AWWA JAW53375

Dynamic variations in the chemical and isotopic character of the lower Missouri River can be explained primarily in terms of the relative contribution of lower basin waters in the river, which can be computed from gauging station data to vary from <5 to 86%. The endmember representing the lower basin component has an average electrical conductivity of 261 uS, a pH of 7.8, an alkalinity of 111 mg/L, sulfate (SO4) of <5 mg/L, total organic carbon (TOC) of 5.9 mg/L, and a o18O value of -6.1, mostly similar to shallow meteoric groundwaters in Missouri. The endmember representing the upper basin has an average electrical conductivity of 814 uS, a pH of 8.2, an alkalinity of 191 mg/L, SO4 of 216 mg/L, TOC of 3.0 mg/L, and a o18O value of -11.6. The normalized volumetric contributions facilitate geographic deliniation of nonpoint source pollutants such as TOC and offer new ways to predict water quality and estimate annual loads. Includes 33 references, tables, figures.