| Clean sampling methods were used to examine the solute (operationally defined as <0.2 μm) and total recoverable geochemistry of the Blackfoot River and Clark Fork River watersheds. The purpose of the first study, conducted in the upper Blackfoot River watershed near a proposed gold mine site, was to measure premining water quality conditions and to characterize the physical relationships between surface water and ground water. Other than for the major elements, most solutes were not well correlated with streamflow. The chemical variations appeared to be a product of the complex interactions among the timing and magnitude of meltwater and rainwater contributions, shifting proportions of the ground water component of the streamflow, and contaminant mobilization in the headwaters of the Blackfoot.; The second study measured both the solute phase and bed sediment in a one-time sampling event of the entire Blackfoot River watershed. The highest metal concentrations were located in the vicinity of the historic mining complex in the headwaters, and these concentrations declined sharply as tributaries joined the mainstem. Comparison of sediment samples with those collected in 1989 and 1995 do not show evidence for basin-scale long-term changes, despite remediation work begun in 1993.; The third project investigated the geochemical responses of the solute and suspended phases to streamflow on bi-hourly, daily, and seasonal timescales. The study was conducted on two rivers and two mountain streams in the Blackfoot and Clark Fork River basins. Generally, the trace element (Al, As, Cu, Fe, Mn, and Zn) patterns were more complicated than those of the major elements (e.g. Ca, K, Mg, Na), which were better correlated with discharge. Suspended sediment, total recoverable trace metals, and some dissolved elements exhibited short-term flushing effects at the onset of high flow conditions associated with spring runoff and a late summer precipitation event. Diel cycling was observed for pH, dissolved oxygen, water temperature, dissolved inorganic carbon, total suspended sediment, and total recoverable metals at some or all sites. For many parameters, short-term variations were small compared with long-term variations. However, the short-term variability of some parameters covered large portions of or exceeded the seasonal variability. These results have important implications for the future design of studies that aim to monitor and characterize the surface water geochemistry of contaminated and pristine watersheds. |
