IMPACT OF UV RADIATION ON THE AQUATIC ENVIRONMENT - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 180

ambient UV 6,76 . The difficulty comes in the generalization of these experimental results
to Antarctic waters where mixing significantly modulates the exposure of phytoplankton
to UV-B. Neale and coworkers 23 found that near-surface UV strongly inhibits
photosynthesis under all modelled conditions and that inhibition of photosynthesis can
be altered by vertical mixing. A sudden 50 % reduction in stratospheric ozone can
decrease daily integrated water column photosynthesis by as much as 8.5 %. This result
confirms the finding of Smith and coworkers 6 who specifically measured in the
marginal ice zone (MIZ), where melt water provides stability and minimizes vertical
mixing. The conclusions of numerous studies are that Antarctic ozone depletion can
inhibit primary productivity, but that natural variability in exposure of phytoplankton to
UV, due to vertical mixing and cloud cover, has a major role in modifying the impact on
net photosynthesis. But it is clear that solar UV is a significant environmental stressor,
and its effects are enhanced by ozone depletion.
The Arctic aquatic ecosystem
The Arctic differs in many respects from the Antarctic 77 being a nearly closed
water mass with limited water exchange with the Atlantic and Pacific oceans. It is
boarded by 25% of the global continental shelf and receives about 10% of the world
river discharge which causes a pronounced stratification and is responsible for high
concentrations of particulate and dissolved organic carbon (POC and DOC), which
strongly attenuate the penetration of solar UV into the water column 77 . These substances
are photochemically attacked by UV-B which increases the palatability and thus
enhances the uptake by bacteria and finally increases the transparency of the water
column. Macroalgae play a more pronounced role in the Arctic than in the Antarctic.
The Arctic aquatic ecosystem is one of the most productive ecosystems on earth and is a
source of fish and crustaceans for human consumption. Productivity in the Arctic ocean
is higher and more heterogeneous than in the Antarctic ocean 78 . Because of the shallow
water and the stable stratification of the water layer, the phytoplankton may be exposed
to relatively high levels of solar UV-B. In addition, many economically important fish
spawn in shallow waters, and many of the eggs and early larval stages are found at or
near the surface, so that harvests of fish for human consumption may be affected.
However, currently we cannot accurately estimate if ozone-related impacts will
influence fishes and other important marine crops.
The Arctic waters are nitrogen and phosphorus limited. This problem is
aggravated by the fact that nitrogen and phosphorus uptake is UV-B sensitive 79 which
also has an effect on the biogeochemical cycles.
7. Potential Consequences
The most direct effect of UV radiation on productivity is loss of biomass which
relays through the food web and affects food sources for human consumption. As
different species are differently affected by solar UV, changes in species composition is
considered. In general smaller organisms are more prone to UV damage than larger