Availability, dynamics and chemistry of groundwater in the Bucklige Welt region of Lower Austria

The Bucklige Welt region in the south-eastern part of Lower Austria experiences occasional shortages in the local water supply during dry periods. Until now a detailed investigation of existing aquifers and their hydrological or hydrochemical characteristics in this region has been lacking. Therefore, a study was carried out to characterise the availability, dynamics and chemistry of shallow groundwater. Collected data include (a) in-situ measurements of discharge (Q) and the physico-chemical parameters water temperature
(WT), electrical conductivity (EC) and pH at 747 springs, (b) river discharge measured within a period of dry weather conditions at 59 sites, (c) in-situ measurements of Q, WT, EC and pH and chemical analyses of major ion concentrations of 135 groundwater samples taken within a period of dry weather conditions, (d) in-situ measurements of Q, WT, EC and pH, chemical analyses 18 of major ion and trace element concentrations and O isotope analyses of 529 water samples collected monthly at 43 springs and three wells over twelve months and (e) in-situ measurements of Q, WT and EC at two springs recorded at 15 minute intervals over a period of six months.
The study area is predominantly composed of mica schist, Augen gneiss and paragneiss, which provide low groundwater yields (1.5 to 6.2 L/s/km² ). Locally, areas of calc-mica schists and quartzites yield more groundwater (26 and 31.8 L/s/km² , respectively).
The most productive aquifers constitute Quaternary valley sediments, which currently cover the water demand of larger settlements. Apart from the sediment aquifers, groundwater occurrences represent shallow fracture aquifers with small recharge areas and highly variable discharge over time. Base flow can increase by a factor of 6 after the snow melt and by a factor of up to 10 in
months of high precipitation. Mean groundwater residence times range from 14 to 21 months. Mineralisation is generally low (the sum of dissolved solids lies between 68 and 351 mg/L), only the occurrences of marble or calc-mica schists in catchment areas result in higher concentrations (395 to 539 mg/L). Austrian national guideline values for drinking water are occasionally exceeded
with respect to Na⁺, Cl^- , NO₃^- , Fe²⁺ , Mn²⁺ , Al and Ni.. Among these  parameters, elevated concentrations of Na⁺ , Cl^- , NO₃^- and Ni are considered to be of anthropogenic origin, and Fe , Mn and Al of geogenic origin.
Our results demonstrate the lack of new potential groundwater resources in the study area. Furthermore, the existing groundwater resources, while of good quality, are shown to exhibit a strong dependency on weather conditions. Based on these findings, local water authorities are currently planning to secure a sustainable supply of drinking water by tapping into aquifers outside the study area.