/l, with the average of 3607 mg/l (Table 2). The K? values in the brines exceed the values in Jizan seawater, and the average value of 1911 mg/l in the groundwater of Dahaban sabkha measured by Banat et al. (2005). The SO 4 2- concentration in seawater of the Jizan area ranges from 4000 to 4400 mg/l, with the average of 4183 mg/l (Table 1). The SO 4 2- concentration in the brines of Jizan sabkha ranges from 465 to 8950 mg/l, with the average of 3861 mg/l (Table 2). The average SO 4 2- concentration in seawater and brines of Jizan area are similar. They are also similar to the average concentration value of 3819 mg/l in the Dahaban sabkha, measured by Banat et al. (2005). However, seven brine samples have SO 4 2- concentration less than the average in Jizan seawater, indicating the removal of SO 4 2- due to gypsum precipitation and/or the reduction of SO 4 2- ions by sulfate-reducing bacteria, similar to observations by Deng et al. (2010), Spadafora et al. (2010), and Glunk et al. (2011). HCO 3 - ions have low concentration in seawater of the Jizan area, as well as in the brines of Jizan sabkha (Tables 1, 2). The HCO 3 - concentration in seawater of Jizan area ranges from 125 to 137 mg/l, with the average of 130 mg/l, whereas the HCO 3 - concentration in the brines of Jizan sabkha ranges from 45 to 189 mg/l, with the average of 103 mg/l. The average HCO 3 - concentration in Dahban sabkha is 204 mg/l (Banat et al. 2005), which is slightly higher than the average values measured for the Red Sea water and sabkha water in Jizan area. The low concentration values of HCO 3 - in seawater and brines in Jizan sabkha are due to their removal during precipitation of the carbonate minerals. The concentrations of ammonia (NH 4 ) in the brines of Jizan sabkha and seawater range from 0.41 to 177, and mg/l, respectively, and their mean values are mg/l and 39.7, respectively. The concentration of nitrite (NO 2 ) ranges from 0.06 to 0.98 mg/l, and the mean value is 0.38 mg/l in the brines of Jizan sabkha. The high values of NH 4 and NO 2 may be due to leakage from septic tanks of the houses in Jizan city, or from fertilizers in nearby agriculture fields. It is worth to mention that during excavation of the lands for the foundations of new houses, high quantities of groundwater having a bad odor have seeped from nearby old houses. This water may provide the elevated NH 4 and NO 2 in the brine of Jizan sabkha. The concentration of fluoride (F - ) in the brine of Jizan sabkha ranges from 0.65 to 2.16 mg/l, with a mean value of 1.45 mg/l. Fluoride is considered as an essential element in health problems that may arise from either deficiency or excess amount (Gopal and Gosh 1985). Fluoride can be considered as one of the main trace element in groundwater, where it occurs generally as natural constituent (Al- Ahmadi 2013). The high concentrations of fluoride are generally due to rocks containing fluoride minerals (Wenzel and Blum 1992; Bardsen et al. 1996). The concentration of phosphate (PO 4 3- ) in the brines of Jizan sabkha ranges from 0.19 to 8.65 mg/l, with a mean value of 1.76 mg/l. The phosphate is usually found in groundwater with a minimal level due to the low solubility of native phosphate minerals and the ability of soil to retain phosphate (Rajmohan and Elango 2005). Total dissolved solids (TDS) in the seawater of Jizan area range from 38,500 to 41,900 mg/l, with the average of 40,366 mg/l (Table 1). The TDS in the brines of Jizan sabkha range from 12,900 to 495,000 mg/l, with the average of 166,980 mg/l (Table 2; Fig. 4c). The TDS values of seawater in Jizan area are nearly similar to TDS value that generally recorded for the Red Sea water. Two brine samples from trenches in Jizan sabkha have a lower TDS value of 17,700 and 12,900 mg/l in samples 4 and 7, than the average TDS in seawater of Jizan area. The brines of these samples may be derived from a mix with rainwater, groundwater of meteoric origin or seepage of sewage water from septic tanks. For the brines of Jizan sabkha that have higher TDS values than the average TDS of seawater (40,366 mg/l), are likely related to extensive evaporation rate with respect to the small groundwater inflow, rainfall or seawater seepage. The very high salinity values of 495,000 and 363,000 mg/l (Table 2) of the sabkha brines may be related to dissolution of halite in the salt dome. The values of electrical conductivity (EC) range from 20,000 to 199,100 ls/cm with a mean value of 99,800 ls/ cm. The high values in EC are attributed mainly to evaporation process and increase in the salinity of the brine. Both TDS and EC are affected by the high concentration values of Na?,Ca 2?,Mg 2?,Cl -, and SO The ph values in the seawater of Jizan area range from 7.52 to 8.09, with the average of 7.86 (Table 1). The ph values in the brine samples of Jizan sabkha range from 6.01 to 7.45, with the average of 6.79 (Table 2), which are lower than the values recorded from the Red Sea water in Jizan area (Fig. 4d). Six brine samples have values slightly \7, which indicate neutral or slightly acidic brines. Whereas, four samples have values more than 7, indicating that all carbonate alkalinity is in the form of HCO 3 - (Stumm and Morgan 1996; Drever 1998). An isochronal map of the cations in the brines of Jizan sabkha indicates that Na? increases to [250,000 mg/l in the halite pans at central western margin of the sabkha area, while low values of Na? (\10,000 mg/l) dominate the

10 105 Page 10 of 17 Environ Earth Sci (2016)75:105 Na K Ca Mg

11 Environ Earth Sci (2016)75:105 Page 11 of b Fig. 5 Contour lines representing the distribution of the major cations and anions in seawater and brine samples of the studied sabkha, Jizan area eastern margin of the sabkha (Fig. 5). K? values follow Na?, where the highest value is 16,000 mg/l in the central western part of the studied sabkha, and the K? concentration decreases to values less than 2000 mg/l in the north, east and southeastern sides (Fig. 5). The low values of Na? and K? concentrations at the eastern margin of the sabkha is attributed to dilution from the landward side of the sabkha, less evaporation and lower salinity (up to 12,900 mg/l) compared to the western margin of the sabkha area. The Ca 2? concentration value is the reverse of the concentration of Na? and K?.Ca 2? concentration is lower at the southwestern part of the sabkha (\1000 mg/l), and increases to 2200 mg/l to the northeastern side of the sabkha (Fig. 5). The Mg 2? concentration increases from 1500 mg/l in the southeastern part of the sabkha to [10,000 mg/l in the central western part of the sabkha, and then increases gradually to 15,000 mg/l in the northern part of the sabkha (Fig. 5). The isochronal map of the anions showed that the concentration of Cl - is similar to Na?, where the highest value of [200,000 mg/l is recorded in the central western margin of the sabkha, and decreases to the east and north sides (Fig. 5). The SO and HCO 3 concentrations are similar, and they increase to the western margin of the sabkha, to values of 9000 and 180 mg/l, respectively (Fig. 5). The concentrations of SO 2-4 and HCO - 3 decrease to the northeastern side of the sabkha to 180 and 45 mg/l, respectively. The concentration of NH 4 shows a narrow range, but it generally increases to the west and north margins of the sabkha (Fig. 5). High concentration of NH 4 and NO 2 in Jizan sabkha may indicate intrusion into the sabkha water from adjacent sewage waters and agricultural areas which receive excess nitrogen fertilizers (such as urea and ammonium nitrate) that are assumed to increase the agricultural production. Brine types The ionic concentrations of the seawater and brines in samples numbers 3, 4, 6, 7, 8, 9, 11 and 13 (Tables 1, 2) have the following general pattern: Na? [ Mg 2? [ Ca 2? [ K?. Some samples, however, (2, 12 and 13) have the abundance Na? [ Mg 2? [ K? [ Ca 2?, and three samples have variable abundances such as Na? [ Ca 2? [ Mg 2? [ K?, or Ca 2? [ Na? [ Mg 2? [ K?, or Mg 2? [ Na? [ Ca 2? [ K? (Tables 1, 2). On the other hand, the abundance of the major anions in all samples is Cl - [ SO 4 2- [ HCO 3 -. The brine type for most samples is sodium chloride, with variable proportions of the major cations Ca 2? and Mg 2? and the major anion SO 4 2- (Tables 1, 2). Three samples have Ca 2?,Mg 2?, sodium chloride brine type, two samples have the following brine types Mg 2?, sodium, SO 4 2-, chloride, or Mg 2?, sodium chloride, and only one sample has the following brine types Mg 2?, Ca 2?, sodium, SO 4 2-, chloride, or Mg 2?, Na?, calcium chloride, or Ca 2?,Mg 2?, sodium, SO 4 2-, chloride, or Ca 2?,Na?, magnesium chloride (Tables 1, 2). Despite the dominance of Na? and Cl - ions in most of the studied brine samples that exhibited a marine-like chemical character (Herczeg et al. 2001), a broad range of secondary processes can significantly affect the evaporative pathways and are responsible for the variables brine types in the Jizan sabkha, similar to the interpretation proposed by Radke et al. (2002). The secondary processes may include mineral dissolution, cation exchange reactions, sulfate reduction, brine mixing, brine reflux, mineral precipitation and recycling of soluble salts within the sabkha. Ion inter-relationship The correlations of the concentration of cations, anions, TDS and ph are shown in Fig. 6. The correlation between Na? and Cl - for most samples (except samples 9 and 11 which have very high Na? values) indicates a positive correlation (R 2 = ) (Fig. 6a). This positive correlation indicates the enrichment of the brines with NaCl (halite) that may be precipitated at high salinity. The correlation between Ca 2? and Mg 2? (Fig. 6b) also indicates a positive correlation (R 2 = ). This is contrary to the fact that the brine should have lower Ca 2? concentration due to the earlier precipitation of CaCO 3 (calcite and/or aragonite) and CaSO 4.2H 2 O (gypsum). Most probably, the relatively high Ca 2? concentration is due to dissolution of carbonate grains in the sediments. No pronounced correlation exists between Ca 2? and SO 2-4 (R 2 = ) (Fig. 6c). This is due to the possible precipitation of CaSO 4.2H 2 O (gypsum) from the brine and dissolution of carbonate grains. No correlation between Ca 2? - and HCO 3 (R 2 = ) (Fig. 6d) in two groups of the brines, may be interpreted as a result of oxidation of organic matter in the sediments and reduction of sulfate ions, which lead to the increase in HCO - 3. There are strong positive relations between TDS and Na? (R 2 = ) (Fig. 6e), and between TDS and Cl - (R 2 = ) (Fig. 6f), and no 2- pronounced relation between TDS and SO 4 (R 2 = ) (Fig. 6g). The positive relations indicate that the TDS is mainly represented by Na? and Cl - ions, whereas changes in SO 2-4 does not affect the TDS of the brine. Plotting of the values of TDS and ph indicates no relation between them (R 2 = ) (Fig. 6h). The ph values of seawater are around 8 that decrease to about 6

12 105 Page 12 of 17 Environ Earth Sci (2016)75:105 Cl SO 4 HCO 3 NH 4 Fig. 5 continued

13 Environ Earth Sci (2016)75:105 Page 13 of a R 2 = b R 2 = c d R 2 = R 2 = e f R 2 = R 2 = g R 2 = h R 2 = Fig. 6 Scatter diagrams showing the correlations between various anions, cations, TDS and ph values with the increases in the salinity of the brine. This result is in agreement with the data of Bąbel and Schreiber (2014). The Mg 2? /Ca 2? ratio of seawater at Jizan area ranges from 2.82 to 4.85, with the average of 3.53 (Table 1; Fig. 7a). Whereas for the Jizan sabkha, the Mg 2? /Ca 2? ratio of the brines range from 0.49 to 8.15, with the average of (Table 2; Fig. 7a). All brine samples have lower Mg 2? /Ca 2? ratio than that measured in Jizan seawater, except samples numbers 8 and 11, which have exceedingly high values of 8.15 and 7.90, respectively (Fig. 7). The low Mg 2? /Ca 2? ratio in most brine samples is most probably due to the dissolution of carbonate grains in the sediments that increases the concentration of Ca 2? ions. Whereas the high Mg 2? /Ca 2? ratio in samples 8 and 11 is due to the removal of Ca 2? ions through precipitation of calcite and gypsum. However, the dominant low Mg 2? /Ca 2? ratio indicates that the brine has a low potential to dolomitize the high Mg-calcite and aragonite minerals. Only the brines in

14 105 Page 14 of 17 Environ Earth Sci (2016)75:105 the precipitation of calcite, aragonite and gypsum. The chemical characters (ionic concentration patterns and brine types) of the studied brine samples in Jizan sabkha and seawater are similar, which indicate that the brine chemistry of Jizan sabkha has been modified from initial seawater composition to the stages of deposition of calcium carbonate, followed by calcium sulfate and finally to sodium chloride dominant composition (Fig. 8). Genesis of the brines Fig. 7 Relationship between Mg/Ca and sample number, and TDS samples 8 and 11 could dolomitize the carbonate grains in the sediments due to their high Mg 2? /Ca 2? ratio. Banat et al. (2005) found that the increases in the Mg?2 /Cl - concentration and decreases in SO 4 2- concentration lead to the formation of protodolomite in the coastal sabkha sediments between Jeddah and Yanbu Al-Bahar. Brine evolution The hydrochemical evolution of the brines of Jizan sabkha can be understood using the analytical data obtained from brine samples as a result of plotting the major cations and anions in the Piper Trilinear diagrams (Fig. 8). The diagrams show that all brine samples in Jizan sabkha have similar affinity and composition, which are similar to the composition of seawater. The diagrams show two groups of samples, the first group shows that the majority of the brine samples of Jizan sabkha fall in the field NaCl type of water. The second group shows approximately equal percentage of the alkali metals (Na?? K? ), and the alkaline earth elements Mg 2? and Ca 2?, whereas the strong acid (Cl - ) greatly exceeds the weak acid (HCO 3 - and CO 3 2- ), and the strong acid (SO 4 2- ) (Fig. 8). Also, from the Piper plot, the deficiency of Ca 2? in the brines of the sabkha is due to Results of the chemical analyses were recalculated for both the major cations and major anions and plotted on a Sulin graph (Fig. 9) to interpret the origin of brine of Jizan sabkha. It is clear that the seawater samples and four brine samples of Jizan sabkha are located in the field of recent marine water origin and of MgCl 2 composition (Fig. 9). However, most of the brine samples in Jizan sabkha are located in the field of old marine water origin and of CaCl 2 composition (Fig. 9). Therefore, the main supply to the brines of Jizan sabkha is through seawater seepage that may be modified with reaction with the old marine water from dissolution of the halite crystals of the Miocene salt dome. This modified seawater is the source of the brines in Jizan sabkha. The localized formation of sinkholes at the floor of the abandoned salt quarries (Fig. 2) and collapse of the buildings of the old Jizan city point to an additional salt dissolution by rain water and fresh and/or sewage waters from houses. The possible contribution of fresh water through Wadi Jizan or occasional rainfall has a minor effect on those samples that are located close to the field of meteoric water origin in Sulin graph (Fig. 9). Bagheri et al. (2014) mentioned three main potential processes that may cause high salinity values in the Kangan gasfield, these are halite dissolution, membrane filtration, and evaporation of water. They indicated that the evaporated ancient seawater trapped in lagoonal and sabkha carbonates, gypsum, and clastic rocks is the cause of salinization based on the concentrations of Cl, Na, and TDS in comparison with Br concentration. Environmental impact of the sabkha brines and minerals Sabkha evaporite brines and minerals cause severe damage to buildings and infrastructure in Jizan area. In addition, partial dissolution of the nearby salt dome can modify the composition of the brines which increases their corrosive effect on steel reinforcement and deterioration of the concrete in the sabkha area. The evaporite minerals gypsum and anhydrite are common in the wet sabkha area. They are recorded with a variable abundance in the capillary evaporation zone of both shallow (36 cm) and deep

15 Environ Earth Sci (2016)75:105 Page 15 of Fig. 8 Piper Trilinear diagrams showing the brine evolution in Jizan sabkha Brine salinity < 40 g/l g/l g/l g/l > 350 g/l Fig. 9 Sulin graph showing the origin and type of the brines, Jizan sabkha r(k + + Na + ) rcl - = 1 r SO rcl - r(k + + Na + ) CaCl 2 Old Marine Water MgCl 2 Recent Marine Water rcl - r(k + + Na + ) rmg 2- > 1 = 1 < 1 NaSO 4 Deep Meteoric Water r Mg r(k + + Na + ) rcl - 2- < 1 rso 4 = 1 > 1 NaHCO 3 Shallow Meteoric Water r(k + + Na + ) rcl - Seawater from tidal flat & mangrove area Brine sample from the water table of the sabkha (150 cm) groundwater. In this area halite is only recorded in saline pans within the sabkha area. These evaporite minerals reflect the salinity and chemical characteristics of the brines. Gypsum is displacively grown as lenticular and rosette crystals in the subsurface sediments of the sabkha down to the underlying water table. Anhydrite forms displacive nodules near the sediment surface. Both gypsum and anhydrite form from brines with salinity \200 %, but halite is recorded as rafts, chevrons and cornets in those pans with salinity exceeding 250 %. The crystallization pressure exerted from displacive growth of gypsum and anhydrite in pore spaces of the foundations causes their

16 105 Page 16 of 17 Environ Earth Sci (2016)75:105 sever damage. The sulfate nature of the brines causes corrosion of the steel reinforcement of infrastructure. Fluctuation of the water table during summer and winter months increases the degree of damage and corrosion in the foundation in the sabkha area. Conclusions The concentrations of cations and anions in most of the sabkha brines exceed their respective values within seawater due to intensive evaporation. However, two brine samples have a lower salinity value and a lower concentration of cations and anions than seawater, and these may be related to the mixing of groundwater with meteoric water, leakage water from septic tanks in Jizan city, or from fertilizers in nearby agriculture fields. Concomitant with the increases in salinity is the increase of Na? and Cl -, and the decrease of K?,Mg 2?,Ca 2?, HCO 3 - and SO 4 2- in the residual brines. These are due to the removal of Ca 2?, HCO 3 - and SO 4 2- ions from the brines due to the precipitation of calcite, aragonite and gypsum. Whereas the remaining brines are oversaturated with Na? (?K? ) and Cl - ions which favor halite deposition at higher salinity values, the relatively high Ca 2? concentration relative to low HCO 3 - and SO 4 2- ions, and the low Mg 2? /Ca 2? ratio are most probably related to dissolution of carbonate sediment. The order of cations dominance in most samples is Na? [ Mg 2? [ Ca 2? [ K?, or Na? [ Mg 2? [ K? [ Ca 2?, or Na? [ Ca 2? [ Mg 2? [ K?. The abundance of the major anions in all samples is Cl - [ SO 4 2- [ HCO 3 -. The dominant brine type is sodium chloride, with variable proportions of the major cations Ca 2? and Mg 2? and the major anion SO The brines of the sabkha have evolved mainly from seawater seepage, with localized minor modification from dissolution of halite in the salt dome, rainfall, floods and leakage from septic tanks and agriculture fields. Capillary evaporation of the groundwater and surface evaporation of these waters have modified the brine chemistry and salinity during deposition of gypsum and halite. Fluctuation of the groundwater table with variable salinity values cause extensive evaporite mineral formation and subsequent corrosion of the steel, deterioration of the concrete and possible damage of buildings in the sabkha area. The composition and texture of the evaporite minerals in the sabkha area, and the brine composition and origin can be used to interpret similar sabkha sediments in the rock record. Acknowledgments This project was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under grant No. (307/145/1432). The authors, therefore, acknowledge with thanks DSR technical and financial support. We thank the reviewers B. Charlotte Schreiber, an anonymous reviewer, and the Editor-in- Chief Olaf Kolditz for their helpful comments which greatly improved the manuscript. Thanks also to Mr. Murad Rajab and Mr. Ali Khofani for their field assistance. Compliance with ethical standards Funding This project was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, Saudi Arabia, under Grant No. (307/145/1432). Conflict of interest of interest. References The authors declare that they have no conflict Abdelrahman SM (1997) Seasonal fluctuations of mean sea level at Jizan, Red Sea. J Coast Res 13(4): Abdelrahman SM, Ahmad F (1995) Red Sea surface heat fluxes and advective heat transport through Bab El-Mandab. 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