Eutrophication sources, impacts and management: A case study from Abu Dhabi

Human activities and coastal development driven by economic growth in countries bordering the Arabian Gulf have increased marine pollution, including eutrophication. In response to growing concerns, the Environment Agency- Abu Dhabi initiated a long-term monitoring survey (2006 to 2019) to study the marine water quality of Abu Dhabi, including the Mussafah South Channel (MSC). This confined area is of eutrophic nature, under pressure due to receiving approximately 400,000 m³ of treated sewage per day and continuous algal blooms incidents with maximum concentration of 18 x 10⁷ cells l⁻¹. Observations made on physical, chemical, and biological parameters, such as temperature (18 -35 °C), salinity (28 – 70 psu), pH (5 to 9), and dissolved oxygen (0.02 – 13 mg l⁻¹) revealed abnormal conditions and a stratified water column. The nutrient values, particularly nitrate (2.90 – 866.06 Mol l⁻¹) and phosphate (1.68 -98.24 Mol l⁻¹), were many times higher than Abu Dhabi’s reference values (3.55 Mol l⁻¹ and 1.58 Mol l⁻¹, respectively) which confirmed its eutrophic nature. Algal blooms were frequently recorded, and were associated with widespread harmful impacts, including hypoxic events (oxygen levels of 0.02 mg l⁻¹), finfish kills (Nematalosa nasus) and subsequent loss of benthic organisms. The deterioration of water quality in the MSC is probably due to the anthropogenic activities, insufficient treatment of municipal and industrial wastewater discharges. Extensive sediment load may also have exacerbated the situation and contributed to eutrophication and subsequent alteration of the ecosystem. The sources, composition and consequences of nutrient enrichment along with the management actions are also discussed in detail.