Environmental Aspects Of Semi-Closed Lagoons In The Sharjah Coastline During Spring/Neap Tides, Southern Arabian/Persian Gulf Coast

The lagoons of Sharjah represent an important economic asset to the region and are particularly vulnerable to pollutants released into the environment by wastewater and vessels' traffic. Given the paucity of information on water quality status in this system, we bring new insights into the water structure and nutrient distribution in the three man-made lagoons on the Sharjah coast. We investigated the lagoons from spring to neap tides in January 2020. The temperature and salinity varied between 20.8 and 19.7 degrees C and 37.8 to 35.8 g/kg, respectively, with a general decrease negative trend from outer to inner areas in Khalid lagoon. The dissolved oxygen levels varied between 7.2 and 10.8 mg/L, and was attributed to the input of cooler freshwater from the fountain in this lagoon. Increased turbidity levels, more evident in Al-Khan (6.0 NTU) and Mamzar (7.9 NTU), compared to Khalid (2.7 NTU), were attributed to current construction activities. Temperature and salinity reductions, together with high turbidity levels, were suggested to play a role in the increased chl-a concentrations towards the lagoons' inner areas. The eutrophication conditions found in Khalid and Al-Khan lagoons suggests a potential threat to the water quality, not evident in Mamzar. The variance in nutrient concentrations was largest for nitrate in all lagoons. The peaks in phosphate (150-160 mu g/L) was attributed to wastewater outfalls and may represent a risk to aquatic life in the lagoons as it can increase the chances of eutrophication or algal blooms. The change of nutrient levels, especially nitrate and phosphate, with that of salinity, suggests that conservative mixing plays a role in nutrient dynamics. However, a lack of significance between most nutrients and salinity implies the presence of other driving factors impacting the nutrients loads. Overall, as this study represents an important update on the status of water quality in the lagoons of Sharjah, the high spatiotemporal fluctuations in nutrient concentrations reveals the need for additional observations at different scale periods to better capture the short-long trends in water quality parameters. (c) 2021 Elsevier B.V. All rights reserved.