Evaluation of Stream Quality Using Benthic Macroinvertebrate Communities as Biological Indicators

Arnold, Jeff; Koel, Todd

The Greater Yellowstone Network (GRYN) is comprised of three National Park Service units: Bighorn Canyon National Recreation Area (BICA), Grand Teton National Park, (GRTE) and Yellowstone National Park (YELL). Maintaining high water quality standards within these parks is of considerable importance in fulfilling the park service mission. The primary objective of this study was to use benthic macroinvertebrates as a bioassessment tool to evaluate the current condition of selected park waters. Benthic macroinvertebrate sampling took place within all parks of the GRYN during a summer period between 06 August and 12 September 2002; and in GRTE and YELL during a fall period between 07 October and 13 November 2002. Four invertebrate sites on 3 streams were sampled in BICA, 16 sites on 8 streams were sampled in GRTE, and 20 sites on 8 streams were sampled in YELL. A Surber net (0.09 meter plot with 500 micron mesh) was used to collect benthic macroinvertebrates from selected streams within the three GRYN parks. A total of 232 invertebrate taxa were identified with 70 taxa collected from BICA and 165 taxa each being collected from GRTE and YELL. A variety of metrics were used to evaluate selected streams and include total number of taxa, invertebrate density, EPT Richness Index Value (total number of distinct taxa belonging to the insect orders Ephemeroptera, Plecoptera, and Trichoptera), invertebrate tolerance values, and modified Hilsenhoff Biotic Index (HBI) values. Overall, number of EPT taxa for BICA was relatively low with a range between 5 and 8 taxa for the downstream site on North Fork Trail Creek and the Crooked Creek site respectively. Results from HBI values indicate that 2 invertebrate sites rate good, 1 site rated fair and 1 site rated fairly poor. Crooked Creek, which had an HBI water quality rating of fairly poor, receives much of its water from a drainage that is dominated by agriculture and rangeland. These land use practices, coupled with severe riparian habitat degradation within park boundaries, are most likely the reason for the high HBI value recorded. The number of EPT taxa for invertebrate sites in GRTE was generally high with a range between 11 and 32 taxa combined for both summer and fall sample periods. Most sites rated good to excellent for both sample periods with the exception of one site each on Cottonwood and Spread creeks which had HBI water quality ratings of fair during the summer sample period. Possible impacts to water quality were evident at both locations with the site on Cottonwood Creek periodically receiving water from an adjacent horse pasture and the site on Spread Creek having severe stream bank and habitat alterations in the direct vicinity of the sample reach. Because of the wide distribution of thermal features in YELL park waters, evaluating stream health using conventional methods becomes particularly challenging. Of the 20 invertebrate sites sampled in 2002, 5 sites were selected in stream segments with thermal influence. The number of EPT taxa for sites in YELL range between 0 and 37 taxa for both sample periods. Generally, streams lacking thermal influence had HBI values that range between good and excellent while streams having thermal influence had higher HBI values and lower stream water quality ratings. The downstream site on Obsidian Creek was the only invertebrate site that lacked an apparent stressor and yet received an HBI water quality rating of fair during the fall collection period. Streams segments which were sampled in areas of thermal activity generally had fewer numbers of total taxa, low numbers of EPT taxa, and higher percentages of tolerant taxa. In addition, the exotic New Zealand mud snail was collected from 3 invertebrate sample locations, all of which receive thermal runoff. (Abstract as submitted by authors).

Evaluation of Stream Quality Using Benthic Macroinvertebrate Communities as Biological Indicators

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