Suspended-Sediment and Solids Sampling

Return to Water >> USGS Transboundary River Monitoring in Southeast Alaska 

Suspended-sediment samples are collected on each visit at both gage and border site locations. These samples are analyzed to determine concentration of sediments of different size classes. This information will be utilized to assess how metals and nutrients are transported through the watershed. Additionally, passive sediment samplers, called Walling samplers, are placed in the stream at each site twice a year to collect suspended-sediment. This allows us to collect samples of sufficient size to do analyses for metals present in the sediment. For reference, it would take approximately 30 gallons of sample from each site on a site visit to have enough sediment to do these analyses. Travel by helicopter means conserving weight which prevents us from doing this. Biannually, DGTs, another passive sampler, are placed in the stream to collect metals information.  

Solids sampling refers to the sampling of all other media than water: fine sediments, moss, and fish tissue. Fine sediments are sampled biannually in spring and late summer and the others are sampled annually in the late summer. All samples are collected for lab analyses of metals concentrations. In addition to collecting solids from gage locations, each border site (Taku, Stikine, and Unuk) will be sampled at least once during the five-year study.

Fine sediments are collected from recently deposited material along the water’s edge. This material is then sorted to remove anything larger than silt-sized particles. Moss samples are collected from rocks near the water’s edge on streambanks and bars. Fish tissue is collected from fish traps placed along streambanks for up to 24 hours. Resident fish, such as sculpin, are targeted as they reflect conditions at the study site.