Are sodium-rich dust inputs from shrinking lakes diminishing southern South American soil fertility?

LAURA GABRIELA BORDA; COSENTINO, NICOLÁS J.; LAURA ANTONELA ITURRI; MARÍA GABRIELA GARCÍA; GAIERO, D. M.

Simposio; Blowing South: Southern Hemisphere Dust Symposium; 2021

IFAECI, Núcleo Mileno Paleoclima, AACS, CR2, UNLPam, INCITAP, CICTERRA, CESIMAR, GEOTRACES, ipam

Dry lake beds exposed by shrinking water bodies in arid regions constitute sodium (Na)-rich mineral dust emission hotspots that may potentially affect agriculture. While several studies have proposed this link based on the dispersive properties of Na, no mass balance has so far been attempted. We modeled 13 years of dust emission from Mar Chiquita (MC), the most extensive saline lake in South America, which has experienced recent shrinking in response to climate variability and anthropogenic water diversion in the upper tributaries. Based on the chemistry of dust, we found that on average between 2005-2017, ~15-150 mg m-2 of MC-derived soluble Na was deposited 300 km from the source in August plus September, the season of strongest MC dust emissions. We compared these values against exchangeable Na stocks measured on agricultural soils at 13 sites across the Pampean plains, with differing rainfall regimes and water holding capacity. We found that infiltrated rainfall water in equilibrium with Na from deposited dust has a low to non-existent short-term, seasonal sodification risk, except in close proximity to the MC dust source (<50 km) where this risk might be severe. However, dilution during the rest of the year, combined with losses of Na, imply that long-term dust-related rises in exchangeable Na are probably negligible at all studied sites, except close to the dust source where deposition rates are maximum. Under scenarios ofenhanced salt-rich dust emissions from shrinking lakes in the 21st century, attention should be paid to soils close to MC and to salt-rich dust sources worldwide, in order to prevent the occurrence of degradation processes related to Na enrichment. However, only by accurate mass balancing of the atmospheric inputs to the soils can this effect be correctly gauged.