龙感湖水体光学特性的观测

Study on Optical Properties of Lake Longgan

基于2002—2003年秋、夏季原位水下光场巡测及连续定点观测资料分析了龙感湖不同湖区及不同风浪条件下水体的光学特性,探讨了光衰减系数、辐照度比的光谱分布、空间差异及不同风浪条件对水下光场的影响.结果表明,水下光谱在紫光波段衰减最强烈,其次是蓝光,红、绿光衰减最弱,并且向下辐照度衰减系数一般要大于向上辐照度衰减系数.秋季L1-L3点向下辐照度400—700nm波段衰减系数的变化范围分别为0.71—3.60、1.06—3.72、0.78—2.89m-1;光衰减系数的空间分布是位于湖中心的12点要略大于两边的L1、L3点;辐照度比的变化趋势极为一致,最低值出现在短波蓝光波段,最高值出现在550—600nm之间;从小风浪到中风浪、大风浪其PAR衰减系数分别是1.74、2.02、2.45m-1;透明度、衰减系数与悬浮物浓度相关性最好,决定系数在0.7以上,但其变化除受悬浮物影响外还要受制于溶解性有机物和浮游植物;440nm波长衰减系数(Kd(440))与悬浮物(SS)、溶解性有机碳(DOC)、叶绿素a(Chl.a)的多元线性回归方程为:Kd(440)=0.514—0.075SS+0.125DOC+0.100Chl.a(R2=0.87,N=8,P≤0.05)

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