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Keywords

aquatic invertebrates, Buffalo National River, monitoring

Abstract

Aquatic invertebrate community structure was used to assess long-term water quality integrity in the mainstem of the Buffalo National River, Arkansas from 2005 to 2013. Nine benthic invertebrate samples were collected from each of six sampling sites using a Slack-Surber sampler. The Stream Condition Index (SCI) developed for Ozark streams was used to assess integrity of the invertebrate communities. This index is calculated using taxa richness, EPT (Ephemeroptera, Plecoptera, Trichoptera) Richness, Shannon’s Diversity Index, and Hilsenhoff Biotic Index (HBI). Sørensen’s similarity index was used to assess community similarity among sites, and scores were then analyzed using ascendant hierarchical cluster analysis. The benthic invertebrate fauna was diverse with 167 distinct taxa identified from all sites, with similarities ranging from 70% to 83%. Cluster analysis showed that sites were clustered in a longitudinal progression, with those sites closest to one another in linear distance generally being the most closely related. Overall, the invertebrate taxa of the Buffalo River are largely intolerant (mean tolerance value= 4.38). Taxa richness was typically greater than 20 among samples, and EPT richness values consistently were greater than 12 for all sites in most years. Shannon’s diversity index values generally ranged from 2.0 to 2.5 among sites and years. Metric values tended to decrease in a downstream direction to Site 4, and then increase to levels observed upstream. The exception was for HBI, which did not show this response and values for this metric generally were below 5. SCI scores among sampling sites were variable but not generally impaired and were fully biologically-supporting. Water quality (temperature, dissolved oxygen, specific conductance, pH, turbidity) met state standards in all instances. Habitat data were summarized, but found to be poorly correlated with invertebrate metrics (<30% significant). Although the condition of invertebrate communities and water quality in the Buffalo River are largely sound and have high integrity, numerous ongoing and projected threats to these resources remain, and those threats largely originate outside of the park’s jurisdictional boundaries. Inherent variability of invertebrate community diversity and density across sites and years highlights the importance of using multi-metric assessment and multiyear monitoring to support management decisions.

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