Oral Presentation Society for Freshwater Science 2026 Annual Meeting

Insect Emergence and Riparian Predator Abundance in Urban Ponds Across a Land Cover and Chemical Gradient (135923)

Jennoa E Fleming 1 , Jackson A Bates 1 , Jeremy M Brooks 1 , Michelle L Hladik 2 , Johanna M Kraus 3 , Dan L Preston 1
  1. Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, Colorado, United States
  2. California Water Science Center, U.S. Geological Survey, Sacramento, California, United States
  3. Columbia Environmental Research Center, U.S. Geological Survey, Columbia, Missouri, United States

Urbanization affects aquatic and terrestrial biodiversity by fragmenting habitats, introducing pollutants, and shifting species composition. The presence of ponds within urban areas may act as refugia for aquatic species, but it is unclear how ecosystem services shift in relation to surrounding land cover and concomitant changes in water chemistry. A significant ecosystem service provided by urban ponds is the emergence of aquatic insects which transfer energy into terrestrial environments. The aim of this study was to determine how the flux of aquatic insect emergence shifts in relation to urban land cover and water chemistry (including nutrients, pesticides, and trace metals), and how riparian predators may be impacted by these rates. Aquatic emergence traps were deployed at 16 ponds along a gradient of urbanization (measured by percent impermeable land surface) within Fort Collins, Colorado for one month in late summer. Bird and spider surveys were conducted at each site to test if emergence was correlated with riparian predator abundances. Ponds with reduced riparian habitat complexity and increased surrounding areas of impervious surfaces appear to have reduced biomass and reduced species richness of insect emergence. The ponds that were most impacted by urbanization had higher concentrations of pesticides and emergence comprised often exclusively of pollution tolerant midges (Chironomidae). Ponds with more complex riparian habitats, less surrounding areas of impervious surfaces, and lower concentrations of pesticides had more diverse taxa such as Trichoptera, Odonata, Ephemeroptera, and Diptera with higher richness and abundance. Preliminary data also shows that riparian spider and insectivorous bird abundance increase with riparian vegetation complexity. These findings indicate that urban ponds may be an important source for energetic subsidies for riparian environments as riparian predators prepare to overwinter or migrate, but water chemistry and local habitat features may regulate the taxonomic composition of subsidies.