Distributions And Significances Of Oxygen Isotope Composition In Dissolved Phosphate In The Jiulong River Basin,the Jiulong River Estuary And Taiwan Strait

Phosphorus(P)is one of the most important biogenic elements needed for the growth of organisms and a ultimate limiting nutrient for system productivity over long timescale in nature.It is usually present as +5 valence phosphate in water.It is defined as phosphate-limited water if phosphate concentration is lower than the Redfield ratio in the water.On the contrary,if it becomes higher than normal,the water will become eutrophication.The application of phosphate concentration for tracing phosphorus cycle is limited as a non-conservative element.Researches on phosphorus cycle with stable isotope of phosphorus cannot be accomplished because it has only one stable isotope-31P.Phosphate will occur oxygen isotope exchange with surrounding water with organism participation.Oxygen isotopes composition in phosphate(?18OP)can reflect some information about the phosphorus sources if the requirement of phosphorus is lower compared with its input and the circulation is incomplete.Thus,?18OP can track the phosphoras sources and the process of phosphorus circulation in water.The studies of 8180p in natural water have been not a lot yet,this study can help us understand the distributions and seasonal variations of ?18OP about Jiulong River Basin,Jiulong River Estuary and Taiwan Strait.During several researches on Jiulong River Basin(West Stream,North Stream)in 2014,it is found that types of field utilization have effects on the phosphorus changes.DIP in North Stream presents a possible trend that is higher in both upper and lower reaches and lower in middle reaches.It has similar seasonal changes and the output velocity during the dry season is higher than that in the wet season.Oxygen isotopes composition in water(?18OW)has sight changes and similar seasonal distribution.That is,either ?18OW or ?18OP,the dry season is higher than the wet season.?18OP in North Stream is usually lower than the average level.While in West Stream,phosphate concentration in the dry season is higher than it in the wet season and ?18OP is usually higher than the average level.DIP,PIP and POP in West Stream is approximately twice as much as North Stream.Both two streams have similar DOP.?18OW and ?18OP differs slightly.In the basin,?18OP is 15.9%o in average.In the research on the Jiulong River Estuary in April 2015,it has found buffering effect does not happen in the middle-and-low-salinity area.The Jiulong River Estuary coincidents with the two end-member mixing model.The ?18OP values distribute mostly near the mixing line,which reflects the distinct physical mixing effect.The role of biological effect to reach equilibrium in the estuary is limited.While the external phosphorus source will have a certain impact on the change of ?18OP.All in all,the change of ?18OP is dominated by the tide in estuary and other phosphate sources.During summers of 2014 and 2015 in Taiwan Strait,the ?18OP distributed near the Jiulong River estuary and Minjiang estuary area showed a lower value.However,a higher value appear near the upwelling area.The process of extracellular enzyme depositing DOP for survival leads to the fractionation of ?18OP,which causes ?18OP in offshore area is lower than the equilibrium level.?18OP contains in the bottom water is usually higher than in the surface water.