Macroinvertebrate Collection Methods
Macroinvertebrates are collected using modified EPA Rapid Bioassessment Protocols (RBP III) for single habitat collections (Barbour et al. 1997). D-frame dip nets are used to sample macroinvertebrates from major habitat types found within each study reach. Examples of habitat types include undercut banks, hard substrate (gravel, etc.) riffles, leaf litter, and woody debris. Dip nets are swept, jabbed, and/or kicked in and through habitats in order to secure a representative sample of the macroinvertebrate assemblage. Samples are processed in the laboratory where the first 200 organisms encountered are identified to the lowest possible taxon (typically genus) and enumerated.
Macroinvertebrate collection consists of jabbing the D-net 20 times in productive habitats. A single jab
consists of aggressively thrusting the net into the target habitat for a distance of approximately 1 meter;
i.e. the distance the net can be swept while standing in one place. This initial “jab” is followed by 2-3
sweeps of the same area to collect dislodged organisms. This level of effort represents a sample area of
approximately 6.2 m2. The following techniques are recommended for sampling the three major
productive habitats in coastal plain streams.
woody snags - Snags, or submerged woody debris, are sampled by jabbing in medium sized snag
material (sticks and branches). Large material (e.g., logs) may be sampled by scraping the net along
the surface. The snag habitat may be kicked first to dislodge organisms.
banks - Stream banks with roots and snag material are sampled similar to snags. Vegetated banks
are preferred over unvegetated banks. The bank habitat may be kicked first to dislodge organisms.
submerged macrophytes - Submerged macrophytes are sampled in deep water by drawing the net
through the vegetation from the bottom to the surface of the water. Macrophytes in shallow water are
sampled by bumping the net along the bottom in the macrophyte bed.
Macroinvertebrate collections are made while moving progressively upstream to avoid low visibility caused
by sediment resuspension. Collections are made in all available velocity conditions and stable habitats. Streams with hard substrates are easily sampled by wading throughout the stream.
Streams with soft substrates may be sampled by wading along the shallow edge of the stream or by
standing on the bank out of the stream channel. |
