DOI : 10.4197/Mar. 24-2.8
115
Assessment of the Present Status of the Red Sea Coastal Zone Between Haql and Yanbu, Saudi Arabia
M.S. Hariri1, M. Kh. Khalil2 and A.E. Rifaat2
1Faculty of Marine Sciences, King Abdulaziz Univ., Jeddah, KSA
2National Institute of Oceanography and Fisheries, Alexandria, Egypt
1[email protected] - 2[email protected]
Abstract. The aim of this study is to assess the concentration level of some heavy metals (Zn, Cu and Fe) in the surface sediments of the coastal area from Haql to Yanbu along the Saudi Arabian Red Sea during 2009. The concentration (µg/g) levels range from 4.38 to 73.25 for Zn; 0.0 to 41.25 for Cu; 1263 to 33763 for Fe in lower intertidal sediments. They range in upper intertidal sediments from 5.13 to 63.0 for Zn; 0.0 to 53.75 for Cu, and 2350 to 89350 for Fe. The present environmental status was assessed using, enrichment factor (EF) and Geoaccumulation index (Igeo), to compensate the influence of natural variability in sediment. The results reveal that both metal enrichment factor (EF) and Geoaccumulation index (Igeo) show that the enrichment of Zn and Cu in most of the study area is insignificant.
However, with respect to a specific site in study area, stations numbered 3, 10, 12, 14, 15, 16, 18 and 22 are highly enriched with Cu and Zn. The reason behind this enrichment is attributed to human activities along the coastal zone (municipal discharges, industrial development, tourism activities, desalination plants … etc.
Keywords: Saudi Arabia, Red Sea, Haql, Yanbu, Coastal Sediments, Heavy metal, Assessment.
Introduction
Coastal areas are often considered as receptacles for pollutants from industrial and urban activities. Overexploitation in modern society has led to elevated inputs of anthropogenic contaminants into coastal and estuarine areas which are vulnerable to human activities (Peters et al.,
1997 and Lewis and Devereux, 2009). Metals are one of the toxic pollutants of great concern because of their potential detrimental effects on aquatic ecosystems (Grimalt et al., 2001 and Prouty et al., 2010).
Meanwhile, metals are readily accumulated by aquatic organisms and subsequently transferred along food chains and ultimately posing a risk to human health through sea food consumption (Wang, 2002 and Gerstenberger et al., 2010).
The coastline of the Kingdom of Saudi Arabia stretches for about 1840 km and accounts for 79% of the eastern coast of the Red Sea. This area provides various habitats for diverse communities of corals and sponges. As one of the largest countries bordering the Red Sea, Saudi Arabia has undergone rapid transformation into a modern industrial country (Badr et al., 2009). As a result, a significant part of the coast has been subjected to extensive exploitation, and metal pollution is becoming a threat to the coastal ecosystem. Incidents of damaged oil wells, oil pipeline leaks, and domestic sewage from coastal cities are contributing significantly to the coastal pollution (Al-Thukair et al., 2007). Sediments can act as a scavenger agent for heavy metal and an adsorptive sink in aquatic environment. It is therefore considered to be an appropriate indicator of heavy metal pollution. Sediments are preferred as a monitoring tool because they generally show less variation over a short period of time than dissolved metals in overlying water columns (Atkinson et al., 2007).
Numerous studies have been carried out on the marine environment of certain area (e.g. El-Sabarouti, 1983; El-Sayed, 1983; Durga prasada Rao & Behairy, 1984; and Basaham & El-Shater, 1994; El-Sayed et al., 2002; Basaham et al., 2006; 2009 and Al-Lihaibi, 2003). To date, limited data exist for an accurate assessment of the metal pollution of coastal environments in Saudi Arabia, especially on the area extending from Haql to Yanbu.
In this paper, the concentration levels of iron, copper and zinc in sediments from the lower and upper intertidal zones (Haql to Yanbu) are determined comparing with the background concentrations.
Area of Study
The study area is located at the eastern coast of the Red Sea is about 1840 km long (Fig. 1). It extends from Haql city (29˚21' 24.6" N, 34˚ 57'
36.7"E) to Yanbu city (24˚ 10' 1.5" N, 37˚ 59' 04.2" E) along the Saudi Arabian Red Sea coast (Fig. 1). It lies between arid land, desert and semi- desert. The average water salinity is 40‰ with overall average water temperature is 22°C. The wind is mostly north to north-northwest throughout the year round. However, the range of the north-northeast current along the Saudi coast is 8-29 cm/s (3-11.4 in/s) (http://en.wikipedia.org/wiki/Red Sea).
Materials and Methods
Representative lower intertidal and upper intertidal zone sediment samples were collected from thirty nine sites along the entire study area (Fig. 1) during 2009.
Fig. 1. Area of study and the locations of the samples.
The sediment samples were analyzed using Folk (1974) technique to determine the mean grain size (Mz) and degree of sorting (σ). Organic carbon (OC) was measured using the sulfo-chromic wet oxidation method (le Core, 1983). Powdered sediment was first treated with phosphoric acid at 110°C to remove carbonate and chloride ions then organic matter was oxidized with a mixture of potassium dichromate and sulfuric acid. The excess dichromate was then back titrated with sodium thiosulfate. The quantity of the thiosulfate corresponds to a definite quantity of total organic carbon, which is then attributed to the weight of the sediment sample. Calcium carbonate (CaCO3) content was estimated by using standard pure CaCO3 (Basaham and El Sayed, 1998).
For the determination of total heavy metals, powdered freeze-dried subsamples were digested using a nitric hydrofluoric acid mixture in a microwave digestion unit (Anton Paar Multiwave 3000). The acid was evaporated to near dryness and the residue was taken in 0.1 M HCl.
Concentrations of major elements were determined using Flame Atomic Absorption Spectrophotometer AAS (Perkin Elmer Analyst 800, equipped with Zeman background correction).
Results and Discussion Grain Size
The lower intertidal sediments in the study area are predominantly sandy. The areas receive sediments from two different sources; the terrigenous (igneous and metamorphic) rock fragments from the Tihama Mountains and biogenic carbonates that are eroded from coral reef terraces and debris of calcareous organisms. The skeletal carbonates have a remarkably limited history of transportation and deposition. However, it is not easy to reveal the hydrodynamic behavior of the skeletal fragments, which is dependent on shape, density and size (Maiklem, 1968 and Braithwaite, 1973). The mean size (Mz) of lower intertidal sediments ranges from 0.1 mm (very fine sand) to 1.42 mm (very coarse sand) with an average (0.65 mm). The sediments of the upper intertidal zone are relatively finer than those of the lower intertidal sediments. The mean size varies between 0.08 mm (very fine sand) and 1.77 mm (very coarse sand) with an average of 0.49 mm (Table 1). Generally, the grain size increases from south (Yanbu) to north (Haql) (Fig. 2). Similar results were also observed by Moussa et al. (1986) and El-Mamoney and Rifaat
(2001) for the Egyptian Red Sea coast. The degree of sorting (Fig. 3) varies from 0.1 (well sorted) to 1.97 (poorly sorted) with average value 0.85 for lower tidal sediments, from 0.19 (very well sorted) to 1.87 (poorly sorted) with average value 0.97 for upper intertidal sediments.
Both the degree of sorting and mean size show similar behavior, increasing from south to north. Folk (1974) suggested that the main factors controlling the degree of sorting are the size range of material supplied to the environment, hydrodynamics and the depositional energy.
Table 1. Ranges and average values for grain size and geochemical parameters for studied samples.
Lower intertidal Upper intertidal
Parameter Range Average Range average
Mean size (mm) 0.1 - 1.42 0.65 0.08 - 1.77 0.49
Sorting (σ) 0.1 - 1.97 0.85 0.19 - 1.87 0.97
CaCO3% 1.5 - 93 28.69 2.5 - 95 30.47
TOC% 0.00 - 3.66 1.3 0.00 - 3.66 1.27
Zn (µg/g) 4.38 - 73.25 22.01 5.13 - 62.13 26.95
Cu (µg/g) 0.00 - 50.00 10.61 0.00 - 78.75 13.01
Fe (µg/g) 1263 - 33763 9814 2350 - 89350 15927
Fig. 2. Mean grain size of lower and upper intertidal sediments from Haql to Yanbu.
Fig. 3. Sorting of lower and upper intertidal sediments from Haql to Yanbu.
Calcium Carbonate and Organic Carbon Contents
The calcium carbonate (CaCO3) and organic carbon (TOC) contents are shown in Fig. 4&5. The CaCO3 content of lower intertidal sediments ranges from 1.5% to 93% with an average of 28.7% which decreases from south to north. On the other hand, CaCO3 content for the upper intertidal sediments ranges from 2.5% to 95% with an average of 30.5%.
In, general the carbonate content decreases from south to north (Fig. 4).
This is also consistent with data of Moussa et al. (1986) and El- Mamoney and Rifaat (2001) for the Egyptian Red Sea coast. The contents of organic carbon range between 0.0% and 3.66% for both lower and upper intertidal sediments with an average of 1.30% and 1.27%, respectively. Similarity, organic carbon content decreases from south to north (Fig. 5). It should be noted, however, that the correlation between organic carbon and carbonate is particularly moderate (r = 0.56) for lower intertidal sediments and (r = 0.76) for upper intertidal sediments (Table 2).
This might suggest that biogenic carbonates resulting from the erosion of coral reefs and debris of calcareous organisms is the most probable source. It could be, also, attributed to the enrichment of organic matter that has not been affected by oxidation. The positive relationship between organic matter and CaCO3 supports this finding.
Fig. 4. CaCO3 distribution of lower and uper intertidal sediments from Haql to Yanbu.
Fig. 5. Total organic carbon distribution of lower and upper intertidal sediments from Haql to Yanbu.
Table 2. Correlation matrix of the data (n=39) bold face values indicate significant correlation (95% significance level).
Mean Sorting CaCO3 TOC Cu Zn Fe
Mean 1.00
Sorting -0.50 1.00
TCO3 -0.01 0.16 1.00
TOC -0.10 0.31 0.56 1.00
Lower intertidal sediments
Cu 0.06 0.07 -0.27 -0.15 1.00
Zn -0.14 0.37 -0.34 -0.07 0.46 1.00
Fe -0.31 0.36 -0.28 0.10 0.37 0.77 1.00
Mean Sorting CaCO3 TOC Cu Zn Fe
Mean 1.00
Sorting -0.52 1.00
TCO3 -0.35 0.52 1.00
TOC -0.24 0.32 0.76 1.00
Upper Intertidal sediments
Cu 0.00 -0.04 -0.23 -0.29 1.00
Zn 0.12 -0.11 -0.46 -0.52 0.55 1.00
Fe 0.20 -0.10 -0.41 -0.46 0.26 0.70 1.00
Heavy Metals
The concentrations of heavy metals in sediments of the study area are shown in (Fig.6). The concentrations of Zn for both lower and upper intertidal zone show the same distribution pattern.
For lower intertidal sediments Zn occurs in concentration varies from 4.38 to 73.25µg/g with an average of 22.01µg/g. On the other hand the concentrations for upper intertidal sediments fluctuated between 5.13 and 62.13µg/g with an average 26.95µg/g. The Cu exhibits values range from 0.0 to 50.00µg/g and an average of 10.61µg/g for lower intertidal samples. For upper intertidal sediments, the Cu concentration varies between 0.0 to 78.75µg/g with average value 13.01µg/g. The Fe content for sediments attributed to enrichment of sediment with iron minerals associated with terrestrial deposit. In the present study the high concentration of Fe for lower intertidal sediments is as high as 33763 µg/g and goes down to the lowest value as 1263µg/g with average value of 9814µg/g. While, the Fe concentrations for upper intertidal zone fluctuated between 89350 µg/g and 2350 µg/g with average value 15927 µg/g. Earlier studies by Santamaria-Fernandez et al.(2005); Svete et al.
(2001) and Alomary and Belhadj (2007) have reported the range of Fe between 3000-40820µg/g in some unpolluted areas. Whereas, studies by
Buykx et al. (2000); Sulivan and Taylor (2003) and Svete et al. (2001) have reported the higher values range between 51000-116000 µg/g for the polluted regions. Comparison of the results of the present study with the results of the earlier workers easily infers that the present lower and upper intertidal sediments can be considered as unpolluted with Fe.
Fig. 6. Distribution of heavy metals in the sediments studied.
Evidence of the dominance of a detrital (terrestrial, lithospheric) origin for this group of elements is given by the negative relationship between all the elements and the CaCO3 content in the sediments (Table 2). The detrital character of Zn is indicated by their high degree of correlation with Fe that is largely detrital in origin. This trend means that these elements are mainly transported and held within the lattices of the detrital minerals (Basaham et al., 2006).
From Table 4, it can be concluded that the average concentrations of Zn and Cu in the sediments of the present study was relatively lower than those of the other different environment. While, the Fe concentration was relatively higher than that reported by others. This behavior could be attributed to the impact of terrestrial and lithophelic origin.
Table 3. Comparison of the average element concentrations for studied sediments and those from different areas.
Location Zn Cu Fe Reference
Beach sediments in Saudi Arabia 22.01 10.61 9814 Present study Tidal sediments in Saudi Arabia 26.95 13.01 15927 Present study Jaddah tidal sediment 24 11.5 3850 Basaham et al., 2009 Sharm Obhur sediments 47 14 7200 Gheith & Hariri, 2010 Coast sediments for eastern Red Sea 39.16 15.64 - Pan et al., 2011 Egyption Mediterranean Sea coast 49.31 14.33 - Skaily, 2008
Assessment of Heavy Metal Contamination
Commonly, geochemical normalization of the heavy metals data to a conservative element such as Al and Fe is employed in order to identify anomalous metal concentration. In our case, we use metal enrichment factor (EF) as an index to evaluate anthropogenic influence of heavy metals in sediment and Geoaccumulation index (Igeo) to evaluate the heavy metal pollution.
EF is a geochemical index based on the assumption that, under the natural sedimentation conditions, there is a linear relationship between a reference (RE) element and other elements. It is preferable that a RE meets some criteria including: (I) High concentration in sediment, (II) free from anthropogenic contribution, (III) easily determined by analytical techniques and (IV) free from contamination during sampling (Chabukdhara & Nema, 2012). Elements which are most often used as reference ones are A1 and Fe. In this study, we did not analyze Al concentration in the sediments. Therefore, we used Fe as a conservative tracer to differentiate natural from anthropogenic components.
In fact, several authors have successfully used iron to normalize heavy metals contaminants (Mucha et al., 2003; Meza-Figueroa et al., 2009; Esen et al., 2010 and Seshan et al., 2010). The EF is defined as follows (Ergin et al., 1991):
EF = (Me/Fe) sample / (Me/Fe) Back ground
Where (Me/Fe) sample is the metal to Fe ratio in the samples of interest;
(Me/Fe) Back ground is the natural background value of metal to Fe ratio. In the present work the background values have been taken equal to metal concentrations of Sharm Obhur coast sediments according to (Basaham et al., 2006).
Zhange and Liu (2002) suggested that if an EF value is between 0.5 and 1.5 (i.e., 0.5≤ EF≤ 1.5), it suggests that the trace metals may be entirely from crustal materials or natural weathering processes. However, if a value of EF is greater than 1.5 (i.e., EF ≥ 1.5), it suggests that a significant portion of trace metal is delivered from non-crustal materials or non-natural weathering processes. Instead, the trace metals are provided by other sources, e.g., point and non-point pollution sources and biota (Klerks and Levinton, 1989 and Zhange and Liu, 2002).
The results from this study show that, in our study area, EF (Zn) ranges from 0.1 to 1.0 for lower intertidal sediments and from 0.1 to 1.4 for upper intertidal sediments while, EF (Cu) enrichment factor, ranges from 0.0 to 10 for lower intertidal sediments and from 0.0 to 5.9 for upper intertidal sediments. As shown in (Fig. 7) most of EF values of Cu and Zn are generally less than 1.5 (EF ‹ 1.5), suggesting that these metal contaminations in most of the study area are not significant. However, with respect to a specific site in study area, stations numbered 3, 10, 12, 14, 15, 16, 18 and 22 are contaminated by Cu and Zn as reflected by the enrichment factor values of these metals that are greater than 1.5 (Fig.7).
The reason behind these elevated values might be man’s activities along the coastal zone (municipal discharges, industrial development, tourism activities, desalination plants … etc.
Geo-accumulation index introduced by Müller (1979) is another geochemical criterion to evaluate heavy metal pollution in sediments and has been used since the late 1960s. In this study, the Igeo for studied sediments was calculated using equation:
Igeo= log2 {Cn / (1.5 Bn)}
Fig. 7. Enrichment factor of Zn and Cu in the investigated sediment samples.
Where Cn is the measured concentration of the examined metal (n) in the sediment and Bn is the geochemical background concentration of the metal (n). Factor 1.5 is the background matrix correction factor due to lithogenic effects. Müller (1981) has distinguished seven classes of geoaccumulation index (Table 4). In the present work, Bn values have been taken equal to metal concentrations of Sharm Obhur coast sediments according to (Basaham et al., 2006).
Table 4. Müller’s classification for the geoaccumulation index (Müller, 1981).
Igeo value Class Quality of sediment
≤ 0 0-1 1-2 2-3 3-4 4-5
≥ 6
0 1 2 3 4 5 6
Unpolluted
From unpolluted to moderately polluted Moderately polluted
From moderately to strongly polluted Strongly polluted
From strongly to extremely polluted Extremely polluted
Figure 8 shows sample percentage according to (Müller, 1981) for Zn and Cu. The results of Igeo values indicate that at most of the study stations Cu and Zn can be considered as unpolluted (Igeo<0) with the exception of few stations which fluctuated between class 1 (0< Igeo<1), Class 2 (1<Igeo<2) and class 3 (2<Igeo<3). For Cu about 4 –7% of the current samples fall in class 1, i.e. unpolluted to moderately polluted and about 8% fall showed moderately polluted (class 2). About 5% for lower
and upper intertidal sediments showed moderately to strongly pollute with Cu. Such contamination could be attributed to remains of woods and shipping activities and man’s activities along the coastal zone (municipal discharges, industrial development, tourism activities, and desalination plants). For Zn about 6% of the sediment samples fall in class 1.
Fig. 8. Distribution of metals according to Müller’s classification.
Conclusions
According to the enrichment factor (EF), indicate that most of EF values of Cu and Zn are generally less than 1.5 (EF < 1.5), suggesting that these metal contaminations in most of the study area are not significant. However, with respect to a specific site in study area, stations numbered 3, 10, 12, 14, 15, 16, 18 and 22 are contaminated by Cu and Zn as reflected by the enrichment factor values of these metals that are greater than 1.5 (Fig.7). The reason behind these elevated values might be man’s activities along the coastal zone (municipal discharges, industrial development, tourism activities, desalination plants … etc.
Also, the results of Igeo values indicate that at most of the study stations Cu and Zn can be considered as unpolluted (Igeo‹0) with the exception of few stations which fluctuated between class 1 (0< Igeo<1), Class 2 (1<Igeo<2) and class 3 (2<Igeo<3).
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