CHAPARRAL CONVERSION AND STREAMFLOW - NITRATE INCREASE IS BALANCED MAINLY BY A DECREASE IN BICARBONATE

Converting Arizona chaparral watersheds to grass by controlling the brush with herbicides increases water yield as subsurface runoff to streams. The increased stream discharge is accompanied by several hundredfold increases in the nitrate concentration of the stream water. Nitrate concentration remained 46-69fold above normal for 11 years or more. Nitrate ion concentration increases were balanced mainly by bicarbonate ion concentration decreases, with little change in the concentration of other anions or cations. One mechanism suggested to explain the decrease in bicarbonate that balances the increase in nitrate is the reaction of H** plus NO//3** minus with HCO//3** minus to give carbon dioxide and water.