Parameters: Chlorophyll, Phycocyanin
Myvatn, or “midge lake” in Icelandic, is a biological jewel located just south of the Arctic Circle. As the name suggested, it produces many midges: in years with high densities, the biomass of midges coming out of the lake is about equivalent to 100 humpback whales. But in some years, the midges almost disappear, with biomass equivalent to a few large dogs. These huge fluctuations in midge abundance drive almost all facets of the Myvatn ecosystem, including cyanobacteria, the nitrogen-fixing phytoplankton that can form scums across the surface of the lake. Cyanobacteria blooms can occur in any year, but they are more likely when midge populations are low. We don’t yet know why.
Myvatn has been studied intensively since the 1970s by Arni Einarsson (the Director of the Myvatn Research Station) and others. Our group from University of Wisconsin-Madison currently has a long-term National Science Foundation grant to work on the lake. One of our objectives is to accumulate long-term data on cyanobacteria blooms. The blooms, when they occur, seem to follow a regular pattern: they start in the small, north basin of the lake and then spread to the larger, south basin (figure 1). Two likely explanations are (i) that the deeper north basin has a relatively long water retention time, allowing time for cyanobacteria to grow, and (ii) the warm springs that feed the north basin provide the ideal incubation conditions for cyanobacteria.
Figure 1: Distribution maps of phycocyanin from a Fluorosense probe, 14 July and 4 August, 2017 (Arni Einarsson).
We have come to depend on our FluoroSense phycocyanin and chlorophyll probes because they allow us to take fast readings to quickly map the evolution of cyanobacteria blooms. We also use them routinely in our long-term monitor procedures and also in experiments, where they allow immediate tracking of experimental results. We have limited equipment in the lab near the lake, and getting real-time field measurements is invaluable for our work.
Tony Ives taking a measurement with a chlorophyll FluoroSense on Myvatn.
Author: Anthony Ives
University of Wisconsin-Madison
Location: Myvatn, Iceland