The southern margin of the Arabian Gulf is a ''classic'' shallow-water, evaporative, carbonate-producing setting. The sediments and early diagenetic products creating the ''Great Pearl Bank'' of the United Arab Emirates to the east and accumulating in the coastal regions of Qatar to the west have long been studied as modern analogs for ancient evaporitic carbonate deposits of the rock record. An integrated study measuring the chemistry of Qatar subtidal coastal waters, evaporating tidal-pond waters (to halite saturation), and meteoric pond waters was undertaken encompassing both the dry (fall) and wet (winter/spring) seasons of 2016-2017. Measured parameters included temperature, pH, dissolved oxygen, and alkalinity, as well as major-ion (Na þ , Ca 2þ , Mg 2þ , K þ , Sr 2þ , Cl -, and SO 4 2-) and stable-isotope (d 18 O and dD) composition. Initial concentration by evaporation (to~90 practical salinity units (psu)) is interpreted to drive minor diagenetic aragonite precipitation. Further evaporation initially causes minor aragonite dissolution followed by gypsum and halite precipitation. One pond showed evidence of ongoing replacive dolomitization interpreted to be driven by H 2 S formation and oxidation in association with microbial breakdown of organic matter. The stable-isotope composition of water in restricted ponds is a function of the degree of evaporation and dilution by meteoric waters during the wet season. Unexpectedly, beyond 350 psu, d 18 O and dD continue to rise reaching values greater than 12 and 60%, respectively. The slope of the d 18 O-dD regression line exhibits no differences between dry and wet seasons.During collection of coastal waters (up to~90 psu), live Pirenella cingulata (previously Cerithidea cingulata) gastropods were collected and their shells analyzed for d 18 O and d 13 C, as well as Sr 2þ and Ca 2þ concentration. The d 18 O of water and Pirenella from the same sample site exhibits a strong correlation (R 2 ! 0.85) with a slope of~1, suggesting that the shells may be a useful chemical archive for the isotopic composition of past oceans. The d 18 O and d 13 C of the shells correlate positively, likely reflecting greater sequestration of 12 C into organic matter in more restrictive evaporative settings. The intercept of the d 18 O and d 13 C correlation shifts between dry and wet seasons, and is interpreted to reflect average seawater temperature differences during recent growth. There is also a strong correlation (R 2 ! 0.85) between shell d 18 O and measured water salinity, reflecting their mutual control by degree of evaporation. The Sr 2þ content of the gastropods does not correlate well with any measured oceanographic parameter, or show evidence of systematic seasonal change.

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A mechanistic model was developed to assist with design of constructed wetlands intended to treat industrial wastewater in the Arabian Gulf region. The model is deterministic in nature and thus allows explicit evaluation of the fate and transport of wastewater constituents throughout constructed wetlands to assess their efficacy in treatment. Although the model was developed for the purpose of evaluating treatment wetlands in the hot and arid climate of the Middle East, the model is generalized in order to allow users to simulate a wide range of climates, any type of wetland, with any configuration, and any selection of material and plants. The model simulates the majority of physical, chemical, and biological processes that could occur in wetlands that are responsible for the removal of constituents. The model is designed to be flexible enough to allow the simulation of any number pre-selected constituents or other constituents of the user’s choice made based on the quality of influent. The model relies on a large body of existing literature to formulate each process. The model development discussed in this report and the resulting model, CWM, is considered “in progress”. During the present stage, the model framework and algorithms have been developed and made functional. Subsequently, model formulations will need to be validated, model limitations analyzed and addressed, and model refinements made, before and during use in full-scale operations and design. As such, it is recognized that the present stage of model development is “experimental”, and future refinements of the model are anticipated. Model results at this time consist of evaluation of key model features and how they perform in Middle Eastern climates.

Chlorine is extensively used as a powerful oxidizing agent in the countries surrounding the Arabian Gulf for water treatment and biofouling control. Its usage has been increasing significantly as demand for water grows considerably both in industry and for domestic use. This is due to the fact that it is a well-tested technology, has had a history of long-term worldwide industrial use and is of acceptable cost. While the Arabian Gulf waters support a range of coastal and pelagic marine habitats including mangrove forests, seagrass meadows and coral reefs, marine organisms in these waters are living close to their tolerance limits due to the extreme environmental stressors like temperature and salinity. Anthropogenic stressors such as chlorine may further exacerbate these natural stressors. In seawater, chlorine produces a mixture of hypochlorous acid and hypochlorite ion. These rapidly react with the bromide ion to form a mixture of hypobromous and hypobromite ion. Total residual oxidants formed by chlorination although are short lived and not persistent in seawater, they can be quite toxic. In the present study, toxicity data were obtained from 7 acute toxicity tests and 3 chronic toxicity tests using Arabian Gulf aquatic species from different trophic levels. The study also examined the effect of temperature and developmental stages on toxicity of chlorine. Furthermore, differences in the species sensitivity distribution between native and non-native species were compared. The main finding of the study showed that there was no significant difference between native and non-native species for chlorine toxicity. This would suggest that toxicity data from different geographic region can be used in deriving site- specific ecological risk assessment of chlorine. Keywords: Chlorine; Arabian Gulf; acute toxicity; chronic toxicity; risk assessment; species sensitivity distribution;