Clean Monthly Total Nitrogen Dataset for Seaward Rivers in Qingdao, China: January-Only Baseline and Reproducible Source Data for Delayed Nitrogen Export Analysis (2020–2025)

This record provides a cleaned, Zenodo-ready data package for monthly total nitrogen (TN) concentrations in key seaward rivers in Qingdao, China, covering January 2020 to January 2025. The dataset supports a Journal of Hydrology manuscript examining hydroclimatic forcing, catchment-scale TN divergence, and diagnostic evidence for delayed nitrogen export from coastal agricultural alluvium. Version 2 replaces the original single Excel workbook with a curated clean data package. Formula-error regions in non-core workbook areas, including #REF! and #VALUE! cells, were excluded from the released clean CSV files. These formula errors do not affect the three primary river series, the January-only baseline calculation, or the reported percentage changes. A formula-error audit table is included for transparency. The package includes: clean monthly TN records for the 98 monitoring sections, primary-catchment TN series for the Dagu, Licun, and Baisha rivers, January-only baseline calculations, hydroclimatic forcing indices, Eckhardt export-capacity scenario outputs, figure source data, a bootstrap script, bootstrap output, a manifest file, and a README data dictionary. The January-only comparison was adopted because January 2025 is the fully auditable cross-catchment endpoint for the three primary catchments. Partial February 2025 values are not used in the main cross-catchment baseline comparison. Missing values were not imputed. The January-only design sacrifices statistical power for cross-catchment comparability. The dataset is intended for reproducibility, data auditing, and supplementary use. Total nitrogen is the measured variable; nitrate-N, groundwater age, isotope source apportionment, and direct groundwater residence time were not measured in this dataset.