Knowledge Resource Center for Ecological Environment in Arid Area
| 不同气候区湖泊地球化学记录的近现代环境演化过程及机理 | |
| 其他题名 | Regularity and mechanism of rencent lake environmental evolution recorded by sedimentary geochemical proxies in lakes of different climate zones |
| 沈贝贝 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 吴敬禄 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 近几十年来，随着社会经济快速发展、城市化规模扩大及人口增加，我国不同区域湖泊均出现不同程度的环境问题，如东部湿润地区湖泊水体的富营养化和污染，西北地区湖泊的干旱咸化及污染问题，并影响了区域社会经济的可持续发展。由于不同区域自然和人类活动等驱动因子的差异，导致不同湖泊环境演化的过程和机理较为复杂，给湖泊环境治理、修复及科学管理带来较大困难。另一方面，有限的湖泊监测资料，也增加了正确认识湖泊环境演化规律、全面理解其变化机理的难度。为此，有必要拓展湖泊环境演化的序列，比较不同类型湖泊环境变化特征，进而剖析不同时期不同类型湖泊环境演化的过程及规律，并探究其机理，以便为区域湖泊环境管理和保护提供科学依据。湖泊沉积物记录了流域自然和人类活动的多重信息，具有信息量大，分辨率高的特点，是开展过去湖泊环境演化序列研究的有效载体。基于此，本项研究重点选择湿润区长江中游网湖、干旱区博斯腾湖和赛里木湖以及半干旱区乌梁素海等不同区域湖泊为对象，在湖泊流域现代气候环境参数分析的基础上，利用有机氯农药（OCPs）、多环芳烃（PAHs）、重金属、正构烷烃，总有机质（TOC）、总氮（TN）、有机碳同位素（δ13C）等湖泊沉积物地球化学指标，开展近百年来不同气候区湖泊环境变化规律及机理研究，并初步取得了如下几个方面的进展：1. 对湿润区和干旱区不同湖泊及其流域表层沉积物多种地球化学代用指标的分析，明确了指标的环境意义。研究表明，不同类型湖泊流域沉积物OCPs和PAHs含量变化反映不同的人类活动方式和强度，OCPs含量变化均反映流域人类农业活动，而高分子量（HMW）PAHs主要受城市化及工业化的影响。沉积物OCPs、PAHs和CuEF等重金属具有较好相关性，均指示了流域人类活动的影响，但是OCPs、PAHs可以更有效地反映不同的人类活动方式。沉积物正构烷烃指标较好地反映了沉积物有机质来源，不同类型湖泊流域表土正构烷烃碳数分布范围均为C14~C33，主要呈单峰模式，具有明显的奇偶优势，较高的陆生/水生植物相对比值（TAR）和高/低碳数同系物比值（H/L），草本类植被区表土正构烷烃主峰碳为C31，木本类植被区正构烷烃主峰碳为C29，结合2C17/(C23+C25)指标较好地反映了流域的不同植被类型。2. 在沉积岩芯210Pb和137Cs定年的基础上，建立了不同湖泊沉积多环境指标序列并进行综合比较，总体上划分了三个不同的湖泊环境演化阶段，揭示了近百年来不同气候区湖泊环境演变的规律。结果表明，近百年来湿润区湖泊与干旱半干旱区湖泊环境变化虽然存在差异，但总体可分为三个阶段。第一阶段，湿润区网湖为1950s以前、干旱半干旱区博斯腾湖、赛里木湖、乌梁素海为1960s以前，该时期湖泊沉积物中TOC、TN、δ13C、正构烷烃、OCPs、PAHs、重金属富集因子等都较低，且相对稳定，表明湖泊水体营养及初级生产力均较低，受流域人类活动影响较小。第二阶段，1950s~1980s（网湖）、1960s~1990s（博斯腾湖、赛里木湖、乌梁素海），沉积记录OCPs含量明显增大，表明流域农业活动开始较明显的影响湖泊环境。TOC、TN、TP含量增加，反映了湖泊营养水平升高，湖泊生态环境出现变化，其中乌梁素海沉积物有机质δ13C高值以及2C17/(C23+C25)低值表明沉水植物开始大量生长，而博斯腾湖、赛里木湖沉积物中表现为较高的δ13C和2C17/(C23+C25)表明浮游藻类有一定的增加，环境变化存在一定的差异。第三阶段，网湖自1980s以来、博斯腾湖、赛里木湖、乌梁素海自1990s以来，是近200年来人类活动最频繁的时期，湖泊水体营养水平继续快速升高，乌梁素海和博斯腾湖出现较为明显的富营养化现象，藻类植物大量繁殖，网湖环境也出现明显变化，主要体现在HMW PAHs、TOC、TN、TP的高含量和2C17/(C23+C25)的高比值。3. 不同气候区湖泊沉积记录了湖泊环境响应流域不同人类活动作用的区域差异。空间上，东部湿润区网湖沉积物中PAHs含量高，尤其是较高的HMW PAHs含量，表明湿润区湖泊受城市化和工业化的影响明显高于西北干旱半干旱区地区湖泊。另外，网湖和乌梁素海沉积物中高含量的OCPs表明半干旱区的河套地区乌梁素海也受明显农业活动影响。不同区域湖泊环境响应人类活动方式也存在明显差异，沉积物正构烷烃和有机质δ13C记录表明，乌梁素海沉积物正构烷烃中链组分向短链变化，δ13C值也出现同步变化，表明湖泊环境发生变化；赛里木湖沉积物长链正构烷烃占优势，δ13C值变化不明显且较集中，湖泊环境受外源有机质影响较大，浮游藻类和大型水生植物相对含量稳定；博斯腾湖沉积物正构烷烃中链组分为主，有向短链浮游藻类的变化趋势，δ13C值变化较明显。时间变化差异方面，湖泊沉积记录表明，东部湿润区网湖人类活动对湖泊环境明显影响出现在大约1950s，而干旱-半干旱区博斯腾湖、赛里木湖、乌梁素海则大约在1960s。通过综合TOC、TN、TP、δ13C、OCPs、PAHs、重金属、正构烷烃序列等不同沉积环境代用指标序列，结合流域社会经济指标和气候数据，分析了不同气候区湖泊近百年来的环境演变规律及其原因。结果表明，不同气候区湖泊环境变化受自然和人类活动的共同驱动，但不同类型湖泊受所处自然背景条件及人类活动影响强度和方式差异明显，湖泊环境的响应特征存在明显不同，而湖泊沉积较好地记录了此种变化。总体上，不同气候区湖泊在20世纪50、60年代之前以自然作用对湖泊环境的影响为主；20世纪50、60年代之后，湖泊沉积记录和器测资料都显示人类活动对湖泊影响的加强；从上世纪80、90年代开始，随着人类活动方式、强度的变化，湖泊生态环境出现明显转化。近年来，人类活动对湖泊的影响已经大大超过自然作用对湖泊的影响，成为影响湖泊环境的主导因素。 |
| 英文摘要 | Over the last few decades China has undergone rapid industrial, urbanization and population growth. This has resulted in a large discharge of industrial, urban and agricultural pollutants into lakes and, as a consequence, has resulted in environmental problems which differ between lakes in different regions, such as eutrophication and contamination in lakes of humid zone in eastern China, whereas increased salinization and contamination in lakes of arid and semi-arid zone in northwestern China. These problems have significantly hindered regional socio-economic development. Driving factors of natural conditions and human activities vary by region, which resulting in more complicated process and mechanism of lake evolution, subsequently, more difficulties to lake environmental remediation and management. Moreover, limited instrumental records bring greater challenges in good knowledge of regularities of lake evolution and comprehensive understanding of their mechanism. Therefore, it is necessary to extent sequence of lake environmental evolution and to compare characteristics of environmental changes in lakes of different type for analysis the process and regularities of lake evolution and its mechanism. These could provide a scientific basis for environmental management and protection of lakes in different regions.Lake sediments represent a major sink for many natural and anthropogenic constituents and have higher sedimentation rates. Consequently, undisturbed sediments represent natural archives for the evaluation and reconstruct historical environmental changes in aquatic environments. Lake environmental changes and its mechanism in different climate zones was investigated using combination of climatic parameters and multi-proxies, including organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), heavy metals, n-alkanes, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP) and organic carbon isotopic (δ13C). The study was performed in Lake Wanghu in middle Yangtze River of humid zone, Lake Bositeng and Lake Sayram in arid area, and Lake Wuliangsu in semi-arid area. The main results of this research are as follows:1. Environmental significance of substitution indices was clarified by analysis of multi-proxies in sediments and soils of lakes and catchment from different climate zones. OCP and PAH concentrations reflect the different types and intensity of anthropogenic activities. High molecular weight (HMW) PAH mirrors local industrialization and urbanization development, whereas OCPs correlate with agricultural activities. There were significant correlations between OCPs, PAHs and heavy metals, e.g., CuEF, implying intensity of human activities, however, OCP and PAH concentrations can reflect different types of anthropogenic activities. Sedimentary n-alkanes can reflect organic sources. The chain-length distribution mainly ranges from C14 to C33 in soil from different regions, with obvious odd-to-even predominance, showing high TAR and H/L values. n-alkanes in soil samples with woody plants have maximum at C29, and maximum at C31 with grass. Combined with 2C17/(C23+C25), n-alkanes provide a reliable information for describing different vegetation types.2. With high-resolution 210Pb and 137Cs dating and organic-inorganic geochemical methods, regularities in the evolution of lake environment were revealed, and environmental changes of lakes in different climate zones during the last ~100 years was divided into three periods. The first period, Lake Wanghu in humid area was prior to the 1950s, whereas Lake Bositeng, Lake Sayram and Lake Wuliangsu in arid and semi-arid area were prior to the 1960s. PAH concentrations were relatively low, and OCPs were almost undetectable in the sediments, indicating minimal human impact, which also demonstrated by low enrichment factors of heavy metals. Low nutrient (TOC, TN, and TP) concentrations suggested low primary production, i.e. trophic status. At that time, lakes in different climate zones were lower-trophic-state lakes with little anthropogenic impact. The second period, Lake Wanghu was from the 1950s to 1980s, whereas Lake Bositeng, Lake Sayram and Lake Wuliangsu were from the 1960s to 1990s. Relatively higher OCP concentrations were related to the intensification of agricultural activities. Higher TOC, TN and TP values in sediments suggested the trophic state of the lake increased gradually as a consequence of intensive farming practices. Higher δ13C and lower 2C17/(C23+C25) values in Lake Wuliangsu indicated increasing contribution from submerged plants. Higher values of δ13C and 2C17/(C23+C25) in Lake Bositeng and Lake Sayram sediments suggested a rapid growth of algae. Slight change of 2C17/(C23+C25) values in Lake Wanghu reflected macrophytes were still predominant in organic matter. The latest period in the history of Lake Wanghu started in the 1980s, Lake Bositeng, Lake Sayram and Lake Wuliangsu started in the 1990s. This period is marked by rapid industrialization and urbanization, inferred from increases in high molecular weight (HMW) PAH concentrations, and enrichment factors of heavy metals. As a result, the trophic state of the lake continued increasing, as shown by the highest nutrient values. At that time, Lake Bositeng and Lake Wuliangsu became obviously eutrophic, inferred from decrease in TAR values and increase in 2C17/(C23+C25) values.3. Sedimentary multi-proxies recorded regional difference in human-driven lake environmental changes in different climate zones. Higher PAH (especially HMW PAH) concentrations in Lake Wanghu of humid zone indicated industrialization and urbanization activities were more intense than those in arid and semi-arid lakes. Moreover, higher OCP concentrations in Lake Wanghu and Lake Wuliangsu implied intensive agricultural activities in humid and semi-arid zones. Lake environmental changes in response to different types of human activities also have regional difference. The chain length of n-alkanes in Lake Wuliangsu sediments shift from middle to short chain, accompanying changes in δ13C values, suggested obvious environmental changes of Lake Wuliangsu. Higher proportion of long chain n-alkenes in Lake Sayram sediments indicated organic matter contributions dominated by terrestrial plants. The abundance of algea and aquatic macrophytes in Lake Sayram were stable, which was in accordance with slightly changes in δ13C values. Middle chain n-alkanes were predominant in organic matter in Lake Bositeng sediments, showing a shift towards shorter chain components which is probably associated with increasing contribution from algal. Correspondingly, δ13C values varied obviously. Sediment records in temporal variation indicate the onset of significant human impact on Lake Wanghu environment started in the 1950s, whereas started in the 1960s in arid and semi-arid lakes including Lake Bositeng, Lake Sayram and Lake Wuliangsu.Combining multiple indexes including TOC, TN, TP, δ13C, OCPs, PAHs, heavy metals, n-alkanes，together with social-economic index and instrumental data, evolution regularities of environment and their forcing factors in the past century were investigated. It reveals that both nature and human activities affect lake environmental changes. However, lake environmental changes showed different patterns under various natural conditions and anthropogenic activities, which were well recorded in lake sediments. General evolution of lakes before the 1950s or 1960s was mainly controlled by natural conditions, thereafter, anthropogenic impacts started to gradually increase inferred from both lake sediment records and instrumental data. Since the 1980s or 1990s, lake environment changed significantly because of intensive human activities, which play a key role in lake environmental changes in recent years. |
| 中文关键词 | 湖泊沉积 ; 地球化学指标 ; 不同气候区 ; 湖泊环境变化 ; 人类活动 |
| 英文关键词 | lake sediments geochemistry indicators different climate zones lake environmental changes human activities |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院南京地理与湖泊研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287893 |
| 推荐引用方式 GB/T 7714 | 沈贝贝. 不同气候区湖泊地球化学记录的近现代环境演化过程及机理[D]. 中国科学院大学,2017. |
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