Effects of artificial ultraviolet-B radiation on experimental aquatic microcosms

1. The effects of prolonged ultraviolet-B (UVB) radiation on freshwater com munities were studied in indoor microcosms (600 L) with artificial light so urces, simulating a clear, shallow, mesotrophic aquatic ecosystem. A range of six intensities (in duplicate) of UVB radiation, ranging from 0 (control ) to 9.56 kJ m(-2) day(-1) at the water surface, was applied for 8 weeks. T he UVB radiation levels, attenuation, shading and scattering were comparabl e to those in Dutch shallow freshwater systems. Physical, chemical and biol ogical variables were monitored weekly. 2. The WE treatment did not affect the abundance, species composition or bi ovolume of the phytoplankton or zooplankton communities, nor did it affect the periphyton or the macroinvertebrate community. A few species showed a s ignificant response on some of the sampling dates, but there was no negativ e UVB effect at the community level. Overall, the ecosystems in the microco sms were not affected by the UVB treatment. 3. In a bio-assay, a laboratory clone of Daphnia pulex, not subjected to UV B radiation, was fed with seston from the microcosms. Daphnia pulex feeding on seston from the control microcosms grew faster, had better survival and better reproduction than D. pulex feeding on seston from the UVB treated m icrocosms. The phytoplankton-zooplankton interaction may have been influenc ed by the UVB treatment. 4. The dissolved oxygen content (DOC) concentrations in the microcosms were around 5 mg L-1. The DOC levels in Dutch systems rarely fall below 10 mg L -1. This might provide sufficient protection against the detrimental effect s of increased UVB radiation.