Effect of underwater light spectrum on primary production of the Taihu Lake

Distribution of light spectrum and primary production in the waterbody of Meiliang Inlet of Taihu Lake was studied. The results show that on the water surface, the intensity of UV-C was low (10 ^-5 μE·m ^-2 ·s ^-1 ), that of UV-B increased with wavelength and that of UV-A was much higher (10 ^-2 μE·m ^-2 ·s ^-1 ) but attenuated rapidly with maximum vertical diffuse attenuation coefficient ( K _d )value up to 12.5 m ^-1 . K _d of visible light could reach as high as 8.2 m ^-1 . In comparison with the value on the surface, the intensity of ultraviolet at 0.5 m was less than 1%, and of visible light around 20%. The primary production was relatively low in the surface, reached peak at the depth of 0.2 m and then decreased with the increase in depth. Direct measurement revealed that dissolved oxygen in the water was high at the depth of 0.2 m. Concentration of chlorophyll-a varied with light intensity in the water. These results show that the distribution of primary production was the result of the joint effect of ultraviolet and visible light.