The dual synchronizing influences of precipitation and land use on stream properties in a rapidly urbanizing watershed

Conversion of natural ecosystems to urbanized land cover dominated by impervious surfaces can alter hydrologic delivery of terrestrially derived materials to aquatic ecosystems. By changing hydrologic regimes, urbanization has important ramifications for water quality, particularly when considering how land use change might interact with other potential environmental stressors. Here, we analyzed a suite of physical, chemical, and biological time series (2007–2008) in 11 streams in a rapidly urbanizing watershed to determine how spatiotemporal synchrony is structured in urban vs. rural stream ecosystems. We further assessed how a doubling of seasonal precipitation influenced the landscape‐level stream synchrony patterns between years via changes to the local hydrologic regime. Consistent with existing theory and observations, physical variables (i.e., water temperature, flow rate) regulated by external climate features operating at broad spatial scales were more synchronous than the variables associated with fluxes of dissolved solutes (i.e., conductivity, salinity, dissolved nutrients), which are typically controlled by local and internal ecosystem processes. Both urbanization and increased precipitation modified synchrony patterns by increasing the temporal coherence of water flow and the concentration of certain dissolved solutes (i.e., conductivity, salinity). Urban streams exposed to more precipitation exhibited the greatest similarity in physicochemical conditions, suggesting an interaction among the dual stressors of precipitation and urbanization to instill ecosystem synchrony. These results suggest that taking a spatially explicit perspective in understanding urbanization and its interactions with a changing climate is critical for the future management of aquatic resources in highly developed landscapes.