Crunch Time...In So Many Ways!

Delor, Jill, and Bayley - last field day!

“Crunch time” represents our past few weeks in Iceland in numerous ways.  It has been time to focus intensively on our field work in an effort to complete our measurements on as many streams as possible before our departure, and time to crunch the data to begin to reveal what we have learned during our seven weeks here.   It has been too long since our last blog post, but we have been hard at work and things have been going very well.  But, very busy!  We have successfully measured nitrogen fixation rates on all of the dominant algal species (typically three or four different types, with 5-6 measurements for each species) on eight individual streams.  We also successfully used our two methods of measuring nitrogen fixation rates on almost all of these samples, which slowed down our progress across the landscape considerably, but we felt that this decision was a good one, as it will help us to evaluate these two methods and to better reveal to the field what each can tell us about nitrogen fixation measurements.  The data are also extremely exciting and a full data analysis indicates that nitrogen fixation rates in the warmest streams are an order of magnitude higher than the highest rates published in the stream scientific literature, which leads us to new questions about why rates are so high and what factors control nitrogen fixation rates in the Hengill streams.   We also observed high rates of nitrogen fixation rates at intermediate stream temperatures, while rates were extremely low and barely measureable in the coldest streams (~6 degrees Celsius).    We still have much work to do to fully complete our data analysis and to place these values into the context of the work of our collaborators here in Iceland, but it is certainly going to be exciting and very important for understanding how streams are responding to temperature across the landscape gradient.  There is also so much potential to expand the work we have started in ways that will contribute to our scientific understanding of the role that nitrogen fixation plays in river ecosystems, and how it influences the cycling of other biologically important elements, including carbon and phosphorus, and how these relationships are affected by changing temperature.

Delor and Jill with the gas chromatograph
in its new location.

While we started this work just a few months ago, we have learned a tremendous amount about these amazing rivers during our time here and everything has come together.  The gas chromatograph has run exceedingly well since its move to the new lab space, and we certainly feel that we have accomplished what we set out to do.  The diversity and complexity of the nitrogen-fixers that we encountered across the streams certainly kept us on our toes and required us to think creatively about how to approach our measurements every time we visited a new site.  It was not a “one approach fits all” situation, and we had to put our heads together every day to develop a plan that would capture nitrogen fixation rates in a rigorous and meaningful way.

Incredible day in the Hengill
fog and rain!

           The weather and the landscape also kept us vigilant, and at times storms kept us indoors when we wished we could continue our field survey.  During a day of record rain, we were able to visit the Hengill and watch our rivers flood, with spectacular waterfalls forming on the rocky hillsides, and the most beautiful fog drifting down and hugging the surrounding mountains.  It was one of our most incredible days in the field, despite the fact that the flood waters carried with it much of the nitrogen-fixers present in the rivers, whisking them downstream and possibly depositing them in nearby coastal and marine environments.    It was a strong reminder of the “reset button” that intense rainfall and episodic flooding provides in river ecosystems, and also got us thinking about the ultimate fate of the nitrogen that enters the rivers through nitrogen fixation – does it fuel more productivity and enter food webs that include insects and fish within rivers, as well as the surrounding terrestrial environment, or is it mostly deposited in marine areas where it may contribute to greater fertility and production there? And, does the fate of the nitrogen vary depending on the species of nitrogen-fixer and where it is located in the landscape?  These questions have important implications for understanding how this source of nitrogen is utilized in aquatic ecosystems, and how, where, and when it has important ecosystem consequences, and may provide future context for our work. 

Yes, it's a little windy and cold, but
just look at that view!  And, no black flies!

Of course, the intense precipitation also aggravated and activated the black flies, which came after us with a vengeance.  They were so intense that it was impossible to get photos that didn't have black flies on the camera lens, not to mention in your ears, eyes, and yes, in your mouth too.  While I suppose that I am not quite as excited about the black flies after this experience, they still did not detract from the wonder and beauty of this amazing place and all that we can learn here!  Going home will be bittersweet indeed, but at least our work is not done, and we will continue to analyze our samples and work with our Iceland collaborators to put the full story together.  We are very excited to see the complete results and to be able to share them and to begin looking toward the next chapter of this exciting project.