The Distribution Of Phosphorus Forms And Affecting Factors In Sediments Of The Yellow Sea And East China Sea

The Yellow Sea (YS) and the East China Sea (ECS) are important marginal seasof northwest Pacific, marine primary productivity and various environmentalparameters are significantly affected by the discharge of the Changjiang River and theYellow River, industrial and agricultural pollutants produced by human activitiesthrough runoff flows, as well as the processes of urbanization and the Three Gorgesand other major hydraulic engineerings. Understanding the biogeochemical cycling ofthe biogenic elements under the impacts of the natural process and human activitiescan provide the scientific basis for marine environmental protection issues andsustainable use of marine resources.In this paper, sediment samples and pore water samples were collected inMarch-Junein2011and October2012in the YS and the ECS. Various phosphorusforms, organic carbon and total nitrogen content in sediments, nutrients, dissolved Feand Mn in pore waters were determined to reveal the biogeochemical processes ofphosphorus. The main conclusions are as follows:(1) Among the different forms of P in surface sediments of the Yellow and East ChinaSeas, the concentrations of Exchangeable P, Fe-bound P, Authigenic Ca-P,Detrital-P and Organic P were0.20-0.89μmol/g,0.37-2.86μmol/g,0.61-3.07μmol/g,6.39-13.73μmol/g and0.54-10.06μmol/g, respectively; the averagepercentage of Exchangeable P, Fe-bound P, Authigenic Ca-P and Detrital-P in TPwere2.7%,8.5%,9.3%,53.4%and25.7%, respectively. IP was the majorspeciation accounting for54%-95%in TP.(2) The distribution of Exch-P, Fe-P and OP seemed to be similar. The concentrationsof Exch-P, Fe-P and OP were slightly higher in the YS than that in the ECS, andlow concentrations could be observed in the middle part of the ECS and southwest off Cheju Island. The distribution of ACa-P was different from those of Exch-P,Fe-P and OP. The concentrations decreased southward, but the maximum ofACa-P appeared in the southeast of the study area. The concentration of Detrital-Phad two high values located in the south and north parts of the Changjiang Estuaryand decreased eastward obviously. The minimum could be observed in thenorthern part of the south YS. The dominant factors affecting the phosphorusconcentration and distribution in surface sediments were anthropogenic activities,sources of input materials, grain size, depositional environments and hydrologicalconditions, in which sources of input materials, grain size and depositionalenvironments were the most important factors.(3) In the YS and the ECS, TP and bioavailable P burial flux were0.82-15.46and0.22-6.45μmol/(cm2·a), respectively. Bioavailable P and TP burial flux showedsimilar distribution and appeared regional differences, which was affected bysedimentation rates, porosity and oxygen concentration in bottom water, but TPcontent and sedimentation rates were crucial factors for TP burial flux.(4) The concentrations of total P ranged from12to25μmol/g and decreased withincreasing distance from the coast. Exchangeable and Fe-bound P were very lowand mostly stable with depth. Organic P was the major burial sink for reactive Pand usually decreased with depth at all sites. Authigenic Ca-P concentrations werestable with depth. Detrital-P was the major speciation for IP, accounting for~35%to70%of total P.(5) Maximum values of iron extracted by CDB occurred in surface sediments anddecreased with increasing depth. Fe/P ratios in CDB were between10and25. Ironoxides were impacted by material source and redox environment. At the recearchstations, the iron contents extracted by CDB also presented decreasing trends withincreasing distance from the coast, and the Fe/P ratios were consistent with resultsof previous studies.(6) Organic carbon contents were very low, and less than1%. OC decreased graduallywith increasing distance from shore; while the same station, the organic carboncontent gradually decreases with increasing depth, which indicated the degradation of organic matter. OC/TN ratios in core sediments showed a littlechange or a slight decreasing trend with increasing depth. Meanwhile, the ratios ofthe OC/TN were affected by the degradation of organic matter, ON waspreferential to degrade relative to OC. At the nearshore stations, OC/OP in surfacesediments was higher than106, then decreased with increasing depth. Thedecrease in C/P ratio with depth in core sediment may be explained by thepresence of relatively labile organic matter deprived of P in the upper layer of thecore caused by preferential P degradation in the water column. The relativelylabile organic carbon was respired upon the degradation of organic matter, and thelittle P that was liberated was immediately re-incorporated in organic compounds.(7) Nutrients, Fe and Mn in pore waters of the East China Sea were mainly controlledby early diagenetic processes. The concentrations of dissolved Fe2+and Mn2+wereusually very low in surface sediments then increased with depth, but peaked atdifferent depth; below this, they decreased and/or remained stable. When theoxygen was completely consumed in the sediments, the Mn oxides were preferredto be the main electron acceptor. Nutrients in pore waters were affected byhydrodynamic conditions, depositional environment and burial efficiency oforganic matter. At the research stations, PO43-concentration increased withincreasing depth. The lower phosphate concentrations indicated that P may be alimiting nutrient. The NH4+concentrations showed the increasing trend, indicatingthe obvious mineralization of organic matter.