Nitrogen removal by streams and rivers of the Upper Mississippi River basin

We used stream chemistry and hydrogeomorphology data from 549 stream and 447 river sites to estimate NO(3)-N removal in the Upper Mississippi, Missouri, and Ohio Rivers. We used two N removal models to predict NO(3)-N input and removal. NO(3)-N input ranged from 0.01 to 338 kg km(-1) d(-1) in the Upper Mississippi River to < 0.01-54 kg km(-1) d(-1) in the Missouri River. Cumulative river network NO(3)-N input was 98700-101676 Mg year(-1) in the Ohio River, 85961-89288 Mg year(-1) in the Upper Mississippi River, and 59463-61541 Mg year(-1) in the Missouri River. NO(3)-N output was highest in the Upper Mississippi River (0.01-329 kg km(-1) d(-1)), followed by the Ohio and Missouri Rivers (< 0.01-236 kg km(-1) d(-1)) sub-basins. Cumulative river network NO(3)-N output was 97499 Mg year(-1) for the Ohio River, 84361 Mg year(-1) for the Upper Mississippi River, and 59200 Mg year(-1) for the Missouri River. Proportional NO(3)-N removal (PNR) based on the two models ranged from < 0.01 to 0.28. NO(3)-N removal was inversely correlated with stream order, and ranged from < 0.01 to 8.57 kg km(-1) d(-1) in the Upper Mississippi River to < 0.001-1.43 kg km(-1) d(-1) in the Missouri River. Cumulative river network NO(3)-N removal predicted by the two models was: Upper Mississippi River 4152 and 4152 Mg year(-1), Ohio River 3743 and 378 Mg year(-1), and Missouri River 2277 and 197 Mg year(-1). PNR removal was negatively correlated with both stream order (r = -0.80-0.87) and the percent of the catchment in agriculture (r = -0.38-0.76).