Characteristics of the diffuse attenuation coefficient of upwelling underwater irradiance in Taihu Lake
太湖水体上行漫射衰减系数的变化特征研究

Diffuse attenuation coefficient of upwelling irradiance is an important optical parameter reflecting variations of upwelling light attenuation, which significantly influences underwater light field variation and water ecological system. However, the variation characteristics of the diffuse attenuation coefficient of upwelling irradiance for Taihu Lake (a typical inland lake) has been not known at present. In this study, optical and water quality parameters were acquired by field observation at 28 sampling stations distributing over Taihu Lake from April 29 to May 2, 2010. Based on analyzing characteristic of spectra and spatial distribution of the diffuse attenuation coefficient of upwelling irradiance, the relationship between the concentration of suspended matter and chl-a, solar elevation angle and the diffuse attenuation coefficient of upwelling irradiance was explored. Our results showed that the spectral properties of diffuse attenuation coefficient of upwelling irradiance was larger at shorter wavelength than that at longer wavelength, and had little variation from 575 nm to 700 nm. There existed a significant correlation relationship between a high value of diffuse attenuation coefficient of upwelling irradiance at 675nm and the concentration of chl-a (r=0.574,n=28,p<0.05). The variation characteristics of the diffuse attenuation coefficient of downwelling irradiance and upwelling irradiance were similar between each other. The D-value between them decreased to less than 400nm, and varied little at 400 to 800 nm, and then increased more than 800 nm. The spatial distribution of the diffuse attenuation coefficient of upwelling irradiance was in the order of Taihu Lake Center > grass-type zone>algae-type zone>grass and algae-type zone, and a high value at 675 nm was observed in the algae-type zone and grass and algae-type zone. The diffuse attenuation coefficient of upwelling irradiance gradually decreased with the increasing of solar elevation angle. And there was the most significant relationship between the concentration of suspended matter and the diffuse attenuation coefficient of upwelling irradiance (r=0.963, n=28,p<0.05).