Nitrogen fixation in a desert stream ecosystem

Nancy Grimm, Kevin C. Petrone

Research output: Contribution to journalArticlepeer-review

94 Scopus citations


Few measurements of nitrogen fixation exist for streams. Desert streams are warm, well lighted, and often support abundant cyanobacterial populations; thus N2 fixation may be significant in these N-poor ecosystems. N2 fixation was measured in situ by acetylene reduction for two patch types (Anabaena mat and an epilithic assemblage). Patch-specific rates were high compared with published values (maximum 775 μg N2 [83 μmol C2H4] mg ch1 α-1 h-1 or 51 mg N2 [5.4 mmol C2H4] m-2 h-1). Daytime fixation was higher than nighttime fixation, and temperature, light and inorganic N concentration explained 52% of variance in hourly rates over all dates. Diel input-output budgets were constructed on five dates when cyanobacteria were present in the stream. Diel N2 fixation rates were measured for comparison with reach-scale diel nitrogen retention, to assess the importance of this vector to N economy of the stream. Fixation accounted for up to 85% of net N flux to the benthos, but its importance varied seasonally. Finally, we applied biomass-specific fixation rates to 1992 and 1993 biomass data to obtain seasonal and annual N2 fixation estimates. Cyanobacteria were absent or rare during winter and spring, thus most of the annual N2 fixation occurred during summer and autumn. Annual rates of nitrogen fixation for 1992 and 1993 (8.0 g/m2 and 12.5 g/m2) were very high compared to other streams, and moderately high compared to other ecosystems. Like other phenomena in this disturbance-prone ecosystem, nitrogen fixation is strongly influenced by the number and temporal distribution of flood events.

Original languageEnglish (US)
Pages (from-to)33-61
Number of pages29
Issue number1
StatePublished - 1997


  • N fixation
  • acetylene reduction
  • cyanobacteria
  • desert
  • nutrient budget
  • stream

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology
  • Earth-Surface Processes


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