Sediment Records On Environment Changes And Human Activities Since Holocene In Huanhe Valley, Henan Province, China

Central Plains in the Yellow River form a major heartland of early civilizations, providing an ideal laboratory for the study of complex and reflexive relations between human societies and their environments from a long-term perspective.Huanhe valley was the seat for two Shang capitals.In this region,agriculture production had began as early as the end of Pleistocene and early Holocene,urban society had began during the Bronze Age,and there are an enormous array of archaeological,textual,and ecological data,which are helpful to research the relationship between human and environment.Thus,Huanhe valley is the perfect region to research the relationship between human and environment in early history and the Bronze Age.The major objective of the research is to select 2 natural sediment profiles formed in Holocene(Wangjiedian profile and Zhangjiadian profile),and get high resolution pollen data and charcoal content to reconstruct the environment change,find out the spoor of human activity;investigate the spatial and temporal configuration of land use in early history and Shang period and probe into the character of nature and dynamics of long-term human-environmental relations.The bottom ages of gray-black clay layer of Wangjiadian profile and Zhangjiadian profile are both about 10000 cal a B.P.,which indicate that the climate was warm,the precipitation was high,and vegetation was exuberance and soil developed in Huanhe valley after 10000 cal a B.P.The bottom age of cover layer upon the clay layer is about 1800 years later than the top age of clay layer,which document the top of gray-black clay layer was a long-term and steady palaeo-physiognomy surface.Palynology analysis of Wangjiedian profile and Zhangjiadian profile show:from 12000 to 3400 cal.a B.P.,the paleo-vegetation was very exuberance and composed of different vegetation types in Huanhe valley,such as warm deciduous broad-leaved forest dominated by Pinus,Quercus,Betula,Juglans,Tilia,Ailanthus,Ulmus,Cotinus,Carpinus,etc.,including semi-tropical evergreen tree types:evergreen Quercus,Fagus,Carya,etc.in higher physiognomy area;meadow dominated by Poaceae,Artemisia,Chenopodiaceae,Compositae, etc.under the forest and in lower physiognomy area.Human planted Poaceae pollen appear firstly in the period of 12000-10000 cal.a B.P.in this 2 profiles,which indicate primordial agriculture appeared since the early Holocene.After 3400 cal.a B.P.,Arbors pollen decrease sharply,Selaginella sinensis spore and herbs pollen percentages increase obviously,especially Chenopodiaceae,Poaceae(including planted Poaceae pollen) and Polygonaceae.The reason for the phenomenon is it just at the flourishing time of Yin culture,the population of Shang period had became great,seriously deforestation,agriculture assart and hunt were done by ancient people for the construction of the town and daily life needs,the paleo-vegetation condition was influence observably:the plain area was used as agriculture land cultivating Poaceae crop on a large scale,covered by Poaceae,Chenopodiaceae,Artemisia,Compositae, Urtica,Polygonum,etc.around agriculture land.We discover from pollen assemblage of Wangjiadian profile that between 11500-10000 cal.a B.P.,the vegetation here may have experienced some fluctuations.Trees started to increase before 11500 cal.a B.P.,but then dropped at about 11500 cal.a B.P.they increased again at 10,000 cal.a B.P.,herb vegetation has increased with in the period including Poaceae, Chenopodiaceae,Artemisia,Compositae,etc.,and there was a small-scale trees increase process in the period.The time periods coincide with the European Younger Dryas oscillation. From 10000 to 8200 cal.a B.P.,trees kept an increase trend with semi-tropical evergreen tree types appear,which document the warming climate with precipitation increasing after the Younger Dryas event.From 8200 to 3400 cal.a B.P.,percentage of arbor vegetation pollen achieve maximum with semi-tropical evergreen trees pollen taxa appear frequently and percentage of herb vegetation pollen decreasing,which indicate the climate of Huanhe valley enter the Megathermal Period with warm temperature and high precipitation.There is abundance Concentricystes be counted from Wangjiadian profile in the period of 10270-3400 cal.a B.P.,which indicate that there was swamp environment in WangJiadian region in this period.After 3400 cal.a B.P.,Concentricystes content and arbors pollen percentage decrease obviously with Selaginella sinensis spore content increasing obviously, which document that the swamp environment disappeared and wash sediment deposited.Charcoal analysis of Wangjiedian profile show:from 12000 to 8200 cal.a B.P.,charcoal content is low,reflecting weak human activity;8200-3400 cal a B.P.,when was the period of Yangshao culture,Longshan culture and early Shang culture,the maximum of charcoal content shows stronger human activity;charcoal content after 3400 cal a B.P.is lower than the anterior period because of the disadvantage of erosion after deforestation to charcoal sediment,but it has an increasing trend,reflecting deforestation activity and agriculture after capital constructed.Charcoal analysis of Zhangjiedian profile show:within period of 12100-3400 cal a B.P.,charcoal content is lower with lesser human activity and is higher after 3400 cal a B.P.because of stronger deforestation and agriculture activities.There is corresponding relationship between the charcoal content and human impact.Along with human impact enhancing,the charcoal content show an approximately increasing trend. Difference of sediment type influence the charcoal content obviously,fluvial wash activity is disadvantage to charcoal sediment,so the charcoal content of fluvial sediment is lower,the swamp environment is advantaged to charcoal sediment,to which need to pay more attention.