Sedimentary records of eutrophication in the Changjiang Estuary upwelling area over last 100 a

The upwelling area in the Changjiang Estuary was selected to collect the core, where the red tide occurred frequently and hypoxic existed. The total organic carbon (TOC), total nitrogen (TN), biogenic silica (BSi) and stable organic carbon isotopic ratios(δ¹³ C_org) were determined on the 210Pb-dated sediment core. The concentrations of TOC, TN, BSi as well as their sedimentation fluxes have increased to some extent since the 1970s. TOC and TN fluxes increased about 45%, 36% respectively. The average δ¹³ C_org value in the core was -23.67×10^-3 which remained nearly constant before the 20 century. The δ¹³ C_org values increased after the 1900s, two marked increases were observed from the 1950s and the 1970s. A simple δ¹³ C_org model was used to estimate the contribution of terrigenous and marine organic matter inputs for the sediment, which indicated the increase in accumulation since the 1970s has been almost exclusively marine. The increasing of marine organic matter accumulation (TOC, TN and BSi) was corresponding with the increasing of fertilizer consumption and the NO₃-N budgets from the Changjiang River. The riverine runoff of fertilizers and nutrients stimulated the algae blooming. Enhanced primary production resulted in an enrichment of organic matter in the sediment. These data support the hypothesis that anthropogenic nutrient loading has been a significant factor on the eutrophication in the Changjiang Estuary.