杭州西湖水体光学状况及影响因子分析

THE LIGHT CONDITION AND AFFECT FACTORS IN HANGZHOU WEST LAKE

2004年10月8日在杭州西湖6个不同湖区共布设10个采样点进行水下光场的测定,并采集水样分析悬浮物、叶绿素a、有色可溶性有机物(CDOM)浓度.结果表明,3类主要光衰减物质总悬浮物、叶绿素a和DOC的浓度分别为3.68～42.76 mg/L、4.64～85.95 μg/L、5.19～9.22 mg/L;CDOM在440 nm波长处吸收系数为0.30～1.46 m-1;PAR衰减系数在1.13～6.04 m-1间变化,均值为4.00±1.69 m-1;对应的真光层深度为0.76～4.08 m,均值为1.54±1.11 m;仅南湖和茅家埠两个湖区真光层深度大于水深,其他湖区由于水深远大于真光层深度,在现有的光照条件和水位下要恢复沉水植物困难较大.对PAR衰减系数、真光层深度、透明度等表观光学参数与主要水色因子进行相关分析发现,水体中浮游藻类和有机颗粒物对西湖水体光学性质影响最大.

The behavior of light in water, particularly its attenuation with depth, has important ecological and water quality implications. The underwater light climate ultimately determines the depth distribution, abundance and primary production of phytoplankton and macrophyte. Light attenuation is regulated by the composition and concentration of various attenuating constituents, which include water itself, gelbstoff, phytoplankton and tripton. Here the vertical attenuation coefficients of downward visible irradiance were measured in 10 different stations in Hangzhou West Lake using 192SA and 193SA light sensors and a SR9910-PC scanning spectroradiometer at the water surface and at different depths. Water chemistry variables such as total suspended solids （TSS）, organic suspended solids （OSS）, inorganic suspended solids （ISS）, chlorophyll-a （Chla）, dissolved organic carbon （DOC）, absorbance of chromophoric dissolved organic matter （a） were measured to determine the relative contribution of dissolved and particulate components in explaining the variation in diffuse attenuation coefficients. The attenuation properties of Hangzhou West Lake vary greatly though it is a small shallow lake. The main attenuators such as TSS, Chla and DOC vary from 3.68 to 42.76 mg/L, 4.64 to 85.95 μg/L, 5. 19 to 9.22 mg/L, respectively. CDOM absorption coefficients at 440 nm are in the range of 0.30-1.46 m^-1. PAR attenuation coefficients range from 1.13 to 6.04 m^-1 with an average value of 4.00±1.69 m^-1 , the corresponding euphotic depth ranging from 0.76 to 4.08 m with an average value of 1.54±1.11 m. Only small south lake and Maojiabu lake regions the euphotic depths are larger than water depths. Therefore, the restoration of macrophyte is difficult under present underwater light condition and water level. Based on regression analysis between PAR attenuation coefficients, euphotic depths, secci disc and main light attenuators, phytoplankton and organic suspended solid play a main role in regulating the attenuation of light.