Metal distribution in Clark Fork River sediments.

Area of Science:

• Environmental Science
• Geochemistry
• Hydrology

Background:

• Gravel river bed sampling is difficult due to large substrate size and abrasive sediment particles.
• Mining activities can lead to significant metal contamination in river sediments.

Purpose of the Study:

• To develop and apply novel sampling techniques for pore water and sediments in gravel-bed rivers.
• To characterize metal distribution and concentration within different sediment fractions in a historically mined river.

Main Methods:

• Utilized a modified core-freezing device for sediment profiling in cobble-gravel substrates.
• Developed a novel pore water sampler for collecting interstitial water.
• Analyzed metal concentrations across various sediment particle size fractions (<63 micrometers, 63 micrometers-2 mm).

Main Results:

• The <63 micrometer fraction, despite low mass (<4 wt %), showed metal concentrations an order of magnitude higher than the 63 micrometer-2 mm fraction.
• The sand fraction (63 micrometers-2 mm) contained 60% of the metals by mass in gravel substrates.
• Metals were primarily associated with sulfides, often coated with oxide rims, explaining low pore water metal concentrations.

Conclusions:

• Accurate characterization of fluvial bed sediment requires analysis across multiple particle size fractions.
• The form of metal (e.g., sulfides with oxide rims) significantly influences metal solubility and bioavailability in riverine environments.
• Developed sampling techniques are effective for studying contaminated river systems.