Aquatic community monitoring at Herbert Hoover National Historic Site, 2008–2017

Land use changes that degrade water quality and stream habitat can negatively impact aquatic communities. Monitoring trends in aquatic community composition and habitat conditions is a robust way to assess stream integrity and health. Herbert Hoover National Historic Site (NHS) is in eastern Iowa where dominant land use consists of row-crop and grassland agriculture. A portion of an unnamed tributary of the West Branch of Wapsinonoc Creek, known as Hoover Creek, flows through the park. In 2008, the Heartland Inventory and Monitoring Network (Heartland Network) of the National Park Service (NPS) began monitoring aquatic communities (fish and invertebrates), physical habitat, and water quality at Hoover Creek within the park. This report summarizes four years of data to assess the baseline conditions of Hoover Creek within Herbert Hoover NHS. Aquatic invertebrate taxa richness ranged from 21 to 32 among all years monitored. Three of these taxa are sensitive to poor water quality and habitat conditions. The invertebrate community was dominated by true flies in the Chironomidae family, Oligochaete worms, and mayflies in the Baetidae family. These taxa are all tolerant of poor water quality and habitat conditions. However, in 2011, the sensitive caddisfly Ceratopsyche was also abundant. Mean Hilsenhoff Biotic Index values indicated the invertebrate community fluctuated over time, ranging from fairly poor in 2017 to good condition in 2011. Ten fish species were collected at Hoover Creek across the four years sampled with seven of those species found in all years. All fish species collected were either moderately tolerant or tolerant to poor habitat and water quality conditions; the community was dominated by johnny darter (Etheostoma nigrum), creek chub (Semotilus atromaculatus), and blacknose dace (Rhinichthys atratulus). Based on the Index of Biotic Integrity developed for Iowa streams, the fish community ranged from fair condition in 2008, 2014, and 2017 to good condition in 2011. Hoover Creek was found to have predominately fine to medium gravel substrate with high embeddedness, and banks were steep and tall and consisted of fine silt substrate. With the exception of turbidity after a rain event in 2008, water quality parameters were within state standards. The four years of stream biota data coupled with habitat data should form a good baseline for assessing changes or trends in the aquatic community and overall stream health of Hoover Creek.