Study On Forms And Distribution Of Phosphorus And Nitrogen In The Sediments Of East China Sea And Yellow Sea

Nitrogen and phosphorus—the major elements controlling marine primary productivity,influence the global biogeochemical cycles. As the amount of nitrogen and phosphoruspresent in marine environment depends on both the riverine transportation and their releaseand retention in the sediments, sediments play an important role in their cycling. Accordingly,it is important to study the forms of phosphorus and nitrogen in sediments for predictingfraction of their availability. An understanding of nitrogen and phosphorus speciation inmarine sediments is essential in evaluating response to environmental changes, understandingtheir cycling, providing a scientific basis for evaluating ecological environment.East China Sea and Yellow Sea are typical continental-margin seas. This study collectedsurface samples from East China Sea and Yellow Sea, core sediments at station za3、zc13、za6a in East China Sea. A selective sequential extraction method (SEDEX) was employed toquantify the different forms of sedimentary phosphorus; Potassium persulfate oxidationmethod was used to study different forms of sedimentary nitrogen. The main results are asfollows.Basically, the inorganic P was the major form, accounting for81.1-90.8%of the total Ppool in Yellow Sea, and84.1-93.9%in East China Sea, while organic P was found to be aminor form. Among the four forms of sedimentary phosphorus, we found that P-Detrital wasthe most important sedimentary phosphorus form in the study area. The average percentage ofeach fraction of P followed the sequence: P-Detrital＞P-CDB＞P-Organic＞P-CFA. Lessthan40%of total P could be potentially bio-available, which represented a minor part of thesedimentary phosphorus pool. The phosphorus content was clearly related to the regionaldistribution. The spatial distribution characteristics of total phosphorus and all the phosphorusforms were similar. Relatively high level of phosphorus had been observed in estuarinesediments, reflecting the influence from the land-source input. The content of totalphosphorus and phosphorus forms was higher in the upper layers of the sediment and tendedto decrease toward the bottom of the core, regardless of the phosphorus species, indicating thephosphorus load had been aggravated with the intensification of human activities and rapid development of industry and agriculture in recent years.The total concentration of nitrogen in the surface sediments in the study area was higherthan total phosphorus. Organic N was the major form, accounting for49.7-85.1%of thetotal N pool in Yellow Sea,58.9-74.2%in East China Sea. While inorganic N was found tobe a minor form. The distribution of nitrogen showed a decreasing trend from north to south,and from outer shelf to inner shelf. Generally, inorganic N increased slightly with depth whileorganic N had a decreasing tendency toward the bottom of the core.Phosphorus content of the sediments was controlled by a number of factors, includingthe rate of sedimentation, sediment type, amount and type of organic matter, intensity ofmineralization of organic matter in the sediment and water column and redox conditions inthe sediment and near bottom water. The vertical distribution characteristics that the contentof nitrogen and phosphorus was higher in the upper layers, indicating that the nitrogen andphosphorus load had been aggravated with the intensification of human activities and rapiddevelopment of industry and agriculture in recent years.