Is Dust Derived From Shrinking Saline Lakes a Risk to Soil Sodification in Southern South America?

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. Plain Language Summary: When lakes rich in dissolved salts shrink, the lakes' bed becomes exposed, and upon drying, these areas may emit salt‐rich dust to the atmosphere. This dust may be deposited on soils used for agriculture in the surrounding areas, and depending on the dust chemistry it may affect soil productivity, with sodium‐rich dust posing the highest potential threat. In this study, we analyzed dust emission from Mar Chiquita lake, the most extensive shrinking saline lake in South America, and its potential effect on agricultural soils in the region. To do this, we sampled dust, characterized its chemistry, modeled dust emission, transport in the atmosphere and final deposition to the soils, sampled soils at sites located at different distances from the lake, and finally compared the inputs of dust‐derived sodium, magnesium, and calcium with preexisting concentrations of these elements in the soils. We found that the short‐term input of sodium to the soils derived from dust is comparatively low, except close to the lake. However, the long‐term effect remains uncertain. Given that more intense dust emissions from shrinking lakes are projected globally in the twenty‐first century, agricultural soils exposed to salt‐rich dust deposition should be monitored to gauge threats to food production. Key Points: Mar Chiquita, the largest South American shrinking saline lake, has emitted ∼0.5 Tg of dust in August plus September of each year since 2004Despite a marked dust enrichment in soluble sodium, dust inputs are low compared to agricultural soil sodium stocks at most studied sitesWhile short‐term soil sodification risk is low, potential long‐term effects and projected stronger dust emissions merit soil monitoring [ABSTRACT FROM AUTHOR]