[Lo-Feature] January 2000 L&O Featured Article now available

[lo-feature-admin@aslo.org]

The featured article in the January issue of L&O is:

Carignan, Richard, Dolors Planas, and Chantal Vis. 2000. Planktonic 
production and respiration in oligotrophic Shield lakes. L&O 45(1): 189-
199.

This article is freely available at the Web address:

          http://aslo.org/lo/toc/vol_45/issue_1/0189.pdf

Instructions for reading PDF files are located on the ASLO web page:

          http://aslo.org/help/loonline.html

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Introductory comments by Patrick Mulholland (L&O Associate Editor)

The balance between primary production and community respiration is 
fundamental to our understanding of carbon flow and food web structure 
in all aquatic ecosystems.  Several recent studies have suggested that 
respiration commonly exceeds photosynthesis in the epilimnion of 
oligotrophic lakes, estuaries, and oceans (del Giorgio and Peters 1993, 
1994; Cole et al. 1994; del Giorgio et al. 1997; Dillon and Molot 1997; 
Duarte and Agusti 1998).  These studies have caused aquatic 
ecologists to reconsider the long-held belief that P:R ratios for most 
aquatic ecosystems are >1, i.e., that food webs are based on 
autochthonous production.  They have also raised important 
considerations for global carbon cycling, suggesting that aquatic 
ecosystems are sources rather than sinks for atmospheric CO2.

In this month's feature article, Carignan et al. (2000) provide data from 
twelve oligotrophic Canadian Shield lakes that contradict this recent 
work. Using a new, precise oxygen method for measuring metabolism 
in these lakes, Carignan and coauthors found that gross photosynthesis 
was almost always larger than community respiration, with a median 
P:R of 1.7.  They also found no significant relationships between 
respiration (or the P:R ratio) and the concentration of dissolved organic 
carbon in these lakes.  The authors suggest that previously low P:R 
ratios reported for oligotrophic lakes may be due to the use of the 14C 
method for measuring photosynthesis.  The photosynthetic parameters 
they derive with their O2 method were considerably higher than past 
values measured with the 14C method in other lakes in the same 
region.  This paper should stimulate considerable debate and new 
research on this most fundamental topic in limnology.

References

Carignan, R., D. Planas, and C. Vis.  2000.  Planktonic production and 
respiration in oligotrophic Shield Lakes.  Limnology and Oceanography 
45: 189-199.

Cole, J. J., N. F. Caraco, G. W. Kling, and T. K. Kratz.  1994.  Carbon 
dioxide supersaturation in the surface waters of lakes.  Science 265: 
1568-1570.

del Giorgio, P. A., and R. H. Peters.  1993.  The balance between 
phytoplankton production and plankton respiration in lakes.  Can. J. 
Fish. Aquat. Sci. 50: 282-289.

--, and --.  1994.  Patterns in planktonic P:R ratios in lakes: Influence of 
lake trophy and dissolved organic carbon.  Limnology and 
Oceanography 39: 772-787.

--, J. J. Cole, and A. Cimbleris.  1997.  Respiration rates in bacteria 
exceed plytoplankton production in unproductive aquatic systems.  
Nature 385:148-150.

Dillon, P. J., and L. A. Molot.  1997.  Dissolved organic and inorganic 
mass balances in central Ontario lakes.  Biogeochemistry 36: 29-42.

Duarte, C. M., and S. Agusti.  1998.  The CO2 balance of unproductive 
aquatic ecosystems.  Science 281: 234-236.

-------------
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