中国科学院海洋研究所机构知识库

Human activities and natural processes are primary factors influencing regional and global change. However, there are great regional differences in when and how human activities as a geological force began to affect the Earth's surface system significantly. We present a comprehensive reconstruction of the vegetation, chemical weathering, and heavy metal emissions in the Pearl River catchment since 7.0 ka BP, using a continuous record of black carbon, clay minerals, and major and trace element concentrations of sediments in Core ZK001 taken from the northwestern South China Sea. By comprehensively comparing the records of climate change and human activities in the East Asian monsoon region, the history of the interaction between the natural environment and human activities in South China in the Middle and Late Holocene is reconstructed. Our study makes up for the scarcity and discontinuity of human activity records in South China.

The provenance analysis showed that the clay-sized fraction in the study area mainly derived from the Pearl River, and the nearby Hainan Island Rivers might have contributed a small amount. The overall provenance has not changed significantly during the last 7.0 ka BP. Therefore, the carbon isotopic composition of black carbon was used to reconstruct the evolutionary history of vegetation composition in South China. The results showed that the biofuels were dominated by C₃ plants during 7.0-2.9 ka BP, which was consistent with the C₃-dominated vegetation composition of the primary forest, and was in accord with the high temperature and heavy precipitation conditions in South China. Climate change was the main factor controlling vegetation evolution and fire activities at this stage. During 2.9‒2.0 ka BP, the black carbon δ¹³C produced by combustion showed a rapid negative shift, no longer coupled with climate change, indicating large-scale human deforestation and burning. Since 2.0 ka BP, black carbon δ¹³C showed a generally positive trend, indicating the increased proportion of C₄ plants in burning. This trend decoupled from the weakening monsoon, indicating that the impact of human activities on regional vegetation and fire activities had exceeded the control of climate change. The priority growth of C₄ grasses after deforestation and the large-scale planting of C₄ plants such as sugarcane might have led to the increase of C₄ proportion as fuel in South China.

The evolution history of chemical weathering intensity in the source area was reconstructed based on the weathering indexes CIA, K/Al, and kaolinite/illite ratios. The results showed that during the period of 7.0‒2.9 ka BP, the chemical weathering in South China showed a decreasing trend in general, which was consistent with the weakened East Asian monsoon, indicating that the decrease in temperature and precipitation were the main reasons for the weakening of chemical weathering intensity. Since 2.9 ka BP, the chemical weathering intensity in the Pearl River Basin increased abnormally, which was contrary to the weakening trend of the East Asian monsoon, but was consistent with the enhancement of human activities, indicating that the influence of human activities had gradually exceeded natural control, and became the dominant factor of chemical weathering intensity. We infer that the intensified soil disturbance and erosion caused by agricultural development are important reasons for the enhancement of chemical weathering.

Based on the heavy metal enrichment factor (EF), we distinguished heavy metals between natural and anthropogenic sources and reconstructed the history of heavy metal emissions caused by human activities. During 7.0‒2.0 ka BP, the heavy metal contents in the study area were close to the background value, mainly derived from the natural weathering of source rocks. Since 2.0 ka BP, anthropogenic heavy metal emissions have been increasing, which might be related to mining and smelting activities since the Bronze Age.

Based on the high-resolution sediment records, combined with archaeological and historical studies, we propose that human impacts in South China can be divided into three stages: a hunting-gathering age (7.0‒2.9 ka BP), a transitional period (2.9‒2.0 ka BP) and an intensive farming age (since 2.0 ka BP). Climate controlled both the vegetation and chemical weathering intensity before 2.9 ka BP, after which forest clearance by human-induced fire became significant. Along with population growth and technological progress, enhanced human activities including deforestation, cultivation, and metallurgical activities, gradually superseded natural processes and profoundly impacted the environment in South China, especially after 2.0 ka BP.

第1章 绪论 1

1.1 研究现状及问题 1

1.1.1 人类活动影响研究的起源及争议 1

1.1.2 自然环境与人类活动相互作用研究现状 3

1.1.3 存在问题 9

1.2 研究内容及目的 10

1.2.1 论文工作内容 10

1.2.2 拟解决的问题 10

第2章 区域概况 12

2.1 地理位置和地貌特征 12

2.2 水文特征 12

2.3 气候与植被特征 13

2.4 区域自然资源 13

第3章 研究材料与研究方法 14

3.1 研究材料 14

3.2 研究方法 16

3.2.1 年代框架 16

3.2.2 沉积物干容重与堆积速率 17

3.2.3 粘土矿物提取与分析 17

3.2.4 Sr-Nd同位素分析 19

3.2.5 常微量元素分析 20

3.2.6 黑碳含量及碳同位素分析 20

3.2.7 粒度分析 22

第4章 沉积物物源 23

4.1 粘土矿物及Sr-Nd同位素组成 23

4.1.1 粘土矿物组成 23

4.1.2 粘土粒级硅酸盐组分Sr-Nd同位素组成 24

4.2 物源分析 25

4.2.1 粘土矿物组成约束物源 25

4.2.2 Sr-Nd同位素约束物源 28

4.2.3 沉积物搬运机制约束物源 30

第5章 7.0 ka BP以来华南植被组成、火历史及其控制机制 31

5.1 黑碳含量、通量及其碳同位素组成特征 31

5.2 黑碳物源分析 32

5.3 黑碳含量、通量及其碳同位素组成的指示意义 34

5.4 7.0 ka BP以来华南植被组成和火历史及其控制机制 36

第6章 7.0 ka BP以来华南化学风化历史及其驱动机制 46

6.1 化学风化的影响因素 46

6.2 化学风化指标及其指示意义 46

6.3 7.0 ka BP以来华南化学风化历史及其驱动机制 47

第7章 7.0 ka BP以来华南重金属排放历史及其控制机制 55

7.1 重金属富集因子及其指示意义 55

7.2 7.0 ka BP以来华南重金属排放历史及其控制机制 56

第8章 7.0 ka BP以来华南自然环境与人类活动相互作用历史 60

第9章 结论 64

参考文献 66

致 谢 97

作者简历及攻读学位期间发表的学术论文与其他相关学术成果 99