A CHLORIDE BUDGET FOR THE MISSISSIPPI RIVER, HEADWATERS TO MOUTH

ABSTRACT Mass budgets for chloride were estimated from 1975‐1978 for the Mississippi River from headwaters to near the mouth to determine the magnitudes of natural and anthropogenic sources. Annual chloride input from precipitation ranged from about 200 kg mi^‐2yr^‐1 at Royalton, Minnesota, to about 350 kg mi^‐2yr^‐1 at Vicksburg, Mississippi. Mass export ranged from about 900 kg mi^‐2yr^‐1 at Royalton to about 8000 kg mi^‐2yr^‐1 at Vicksburg. As much as 80 percent of the residual, the difference between input and export, probably is contributed by anthropogenic sources. In particular, semi‐logarithmic scatterplots of monthly total discharge against chloride concentration show that, during early spring, chloride elevations in the Mississippi River and Ohio River are elevated, possibly because of flushing of road salt and leaching of chloride from the accumulated snowpack.