Industrial dumping impact on oxygen and nitrogen fluxes in Abu Qir Bay, Southeastern Mediterranean Sea

An input/output flux model was used for the technical assessment of the effects of the present as well as the proposed reduction in the discharge of a major wastewater (industrial and sewage) dumping site on the dissolved oxygen, and nitrogen regimes in the vicinity of the outfall. Existing data and field measurements were used to feed the model. During summer stratification characterized by maximum discharge, mass balance equations identified different fluxes of nitrogen and oxygen above and below the pycnocline layer, as well as in the top sediment layer of the receiving system. Parameters such as effluent discharge, atmospheric reaeration, organic matter decomposition, nitrification, photosynthesis/respiration, benthic nutrient regeneration, resuspension and particles deposition were used to represent the physical, chemical, and biological processes included in the model. Different scenarios for showing the impact of dumping on the receiving system were exercised. A 50% reduction in the amount of discharge keeps dissolved oxygen levels in the water column near saturation, accompanied by an increase in: 1) NH4+1 and NO3−1 concentrations below the pycnocline; and 2) a 16% increase in the productivity of the upper layer. Sediments appeared to be impacted with the discharge of oxygen demanding wastes, showing a 30-fold increase in organic content over baseline conditions

Hypoxia in the central Arabian Gulf Exclusive Economic Zone (EEZ) of Qatar during summer season

Abstract One of the most fascinating and unexpected discoveries during the Qatar University Marine Expeditions to the marine Exclusive Economic Zone (EEZ) of Qatar in 2000–2001, was the detection of a hypoxic water layer in the central region of the Arabian Gulf in waters deeper than 50 m. Hypoxia was defined as the region where the concentration of dissolved oxygen was less than 2 mg L−1. This article presents the discovery of hypoxia in the Arabian Gulf, based on samples collected (mainly during evening or night time) from vertical profiles along transects of the EEZ of Qatar and analyzed for physico-chemical properties, nutrients and chlorophyll-a. Hypoxia occurred in the summer months caused by an interaction between physical stratification of the water column that prevents oxygen replenishment, and biological respiration that consumes oxygen. Strong south-westerly winds (the SW monsoon) from June to September drive the relatively low-salinity nutrient-rich surface water from the Arabian Sea/Arabian Gulf (Sea of Oman) through the Strait of Hormuz into the central-Arabian Gulf, and this surface current penetration fertilizes the deep central-Arabian Gulf during the summer period. A strong seasonal pycnocline is formed between deeper waters at an ambient temperature of 20.9 °C and surface waters at 31.9 °C. This prevents the mixing of supersaturated O2 (>100–130%) water from the upper layer that would otherwise raise concentrations of dissolved oxygen below the thermocline, thus resulting in deep water hypoxia, i.e. dissolved oxygen levels of less than 0.86 ml L−1 at 17.3% saturation. These are the lowest values ever recorded for the Arabian Gulf.The calculated area of hypoxia is around 7220 square kilometers, and occurs in a layer about ≥15 m thick above the sea floor which extends toward the deep part of the Qatar Exclusive Economic Zone (EEZ). The biological consequences of this hypoxia on the sea floor are yet to be investigated