杭州西湖冬、春季水体光学特性比较

于2007年冬、春季对杭州西湖主要湖区的水下光合有效辐射进行了研究，主要从光学角度讨论西湖的水质状况及其影响因素. 选用美国LI-COR公司的水下光量子仪(LI-COR 192SA)分层测定光合有效辐射(PAR)，同时测定透明度，叶绿素a，悬浮物(SS)，总氮和总磷等理化因子. 通过对不同深度处水下辐照度进行指数回归得到光学衰减系数(K_d). 结果表明，西湖水质和水体光学条件冬季优于春季，ρ(叶绿素a)和ρ(SS)低，透明度和真光层深度高. 水下光合辐射的垂直分布呈指数衰减. 从总体上来看，K_d冬季小于春季，外西湖高于其他湖区，并且由南至北逐渐升高. 冬、春季K_d分别为0.49～2.25和0.59～3.45 m－1. K_d与ρ(叶绿素a)和ρ(SS)呈正相关.浮游植物和悬浮物是影响西湖水下光照的重要因素. 降低浮游植物和悬浮物含量是改善西湖水体光学条件的重要内容. 

Comparison of Optical Characters of Hangzhou West Lake in Winter and Spring

In order to improve the water quality of Hangzhou West Lake from the optics aspects, the Phyotosynthetically Available Radiation (PAR) as well as its relative factors in winter and spring, 2007 was researched. PAR was measured using LI-COR 192SA light sensors at water surface and different depths. Water physiochemical variables such as transparency, chlorophyll-a (Chla), suspended solids(SS), total nitrogen and total phosphorus were measured. The vertical attenuation coefficients K_d were obtained by regression of underwater visible irradiance at different depths. It showed that winter had a better water quality and optical condition than spring, with lower chlorophyll-a and suspended solids density,and higher secchi disc transparency and euphotic depth. The vertical distribution of underwater visible irradiance exhibited an exponential decay. Generally speaking, the attenuation coefficient K_d was lower in winter than in spring,and higher in the outer than in other parts of the lake and it increased gradually from south to north. It varied from 0.49 to 2.25 m－1 in winter and 0.59to 3.45 m－1 in spring. The attenuation coefficient K_d had positive relationship with chlorophyll-a and suspended solid. Therefore, phytoplankton and suspended solid were the most significant factors to influence the underwater light in West Lake. It is necessary to lower the concentration of both in order to improve the wateroptical characters of West Lake.