engleski

Modeling Seasonal Soil Moisture Dynamics in Gley Soils in Relation to Groundwater Oscillations

The constant change in the soil moisture as a result of precipitation and groundwater oscillations makes modeling in the unsaturated zone rather complex. This change can have a large effect on crop production and various environmental processes. The study aimed to determine the water regime of the unsaturated soil zone of gley soils while taking into account seasonal variations of shallow groundwater table and a nearby river water level. The field site was located in the Biđ field (eastern Croatia), where a detailed soil survey was performed during 2016. Soil hydraulic parameters (SHP) were determined for first two layers, while the soil water leachate was monitored using the in-field zero- tension lysimeters. Piezometers were used to monitor groundwater level (GWL) daily oscillations, while simultaneously collecting the data regarding Sava river levels. Numerical modeling of vadose zone water dynamics was performed using HYDRUS-1D. Saturated water content, θs, and the hydraulic conductivity, Ks, were measured, other parameters which describe the soil water retention curve (α and n) were optimized during the model calibration, using Shuffled Complex Evolution (SCE) algorithm. The model was validated using the data obtained from the zero-tension lysimeters. The modeling performance was estimated using the coefficient of determination (R2): 0.86 – 0.91 ; root-mean- square error (RMSE): 3.68 – 4.73 cm (annually) and Nash-Sutcliffe model efficiency (NSE): 0.20 – 0.59. Optimized SHP based on van Genucthen Mualem model were able to successfully estimate seasonal water regime dynamics. Different groundwater levels were recorded at each location, which had a major influence on soil water content (WC) and pressure head (PH) oscillations in the upper soil layers of gley soils. The statistical analysis showed a strong positive correlation between GWL and soil water regime (WC and PH) in the upper layers (0 - 50 cm) throughout the year, in comparison with the precipitation effect. The low amount of precipitation in the observed year accentuated the effect of groundwater level on soil water in the root zone. Results signify the importance of groundwater resources in agricultural production due to its major influence on soil upper layers moisture.

vadose zone ; water table ; numerical simulations ; HYDRUS, soil hydraulic properties optimisation

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