64 Going to GROUND
Heightened demand for water resources means the world has turned its focus to groundwater.
BY TONY JONES
runs dry for part of the year. As a result, humankind is turning increasingly to groundwater as a resource. Like oil re- serves, the true extent of groundwater reserves is difficult to estimate. Because of this, most exploitation has been based on relatively unsophisticated exploratory methods and estimates of global re- sources based on limited data. Groundwater is generally rated as the
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second largest store of freshwater in the world, after the ice sheets and glaciers. It tends to be more conveniently located closer to the majority of the world popu- lation centers than ice resources, but its distribution and exploitable volumes depend on suitable rocks, as well as the climatic water balance. Many cities are heavily dependent on groundwater sup- plies, and much of the world’s agriculture would not exist without it, especially in the Middle East and North Africa. The most important property of
groundwater is that most of it is renew- able. It is normally recharged annually by rainwater and seasonal meltwaters that seep into the ground. However, some deep groundwater bodies are essen- tially “fossil.” Fossil groundwater bodies now being exploited in Libya and Saudi Arabia have received no significant re- charge since the wetter Pluvial Period around the end of the last ice age, some 10,000 years ago. In essence, this exploi- tation is unsustainable; it is mining a fi- nite resource.
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s the world population bur- geons, human demand for wa- ter continues to expand, while in contrast, one in ten rivers
But when is mining not mining? The
question is not easily answered, partly because of a lack of data, but more impor- tantly because of the natural variability of the climate. One year’s rainfall is rarely the same as the next, and apparently ran- dom fluctuations can create sequences of wet years or drought years; short re- cords can produce erroneous estimates. In addition to “random” fluctuations, cli- mates tend to operate in cycles ranging from two to 100,000 years or longer that superimpose upon each other in bewil- dering combinations. These cycles are semi-regular, but each varies in intensity and duration. The combination of these cycles and fluctuations makes estimat- ing average recharge rates very difficult. Indeed, there is no such thing as a stable average, which means that groundwater resources are forever changing. Overexploitation or “overdraft” is
the worst problem affecting present-day groundwater resources. Most of the west- ern U.S. is suffering moderate to high levels of overdraft. Falling water tables in the Ogallala aquifer extending from Nebraska to Texas have been a major concern for some time, with levels falling by a meter a year. Many major cities have also been overdrawing their groundwa- ter. A side effect of falling water tables beneath Tokyo and Bangkok has been land subsidence. Another critical problem affecting re-
sources is water quality. In some cases, poor quality groundwater is a natural phenome- non, but increasingly it is due to human pol- lution. Deep groundwater is naturally high in salts produced by chemical weathering of the rocks. The longer the water remains in the aquifers, the poorer the water quality. Specific impurities in groundwater are re- sponsible for human disease or poisoning, but perhaps the greatest worry is direct pollution from urban, industrial, and agri- cultural sources. While developed coun- tries are improving their control of urban- industrial sources through groundwater
Even in developed countries, ag-
riculture remains problematic, pollut- ing groundwater with nitrates and fe- cal material. The slower turnover time in groundwater compared with surface water means that natural cleanup takes much longer—a powerful reason for ac- cording groundwater the highest level of protection now. PE
TONY JONES is a Professor of Geography and Ear th Sciences, University of Wales, UK, and chairs IGU’s Water Sustainability Commission.
protection zones and the European Wa- ter Framework Directive, the developing world is not. Special concern focuses on emerging economies, where rapid eco- nomic growth, poor sewage treatment, and dirty industries are causing unsus- tainable pollution.
Testing samples of the soil and groundwater for water quality. Deep groundwater is naturally high in salts.
PLANET EARTH \\ WATER RESOURCES
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