Effects of rainstorm on the spectral absorption properties of chromophoric dissolved organic matter and particles in Lake Qiandao

Abstract

为了研究暴雨事件对千岛湖有色可溶性有机物（CDOM）和颗粒物吸收光谱的影响，利用2016年暴雨前（3月1-6日）和暴雨后（4月6-11日）采集的水样，对暴雨前、后千岛湖水体CDOM、浮游藻类和非藻类颗粒物的吸收光谱特征进行分析，探讨暴雨事件对其造成的影响.结果表明：千岛湖作为典型的深水型内陆湖泊，其CDOM、浮游藻类颗粒物和非藻类颗粒物的吸收强度较太湖等浅水型湖泊弱.暴雨前，CDOM光谱吸收系数a_CDOM（λ）值在0~0.6 m^-1范围内变化，其光谱拟合系数S_CDOM的均值为0.0158±0.00145 nm^-1.暴雨前浮游藻类光谱吸收在总颗粒物中占主导，a_ph（λ）在0~0.35 m^-1范围内变化，非藻类颗粒物光谱吸收系数a_NAP（λ）在0~0.15 m^-1范围内变化，其光谱拟合系数S_NAP均值为5.62±0.57 μm^-1；暴雨后CDOM光谱吸收系数a_CDOM（λ）值在0~1.6 m^-1范围内变化，其光谱拟合系数S_CDOM的均值为0.0157±0.00101 nm^-1.暴雨后浮游藻类光谱吸收系数a_ph（λ）在0~2.5 m^-1范围内变化，非藻类颗粒物光谱吸收在部分区域已占据主导地位，a_NAP（λ）在0~0.8 m^-1范围内变化，其光谱拟合系数S_NAP均值为5.72±0.68 μm^-1.由CDOM吸收特征值相对分子质量M值得出，暴雨前、后千岛湖不同区域CDOM组成都以富里酸为主，且暴雨前M值分布较均匀，暴雨后M值呈现从新安江向缓冲区、东南区递增的趋势，这说明西北区随暴雨输入的腐殖酸增加了CDOM的相对分子质量.暴雨对S_NAP值影响较大的区域为西北区、西南区、东北区，对西南区影响最小.本研究为使用光学手段深入探讨暴雨事件对千岛湖水环境的影响提供重要依据.;To study the influence of heavy rainfall on absorption characteristics of chromophoric dissolved organic matter (CDOM) and particles in Lake Qiandao, the samples were collected on March 1-6, 2016 (before the rainstorm) and April 6-11, 2016 (after the rainstorm). The spectral absorption of CDOM, phytoplankton and non-algal particles (NAP) in the lake were analyzed and the influence of rainstorm was discussed. The results showed that Lake Qiandao, as a typical deep inland lake, its spectral absorption coefficients of CDOM, phytoplankton and NAP is small, compared with shallow lakes like Lake Taihu. The CDOM spectral absorption coefficients varied in the range of 0-0.6 m^-1, the mean value of the spectral fitting coefficient of CDOM(S_CDOM) was 0.0158±0.00145 nm^-1 before the rainstorm. The spectral absorption of phytoplankton before the rainstorm dominated the absorption of total particles, varied in the range of 0-0.35 m^-1. The spectral absorption coefficients of NAP varied in the range of 0-0.15 m^-1, and the mean value of spectral fitting coefficient of NAP(S_NAP) was 5.62±0.57 μm^-1 before the rainstorm; The CDOM spectral absorption coefficients varied in the range of 0-1.6 m^-1 S_CDOM was 0.0157±0.00101 nm^-1 after the rainstorm. The spectral absorption of phytoplankton varied in the range of 0-2.5 m^-1. NAP absorption dominated the absorption of particles in some regions after the rainstorm, a_NAP(λ)varied in the range of 0-0.8 m^-1 and S_NAP was 5.72±0.68 μm^-1. The M value showed that CDOM composition of the different regions of the lake is mainly fulvic acid both before and after the rainstorm, the spatial distribution of M value is relative even before the rainstorm. However, the M value showed an increasing trend from the Xin'anjiang to the buffer area and southeastern area after the rainstorm, which indicates that humic acids increased the relative molecular mass of CDOM in the northwestern area. Rainstorm had the greatest impact on the northwestern, southwestern and northeastern areas regarding the value of S_NAP, with the smallest impact on the southwestern area. This study provides an important basis for the use of optical means to further explore the impact of heavy rainfall on aquatic environment of Lake Qiandao.