Online screening tool for precipitation stable isotopes records: Hybrid distance / density based outlier filtering approach via Interactive web application

The ratio between the heavy and light stable isotopes in precipitation is an effective tool in answering questions in e.g., hydrology, climatology, biogeochemistry etc., but only if spatiotemporally sufficient data is available provided by precipitation monitoring networks. However, when data from multiple sources are gathered into large databases these can contain errors that can severely impact research outcomes. The most common practices of stable isotope database filtering applied static thresholds not accounting for the spatially dynamically changing nature of the variable. We propose a distance-based outlier detection approach to identify erroneous or inconsistent data points by deriving adjustable elevation corrected averaged isotope values for nearby stations within an adjustable search radius (0 < R ≤ 500 km, default: 100 km), thus dynamic error threshold.

The IsoQC tool is showcased on the records from the precipitation stable isotope network of Slovenia and its vicinity. It enables an objective and reproducible analysis of spatial and temporal patterns of nearby precipitation stable isotopic records by employing thresholds for dissimilarity between regional averages and individual station records. The interactive nature of the application allows users to explore spatial and temporal variations in precipitation isotope compositions, identify anomalous data points, and assess regional isotope patterns in real time.

The IsoQC app allows users to upload their own datasets to analyze stable isotope records from monthly precipitation samples. The data upload module supports MS Excel and CSV formats. To ensure proper functionality, the uploaded data must contain specific columns like station identifier, date, coordinates and isotope data. The proposed tool supports the standardized quality control of isotope records across different databases and facilitates harmonious interoperability based on FAIR data principles.

Keywords: precipitation stable isotopes, δ²H, δ¹⁸O, d-excess, outlier detection, Slovenia

Acknowledgement: The research leading to these results received funding from Slovenian Research and Innovation Agency under Grant Agreements P1-0143, J6-3141, J6-50214, N1-0054, N1-0309, from IAEA under Grant Agreements F31006, F33024, F33031, RER7013, RER7017 and SLO7001; and from the National Research, Development and Innovation Office (NRDI) Fund project No. SNN-143868.