Root zone salinity and sodicity under seasonal rainfall due to feedback of decreasing hydraulic conductivity

• Published in: Water resources research 2014-12, Vol.50 (12), p.9432-9446
• Main Authors: van der Zee, S. E. A. T. M., Shah, S. H. H., Vervoort, R. W.
• Format: Article
• Language: English
• Subjects: Accumulation; Annual variations; Buffers; california; Capillary flow; Cation exchange; Cation exchanging; Cations; Climate; Conductivity; Degradation; Direction; Drainage; Drought; Drought periods; Dynamical systems; Dynamics; ecohydrology; Feedback; Fluxes; Groundwater; Hydraulic conductivity; infiltration; irrigation; Leaching; management; quality; Rain; Rainfall; Root zone; Salinity; Salinity effects; Salt advection; Salts; saturated hydraulic conductivity; Seasonal rainfall; Seasonal variations; sodicity; Sodium; Soil; soil salinity; Soil structure; soil-moisture dynamics; Soils; stochastic hydrology; Surface hardness; System dynamics; systems; Time; transport; variability; Vulnerability; wastewater
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2013WR015208

Soil sodicity, where the soil cation exchange complex is occupied for a significant fraction by Na+, may lead to vulnerability to soil structure deterioration. With a root zone flow and salt transport model, we modeled the feedback effects of salt concentration (C) and exchangeable sodium percentage (ESP) on saturated hydraulic conductivity Ks(C, ESP) for different groundwater depths and climates, using the functional approach of McNeal (1968). We assume that a decrease of Ks is practically irreversible at a time scale of decades. Representing climate with a Poisson rainfall process, the feedback hardly affects salt and sodium accumulation compared with the case that feedback is ignored. However, if salinity decreases, the much more buffered ESP stays at elevated values, while Ks decreases. This situation may develop if rainfall has a seasonal pattern where drought periods with accumulation of salts in the root zone alternate with wet rainfall periods in which salts are leached. Feedback that affects both drainage/leaching and capillary upward flow from groundwater, or only drainage, leads to opposing effects. If both fluxes are affected by sodicity‐induced degradation, this leads to reduced salinity (C) and sodicity (ESP), which suggests that the system dynamics and feedback oppose further degradation. Experiences in the field point in the same direction. Key Points: The rate of change of ESP is slower than for C For seasonal climates and full FB, the long‐term ESP becomes smaller For Poisson climate and elevated ESP, the reduction of Ks is insignificant