Investigation of Hillslope Vineyard Soil Water Dynamics Using Field Measurements and Numerical Modeling

Abstract

Soil heterogeneities can impact hillslope hydropedological processes (e.g., portioning between infiltration and runoff), creating a need for in-depth knowledge of processes governing water dynamics and redistribution. The presented study was conducted at the SUPREHILL Critical Zone Observatory (CZO) (hillslope vineyard) in 2021. A combination of field investigation (soil sampling and monitoring campaign) and numerical modeling with hydrological simulator HYDRUS-1D was used to explore the water dynamics in conjunction with data from a sensor network (soil water content (SWC) and soil-water potential (SWP) sensors), along the hillslope (hilltop, backslope, and footslope). Soil hydraulic properties (SHP) were estimated based on (i) pedotransfer functions (PTFs), (ii) undisturbed soil cores, and (iii) sensor network data, and tested in HYDRUS. Additionally, a model ensemble mean from HYDRUS simulations was calculated with PTFs. The highest agreement of simulated with observed SWC for 40 cm soil depth was found with the combination of laboratory and field data, with the lowest average MAE, RMSE and MAPE (0.02, 0.02, and 5.34%, respectively), and highest average R2 (0.93), while at 80 cm soil depth, PTF model ensemble performed better (MAE = 0.03, RMSE = 0.03, MAPE = 7.55%, R2 = 0.81) than other datasets. Field observations indicated that heterogeneity and spatial variability regarding soil parameters were present at the site. Over the hillslope, SWC acted in a heterogeneous manner, which was most pronounced during soil rewetting. Model results suggested that the incorporation of field data expands model performance and that the PTF model ensemble is a feasible option in the absence of laboratory data.

Estimation of Precipitation Fraction in the Soil Water of the Hillslope Vineyard Using Stable Isotopes of Water

“…In this case, it is very interesting to see that, in the northwestern part of the footslope, there are the lowest values of bulk density in the first 40 cm depth, and the highest in the deepest parts. On the other two points in the footslope, values of bulk density are totally opposite with depth, as shown by Krevh et al [59]. In the end, the influence of the slope of the vineyard on the surface and subsurface flow should not be neglected, which is from the northwest to southeast (Figure 1), although results from this study indicate that slope does not have a lot of impact on the variability of the soil water content, which corresponds to previous research where it was shown that the retention of soil water on the slope is more influenced by soil properties [5].…”

“…Granulometric soil composition analysis was performed according to [57], while organic carbon content (C org ) was determined using sulfochromic oxidation according to [58]. Values of the bulk density have been estimated using HYPROP-FIT for the hilltop, backslope, and footslope for 4 depths (0-20, 20-40, 40-60, and 60-90 cm) and 3 vineyard rows [59], while, for this research, only the average values for depth up to 40 cm have been used. According to the United States Department of Agriculture soil classification system (USDA) [60], soils have been classified as silt loam or silty clay loam for all three depths [55].…”

“…C org shows a similar trend in all locations, i.e., a decrease with depth, with the highest average values in the footslope. As previously mentioned, values of bulk density are presented in detail in Krevh et al [59]. In this research, only average values of bulk density to a depth of 40 cm were used for the correlation analysis and interpretation purposes.…”

“…Results related to the estimation of the precipitation fractions captured by wick lysimeters suggested great variability and dependence to different physicochemical parameters in different parts of the vineyard, which is expected due to heterogeneity and more and less pronounced erosion, especially in the footslope part. In order to statistically define the relationship between precipitation infiltration and physicochemical parameters, correlation analysis has been performed using values for first 30 cm depth, which are related to the granulometric composition, and C org , while average bulk density values for first 40 cm depth were used based on the HYPROP-FIT estimation presented in Krevh et al [59]. In Table 3, correlation matrix is presented, while statistically significant results are marked in red (α = 0.05).…”

Investigating Near-Surface Hydrologic Connectivity in a Grass-Covered Inter-Row Area of a Hillslope Vineyard Using Field Monitoring and Numerical Simulations

“…Disturbed soil samples were taken across the inter-row area from three positions (hilltop, backslope, and footslope), covering two soil depths (0-30 and 30-60 cm) at each position. This was replicated in three inter-rows to determine soil texture and soil organic carbon (SOC) [43] (Table 1). The texture was determined by combined sieving and sedimentation (ISO 11277:2020), and the organic carbon content by sulfochromic oxidation (ISO 14235:1998).…”