Selenium Determination, Distribution, Behavior, Sources, and Its Relationship to the Physico-Chemical Parameters in Coastal Polluted Lagoon along Jeddah Coast, Red Sea

Abstract

We determined the total dissolved selenium (TDSe) concentrations in the surface and bottom waters of Reayat Al-Shabab lagoon along Jeddah coast, eastern of Red Sea. The lagoon is a heavily polluted body water due to the dumping of untreated sewage effluents. Our aim is to understand the factors that control the vertical and horizontal distribution, behavior, and sources of selenium. The average concentration of the TDSe in the surface and bottom were 1.56 and 0.45 nM, respectively. The surface concentration of TDSe decreased from the eastern lagoon to lagoon mouth with the highest value of 2.51 nM near the eastern part. The annual selenium flux to the lagoon and the average selenium residence time were 1.0 kg/year and 31 days, respectively. Surface TDSe showed significant positive correlation with nitrate (R² = 0.60, P ˂ 0.05), reflecting its role in the biological process. In addition, the TDSe concentration significantly correlated well with chlorophyll a (R² = 0.70, P ˂ 0.05), indicating its role as a nutrient. The TDSe did not reach the toxic level of selenium, thus it can be utilized by marine organisms for normal growth. The bioavailability and mobility of dissolved selenium mainly depend on the dissolved oxygen availability (redox potential), so in this study, we suggest that in the surface water selenium has more mobility and bioavailability in comparison to bottom water. In the absence of strong and negative correlation of selenium with salinity, the concentration of selenium is mainly controlled by biogeochemical processes (conservative behavior) such as utilization by marine organisms, redox potential, and diffusion from sediments.