Ecology of UV
UV introduction and basic optics
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Though water attenuates solar radiation, organisms in clear aquatic systems (with low dissolved organic compounds) can still receive damaging levels of UV radiation. The amount of UV radiation recieved by aquatic organisms depends on such factors as the time of year, the geographic elevation of the lake, the depth distribution of the species, and cloud cover on any given day. Many organisms can repair DNA damaged by UV radiation through photoenzymatic repair (PER) using the enzyme photolyase, in the presence of photorepair radiation (PRR)(UV-A and visible light). Biological weighting functions have been used to model UV radiation damage in organisms in an attempt to predict the short-term effects of a changing UV environment. One assumption of these studies is that reciprocity holds. Reciprocity is only satisfied when the effect of a total radiation exposure (dose) is independent of the time over which the exposure occurred (independent of dose rate).
If reciprocity holds for organisms, then survival under laboratory dose rates can be extrapolated to varying field conditons and different dose rates. These species can be used to model effects of UV during different seasons, at different elevations, and at different depths within the lake.
However, there is evidence that if photoenzymatic repair is a strong component of an organism's defense against UV damage, then reciprocity does not hold for that organism. In these cases, the way that a dose is administered plays a role in the survival of the organism.
If reciprocity does not hold, survival under laboratory dose rates can not be easily extrapolated to varying field conditons and different dose rates. In these cases, modelling becomes much more difficult due to confounding variables. One of the goals of this 5 year project is to sort out the confounding variables and make modelling in a complex environment feasable.
To learn more about this topic, please refer to the following articles:
Grad, G., C.E. Williamson, and D.M. Karapelou. 2001. Zooplankton survival and reproduction responses to damaging UV radiation: A test of reciprocity and photoenzymatic repair. Limnol. Oceanogr. 46: 584-591. PDF file.
Kouwenberg, J.H.M., H.I. Browman, J.J. Cullen, R.F. Davis, J.-F. St.-Pierre, and J.A. Runge. 1999. Biological weighting of ultraviolet (280-400 nm) induced mortality in marine zooplankton and fish. I. Atlantic cod (Gadus morhua) eggs. Mar. Biol. 134: 269-284.
Cullen, J.J., and P.J. Neale. 1997. Biological weighting functions for describing the effects of ultraviolet radiation on aquatic systems, p. 97-118. In D.-P. Hader (ed.), The effects of ozone depletion on aquatic ecosystems. Academic Press.
Trocine, R.P., J.D. Rice, and G.N. Wells. 1981. Inhibition of seagrass photosynthesis by ultraviolet-B radiation. Plant Physiol. 68: 74-81.
