Stable and radioactive isotope and multielement measurements from the Koppány and Ledava catchments

Regular monitoring approaches do not provide sufficient information on loads, pollution sources and emission pathways. Therefore, our research aimed to implement a novel comprehensive, targeted monitoring approach in a Hungarian and a Slovenian catchment to enhance the understanding of contaminant pathways, quantify particulate transport, and delineate surface versus subsurface contributions to elements of the catchment scale water cycle. The Hungarian pilot catchment is located in SW Hungary, covering most of the Koppány Stream catchment above Tamási. It is a hilly catchment, ca. 660 km2 with a significant (~78%) agricultural share and extended undisturbed forests (~20%). The headwater area of the Koppány contends with substantial wastewater discharge. The Ledava catchment is a HU / SI cross-border area (1940 km2). It is a hilly to lowland agricultural area covered by 20 % forest. The sampling program included (i) regular stream water sampling (automatic samplers were installed in existing river gauges to sample high flow events); (ii) monitoring campaigns conducted to survey the longitudinal profile of the main branch and the tributaries; (iii) drilling of shallow groundwater wells along the riverbed; (iv) monthly collection of bulk precipitation; (v) composite sampling from the direct wastewater discharge. In addition to the water chemistry (basic ions, total suspended solids, nutrients, and potentially toxic elements (PTE)), stable and radioactive isotopes were measured as natural tracers to investigate hydrological pathways and residence times. The tasks of lab measurements were shared between the participating institutions: BME (general water chemistry), Jožef Stefan Institute (stable isotopes and PTE), HUN-REN Institute for Nuclear Research (tritium). The research and the measurements were implemented within the Slovenian-Hungarian research project titled “Validation of watershed-scale pollutant transport models based on isotopic and multi-component measurements.” co-financed by the National Research, Development and Innovation Office Hungary under grant No. SNN-143868 and the Slovenian Research Agency, research project N1-0309 and programme group P1-0143. The research presented in this article was supported by the project titled “National Laboratory for Water Science and Water Safety”, Nr RRF-2.3.1-21-2022-00008, NRDIO Hungary. (2026-03-20)