| Popis: |
In this study, underwater light field and optical properties in Lake Longgan were studied by applying in situ measurement data from 2002 to 2003. Incident downwelling photosynthetically available irradiance (PAR, 400 -700 nm) at the water surface and at different depths were measured using a 192SA light sensor connected to a Li -1400 datalogger. Underwater spectral irradiance was measured with a high-resolution spectroradiometer ( SR -9910; Macam Photometries, Livingston, Scotland) equipped via a 4 - m light guide with a cosine-corrected light collector. The spatial distribution of light attenuation, the spectral distribution of attenuation coefficients, and the effect of different wind and wave on underwater light field were assessed. The ultraviolet light was most strongly attenuated and its attenuation decreased with the increase of wavelength. The downward attenuation coefficients were larger than upward attenuation coefficients. The ranges of spectral attenuation coefficient from 400 to 700 nm were 0. 71 - 3. 60, 1.06 -3.72 and 0.78 -2.89 m-1 at sampling station L1, L2 and L3, respectively. There were insignificant spatial differences in the optical properties, only attenuation coefficients being larger at sampling station L2 than those at sampling station station L1, L3. No significant differences of spectral irradiance ratio at sampling station L2, L3, being minimal values during blue wavelength and maximal values during550 -600 nm. In open, wind-exposed lake region with silty sediment, the increase in total suspended solids resulted from the wind and wave would increase the attenuation of light. The attenuation coefficients of PAR increased from 1. 74 to 2. 02, 2. 45 m-1 under three different wind and wave processes. The most significantly positive correlation was found between transparency, attenuation coefficient and total suspended solids. Light attenuation was predominantly correlated to the concentration of total suspended solids and dissolved organic carbon, chlorophyll a. Multiple linear regression equation at 440 nm was listed: Kd(440) =0.514-0.075SS+0. 125DOC+0. 100Chl. a |
