The value of the world's ecosystem services and natural capital Robert Costanza , Ralph C. d’Arge , R.S. de Groot +10 more 1997 Nature 21252 citations
Regional nitrogen budgets and riverine N & P fluxes for the drainages to the North Atlantic Ocean: Natural and human influences Robert W. Howarth , Gilles Billen , Dennis P. Swaney +12 more 1996 Biogeochemistry 1327 citations