Nitrogen Fixation by Epilithic Periphyton in Small Arctic Lakes in Response to Experimental Nitrogen and Phosphorus Fertilization

Epilithic periphyton played a moderate role in the nitrogen budget of four small arctic lakes located at Saqvaqjuac, N.W.T. The acetylene reduction technique used to estimate nitrogen fixation indicated that periphyton in 0–2 m water depth were capable of fixing up to 0.86 mg N∙m−2∙h−1 during the period of active nitrogen fixation from July to September 1981. Far Lake was fertilized with Phosphorus for 3 yr and had a higher rate of fixation than did a P- and N-fertilized lake or a control lake, in agreement with similar studies on temperate and subarctic lakes. A numerical model based on incoming light was used to perdict the amount of nitrogen fixed in each study lake throughout the season. The calculated contribution of periphyton to the overall N budget for 1981 was 5% for the P- and N-fertilized lake, 16% for the control lake and 28% for the P-only fertilized lake.