浅水湖泊水动力过程对藻型湖区水体生物光学特性的影响

基于2010年7月底至8月初对太湖藻型湖区梅梁湾沿岸带水域不同风速条件下水下光场的原位连续高频观测,通过对水下辐照度、光束衰减系数、吸收系数、相关理化参数及气象水文参数的测定与分析,揭示了该区域水体的生物光学特性变化及其与水动力过程的关系.结果表明,总颗粒物吸收系数ap(440)、非色素颗粒物吸收系数ad(440)、浮游植物吸收系数aph(440)及有色可溶性有机物吸收系数aCDOM(440)在小风(30 min内平均风速<3 m.s-1)、中风(3 m.s-1<风速<5 m.s-1)和大风(风速>5 m.s-1)作用下分别为3.97、3.97、6.58 m-1;1.69、2.17、4.20 m-1;2.28、1.80、1.33 m-1;1.05、1.04、1.08 m-1,其中变幅最大的为非色素颗粒物,CDOM吸收系数在不同风速条件下差别不大.水体各组分在PAR波段积分值的贡献率的变化规律为:小风速下浮游植物吸收系数的贡献最大(达42.5%),随着风速的增大,CDOM、浮游植物、纯水吸收系数的贡献率均有降低的趋势,而非色素颗粒物的贡献率则显著增大,分别为33.0%、41.7%、52.0%.PAR漫射衰减系数与10min平均风速呈显著线性相关,风速引起的沉积物再悬浮对PAR漫射衰减系数的影响显著,从小风到大风,PAR漫射衰减系数增加了80.0%,对应真光层深度降低了42.2%.PAR漫射衰减系数、750 nm波长处的光束衰减系数、总悬浮物浓度与风速、波高、波切应力均存在显著正相关,其中又以PAR漫射衰减系数的相关性最为显著.高频观测结果揭示了浅水湖泊藻型湖区水动力过程通过引起沉积物再悬浮、浮游植物的混合及迁移显著改变水体生物光学特性短期变化.

Effects of Hydrodynamic Process on Bio-optical Properties in Algal-Dominated Lake Region of Shallow Lake

An in situ field high-frequency bio-optical measurement was carried out in the littoral region in Meiliang Bay of Lake Taihu, a large shallow lake of China from 24 July to 1 August in 2010. The underwater irradiance, beam attenuation coefficient and absorption coefficient, the related physical-chemical and meteorological parameters were measured and analyzed, in order to determine the relationship between water bio-optical properties and wind waves process. The absorption coefficients of particles a_p(440), non-phytoplankton a_d(440), phytoplankton a_ph(440) and chromophoric dissolved organic matter (CDOM) aCDOM(440) were 3.97, 3.97, 6.58 m^-1; 1.69, 2.17, 4.20 m^-1; 2.28, 1.80, 1.33 m^-1; 1.05, 1.04, 1.08 m^-1 with the corresponding 30-minute average wind speed of<3, 3-5 and>5 m·s^-1 under small, middle and large wind and waves, respectively. Phytoplankton particles contributed the most to total absorption coefficient integrated over a range of photosynthetically active radiation (PAR) (400-700 nm) with a value of 42.5% during small wind waves. With the increase of wind speed, the relative contributions of phytoplankton, CDOM and pure water deceased but the relative contribution of non-phytoplankton significantly increased with the values of 33.0%, 41.7% and 52.0% during small, middle and large wind waves, respectively. A significantly positive linear relationship was found between PAR diffuse attenuation coefficients and the mean wind speed within 10 minutes. Sediment resuspension caused by wind waves had a significant effect on PAR diffuse attenuation coefficient. From small wind waves to large wind waves, PAR diffuse attenuation increased 80.0% but the euphotic depth decreased 42.2%. Significant linear relationships were found between PAR diffuse attenuation coefficient, the beam attenuation coefficients at 750 nm, total suspended solid concentration and wind speed, wave height, wave shear stress, in which the correlation between PAR attenuation coefficients and meteorological hydrology factors was most significant. High-frequency bio-optical measurement showed that hydrodynamic process significantly affected the short-term variation of bio-optical properties in algal-dominated lake region of shallow lake through sediment resuspension, mixing and migration of phytoplankton.