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Environment and health
Several practical problems are associated with using saline water on the Qatari farms. The most serious ones are groundwater pollution, degradation of soils and consequent abandonment of farms. Groundwater pollution is caused by several factors, the main one being uncontrolled and excessive pumping from wells. The present extraction rate is estimated to be about four times the average recharge from rainfall, which leads to a lowering of the water table and the consequent up-flow of brackish water from the underlying aquifer, thus increasing the water salinity. The average annual rate of increase in water salinity in the wells during the period 1982ľ2004 was estimated at 2.2, 1.6 and 1.7 percent for representative farms in northern, central and southern regions of the country respectively (Table 8). Seawater intrusion is a common worldwide problem along sea coasts, peninsulas and islands. In Qatar the problem is more severe, because the high permeability of the fractured limestone aquifer containing freshwater permits the rapid intrusion of seawater. The return flow from irrigation to groundwater reservoirs is estimated at an average of 25 percent of the gross water application. This has been determined from lysimeter observations. Although this irrigation return flow increases the recharge to groundwater, it deteriorates the water quality because the percolating poor quality water dissolves salts from the soil and underlying strata and carries them to those aquifers bearing relatively fresh water. Moreover farmers sometimes use large quantities of low quality water to wash the salts away and avoid plants wilting and also apply heavy chemical fertilizers to increase the yield. This practice is not necessarily beneficial, because it may contribute to groundwater pollution. On the Government Experimental Farm, drainage water analysis shows a significant increase in nitrate derived from nitrogenous fertilizers.
Scarcity of water resources, severe climatic conditions, pollution of groundwater, unsuitable cropping patterns, incorrect cultural practices, overgrazing and socioeconomic development all lead to soil degradation and cause desertification. In addition to these factors, improper farm layouts and erroneous irrigation designs together with poor water management intensify the problem of desertification. The accumulation of salts year after year degrades the soils and renders them unproductive and is considered the main reason for abandonment of farms. Most of the degraded soils are found in farms located near the coasts because of the effect of the high saline irrigation water or in inland farms where heavy textured soils become saline. Of a total number of 434 farms during the 1975/76 season, 259 were in operation and 175 abandoned. During the 2004/05 season the total number of farms increased to 1 285 and abandoned farms numbered 293 (DAWR, Irrigation and Drainage Unit, 2006). There is no irrigation induced waterlogging in the farms because the water table is very deep. However, waterlogging occurs in the non-irrigated areas of the sabkha soils and covers an area of 61 000 ha approximately (Awiplan Qatar & Jena-Geos, 2005).