Stochastic modeling of salt accumulation in the root zone due to capillary flux from brackish groundwater

• Published in: Water resources research Vol. 47; no. 9
• Main Authors: Shah, S. H. H., Vervoort, R. W., Suweis, S., Guswa, A. J., Rinaldo, A., van der Zee, S. E. A. T. M.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01.09.2011; John Wiley & Sons, Inc
• Subjects: active-role; bodem-plant relaties; bodemchemie; capillary upflow; eucalyptus-camaldulensis; Evapotranspiration; Flow rates; grondwater; Groundwater; hydraulic redistribution; Hydraulics; hydrologic processes; Hydrology; irrigation; Leaching; modellen; Moisture content; Net losses; Precipitation; Rain; Root zone; root zone flux; Salinity; Salinization; salt accumulation; Salt balance; semi-arid climate; soil chemistry; soil plant relationships; soil-moisture dynamics; Soils; solute transport; stochastic; Vegetation; verzilting; Water flow; Water quality; water-controlled ecosystems; Wet climates; wortelzonestroom
• DOI: 10.1029/2010WR009790
• ISSN: 0043-1397

Groundwater can be a source of both water and salts in semiarid areas, and therefore, capillary pressure–induced upward water flow may cause root zone salinization. To identify which conditions result in hazardous salt concentrations in the root zone, we combined the mass balance equations for salt and water, further assuming a Poisson‐distributed daily rainfall and brackish groundwater quality. For the water fluxes (leaching, capillary upflow, and evapotranspiration), we account for osmotic effects of the dissolved salt mass using Van‘t Hoff's law. Root zone salinity depends on salt transport via capillary flux and on evapotranspiration, which concentrates salt in the root zone. Both a wet climate and shallow groundwater lead to wetter root zone conditions, which in combination with periodic rainfall enhances salt removal by leaching. For wet climates, root zone salinity (concentrations) increases as groundwater is more shallow (larger groundwater influence). For dry climates, salinity increases as groundwater is deeper because of a drier root zone and less leaching. For intermediate climates, opposing effects can push the salt balance either way. Root zone salinity increases almost linearly with groundwater salinity. With a simple analytical approximation, maximum concentrations can be related to the mean capillary flow rate, leaching rate, water saturation, and groundwater salinity for different soils, climates, and groundwater depths. Key Points Root zone salinity depends on the mean fluxes (P,U,L,ET) Root zone salinity increases almost linear with groundwater salinity If U>L root zone concentration becomes larger than in groundwater and vice versa