Aquatic invertebrate monitoring at Agate Fossil Beds National Monument: 2019 data report

Monitoring ecosystems is vital to understanding trends over time and key to detecting change so that managers can address perturbations. Freshwater streams are the lifeblood of the surrounding landscape, and their health is a measure of the overall watershed integrity. Streams are the culmination of upland processes and inputs. Degradation on the landscape as well as changes to the stream itself can be detected using biota living in these ecosystems. Aquatic invertebrates are excellent indicators of ecosystem quality because they are relatively long-lived, sessile, diverse, abundant and their tolerance to perturbation differs. Aquatic invertebrates were monitored at three sites along the Niobrara River at Agate Fossil Beds National Monument in 2019 completing 23 years of data using Hester-Dendy and Hess samplers. Hess samplers are artificial multi-plate samplers suspended in the water column to allow invertebrates to colonize and Hess samples collect invertebrates in a known area on natural substrate and vegetation. We identified 45 invertebrate taxa from four phyla (Annelida, Arthropoda, Mollusca, Nematoda) using both samplers in the Niobrara River (Appendix A and B). Hester-Dendy samplers collected 4 taxa not found in Hess samples and Hess samples collected 17 taxa not collected with Hester-Dendy samplers. Hess samples captured more (91%) than Hester-Dendy samples (62%). Crustacea, Diptera and Ephemeroptera were the most abundant groups of invertebrates collected in the Niobrara River. The proportion of Insecta, Annelida, Trichoptera and Diptera differed between Hester-Dendy and Hess samples (p < 0.05). EPT richness, proportion EPT taxa and Hilsenhoff’s Biotic Index (HBI) (p < 0.0001) differed between sampler types, but taxa richness, taxa diversity and evenness (p > 0.29) did not. We collected the highest density of invertebrates at the Agate Middle site. Agate Spring Ranch had the lowest taxa richness and HBI, and the highest proportion of EPT taxa. HBI at the sites ranged from 4.0 to 6.3 (very good to fair from Hilsenhoff 1987) using the Hester-Dendy and 5.2 to 6.9 (good to fairly poor from Hilsenhoff 1987) using the Hess sampler.