Influence of suspended particulate matters on P dynamics and eutrophication in the highly turbid estuary: A case study in Hangzhou Bay, China

Phosphorus (P) is an essential biogenic element in ecosystems; but excessive or insufficient P in coastal waters caused by human activities has led to serious ecological issues. However, the understanding of the dynamic processes of different P forms in high turbidity estuaries/bays, as well as their impact on eutrophication and coastal algal blooms, is still relatively limited. To address this issue, we analyzed P dynamics and their impact on eutrophication in Hangzhou Bay (HZB), which is typical of eutrophic and turbid bay worldwide. The concentration of particulate P (PTP) was 3–5 times higher than that of dissolved inorganic phosphorus (DIP). Seasonal sediment resuspension led to the accumulation of suspended particulate matter (SPM) and PTP with regional variation, both maintaining DIP concentrations above 1 μmol/L within the bay. Furthermore, 3000 tons of bioavailable P were retained in the fine-grained SPM, with the potential for outward transport, fueling subsequent harmful algal blooms. A comparative analysis of global coastal waters highlighted that different turbidity levels significantly affect P cycling. Therefore, understanding the relationship between SPM and P in highly turbid waters is crucial for effective management of eutrophication. Note: Stock is P storage in seawater; the pie charts with yellow circles represent the total particulate P (PTP) composition in the dry season, whereas those without yellow circles represent the PTP composition in the wet season, with the pie size representing the PTP content. [Display omitted] •P distribution and partition in turbid Hangzhou Bay were analyzed as a case study.•Particulate P concentration 3–5 times higher than DIP, buffering DIP >1 μmol/L.•Changes in P particle-reactivity increase HABs risk beyond turbidity front.•P behavior in varied turbid waters globally was compared for universal insights.