The 3% NaCl content of the water would be of no significant concern on the already saline playa under discussion.(Of which many others of similar saline character can be found) The volume of soils in which it would be mixed, over decades, would be be of no concern. On the other hand, if it is seen as a desireable commodity, the locus of the spray heads and their localized retention podns can be changed frequently, and the prior spray surface allowed to dry, at which time the NACl can be scraped up and utilized Other places. One way, or the other, it's not a problem.
Carbon sinks include long-lived trees, limestone (formed from the carbon-containing shells of small sea creatures that settle to the ocean bottoms and build up into thick deposits), plastic (a modern invention, but very long-lived), and the burial of organic matter (such as those that formed the fossil fuels we use today). Carbon sources include the burning of fossil fuels and other organic matter, the weathering of limestone rocks (which releases ), and the respiration of living organisms. Release agents include volcanic activity, forest fires, and many human activities.