and splitting the remaining sample. Qualitative samples are sieved to a standard size of 210-212 µm, whereas semi-quantitative samples are retained on a sieve with openings of 425 µm. Additional samples using smaller mesh sizes can be collected for semi-quantitative samples if conditions in the study unit warrant collecting smaller invertebrates. For example, using a smaller mesh size can be particularly helpful when collecting samples in streams with unstable sand or fine gravel beds where small oligochaetes and chironomids are expected to dominate the benthic invertebrate communities.
All sample containers are labeled internally and externally using standardized waterproof labels and a unique 16-character code that identifies the study unit, sampling date, type of sample, sample number, and sample component. All samples are fixed in 10-percent buffered formalin and shipped to an outside contractor for identification and enumeration of benthic invertebrates under the guidance of the Biological Quality-Assurance Unit, Arvada, Colo. This Unit has responsibility for contract development, laboratory quality assurance and quality control, entry of contractor data, national coordination of taxonomic identifications, and storage and maintenance of taxonomic collections. In addition, the BQAU monitors the effectiveness of field elutriation and splitting techniques by analyzing the elutriate and split samples from 10 percent of study-unit sample reaches.
Proper safety and health procedures need to be followed when sampling. Field personnel should be trained in the safe and proper operation, storage, transportation, and maintenance of equipment. Safety equipment must be available and must be used to prevent injury when personnel are working in fast or deep water or are handling chemicals such as formalin. Field personnel should be instructed in the recognition of poisonous plants and animals. A list of medical facilities close to each sampling site, as well as a cellular phone, should be kept with each field vehicle for use in medical emergencies.