Water column phytoplankton, effect radiation

Comparison with other Studies. How do the results of our investigation compare with similar studies Our results corroborate the data provided in a similar study of the effect of UV-B on primary productivity in the southeastern Pacific Ocean (35). In the latter study, it was noted that enhanced UV-B radiation caused significant decreases in the productivity of surface and deep samples. Compared to ambient, primary productivity decreased with increasing doses of UV-B. In another study in which in situ experiments using natural Antarctic phytoplankton populations, it was noted that incident solar radiation significantly depressed photosynthetic rates in the upper 10-15 meters of the water column (36). It was also found that the spectral region between 305 and 350 nm was responsible for approximately 75 percent of the overall inhibitory effect. 

Phytoplankton can be exposed to an in situ field of radiation by using UV-transparent (see section 11.2.3) bottles hanging from a line or tubes placed in trays (Figure 1) which are incubated at different depths in the water column [18,20]. One disadvantage with this approach is that phytoplankton cells are kept at a fixed depth for the entire incubation period (e.g., few hours), thus receiving a constant proportion of the surface incident radiation. In the water column, however, cells are moving within the upper mixed layer (UML) and thus exposed to a variable field of irradiance [21] (see Chapter 4). So far, few studies have addressed the importance of mixing rates on the phytoplankton photosynthesis [21-23], and with the exception of the experiments performed by Marra [24] on the effects of PAR, we are not aware of such studies done under in situ conditions. 

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