2022 Early Hearing Detection & Intervention Virtual Conference

March 13 - 15, 2022

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5/26/2021  |   8:30 AM - 10:30 AM   |  Progression of N fixation during a riverine algal bloom   |  Virtual Platform

Progression of N fixation during a riverine algal bloom

The Upper Clark Fork River (UCFR) suffers from anthropogenic (N) enrichment that, coupled with naturally high Phosphorous (P) availability and sunlight, lead to annual nuisance filamentous algae (Cladophora) blooms often leading to a secondary N-fixing cyanobacterial bloom reflecting N-limitation. Under such conditions, N-fixation can play a significant role in stimulating primary productivity. We used the acetylene reduction technique to quantify N-fixation along the progression of blooms in a 5th-order section of the UCFR. A suite of associated environmental variables was measured in order to determine the environmental controls to N fixation and the consequences of enhanced N-fixation to the system. Over the course of the algal bloom, standing crops of phycocyanin increased linearly to a maximum of 65 mg/m2). Following dominance by Cladophora, N-fixation rates increased from 0.15 to 3.3 mg/m2*h-1, then slowly decreased towards the end of the growing season. The N/P ratios of the water column shifted from 0.3 to 9.3, mostly due to the increase in availability of ammonium. Light and temperature explained 70% of the variation in phycocyanin corrected N fixation. Enhanced algal growth due to N-Fixation was associated with declines in ambient P concentrations.

  • Biogeochemistry
  • Ecosystem functioning
  • Nutrients

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Presenters/Authors

Rafael Feijó de Lima (), University of Montana, rafael.feijo@mso.umt.edu;


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Thomas Horner (), University of Montana, thomas.horner@umconnect.umt.edu;


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Marc Peipoch (), Stroud Water Research Center, mpeipoch@stroudcenter.org;


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H. Maurice Valett (), University of Montana, Division of Biological Sciences, maury.valett@umontana.edu;


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