222 Determining the effects of urbanization on stream metabolism of Duluth streams

Tuesday, May 19, 2009
Ambassador Ballroom
Jeremy M. Erickson , Center for Water and the Environment, Natural Resources Research Institute, Duluth, MN
LaRae Lehto , Mid-Continent Ecology Division, Environmental Protection Agency, Duluth, MN
Lucinda B. Johnson , Natural Resources Research Institute, University of Minnesota Duluth, Duluth, MN
Richard Axler , Center for Water and the Environment, Natural Resources Research Institute, Duluth, MN
Brian Hill , Mid-Continent Ecology Division, Environmental Protection Agency, Duluth, MN
The North Shore streams of Lake Superior are known for their clear cool waters that flow through expanses of undeveloped land. However, many North Shore watersheds are experiencing rapid urbanization, resulting in increased impervious surface development. Previous research on the impact of ecological disturbances to stream health has primarily relied on biotic community, physical habitat, or water chemistry studies, with few  focusing on ecosystem processes such as stream metabolism. This study assesses the effect of increasing urbanization on summer whole stream community respiration (CR) and gross primary production (GPP) rates on nine low productivity, heterotrophic streams spanning an impervious surface gradient (0.8 % to 20.1 %). Stream metabolism rates were determined using single station diel dissolved oxygen changes.  We used propane evasion to estimate stream reaeration rates. We also measured total nitrogen and total phosphorus levels, canopy shading, and epilithon chlorophyll-a.  GPP estimates ranged from 0.07 g O2 m-2d-1 to 2.03 g O2 m-2d-1 and CR  from 0.18 g O2 m-2d-1 to 6.58 g O2 m-2d-1.  Preliminary results for July and August indicate a positive relationship between increasing impervious surface and CR and a very weak positive or no relationship with GPP.