Environmental evolution of the Moguhu Wetland of Shihezi City in Xinjiang since 4800 cal.aBP

Wetland is a transitional environment between terrestrial and aquatic systems.It is a key component of earth ecosystem and performs a great deal of vital ecological functions, such as purifying water, maintaining regional ecological balance, mitigating the unfavorable impacts of global climate change, protecting environments for human survival, and preventing flooding by holding water.Holocene climate events on different time scales have a profound impact on the distribution of wetland vegetation in the arid zone.A lot of wetlands in Xinjiang have degenerated gradually or even disappeared.Therefore, it is necessary to strengthen the research on vegetation and environmental evolution of wetlands, and to evaluate the natural and anthropogenic forces shaping wetland vegetation.The Moguhu Wetland is situated between the southern margin of the Junggar basin and the middle reaches of the Manas river valley on the northern slope of Tianshan Mountain.High resolution record of fossil pollen data from a 120 cm sediment core collected in Moguhu Wetland (44°25′39.3″N, 85°54′356″E) is applied to extract the information of climate and environment change in order to reconstruct the paleoenvironment and paleovegetation of Moguhu Wetland since 5000 aBP.The pollen data is calibrated with carbon-14 dating.Results show that in the period between 4770 and 3700 cal.aBP, Picea pollen were relatively rare indicating a dry climate condition.During the period from 3700 to 3120 cal.aBP, however, pollen Picea increased obviously and AP/NAP (arboreal/nonarboreal pollen) ratio was higher than that in previous period.The climate became moist.The Zone Ⅲ is characterized by a noticeable increase in the percentages of Picea (38.87%) and the maximum values of aquatic plants, suggesting a wetter climate occurred for a hundred years around 3120~3020 cal.aBP.At about 3020~2340 cal.aBP, the A/C (Artemisia/Chenopodiaceae) value exhibits an abrupt increase to 0.4 and Picea percentage was also high.From 2340~1340 cal.aBP, the climate became dry again, as indicated by the significantly reduced Picea pollen spectra and the lowest A/C values.Therefore, between 4800 and 1340 cal.aBP, a wetland environment was present in Moguhu area, and Thelypteris palustris grew in the local environment.The study area had experienced a climate transition from dry to humid and then back to dry during that period.From 4770 to 3700 cal.aBP, the climate was dry.Then it became humid.After more than 1000 years of wet climate conditions, it became dry again at about 2340 cal.aBP.Moguhu fossil pollen data suggested a typical freshwater wetland ecosystem, as accompanied by Phragmites, Thelypteris palustris and Sparganium since 5000 cal.aBP.Modern vegetation investigations in 2010-2016 showed that Betula microphylla is on the edge of extinction.Thelypteris palustris species are disappearing at an extremely rapid rate as a consequence of global warming and increasing human intervention such as overuse, reclamation, city construction.Therefore, in order to protect the earth's ecological environment and reduce the destruction of natural wetlands, it is necessary for us to pay more attention to strengthen wetland conservation and ecological construction in the Xinjiang region.