Desalination, the process of removing salt from seawater, is increasingly being used to address water scarcity around the world.
More than 2 billion people live in “water stressed” countries. These are territories where more than 25% of the resources of the fresh water available are extracted for human use each year.
Approximately 16,000 desalination plants now produce 35 billion liters of fresh water a year. And Jordan, a country located north of the Red Sea, is planning a large desalination plant in the Gulf of Aqaba that will increase its desalination capacity from 4 billion to 350 billion liters per year.
But desalination tends to be energy-intensive and produces saline wastewater called brine. Returning to the sea, brine can damage marine ecosystems. The investigation suggests that desalination may be making some bodies of water, including the Red Sea, Persian Gulf and Mediterranean, saltier.
We analyze whether current and future desalination plans pose a threat to salinity levels in the Red Sea and Gulf of Aqaba. For both bodies of water, the salinity increase is likely to be undetectable and less than natural seasonal variations, in which case it would not harm marine life.
An important marine habitat
The Red Sea is connected to the Indian Ocean at its southern end through a narrow, shallow strait. The Gulf of Aqaba branches off at its northern end and is connected to the Indian Ocean only through the Red Sea.
None of the water bodies have a freshwater inlet, so salinity levels are determined by evaporation and the flow of water in and out of the Indian Ocean. Water entering the Red Sea flows north, where it evaporates and cools, increasing its salinity and density. At the head of the Red Sea, this more saline water sinks and flows south as a deeper layer of water back to the Indian Ocean.
Between where water enters the Red Sea and where salinity peaks at the northern end of the Gulf of Aqaba, salinity naturally increases by 10% from about 36.8 to 40.6 practical salinity units (psu). One power supply is equivalent to 1g of salt dissolved in 1000g of water. Marine life in the region has adapted to the natural salinity level of its location.
UNESCO Natural Heritage
Several UNESCO Natural Heritage sites are located in the northern Red Sea, including the Sanganeb and Dungonab Bay marine national parks and Mukkawar Island. National parks are home to coral reefs, seagrass beds, mudflats, mangroves and beaches. These habitats have significant scientific and conservation value as they are home to a wide range of marine species, including the endangered dugong.
Most marine species can tolerate small variations in salinity but cannot withstand significant and sustained changes. the investigations reveal that the rates of photosynthesis and respiration in Stylophora pistillata , a species of Red Sea coral, are reduced by up to 50% when salinity levels increase from 38 psu to 40 psu. Most colonies of this coral will die if salinity is maintained at this level for an extended period.
Desalination versus the future of an even saltier sea
Our research used scenario analysis. It is here that various plausible future scenarios are modeled and their consequences explored.
The most extreme scenario we developed involved high population growth, rapid economic development and falling desalination costs in the Middle East. Nearly 10 trillion liters of water could be desalinated along the Red Sea coast by 2050 and over 2.5 trillion liters along the Gulf of Aqaba in that case.
A less extreme scenario assumed limited population growth and restricted domestic water consumption. Nearly 2 trillion liters of water could be desalinated in the Red Sea and over 560 billion liters in the Gulf of Aqaba by 2050.
For both scenarios, salinity in the Red Sea increased by less than 0.1%. This increase would be less than the natural seasonal variation in salinity levels and would likely be undetectable.
The Gulf of Aqaba, however, is smaller and more isolated from the Indian Ocean. Therefore, salinity in the northern Gulf naturally varies between 40.2 psu and 40.75 psu. We found that the high-growth scenario could increase salinity in the Gulf headwaters by 0.5%, from approximately 40.6 psu to 40.8 psu. But even this increase is close to the maximum increase in salinity caused by natural variability.
In contrast, the average growth scenario would produce less change than natural seasonal variation and would again be undetectable.
Desalination to tackle water shortages in the Middle East
Our research suggests that, if managed carefully, increased desalination rates may not harm marine ecosystems in the region. This is particularly important as there is likely to be considerable growth in desalination in the Middle East.
Saudi Arabia plans to build an entirely new city in the northwest of the country, called Neom, to accommodate 9 million people and water-intensive sectors such as agriculture by 2045. The city will depend on desalinated water from the Red Sea and the Gulf . from Aqaba.
Beyond the immediate vicinity of each desalination plant, increasing desalination rates are unlikely to affect broader salinity levels in the region. But good plant design and strict environmental regulations will continue to be essential to avoid environmental damage.
The plant’s outfalls, through which the brine is channeled to the sea, must ensure rapid dilution, dispersing the brine into the deeper water layer of the Red Sea. Ocean currents can carry the brine into the Indian Ocean, where it will dilute further.
Desalination will continue to grow around the world. If implemented carefully, it could be a crucial tool for dealing with water scarcity without harming fragile marine ecosystems.
This article was written by Jonathan Chenoweth, Senior Lecturer in Environment and Sustainability at the University of Surrey, and Raya A. Al-Masri, Resource Governance and Sustainability Researcher at the University of Surrey.
Republished from The Conversation under a Creative Commons license.
