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My assignment is to try to give you the sense of how our manipulative experiments of lakes may contribute to our understanding of what might happen in the ocean with iron fertilization.

The reason one studies lakes is generally not that you can manipulate them and mimic the ocean. You study lakes because you like to study lakes. So the experiments I'm going to talk about were not designed to answer oceanographic questions but lake manipulations can give insights into some oceanographic processes.

imageI'm going to address several questions here: Does the addition of limiting nutrients to whole lakes result in atmospheric CO2 drawdown and increase carbon storage? What's the time scale for this drawdown months, years? What happens to the lake ecosystem? Does the food web in the lake regulate the effect of nutrients on carbon storage? In other words, does the fish and zooplankton community in any way impinge on the way that carbon sequestration occurs in the deep portions of lakes?

Finally, I'd like to talk about nutrient fertilization in lakes to increase fish yields. There is interest in whether iron fertilization could increase fish production, especially for human consumption.

imageKeep in mind that lakes are not oceans. They're very different in size and in time-scales, and that's where things get complicated.

With respect to the functional aspects of lakes and oceans, they have many things in common. Both have plankton and pelagic zones and very similar biology and food chain structure. Sometimes the species are the same; sometimes different, but they functions in a very similar manner.

imageThe idea to use lakes as experimental models of the ocean is pretty old. This reference is not the oldest record I could find, but it's a relevant one because it had to do with a real-world problem.

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In the early 1960s, Gene Likens was a graduate student, and Art Hassler who recently passed away in his mid nineties, was early in his career as a professor. They were interested in getting some money from the Atomic Energy Commission, which was interested in radionuclide disposal in the ocean. The question posed by the scientists was could they use stratified lakes as a model for the ocean disposal? Hassler got the funding and Gene got his degree and is now Director of the Institute of Ecosystem Studies, where I reside.

Small, stratified lakes can indeed be used as pilot models in the study of marine problems that are handicapped by the vastness of the sea.

Any of you who knew Art Hassler know that's classic Art Hassler speech. But it's exactly the rationale for thinking about oceans as microcosms of lakes.

imageStarting in the 1960s in Canada, there developed a really great collaboration between oceanographers and limnologists. The main players were Dave Schindler, a Canadian limnologist, and Wally Broecker, an American oceanographer. These two did some experiments up in the Experimental Lakes Area of Canada that Schindler directed and many of their former students--are now leading oceanographers in the field.

Broecker was particularly interested in CO2 gas loss from lakes to the atmosphere, and Schindler was interested in eutrophication, that is, excess enrichment of nutrients to lakes.

imageMany of you may not realize how important this work in lakes was to oceanography, but a lot of what we know about gas flux in marine systems was worked out on lakes, particularly those of the Experimental Lakes Area in Canada. Also many of the tracers, like sulfuric hexafluoride-SF6 and Helium-3 were first tested in lakes. Many of the carbon flux models were developed in lakes. More relevant for the discussion today, were the first whole-lake fertilization experiments that included CO2 degassing. The publications are from the 1970s, and the experiments started in the 1960s. There's still an ongoing, long-term fertilization experiment of one of the lakes up there.

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