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After adding a little sodium hexametaphosphate dispersant, we use a plunger to carefully stir the cylinder then let it settle, to ensure good mixing and standardized suspension of the sediment.

For some projects, scientists want to calculate sediment settling velocity and need to measure particle size using gravity. We use custom-built settling tubes filled with water – three at 2 meters tall (like the one shown here) and one 3 meters tall.

After releasing sediment into the top of a settling tube filled with water, a pan and microbalance collects and weighs the sediment as it slowly reaches the bottom of the tube. A computer records the cumulative sediment weight over time, as well as how long it took each particle to reach the pan.

The settling tube is filled with water and a pre-weighed sediment sample of mixed particle sizes is poured onto this brass "gate" at the top of the tube. When the operator flips the switch, the gate opens quickly like a venetian blind, releasing the whole sediment sample into the water column at the same time.

Washing a sediment sample through two sieves with distilled water lets us measure the fractions of gravel (bigger than 2 millimeters or -1 phi) and sand (2 millimeters to 63 microns, -1 phi to 4 phi). Smaller sediment passes through the sieves into a standard 1-liter graduated cylinder.

We slip split cores into a labeled D-tube, and both are stored on specialized core racks in a walk-in sample refrigerator. USGS and non-USGS scientists often use our core and sample archives for new research. Contact the lab manager for access policies and other details.

Sediment cores may be subsampled for further processing and analysis in other labs, like the Sediment Lab which is across the hall from the Core Lab.

Lab technician Angela Tan takes a sample of the sediment suspended in liquid, for analysis in one of several ways.

The UIC CM5230/CM5015 analyzes total inorganic carbon content. It's less automated than other analyzers, but often easier to use.

Each half of a split sediment core is wrapped in plastic to prevent drying and contamination. For long-term storage, we can shrink-wrap one half with a thick film that prevents moisture loss.

The Micromeritics Sedigraph III uses X-rays to automatically analyze settling times for sediment sizes between 300 microns and 0.1 microns (2 phi to 13 phi).

Scientists from the USGS Western Ecological Research Center deploy to Big Sur to study seabird populations.

Andrew Stevens runs a personal watercraft rigged with sonar and precision GPS to survey northern Monterey Bay, California.

Litterfall and throughfall monitoring for mercury dry deposition

Alex Snyder (left) and SeanPaul La Selle stay in radio contact with a personal watercraft operator offshore in order to provide supplies and safety near Moss Landing, California. 

Width measurement for Pacific pocket mouse forefoot print on track card

Mohawk River at Lock 8 near Schenectady (01354330) Live Ice Jam Web Camera

Super Gage-School Branch at CR750N at Brownsburg, IN 

USGS IN staff collecting biological samples

Dan Hoover takes a break near Moss Landing, California. Dan drives the all-terrain vehicle seen behind him to rapidly survey long sections of beach using precision GPS. 

The refrigerated sample repository of the USGS Pacific Coastal and Marine Science Center in Santa Cruz, CA includes easily accessible shelving space which can store thousands of samples.