Enhanced riverine delivery of terrestrial nitrogen (N)has polluted many freshwater and coastal ecosystems, degradingdrinking water and marine resources. An emerging view suggests a contribution of land N memory effects–impactsof antecedent dryconditions on land N accumulationthat disproportionately increasesubsequent river N loads. To date, however, sucheffectshaveonlybeen explored for several relatively small riverscoveringa few episodes. Here weintroduce anindexfor quantifyingland N memory effectsand assess theirprevalenceusingregional observations and global terrestrial-freshwaterecosystem model outputs.Modelanalyses imply that land N memory effects areglobally prevalent butvarywidely in strength.Strongeffectsreflectlarge soil dissolved inorganic N (DIN) surplusesby the end ofdry years.During the subsequent wetter years,thesurplusesareaugmented bysoil net mineralizationpulses, whichoutpace plant uptakeand soil denitrification, resultingin disproportionately increased soil leaching and eventualriverloads.These mechanisms aremost prominent in areas withhigh hydroclimatevariability, warm climates,andecosystem disturbances. In 48 of the 118 basins analyzed,strongmemoryeffects produce 43%(21-88)% higher DIN loads following droughtyears than following average years. Such a marked influence supports close consideration of prevalent land N memory effects in water-pollution management efforts.