ISOTOPIC AND ELEMENTAL HYDROGEOCHEMISTRY OF A MAJOR RIVER SYSTEM - FRASER-RIVER, BRITISH-COLUMBIA, CANADA

The Fraser drains one quarter of British Columbia, but within its watershed there occurs a disproportionately large share of the province's economic activity. Agriculture, fishing, forestry, mining and tourism are all important, the Fraser being the world's largest source of salmon. To preserve this range of activities, the quality of its waters must be ensured. This study documents the chemistry of the waters. Samples from seventeen sites along the Fraser and its principal tributaries were analyzed for major anions and cations, for 28 dissolved trace and ultratrace elements, and for the isotope ratios of O, H, S, C and Sr. The data show that the primary control on chemistry is the diverse geological terranes that are drained. For example, SO4 in the headwaters comes from dissolution of sedimentary sulphate minerals. Towards the coast, weathering of sulphide minerals become progressively more important as a source of SO4, including igneous sulphides that contribute a substantial flux of elements such as Se and Sb. Superimposed on the natural fluxes are anthropogenic contributions. Some, such as dissolved organic carbon and NaCl from pulp mills, can be readily identified. The sources of others are less certain. Molybdenum is much higher in the Fraser than in the Ottawa River. But it is not clear if this high level of Mo is natural or is the result of mining for this metal. During the period of peak flow in July, 1993, Fraser waters had an unusually high level of CO2. The CO2 is derived from the decay of vegetation on land and may have been influenced by timber operations.