洱海CDOM吸收光谱特征变化及其影响因素

THE CHARACTERISTICS OF CDOM OPTICAL AND ITS INFLUENCE FACTORS IN ERHAI LAKE

为了解溶解性有机质(CDOM)光学特性及影响因素,在2018年11月至2019年10月期间采集了洱海120个表层水样本,利用紫外吸收光谱解析了CDOM的组成及来源,主成分分析法(PCA)阐明光学特性与环境因子之间的相关性。结果表明:CDOM吸收系数[a(440)]范围为0.22—0.90/m,随时间变化显著(P<0.01),营养水平差异较小(P=0.97)。[a(440)]与溶解性有机碳(DOC)关系显著(P<0.01),有利于建立遥感模型监测CDOM时空分布特征。基于芳香度(SUVA_(254))、斜率比值(S_(R))、分子量参数(M)和吸收光谱斜率(S275—295)等吸收特征参数发现CDOM光学特性随季节变化差异显著,由非度量多维尺度(NMDS)分析可分为以下2个时期:2018年11月至2019年7月和2019年8—10月,后者CDOM的SUVA_(254)显著低于前者。吸收特征参数表明洱海CDOM分子量较小,主要为内源产生。在不同时期,水温、pH和TP始终对CDOM吸收特征产生较大影响。文章阐明了洱海表层水体CDOM分布特征及影响因素,为洱海水体污染治理提供理论依据。

Chromophoric dissolved organic matter(CDOM)is a chemical intermediary substance between terrestrial ecosystems and lake ecosystems,which has a profound impact on the structure and function of lakes.In order to understand the optical characteristics of CDOM and its influencing factors,120 surface water samples from Erhai Lake were collected from November 2018 to October 2019.The composition and source of CDOM were analyzed by UV-Vis,and the correlation between optical properties and environmental factors was clarified by the principal component analysis(PCA).The result showed that CDOM absorption coefficient[a(440)]ranged from 0.22 to 0.90/m with significant difference in temporal distribution(P<0.01)but no difference in trophic state(P=0.97).There was a positive correlation between[a(440)]and dissolved organic carbon(DOC)(P<0.01),which was conducive to establish a remote sensing model for monitoring the spatial and temporal distribution characteristics of CDOM.Based on SUVA_(254),S_(R),M and S275—295,it was found that optical characteristics of CDOM were significantly different with seasonal changes.All samples were mainly divided into the following two periods by the NMDS:November 2018 to July 2019 and August to October 2019.The latter SUVA_(254)was lower than the former.The molecular weight of CDOM in Erhai Lake was relatively small,mainly due to endogenous production.In different periods,water temperature,pH and TP always have a greater impact on CDOM absorption characteristics.This paper clarified distribution characteristics of CDOM and its influencing factors,and provided a theoretical basis for the water management in Erhai Lake.