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

Abstract

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 chromophoric 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, P0.001). 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.