Element concentration, stable and radioactive isotope data from multiple environmental matrices in two mid-sized...

This article presents a comprehensive multi-matrix dataset collected to support the investigation and validation of catchment-scale contaminant transport processes using combined hydrochemical, multi-element, and isotopic approaches. The dataset was generated within a targeted monitoring program conducted in two medium-sized Central European catchments, the Koppány River (Hungary) and the Ledava River (Slovenia), both characterized by intensive agricultural land use, wastewater inputs, and erosion-sensitive conditions. The dataset integrates measurements from multiple environmental compartments, including precipitation, surface water, groundwater, wastewater, soil, riverbed sediment, and suspended particulate matter (SS). Sampling was designed to capture both baseflow conditions and hydrologically dynamic periods, with particular emphasis on high-flow events associated with enhanced erosion and material transport. River water samples were collected through a combination of grab sampling and flow-proportional automatic sampling, while suspended sediments were obtained using passive samplers during flood events. Soil and sediment samples were collected at representative locations and processed to fine fractions prior to analysis. The analytical data include conventional hydrochemical parameters (e.g. major ions, nutrients, pH, electrical conductivity, turbidity), alongside detailed multi-element composition comprising potentially toxic elements, rare earth elements, and geological normalizers. Elemental concentrations were determined using inductively coupled plasma mass spectrometry (ICP-MS) following microwave-assisted digestion or selective extraction procedures. In addition, isotope-based tracers were incorporated, including water stable isotopes (δ²H, δ¹⁸O), radioisotope data (e.g. ³H, ¹⁴C) indicating groundwater age information, and nitrate stable isotopes (δ¹⁵N_NO3, δ¹⁵O_NO3), enabling the characterization of hydrological pathways and nutrient sources. The dataset combines newly acquired measurements with pre-existing hydrological, hydrochemical, and land use data into a harmonized database structure. This integration enables the comparison of elemental and isotopic signatures across environmental matrices and hydrological conditions, supporting applications such as source characterization, assessment of particulate and dissolved transport processes, and evaluation of hydrological flow components. The data are provided with detailed metadata on sampling conditions, analytical procedures, and quality control, including the use of certified reference materials and replicate analyses. Limitations related to incomplete parameter coverage, variable hydrological data availability, and missing metadata for a subset of groundwater samples are documented. This dataset provides a consistent, multi-tracer observational basis for the analysis of contaminant transport processes in agriculturally impacted catchments and for the evaluation of catchment-scale modelling approaches.