The imprint of desalinated seawater on recycled wastewater: Consequences for irrigation in Lanzarote Island, Spain

Seawater desalination and recycling of urban wastewater originating from desalinated seawater are the only sources of irrigation water on the extremely arid (∼150 mm year−1) Spanish island of Lanzarote. Irrigation with these two types of water has been introduced over the past few decades in traditional rainfed agriculture systems as a means to increase crop production. The present study was carried out to evaluate the long term impact (5–30 years) of irrigation with desalinated seawater (DSW) and recycled wastewater originating from desalinated water (RWW) on the islandʹs soils used for farming. The effects of irrigation were studied by evaluating the chemical characteristics of the topsoil of DSW-irrigated plots, RWW-irrigated plots and adjacent rainfed plots used as controls. The data indicate that irrigation with DSW and RWW has increased soil salinity by a factor of 1.9 and 3.4, respectively, and boron concentrations by a factor of 1.8 and 1.9, respectively, in relation to the control soils. Irrigation with RWW has also led to a rise in sodicity, where SAR values increased by a factor of 1.6 with respect to the control soils. Apart from these effects DSW irrigation was not found to cause further adverse effects in regards to soil fertility. The long-term sustainability of these farming systems requires substantial improvements in DSW quality, which in turn will improve the quality of the RWW.