QUADICA v2: Extending the large-sample data set for water QUAlity, DIscharge and Catchment Attributes in Germany

Abstract. The QUADICA version 2 dataset significantly expands upon the first version of QUADICA (water QUAlity, DIscharge and Catchment Attributes for large-sample studies in Germany), by incorporating more recent data, additional water quality and driver variables, and more stations with concurrent water quantity data. Specifically, QUADICA v2 extends the time series of the first version up to 2020 and introduces new water quality variables, including water temperature, oxygen, and chlorophyll-a concentrations, as well as concentrations of ammonium, sulfate, and geogenic solutes like calcium. These additions enable a more comprehensive understanding of ecological impacts, including eutrophication effects, and water quality dynamics across catchments. Furthermore, we have integrated QUADICA with the hydrological large-sample datasets CAMELS-DE and Caravan-DE, effectively doubling the number of stations with combined water quality and quantity data to 637 out of the 1386 stations in total. The inclusion of time series on point and diffuse sources of both nitrogen and phosphorus allows for more thorough investigations of driver-response relationships and nutrient export from catchments. To facilitate visualization and exploration of QUADICA, we provide a user-friendly, interactive R application along the online data repository. This makes QUADICA v2 a comprehensive dataset that spans from driver to impact variables, offering a valuable resource for researchers and practitioners.