Environmental changes and human activities over the last about 220 years revealed by the pollen record of Lake Lianhuan in Heilongjiang Province

Abstract

通过²¹⁰Pb测年建立年代标尺，利用黑龙江省连环湖阿木塔泡高分辨率的孢粉记录，探讨了研究区约220年的环境变化与人类活动.研究表明，1790—1820 AD期间，植被类型可能是以禾本科为主的草甸草原植被，沙地类型以固定沙地为主，气候相对较凉湿或环境几乎不受人类活动的破坏，湖泊营养较丰富.1820—1930 AD期间，草甸草原植被中禾本科和菊科植物比例下降，藜科和蒿属植物比例增加，固定沙地减少、半固定沙地逐渐增加，气候逐渐变干或可能伴随人类破坏环境的活动增强，湿地面积减少.1930—1980 AD期间，针叶乔木松树比例有所增加，草甸草原植被中菊科植物比例是220年来最高的，藜科植物也略有增加，而禾本科和蒿属植物比例下降，推测此阶段固定沙地持续减少，半固定沙地扩张到220年以来面积最大，指示气候进一步变干且伴随着人类活动对自然环境的破坏强度增加，湖泊湿地面积进一步减少.1980—2000 AD期间，草原植被中藜科植物的比例是220年以来最高的，流动沙地面积明显增加，湖泊湿地面积锐减，结合气象数据，得出此期的植被变化是由人类大范围围湖造田以及湿地水田化等活动导致的.2000—2010 AD期间，研究区周围以桦木/鹅耳枥属和栎属为主的落叶阔叶乔木比例增加，草原植被中藜科和菊科植物比例是220年以来最低的，揭示流动沙地和半固定沙地面积明显减少，结合气象数据，认为此期孢粉组合揭示的植被变化主要受人类退耕还草还林，种植桦木/鹅耳枥属、榆属等阔叶植物以及在八支干渠建闸引水至连环湖等活动的影响.;Based on the chronology established through the ²¹⁰Pb dating and the high-resolution pollen record of Amutapao in Lake Lianhuan, Heilongjiang Province, the environmental changes and human activities over the last about 220 years in the study area were discussed. The results showed that during 1790-1820 AD, the vegetation type was probably meadow steppe dominated by Poaceae, and the sandy type was mainly fixed sand. The climate was relatively cool and wet or the environment was hardly damaged by human activities, and lake was of relatively high nutrition. During 1820-1930 AD, the proportion of Poaceae and Compositae plants in the meadow steppe decreased, while that of Chenopodiaceae and Artemisia plants increased. The area of the fixed sand decreased, and the area of the semi-fixed sand gradually increased. The climate gradually became dry or it may be accompanied by the increased human activities, and the wetland area decreased. During 1930-1980 AD, the proportion of coniferous tree Pinus increased, and the proportion of Compositae plants in the meadow steppe was the highest in the past 220 years, and the proportion of Chenopodiaceae plants also increased slightly, while the proportion of Poaceae and Artemisia plants decreased. It is speculated that the fixed sand continued to shrink during this period, and the semi-fixed sand expanded to the largest area for the last about 220 years. It indicates that the climate became further dry and with the increased human activities, and the area of the wetland further decreased. During 1980-2000 AD, the proportion of the Chenopodiaceae plants in the steppe was the highest for the last about 220 years, the area of the mobile sand increased significantly, and the area of the wetland decreased sharply. Combined with the meteorological data, it was concluded that the vegetation changes in this period were caused by human activities such as large-scale lake reclamation and wetland paddy field. During 2000-2010 AD, the proportion of deciduous broad-leaved trees dominated by Betula/Carpinus and Quercus around the study area, and the proportion of Chenopodiaceae and Compositae plants in the steppe was the lowest in the last about 220 years, revealing a significant decrease in the areas of mobile sand and semi-fixed sand. Combined with the meteorological data, it is considered that the vegetation changes during this period revealed by the pollen assemblage were mainly influenced by humans returning farmland to grassland and forest, planting broad-leaved trees such as Betula/Carpinus and Ulmus et al., and building sluices in eight main canals to divert water to Lake Lianhuan.