中文摘要：

通过对广东省湛江市湖光岩玛珥湖晚全新世沉积物中叶蜡烷烃（n-C29，n-C31，n-C33）及其碳同位素（δ13C）进行分析，探讨该湖区约3.5 ka BP以来的植被变化历史，重点讨论了人类活动对该区域植被变化可能带来的影响。叶蜡烷烃δ13C在1.7 ka BP以前偏轻，例如长链烷烃碳同位素在1.78 ka BP为-33.27‰，表明湖区C3植物占绝对优势，表现为典型的C3型生态系统；在1.7 ka BP之后碳同位素明显快速偏重，在1.63 ka BP为-28.26‰，指示了C4植物出现和C4比例上升的过程。C4植物的出现通常指示气候的干旱化，但是烷烃Paq和ACL指数（平均链长）则显示湖区气候可能在1.7 ka BP后变湿润。通过与研究区甘蔗的同位素和ACL指数的比较分析，推测这一矛盾现象可能与湖区开始有一定规模的甘蔗种植活动有关。

英文摘要：

In this study, late Holocene sedimentary records of leaf wax n-alkanes and theirδ13 C from Huguangyan Maar Lake （H.M.L） in Zhanjiang, Guangdong Province, were used to reconstruct the vegetation variations as well as human activities in the lake catchment over the past 3500 years. Carbon isotopic compositions （δ13C） of leaf wax n-alkanes （n-C29, n-C31 and n-C33） were predominantly lighter than-32‰before 1.7 ka BP, suggesting that a typically pure C3 ecosystem might exist before 1.7 ka BP; for example, carbon isotope average value of long-chain n-alkanes was -33.27 ‰ in 1.78 ka BP; after that δ13C values increased rapidly and significantly, carbon isotope value was-28.26‰in 1.63 ka BP, indicating the emergence and increase of C4 plants. C4 plants usually indicate an arid climate, however, the n-alkanes indices that both increased Paq and reduced ACL indicate a humid climate after 1.7 ka BP. This contradiction can be well explained by invoking anthropogenic sugarcane plantation in the catchment at 1.7 ka BP. Furthermore, when it comes to the isotope change of samples, we find that both C27/C29 andΔδ13 Ct had notable positive correlation with the increasing cultivation time, showing that the emergence of C4 plants might be caused by constant vegetation transformation from human. Thus, we believe that human activities characterized by sugarcane plantation occurred after 1.7 ka BP. This study can be referential for discriminating the impacts of natural and human factors on environment and vegetation changes during the past thousands of years.