• 关键词：溶解性有机碳  长江  巢湖  鄱阳湖  化学组成  二氧化碳分压

• 基金项目：国家重点研发计划重点专项（No.2016YFA06010004）；国家自然科学基金（No.41371454，21177126，41671479）

• 吕书丛
• 中国科学院地理科学与资源研究所, 北京 100101

• 焦茹媛
• 中国科学院生态环境研究中心, 北京 100085

• 王芳
• 中国科学院地理科学与资源研究所, 北京 100101

• 余其彪
• 中国科学院地理科学与资源研究所, 北京 100101

• 李新艳
• 中国科学院南京地理与湖泊研究所, 南京 210008

• 张路
• 中国科学院南京地理与湖泊研究所, 南京 210008

• 晏维金
• 中国科学院地理科学与资源研究所, 北京 100101

• 摘要：河流、湖泊等水环境的溶解性有机碳（DOC）是流域碳循环的重要组成部分，水环境中的DOC来源、化学组成及迁移转化是碳的生物地球化学循环的核心问题.文章选择长江下游-河口区河段、巢湖、鄱阳湖，研究了DOC化学组成、荧光特征的时空变化以及其与二氧化碳分压的关系.结果表明，湖泊和河流系统的DOC浓度、化学组成和荧光特征均存在显著空间差异.巢湖与鄱阳湖水体中DOC浓度的均值分别为（3.67±1.08）和（3.50±1.63）mg·L^-1，显著高于长江下游-河口区河段的（1.82±0.43）mg·L^-1.在化学组成方面，巢湖DOC的化学组成以类蛋白I类和类蛋白Ⅱ类物质为主，所占比例在70%以上；鄱阳湖DOC则以微生物代谢物、腐殖酸类物质为主，比例达55%以上；而长江下游-河口区河段DOC中各组分所占比例比较接近.巢湖DOC的荧光指数均值为2.03，新鲜度指数均值为1.19，表明巢湖主要为内源性DOC，降解程度较低；而长江下游-河口区和鄱阳湖的荧光指数均值分别为1.78和1.73，新鲜度指数均值分别为0.91和0.96，表明陆源DOC的贡献较大，降解程度较高.长江下游-河口区河段DOC化学组成和特性存在显著季节变化，DOC腐殖类物质比例在夏季显著高于冬季，陆源土壤侵蚀是长江夏季DOC的重要来源；荧光指数均值从夏季的1.72增加到冬季的1.87，也表明长江DOC夏季外源的贡献高于冬季.巢湖的DOC浓度在夏季高于冬季，但其各化学组成和荧光指数变化相对较小，表明巢湖DOC化学组成和来源受季节变化影响不大.新鲜度指数在长江下游-河口区河段和巢湖中均为夏季略高于冬季，表明夏季水体中新近产生的DOC多于冬季.相关分析表明，类蛋白I类和类蛋白Ⅱ类的比例与荧光指数显著正相关、与新鲜度指数显著正相关，是内源性DOC和新近产生的DOC的重要成分；二氧化碳分压与微生物代谢物的比例正相关，与类蛋白Ⅱ类比例负相关，反映了微生物代谢活动及类蛋白Ⅱ类物质的分解消耗对二氧化碳分压的重要贡献.微生物代谢产物和类蛋白Ⅱ类物质可能是反映DOC降解过程以及水体二氧化碳分压的关键化学组成.

• Abstract：Dissolved organic carbon (DOC) in rivers and lakes plays an important role in the carbon cycle and the sources, the chemical composition and transformation characteristics of DOC are also critical issues in the global carbon cycle. In this study, we selected three study sites:Chaohu Lake and Poyang Lake located in the lower Changjiang river basin, and the estuary of Changjiang river to identify the chemical composition and characteristics of DOC and to explore the temporal and spatial variations of fluorescence characteristics relation to the partial pressure of carbon dioxide. The results showed that there were significant spatial differences in DOC concentration, the chemical composition and fluorescence characteristics of the lake-river systems. DOC concentration in Chaohu Lake and Poyang Lake were (3.67±1.08) mg· L^-1 and (3.50±1.63) mg· L^-1, respectively, which was significantly higher than that in estuary of the river (1.82±0.43) mg· L^-1. In terms of the chemical composition, the chemical composition of DOC in Chaohu Lake was dominated by Aromatic Protein I and Ⅱ, accounting for over 70% of the total. DOCs in Poyang Lake were dominated by microbial metabolites and humic substances more than 55%. While in the estuary of the river, DOC in the proportion of each component was relatively close. The average fluorescence index of DOC in Chaohu Lake was 2.03 and the average of freshness index was 1.19, indicating that Chaohu Lake was mainly endogenous DOC with a relatively low degree of degradation. The average fluorescence index for the estuary of Changjiang River and Poyang Lake was 1.78 and 1.73 respectively and the mean of freshness index was 0.91 and 0.96, respectively, which indicated that the contribution of terrestrial DOC was larger and the degree of degradation was higher. The chemical composition and characteristics of DOC in the estuary had significant seasonal changes. The proportion of DOC humus was significantly higher in summer than that in winter, and terrestrial soil erosion was an important source for DOC in summer. The mean of fluorescence index increased from 1.72 in summer to 1.87 in winter, which also indicated that the contribution of exogenous DOC in Changjiang River was higher in summer than that in winter. DOC concentration in Chaohu Lake was higher in summer than that in winter, but the changes of the chemical composition and fluorescence index were relatively small. Freshness index was slightly higher in summer than in winter in the estuary and Chaohu Lake, indicating that more DOC was newly produced in summer than in winter. Correlation analysis showed that the proportion of Aromatic Protein I and Ⅱ was positively correlated with the fluorescence index and positively correlated with the freshness index and they were important components of endogenous DOCs and newly produced DOCs. The partial pressure of carbon dioxide was positively correlated with the proportion of microbial metabolites and negatively correlated with the proportion of Aromatic Protein Ⅱ, indicating an important contribution of the microbial metabolic activity and the decomposition to the partial pressure of carbon dioxide. It is suggested that microbial metabolites and Aromatic Protein Ⅱ may be key chemical components that reflect the DOC degradation process and the partial pressure of carbon dioxide in the water bodies.

• Key words：dissolved organic carbon  Changjiang River  Chaohu Lake  Poyang Lake  chemical compositions  carbon dioxide partial pressure

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