Terrestrial input and nutrient change reflected by sediment records of the Changjiang River Estuary in recent 80 years

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 SiO 3 2− 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 unbalance in nutrient structure. Multi-nutrient proxies in sediment can reflect the natural environmental changes as well as influence of human activities.