Positive Identification!

Enteromorpha inside a metabolism chamber

Dr. Welter and Dr. Jim Hood (the postdoctoral researcher running the field project here in Iceland as part of the U.S. team) took me and Delor out to the field to practice the chamber metabolism procedure and run through the field protocol step by step.  The field day was a practice run that would allow us to become familiar with the chambers, get an understanding for how the algae would respond to the chamber conditions, and to collect some samples to observe under the microscope for species identification.  The research team that we are collaborating with here has been placing tiles with attached algae inside the chambers, so the algae are largely stationary and fixed to the tile.  However, we are trying to place large flowing filaments of algae into the chambers and we discovered that there are a few complications.  There is a stir bar inside the chamber that keeps the water circulating, and we found that the algae gets caught as the bar rotates, which inhibits its purpose (see Delor’s Troubleshoot-ology blog as well for some details).  Since this discovery last week, Delor has been trying to create some sort of cage for the stir bar, so that it is able to circulate the water without interacting with the algae.  After trying several different size cages and mesh pouches, I think she has developed the perfect size to contain the stir bar and still allow water to flow!  We have tested it a few times under different conditions, and it seems to be working very well.

Nitrogen-fixing cyanobacteria under the microscope.
Photo by B. Lawrence

Using a survey of samples that we collected across all 13 streams, I have been doing my best to identify the different algal and cyanobacterial species.  Having never worked with algal species, the identification process was challenging.  When we were collecting the samples, Dr. Welter described and showed me the physical characteristics of different nitrogen-fixing species, like Nostoc, Anabaena, and Rivularia.  Having this background information was really helpful in the initial identification, but in order to more definitively classify them, I needed to look at the cells at a microscopic level.  For this, I have had the help of algal identification expert Dr. Paula Furey, a postdoctoral researcher working with Dr. Welter in her lab at St. Kate’s.  I also  studied several scientific journal articles and algal classification keys to give myself a good background and some valuable resources when looking at the species for the first time under the microscope.  Using these tools, I have positively identified nitrogen-fixers in our streams, including Nostoc, Anabaena, and Oscillatoria!!   

            We continued to venture out into the field this past week and I am also happy to report that we successfully measured nitrogen fixation rates.  We placed some of the dominant species from Stream 5 in chambers, collected gas and algal samples, and worked out the procedure for the new isotope method that we will be using in some of our nitrogen fixation surveys.  Delor ran the first set of gas samples, and we can positively say that there is indeed nitrogen fixation occurring in these streams, at what appears to be a high rate, even under the fairly common overcast conditions!! YAY!!  After looking at the samples under the microscope, I was fairly confident that we had identified nitrogen-fixers, but the gas readings have officially confirmed that they are fixing nitrogen gas from the atmosphere.  At first glance, it appears that Anabaena is fixing nitrogen at a much higher rate the Nostoc, but we need further sampling and some additional calculations to know for sure.   We plan to complete full surveys of nitrogen fixation rates in at least two more streams this week, so we will have more data to report soon!