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

LAURA GABRIELA BORDA; NICOLÁS COSENTINO ; LAURA ANTONELA ITURRI; MARÍA GABRIELA GARCÍA; DIEGO GAIERO

Journal of geophysical research: Earth surface

John Wiley and Sons

Año: 2022 vol. 127

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 capacity. At most sites, dust-equilibrated infiltrated rainfall water had a Na concentration 8-7000 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 21st century, agricultural soils close to salt-rich dust sources worldwide should be monitored for potential Na enrichment related to Na-rich dust.Plain Language SummaryWhen 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 pre-existing 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 21st century, agricultural soils exposed to salt-rich dust deposition should be monitored to gauge threats to food production.