Variability in the macrofauna of a single riffle in Prosser Creek, California, as indicated by the Surber sampler

To determine the variability of the macrofauna in a single riffle, 100 bottom samples were taken in Prosser Creek, Nevada County, California, using the Surber Square Foot Sampler with a Latin Square experimental design. Statistical analyses of the results indicate that 194 samples would be required to give significant figures on total wet weights at the 95 per cent level of confidence. Total numbers would require 73 samples. The number of square foot samples necessary to ensure representation of the commonest genera or higher groups of aquatics, on the other hand, was quite low; therefore, because of its saving in labor and time, qualitative sampling rather than volume or weight, is recommended for use in pollution studies. Possibly because of the uniformity of the riffle, no correlation was found between types of organisms and different types of bottom, but striking correlations were observed with depth and speed of current. The majority of genera preferred both moderate depths and water speeds although for others the reverse was true.