WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2013 13 Editor’s Note Lester Brown, President of the Earth Policy Institute and editor of the well-regarded State of the World yearbook series, published an article in July claiming that “the real threat to our future is peak water.” Peak water refers to limitations on the availability and use of finite freshwater resources in specific locations and is described by a characteristic bell-shaped curve. Although there has been widespread media coverage of peak oil, less attention has been devoted to peak water, which Brown believes may be upon us. The concept of peak water was elaborated in a seminal paper by Peter Gleick and Meena Palaniappan and published in PNAS in 2010. They define three classes of peak water. Peak renewable water occurs when water flow constraints limit total water availability over time. Most water used in agriculture and freshwater aquaculture is derived from diversions of surface flow, which is continuously renewed in the water cycle. Peak nonrenewable water occurs where production or withdrawals exceeds natural recharge rates of groundwater aquifers. It is characterized by an increase in supply to a peak, followed by a decline as the aquifer is depleted. This is the form of peak water referred to by Brown. Finally Gleick and Palaniappan identify a third type of peak water, peak ecological water, where total costs of ecological disruptions and damages exceeds the total value to humans of uses of that water. In countries that are highly dependent on groundwater for irrigation, constraints on water availability have led to declines in grain production, especially in the Middle East. Although food can be grown without oil, there is no substitute for water. Of course, water is an obvious and essential requirement for aquaculture. Brown focuses on large reservoirs of so-called “fossil” groundwater supplies in aquifers that recharge at a slow rate and that are effectively mined as a non-renewable resource. The three countries – China, India, and the USA – that produce half the world’s grain are among the 18 countries that are overpumping groundwater aquifers. The dependence on groundwater among the major grain-producing countries is variable. In China, 80 percent of grain is produced on irrigated land, but most is produced using surface water. The aquifer beneath the North China Plain has been severely overpumped. India is more dependent and thus more vulnerable to overpumping of groundwater aquifers. About 60 percent of grain is produced on irrigated land in India, but nearly all irrigation water is groundwater. Weak regulation of well drilling and aquifer overpumping represents a serious threat to food security in India. In the US, the area of irrigated grain production in the western Great Plains has declined as a result of overpumping of the Ogallala aquifer. Globally, aquifers are being overpumped in 18 countries containing half the world’s population. Rice is the main grain crop irrigated with groundwater, especially in China and India. Consumptive water use in rice farming is similar to that of conventional freshwater pond aquaculture as practiced in the main rice-growing countries. Of course, the area of rice farming dwarfs that of pond aquaculture. Nonetheless, these areas often overlap and constraints on the supply of water for rice farming will likely extend to pond aquaculture. Given that most farmed fish are produced in freshwater ponds, it seems possible that future expansion of freshwater pond aquaculture will be limited in areas where there are multiple competing interests for groundwater, acutely so in areas where pond aquaculture is based on nonrenewable fossil groundwater. Perhaps of greater concern in the long run is the effect of peak water on the production, price and availability of grains for animal feeds, including aquafeeds. Rice bran is widely used direct pond input and is incorporated into aquafeeds where available. Most wheat, corn, and soybeans are produced as rain-fed crops, although the area of irrigated corn is expanding. Thus, it seems that the supply of the main ingredients of aquafeeds is safe, at least for now, although peak water could be one of many factors that constrain grain production going forward. All of this discussion refers specifically to freshwater aquaculture, arguably the most important part of aquaculture because many millions of people, especially in Asia, are dependent on fish from aquaculture as their main protein source. As eloquently laid out by Patrick Sorgeloos in a feature article in this issue of World Aquaculture, this is an example of ‘food aquaculture.’ In part on the basis of future limitations on the availability of freshwater, Patrick argues for concerted development of the marine environment for aquaculture. We are not there yet, although peak water in some areas could push culture activities into the marine environment. Beyond the marine environment, we should be looking to develop more pond aquaculture in marginal lands, such as those with saline soils, and use ‘degraded’ water, such as irrigation tailwaters. The robust pond aquaculture sector for tilapia in Egypt is an excellent example of this. We also need to make the case for aquaculture as a first use of groundwater allocated to agriculture. Perhaps biosecurity is the most compelling argument for first use of groundwater. In any case, water use rights are complicated and allocation is highly politicized, so rational, science-based arguments are unlikely to determine making water policy. Although peak water has not yet had a demonstrable effect on the expansion of aquaculture, it seems likely that it will in some places in the future. Aquaculture will need to become a more efficient user of fresh water if it is to remain viable or expand in areas where food security is put in jeopardy as a consequence of peak water. — John A. Hargreaves, Editor-in-Chief Will “Peak Water” Mean Peak Aquaculture?
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