Evaluation des impacts de l’irrigation par les eaux du barrage de BENI HAROUN sur les plantes et les sols de la région de Mila.

Abstract

The Beni Haroun dam is a vital source of water for drinking and irrigation in the city of Mila, Algeria. In this study, an assessment of the quality of irrigation water and its impacts on the properties of irrigated soils was carried out, as well as an assessment of the contamination by heavy metals (Cd, Cu, Zn, Pb, Cr and Fe) of edible vegetables, tomato (Solanum lycopersicum), Melon (cucumis melo) and Lettuce (Lactuca sativa). To this end, sampling was conducted at eight water stations between May 2014 and April 2015 on a monthly basis. Soil samples were collected at 14 stations. 12 on irrigated soils, and 2 on non-irrigated control soil, seasonally at four depth levels (0.10, 20 and 30 cm). The results revealed that the chemical facies of the waters are chlorinated calcium magnesium sulphate with a low content of heavy metals, a pH between (6.5 and 8.4), excess chloride and bicarbonate. A high conductivity where (38.53%) of the samples are not recommended for irrigation, the Richard diagram shows four classes, 1) C3S1 (61.45%) average to poor quality, 2) C4S1 (30.2%) poor to bad, 3) C4S2 (5.2%) very bad and 4) C5S3 (3.12%) of water unfit for irrigation ,while the Wilcox diagram showed that (58.33%) of the samples are of good quality and (41.66%) are not suitable for irrigation. Water is safe for irrigation based on quality indices: MH, IP, KR and RSC. For soils irrigation has increased their pH, EC, MO and total CaCO3, which is leached and accumulated in the deep layers, the metal contents in the irrigated soils have been found to be higher than the control soil but still below the recommended international limits, Fe is the most bioavailable element in soil with levels ranging from 97.24 to 936.39 µg/mg, Zn (11.9 and 497.8 µg/mg), Pb (27.30 and 40.40 µg/mg). However, Cr (0.92-2.26 µg/mg), Cu (0.20-0.51 µg/mg) and Cd (0.11-0.25 µg/mg) have very low bioavailability. Whereas according to the Factor of enrichment they are classified as follows: Zn>Cu> Cd> Cr> Fe >Pb, Consequently, these soils present a risk of contamination during a long period of irrigation. Plant metal concentrations do not exceed standards, but Cd and Pb levels are higher than normal. The organ type factor influences the accumulation of metals, and the roots of Tomato and Melon, and lettuce leaves are the organs accumulating the most metals, the highest Transfer Factors are those of: Cd (1 , 61) in lettuce leaves, Cu (1.48) in tomato and melon fruits, Cr (0.89) in lettuce leaves, the study indicates a potential ecological risk to plants which could result in risks to human health. The study concludes that strict protection measures and guidelines are needed to minimize the negative impacts of irrigation by these waters in the study area.