9411380 Dodds Periphyton (benthic algae and associated heterotrophs) is the most important source of fixed carbon in many shallow aquatic systems. The upper layer of the algal assemblage is exposed to high levels of irradiance, and thus may be susceptible to inhibition from increased UV radiation. Data on the effect of expected increases in incident UV radiation on photosynthetic rates of periphyton are extremely limited; if such effects are severe, they could impair ecosystem function. Equipment will be constructed to explore the relationships between high UV irradiance and photoinhibition in intact periphyton assemblages using O2 microelectrodes to estimate in situ photosynthetic rates, and light microprobes will be developed to assess UV exposure and light attenuation. UV will be supplemented with a passive solar UV concentrator. The concentrator will use parabolic mirrors to concentrate sunlight, and remove all but the ultra-violet regions of the spectrum with filters, and guide the light to periphyton assemblages with fiber optics. This proposal will allow construction and testing of the solar UV concentrator. The system will be tested with experiments of several weeks duration on periphyton inhabiting the streams of Konza Prairie Research Natural Area. The proposed research is unique because long term (weeks) UV supplementation experiments of natural assemblages have not occurred. The techniques developed will allow assessment of long term effects of global increases of UV irradiance.
