2006 BES Annual Meeting Presentation and Poster Abstracts
Variance and Extremes of Thermal Fluxes and Temperatures in Urban Streams: the Effects of Impervious Surface Cover and Runoff
Co-Authors: Hyun Jin Kim (UMBC), Kenneth Belt (US Forest Service), Claire Welty (CUERE, UMBC), Richard Pouyat (US Forest Service), Gordon Heisler (US Forest Service), Mike McGuire (CUERE), and William Stack (Baltimore City Department of Public Works)
Abstract: Small urban headwater catchments need to be studied as unique functional hydrologic units. These catchments are different in character and function from their larger receiving streams because of their extensive, direct connections to impervious surface cover (ISC) and their sometimes buried nature. We collected water temperature data at 2-minute intervals at over twenty small catchments representing various mixtures of forest and ISC as part of Forest Service research within the Baltimore Ecosystem Study LTER project. Catchments with greater ISC generally had higher summer water temperatures. However, some suburban catchments with most of their channel drainage within storm drain pipes also showed cool baseflow temperatures, but with a subdued diurnal variation and large transient spikes during summer runoff events. There was often a pronounced upstream-downstream effect, whereby nested small headwater catchments experienced more frequent, larger summer runoff temperature spikes. Surprisingly, runoff-initiated temperature elevations at suburban small stream sites persisted much longer than the surface runoff portion of the storm runoff hydrograph, suggesting the possibility of large thermal fluxes related to groundwater flows. Greater temperature effects were observed at the highly urban sites. Summer temporal cumulative temperature distributions showed that lethal tolerance levels for common fish were exceeded for significant periods of time at the higher ISC catchments. These observations suggest that for small headwater catchments, urban landscapes not only induce an ambient, ˇ°heat islandˇ± effect on stream temperatures, but also experience transient runoff spikes that represent thermal disturbance regimes that are not trivial to aquatic biota.