[L&O Featured Article]Vol 47, Issue 6 (November 2002)

[lo-feature@aslo.org]

Current Featured Article

The Featured Article in the November 2002 issue of L&O is:

Cole, Jonathan J., Stephen R. Carpenter, James F. Kitchell, and 
Michael L. Pace. 2002. Pathways of organic carbon utilization in 
small lakes: Results from a whole-lake 13C addition and coupled 
model. Limnol. Oceanogr. 47(6): 1664-1675.

This paper is freely available at this Web address:

          http://aslo.org/lo/toc/vol_47/issue_6/1664.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 Ray Hesslein, the Associate Editor for the 
paper

This issue's featured article "Pathways of organic carbon utilization 
in small lakes: Results from a whole-lake 13C addition and coupled 
model" by Cole, Carpenter, Kitchell, and Pace uses three sets of 
equations to understand the carbon dynamics of East Long Lake in 
Wisconsin. It substantially increases our understanding of the carbon 
cycle in lakes by simultaneously closing both 13C and 12C budgets. 

Rarely in whole natural systems is it possible to add isotopes as 
tracers (14C or 13C) to study the dynamics of carbon. Coming from a 
long association with the Experimental Lakes Area, I am a committed 
proponent of these kinds of experiments. This paper illustrates the 
strength of this approach. Although this lake was augmented by modest 
nitrogen and phosphorus nutrient additions, the lake had high DOC, 
maintained CO2 above atmospheric levels, and had a net heterotrophic 
metabolism, indicating that terrestrial organic matter supported a 
significant fraction of total respiration. Nevertheless, the food 
web, represented by zooplankton and small fish, is strongly and 
disproportionately dependant on organic carbon fixed by primary 
producers in the lake. Evidence that this is the case for most lakes 
has been accumulating at an increased pace in recent years (France et 
al. 1997, Jones et al. 1999,Grey et al. 2001). The comprehensive 
model presented by Cole et al. will be useful as a template for 
assessment of these and other data. 

Even feature articles have their "issues." An outstanding one with 
this paper is that the fractionation by phytoplankton determined by 
the model is only 6 per mil. Given the relatively low growth rates 
and the very high pCO2, this seemed very unlikely to me. However, 
neither the reviewers nor I were able to find any error in the data 
or analysis that could account for this result. I must admit that I 
am still puzzled and leave it to the readers of L&O to ponder this 
result. Often the value of an article is not only in the answers it 
delivers, but also in the work that it stimulates. I think readers 
will find this article stimulating with both answers and questions.

References 

France, R. L., P. A. del Giorgio, and K. A. Westcott. 1997. 
Productivity and heterotrophy influences on zooplankton d13C in 
northern temperate lakes. Aquat. Microb. Ecol. 12: 85-93. Grey, J., 
R. I. Jones, and D. Sleep. 2001. Seasonal changes in the importance 
of the source of organic matter to the diet of zooplankton in Loch 
Ness, as indicated by stable isotope analysis. Limnol. Oceangr. 46: 
505-513. 

Jones, R .I. J. Grey, and L. Arvola. 1999. Stable isotope analysis of 
zooplankton carbon nutrition in humic lakes. Oikos 86: 97-104. 

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