A 30-year record of sedimentary phosphorus species in a coastal salt marsh southwest of Hangzhou Bay, China

Abstract In this study, two sediment cores (C1 and C2) were collected from the Andong salt marsh southwest of Hangzhou Bay and analysed to determine their different sedimentary phosphorus (P) forms. The changes in the sedimentary P forms over the past 30 years and the implication of these changes on environmental risks were determined. The low mean total P (TP) contents along C1 (30.42 mg/kg) and C2 (68.60 mg/kg) indicate no P pollution in the Andong salt marsh. The sedimentary TP and all P forms decreased towards the present due to a reduction in particle size and an overall decrease in nutrient input. The sedimentary P contents were also affected by other factors, such as typhoons, bridge construction and aquaculture activities that facilitated erosion and increased P input, whereas drought caused a reduction in sedimentary P. Organic P (OP) represented more than half of the TP, and NaOH-P (P bound to Fe and Al oxides and hydroxides) represented more than half of the inorganic P (IP), indicating an overall high level of bioavailable P. Thus, the sediments in the Andong salt marsh could be releasing P during organic matter decomposition and under anoxic conditions.