4.1.1 Environmental Impacts

Desalination is considered an expensive and often environmentally harmful process. However, constant innovations in water treatment processes make it possible to produce good quality freshwater from seawater at lower costs. Non-economic concerns, such as environmental impact and energy consumption, also benefit from those innovations (Tsiourtis, 2001; Boutkan and Stikker, 2004).

Among the major concerns are: (1) high production costs; (2) energy intensive process; (3) desalination plants are considered heavy industry plans; and (4) by-product brine represents a threat to the environment. However, in the last five years all these issues have been studied and addressed resulting in major improvements in the process (Tsiourtis, 2001; Boutkan and Stikker, 2004). Because desalination plants have the potential of affecting the environment in several ways, it is extremely important to choose the best location to build a desalination plant in order to minimize these impacts on the surrounding natural habitats.

Some of the environmental impacts resulting from a desalination plant will be restricted to the construction phase, and other will arise during the operation phase. The emission load and its impact are site specific, and depend on the type and size of the plant. The local environment’s sensitivity also plays a role in determining the extent of the potential damage that the plant may inflict. Höpner and Windelberg (1996) divided the coastal sub-ecosystems of the Arabian Gulf into 15 categories according to their sensitivity to the effects of desalination plants (Table II). Some of these sub-ecosystems are comparable to the ones present in the Loreto region like the rocky coasts, estuaries and lagoons, and seaweed bays and shallows.

Land use and construction

There is an advantage of placing the desalination plant close to the shoreline for engineering and economic reasons. However, in areas like Loreto where shoreline properties have great real-estate and environmental value, disagreements may arise on where the optimal site for a desalination plant may be. The land requirements of a desalination plant include the area of the plant, the marine pumping station, corridors for the pipe system, and water pools (Einav and Lokiec, 2003). For example, a plant that produces 100 million m3/yr occupies an area of approximately 25 acres. Coastal areas may become sites for industrial plants and pumping stations rather that areas dedicated for recreation, tourism, or conservation purposes (Einav et al., 2002; Einav and Lokiec, 2003; Qutob, 2004).

Desalination plant infrastructure includes all infrastructures on land plus all pipelines for water intake and byproduct discharge. Construction of water intake structures and pipelines for feed water and concentrate discharge may cause disturbance to environmentally sensitive areas (Einav and Lokiec, 2003; Younos, 2005). This initial impact is temporary and confined to the location of the works, but it may be significant especially in rocky habitats and coral reefs. The extent of the damage is a function of the level of disturbance to the environment and the sensitivity of the natural habitats (Einav et al., 2002). To minimize impacts on the seabed and marine life during this stage it is important to select carefully the route of the pipelines, and avoid the use of explosives during the building process (Younos, 2005).

Energy consumption

Energy represents between 25-40% of the total cost of desalinated water because the process of separating fresh water from salts and minerals requires great amounts of energy. The plant’s energy consumption is a function of the salt concentration and temperature on the feed-water, the quality of the water produced and the desalinating technology being used. For this reason it is very important to consider the availability of energy, the cost of production, the environmental effects and the desalination process to be used (Tsiourtis, 2001; Einav and Lokiec, 2003).

Desalination plants can operate using non-renewable or renewable energy. Fossil energy, a kind of non-renewable energy, can be in the form of thermal or electrical energy, but it has the disadvantage of producing greenhouse gases. The state of Baja California Sur receives a great deal of solar energy , with the potential of producing between 5 and 6 Kwh./m2/day; and on the western coast of the state there is the potential of producing 300 to 400 Watts/m2 through wind power, with an estimated 3,000 MW of wind power for the state (Lamp, 2005). Renewable energy however, such as geothermal, wind, solar and hydropower have limitations for application in the desalination processes and their use is very limited (Tsiourtis, 2001).

Groundwater contamination

Groundwater aquifers run the risk of being contaminated when desalination plants are located nearby. Pollution may occur during the building process, when drilling is being done to install feed-water pumps. Leakage from pipes is also a point of concern since feed water and concentrated brine may percolate underground causing damage to the aquifers or the subsurface interflow balance (Einav and Lokiec, 2003; Younos, 2005).

Feed-water intake

There are impacts associated to the extraction of large quantities of water on marine habitats and organisms. Screens are often provided between the intake structure and the feed-water pumps in order to prevent debris and marine organisms from entering the desalination plant system. In general the screens have a mesh of 5 mm so that large organisms cannot enter, however water suction can cause organisms to collide with the screens and it can still pull smaller organisms into the feed-water system (Morton et al., 1996).

Small organisms, such as phytoplankton, zooplankton, eggs and larvae are entrained when water is drawn from the natural environment. This can lead to a decrease in recruitment to the local habitat, as well as a decrease in the overall productivity of the ecosystem. Therefore, commercially important species can be affected, and the magnitude of the impact is related to the abstraction rate and the importance of the area as a potential nursery (Morton et al., 1996).

Power plants have water intake structures very similar to those used by desalination plants and they are used to draw water from ocean and rivers to cool down the system in a process called once-through cooling. Studies show that power plants that use sea water for cooling damage the coastal ecosystems (Clean Air Task Force, 2004; Rodgers, 2006). The high mortality caused by water intake structures has contributed to the collapse of some fisheries in some areas. For example, a series of power plants located on New York’s Hudson River were found to reduce nearly 80% of certain fish species in some years. Studies from Delaware, Florida and Texas show that annual recreational and commercial fish losses from power plant intakes have been estimated at tens of millions per year (Clean Air Task Force, 2004).

Thermal impacts

Elevated temperatures can alter the concentration of dissolved oxygen in the water restricting the life forms to only those that can exist at low oxygen levels. Extreme temperatures may result in death, while sublethal temperatures can modify the rate at which biological processes occur, thus influencing movement, onset of maturity, life stage development, and growth and size. At a species level, high temperatures may lead to changes in individual abundance and population diversity (Morton et al., 1996).

Chemical impacts

Desalination plants can generate air and water pollution. Although the focus of this paper is on the marine impacts, we can briefly mention that air pollutants result from fuel combustion, like carbon monoxide, nitrogen oxides, unburned hydrocarbons and sulphur oxides (Al-Mutaz, 1991). Water pollution is caused by the disposal of the brine. The constant discharge of brine represents a source of pollution; therefore it is important that the point of discharge be located far away from beaches or areas used by locals and tourists for recreational activities and fishing (Einav et al. 2002).

Besides the thermal and saline pollution from brine discharge, there can also be toxic effects caused by different chemicals used in pre and post treatment processes (Al- Mutaz, 1991; Einav et al., 2002). Feed-water is pretreated with additives to control scaling, fouling and corrosion, and the types and amounts of these chemicals depend on the technology used and quality of water produced. Although the levels of these chemicals are relatively low and generally do not exceed 10 ppm, some are known to affect marine organisms. Chemicals used in desalination plants fall into three categories: Biocides, scale control and anti-foams (Morton et al., 1996; Younos, 2005; Ruiz, 2005).

Concentrate (brine) discharge

Desalination plants generate clean water and a byproduct consisting of concentrate, also known as brine, which is usually discharged back into the sea. Concentrates are high in salinity and may contain low concentrations of chemicals and elevated temperatures. Characteristics of the brine depend on the type of desalination technology used and proper disposal can mitigate the concentrate’s impact on the marine environment (Ruiz, 2005; Younos, 2005).

The main environmental impact caused by desalination plants is caused by the discharge of the resulting brine. The concentration of the brine can be up to double that of natural seawater. The salts in that concentrate are the same that are present in the feed water, but they are at higher concentrations. In plants using reverse osmosis for example, discharge concentration is 30-70%, or 1.3-1.7 times that of the original seawater. The magnitude of this impact depends on environmental and hydro-geological factors like the concentration of the brine, discharge rate, bathymetry, wave action, and currents among others. All these factors determine how much the brine mixes as it is discharged and the area it will affect (Einav et al., 2002; Einav and Lokiec, 2003).

Despite the increase in desalination plants worldwide, there have been few studies dealing with the effects of hypersaline brine inputs on benthic communities (Raventos et al. in press). The amount of concentrate produced is a factor of the desalination process’ recovery rate (product water/feedwater) (Younos, 2005). It is important to carry out surveys of fish and benthic communities in order to monitor the effects of the brine discharge.

Density is a critical parameter that needs to be considered when analyzing the impacts of brine on the environment. Brine has a higher density than freshwater and seawater due to increased salt concentrations. When it is disposed into the sea it forms a plume of highly saline seawater that sinks to the sea floor causing damage to organisms living around the discharge point (Einav et al., 2002; Einav and Lokiec, 2003; Younos, 2005).

The effect seen on marine biota is related to the increase in salt concentration in the surrounding water. Salinity values in most seas and oceans vary between 32-38‰ and most marine organisms are adapted to this range (Einav et al., 2002); however brine can reach salinity values of up to 68-90‰ (Ruiz, 2005). The combination of local characteristics, such as sea floor topography, currents and waves, will determine the way brine moves in the water and the extent of its impact (Einav and Lokiec, 2003; Ruiz, 2005). Brine forms a dense mass of water over the bottom that moves along the steepest floor inclinations and because of the great differences in density, water stratification makes it hard for dilution to take place. These two conditions determine the distance the hypersaline water mass travels (Ruiz, 2005).

Marine organisms exist in an osmotic balance with their environment so an increase in salinity may result in dehydration of cells and even death. Sensitivity to salinity fluctuations varies from species to species; some species are able to tolerate higher salinities after a period of acclimatization. Organisms that are most vulnerable are larvae and young adults, as well as benthic organisms, in particular sessile species (Einav et al., 2002; Ruiz, 2005).

Systematic monitoring, although crucial, is rarely done and so data on the impacts of hypersaline inputs on benthic communities and other marine organisms is rare (Ruiz, 2005; Raventos et al., in press). A monitoring program of a desalination plant in Dhkelia, Cyprus showed that coastal communities have suffered some type of damage, including the disappearance of some species due to higher salinity levels (Einav et al., 2002). In Egypt’s Red Sea coasts, specifically in the Hurghada area, fish populations have been reduced and in some cases even disappeared due to the brine discharge. Planktonic species, which are especially vulnerable to changes in total dissolved solids (TDS) and water temperature, have also disappeared from the area around the desalination plant (Mabrook, 1994).

In some cases, the natural conditions altered by the brine discharge have caused changes in the communities found in the vicinity of the discharge area. In Antigua, for example, there were no live barnacles within the vicinity of the plume where salinity reached 40 ppt, however Enteromorpha, a green alga adapted to polluted waters that is also common in the Gulf of California, was very abundant in the area (Blake et al., 1996).

Changes in communities not only imply the disappearance of a species and an increase in abundance of another. A change in community structure can result in a change in the entire ecosystem. In a study focusing on the impacts of desalination plants on benthic communities, Ruiz (2005) describes how concentrate discharge from the plants has affected entire communities of the Mediterranean seagrass Posidonia oceanica. This is an architectural species that provides suitable habitat for many other species of organisms; however it has been affected over the past decades and has decreased in abundance thus affecting the structure of the entire community. As Posidonia decreases so do many of the species that depend on it for food and shelter.

Seagrass beds, seaweed beds and mangrove flats are among the most sensitive habitats. Beds of the brown seaweed Sargassum are common on the shallow rocky shores of the Loreto region. Sargassum is also an architectural alga that grows seasonally and creates a unique habitat for many species that use it to find food or shelter. For instance, they are a critical nursery habitat for the leopard grouper (Mycteroperca rosacea). Any decrease in abundance of Sargassum beds will cause a decrease in the recruitment of the leopard grouper (Aburto-Oropeza et al., in prep.).

Mangroves, considered critical habitats for many species, can also be found in some areas of the region. Although they form small patches on some islands, they are more abundant along the coast, especially in places like Puerto Escondido, Nopoló and San Bruno. According to Table II mangroves are considered to be the most vulnerable to brine discharge (Raventos et al. in press; Dome, 2004).