| 引用本文: | 朱正杰，肖 军，龚业超，杨洪永，张 雄, 双 燕，毛玲玲.2016.湖泊沉积多指标记录的长寿湖近60年来营养化过程[J].地球环境学报,(3):292-300 |
| ZHU Zhengjie, XIAO Jun GONG Yechao, YANG Hongyong,
ZHANG Xiong, SHUANG Yan, MAO Lingling.2016.Trophication evolution recorded by multi-proxy evidences in Lake Changshou, Chongqing during the recent 60 years[J].Journal of Earth Environment,(3):292-300 |
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| 湖泊沉积多指标记录的长寿湖近60年来营养化过程 |
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朱正杰，肖 军，龚业超，杨洪永，张 雄, 双 燕，毛玲玲1,2,3
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1. 外生成矿与矿山环境重庆市重点实验室 重庆地质矿产研究院，重庆 400042;2. 煤炭资源与安全开采国家重点实验室重庆研究中心，重庆 400042;3.中国科学院地球环境研究所 黄土与第四纪地质国家重点实验室，西安 710061
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| 摘要: |
| 长寿湖位于重庆市长寿区境内，是重庆市最大的湖泊旅游风景区和淡水鱼养殖基地之一。近年来，其营养化日趋严重。本文通过对有机质碳、氮含量、碳氮比值、有机质碳同位素等有机质指标的分析，结合137Cs放射性核素定年，探讨了长寿湖近60年来有机质转化及营养演化过程。结果表明：长寿湖有机质主要来源于水生植物藻类，受陆源影响较小；湖泊环境演化分为两个截然不同的阶段：1980年以前，有机质碳、氮含量较低，C / N比值较小，有机质碳同位素值较大，暗示湖泊营养环境为贫营养化。1980年以后，有机质碳、氮含量较高，C / N比值较大，有机质碳同位素值偏负，说明湖泊已经处于营养化阶段，人为活动的增强及养殖业的发展是导致湖泊生产力增大的主要因素。长寿湖沉积物多指标忠实记录了湖泊环境的演化过程。 |
| 关键词: 长寿湖 有机质碳同位素 营养化 人为活动 |
| DOI：10.7515/JEE201603007 |
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| 基金项目:重庆市基础与前沿研究计划项目（cstc2013jcyjA20001） |
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| Trophication evolution recorded by multi-proxy evidences in Lake Changshou, Chongqing during the recent 60 years |
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ZHU Zhengjie, XIAO Jun GONG Yechao, YANG Hongyong,
ZHANG Xiong, SHUANG Yan, MAO Lingling1,2,3
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1. Chongqing Key Laboratory of Exogenic Mineralization and Mine Environment, Chongqing Institute of Geology and Mineral Resources, Chongqing 400042, China;2. Chongqing Research Center of State Key Laboratory of Coal
Resources and Safe Mining, Chongqing 400042, China;3. State Key Laboratory of Loess and Quaternary Geology,
Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
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| Abstract: |
| Background, aim, and scope Lake Changshou, located in Changshou District, is one of the largest lake scenic spots and most important freshwater fish breeding bases in Chongqing. Recently, the eutrophication of this lake is increasing seriously. The aim of this study is to evaluate the process of eutrophication of Lake Changshou by using organic proxies, including carbon and nitrogen content of organic matter, C/N ratios, and carbon isotope composition of organic matter. Materials and methods Sediment core named CS1 and CS2 were retrieved from the central part of Lake Changshou in 2013 using a self-designed gravitational sediment sampler. Sediment samples were sectioned at 1 cm interval and put into plastic bags in the field. Sediment samples were dried using a vacuum freeze drier. Core CS1 samples were used for geochemical analysis, and CS2 samples were used for analyzing radionuclide 137Cs activities. Element analyses of total organic carbon (TOC) and nitrogen were measured by the element analyzer. Samples for organic carbon analysis were pretreated with HCl (1 mol ∙ L−1), then placed in water bath for two hours at 60℃ to remove carbonates, and rinsed repeatedly with distilled water for four times. After that, δ13C values of organic matter were measured on the Finnigan Delta Plus isotope ratio mass spectrometer. A number of duplicate samples were also measured to monitor the measurement accuracy. The activity of 137Cs was measured at 661.6 k eV by γ-spectrometry using low-background germanium detector. Results Data of 137Cs demonstrate that the average sedimentation rate of Lake Changshou is 0.85 cm ∙ a−1. Total organic carbon contents vary between 0.85% and 4.3%, with the mean value of 1.75%. Before 1980 AD, the average TOC is 1.25%, and after 1980 AD, the average TOC is 2.43%. Nitrogen contents and C/N ratios show similar variations with TOC. However, carbon isotope composition of organic matter shows contrast variations. The results indicate that the source of organic matter in Lake Changshou is derived from aquatic plants and algae, rather than terrestrial plants, or little affected. The environmental evolution of Lake Changshou can be classified into two periods with the contrasting characteristics during the past 60 years. The change time of lake environment happened approximately in 1980 AD. Discussions C/N ratios can be used to identify the source of organic matter. In general, C/N ratios in algae are less than 10, while C/N ratios in terrestrial plants are high, varying between 20 and 200. In addition, δ13C values are significantly different between aquatic and terrestrial plants. Therefore, C/N ratios and δ13Corg are effective proxies to distinguish the source of organic matter from lake sediments. In Lake Changshou, data plot within the field of aquatic plants, rather than C3/C4 plants, implies that the source of organic matter is derived from aquatic plant. While TOC and TN are indicators of lake productivity and eutrophication. The increase of δ13Corg value is interpreted as the increase of lake productivity. Based on the organic indicators, the environment evolution of Lake Changshou can be divided into two periods. Before 1980 AD, stable values of carbon isotope of organic matter, the low carbon and nitrogen content of organic matter, and low C/N ratios suggested that the lake environment was oligotrophication. After 1980 AD, notable increase of carbon and nitrogen content of organic matter, C/N ratios, and decrease of carbon isotope values of organic matter, demonstrated that the increase of lacustrine productivity and the eutrophication was the result of strong human activities and the development of fish breeding. Therefore, multi-proxy has reliably recorded the environment evolution of Lake Changshou. It is obvious that there is a negative correlation between δ13C and TOC, inconsistent with the previous views that such an increase in productivity would produce higher δ13C values of organic matter. We believe that the degradation of aquatic algae during the process of eutrophication is the primary factor resulting in the decrease of δ13C values of organic matter with the increase of productivity in Lake Changshou. Conclusions C/ N ratios and carbon isotope composition of organic matter reveal that the origin of organic matter in Lake Changshou is aquatic plant, rather than terrestrial plant. The trophication state of Lake Changshou can be divided into two periods. Before 1980 AD, the lake was oligotrophication and was little affected by human activity. After 1980 AD, strong human activities and the development of fish breeding led to the serious trophication state. The eutrophication of Lake Changshou after 1980 AD produced the decrease of δ13C values of organic matter. It is proposed that degradation of aquatic plant likely controls the carbon isotopic composition of organic matter. Recommendations and perspectives Thus, multi-proxy have reliably recorded the environmental evolution of Lake Changshou. The eutrophication of Lake Changshou should be paid much attention, especially on the controls of the human impacts. |
| Key words: Lake Changshou organic carbon isotope eutrophication human activity |
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