The Influence Of Summer Hypoxia On Sedimentary Phosphorus Biogeochemistry In A Coastal Scallop Farming Area, North Yellow Sea

In situ field investigations coupled with laboratory incubations were employed to explore the surface sedimentary phosphorus (P) cycle in a mariculture area adjacent to the Yangma Island suffering from summer hypoxia in the North Yellow Sea. Five forms of P were fractionated, namely exchangeable P (Ex-P), iron-bound P (Fe-P), authigenic apatite (Ca-P), detrital P (De-P) and organic P (OP). Total P (TP) varied from 13.42 to 23.88 mu mol g(-1) with the main form of inorganic P (IP). The benthic phosphate (DIP) fluxes were calculated based on incubation experiments. The results show that the sediment was an important source of P in summer with similar to 39% of the bioavailable P (Bio-P) recycled back into the water column. However, the sediment acted a sink of P in autumn. The benthic DIP fluxes were mainly controlled by the remobilizing of Fe-P, Ex-P and OP under contrasting redox conditions. In August (hypoxia season), similar to 0.92 mu mol g(-1) of Fe-P and similar to 0.52 mu mol g(-1) of OP could be transformed to DIP and released into water, while similar to 0.36 mu mol g(-1) of DIP was adsorbed to clay minerals. In November (non-hypoxia season), however, similar to 0.54 mu mol g(-1) of OP was converted into DIP, while similar to 0.55 mu mol g(-1) and similar to 0.28 mu mol g(-1) of DIP was adsorbed to clay minerals and bind to iron oxides. Furthermore, scallop farming activities also affected the P mobilization through biological deposition and reduced hydrodynamic conditions. The burial fluxes of P varied from 11.67 to 20.78 mu mol cm(-2) yr(-1) and its burial efficiency was 84.7-100%, which was consistent with that in most of the marginal seas worldwide. This study reveals that hypoxia and scallop farming activities can significantly promote sedimentary P mobility, thereby causing high benthic DIP flux in coastal waters. (C) 2020 Elsevier B.V. All rights reserved.