Chironomidae Contributions to the Macroinvertebrate Assemblage, Index of Biotic Integrity and Relationships to Water Quality Impairment for Eastern South Dakota Streams

Regional biological monitoring tools are needed to account for natural and human mediated variation in natural resource condition. Contribution of Chironomidae to macroinvertebrate assemblage structure has not been explored extensively from wadeable perennial streams of the Northern Glaciated Plains (NGP). Moreover, no effort has been attempted to develop a multimetric index of biotic integrity (IBI) using Chironomidae larvae. The objectives of this research were to (1) assess the contribution of Chironomidae assemblage structure to the total macroinvertebrate assemblage, (2) develop an IBI and validate the index against streams of known condition, and (3) evaluate a Chironomidae IBI relative to a total macroinvertebrate assemblage IBI for assessing wadeable perennial streams within the NGP. Macroinvertebrates were collected from 41 stream sites from June to August of 2010 and 2011 and were identified to genus. Chironomidae comprised 39% of total assemblage abundance and generic richness, five of seven functional feeding guilds and four of seven habit guilds represented by the total assemblage. Intolerant chironomid genera comprised 61% of total intolerant macroinvertebrates and tolerant chironomid genera comprised 41% of total tolerant macroinvertebrates. Tolerance values ranged from 0 to 10 among genera of the total assemblage and 2 to 10 among Chironomidae genera. Polypedilum, Paratanytarsus, Chironomus, Rheotanytarsus, and Stictochironomus were the most frequently encountered and abundant chironomid genera. Collector-gatherers, shredders, burrowers, and climbers were abundant functional guilds and the mean Hilsenhoff biotic index (HBI) was 6.6 among chironomid assemblages. Percent Tanytarsini, climbers, shredders, and HBI were significantly correlated with total suspended solids, dissolved oxygen, and percent fine substrates. These results suggest that Chironomidae could be useful for prairie stream assessment. Sixty four chironomid assemblage metrics were sequentially screened to identify discriminating metrics among stream classes from which final IBI scores were generated. This process retained % climbers, HBI, % burrowers, and % collector-gatherers. Chironomidae IBI scores ranged from 1 to 99 ( ̅ = 52) across all sampling sites; and scores were significantly higher from unimpaired versus impaired sites. IBI scores were positively correlated with stream dissolved oxygen. Our results suggest that a Chironomidae IBI can successfully be employed to identify impaired streams within the NGP of South Dakota. A total macroinvertebrate assemblage IBI (MIBI) was generated independently following similar procedures. Ninety total assemblage metrics were screened from which only % climbers, HBI, % insects, and Trichoptera generic richness passed all screening tests. MIBI scores ranged from 6 to 87 ( ̅ = 44) across all sampling sites. Both CIBI and MIBI were successfully capable of discriminating impaired versus unimpaired stream sites; however, CIBI explained only 33% of the variations in MIBI. Furthermore, CIBI was consistently higher than MIBI. MIBI scores were strongly correlated with stream dissolved oxygen, total phosphorus, and % fine bed substrates than CIBI. Our results suggest that CIBI would detect biotic impairment less frequently than MIBI. Thus, the Chironomidae assemblage should not be used alone as a surrogate for total macroinvertebrate assemblage assessments in the NGP ecoregion