Red Sea Coastline Research Articles

MEDITERRANEAN IMPRINT ON CORAL DIVERSITY IN THE INCIPIENT RED SEA (BURDIGALIAN, SAUDI ARABIA)

Abstract Globally, scleractinian coral diversity peaked in the Early Miocene (Burdigalian) and declined afterwards. In contrast to this global trend, scleractinian coral diversity in the Lower to Middle Miocene was low in the Red Sea, which had begun to open in the Oligocene and experienced its first marine incursion in the Burdigalian. Here, we report on coral diversity of reefs assigned to the Burdigalian to Langhian Wadi Waqb Member (Jabal Kibrit Formation) from outcrops exposed in the foothills behind the Red Sea coastline near Umluj, Saudi Arabia. Compared to the global records from the Paleobiology Database and the literature, the fossil record from the Wadi Waqb member suggests a relation of the taxonomic spectrum to the Arabian Gulf and the Mediterranean. No clear relation to the taxonomic spectrum to the Indian Ocean is observed. These faunal differences are consistent with the hypothesis that the young Red Sea was connected to the Arabian Gulf via the Mediterranean through the Gulf of Suez, but there was no connection between the Red Sea and the Indian Ocean because of the Afar mantle plume that uplifted the southern area of the Red Sea rift and blocked direct exchange of marine biota.

Consistent Symbiodiniaceae community assemblage in a mesophotic-specialist coral along the Saudi Arabian Red Sea

IntroductionThe Red Sea is a narrow rift basin characterized by latitudinal environmental gradients which shape the diversity and distribution of reef-dwelling organisms. Studies on Symbiodiniaceae associated with select hard coral taxa present species- specific assemblages and concordant variation patterns from the North to southeast Red Sea coast at depths shallower than 30 m. At mesophotic depths, however, algal diversity studies are rare. Here, we characterize for the first-time host-associated algal communities of a mesophotic specialist coral species, Leptoseris cf. striatus, along the Saudi Arabian Red Sea coast.MethodsWe sampled 56 coral colonies spanning the eastern Red Sea coastline from the Northern Red Sea to the Farasan Banks in the South, and across two sampling periods, Fall 2020 and Spring 2022. We used Next Generation Sequencing of the ITS2 marker region in conjunction with SymPortal to denote algal assemblages.Results and discussionOur results show a relatively stable coral species-specific interaction with algae from the genus Cladocopium along the examined latitudinal gradient, with the appearance, in a smaller proportion, of presumed thermally tolerant algal taxa in the genera Symbiodinium and Durusdinium during the warmer season (Fall 2020). Contrary to shallow water corals, our results do not show a change in Symbiodiniaceae community composition from North to South in this mesophotic specialist species. However, our study highlights for the first time that symbiont communities are subject to change over time at mesophotic depth, which could represent an important phenomenon to address in future studies.

Phytochemical Composition, Antimycotic and In Vivo Antiinflammatory Activities of Marine Algae Inhabiting South Jeddah Seashore, Red Sea, Saudi Arabia

The Red Sea coastline is known for its diverse range of seaweeds, which have been hypothesized to possess therapeutic attributes. The primary aim of this research was to evaluate the antifungal and anti-inflammatory characteristics of the ethanol crude extract obtained from two types of algae, namely Padina pavonica (P. pavonica) and Laurencia catarinensis (L. catarinensis) from the Red Sea. It was revealed from FTIR analysis of P. pavonica and L. catarinensis ethanolic extracts that the strong band at 3366 cm−1 and 3339 cm−1 corresponds to alcoholic O-H stretching in both extracts. GC-MS phytoconstituent profile of the extract was dominant with a wide range of chemical classes mainly steroids, terpenes, fatty acids, fatty acid esters, retinoid derivatives, alcohols, carotenoids and alkanes. The results of the antifungal activity assay indicate that P. pavonica had the strongest activity against Aspergillus fumigatus, with a mean value of 23.50 ± 0.55 mm. Similarly, L. catarinensis demonstrated significant antifungal activity against Candida albicans, with a mean value of 21.00 ± 2.64 mm. The hemolysis exhibited a positive correlation with the dosage of extracts, with an observed increase in hemolysis as the dosage increased. Besides the antiinflammatory activity of the algal extracts induced by carrageenan demonstrating a dose-dependent relationship between the inhibition of paw edema and the dosage of the extract.

Phytochemical Composition, Antimycotic and In vivo Antiinflammatory Activities of Marine Algae Inhabiting South Jeddah Seashore, Red Sea, Saudi Arabia

The Red Sea coastline is known for its diverse range of seaweeds, which have been hypothesized to possess therapeutic attributes. The primary aim of this research was to evaluate the antifungal and anti-inflammatory characteristics of the ethanol crude extract obtained from two types of algae, namely Padina pavonica (P. pavonica) and Laurencia catarinensis (L. catarinensis) from the Red Sea. It was revealed from FTIR analysis of P. pavonica and L. catarinensis ethanolic extracts that the strong band at 3366 cm−1 and 3339 cm−1 corresponds to alcoholic O-H stretching in both extracts. GC-MS phytoconstituent profile of the extract was dominant with a wide range of chemical classes mainly steroids, terpenes, fatty acids, fatty acid esters, retinoid derivatives, alcohols, carotenoids and alkanes. The results of the antifungal activity assay indicate that P. pavonica had the strongest activity against Aspergillus fumigatus, with a mean value of 23.50 ± 0.55 mm. Similarly, L. catarinensis demonstrated significant antifungal activity against Candida albicans, with a mean value of 21.00 ± 2.64 mm. The hemolysis exhibited a positive correlation with the dosage of extracts, with an observed increase in hemolysis as the dosage increased. Besides the antiinflammatory activity of the algal extracts induced by carrageenan demonstrating a dose-dependent relationship between the inhibition of paw edema and the dosage of the extract.

Risks Assessment of Potentially Toxic Elements’ Contamination in the Egyptian Red Sea Surficial Sediments

The potential impact of tourism, industrial, and urban activities on Egypt’s Red Sea coastline, which is well-known for its economic and environmental importance, was investigated at fifteen coastal sites. In the present study, the concentration of cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) in marine sediments from these sites, was determined using Inductively Coupled Plasma Mass Spectrometers (ICP-MS). In detail, various pollution indices, statistical analyses, and spatial distribution patterns were used to assess the pollution status, impacts of human activities, ecological risks, and sources of potentially toxic elements (PTEs) in surface marine sediment. A detailed comparison with up-to-date data was conducted. These sediments were composed predominantly of fine and very fine sands. Mean grain size distribution typically depends on the source of the sediment from the following two prime sources: terrigenous (autochthonous) and biogenic (allochthonous). The detected PTE mean concentrations were as follows: Fe > Mn > Zn > Cr > Ni > Pb > Co > Cu > Cd. Multivariate statistical analysis results revealed their close distribution and association. Cd and Pb levels in the studied area have been slightly impacted by anthropogenic inputs. According to the calculated pollution indices, although a minimal or moderate contamination degree was detected in the study area, it was determined that there was a low to moderate ecological risk. The slightly high degree of contamination and risk centered in the middle of the study area around phosphate mining and related activities. More attention should be given to the concentrations and sources of Cd, Ni, and Pb as the main pollution factors.

Sustainability Estimates of Coastline Fish Hatcheries in Saudi Arabia

AbstractThis study examined Red Sea and Arabian Gulf coastline fish hatcheries of the leading aquaculture companies in Saudi Arabia for future sustainability strategies. Evaluations were performed on seven marine fish hatchery facilities in 2021. The factors estimated were production capacity, existing infrastructure, main cultured fish species, source of broodstock and seed stock, and range of water temperature and salinity. Six of seven coastline marine fish hatcheries lacked broodstock capacity. The water supply to all hatcheries is adequate from the Red Sea and Arabian Gulf coastline. In five hatcheries, discharge limitations will serve as constraints in their expansion and development. A live food production section was absent in five hatcheries. Most of the cultured species in hatcheries were Asian Seabass Lates calcarifer, Gilthead Bream Sparus aurata, Sabaki Tilapia Oreochromis spilurus, and Sobaity Seabream Sparidentex hasta. Only two hatcheries produced fry, with an average monthly fry production of 500,000–1,000,000 individuals. The source of seed stock in five hatcheries depended on imports or other hatcheries. Sustainability strategies should focus on increasing broodstock capacity, live food production, and new culture species.

Empirically derived thermal thresholds of four coral species along the Red Sea using a portable and standardized experimental approach

AbstractGlobal warming is causing an unprecedented loss of species and habitats worldwide. This is particularly apparent for tropical coral reefs, with an increasing number of reefs experiencing mass bleaching and mortality on an annual basis. As such, there is a growing need for a standardized experimental approach to rapidly assess the thermal limits of corals and predict the survival of coral species across reefs and regions. Using a portable experimental system, the Coral Bleaching Automated Stress System (CBASS), we conducted standardized 18 h acute thermal stress assays to quantitively determine the upper thermal limits of four coral species across the length of the Red Sea coastline, from the Gulf of Aqaba (GoA) to Djibouti (~ 2100 km). We measured dark-acclimated photosynthetic efficiency (Fv/Fm), algal symbiont density, chlorophyll a, and visual bleaching intensity following heat stress. Fv/Fm was the most precise response variable assessed, advancing the Fv/Fm effective dose 50 (ED50, i.e., the temperature at which 50% of the initial Fv/Fm is measured) as an empirically derived proxy for thermal tolerance. ED50 thermal thresholds from the central/southern Red Sea and Djibouti populations were consistently higher for Acropora hemprichii, Pocillopora verrucosa, and Stylophora pistillata (0.1–1.8 °C above GoA corals, respectively), in line with prevailing warmer maximum monthly means (MMMs), though were lower than GoA corals relative to site MMMs (1.5–3.0 °C). P. verrucosa had the lowest thresholds overall. Despite coming from the hottest site, thresholds were lowest for Porites lobata in the southern Red Sea, suggesting long-term physiological damage or ongoing recovery from a severe, prior bleaching event. Altogether, the CBASS resolved historical, taxonomic, and possibly recent environmental drivers of variation in coral thermal thresholds, highlighting the potential for a standardized, short-term thermal assay as a universal approach for assessing ecological and evolutionary variation in the upper thermal limits of corals.

Dietary metal intake from four widely consumed marine fish species and its repercussions for human health at the west coast of Yemen

The concentrations of Cu, Zn, Cd, Pb, and As were measured in the muscles of four widely consumed fish species (Thunnus albacares, Rastrelliger kanagurta, Megalaspis cordyla, and Katsuwonus pelamis) collected from four locations at Yemen’s Red Sea coastline. The results exhibited that metals concentrations were significantly different (P< 0.05) between sites. Zinc revealed the highest concentration in the studied muscles, followed by Cu, As, Cd, and Pb. Fish of Al-Salif port (site 2) and Al-Kathib beach (site 3) showed the highest metal concentrations. Moreover, the edible tissues of R. kanagurta and M. cordyla bioaccumulated higher metals content in comparison to the other two studied species. Principal component analysis (PCA) exhibited that sampling sites were clearly separated into two distinct groups and indicated that anthropogenic activities might be the main source of Cd, Pb, and As. The target hazard quotient (THQ) values of the analyzed metals were in safe limits except for arsenic that showed risk values in most cases, demonstrating that consumption of the examined fish species may pose arsenic-related health risks. Regarding target cancer risk (TR) values, arsenic pollution poses a carcinogenic threat to fish consumers. The Zn and Pb concentrations resulted in the highest allowable daily consumption rate (CRlim) values compared to the other examined metals, whereas those based on As were the lowest. Generally, the consumption of the studied fish may pose both carcinogenic and non-carcinogenic threats to fish consumers at the study area. This study contributes valuable details about state of metal pollution in the studied species. It warns local residents about the health hazards of consuming these four commonly consumed and commercially valuable fish species.

The key role of conjugate fault system in importing earthquakes into the eastern flank of the Red Sea

This study aims to synthesize seismic observations with gravity and magnetic data and to suggest a new scenario on the development of the Harrat Lunayyir (HL) tectonic system on the eastern Red Sea coastline, Saudi Arabia. Gravity and aeromagnetic anomalies distinctly mapped the NE and NW trends, while the InSAR data depict a small NW–SE graben and an NW–SE dyke. High-resolution relocations, which are well-consistent with the focal mechanism solutions for events with magnitudes greater than 3.0, admit two distinctly fault styles of different orientations. Thus, leading to the NE and NW fault planes’ reactivation related to the Precambrian basement faults and the Red Sea rift system, respectively. The spatiotemporal distributions of epicenters and focal mechanism solutions suggest a new seismic deformation scenario of the 2009 earthquake seismic activity. The low static frictions of 0.2–0.35 obtained from the stress inversion indicates reactivation of preexisting faults in the respective seismogenic zones. The obtained results give rise to a swarm-like sequence of tectonic implications, two activated fault styles differently oriented, and an NE conjugate fault system inherited in the region, which plays a vital role in transferring the ambient stress regime into the Red Sea’s eastern flank.

Diatom Assemblages From Surface Sediments of Two Coastal Lagoons, the Central Part of the Red Sea, Saudi Arabia and Their Associated Environmental Variables

The composition and distribution pattern of diatom assemblages in the surface sediments of Sharm Al-Kharrar and Al-Shuaiba lagoons, situated on the central part of the Red Sea coastline of Saudi Arabia, were analyzed. A total of 191 diatom species from 53 genera were identified. A highly diverse diatom flora dominated by the genera Mastogolia, Amphora sensu lato, Lyrella, and Navicula sensu lato species was observed. Diatom species composition showed the dominance of the benthic forms over the epiphytic and planktonic ones, which can be attributed to the shallowness of the environments. The relationship between the recognized diatom taxa and measured environmental variables was explored using multivariate statistical techniques. Hierarchical ascending clustering and detrended correspondence analyses differentiated six representative diatom assemblages in each Lagoon. Canonical correspondence analysis revealed that grain size, organic matter content, and water depth appeared to be significant environmental factors affecting the distribution and structure of the documented diatom assemblages, while pH, salinity, and temperature were less influential. The majority of species recorded were polyhalobous benthic diatoms, accompanied by a limited abundance of mesohalobous and substantial amounts of oligohalobous forms, which are probably of allochthonous origin and resulting from freshwater input of near seasonal wadi streams and human activities. A comparison between the recognized diatom assemblages and the previously recorded taxa in surrounding areas was made.

Evaluation of the carbon sequestration capacity of arid mangroves along nutrient availability and salinity gradients along the Red Sea coastline of Saudi Arabia

Summary In the present work, we assessed the carbon sequestration capacity of mangrove forests (Avicennia marina) in relation to nutrient availability and salinity gradients along the Red Sea coast of Saudi Arabia. This was achieved through estimating the sediment bulk density (SBD), sediment organic carbon (SOC) concentration, SOC density, SOC pool, carbon sequestration rate (CSR) and carbon sequestration potential (CSP). The present study was conducted at 3 locations (northern, middle and southern), using 7 sites and 21 stands of mangrove forests (A. marina) along ∼1134 km of the Red Sea coastline of Saudi Arabia (from Duba in the north to Jazan in the south), all of which are in an arid climate. The correlation coefficients between the water characteristics and the first two Canonical Correspondence Analysis (CCA) axes indicated that the separation of the sediment parameters along the first axis were positively influenced by TDS (total dissolved solids) and EC (electric conductivity) and were negatively influenced by total N and total P. On the other hand, the second axis was negatively correlated with total N, total P, EC and TDS. The SOC pools at the northern (10.5 kg C m−2) and southern locations (10.4 kg C m−2) were significantly higher than the SOC pool at the middle location (6.7 kg C m−2). In addition, the average CSR of the northern (5.9 g C m−2 yr−1) and southern locations (6.0 g C m−2 yr−1) were significantly higher than they were in the middle location (5.0 g C m−2 yr−1).

Another look at the 2009 seismic activity, Harrat Lunayyir, Saudi Arabia

This study aims to recognize the influence of source- and path-effects on seismic spectra using the waveform data from the 2009 seismic activity, Harrat Lunayyir (HL), eastern flank of the Red Sea coastline, Saudi Arabia. This seismic activity is considered as a series of continuously evolving events reaching at some stage the maximum on 19 May 2009, with the largest shock of Mw 5.4, and then decayed. A total number of 218 events of magnitudes ML ≥ 2.0 were analyzed, which include the largest shock, 101 and 116 seismic events representing the seismic events within the early and decay stages, respectively. The data analysis using Frequency-time analysis revealed diversity patterns of frequency contents along the recorded seismic stations. Moreover, the modified WADATI diagram showed VP/VS variations of 1.7 ± 0.003 and 1.72 ± 0.002 before and after the occurrence of the largest-sized event among the HL seismic activity, respectively. Using the grid-search method to recover the space parameters representing the average source spectrum of each earthquake over the recorded seismic stations, estimates of source sizes and stress drops imply variations in self-similarity scaling relationship among the HL seismic activity. According to the results obtained from the current analyses, we propose a scenario began with an emplacement of seismic activity due to the local stress accumulation imports from an upward dike injection that is blocked by cooled and hardened magmatic materials in the upper crust from the earlier intrusions. The stress accumulation continued and was then released, at some stage, by the event having the maximum magnitude followed by seismic activities released due to stress relaxations.

Use of unmanned aerial vehicles for efficient beach litter monitoring

A global beach litter assessment is challenged by use of low-efficiency methodologies and incomparable protocols that impede data integration and acquisition at a national scale. The implementation of an objective, reproducible and efficient approach is therefore required. Here we show the application of a remote sensing based methodology using a test beach located on the Saudi Arabian Red Sea coastline. Litter was recorded via image acquisition from an Unmanned Aerial Vehicle, while an automatic processing of the high volume of imagery was developed through machine learning, employed for debris detection and classification in three categories. Application of the method resulted in an almost 40 times faster beach coverage when compared to a standard visual-census approach. While the machine learning tool faced some challenges in correctly detecting objects of interest, first classification results are promising and motivate efforts to further develop the technique and implement it at much larger scales.

Climatology of sea breezes along the Red Sea coast of Saudi Arabia

Long‐term near‐surface observations from five coastal stations, high‐resolution model data from Modern Era Retrospective‐Analysis for Research and Applications (MERRA) and high‐resolution daily sea surface temperature (SST) from National Ocean and Atmospheric Administration (NOAA) are used to investigate the climatology of sea breezes over the eastern side of the Red Sea region. Results show existence of separate sea breeze systems along different segments of the Red Sea coastline. Based on the physical character and synoptic influences, sea breezes in the Red Sea are broadly divided into three regions: the north and the middle Red Sea (NMRS), the Red Sea convergence zone (RSCZ) and the southern Red Sea (SRS) regions. On average, sea breezes developed on 67% of days of the 10‐year study period. Although sea breezes occur almost all year, this mesoscale phenomenon is most frequent from May to October (78% of the total sea breeze days). The sea breeze frequency increases from north to south (equatorwards), and sea breeze characteristics appear to vary both temporally and spatially. In addition to land–sea thermal differential, coastline shape, latitude and topography, the prevailing northwesterly at NMRS region, the convergence of northwesterly and southeasterly wind system at RSCZ region and the northeast and southwest monsoon at SRS region play an important role in defining the sea breeze characteristics over the Red Sea.

Mapping Mangroves Extents on the Red Sea Coastline in Egypt using Polarimetric SAR and High Resolution Optical Remote Sensing Data

Mangroves ecosystems dominate the coastal wetlands of tropical and subtropical regions throughout the world. They are among the most productive forest ecosystems. They provide various ecological and economic ecosystem services. Despite of their economic and ecological importance, mangroves experience high yearly loss rates. There is a growing demand for mapping and assessing changes in mangroves extents especially in the context of climate change, land use change, and related threats to coastal ecosystems. The main objective of this study is to develop an approach for mapping of mangroves extents on the Red Sea coastline in Egypt, through the integration of both L-band SAR data of ALOS/PALSAR, and high resolution optical data of RapidEye. This was achieved via using object-based image analysis method, through applying different machine learning algorithms, and evaluating various features such as spectral properties, texture features, and SAR derived parameters for discrimination of mangroves ecosystem classes. Three non-parametric machine learning algorithms were tested for mangroves mapping; random forest (RF), support vector machine (SVM), and classification and regression trees (CART). As an input for the classifiers, we tested various features including vegetation indices (VIs) and texture analysis using the gray-level co-occurrence matrix (GLCM). The object-based analysis method allowed clearly discriminating the different land cover classes within mangroves ecosystem. The highest overall accuracy (92.15%) was achieved by the integrated SAR and optical data. Among all classifiers tested, RF performed better than other classifiers. Using L-band SAR data integrated with high resolution optical data was beneficial for mapping and characterization of mangroves growing in small patches. The maps produced represents an important updated reference suitable for developing a regional action plan for conservation and management of mangroves resources along the Red Sea coastline.

Sensing coral reef connectivity pathways from space

Coral reefs rely on inter-habitat connectivity to maintain gene flow, biodiversity and ecosystem resilience. Coral reef communities of the Red Sea exhibit remarkable genetic homogeneity across most of the Arabian Peninsula coastline, with a genetic break towards the southern part of the basin. While previous studies have attributed these patterns to environmental heterogeneity, we hypothesize that they may also emerge as a result of dynamic circulation flow; yet, such linkages remain undemonstrated. Here, we integrate satellite-derived biophysical observations, particle dispersion model simulations, genetic population data and ship-borne in situ profiles to assess reef connectivity in the Red Sea. We simulated long-term (>20 yrs.) connectivity patterns driven by remotely-sensed sea surface height and evaluated results against estimates of genetic distance among populations of anemonefish, Amphiprion bicinctus, along the eastern Red Sea coastline. Predicted connectivity was remarkably consistent with genetic population data, demonstrating that circulation features (eddies, surface currents) formulate physical pathways for gene flow. The southern basin has lower physical connectivity than elsewhere, agreeing with known genetic structure of coral reef organisms. The central Red Sea provides key source regions, meriting conservation priority. Our analysis demonstrates a cost-effective tool to estimate biophysical connectivity remotely, supporting coastal management in data-limited regions.

Ancestral genetic diversity associated with the rapid spread of stress-tolerant coral symbionts in response to Holocene climate change

Coral communities in the Persian/Arabian Gulf (PAG) withstand unusually high salinity levels and regular summer temperature maxima of up to ∼35 °C that kill conspecifics elsewhere. Due to the recent formation of the PAG and its subsequent shift to a hot climate, these corals have had only <6,000 y to adapt to these extreme conditions and can therefore inform on how coral reefs may respond to global warming. One key to coral survival in the world's warmest reefs are symbioses with a newly discovered alga,Symbiodinium thermophilum Currently, it is unknown whether this symbiont originated elsewhere or emerged from unexpectedly fast evolution catalyzed by the extreme environment. Analyzing genetic diversity of symbiotic algae across >5,000 km of the PAG, the Gulf of Oman, and the Red Sea coastline, we show thatS. thermophilumis a member of a highly diverse, ancient group of symbionts cryptically distributed outside the PAG. We argue that the adjustment to temperature extremes by PAG corals was facilitated by the positive selection of preadapted symbionts. Our findings suggest that maintaining the largest possible pool of potentially stress-tolerant genotypes by protecting existing biodiversity is crucial to promote rapid adaptation to present-day climate change, not only for coral reefs, but for ecosystems in general.

A mitigation strategy for reducing flood risk to highways in arid regions: a case study of the El‐Quseir–Qena highway in Egypt

AbstractDuring the past 20 years, there has been a rapid increase in tourism development along the Red Sea coast of Egypt. In the resort of Hurghada, for example, the number of hotel rooms increased from a few hundred in 1989 to 35 000 in 2004, and the entire Egyptian Red Sea coastline has experienced growth. Accordingly, car and lorry traffic between the major cities of Upper Egypt and the Red Sea coast along the El‐Quseir–Qena highway has increased tremendously. The road provides access to tourist destinations and is an essential commuting route for workers. The El‐Quseir–Qena highway is subject to flash flooding, and several serious traffic accidents have occurred during flash floods. Therefore, this study performed an assessment of run‐off water and sediment yield for different parts of the El‐Ambagi basin using the Hydrologic Modeling System and the Kinematic Runoff and Erosion Model. In addition, the study aimed to determine the impacts of run‐off water and sediment yields on the El‐Quseir–Qena highway. The study proposed possible mitigation strategies for reducing flood risk and utilising the run‐off water to recharge the basin's alluvial, fractured‐carbonate, and fractured‐basement aquifers.

Impact of well intake systems on bacterial, algae, and organic carbon reduction in SWRO desalination systems, SAWACO, Jeddah, Saudi Arabia

The intake system can play a significant role in improving the feed water quality and ultimately influence the performance of downstream components of the seawater reverse osmosis desalination processes. In most cases, open-ocean intakes produce poor feed water quality in terms of the abundance of naturally occurring organic matter, which increases the risk of membrane fouling. An alternative intake is the subsurface system, which is based on the riverbank filtration concept that provides natural filtration and biological treatment of the feed water prior to the entry of the water into the desalination plant. The use of subsurface intakes normally improves the raw water quality by reducing suspended solids, algae, bacterial, and dissolved organic carbon concentrations. Therefore, the risk of biofouling caused by these substances can be reduced by implementing the appropriate type of intake system. The use of well intake systems was investigated along the Red Sea shoreline of Saudi Arabia in the Jeddah region. Data were collected from a seawater reverse osmosis (SWRO) plant with a capacity of 10,000 m3/d. The well system produces feed water from an artificial-fill peninsula that was constructed atop of the seabed. Ten wells have been constructed on the peninsula for extracting raw seawater. Water samples were collected from nearby surface seawater as a reference and from selected individual wells. The percentage of algae and bacterial removal by induced filtration process was evaluated by comparison of the seawater concentrations with the well discharges. Transparent exopolymer particles and organic carbon fractions reduction was also measured. The quality of raw water extracted from the well systems was highly improved compared with the raw seawater source. It was observed that algae were virtually 100% removed and the bacterial concentration was significantly removed by the aquifer matrix. The detailed analysis of organic carbon fraction using liquid chromatography-organic carbon detection instrument showed a high-percentage removal of the organic fractions consummate with the molecular weight. The results of this study can be used to improve the intake system design of existing SWRO facilities that might require expansion in future or new facilities that will be located along the Red Sea coastline.

Estimation of source parameters and attenuation using digital waveforms of Al-Ays 2009 earthquake, Saudi Arabia

On 19 May 2009, an earthquake sequence of M w = 4.8 occurred at 25.20°N 37.76°E about 60 km onshore of the Red Sea coastline, Saudi Arabia. In the present study, the digital waveform data from the largest four events were used to estimate the source parameters and attenuation characteristics along the source-to-station path in the Arabian Shield. A grid search technique, combined with an assumption of circular source model, was applied to find the best-fit spectral amplitude over the space parameters: long period spectral level (Ω 0), corner frequency (f 0) and asymptotic high-frequency fall-off (γ). Consequently, the spectral parameters were used to estimate source parameters: seismic moment, fault radius (assumed circular rupture model) and stress drop. Seismic moments are founded to be within the range of 2.34E+14 to 2.83E+16 Nm and their corresponding moment magnitudes range from 3.5 to 4.8; the fault radius ranges from 369 to 1,498 m, and stress drops are observed in the range of 8.7 to 32.0 b. The spectral slopes beyond the corner frequency displayed ω −2.4 to ω −2.6 behaviours in contrast with Brune's source model of ω −2. This finding requires more detailed investigations on large data sets to distinguish the behaviour mechanism of the spectral slopes at high frequencies. By taking the ratio between observed and calculated spectra, the attenuation curves for P and S waves were derived along the source-to-station paths. The preliminarily results exhibited high quality factors of Q α = 3,883 and Q β = 3,530 for P and S waves, respectively. To this end, the ratio Q β/Q α is founded to be slightly less than unity indicating that the body waves from source-to-station paths crossed a crustal volume that is partially saturated with fluids causing lower attenuation effect on P waves than on S waves in the Arabian Shield.