Streamwater chemistry of the Spring River, Arkansas, is explained as a mixture of ground water, overland/subsurface flow, and bank storage. These end-member components are considered to be invariant in space and time, with overland flow being chemically identical to subsurface flow. Binary mixing models were used to identify the end members, with solutes Ca2+, Na+, Si, NO3−, PO43−, and DOC having sufficient variation in the streamwaters. These end members were used in a ternary mixing model to assess the relative contributions of end-member components to streamwater chemistry. The percentage of variance explained by the end-member mixing analysis ranges from 38 to 99%, with the results of this model being reasonable in light of hydrograph separation and mass-balance calculations. Constraining the end-member compositions and allowing their composition to change over time will provide results that more accurately reflect streamwater chemistry.