Human impact on nitrate export: An analysis using major world rivers

We developed a simple model that related NO3 export to point-source N loadi ng and nonpoint source N loads from chemical fertilizers and NOy deposition and tested it at the global scale using data from 35 large rivers with a g lobal distribution. The model explained well (r(2) > 0.8) the nearly 1000-f old variation in NO3 export from different regions of the world. The model suggests that human activity is the dominant control of NO3 export even tho ugh less than 20 of the 100 Tg N yr(-1) added to land in fertilizer and NOy deposition is at present exported from rivers as NO3. Watershed export to rivers may increase in the future due to either increased loads to the wate rshed or decreased watershed retention. Simple models, coupled with continu ed measurements of NO3 in rivers, will be of use in interpreting these regi onal changes.