QUADICA in RDF: Water Quality, Discharge and Catchment Attributes for Germany as a Knowledge Graph

This dataset presents an RDF (Turtle syntax) re-publication of the QUADICA collection (water QUAlity, DIscharge and Catchment Attributes for large-sample studies in Germany), converted from the original tabular resources using the open-source HydroTurtle tool. The goal is to enhance the interoperability, reusability, and FAIRness of German river water-quality data in the spirit of the Semantic Web and Linked Open Data. About QUADICA (source data). QUADICA is the first large-sample water-quality dataset assembled for 1,386 German catchments, combining water quality and quantity time series with meteorological drivers, diffuse nitrogen inputs, and >100 catchment attributes spanning topography, climate, land cover, lithology, and soils. This RDF version. We convert the public QUADICA tables into a Linked Data graph and mint stable URIs for stations, catchments, variables, and individual observations. Where appropriate, we expose monthly and annual WRTDS (Weighted Regressions on Time, Discharge, and Season) outputs with flow-normalized concentrations and mean fluxes, together with medians of observed discharge, and the long-term monthly climatologies. Ontologies and vocabularies used SOSA/SSN (observations, features, sensors) QUDT (quantity values and units) GeoSPARQL (spatial features/geometries, where available) Dublin Core, Schema.org, SKOS (metadata and classification) EnvThes (environmental terminology; e.g., catchment concept) HM-Ontology (a custom ontology developed as part of this project, to cover hydrological and meteorological concepts not addressed by existing vocabularies.) URIs are assigned to individual catchments, variables, and observations, enabling integration with other Linked Data sources and facilitating semantic queries. The RDF output is organized per catchment as multiple Turtle (.ttl) files. When loaded into a triple store, these can be unified into a single graph for querying and reasoning. This conversion was developed as part of the NFDI4Earth inititative. The dataset is licensed under CC-BY 4.0. This dataset is intended to support researchers and developers working on hydrology, environmental data integration, knowledge graphs, and natural language question answering over Linked Data.