Who pollutes, who bears: transboundary responsibility and inequality of river-borne nutrient burdens

This repository contains the analysis code and derived data tables that reproduce the country-level nutrient responsibility ledger, the century-scale (1900–2000) reconstruction, the in-transit retention analysis, and all figures of the manuscript by Yiran Li (Graduate School of Economics, Kobe University). Because most of the world's large rivers cross international borders, the nitrogen and phosphorus a country releases into its catchment are frequently delivered as a water-quality burden to its downstream neighbours. Combining the HydroBASINS river network with the IMAGE-Global Nutrient Model reconstruction of national nutrient export, the code builds a directed country-to-country connectivity operator and, for each country, separates the nutrient it exports within its own territory from the foreign upstream nutrient imposed on it. In 2000, 27.5% of the nitrogen (10.0 Tg N yr⁻¹) and 24.2% of the phosphorus reaching the world's rivers crossed at least one international border, and 48 countries were net downstream bearers. The resulting benefit–cost asymmetry is regressive with national income (r = −0.37 for nitrogen, −0.35 for phosphorus), has deepened over a century in which the cross-border burden rose 1.7-fold, and is buffered by in-transit retention that removes 39% of nitrogen and 52% of phosphorus before delivery. Contents. scripts/ — Python scripts that build the N and P responsibility ledgers and bilateral matrices, the 1900–2000 time series, the retention analysis, and the manuscript and supplementary figures. data_derived/ — the directed country-to-country river network operator, per-country ledgers, bilateral transfer matrices, decadal time series, and retention tables. data_input/GNM_mouth/ — an empty folder in which the public IMAGE-GNM river-mouth files are placed to regenerate the time-series and retention outputs. A README documents the full layout and reproduction steps. The core responsibility ledger runs from data_derived/ alone. Input data (public, not redistributed here). HydroBASINS v1c level-6 (hydrosheds.org); the IMAGE-Global Nutrient Model river-mouth nitrogen and phosphorus load and retention, 1900–2000 (DANS, doi:10.17026/dans-zgs-9k9m); Natural Earth country boundaries and attributes (naturalearthdata.com). Requirements. Python ≥ 3.10 with numpy, pandas, matplotlib, geopandas (0.13.2) and pyogrio. Licence. Code: MIT. Derived data tables: CC-BY-4.0. Please cite the associated article and the input datasets.