International Commission on Irrigation & Drainage Commission Interationale des Irrigation et du Drainage



Pollution and Irrigation

It is well known that agriculture is the single largest user of freshwater resources, using a global average of 70% of all surface water supplies. Except for water lost through evapotranspiration, agricultural water is recycled back to surface water and/or groundwater. The water that is lost through evapotranspiration leaves its share of salts in the irrigation water that returns to the other downstream water bodies. In addition, it carries with it various chemicals from fertilizers, pesticides and other additives used in crop production.Through desalinization and drainage practices to relieve waterlogging of irrigated land, the drainage water, rich in salts also poses a challenge, if not disposed of in a planned manner.  At the same time there is a net loss of soil due to poor agricultural practices.

 

With increasing use of recycled wastewater, especially in developing countries of arid and semi-arid regionsand its likely impact to public health, food safety and environmental quality. Particularly in cases where the wastewater is a mix of domestic as well as industrial effluents, the presence of certain chemicals have impact not only the water but also the productivity of soil.

 

Pollution by sediment has two major dimensions – physical, and chemical.Sediment, as a physical pollutant, impacts receiving waters in the following ways. High levels ofturbiditylimit penetration of sunlight into the water column, thereby limiting or prohibiting growth of algae and rooted aquatic plants. The hypertrophic (nutrient rich) status of many shallow lakes, especially in developing countries, would give rise to immense growth of algae and rooted plants were it not for the limiting effect of light extinction due to high turbidity.High levels ofsedimentationin rivers lead to physical disruption of the hydraulic characteristics of the channel.

 

The role of sediment in chemical pollution is tied both to the particle size of sediment, and to the amount of particulate organic carbon associated with the sediment. Organic chemicals associated with sediment enter into the food chain in a variety of ways. Ultimately, toxic compounds bio-accumulate in fish and other top predators. In this way, pesticides that are transported off the land as part of the runoff and erosion process accumulate in top predators including man.

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