云南高原湖泊有色可溶性有机物和颗粒物光谱吸收特性

Spectral absorption properties of chromophoric dissolved organic matter and particulate matter in Yunnan Plateau lakes

云南高原湖泊是我国湖泊分布最密集的五大湖群之一,不但湖泊数量众多而且类型多样.由于湖泊所处位置海拔较高,容易受日益增强UV-B辐射影响.通过对云南高原34个湖泊有色可溶性有机物和颗粒物吸收测定,分析其光谱吸收特性及对总吸收的贡献,有利于深刻理解紫外辐射在高原湖泊内衰减.不同湖泊间CDOM吸收差异明显,其大小与水体营养盐状况相关,CDOM吸收系数与水体总氮存在显著正相关.增加背景项的指数函数模型能最好模拟CDOM光谱吸收.除在浮游植物浓度非常高的杞麓湖、听湖、星云湖,颗粒物吸收系数在675nm附近存在一个吸收峰外,其它湖泊总颗粒物光谱吸收大致随波长的增加吸收系数逐渐降低,呈现非色素颗粒物光谱吸收特征,整体上颗粒物吸收以非色素颗粒物为主.CDOM对总吸收的贡献主要集中在600nm以下波长,尤其是400nm以下的紫外波段,其在紫外波段(350-400nm)的贡献明显要大于光合有效辐射波段(400-700nm)(ANOVA,P<0.001).特别对于透明度SD≥1.0的清澈型湖泊,CDOM吸收对紫外辐射衰减的贡献更大,其吸收很大程度上决定了紫外辐射的影响深度.

The Yunnan Plateau lakes with different lake types, located in Yunnan Province in southwestern China, are one of the five densest lake areas in China. The lakes, which are generally distributed at elevations from 1200m to 4000m above sea level, receive high intensity UV-B radiation. In this study, the spectral absorption properties of chromopboric dissolved organic matter（CDOM） and particulate matter are studied based on a wide investigation including 34 lakes in the Yunnan Plateau. The study will be helpful in the understanding of the ultraviolet radiation attenuation and the effects of increased UV-B radiation on lake ecosystems. A wide range of variability in CDOM absorption was found among the Yunnan Plateau lakes, CDOM absorption coefficient generally corresponded to the nutrient level with a significantly positive linear correlation between aCDOM（320） and total nitrogen concentration. Exponential model with constant parameters of background items could give the most approximate estimation of CDOM absorption spectra. A marked phytoplankton absorption peak around 675nm was only observed in Qiluhu, Tinghu and Xinyunhu with very high chlorophyll a concentration. High contribution of CDOM to the total absorption was found during the wavelength range lower than 600 nm especially in the ultraviolet range lower than 400nm. The contribution of CDOM to the total absorption was significantly higher in UVR range （350-400nm） than in PAR range （400-700nm） （ANOVA, P〈0.001）. For the clear lake water with secchi disc： SD≥ 1.0, the contribution of CDOM absorption to the diffuse attenuation of ultraviolet radiation would increase, and CDOM absorption, with a large probability, would determine the attenuation depth of ultraviolet radiation.