Desiccation-crack-induced salinization in deep clay sediment

Abstract

Abstract.A study on water infiltration and solute transport in a clayey vadose zone underlying a dairy farm waste source was conducted to assess the impact of desiccation cracks on subsurface evaporation and salinization. The study is based on five years of continuous measurements of the temporal variation in the vadose zone water content and on the chemical and isotopic composition of the sediment and pore water in it. The isotopic composition of water stable isotopes (δ 18 O and δ 2 H) in water and sediment samples, from the area where desiccation crack networks prevail, indicated subsurface evaporation down to ∼ 3.5 m below land surface, and vertical and lateral preferential transport of water, following erratic preferential infiltration events. Chloride (Cl − ) concentrations in the vadose zone pore water substantially increased with depth, evidence of deep subsurface evaporation and down flushing of concentrated solutions from the evaporation zones during preferential infiltration events. These observations led to development of a desiccation-crack-induced salinization (DCIS) conceptual model. DCIS suggests that thermally driven convective air flow in the desiccation cracks induces evaporation and salinization in relatively deep sections of the subsurface. This conceptual model supports previous conceptual models on vadose zone and groundwater salinization in fractured rock in arid environments and extends its validity to clayey soils in semi-arid environments.

Soil–aquifer phenomena affecting groundwater under vertisols: a review

“…2), under dry conditions, deep soil cracks are relevant for their evaporation capacity from deep parts of the soil column. Kurtzman and Scanlon (2011), Baram et al (2013) and others have reported the low water content and high salinity typical of the sediment matrix under uncultivated vertisols. Deep chloride profiles under native-land vertisols often show an increase in salinity down to 1-3 m and a relatively constant concentration in deeper parts of the vadose zone (e.g., Radford et al, 2009;Kurtzman and Scanlon, 2011;Silburn et al, 2011).…”

“…Therefore, a dry (relatively immobile) and salty deep unsaturated matrix, developed for centuries-millennia under these non-cultivated vertisols. Nevertheless, some fresh recharge to the underlying aquifer through preferential paths related to cracks during heavy rain events creates an anomaly whereby relatively fresh water in the aquifer (e.g., ∼ 250 mg L −1 chloride; Kurtzman and Scanlon, 2011) lies beneath a salty and immobile unsaturated zone with porewater chloride concentration of a few thousands of milligrams per liter (O'Leary, 1996;Kurtzman and Scanlon, 2011;Tolmie et al, 2011;Baram et al, 2013). River, mountain-front, paleo-or other types of recharge may contribute, as well, to a situation where a relatively fresh aquifer exists under a saline vadose zone.…”

“…Both localand higher-scale observations and analyses point to a possible significant role of soil cracks as deep evaporators in dry periods. Baram et al (2013) Baram et al (2013). Convective instability of air in soil cracks, occurring mainly at night, leads to drying and salinization of the unsaturated zone.…”

Real-time monitoring of nitrate transport in the deep vadose zone under a crop field – implications for groundwater protection

“…The recent development of a vadose-zone monitoring system (VMS) enables continuous monitoring of the hydrological and chemical properties of percolating water in the deep vadose zone under agriculture settings (Turkeltaub et al, 2014(Turkeltaub et al, , 2015b and other hydrological settings (e.g., Dahan et al, 2009;Baram et al, 2013). Data collected by the system comprise direct measurements of the water-percolation fluxes and the chemical evolution of the percolating water across the entire unsaturated zone.…”

“…Nitrate fate in the subsurface has been investigated by various approaches, such as (i) isotopic signature analysis in groundwater systems (Oren et al, 2004;Wassenaar et al, 2006;Showers et al, 2008;Baram et al, 2013), (ii) cropmanagement strategies, which combine crop production and nitrate leaching to the subsurface (Hanson et al, 2006;Doltra and Muñoz, 2010;Beggs et al, 2011), and (iii) studies based on data from the deep vadose zone (Dann et al, 2010;Nolan et al, 2010;Botros et al, 2012;Kurtzman et al, 2013;Dahan et al, 2014;Turkeltaub et al, 2015b). Nevertheless, estimates based on data obtained from excavated soil profiles and pore-water sampling during a short period of time represent a snapshot in time of the sediment's chemical state rather than dynamic temporal variations.…”