Friday, 25 April 2014

The carbon dioxide devil is the small scale detail

 Science is good at generalising, sometimes even when it shouldn't. One of the twentieth century's great ecological insights, the ecosystem as a formal idea, is essentially a means of generalising habitats into a series of flows and reservoirs of gases, energy or nutrients. You can scale this up to a whole planet. Scaling down might be trickier. Pete is experimenting with scaling down, measuring carbon dioxide and methane exchange rates in different ponds. Here he is at Hauxley using the gas analyser (the yellow box) linked to a plastic chamber floating on one of the experimental ponds and allowing small scale measures as the gases exchange between the water under the box and air trapped inside. In this case carbon dioxide was bring dissolved down into the water. At the same time the pH in the pond was high, ~9.0 which is markedly more than you'd expect for a natural, clean pond in north east England. Except that this pond was being blasted by mid afternoon sunshine and, being full of plants, it is likely that photosynthesis was elevating the pH as the plants strip out HCO3 ions toget at the CO2 but in the process release  OH- ions into the water raising the pH. Here is the gas chamber with the pH probe just to the top left

Pete also tried the measures in the pond next door. This time the pond appeared to be a net releaser of  CO2 gas. Generalising for these two, adjacent ponds would be tricky. The variability of animals and plants between near by ponds is well established, one of the reasons they are such biodiveristy hot spots at the landscpae scale. It is beginning to look like they are just as variable in the way their gas fluxes work. the fine scale detail matters, whether it is counting up numbers of ponds, the variation of animal and plant communities between sites or the geochemistry.

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