Effect of treated sewage effluents on plant cover and soil at Wadi Al Rummah, Qassim Region, Saudi Arabia

Abstract

The effect of tertiary treated sewage effluents on the plant cover and the physico-chemical properties of the surface soil (environmental characteristics) before and after the Al Rass sewage plant was investigated. The data were illustrated via TWINSPAN and canonical correspondence analysis (CCA). Five sites, 1 km apart, after the discharge point and one site (control site) before the sewage plant were examined. Eleven vegetation characteristics and ten physico-chemical properties of surface soil were studied. The obtained results revealed that discharging of treated sewage effluents altered quantitatively and qualitatively the pattern of species dominance and the physico-chemical properties of the soil. Soil electrical conductivity (EC), total dissolved solids (TDS), organic matters (OM), soluble cations, and soluble anions showed increased values compared to the control (resulting in salination), whereas soil pH decreased as a result of sewage disposal. It was also noticed that the physico-chemical values of EC, TDS, Ca⁺⁺, Mg⁺⁺, Na⁺, Cl^– after the sewage plant were higher than the permissible limits for agriculture recommended by FAO, whereas K⁺ and HCO₃^– were within the recommended values. The dominance of Suaeda vermiculata Forssk. ex J.F.Jmel. after the sewage plant and its absolute absence before the sewage plant may be used as an environmental bioindicator of pollution.