Phosphorus speciation and sedimentary phosphorus release in an urban bay (Dachan Bay, China) impacted by multiple anthropogenic perturbations

Sedimentary phosphorus (P) release and retention are important in controlling P dynamics in coastal waters. Here, two sediment cores were analysed to understand the P speciation and sedimentary P release characteristics in Dachan Bay, Shenzhen, where was highly influenced by human activity. Total phosphorus (TP) concentrations, 52.3 to 1119 μg g^-1, fluctuated greatly with depth. Four P binding forms were fractionated: iron-bound P (FeP), authigenic apatite (CaP), detrital P (De-P), and organic P (OP) with the following order of concentration: Fe-P > OP > De-P > Ca-P. The P pollution index (PPI) revealed the contamination of sediment with P in recent years. Additionally, the potentially mobile P pools and long-term P release in the sediments were estimated, and the results indicated that, sediment was an important potentially mobile P pools in the water column, especially in nearshore areas, which required the attention of management departments.

Effects of sediment oxidation on phosphorus transformation in three large shallow eutrophic lakes in China

Oxidation of surface sediments is an important means for altering phosphorus (P) exchanges across sediment-water interface (SWI) in shallow lakes. In this study, the potential and composition of regenerated oxidation capacity (OC) of surface sediments were evaluated in three large shallow lakes (Tai Lake, Chao Lake, and Dianchi Lake) in China; the transformation of sedimentary P was quantified through P fractionation scheme. The composition of the regenerated OC differed among these three lakes, with Fe(III) and SO₄^2- dominant in Dianchi Lake, Mn(IV) and Fe(III) in Chao Lake and Tai Lake. Oxidation of sediments enhanced the transformation of sedimentary P and altered P exchanges across the SWI. In Chao Lake, the HCl-P was transformed to BD-P; in Tai Lake, the NaOH-P was involved too, and transformed to BD-P; whereas in Dianchi Lake, an increase in NH₄Cl-P was also observed except for the transformation from HCl-P to BD-P. The sediment-to-water flux of P was enhanced with 0.17 mg/g DW in Dianchi Lake and 0.08 mg/g DW in Chao Lake, while a contrary water-to-sediment flux of P was observed in Tai Lake, reaching 0.01 mg/g DW. This study advances our knowledge on the impacts of sediment oxidation on P cycles in lakes, which will be beneficial to eutrophication control.

Bulk sedimentary phosphorus in relation to organic carbon, sediment textural properties and hydrodynamics in the northern Beibu Gulf, South China Sea

Bulk sedimentary phosphorus (P) is studied to evaluate its source, distribution, preservation and enrichment in relation with organic carbon (OC), sediment textures and moisture contents in the northern Beibu Gulf. Approximately 80% of surface sediments in the investigated sites were composed of coarse sandy texture (>63 μm). Total P (TP), inorganic P (IP) and organic P (OP) contents were lower to medium range compared to the levels reported for other marginal seas. Sedimentary OC and P were derived from mixed sources, with high terrestrial influence in the coastal areas (molar OC/OP ratios >250:1). The distribution of P corroborated with the variation tendency of fine-grained sediments, moisture contents and OC. Both IP and OP may significantly influence the trophic state of seawater if released from surface sediments. Influenced by hydrodynamics, frequent resuspension and high abundance of sand, TP is less preserved, and shows low to moderate enrichment in surface sediments.