Sediment grain-size distributions from vibracores collected in Searsville Lake, Jasper Ridge Biological Preserve, Stanford, California

Cores were collected on October 29, 2018. A handheld global satellite navigation system (GNSS) receiver was used to determine the locations of sediment samples. Sediments were subsampled from cores by hand in the laboratory at 0.5 and 1.0 cm vertical intervals.

The grain-size distributions of samples were determined in the USGS Pacific Coastal and Marine Science Center sediment lab. Approximately 20 g of sediment was sub-sampled and 10 mL of 35 percent hydrogen peroxide was added to remove organic material in the sample. The sample was heated at 250 degrees C to remove any remaining hydrogen peroxide and was placed in an ultrasonic bath to liberate the fine fraction. Subsequently, the sample was centrifuged for 1.5 hours to remove soluble salts. Samples were funneled through 2 mm and 63 um sieves to separate the gravel (greater than 2 mm), sand (63 um to 2 mm), and mud (less than 63 um). The sand and gravel fractions were dried in an 80-degree C oven and weighed. Five mL of sodium hexametaphosphate was added to the mud fraction and a 20 mL aliquot was taken from a 1 L graduated cylinder to determine the weight of the mud. The sand fraction was run through a 2m settling tube. Measured settling velocities were converted to sizes of equivalent quartz spheres in quarter-phi size intervals. The particle-size distribution of the mud fraction was analyzed separately using a Beckman Coulter LS 13 320, and the gravel, sand, and mud results were integrated into a single grain-size distribution for each sample.