Geochemical forms and seasonal variations of phosphorus in surface sediments of the East China Sea shelf

- P biogeochemistry in sediments of the East China Sea shelf was found to be dynamic.
- Seasonal variations in P geochemical forms between spring and autumn were obvious.
- Primary production and summer hypoxia may result in changes of Ads-P, Fe-P and OP.
- Changes in Au-P and De-P may relate to the transformation of P and hydrodynamics.
- Higher burial fluxes of Bio-P and TP were found in spring and autumn, respectively.

Geochemical characteristics of phosphorus (P) in the surface sediments of the East China Sea shelf (ECSS) were studied in spring and autumn, 2014. Distributions, seasonal variations, transformations and their influencing factors were discussed. Besides, burial fluxes of P in different seasons were also calculated. Five operationally defined forms of P, namely exchangeable or loosely sorbed P (Ads-P), iron-bound P (Fe-P), authigenic P (Au-P), detrital apatite plus other inorganic P (De-P) and organic P (OP), were obtained using a sequential extraction procedure. Generally, the concentrations of Ads-P, Fe-P, Au-P and OP decreased seaward and the concentrations of De-P increased seaward in both seasons. In spring, the average concentrations of Ads-P, Fe-P, Au-P, De-P and OP were 13.8 ± 5.0, 21.9 ± 7.6, 148.5 ± 44.5, 153.1 ± 55.8 and 91.7 ± 21.5 μg g− 1, respectively. The corresponding concentrations in autumn were 11.4 ± 4.3, 20.0 ± 10.9, 170.4 ± 53.6, 225.6 ± 101.7 and 77.1 ± 33.9 μg g− 1, respectively. The average percentages of P fractions in total P (TP) in spring and autumn were both in the order: De-P > Au-P > OP > Fe-P > Ads-P. The average concentrations of Bio-available P (Bio-P) were 127.4 ± 31.4 μg g− 1 in spring and 108.5 ± 47.2 μg g− 1 in autumn, accounting for 29.8% ± 7.3% and 21.5% ± 8.2% of corresponding TP, respectively. Seasonal variations of the primary production, hydrodynamic conditions, hypoxia and other environmental conditions were responsible for the seasonal variations of different phosphorus forms. The calculation of burial fluxes reflected that, in most parts of the studied area, TP had relative high burial fluxes in autumn, while Bio-P had relatively high burial fluxes in spring. The burial fluxes of other phosphorus forms also showed different seasonal variations in different parts of the studied area.