| Phosphine, a volatile constituent of the global biogeochemical phosphorus cycle, has been proved to be widespread in the environment; however, its function and status in the biogeochemical recycle has not been identified so far. It exists in two different forms: free gaseous phosphine and matrix-bound phosphine (MBP). Now people have focused mainly on researches of phosphine in air, land, marsh and lake. Nevertheless, little information is available on the function of phosphine in marine environment. Therefore, it is of great significance to study the distribution, emission, transfer, transformation of phosphine in marine environment and its possible link to phosphorus cycle.Both field and laboratory experiments were carried out to study the distribution characteristics, emission flux, transformation mechanism of phosphine in marine sediments and its possible influence on the growth of micro-algae. Phosphine was analyzed by an improved GC-NPD method, coupled with cryo-trapping enrichment technology. The distributions of matrix-bound phosphine and environmental factors in marine sediments under different environments, such as the coast of China, the Changjiang River Estuary and Lake Illawarra in Australia were investigated. Then, the flux and estimating emission level of phosphine from sediment and water to atmosphere in Jiaozhou Bay were measured. Furthermore, the transformation process of phosphine and its possible role on the aquatic environment were represented. The result of this study not only contributes to the global biogeochemical phosphorus cycle, but also supplements the possible occurring mechanism of harmful algae blooms. The main results are given as follows: Matrix-bound phosphine (MBP) concentrations in surface sediments collected from 37 stations along the coast of China in 2006 are reported. MBP was found in all samples and the average concentration was 6.30 ng/kg dry weight (dw). The distribution of MBP showed certain spatial variation characteristics with high MBP concentrations at stations near to the coast. The average concentrations of MBP in the northern Yellow Sea, the southern Yellow Sea, the northern area of East China Sea, the southern area of East China Sea, and South China Sea were 5.57±3.78, 3.78±2.81, 5.27±3.07, 5.48±4.05 and 13.52±7.86 ng/kg dw respectively. The seasonal and spatial distributions of MBP in the Changjiang River Estuary were also studied and MBP ranged from 1.93 to 94.86 ng kg-1 dry with an average concentration of 17.14 ng kg-1 dw. The concentrations of MBP in the upper estuary were remarkably higher than those in the lower estuary which could be attributed to more pollutant inputs in the upper estuary. The concentrations of MBP also varied with seasons and generally showed a decreasing order of November > August > May > February. The vertical distribution of MBP in core sediment samples in Lake Illawarra showed that high MBP concentrations generally existed in the middle and bottom layers. The MBP concentrations in Lake Illawarra were remarkably higher than in other investigations.The relationships between MBP and the sedimentary environmental factors indicated that MBP was strongly influenced by various factors. High total phosphorus (TP), organic phosphorus (OP), organic carbon (OC), inorganic phosphorus and total nitrogen (TN) concentrations are favorable for the production of MBP; small grain size and low redox potential (Eh) favor high MBP concentrations; water depth, disturbances and hydrodynamics, etc. also have certain roles on MBP concentrations. The significant, strong correlations between MBP and OP also provided evidence to support the viewpoint that phosphine originated from OP decomposition by microorganisms under anaerobic conditions. Furthermore, it was interesting to find that there also existed positive linear relationships between the concentrations of soluble reactive phosphorus, TP, chlorophyll a in bottom water and MBP in sediments which might be very complicated and need further exploring.The emission fluxes of phosphine from sediments in Jiaozhou Bay were also studied; Average phosphine fluxes of 27.77 and 17.37 ng/(m~2·h) from sediment and seawater to atmosphere were found respectively. A total of 75.75 kg/year phosphine was estimated to be released from Jiaozhou Bay. The phosphine fluxes varied in different kinds of sediments with the highest flux from sediment in culture farms for shrimp. Phosphine was also detected in the atmosphere in Jiaozhou Bay which might be influenced by the light intensities and emission sources.The transformation process of phosphine in seawater and its possible influences on the growth of marine microalgae were also studied. The effects of environmental factors on the transformation process of phosphine in seawater demonstrated that the phosphine concentration decreased quickly at the initial hours and kept constant thereafter. Most of the transformed phosphine existed in forms of orthophosphate in the seawater and other phosphorus forms, such as hypophosphite and phosphite might also exist. The effects of phosphine, hypophosphite and phosphite on the growth of marine micro-algae under phosphorus limitation showed that the three kinds of reduced phosphorus, especially phosphine, might stimulate the growth of P. donghaicense and H. akashiwo to certain degree. This work is the first comprehensive study of the distribution, release, transformation of MBP in marine sediments and its relationships with environmental factors which will lead to a better understanding of the phosphorus biogeochemical cycle in the marine environment.
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