Using Aquatic Macroinvertebrates as Indicators of Stream Flow ...

North CarolinaAquatic macroinvertebrates are included in methodology developed to determine flow durationin North Carolina streams (NC Division of Water Quality, 2005). A recommended list ofperennial taxa has been generated, the majority of which are mayflies, caddisflies, and stoneflies,in addition to a few families of true flies, beetles, and mollusks. Several of the recommendedperennial indicator families, such as water penny beetle larvae, riffle beetles, and freshwatermollusks, have also been shown to be more common in or restricted to perennial waters instudies detailed above, and the larger number of EPT families considered as perennial indicatorsagrees with the overall higher proportion of EPT found in perennial waters in other studies.However, several of the individual EPT families specified as perennial indicators contain generaand/or species that can be considered facultative in Oregon and are not perennial-obligate; some,such as the limnephilid caddisflies, are known to have life history adaptations that allowexploitation of temporary habitats (Clifford, 1966; Tew, 1971; Wiggins, 1973; Mackay &Wiggins, 1979; Anderson & Dieterich, 1992).For the assessment process, diversity and abundance of benthic macroinvertebrates found atdifferent ranges of search effort is recorded, with rankings of “absent”, (no macroinvertebrates),weak (macroinvertebrates observed after intensive searching, i.e. >10 min.), moderate(macroinvertebrates observed after moderate searching, i.e. >1-2 min.), or strong(macroinvertebrates found easily). The procedure recommends sampling a variety of habitats,though little methodology is given, and alternative sampling methods for high flow versus lowflow conditions are not addressed. The stated sampling effort times are low, and are thusunlikely to allow representative sampling of different habitats within a stream reach, especiallyby practitioners who are not trained as entomologists, which could result in a skewed rating. TheFairfax County Perennial Stream Mapping Project (VA) uses a stream identification methodbased on the North Carolina protocol(www.fairfaxcounty.gov/dpwes/watersheds/ps_protocols.pdf) , but because mostmacroinvertebrates are identified only to order in this assessment, they are considered to be onlya secondary indicator of stream type.Macroinvertebrates in Oregon stream duration assessmentTaxonomic considerationsIn the majority of stream duration studies, taxa indicated as predominant in a given stream typeare identified to genus or species level. Identification to the family level, although it can be donefairly rapidly in the field, introduces an unavoidable aspect of uncertainty. For example,indicator species analyses performed on macroinvertebrates in 20 streams in the Central OregonCoast Range found that Dolophilodes, a genus of caddisfly in the family Philopotamidae, wasfound most commonly in perennial streams, but Wormaldia caddisflies, a genus that is also in thefamily Philopotamidae, were associated with intermittent sites (Banks, 2005). The need toidentify macroinvertebrates to family for the purposes of the Oregon assessment tool will notallow the variety of genus- and species-level differences in life history traits to be taken intoaccount. In addition, estimates of taxa richness will be lower, since multiple species may bepresent within a single family or order within a stream. For example, a study of intermittentstreams in western Oregon (Dieterich, 1992) found the highest species richness comprised bymembers of just a single family, the Tipulidae (crane flies); the same study found that caddisfliesMacroinvertebrates as indicators of stream flow duration,The Xerces Society for Invertebrate Conservation13