黄东海陆架区沉积物中磷的形态分布及生物可利用性

Abstract

Phosphorus is the most important limiting factor in nutrient cycling.It is also the key element controlling primary production in aquatic environments.Sediments act as both a sink and a source of phosphorus because of continuous transport of phosphorus species across the sediment-water interface.Phosphorus is intimately involved in both the terrestrial and marine biogeochemical cycles.However,not all fractions of phosphorus in sediments are released to the overlying water.Therefore the effects of phosphorus in sediments in promoting aquatic environment eutrophication can be more efficiently evaluated by studying phosphorus fractions,rather than total phosphorus(TP).In this study,the forms and bioavailability of phosphorus in the sediment were analyzed by means of SEDEX(Ruttenberg KC) to determine the geochemical characteristics of phosphorus in the Huang Dong Hai continental shelf.According to this method,there are five types of phosphorus: iron-phosphorus(Fe-P),organic-phosphorus(Or-P),detritus-phosphorus(De-P),exchangeable-phosphorus(Ex-P),and autologous-phosphorus(Au-P).They differ from each other in occurrence,origin and geochemical features.The horizontal and vertical distribution of six forms is presented.The profiles of age deposition were also investigated to reveal changes in the contents of the different phosphorus forms over about two hundred years.The rank order of the contents of phosphorus fractions in the surface sediment was Au-P(140.72 μg/g) De-P(59.23 μg/g) Or-P(32.69 μg/g) Fe-P(29.91 μg/g) Ex-P(5.92 μg/g).The contents of Au-P and Or-P decreased from offshore to the open sea,and values for De-P were uniformly distributed over the whole sea area.High contents of TP and Ex-P were present in the Yangtze estuary area.TP,Fe-P,Or-P,De-P,Au-P and Ex-P contents in the sediments were in the range 310.23—941.78μg/g,5.46—58.11μg/g,4.87—80.57μg/g,12.68—282.15μg/g,31.86—271.38μg/g,and 1.32—20.95μg/g,respectively.The vertical distribution of the different fractions of phosphorus at four sampling stations varied.The distribution of different phosphorus fractions in different sediments reflected changes in the early diagenesis of phosphorus.The concentration of Au-P in H1-18 was much lower than at the other three stations.In the study area,the relative contributions of Fe-P,Ex-P,and Or-P were 5.96%,1.18%,and 6.51% of TP,respectively.Fe-P is considered to be the most labile fraction of phosphorus fraction in the sediments.It will change when the oxidation-reduction environment changes in the surface sediments.Fe-P can be used to determine the source of phosphorus and indicate the extent of environmental pollution.Or-P can be released during the decomposition of organic matter in the early diagenetic process,and even convert to other forms of phosphorus.When organic matter degrades,the phosphorus is released into the overlying water.Consequently,the degradation of Or-P is an important process in its influencing of the contents of phosphorus fractions in sediments.Ex-P is influenced by particle size of the sediments and released into the overlying water mainly through ion exchange.Hence it is important to understand under what conditions phosphorus can be changed from one fraction into another and phosphorus in sediments can be released into the overlying water.Fe-P,Ex-P,and Or-P are biologically available fractions of phosphorus in our study area.The results showed that potentially biological available phosphorus accounted for 13.55% of the total phosphorus.