Long term effect of irrigation with the treated sewage effluent on some soil properties of Al-Hassa Governorate, Saudi Arabia

A case study was undertaken to assess the long-term effect of sewage irrigation on some soil properties and heavy metals concentrations in the soils of the date palm at Al-Hassa Governorate, Saudi Arabia. Eighty-two surface soil samples were collected from the studying area. Half of it was collected from an area irrigated for more than 13 years with treated sewage effluent. Meanwhile the rest of soil samples were collected from an area irrigated with well water. Furthermore, samples from sewage effluents and well water used for irrigation were collected and analyzed mainly for their chemical composition and their metal contents. The obtained results pertaining irrigation water analysis indicated that sewage effluents were found to contain higher content of Pb, Zn, Cu, Co, Cr, As, Cd, Fe, Mn and Ni compared to well water. On the other hand data emphasized the role of sewage effluent irrigation on increasing heavy metals as well as organic matter contents in the soil samples when comparing with the respective values found in the soil irrigated with well water. The soil salinity ranged from 3.58 to 20.7 dS m−1 with an average of 7.9 dS m−1 due to irrigation with well water. While the respective soil salinity due to irrigation for long period with the treated sewage effluent ranged from 2.5 to 3.69 dS m−1 with an average of 2.8 dS m−1. There was an increase in organic matter content ranging from 17% to 30% in sewage-irrigated soil samples as compared to well water-irrigated ones. On an average, the soil pH dropped by 0.3 U as a result of sewage irrigation. Long term sewage irrigation resulted in significant build-up of total concentration of Zn (130%), Pb (55%), Fe (82%), Ni (84%), Mn (30%), Cu (40%), Cr (75%), Co (78%) and As (67%) in sewage-irrigated soil samples over adjacent well water-irrigated soil samples.