USGS-NWQL: B-9135-00 (Taxonomic ID): Benthic Macroinvertebrate Sample Processing: Taxonomic Identification
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Official Method Name
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Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory - Processing, Taxonomy, and Quality Control of Benthic Macroinvertebrate Samples |
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Current Revision
| 2000 |
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Media
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WATER |
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Instrumentation
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Visual Comparison |
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Method Subcategory
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Population/Community |
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Method Source
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Citation
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Moulton II, S.R., Carter, J.L., Grotheer, S.A., Cuffney, T.F., and Short, T.M., 2000, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-- Processing, taxonomy, and quality control of benthic macroinvertebrate samples: U.S. Geological Survey Open-File Report 00-212. |
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Brief Method Summary
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Three levels of taxonomic assessment are available for Benthic Macroinvertebrate (BMI) samples. These levels include (1) the Standard Taxonomic Assessment (STA), (2) the Rapid Taxonomic Assessment (RTA), and (3) the Custom Taxonomic Assessment (CTA). Each provides a different basic level of taxonomic resolution to address various water-quality and related data-analysis objectives. The STA and RTA are adapted from the U.S.Environmental Protection Agency Rapid Bioassessment Protocols (RBP).
Taxonomic identification of BMIs depends upon experienced personnel trained in zoologic taxonomic principles and having a broad knowledge of all aquatic macroinvertebrate groups. Typically dichotomous keys are used to identify organisms, which offer a formal, stepwise method for arriving at a name for an organism based primarily on its morphological characteristics. Progression through the dichotomous key results in classification of the organism according to a nomenclatural hierarchy of increasing morphological similarity. It is desirable to achieve the lowest level of taxonomic classification possible because ecological characteristics and responses to water-quality conditions are more specific at lower taxonomic levels than at higher levels. However, identification at the species level is not always possible because of maturity, condition of the specimen, or the current state of taxonomic knowledge about organisms. |
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Scope and Application
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The U.S.Geological Survey's National Water Quality Laboratory Biological Group (BG) processes BMI samples that have been collected by using a variety of techniques from diverse aquatic habitats throughout the United States. The BG has developed well-defined qualitative and quantitative processing methods that are sufficiently flexible to satisfy most data-analytic methods currently (2000) used including estimates of BMI community composition in water-quality studies.
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Applicable Concentration Range
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Interferences
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Most larval identification keys, unless otherwise stated by their authors, are constructed on the basis of morphological characters that are found in mature larvae. In practice, many organisms collected in field samples are either too immature or are damaged during collection, shipping, and laboratory processing. Consequently, the morphological characters required to identify the organism are often missing or obscured, and the identification of an organism is frequently terminated at a higher taxonomic level than desired. Consquently, higher level determinations are justified on the bench data sheet to facilitate the interpretation of taxonomic data used for analyses. The BG uses several standardized supporting notes for this purpose, including others that convey additional information about the determination. Even though determinations to the recommended levels are not always possible, BMI taxonomists, who are familiar with regional or local faunas, the taxonomic literature, and have access to a verified reference collection, can sometimes make a determination at a lower taxonomic level. The BG also uses several standardized provisional or conditional designations to convey as much taxonomic information as possible when the taxonomy of a group is incomplete or unclear, or when a potentially undescribed taxon has been discovered. |
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Quality Control Requirements
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Steps include (1) verification of taxonomic identification that simultaneously checks the accuracy of identifications and the precision of individual taxonomists; (2) review of benthic macroinvertebrate data to ensure the accuracy of the original count; (3) bench sheets are reviewed before data entry to identify corrective actions; and (4) the QC Officer examines all errors involving identification, enumeration, and bench-data-sheet completeness and determines what if any corrective actions are necessary. |
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Sample Handling
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BMI samples can be processed onsite to create several different sample components (main-body, large-rare, elutriate, and split). The extent of this process depends not only on decisions made onsite at the time of sample collection but on the subsequent laboratory processing methods desired. A brief description of each of these components is presented in Appendix 1. |
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Maximum Holding Time
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Relative Cost
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$201 to $400 |
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Sample Preparation Methods
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