Diffuse agricultural water pollution in india

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Déc, 1998
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« Concern over agricultural diffuse pollution sources in integrated water quality management has been growing recently. Such sources are likely to be even more critical in developing countries, including India; where agriculture and rural habitats are still dominant, unlike the G7 or other affluent industrialised nations. A number of special features of the Indian scene need to be considered. These include: (i) extremely varying rainfall and stream-flow patterns; (ii) still largely traditional agricultural practices with average application of fertilizers and pesticides and significant areas under dry farming or only marginal irrigation; (iii) a very large cattle population, with agriculture almost always linked with animal husbandry; (iv) a culture of living close to the river (if not in the river) with dominating instream uses of bathing, washing, cattle wading, waste disposal, etc. and large-scale floodplain farming; and (v) scant respect for rules, regulations and laws alongside an extremely weak law-enforcement machinery.The paper shows that in the non-monsoon (non-flood) periods, which may account for all but 2 months of a year, agricultural diffuse pollution sources seem to have no impact on stream water quality. During these periods flows are low to minimal and pollution is dominated by the in-stream uses, sullage waters of rural communities and point discharges from urban/industrial sources, if any. Pollution due to agricultural return waters, either as wash-off or as seepage, appears to be rare during the 8-10 fair weather months. However, surface wash-off of pollutants from agricultural sources becomes the dominant factor during flood flows, and seepage/drainage from agricultural fields/soils continues to pollute streams far a month or two after the monsoons are over.Application of chemical fertilizers and pesticides (or any other agricultural chemicals) in India is still low compared to developed countries, and while eutrophication due to high levels of washed-off nutrients is observed in rural ponds and other stagnant bodies of water receiving agricultural drainage, and excessive pesticide residuals are often reported for vegetables, fodder, milk, etc., monitoring of streams and rivers does not show any significant pollution due to nutrients or pesticides from agricultural diffuse pollution during fair weather months. High nitrate concentrations have been reported in groundwater and in many areas, such as Punjab and Haryana, these can often be linked directly to diffuse agricultural sources. The major problem of agricultural diffuse pollution appears to be the heavy silt loads, along with large quantities of dissolved salts, nutrients, organics and even heavy metals and bacterial contaminants washed off during floods. The silt tends to clog up the flow channel to further encourage seasonal floodplain agriculture. This results in a vicious circle, which degrades the channel. increases flood-damage and is undesirable from ecological and sustainability points of view. High concentrations of salts and nutrients encourage growth of weeds and macrophytes after the floods have passed. The presence of organics, heavy metals and bacterial contamination renders the streamwater unfit for in-stream use or abstraction.With the introduction of intensive agriculture and adoption of modern farming techniques involving the application of much irrigation water and agricultural chemicals, the problems caused by diffuse agricultural pollution are bound to grow. Routine pollution control methods of discharge permits (or consent letters), EIAs or environmental audits, and normal enforcement measures by regulatory agencies are not likely to work for control of such pollution. Using the example of a small river in central India, Paisuni (Mandakini), the paper brings out the nature of the problems, and suggests a possible management approach. »

Source : Pubmed