Can Soil Hydraulic Parameters be Estimated from the Stable Isotope Composition of Pore Water from a Single Soil Profile?

Abstract

Modeling water and solute transport in the vadose zone for groundwater resource management requires an accurate determination of soil hydraulic parameters. Estimating these parameters by inverse modeling using in situ observations is very common. However, little attention has been given to the potential of pore water isotope information to parameterize soil water transport models. By conducting a Morris and Sobol sensitivity analysis, we highlight the interest of combining water content and pore water isotope composition data in a multi-objective calibration approach to constrain soil hydraulic property parameterization. We then investigate the effect of the sampling frequency of the observed data used for model calibration on a synthetic case. When modeling is employed in order to estimate the annual groundwater recharge of a sandy aquifer, it is possible to calibrate the model without continuous monitoring data, using only water content and pore water isotopic composition profiles from a single sampling time. However, even if not continuous, multi-temporal data improve model calibration, especially pore water isotope data. The proposed calibration method was validated with field data. For groundwater recharge estimate studies, these results imply a significant reduction in the time and effort required, by avoiding long-term monitoring, since only one sampling campaign is needed to extract soil samples.

Pore water isotope fingerprints to understand the spatiotemporal groundwater recharge variability in ungauged watersheds

“…However, values for the Mualem–van Genuchten parameters α and n obtained for the three permeability classes differ greatly (Table 6). These two parameters were identified as the being most influential parameters in the sensitivity analysis previously carried out for the model (Mattei et al., 2020). Only a slight modification of these two parameters could lead to very different infiltration profiles.…”

“…Thirteen parameters (i.e. α 1 , n 1 , S min1 , S max1 , K r1 , F 1 , α 2 , n 2 , S min2 , S max2 , K r2 , F 2 , and λ) were therefore calibrated for each study site to describe their soil hydraulic and transport properties, according to Mattei et al., 2020.…”

“…At the profile scale, and based on a single field campaign, pore water stable isotopes have been shown to be valuable tools to obtain insights into vertical water flow under various climatic, geological, and land cover conditions (Barbecot et al., 2018; Sprenger, Seeger, Blume, & Weiler, 2016; Stumpp, Maloszewski, Stichler, & Maciejewski, 2007; Stumpp, Stichler, Kandolf, & Šimůnek, 2012). Easy to sample in the field, and fast to measure in the laboratory, thanks to the development of H 2 O liquid –H 2 O vapor equilibration methods (Mattei et al., 2019; Wassenaar, Hendry, Chostner, & Lis, 2008), pore water isotopes are also relevant to calibrating unsaturated zone models (Sprenger, Volkmann, Blume, & Weiler, 2015), even without temporal monitoring (Mattei et al., 2020). In ungauged watersheds, pore water stable isotope fingerprints can provide valuable information to estimate soil hydraulic parameters accurately and quickly, and thus recharge at a lower cost when meteorological conditions are known.…”

Global Sensitivity Analysis of Quantiles: New Importance Measure Based on Superquantiles and Subquantiles

“…By applying the quantile deviation l as a new measure of sensitivity, contrast Q indices defined by Fort [63] can be rewritten in a new form; see Equations (8)- (12). By substituting l with l 2 , Q indices can be rewritten as the new K indices, which are based on the decomposition of l 2 , similarly to the way Sobol indices are based on the decomposition of variance; see Equations (13)- (17).…”

“…Variance-based SA (generally called Sobol SA) introduces uncertainty as variance and decomposes the variance of the output of the model or system into portions that can be attributed to inputs or sets of inputs [2,3]. Sobol SA is very popular; the principles of the method are often mentioned [4][5][6][7][8] and many articles have applied Sobol SA in their research [9][10][11][12][13].…”