岷江上游水体中DOM光谱特征的季节变化

川西北高原湿地和高山峡谷区是岷江等河流重要集水区,地表水体中溶解性有机质(DOM)更多受环境背景影响,DOM来源与结构特征对认识流域有机碳输出通量及模式有重要意义.本文对岷江上游在4月(枯水期末)和10月(丰水期末)分别进行沿程地表水采样并测定了DOM三维荧光光谱(EEM),结合平行因子模型(PARAFAC)分析岷江上游水体DOM沿程和季节变化特征.结果表明,DOM荧光峰(类腐殖峰A、C和类蛋白峰B、T)沿程波动趋势和程度不同;枯水期末(4月)A、C峰强而丰水期末(10月)B、T峰强.PARAFAC识别出3个荧光组分,即C1(250~260/380~480 nm,类腐殖质,占比48.68%~65.02%),C2(300~330/380~480 nm,类腐殖质,占比23.17%~29.83%)和C3(270~280/300~350 nm,类蛋白质,占比11.83%~21.53%);枯水期末(4月)组分沿程波动更明显,其中C1沿程波动最显著.荧光指数(FI)均值在1.4~1.9之间,说明不同季节DOM均有内外源混合特征;枯水期末(4月)DOM腐殖化、芳香性和疏水性高,表明DOM陆源贡献更大,而丰水期末(10月)DOM自生源贡献比枯水期更高.CDOM浓度a(355)]与类腐殖质浓度Fn(355)]极显著正相关,这也证实岷江上游水体中DOM的陆源输入.C1、C2在枯水期末(4月)相关性极显著而丰水期末(10月)相关性未达到显著性水平,进一步表明岷江上游水体中DOM的外源性及季节性差异.

Seasonal Variations of DOM Spectral Characteristics in the Surface Water of the Upstream Minjiang River

Alpine wetlands and valleys of northwestern Sichuan are the main catchment areas of Minjiang River, where dissolved organic matter (DOM) in surface waters comes mainly from the natural background environment. Sources and structure parameters of DOM are important for calibrating the flux and pattern of organic carbon exports from plateau wetlands and alpine rivers. In this study, surface water samples along the upstream Minjiang River were collected at the end of dry season (April) and rainy season (October). Excitation emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) was used to characterize seasonal variations of DOM along Minjiang River. Results showed fluorescence peaks (humic-like peaks A and C, protein-like peaks B and T) were different along the river. Peak A and peak C were more obvious at the end of dry season, while peak B and peak T were more obvious at the end of rainy season. PARAFAC produced a three-component model including two humic-like componentsC1 (250-260/380-480 nm) and C2 (300-330/380-480 nm)] and one protein-like componentC3 (270-280/300-350 nm)], accounting relative intensity 48.68%-65.02% for C1, 23.17%-29.83% for C2, and 11.83%-21.53% for C3. Fluorescence components showed variations along the river more prominently in April than October, in which the most significant one was C1. Average fluorescence index (FI) values ranged from 1.4 to 1.9, indicating that DOM consisted of both autochthonous and allochthonous components. Moreover, higher degrees of humification, aromaticity and hydrophobicity were found in April than those in October, suggesting more terrigenous sources at the end of dry season and more biological sources at the end of rainy season. Additionally, chromophoric dissolved organic matter (CDOM)a(355)] correlated significantly with humic-like substanceFn(355)], which also indicated that DOM components originated from terrigenous input in the upstream Minjiang River. The results also showed significant positive correlation between C1 and C2 in April, with no significant correlation in October, which further proved that exogenous input and seasonal variations characterized DOM sources in the upstream Minjiang River.