Relationship of geology and pollution to potable groundwater resources in three South China coastal provinces

The annual amount of rainfall in the tropical and near-tropical parts of south China’s Guangdong, Fujian, and Hainan provinces is large yet their potable ground-water resource is insufficient.  The average annual rainfall in these coastal provinces is about 56 to 80 inches (1400-2000 mm) most of which falls during the summer monsoon season of May to December; during the six-month winter monsoon rainfall may only reach 6 to 12 inches (150-300 mm).  The hilly and mountainous areas here are composed largely of granite and other associated igneous and metamorphic rocks (Figure 1), rocks which are hard, dense, have low permeability and few pore spaces to hold groundwater.  The water that does collect in them is held in small, widely scattered cracks and joints.  As a result, heavy rainfall runs off granitic hills quickly into surrounding, low-lying farmland, sometimes causing damaging floods and severe soil erosion.  Deforested hills add to the severity of the problem.

These provinces have a combined population of at least 150 million people (2010 China census), about half that of the entire United States.  Guangdong, the size of the U.S. state of Missouri, has a population of 104 million.  To provide for water needs, China has constructed many dams and reservoirs among the granite hills.  The reservoirs fill during the rainy, summer monsoon season and are depleted heavily during the dry, winter monsoon season and other periods of drought.  (Limestone and dolostone karst areas of lesser areal extent also exist in these provinces but are dealt with separately in this blog in, Problems South-China farmers face in a carbonate-rock terrane.)

So.Chinagranitemap

Figure 1.  Map shows the general distribution of exposed, granitic rocks in three coastal China provinces.  Such areas of Guangdong, Fujian, and Hainan have insufficient potable ground-water resources (Source: Geol. Survey of China maps.)

In contrast, alluvial sediments cover much of the flat, low-lying farmland lying between the numerous granitic hills.  Without expensive drilling equipment, a farmer relies largely on hand-dug wells to reach shallow groundwater.  This ancient process requires the use of hand tools to dig a hole deep enough in soft ground to penetrate the water table, and then lining the well’s sides with bricks or stones to prevent collapse.  Lastly, the well opening is covered with a protective wood or cement cap.  Simple machinery might be used for the well-digging process but this expense may lie beyond the small-farmer’s means.

Because the ground-water table falls during the dry season as well during times of drought, such wells may run dry and require deepening.  Similarly, water levels in the wells rise during the wet season.  The water in the valley-filled, alluvial sediments and the water in local waterways are all part of one, interconnected system.  Thus, what happens to water levels in wells happens to water levels in the local streams and rivers and vice versa.  Consequently, polluted river water carrying industrial, urban, or farm wastes can move through the alluvium into water wells.  Then too, commercial fertilizers, herbicides, pesticides, and agricultural wastes applied to farm fields move downward to groundwater, into wells, and into nearby streams and rivers.  The Water Resources Department of Guangdong and Xinhua in 2007 reported that although Guangdong has a plentiful water supply much of it is unfit for human consumption because of pollution; forty percent of Guangdong’s rivers are too polluted for use as drinking water and about 60 percent of the province’s waste water is released untreated.  The Chinese Ministry of Health reported in 2008 that their national survey showed that 75 percent of drinking water in rural areas comes from groundwater and, of this, 46 percent is not safe to drink.  To complicate matters further, fallout of air pollutants derived from coal-fired power plants and certain industries  contaminate the soil with hazardous heavy-metals which themselves can be leached into the groundwater by rainfall or irrigation waters.

Effective and well enforced soil, water, and air pollution controls offer valuable opportunities to increase potable water supplies and to improve public health in these provinces but little evidence exists today that such is the case.  Population continues to grow and increases the demand for safe water.  Farming on the alluvial soils will continue.   China has known since 2007, that the loss of further arable land will jeopardize the country’s ability to feed its 1.3 billion people.  Concern was so great that the Minister of Land and Resources established a “red line” below which China’s arable land would not be allowed to fall.  Nevertheless, the amount of arable land is still decreasing.

Realistically, any significant changes in the geologic makeup of these provinces is unlikely within the human timeframe, but wise environmental decisions by China’s leaders could significantly reduce pollution today and increase the availability of safe drinking water for its people.

Walter Parham, Ph.D.,  August 2013

     

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