The impact of replacing groundwater by treated sewage effluent on the irrigation requirements of Al Ghaf (Prosopis cineraria) and Al Sidr (Ziziphus spina-christi) forests in the hyper-arid deserts of Abu Dhabi

Law No 5 of 2016 on the regulation of GW has been passed by the Government of Abu Dhabi to reduce GW abstraction. Abu Dhabi has a supply of tertiary-treated sewage effluent (TSE) that could be used as an alternative for irrigation. Experiments near Madinat Zayed in the Al Dhafra region of Abu Dhabi on two arid-forest species: Al Ghaf (Prosopis cineraria) and Al Sidr (Ziziphus spina-christi), were setup. The GW in this region is very high in nitrates (38.4 ± 9.2 mg-NO3 L−1), and this was not significantly different from the TSE (53.7 ± 11.8 mg-NO3 L−1). Quantified the differences in the ETc patterns for both the GW and TSE irrigated trees of both species over 3 years. Both species showed positive growth-responses to TSE, relative to the GW, and we consider this to be due to the lower electrical conductivity of the TSE water. Because of this growth response the ETc of the TSE by the Ghaf trees was, on annual average 17% higher than GW, and for the Sidr it was 39%. Furthermore, to achieve the same tree-health outcome as with the GW, even less TSE need be applied. Irrigation requirements for TSE were at least 25% less than for GW.