National Park Service


Date of this Version


Citation February 2012


Aquatic invertebrates have been collected along the Niobrara River at Agate Fossil Beds NM since 1989 using Hester-Dendy samplers. These samplers consist of 9 plates that are colonized by invertebrates while they are suspended in the water for 30 days. Aquatic invertebrates are typically identified to genus and counted. Bioassessment metrics are calculated based on invertebrate data to estimate ecosystem health. One bioassessment metric is Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness, which counts the number of taxa that are mayflies, stoneflies, and caddisflies. Insects in these orders tend to be sensitive to ecosystem health, thus more EPT means better ecosystem health. Another bioassessment metric is Hilsenhoff’s Biotic Index (HBI) that uses values (0 to 10) to describe how tolerant invertebrates are to pollution. A value of 0 indicates that the invertebrate is extremely sensitive to pollution and a value of 10 indicates that the invertebrate is very tolerant of pollution. Tolerant invertebrates will live in all types of streams, but sensitive species will be absent in streams with poor ecosystem health.