DOC and nitrate in farmland represent key chemical species that determine the water quality in the Karst Critical Zone (KCZ). The work reported here focuses on quantifying fluxes of these species in an experimental farm site (University of Leeds Farm, UK) overlying a dolomitic karst aquifer of Permian age. In this research, the Transect Method was applied for the first time to farmland by combining hydrochemical data from soil and groundwater for computation of mass fluxes. The Transect Method, developed for management of industrially contaminated sites, was applied to a farm source due to the presence of localised contamination from application of pig slurry.Required inputs for our approach include concentrations of nitrate and DOC in soil water and groundwater, net recharge flux (here derived from a MODFLOW-2005 model) and local hydraulic gradient and conductivity measurements. Key outputs are fluxes and downstream groundwater concentrations of DOC and nitrate. Downstream concentrations were validated against direct groundwater measurements, demonstrating the veracity of the approach. The approach shows that the localised contamination has a significant impact on both concentrations of nitrate and DOC in groundwater, although the DOC impact is greater, because the upstream land uses also produce nitrate as a result of agricultural practices that are widespread in the region.The results of the study also constrain the zone vulnerable to contamination to the upper ~40 m below the ground surface. Future modelling efforts on solute contaminant transport should focus on this shallow vulnerability zone (0-40 mBGL) and the Transect Method applied in this work can be used to define boundary conditions. Hence, following this research, we envisage to export a generic approach that combines physical flow parameters and hydrochemical analyses for computation of subsurface mass fluxes using the Transect Method, to identify the degree of impact of specific point sources and to support conceptualization and modelling of contaminant transport in the KCZ of farm areas.

Lake Velence is a shallow soda lake whose water level and water quality show a severely deteriorating tendency in recent years. Until recently, the groundwater component in the lake’s water budget has not been taken into consideration. To integrate the lake into the groundwater flow system at the regional scale, methods of “basin hydraulics” were applied. In addition, 17 water samples were collected for δ2H and δ18O, and for ΣU, 226Ra and 222Rn activity measurements to use these parameters as environmental tracers of groundwater contribution. Groundwater mapping revealed that groundwater recharges in Velence Hills and the local elevations south of the lake, whereas discharge occurs by the lake’s shoreline and along surface watercourses. The results indicated that Lake Velence is the discharge point of local groundwater flow systems known to be more sensitive to climate changes and anthropogenic activities (e.g., contamination, overexploitation). Groundwater and lake water have similar uranium activity concentrations serving as another sign of groundwater inflow into the lake. Therefore, it is necessary to consider both the groundwater component in the lake’s water management and its vulnerability regarding local and short-term changes in the catchment area.

In Hungary the drinking water supply is mainly based on groundwater, in which radionuclides are common components. Since the mobility of the most common radionuclides, uranium and radium, is strongly influenced by the geochemical conditions, knowledge on the geochemical parameters of water is required. This depends on the flow system and the flow regime. Therefore, hydrogeology has a crucial role in revealing the origin of elevated activity concentrations. This research presents a case study in Hungary where the drinking water supply is provided by bank filtered and karst wells. In most of the wells of the research area the gross alpha values are above the screening level, 0.1 Bq L 1. The aim of this study is to determine which radionuclides may cause the elevated radioactivity and explain their occurrence using the hydrogeological approach. All samples of the study were analysed for (U-238þU-234), Ra-226, Rn-222. Alpha spectrometry applied on Nucfilm discs was used to measure the uranium and radium activity while radon activity was determined by liquid scintillation. The study revealed the correlation between the river water level fluctuation and the uranium content of the wells. The results of this study highlighted the transient nature of river bank filtered systems, which should be taken into account in the monitoring and water supply strategy.

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