Ground water nitrate pollution in Tadla (Morocco)

In Morocco, diffuse ground water pollution by nitrates in irrigated areas has caused an increase in the risk of water quality deterioration. This has generated a health risk in rural areas, since most of the rural population get their drinking water supply from the aquifer. The present study was carried out in the Tadla region. The plain of Tadla is situated in the centre of Morocco, in the Oum Erbia river basin. It covers a surface area of 3600 km super(2). The irrigation water comes from the Oum Erbia river, the Bin El Ouidane dam and from two important waters tables: Beni Amir (190 Mm super(3)) and Beni Moussa (250 Mm super(3)). The objectives of this study were to quantify the degree of ground water contamination by nitrates and to identify the potential causes of this pollution. The monitoring of nitrate concentrations in ground water was carried out during the period of August 1996 to April 1998, in 100 wells in the region of study. The results are presented by thematic maps using a geographical information system. The level of ground water nitrate pollution is becoming a serious problem. The point pollution is localized around or downstream of urban built up areas such as Fquih Ben Saleh, Beni Mellal, Souk Sebt and Oulad Ayad. This pollution, caused by household wastes, is likely aggravated by waste dumping from the sugar refineries (SUBM, SUTA and SUNAT) as well as by waste water reuse in agriculture. Other zones with nitrate concentrations more than 50 mg NO super(-) sub(3) times L super(-1) were observed in wells situated downstream from Beni Amir and east of Beni Moussa. West Beni Moussa was generally not as polluted as east Beni Moussa, but an increase in ground water nitrate levels was observed in some downstream wells in west Beni Moussa. The diffuse nitrate pollution has been attributed to land use, irrigation and fertilization practices. These practices may be responsible for nitrate leaching beyond the root zone during the cropping season and may generate large quantities of residual inorganic nitrogen at harvest time. This represents a potential risk of nitrate ground water pollution in the next draining period. The physical characteristics of soil texture (clay, clay-silt and silty clay), percentage clay (29%-55%) and their correlated parameters (especially the useful storage capacity) act to reduce the risk of nitrate leaching and ensures a control on ground water nitrate pollution. However, other observations including: a low water lev