Factors controlling the daily change in groundwater level during the growing season on the Great Hungarian Plain: a statistical approach

Abstract

The phenomenon of diurnal fluctuation in the groundwater level (GWL) often reflects the water uptake by plants. The rate of evapotranspiration from the groundwater (ETgw) can be calculated from the daily rate of change in GWL, but several factors may influence the vertical groundwater dynamics. The occurrence of diurnal fluctuation and the daily rate of change in GWL were determined in 20 monitoring wells on the Great Hungarian Plain with different vegetation cover (Quercus robur L., Robinia pseudoacacia L., Populus × euramericana and unforested control sites) and with differences in the water table depth (WTD) and in soil and salinity characteristics. ETgw was calculated for eight selected sites. Forest vegetation significantly increased the occurrence of diurnal fluctuation (8 out of 11 cases), and the mean daily change in GWL multiplied by the specific yield (S y) was 2.2 times higher for forest sites than for the unforested control sites. The median daily change in GWL showed a significant negative correlation with S y, where the vegetation effect was manifested as ETgw-induced diurnal fluctuation. A significant correlation was obtained at each monitoring well between the meteorological parameters controlling the evaporative demand and the daily rate of change in GWL. A reduction in groundwater uptake after rainfall events and increasing groundwater consumption during dry periods were also revealed. A significant positive correlation was found at some study sites between the daily change in GWL and WTD, and between ETgw and the leaf area index (LAI). Mean ETgw was 8.2 mm day−1 for oak stand and 0.4 mm day−1 for black locust stand, while it ranged from 1.7 to 6.0 mm day−1 for the four poplar stands, which may reflect the variability in water demand, LAI, groundwater and soil characteristics.