Influence of UVB radiation on aquatic ecosystems

The impact of increased UVB (290-320 nm) radiation due to stratospheric ozone depletion is placed in context with how historical levels of both UVB and UVA (320-400 nm) have influenced the structure of aquatic communities and geochemistry of lakes and their drainage basins. Suggestions for the development of generalized models for predicting the impact of UV radiation are provided and illustrate that both the response of a particular process as a function of wavelength and reliable predictions for underwater spectral irradience are needed. Direct effects on organisms are discussed in light of problems due to adaptation, avoidance, repair and consequences of changes from sensitive to tolerant species composition. Indirect effects mediated through photochemically produced highly reactive reduced oxygen species are introduced and related to redox reactions and metal speciation using the mercury cycle as an example. Although neglected in existing global carbon budgets, UV radiation is responsible for significant release of carbon dioxide and carbon monoxide as well as many other organic metabolites from refractory dissolved organic carbon (DOC). Finally, it was argued that some lakes are losing the "sun screen" provided by DOG, the principal attenuator of UV radiation, due to increased acidification and lower DOC export due to the warmer drier climate conditions.