Sodium-rich water containing calcite can stabilize soil macroaggregates in arid regions

Abstract

Sodium-rich water may deteriorate calcite-stabilize soil. The objective of this work was to determine whether calcite solution prepared with sodium-rich water were capable of forming stable soil macroaggregates. Calcite solutions were 2.6 g Ca2+ L−1 of CaCO3 mixed with water containing 2.6, 5 or 10 g Na+ L−1 from NaCl. Arid desert soil (5 cm layer, packed at 1.1 g cm−3) was moistened with calcite solution at 50% or 75% of the water holding capacity. Then, the calcite-treated soil was incubated for up to 30 d at average 35 °C and 19% relative air humidity. Clay flocculation rate was estimated from the decline in extractable Ca2+ and Na+ concentrations during macroaggregate formation. We observed carbonate precipitation in voids of the macroaggregates using micro-CT scanning, which is evidence of cementation. Aggregate stability was the mean weight diameter of macroaggregates. Macroaggregate stability depends upon calcite interactions with clay, so a higher proportion of Ca2+ to Na+ favors the formation of flocculants and cements the flocculants within macroaggregates with carbonate materials, which is surmised to be sodium carbonate with low resistance to abrasion. There was 40% more cementing material within macroaggregates treated with pure calcite and Ca2+: Na+ solutions than with solutions containing Ca2+: 2 Na+, Ca2+: 4 Na+ and Na+. We conclude that calcite-stabilized macroaggregates will persist longer when formed by a calcite solution with equal proportions of Ca2+:Na+, since macroaggregates disintegrate more quickly when formed from calcite made with brackish water at ratios of Ca2+ ≤ 2 Na+.