Friday, August 10, 2007 - 9:20 AM

OOS 49-5: Fixing the nitrogen budget in oligotrophic arctic lakes: Reassessing the importance of benthic and pelagic nitrogen fixation

Gretchen M. Gettel, University of New Hampshire, Anne E. Giblin, Marine Biological Laboratory, Robert W. Howarth, Cornell University, and Lyndon Q. Valicenti, Columbia University.

Dinitrogen (N2) fixation may be important to the N budgets of oligotrophic lakes in the Arctic because N inputs from other sources are very low.  However, N2 fixation has not been considered thus far in arctic lake N budgets, and few measurements exist.  We performed a survey of benthic and pelagic N2 fixation measurements in 12 lakes across the landscape near Toolik Field Station, Alaska and examined the importance of N2 fixation to the N budget of a headwater lake (Lake Fog 2).  Benthic N2 fixation ranged from 12 to 90 mg N m-2 year-1 in the survey lakes.  On an areal basis, this is an important input similar to or greater than input from precipitation, which is 25 mg N m-2 year-1.  On a whole-lake basis, benthic N2 fixation contributed only 1% of the inputs to Fog 2, but accounted for a significant portion of the N flux from sediments to the water column (5.5 – 11%).  Depth-integrated water-column N2 fixation ranged from 129 to 626 mg N m-2 year-1 in the survey lakes, which is much higher than has been previously measured for other oligotrophic lakes and is similar to oligotrophic oceanic regions.  Water-column N2 fixation was by far the most important source of N to Lake Fog 2 and accounted for nearly 75% of annual N inputs. Total N2 fixation including both benthic and pelagic habitats exceeds measured rates in terrestrial arctic ecosystems (672 mg N m-2 year-1 vs. 255 mg N m-2 year-1 respectively).  Thus, lake ecosystems can be considered hot spots for N inputs via fixation in the arctic landscape.

See more of OOS 49 - Controls over nitrogen fixation: A global perspective
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