By César Guerrero and Antonieta Valenzuela

One of the main primary food supply sources in Northwestern Mexico and Southwestern United States is the agricultural area of Baja California, especially the San Quintín Valley, where water is undoubtedly the fundamental resource for agriculture.

Constant food demand and depletion of primary resources used for agricultural production force farmers in the area to use technologies that help them meet said food demand quickly and efficiently. 

Quality standards required in water available for agriculture are not met due to the absence of atmospheric precipitation and the excessive groundwater extraction in the San Quintín Valley. 

The salt and chemical concentration in brine can be toxic for marine species and the environment. Photo by Enrique Alfaro.

The effects of saltwater intrusion into the groundwater levels—from which water for agriculture is extracted—are irreversible; water with high concentrations of salts is not ideal for agriculture and it reduces (or even prevents) the performance of agricultural production.

Due to the undeniable need of maintaining agricultural production and the inability of providing faster methods of groundwater recharge, the technology of desalination plants is now being used to solve the problem in the short term, but with negative—and sometimes irreversible—effects that have to be considered when they are evaluated and implemented.

The desalination process consists in withdrawing large volumes of seawater and filtering it for irrigation, industrial processes, agriculture or human use. On average, a desalination plant withdraws 2 gallons of seawater, from which it produces 1 gallon of desalinated water (Cooley et al. 2013).

Currently, there are at least 11 brine discharge locations registered in the San Quintín Bay. Photo by Enrique Alfaro.

Most desalination plants use reverse osmosis technology, which applies pressure to separate salt from seawater by passing it through semi-permeable membranes; wastewater (brine) is a result of this process and is later discharged back into the sea (Cooley et al. 2013).

Brine has a much higher saline concentration than that of the sea, and it can even present higher temperatures. It is composed of large quantities of suspended solids, variable pH and dissolved salts, as well as chemicals used during the desalination process like detergents, coagulants (ferric chloride), anti-scaling agents (polyacrylate), anticorrosive agents (sodium bisulfite) and biocide (sodium hypochlorite) (Mauguin et al. 2005). This salt and chemical concentration in brine can be toxic for marine species and the environment.

Currently, there are at least 11 brine discharge locations registered in the San Quintín Bay. Their salinity levels reach up to 62,000 mg/L, almost duplicating the average seawater salinity of 35,000 mg/L.

The impact on the marine environment can be negative when the brine discharge zones coincide with sensitive ecosystems like the San Quintín Bay. Photo by Enrique Alfaro.

The impact on the marine environment can be negative when brine discharge zones coincide with sensitive ecosystems, closed and shallow sites with a high concentration of marine life (Latterman & Höpner, 2008), as well as with shallow areas with low wave energy or sites of ecological importance like wetlands and seagrass beds.

Likewise, marine resources in the areas close to desalination plants can be affected by the quantity and quality of the brine; organisms that are found near the discharge areas can even be killed (Arreguin & Martin, 2000), causing massive mortality in sessile species or species of limited mobility that indirectly affect the food web and energy exchange to superior links in the food chain.

This can also cause a decrease in productivity and seaweed photosynthesis, diminish marine productivity and affect phytoplankton (Arreguín & Martín, 2000), which is essential in the food chain and plays an important role in the regulation of carbon dioxide levels in the atmosphere.

Wastewater discharge into the ocean near Laguna Figueroa, Baja California. Photo by Enrique Alfaro.

Good management of wastewaters (brine) should not have any consequence, but bad management has a significant negative effect that has to be taken into account in the decision-making process, especially regarding a semi-closed water body like the San Quintín Bay; with the accumulation of brine discharges in the bay, the negative impact on water quality would be immediate.

The problem lies in the bad use or disposal of brine, since most of it is discharged back into the sea or directly to the ground, where it accumulates and dries up, creating salt crusts that make any type of plant growth impossible in those grounds.

Another one of the most significant threats to the environment related to the desalination of seawater is the entrainment and impingement of organisms in the desalination process (Cooley et al. 2006), because as Correa (n.d.) states: “Seawater is not just a simple saline solution, it is actually an active biological environment that, besides containing salts, it also presents different types of molecules, particles and living organisms.”

In the desalination process, entrainment is mainly associated with fish eggs and larvae, plankton, crustaceans and seaweed propagules that inhabit the environment and that are entrained by the current of water flow. On the other hand, the impact of impingement is associated with adult fish or crustacean species. These are entrained by the adduction structures and hit the filter barriers or are collected by the structure’s cleaning systems (Vásquez et al. 2008).

When brine is discharged on the ground, it forms salt crusts that make any type of plant growth impossible. Photo by Enrique Alfaro.

The effects of brine discharges will not only be seen on San Quintín Bay’s wildlife and the development of its aquatic life, but also on the production activities that take place in the bay such as bivalve mollusk cultivation, hunting activities, and commercial and sports fishing.

There are different technologies and techniques that allow adequate management and disposal of brine; however, given that the technology used in desalination plants is relatively new in Baja California and Mexico, there are no current regulations that control them, which results in bad practices, no mitigation actions and, mainly, no preventive measures for their impact.

For this reason, it is crucial to take preventive and protection measures for the areas of ecological importance that are being affected by the inappropriate use of reverse osmosis technology and for not taking its ecological repercussions into account. 

References

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