Tianjin Wetland Sediment Organic Carbon And Nitrogen And The Isotope Composition Characteristics And Environmental Significance

As an essential part of the wetland system, wetland sediment is an important carrier of climate change, which records much of the local biological, physical and chemical information, such as relative humidity, salinity, temperature, precipitation, biomass, bio-diversity and pollution extent. Hydrological characteristics, vegetation situation, ecological pollution of wetland and even the reconstruction of paleoenvironment can be illustrated by analyzing these indices. Due to the intense attention paid by the whole society to global change, in recent decades, resulting wetland sediment relative research grows faster, aiming to reconstruct the regional paleoenvironment and to predict the future trend of climate change.Tianjin is located beside the Bohai Sea and has lots of rivers and wetlands within the city. With the fast development and the establishment of economical center of North China, environmental issues of Tianjin City have emerged. This January, Binhai New Area launched the Wetland Protection and Renovation Program, hoping to cover more than20%of this area with wetland. As a result, more professional researches about wetland in Tianjin are needed to support this program. However, there’s few research pointing to the reconstruction of paleoenvironment and paleoclimate applying the methods of stable carbon and nitrogen isotopes.After a serious work of research, sampling and experiment, a set of data of TOC, TN, T/N ratio,δ13C,δ15N and the grain size of wetland sediment, in Dahuangbu, Qilihai and Beidagang has-showed here to rebuild the paleo-process of the vegetation and sediment successions of this area, and provide theoretical support to wetland renovation program.The data of Dahuangbu shows that the sediment organic matter is mostly sourced to terrestrial C3-plant and goes through a process of inland-to-water environment. Correspondently, the paleoclimate is reconstructed to cold/wet-frequent floods-deteriorated climate-turning warm-warm/dry. The sediment organic matter of Qilihai is mostly resourced to C3-plants and mainly is from terrestrial and aquatic tracheophyte. The routine of δ13C follows the four stages of increasing-stable-increasing-stable, while the routine of δ15N is not so obvious. Correspondingly, the paleoclimate is reconstructed to cold/wet-sub cold/wet-turning warm-warm/dry.The paleo-vegetation of Beidagang is dominated by C3-plant, and turning from terrestrial plant dominated to water algae dominated. The changes of δ13C are more regular, while δ15N’s more complicated. Correspondingly, the paleoclimate is reconstructed to cold/wet-deteriorated climate-turning warm-warm/dry.According to the estimated paleoenvironment from all of three profiles above, the paleoenvironmental characteristics of Tianjin in Middle and Late Holocene (covered by the sampled cores) can be described:for the overall trend, Tianjin has went through the climate changes from cold/wet to warm/dry during the Middle and Late Holocene; there might be a short-spanned environment deteriorating event which might be coincided with a environment deteriorating event4000a B.P. during the Middle Holocene.