index

Impacts on ecosystems

(http://www.baproducts.com/md2002.htm)

UV-B has the potential to indirectly influence entire ecosystems by altering nutrient cycles and decreasing overall productivity. In the meantime, an ecosystem can shield organisms from the deleterious effects of UV-B. Alternatively, environmental factors within an ecosystem, such as pollution or climate change, can confound the effects of UV-B and reduce susceptibility to UV-B damage, or further stress organisms.

Nutrient cycling and productivity
UV-B alters nutrient cycling by microorganisms and phytoplankton and reduces plant productivity. UV-B has been shown to inhibit phosphorus uptake (Aubriot et al. 2004), dimethyl sulphonium propionate (a sulfur source) production, and nitrogen uptake in marine phytoplankton (Karentz and Bosch 2001), and also inhibit phosphorus uptake by lake phytoplankton (Allen and Smith 2002). Observed decreases in primary production in response to UV-B can translate into reduced trophic energy transfer in aquatic and terrestrial ecosystems that has the potential to destabilize the structure of food webs. As an example of reduced productivity, marine phytoplankton productivity is predicted to decrease by <1-9% because of increased levels of UV-B (Karentz and Bosch 2001).

Environmental shielding
Ecosystems such as wetlands, and other colored (by dissolved organic matter) or cloudy (by particulates) waters, may shield the organisms inhabiting them from UV-B. In aquatic ecosystems, UV penetration into the water column depends upon concentrations and types of dissolved organic matter, phytoplankton and particle abundance, and also the optical properties of water itself. The less “stuff' in the water, the deeper the UV can penetrate. For instance, Peterson et al. (2002) suggest that UV-B was quickly attenuated in Minnesota and Wisconsin wetlands because of the high concentrations of dissolved organic matter (DOM). In contrast, UV-B will penetrate deeper in alpine lakes with lower concentrations of DOM. The UV-B exposure of organisms suspended in the water column is also dependent upon the vertical mixing of the water since it determines how often and for how long they are at or near the water's surface, where UV-B levels are greatest.

It is important to account for the environmental shielding and other environmental factors when conducting experiments on responses of organisms. The natural environment is often different from laboratory conditions with respect to temperature, oxygen, food, amount and duration of UV-B and other light exposure. Thus, in order to determine the probable effects of and responses to UV-B by organisms, experiments yielding the most true-to-life results will be conducted in the field, or under conditions expected in the field, especially with regard to the amount and duration of light. For example, Bridges and Boon (2003) observed that carbonyl (an insecticide) did not become more toxic to the southern leopard frog in the presence of UV-B in a field experiment, whereas it was shown to become more toxic in previous studies. They attributed their findings to the protective absorption of UV-B by the colored, DOM rich waters of the natural environment.

Confounding environmental factors
In some cases, environmental factors, such as pollution and climate, can confound the effects of UV-B on organisms and ecosystems. Kiesecker et al. (2001) noticed that the waters where western North American toads laid their eggs were shallower during dry years. The shallow water exposed the eggs to higher levels of UV-B and increased the likelihood that the embryos would be infected by Saprolegnia ferax . The death rate for eggs in 20 cm deep water was 80% while it was 12% for eggs laid in water deeper than 50 cm.

Meanwhile, changes in the dynamics of nutrient cycling and productivity may feedback to the climate system. For instance, the observed decrease in dimethyl sulphonium propionate (DMS) production by marine phytoplankton may impact cloud patterns since DMS aerosolizes and is believed to serve as cloud nuclei (Häder et al. 1991).

NASA SOHO Mission,Yohkoh science team	*Ecological impacts of* *UV-B radiation*
Introduction	Impacts on ecosystems (http://www.baproducts.com/md2002.htm) UV-B has the potential to indirectly influence entire ecosystems by altering nutrient cycles and decreasing overall productivity. In the meantime, an ecosystem can shield organisms from the deleterious effects of UV-B. Alternatively, environmental factors within an ecosystem, such as pollution or climate change, can confound the effects of UV-B and reduce susceptibility to UV-B damage, or further stress organisms. Nutrient cycling and productivity UV-B alters nutrient cycling by microorganisms and phytoplankton and reduces plant productivity. UV-B has been shown to inhibit phosphorus uptake (Aubriot et al. 2004), dimethyl sulphonium propionate (a sulfur source) production, and nitrogen uptake in marine phytoplankton (Karentz and Bosch 2001), and also inhibit phosphorus uptake by lake phytoplankton (Allen and Smith 2002). Observed decreases in primary production in response to UV-B can translate into reduced trophic energy transfer in aquatic and terrestrial ecosystems that has the potential to destabilize the structure of food webs. As an example of reduced productivity, marine phytoplankton productivity is predicted to decrease by <1-9% because of increased levels of UV-B (Karentz and Bosch 2001). Environmental shielding Ecosystems such as wetlands, and other colored (by dissolved organic matter) or cloudy (by particulates) waters, may shield the organisms inhabiting them from UV-B. In aquatic ecosystems, UV penetration into the water column depends upon concentrations and types of dissolved organic matter, phytoplankton and particle abundance, and also the optical properties of water itself. The less “stuff' in the water, the deeper the UV can penetrate. For instance, Peterson et al. (2002) suggest that UV-B was quickly attenuated in Minnesota and Wisconsin wetlands because of the high concentrations of dissolved organic matter (DOM). In contrast, UV-B will penetrate deeper in alpine lakes with lower concentrations of DOM. The UV-B exposure of organisms suspended in the water column is also dependent upon the vertical mixing of the water since it determines how often and for how long they are at or near the water's surface, where UV-B levels are greatest. It is important to account for the environmental shielding and other environmental factors when conducting experiments on responses of organisms. The natural environment is often different from laboratory conditions with respect to temperature, oxygen, food, amount and duration of UV-B and other light exposure. Thus, in order to determine the probable effects of and responses to UV-B by organisms, experiments yielding the most true-to-life results will be conducted in the field, or under conditions expected in the field, especially with regard to the amount and duration of light. For example, Bridges and Boon (2003) observed that carbonyl (an insecticide) did not become more toxic to the southern leopard frog in the presence of UV-B in a field experiment, whereas it was shown to become more toxic in previous studies. They attributed their findings to the protective absorption of UV-B by the colored, DOM rich waters of the natural environment. Confounding environmental factors In some cases, environmental factors, such as pollution and climate, can confound the effects of UV-B on organisms and ecosystems. Kiesecker et al. (2001) noticed that the waters where western North American toads laid their eggs were shallower during dry years. The shallow water exposed the eggs to higher levels of UV-B and increased the likelihood that the embryos would be infected by Saprolegnia ferax . The death rate for eggs in 20 cm deep water was 80% while it was 12% for eggs laid in water deeper than 50 cm. Meanwhile, changes in the dynamics of nutrient cycling and productivity may feedback to the climate system. For instance, the observed decrease in dimethyl sulphonium propionate (DMS) production by marine phytoplankton may impact cloud patterns since DMS aerosolizes and is believed to serve as cloud nuclei (Häder et al. 1991).
UV-B background information

Spatial and temporal distributions
Organismal effects and responses Molecular photobiology Microorganisms Plants Animals
Impacts on ecosystems
Conclusion
References
Links
Biology 217 home