Is dust derived from shrinking saline lakes a risk to soil sodification in southern South America?

Abstract

Dry lakebeds exposed by shrinking water bodies in arid regions constitute sodium (Na)-rich mineral dust emission hotspots that may potentially affect agriculture through soil sodification. However, no soluble Na mass balance has so far been attempted. We modeled 13 years (2005–2017) of dust emission from Mar Chiquita (MC), the most extensive shrinking saline lake in South America. Based on a chemical characterization of dust, we found that a mean ∼15–150 mg m−2 of soluble Na was deposited 300 km from the source during the season of strongest dust emissions. We estimated the impact of this atmospheric input on 13 agricultural soils, with different rainfall regimes and water holding capacities. At most sites, dust-equilibrated infiltrated rainfall water had a Na concentration 8–7,000 times lower than the lowest concentration threshold proposed to trigger sodification. Additionally, this rainfall water is diluted ∼2–20 times as it infiltrates in saturated soils, and its sodium adsorption ratio is probably reduced due to the abundance of soluble calcium and magnesium in the soil solution. Thus, there is no risk of short-term, seasonal sodification, except possibly at two sites and in close proximity to the dust source (<50 km), where dust deposition is maximum. At these sites, we estimated potential dust-related rises in the proportion of soil exchangeable Na. Under scenarios of enhanced salt-rich dust emissions from shrinking lakes in the twenty-first century, agricultural soils close to salt-rich dust sources worldwide should be monitored for potential Na enrichment related to Na-rich dust.