Environmental status and nutrients and dissolved organic carbon budget of two Saudi Arabian Red Sea coastal inlets: a snapshot statement

Two Red Sea coastal inlets situated on the Saudi Arabian western coast were visited 7 years after the implementation of a rehabilitation program including the official cessation of wastewater discharge, dredging of bottom sludge, and deployment of 28 air pumps to enhance water mixing and aeration. Visual observations indicated the presence of active sewage disposal points and apparent eutrophication. Chemical analysis of surface water supported this observation by providing measurable evidences, such as salinity lowering to about 30 and decrease of pH near the active effluents. Moreover, the extremely high concentrations of inorganic nitrogen (95 % as ammonium), phosphorus, and dissolved organic carbon are comparable to concentrations measured before the implementation of the program. Based on the apparent conservative behavior of phosphate, inorganic nitrogen, and dissolved organic carbon, concentrations of these variables at zero salinity were calculated and their budgets were estimated and compared with the measured quantities present in the surface mixed layer. The role of nitrogen and phosphorus as limiting elements was investigated using the nitrogen and phosphate ratio and the correlative plot of total inorganic nitrogen and phosphate against salinity. The pollution load, calculated using concentrations at zero salinity and nominal hydraulic flow of the effluents, amounted to 2,737 and 285 kg/day of inorganic nitrogen and phosphorus, respectively. Potential algal mass production that may result from the total assimilation of this nutrient influx is equivalent to 23-30 tons/day, which is several times higher than the direct organic matter input from the sewage effluents.