ESTIMATING PROCESSING TIME OF STREAM BENTHIC SAMPLES

Multiple regression analysis was used to generate equations relating time required to sort and tabulate benthic invertebrates to size characteristics of benthic samples collected from a 5th-order river and a 3rd-order woodland stream. Number of invertebrates in a sample was the primary determinant of sample sorting time. Amount of detritus, occurrence of filamentous algae (Cladophora) and source stream contributed significant but minor additional variability to estimates (cumulative R2 = 0.95). When number of animals was excluded as a variable, amount of detritus and presence/absence of Cladophora alone could be used to predict sorting time (R2 = 0.81). A typical sample containing Cladophora required 29% longer to sort than samples containing equivalent amounts of organic material but no Cladophora. The influence of sampler size and subsampling on processing and sorting time are considered. A general equation was derived to provide guidelines for selecting a size of stream sampler that subsequently minimizes total processing time required to estimate density of benthos with acceptable, constant precision. Overall sample processing and sorting time are reduced by-using a smaller sampler or by subsampling only if benthic densities of animals are high. Use of regression equations to anticipate processing and sorting time required for a particular sampling program permits development of more efficient designs.