Experimental equations of seawater salinity and desalination capacity to assess seawater irrigation.

A central question in science and technology of desalting is, can we predict optimal coastal sites to implement seawater irrigation? Freshwater only makes up 2.5% of all water on Earth but crop irrigation is responsible for 70% of freshwater demand. First, we compared the growth rates and the dehydration rates of 5 alternative seawater irrigation experiments of wheatgrass over 3 weeks' periods. The average salt tolerance threshold of wheatgrass is 6 dS m-1. When seawater salinity is increased >10.50 dS m-1, the growth, drainage volumes, leaching, and drainage salinities of wheatgrass did not show significant variations. When seawater salinity is increased to 12.25 dS m-1, grass leaves gradually turned light green, bent, and fell. Notably, pH in soil remained nearly constant in all experiments with mean pH of 6.05 ± 0.25 (mean ± SD). Next, we derived experimental equations to define a mechanistic link between salinity and desalination capacity in a Modified Saline Adjustable Desalination System (MSADS). A cost-benefit analysis for a MSADS in a coastal location of southern California indicated that this system is $0.84 m-3 more expensive than using water from a natural reservoir, but $0.08 m-3 less expensive than importing water. This study provides a general framework to assess the implementation of a desalination system in coastal locations.