Terrestrial input and nutrient change reflected by sediment records of the Changjiang River Estuary in recent 80 years
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摘要: 近几十年,长江口及邻近海域富营养化,有害赤潮藻华以及缺氧等环境问题凸显.应用沉积物生源要素指标研究古环境可以重建长江口的环境变化历史.从长江口及邻近海域采集了2个柱状样,并分析了其TOC、N、BSi、TP和P形态的特征.通过沉积物营养盐指标记录,长江口及毗邻海域的环境变化经历了三个阶段: 1950s末期,随着农业的发展和化肥的过度使用,长江口水体中的营养盐浓度迅速升高;1960s至1980s,长江口营养盐浓度保持较高水平,初级生产力不断增大,而伴随1970s以来长江硅酸盐浓度和通量的降低,硅藻生物量和比例开始减少;从1990s至今,由于流域水库和跨海大桥等设施的建造,长江径流量和河口水动力条件有所减弱,可能加剧了营养盐结构和浮游植物群落的失衡.研究表明,沉积物的多种营养盐指标能够反映自然环境和人类活动的影响.Abstract: A variety of environmental problems have been observed in the Changjiang River Estuary and adjacent coastal area, including eutrophication, harmful algal blooms (HABs), and hypoxia in recent decades. Application of sedimentary biogenic element indicators on the study of paleoenvironment can reconstruct environmental evolution history of waters. Two 210Pb-dated cores were collected from the Changjiang River Estuary (S3) and adjacent coastal area (Z13), and total organic carbon (TOC), total nitrogen (TN), biogenic silicon (BSi), total phosphorus (TP) and phosphorus (P) species were analyzed. Three stages of environmental changes are deduced by the nutrient sedimentary records. First, nutrient concentration increased rapidly since the 1950s, which attributed to agriculture development and overused chemical fertilizers. Second, nutrient concentration kept high and primary production began to promote during the 1960s to 1980s, while diatom abundance and proportion began to decline since the 1970s, accompanied by reduced SiO32- concentration and flux from the river. Third, due to several dams and bridges constructed, river runoff and coastal hydrodynamic conditions reduced to a certain extent since the 1990s, which aggravated the unbal-ance in nutrient structure. Multi-nutrient proxies in sediment can reflect the natural environm-ental changes as well as influence of human activities.
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Key words:
- biogenic elements /
- phosphorus species /
- sediment cores /
- Changjiang River Estuary
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