Aquatic invertebrate monitoring at Herbert Hoover National Historic Site, 2008

Bowles, David; Dodd, Hope; Luraas, Jessica

An unnamed tributary, known unofficially as Hoover Creek, of the west branch of WapsinonocCreek runs through the Herbert Hoover National Historic Site (HEHO) in eastern Iowa. TheHoover Creek watershed has historically been dominated by agricultural land use. However, inrecent years, agricultural land use has declined as the city of West Branch expands west into the watershed. Such land use changes have dramatically altered the water quality and streamhydrology throughout the watershed by creating more dynamic surface water flow regimesresulting in periodic flash-flooding. The creek flows through an 81-acre restored tallgrass prairieat HEHO, but it also drains the impervious cover within the historic site. Historic structures andmany cultural resources are in the flood plain. Stream-side vegetation in the Historic Siteconsists largely of a manicured lawn up to the stream edge. A native vegetation community islacking which exacerbates flooding. The altered hydrological regime has caused substantialstream bank erosion in the historic site. Hoover Creek also has degraded water quality attributed to point and non-point agricultural and urban impacts in the watershed. The creek is listed by the Iowa Department of Natural Resources as an impaired stream under Section 303(d) of the Clean Water Act.The Heartland Inventory and Monitoring Network (HTLN) of the National Park Service (NPS)began monitoring water quality and aquatic invertebrate community structure in Hoover Creek,HEHO in 2008 as a gage of stream ecological integrity. Aquatic invertebrates are an important biological tool for understanding and detecting changes in stream ecosystem integrity and can be used to reflect cumulative impacts that cannot otherwise be detected through traditional water quality monitoring. The objectives of this monitoring are: 1) determine the status and trends of invertebrate species diversity, abundance, and community metrics, and 2) relate the invertebrate community to overall water quality through quantification of metrics related to species richness, abundance, diversity, and region-specific multi-metric indices as indicators of water quality and habitat condition.The invertebrate community data collected during this initial study suggests that Hoover Creek is impaired. Total taxa richness and Ephemeroptera, Plecoptera, Trichoptera (EPT) richness forHoover Creek were roughly one-third that expected for regional reference streams, and thedominant EPT taxa represented were all tolerant genera. EPT taxa are, in general, sensitive topoor water quality conditions. Overall, the invertebrate fauna in Hoover Creek is judged to betolerant of the various disturbances that affect this stream. Future invertebrate sampling events at Hoover Creek should include a composited multihabitat sample in order to allow investigators to calculate the IOWATER Advanced Benthic Macroinvertebrate Indexing Methods. This will allow site managers to evaluate the invertebrate community structure relative to Iowa reference streams in addition to assessing long-term trend in this resource.There are few available options to park management for mitigating water quality impairment ofHoover Creek flowing through HEHO because some of the impacts to water quality and viassociated effects on the invertebrate communities originate upstream of the park boundaries.The impacts of urbanization and agricultural practices often are so pervasive that mitigationstrategies are rarely effective. However, widening and maintaining of riparian buffer zones alongthese streams within the park will aid in protecting aquatic life as well as in-stream habitat fromlocal chemical runoff and sedimentation. Riparian buffers can be improved by restoring nativegrasses to areas where they occurred historically. Improved buffer zones will reduce bankerosion within HEHO by reducing stream velocity and the amount of water entering the creek.

Aquatic invertebrate monitoring at Herbert Hoover National Historic Site, 2008

Series