Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory; processing, taxonomy, and quality control of benthic macroinvertebrate samples

[摘要] Qualitative and quantitative methods toprocess benthic macroinvertebrate (BMI)samples have been developed and testedby the U.S. Geological Survey?s NationalWater Quality Laboratory Biological Group.The qualitative processing method isbased on visually sorting a sample for up to2 hours. Sorting focuses on attaining organismsthat are likely to result in taxonomicidentifications to lower taxonomic levels (forexample, Genus or Species). Immature anddamaged organisms are also sorted whenthey are likely to result in unique determinations.The sorted sample remnant isscanned briefly by a second person to determineif obvious taxa were missed.The quantitative processing method isbased on a fixed-count approach that targetssome minimum count, such as 100 or300 organisms. Organisms are sorted fromrandomly selected 5.1- by 5.1-centimeterparts of a gridded subsampling frame. Thesorted remnant from each sample is resortedby a second individual for at least 10percent of the original sort time. A large-rareorganism search is performed on the unsortedremnant to sort BMI taxa that werenot likely represented in the sorted grids.After either qualitatively or quantitativelysorting the sample, BMIs are identified byusing one of three different types of taxonomicassessment. The Standard TaxonomicAssessment is comparable to theU.S. Environmental Protection AgencyRapid Bioassessment Protocol III and typicallyprovides Genus- or Species-level taxonomicresolution. The Rapid Taxonomic Assessmentis comparable to the U.S. EnvironmentalProtection Agency Rapid BioassessmentProtocol II and provides Familyleveland higher taxonomic resolution. TheCustom Taxonomic Assessment providesSpecies-level resolution whenever possiblefor groups identified to higher taxonomiclevels by using the Standard TaxonomicAssessment. The consistent use of standardizeddesignations and notes facilitatesthe interpretation of BMI data within andamong water-quality studies. Taxonomicidentifications are quality assured by verifyingall referenced taxa and randomly reviewing10 percent of the taxonomic identificationsperformed weekly by BiologicalGroup taxonomists. Taxonomic errors discoveredduring this review are corrected.BMI data are reviewed for accuracy andcompleteness prior to release. BMI data arereleased phylogenetically in spreadsheetformat and unprocessed abundances arecorrected for laboratory and field subsamplingwhen necessary.

[发布机构] U.S. Geological Survey

[学科分类] 地球科学(综合)