ICAM, an in situ Integrating Cavity Absorption Meter, factory configured with nine (9) wavelengths from UV (365nm) to Red (676nm) was at a dockside demo for the OCEANS MTS/IEEE conference in September 2016.
The ICAM was used to measure two algal cultures, Tetraselmis and Cyanothece, in an effort to show how it can resolve differences between algae that have characteristic pigment signatures. Figure 1 below shows very distinct spectra correlating to the specific pigments within each algal culture measured. The absorption in the near-red region of the spectrum indicates presence of phycobilins, typically found in cyanobacteria such as Cyanothece, versus weak absorption at those same wavelengths for Tetraselmis, which lacks phycobilins.
Figure 1: Spectral results of algal cultures analyzed using the ICAM during a dockside demo at Oceans MTS/IEEE on September 2016.
Harbor water at the demo site was also measured from two locations that were about 10 feet apart. The major difference between the two sites was that Location A had macrophytic algae attached to the dock whereas Location B had no plant material at all as shown in figures 2 and 3, respectively.
Spectral results (figure 4) show repeatable differences between the two locations in the near-red region (555nm to 630nm), the part of the spectrum that is correlated with phycobilin absorption.
Figure 4: Spectral results of harbor water at two locations along the same dock during the ICAM demo at Oceans MTS/IEEE on September 2016.
The macrophytic algae at Location A must contain phycobilins indicated by the absorption observed in the near-red wavelengths. The lack of absorption for that spectral region at Location B was expected as there was no plant material attached at that location. The fact that the ICAM was able to resolve differences in water from the same harbor, separated by only 10 feet, on the same dock speaks to the instrument’s sensitivity with respect to absorption characteristics of water.