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 cover (ISC). Previous research on the impact of ecological disturbances on stream health have seldom focused on ecosystem processes such as stream metabolism. This study assesses the effect of increasing urbanization on whole stream community respiration (CR) and gross primary production (GPP) rates during summer and autumn base flow periods for nine low productivity, heterotrophic streams spanning a watershed ISC gradient. Land cover was measured as a percentage of the whole watershed and by distance-weighting to evaluate the possible influence of spatial position of land cover on stream function. Stream metabolism rates were determined using high frequency diel dissolved oxygen changes at a single station coupled with propane evasion to estimate stream reaeration rates. GPP estimates ranged from 0.02 to 2.02 g O2 m-2d-1 and CR from 0.17 to 6.09 g O2 m-2d-1. During summer base flows there were strong correlations between urban development measures and both stream metabolism and nutrients. However, the associations between land use and stream metabolism were not observed during the autumn base flow period. Our data suggest the variability in stream flow and leaf off along with stream temperature changes appear to be the dominant factors influencing the relationship between land use and stream metabolism in these Lake Superior tributary streams. Distance-weighting did not improve the predictive power on stream metabolism and water chemistry variables.
University of Minnesota Master of Science thesis. January 2011. Major: Water Resources Science. Advisor: Lucinda B. Johnson. 1 computer file (PDF); vi, 51 pages.
Erickson, Jeremy Michael.
Stream Metabolism Along an Urban to Rural Gradient in Lake Superior Tributary Streams.
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