Preliminary Study On Distribution Characteristics And Biogeochemistry Of Various Phosphorus Forms In The Sediments Of The East China Sea And The Yellow Sea

Phosphorus is one of the key elements in global biogeochemical cycles.Marine sediments play an important role in phosphorus cycle as a source or a sink.The evolution of a comprehensive environmental information is recorded in the sediments, which makes it possible to become a key factor in understanding marine depositional environment changes.The forms of phosphorus in sediments include organic phosphorus and inorganic phosphorus.The latter can be separated into iron-bound phosphorus,authigenic calcium-bound phosphorus and detrital apatite phosphorus. Studying on these phosphorus speciation in sediments will help to evaluate the bioavailability of this element in marine environment,to record nutritional status of water bodies,to predict the future trend of environmental changes,to understand the substances transfer,diagenetic processes and phosphorus cycling,as well as the cycles of carbon,sulfur,oxygen and nitrogen.The East China Sea and the Yellow Sea are typical continental margin seas. Studies on the phosphorus forms in sediment in these sea areas were focused mainly on multi-tube sediments about 30cm depth,and were seldom on long core sediments. Three phosphorus forms(TP,IP and OP) of these core sediments have been analyzed in our lab using a sing-step extraction method.A further study of phosphorus forms on these core sediments is urgently needed.In addition,the former method on quantification of phosphorus in the Fe oxyhydroxides fraction had low analytical reproducibility,or need expensive instrument and not available in most laboratories.This thesis applies the Mg(OH)₂ coprecipitation method to determinate feric-bound phosphorus to get good precision.Four phosphorus forms in eight core sediments of the East China Sea and the Yellow Sea and some surface sediments of Jiaozhou Bay were measured by the revised sequential extraction method.The geochemical characteristics of phosphorus forms,the controlling factors as well as the environmental significance were presented.The main results are as follows.1) The ratio of liquid/solid is 130(mL/g) in the single-step extraction method.All of the extracted phosphate was measured by standard addition calibration curve method.The recoveries of this method ranged from 97.8%to 106.4%with precision within 2.04%-3.17%.There was no significant difference between the single-step extraction method and the sequential extraction method by F-test at the P=0.05 probability level.2) The various forms of phosphorus in the surface sediments showed high values in the eastern Jiaozhou Bay.The highest values of TP,Fe-P and OP located near the Licun River mouth in the eastern part of Jiaozhou Bay.3) The concentrations of various forms of phosphorus in the upper 0 to 2cm sedi-ments showed significant differences in the investigated sea areas due to their special environments.The semi-closed basin has been modified extensively by human activi-ties. Such as large-scale aquaculture of filter-feeders could have been an important factor in the decrease of diatom,which results in the low concentration of OP and ACa-P.In addition,the construction of dams in the upper reaches of river also results in the decreasing of phosphorus.The contents of various forms of phosphorus in the estuary areas are rather abundance especially the highest concentrations of DAP, because of the tremendous terrigenous input.The upwelling zone near the Zhejiang province is good for the formation of organic matter,so the content of OP here is highest.The Kuroshio water which is high temperature and salinity has an important affection to ACa-P.The concentrations of various forms of phosphorus(besides the DAP) are comparatively low in the centre region of the East China Sea shelf for the input is scarce.4) The vertical distribution of the various forms of phosphorus also had significant differences in 60 years sedimentation depth.The concentration of phosphorus increased distinctly with depth from 1990(besides Z station of Jiaozhou Bay).The vertical distribution difference of DAP was not distinct.While Fe-P,ACa-P and OP had high concentrations in surface sediments or subsurface sediments,and then fell sharply.The wave range of vertical distribution in E4 station was the most significantly different related to the high sedimentation rate and complicated hydrodynamic environment.5) In general,the mean concentration near the shore was higher than that far away from the shore,the phosphorus content in the East China Sea is higher than that in the Yellow Sea and the phosphorus content in estuary region is higher than that in open sea.IP was the main form of TP,and its content is much higher than OP's. Among different forms of IP,DAP was the dominant form,and Fe-P was the second main form.The smallest form of TP was ACa-P except some stations.