Sources and gradients of nutrients in the Jeddah Metropolitan Area, Red Sea

Inputs and dispersion of nutrients from the Jeddah Metropolitan Area were studied within the framework of a bilateral project between Germany and Saudi Arabia (Development of a Coastal Monitoring System for the Sustainable Environmental Planning of Jeddah Coastline, Saudi Arabia).

Nährstoffquellen und -gradienten in den Küstengewässern von Jeddah, Saudi-Arabien
Stagnant city lagoons and nearshore areas receive a considerable amount of Jeddah's wastewater.

Duration: 2011-2013

The oligotrophic coastal ecosystem of the Red Sea with its coral reefs, seagrass beds and mangroves is particularly sensitive to nutrient pollution. Because of the absence of any permanent riverine inputs the discharge of wastewater may constitute a major source of anthropogenic nutrient inputs to the area and may contribute significantly to the overall nutrient budget of the Red Sea. With a population of 3.5 mill. the Jeddah Metropolitan Area is the main point source of wastewater to the Red Sea. 

Daily loads of total nitrogen and phosphorus amount to 6,600 kg TN and 2,200 kg TP with a share of 83 % for dissolved inorganic nitrogen and 33 % for dissolved phosphate. Steep gradients prevail nearshore, ranging from 2000 µM TN and 250 µM TP in the hypertrophic city lagoons to 6 µM TN and 0.4 µM TP in the adjacent oligotrophic water.

Verteilung des Gesamtstickstoffs und des Gesamtphosphors [µM] in den Küstengewässern von Jeddah, April 2011
Total nitrogen (TN) and phosphorus (TP) concentrations [µM] at local sources of nutrient inputs (scaled grey dots) and gradients in the coastal water in April 2011


A numerical water quality model has been developed in order to study the impact of anthropogenic wastewater discharge on nutrient dispersion and phytoplankton biomass in the coastal waters of Jeddah. The model is based on the Delft-3D modelling software and addresses the main transformation processes for nitrogen and phosphorus. Scenario runs were carried out assuming a future reduction in nutrient loads by 80 % as well as an increase of loads by 50 % according to the anticipated increase in population density by 2019.

Simulation der Chlorophyll-a-Konzentrationen im Oberflächenwasser der Bucht von Jeddah als Folge eines 50%igen Anstiegs der Nährstofffrachten
Simulated patterns of surface chlorophyll-a concentrations as a result of a 50 % increase in nutrient loads

The scenario simulations suggest that nitrogen load variations have a higher impact on chlorophyll-a levels than those of phosphorus. An 80 % reduction of nitrogen loads resulted in a 30 % decrease in phytoplankton concentrations in the near coastal area whereas an increase by 50 % resulted in an enhancement of phytoplankton biomass levels of about 100 %. It thus appears that a reduction of nitrogen loads would be a more efficient measure to mitigate eutrophication effects in the coastal ecosystem of Jeddah. As a secondary option it should be considered to dump the treated wastewater through extended multiport diffuser pipes towards the deeper water body exhibiting sufficient cross cutting currents to allow for a rapid dilution.

Research Division:

Coordination:

  • Dr. Karl-J. Hesse

Staff:

  • M.Sc. David Santiago Peña García
  • Dr. Norbert Ladwig
  • Technician Daniela Koch

Partner:

  • King Abdulaziz University, Jeddah, Saudi Arabia
  • CORELAB - Group Remote Sensing Systems

Funded by:

  • King Abdulaziz University, Jeddah, Saudi Arabia