The Sustainability of Treated Wastewater Irrigation: The Impact of Hysteresis on Saturated Soil Hydraulic Conductivity. Issue 3 (26th February 2022)

• Record Type: Journal Article
• Authors: Kramer, Isaac; Bayer, Yuval; Mau, Yair
• Is Part Of: Water resources research. Volume 58:Issue 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-26
• Subjects: salinity -- sodicity -- degradation -- rehabilitation -- modeling; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2021WR031307
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Models for the effect of salinity and sodicity on saturated soil hydraulic conductivity, K s, have yet to consider hysteresis. Ignoring hysteresis limits our ability to assess the risk posed by irrigation with saline and sodic water, such as treated wastewater (TWW). We introduce SOTE 2.0, the first model to consider hysteresis in K s, as driven by different climate and irrigation regimes. The new model integrates the SOTE 1.0 model for salinity and sodicity dynamics with a model for the effect of saline and sodic water on K s that explicitly includes hysteresis. SOTE 2.0 is used to demonstrate how hysteresis significantly alters our understanding of degradation and rehabilitation. SOTE 2.0 relies on weight functions to highlight soil‐specific differences in degradation and rehabilitation patterns. While TWW irrigation can be crucial to mitigating water scarcity, simulations show that salinity and sodicity have the potential to irreversibly damage soil structure, as measured by declines in K s . Compared to the McNeal model used by Hydrus and others, SOTE predicts up to 50% degradation risk in settings where the McNeal model predicts none. The SOTE model also predicts slower rehabilitation: up to 100 days, compared to 0 days when using the McNeal model. Results highlight the difference between susceptibility and risk, showing that the probability of degradation is not solely dependent on initial susceptibility to degradation. To fully characterize a soil, we must also know its propensity to rehabilitation. Plain Language Summary: Models for the assessment of how irrigation water affects soils have always assumed that "what goes down must come back up." While significant research has investigated how low‐quality irrigation water causes soil degradation, almost none has studied the process in reverse: how easily can a degraded soil be rehabilitated? We use a mathematical model to demonstrate that this question is crucial to understanding the risk of irrigation with treated wastewater (TWW). TWW irrigation—increasingly common in water‐scarce regions—can cause irreversible damage to soils, if the water is saline and sodic. In this paper, we model degradation and rehabilitation as separate processes, as experimental evidence indicates they should be. The mathematical framework introduced here is capable of reflecting the fact that rehabilitation and degradation likely occur on much different time scales, with changes in soil structure dependent on a soil's history of degradation and rehabilitation. When using the new model, risk of degradation moves from 0% to over 50%. Likewise, our model estimates that the cost (time and resources) of rehabilitation are likely to increase. More accurate models facilitate smarter decision making, giving us the ability to continue irrigation with TWW in ways that minimize long‐term risk of soil degradation. Key Points: Hysteresis‐based results show higher degradation risk and slower rehabilitation when irrigating with saline and sodic treated wastewater Actual degradation risk results from dynamic interplay between a soil's susceptibility to degradation and its ability to rehabilitate SOTE model is first to consider effects of hysteresis on changes in saturated soil hydraulic conductivity under saline and sodic conditions