Assessing ground water quality in the irrigated plain of Triffa (north-east Morocco)

Abstract

Irrigated agriculture in (semi-)arid regions may exert serious pressures on groundwater resources and jeopardise further agricultural and socio-economical developments. For assessing these pressures, we present in this paper results from a groundwater quality survey performed in 2005 within the irrigated agricultural Triffa plain in north-east Morocco. The study focuses on the physico-chemical and bacteriological quality of the groundwater body within the plain and exploits the correlation and spatial dependency of the quality parameters. It is demonstrated that the water quality in this region is critical. Nitrate levels are situated between 2 and 153 mg/l, with 73% of the observations exceeding the critical level of 50 mg/l. Nitrite, ammonia, orthophosphate and dissolved organic matter content do not exceed existing norms. Bacteriological residues (faecal, total coliforms, faecal streptococcus and clostridium sulfido-reductants), however, are retrieved in nearly all water samples. Bacteriological contamination is merely correlated with nitrite and ammonia content rather than with nitrate content, indicating a possible contribution of local pollution sources to groundwater deterioration. The variability of the nitrate and bacteriological pollution is important and spatially correlated. The spatially dependency is modelled using spherical and Gaussian semi-variograms and is used to map the nitrate and bacteriological contamination using ordinary kriging techniques. The results shown are significantly different as compared to earlier studies on groundwater quality for the studied aquifer. The differences may be explained partially by modified but inappropriate fertilizer management practices in combination with intensive irrigation. Given the agricultural developments in this area, further deterioration of the groundwater quality is expected if no mitigation strategies are developed.