天目湖流域DOM和CDOM光学特性的对比

对2011年1—12月天目湖流域河流及湖体中DOM(可溶性有机物)、CDOM(有色可溶性有机物)的光学特性进行了研究,对比分析了河流和湖体DOM、CDOM的a₃₅₀(350 nm处的吸收系数)、S280~500(280~500 nm波段指数函数拟合曲线斜率)、S_R(光谱斜率比)以及M(a₂₅₀/a₃₆₅)值. 结果表明,天目湖流域a₃₅₀(CDOM)/a₃₅₀(DOM)的年均值为0.856 4,说明CDOM对光的吸收占主导. 河流DOM、CDOM的a₃₅₀年均值分别为(4.24±1.89)、(3.40±1.48)m-1,明显大于湖体的(2.42±0.84)、(2.22±0.83)m-1,表明外源河流输入是天目湖中DOM的主要来源. 河流DOM、CDOM的S280~500年均值分别为(15.98±0.83)、(17.96±0.81)μm-1,湖体的分别为(19.20±1.65)、(20.34±1.73)μm-1；河流的S280~500及S_R均显著低于湖体,表明天目湖流域河流和湖体中CDOM的组成存在明显差异. 天目湖流域DOM与CDOM的M值与S280~500呈显著线性相关,河流DOM与CDOM的M值年均值分别为(5.54±0.81)、(6.54±0.95),显著小于湖体的(7.54±0.98)、(8.28±1.23),表明湖体中的DOM分子较小. 受人类活动、土地利用、降雨径流等因素影响,天目湖流域DOM、CDOM的丰度及光学特性均呈明显的季节性差异,a₃₅₀与S_R在DOM与CDOM中表现的季节性差异较为一致,可以相互参考. 

Comparison of Optical Properties of DOM and CDOM in Lake Tianmuhu Catchment

Optical properties of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM), including absorption coefficient at 350 nm (a₃₅₀), spectral slope of exponential function fitting between 280-500 nm (S_280-500), spectral slope ratio (S_R) and the ratio of absorption coefficients at 250 and 365 nm (M), were investigated in Lake Tianmuhu and its catchment in 2011. CDOM absorption accounted for 85.64% of the absorption of DOM in the whole catchment. The annual averages a₃₅₀ of DOM and CDOM were significantly higher in samples for the river (4.24±1.89) and (3.40±1.48) m-1 than those for the lake (2.42±0.84) and (2.22±0.83) m-1, reflecting the important contribution of all ochthonous river inputs to lake DOM. The annual average S_280-500 was (15.98±0.83) and (17.96±0.81) μm-1 for DOM and CDOM in the river samples, and the corresponding values were (19.20±1.65) and (20.34±1.73) μm-1 in the lake samples. The significant differences of S_280-500 and S_R highlighted the composition differences of DOM and CDOM in the river and lake samples. There was a significant linear relationship between M value and S value in the DOM and CDOM samples in Lake Tianmuhu catchment. The annual average M value of DOM and CDOM in the river samples ((5.54±0.81) and (6.54±0.95)) were significantly lower than those in the lake samples ((7.54±0.98) and (8.28±1.23)), indicating that DOM and CDOM have smaller molecules in the lake samples than in the river samples. Because of the effects of human activity, land use, rainfall runoff and other factors, DOM and CDOM concentrations and composition parameters (a₃₅₀, S_280-500, S_{R, M}) in the surrounding rivers and Lake Tianmuhu showed marked seasonal variations. The characteristics of a₃₅₀ and S_R value in DOM and CDOM samples showed the same seasonal variation; the samples can be used as references for each other.