Associations of event‐scale flow hydrology with fish richness in urbanizing Canadian watersheds of Lake Ontario

Abstract

Urbanization is associated with declines in aquatic biodiversity and changes to flow regimes. This empirical research examined high temporal resolution (15 min) hydrologic records and associations with fish species richness in eight river systems in theToronto region, Canada. The dataset spanned approximately five decades and covered the annual post-freshet period to mid-November. The high-temporal resolution flow records allowed estimation of flow acceleration (a measure of the rate of change in flow) in response to rain events. Maximum rising limb event flow acceleration and skew in instantaneous runoff explained a higher proportion of variation than percent urban land use in empirical models with long-term fish records. Models fit using only the most recent decade of records did not produce the same results, likely indicating that analyses of flow with fish diversity require sufficient range in flow conditions for the statistical signals to be detected. Historic fish data are difficult to obtain and pose analytical challenges due to bias and inconsistent collection methods. Despite the data limitations, the study results point to the need for more research into potential causal factors contributing to negative fish richness in urbanizing watercourses with periods of high flow acceleration.

SWM and urban water: Smart management for an absurd system?

“…These systems alter water flows, chemistry and temperature. The changes in flow regime have serious consequences for fish diversity in urban streams (Trudeau & Morin, 2017). Aquatic community health is anomalous in that it continues to decline as prosperity increases (Vörösmarty et al, 2010), and freshwater habitats are among the most threatened in the world (World Wildlife Fund, 2017).…”