Management of groundwater quality in an agricultural context has several dimensions: the pollution caused by agriculture (e.g. salinization due to fertilizer use, contamination of groundwater by pesticides, overpumping of coastal aquifers and sea water intrusion, overabstraction of aquifers with underlying saline water); and the pollution caused by other actors, but with a negative impact on water quality also for irrigators.
In terms of the management instruments to be used in the first case, these range from educating farmers about the appropriate amounts of fertilizers and options for integrated pest management to avoid contamination of the groundwater to phasing out certain products, to increasing prices of harmful products in order to discourage their use. Unfortunately, non-point source pollution is very difficult to manage and there are not many successful examples.
With regard to salinization due to overabstraction, the same approaches as discussed earlier apply: groundwater abstractors need to be made aware of the problem, solutions need to be developed and a number of instruments are available - ranging from peer pressure to introduction of groundwater use rights and pricing instruments - to curb demand. Unfortunately, salinization is reversible only at enormously high costs and should therefore be avoided rather than mitigated.
The pollution by growing urban centres and industries is not the topic of this chapter; therefore suffice it to say that even here integrated approaches are needed and that with growing populations, especially in Asia, the interface between urban and agricultural water quality management is becoming more pronounced.
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