Baltimore Ecosystem Study Institute of Ecosystem Studies

2011 BES Annual Meeting Presentation and Poster Abstracts

Stream temperatures in urban watersheds: interactive effects of riparian cover, scale and the built environment.
Belt, Ken
Co-Authors: Belt, K.T., Noonan, E., and P. Groffman

Abstract: Stream temperatures in urban watersheds are highly dynamic and spatially and temporally complex due to modulation by extensive impervious and vegetated cover that is greatly connected by "engineered" drainage networks. We measured water temperature continuously in over twenty small catchments with varying riparian forest and impervious surface cover in the Gwynns Falls and Gunpowder River in Baltimore, MD. The largest differences in daily mean temperatures between forested and urbanized sites were in the summer (ca 3-5 C), with little separation in the winter. Sites with similar structures but differing amounts of hardscape and forest cover showed large differences in summer temperatures (e.g., ca 4-7 C difference.) Generally, downstream sites had higher temperatures, e.g., the Gwynns Falls at Carroll Park (26 C), which had less riparian canopy cover and was located at the warm end of the urban-rural heat gradient. However the highest temperature occurred in Dead Run (27 C) which although it is a small catchment, has a lot of hardscape and little riparian cover. In buried streams, temperatures were cool (ca 19 C), cooler than forested streams (16-20 C) but in ultra urban areas were warmer and more variable (ca 22-24 C). During summer storms, urban headwater catchments experienced large temperature spikes (up to 13 C); these were more frequent and larger than at downstream sites. Urban landscapes not only induce a heat island effect on ambient stream temperatures, but also introduce thermal disturbance regimes that are not trivial to biotic communities.