Fig. 8. Regional source apportionment of the nitrogen load of the Scheldt. Sum of the cumulative loads of the four regions exceeds the observed load at Hemiksem by 14–20% (Figs. 4 and 6). This is probably because of uncertain estimates of water exports toward Dunkirk at the French-Belgian border and toward Western Flanders at Gent and the neglection of in-stream retention with these full-catchment instantaneous balance estimates (Olde-Venterink et al. 2003, Billen et al. 2005).