Salinity

Salinity is the most important criterion for evaluating irrigation water quality because of the potential crop yield reductions resulting from using salty water that might prevent water uptake by plants. There are different causes, both natural and human, that can induce accumulation of salt in water resources. Irrigation can cause the mobilization of salts accumulated in soils and therefore provoke the salinization of water bodies. Intrusion of saline seawater in aquifers is another important cause of salinization of water resources in coastal areas. This intrusion is frequently due to excessive groundwater extractions for agriculture.

Major soil and water salinity problems have been reported in big irrigation schemes in China, India, United States, Argentina, Sudan and many countries in Western and Central Asia, where more than 16 million hectares of irrigated land are salinized. Globally, the extent of the problem is much higher with estimates of 34 million irrigated hectares salinized.

Leaching and drainage are required to maintain salt balance in the soil profile and to sustain crop yields in arid areas. However, this drainage needs to be carefully managed to prevent salinization of water bodies. Some drainage water management options include drainage minimization through water conservation, drainage water reuse, safe drainage water disposal or drainage water treatment.

Another crucial issue in coastal areas is the prevention of saline intrusions. Rising ocean levels, drought, and people’s increased use of water, specially for agriculture, all contribute to increased saltwater intrusion into freshwater bodies. Two main approaches taken in dealing with this problem are to: (i) reduce water extraction from groundwater in coastal areas and (ii) create salt water intrusion barriers through injection of water into aquifers.

Nutrients and pesticides

Water pollution by nutrients (specially nitrate) and pesticides has been worsened by the introduction of intensive farming methods involving increased use of chemical fertilizers and higher concentrations of animals in smaller areas. Sources of pollution are diffuse, i.e. multiple discharges difficult to locate.

The 1980s saw a progressive worsening of water quality owing to the growth of intensive livestock farming (chickens, pigs) in areas that were already saturated, and of intensive crop-growing involving the use of chemical weedkillers and overfertilisation. Developed countries have had major problems of water pollution from agriculture and trends indicate that intensified farming systems and agrochemical consumption are being extended in emerging economies.

Management for remediation of pollution from agriculture should occur within broader integrated land and water management frameworks that ensure a comprehensive overview of the problems. Specific actions need to be implemented by polluters at the appropriate scales (e.g. national, regional, municipal, local, project-level). Improved agricultural practices to minimise environmental impacts include integrated nutrient management, integrated pest management and proper livestock waste management. In addition sustained regulation and water quality monitoring programmes at all scales are essential for planning and assessment purposes.