Anthropogenic and landscape factors control stream nitrogen transformations at multiple spatial scales

Doctoral Dissertation


Anthropogenic alterations to the global nitrogen (N) cycle have doubled reactive N flux into the biosphere and altered aquatic ecosystem function. Streams modify N loads carried to coastal ecosystems by converting N to organic forms or removing it as gaseous N. Understanding how streams transform N can offer insight to ecologists and land managers about how stream ecosystems function under elevated N loads. I researched how anthropogenic and landscape factors affect N transformations by studying streams in two distinct biomes and at multiple spatial scales.

At the landscape scale, I studied N concentrations in streams draining the Teton Range (Wyoming, USA), a sub-alpine and alpine ecosystem with variable lithology. Streams draining crystalline geology had higher N compared to streams draining carbonate geology, which had more vegetation, suggesting that lithology mediated patterns in vegetation and terrestrial N retention. At the reach scale, I studied how land use influenced N uptake and transformation in Midwestern streams (Michigan, USA) and found that dissimilatory N transformation rates (i.e., nitrification and denitrification) within streams were not affected by riparian zones, which are commonly used to mitigate water quality degradation. Dissimilatory N transformation rates were always < 10% of whole-stream N uptake and nitrification rates balanced denitrification rates, implying that denitrification did not represent net N loss from the water column. At the substratum scale, sediment organic carbon content correlated with denitrification, but only when nitrate concentration exceeded a threshold. Finally, I returned to the Tetons and found that grazing activity by invasive snails can increase periphyton N fixation rates in a stream with low N concentrations.

A synthesis of my findings from high N streams in the Midwest suggests that land-use practices have increased temporary N removal at the expense of permanent N removal. In the low N streams of the Tetons, observations from different spatial scales suggest that landscape factors that lower stream N concentrations and high rates of grazing together can influence the importance of N fixation in streams. My dissertation highlights multiple constraints on N processing in streams and emphasizes that basic ecological research can yield important results for management agencies.


Attribute NameValues
  • etd-06202007-004256

Author Clay Porter Arango
Advisor Jennifer L. Tank
Contributor Steve K. Hamilton, Committee Member
Contributor Jennifer L. Tank, Committee Chair
Contributor Charles F. Kulpa, Committee Member
Contributor Gary A. Lamberti, Committee Member
Degree Level Doctoral Dissertation
Degree Discipline Biological Sciences
Degree Name PhD
Defense Date
  • 2007-05-29

Submission Date 2007-06-20
  • United States of America

  • denitrification

  • nitrification

  • stream ecosystem

  • nitrogen cycle

  • nitrogen fixation

  • herbivory

  • University of Notre Dame

  • English

Record Visibility Public
Content License
  • All rights reserved

Departments and Units


Please Note: You may encounter a delay before a download begins. Large or infrequently accessed files can take several minutes to retrieve from our archival storage system.