In last year’s experiment, around this time, chlorophyll levels were at a bloom-peak in the 40 range. Same time this year, we are averaging a low 3. The reason for this is a simple change in the mesocosms – a mesh bag covering the entire surface of the bag, and a cute “shower cap” on the top, which aim to correct light intensity by lowering it around 55%.
The reason for these mesh bags was to slow down the progress of the bloom, so we could get more data points during the huge increase in biomass that happens during a phytoplankton bloom. And since autotrophs (read: anything with chlorophyll) need light to photosynthesize, our chlorophyll readings show that these covers have been doing a pretty good job of cutting out a lot of light from the system. We do this by filtering the water we collect from the mesocosms, and analyzing the amount of chlorophyll present using a fluorometer.
Now, to the process of analyzing the chlorophyll itself: first, after sampling, a certain volume is filtered (less water is filtered when we predict more biomass to be present). These samples are put in acetone and are sent to the freezer, which effectively burst the cells and free the chlorophyll into the solution.
After 24 hours, the samples are removed from the filters and are analyzed using a fluorometer. The values this machine spits out are recorded, and manipulated to give a reading of chlorophyll mass (in ug/L). By recording these numbers, we can see how much photosynthesizing biomass is present in the system, which is a useful piece of information to have when looking at other variables of the experiment like types of phytoplankton, number of grazers, and progression of phytoplankton blooms.