The effect of catchment urbanization on nutrient uptake and biofilm enzyme activity in Lake Superior (USA) tributary streams

LaRae L P Lehto, Brian H Hill

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


We compared landscape, habitat, and chemistry variables with nutrient spiraling and biofilm extracellular enzyme activity (EEA), to assess the response of nine Lake Superior tributaries to the level of urbanization in their catchments. We found no significant correlation between uptake metrics for NH4 + and PO4 3- and the level of catchment urbanization. NH4 + and PO4 3- uptake velocities (V f) were, however, positively correlated with biofilm EEA and with biofilm respiration (DHA). In general, biofilm EEA was negatively correlated with indicators of increased urbanization (e.g., % impervious surface cover and Cl- concentration) and positively correlated with % forest cover. Biofilm respiration measured as dehydrogenase activity (DHA) decreased with indicators of increased urbanization (e.g., % ISC, storm sewer length, % of the stream channel shaded by the riparian canopy, and Cl-) and increased with non-urban indicators (e.g., % forest, % wetland, and stream width and depth). Regression of V f and uptake rate (U) versus ambient nutrient concentrations indicated phosphorus limitation in the study streams, a result supported by regression biofilm peptidase versus phosphatase activity. There was no evidence of NH4 + saturation or limitation. This is the first study to demonstrate correlations between nutrient uptake and biofilm EEA in streams, with linkages to catchment-scale disturbances.

Original languageEnglish (US)
Pages (from-to)35-51
Number of pages17
Issue number1
StatePublished - Aug 2013

Bibliographical note

Funding Information:
Acknowledgments This research was funded through the University of Minnesota–US Environmental Protection Agency Cooperative training partnership in Aquatic Toxicology and Ecosystem Research (CR83341401). We would like to thank Dr. Lucinda Johnson and Dr. John Pastor for all of their guidance in the development of this study and helpful editorial comments. We would also like to thank Jeremy Erickson who was instrumental in the completion of this study, along with Robert Hell and Noah Kroening at the Natural Resources Research Institute for their wonderful field assistance. Colleen Elonen and Lindsey Seifert provided expert laboratory sample analysis. Thank you to Terri Jicha for her field work and statistical analysis help and to Tom Hollenhorst and Matthew Starry for their GIS expertise. The views expressed in this paper are those of the authors and do not necessarily reflect the views or policies of the US Environmental Protection Agency. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.


  • Extracellular enzyme activity
  • Nutrient uptake
  • Respiration
  • Streams
  • Urbanization


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