WWRC 91-22
Biases Associated with Four Stream Substrate Samplers
Abstract
We compared samples collected from 10 substrates of various compositions with a single-probe freeze-core
sampler, a triple-probe freeze-core sampler, a McNeil sampler, and a shovel. The accuracy with which these
devices sampled particles larger than 50 mm in diameter varied; they were oversampled by the freeze-core
devices, sampled in proportion to their availability by a shovel, and sampled inconsistently by the McNeil
sampler. The geometric mean particle size and variance of single-probe freeze-core samples consistently
exceeded those of samples collected with the other devices. Most sample means also exceeded the test substrate
means. By excluding the proportions of particles larger than 50 mm in diameter in our analyses, we found that
proportions of several particle sizes in samples collected by different methods differed significantly from the
actual proportions in test substrates. There were few differences between the single- and the triple-probe
freeze-core samples or between McNeil and shovel samples. All four samples were biased, but the McNeil sampler
most frequently produced samples that approximated the true substrate composition.
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