| Phosphorus(P)is an indispensable biogenic element in marine ecosystem,and among the essential macronutrients that induce eutrophication and harmful red tide in estuaries and bays.P plays a key role in the marine primary productivity,global carbon cycle and biogeochemical cycle of other biogenic elements.Thus,it is of great scientific significance to study and understand the biogeochemical characteristics of P for the ecological sustainability of marine environment and global climate change.In this work,both surface water and sediment samples were collected from fifteen stations in different estuaries of the Maowei Sea,in July 2018.The concentrations of different P species were extracted in different media,including surfer water,suspended particulate matter(SPM)and surface sediment.Combined with the physicochemical parameters of water and sediment,the distribution characteristics,influencing factors,migration or transformation,and bioavailability of different P species were systematically explored.The major results are summarized as follows:(1)Total dissolved P(TDP)is the main form of total P(TP)considering the dissolved and particulate phases in surface water of the Maolingjiang River estuary(MRE)and Qinjiang River estuary(QRE)area,and averagely accounted for 61.2% and 70.6% of TP pool,respectively,while the average proportion of total particulate P(TPP)was relatively lower.The average concentration of TDP was 3.81 ± 0.70 ?M in surface water of the MRE area,of which dissolved inorganic P(DIP)was 1.60 ± 0.99 ?M,while dissolved organic P(DOP)was 2.20 ± 0.97 ?M.In the QRE area,the average concentration of TDP was 3.78 ± 0.60 ?M,of which DIP and DOP were 1.41 ± 0.56 ?M and 2.37 ± 0.99 ?M,respectively.In the dissolved phase,DOP was the predominant of TDP in surface water.The average concentration of TPP was 2.51 ± 0.98 ?M in surface water of the MRE.Within the TPP pool,the average concentration of particulate inorganic P(PIP)was 1.75 ± 0.84 ?M and particulate organic P(POP)was 0.76 ± 0.27 ?M.The average concentration of TPP was 1.59 ± 0.41 ?M in the area of QRE,of which the average concentration of PIP and POP were 1.09 ± 0.34 ?M and 0.49 ± 0.17 ?M,respectively.In the particulate phase,PIP played a dominant role in the dynamics of TPP in surface water.(2)The concentration of DIP in the river mouth surface water was higher than that in the bay mouth area.While higher DOP values were found in the bay mouth area,in the concentrations of DOP in the river mouth was relatively lower.PIP concentrations decreased gradually from the river mouth to the bay mouth in surface water of the MRE area.However,the concentration of PIP decreased first,and then subsequently increased from the river mouth to the bay mouth in surface water of the QRE area.The distribution of different forms of P was affected by riverine input,water environment characteristics,biological process and hydrodynamic conditions.The results of Principal Component Analysis revealed that physicochemical parameters such as salinity,pH,dissolved oxygen,redox potential,Chlorophyll-a and suspended particulate matter(SPM)were the major factors affecting the different P species in surface water.The correlation indicates that there was a certain mutual transformation behavior between the forms of P in the dissolved and particulate phases in surface water,and the biological factors played an important role during the process too.There was a strong particle reaction activity of P in the study area,and it had an important influence on regulating the distribution of P between dissolved and particle phases,which is controlled by physicochemical and biological factors.Based on the two-end-member mixing model,the results show that 0.57 ± 0.31 ?M and 0.39 ± 0.31 ?M of DIP was removed by biological uptake in the MRE and QRE area,respectively.(3)Ferric(Fe)-bound(Fe-P)was the dominant form of PIP,of which the average concentration was 0.71 ± 0.58 ?M,accounting for 25.0 ± 11.1% of TPP content in SPM,in the MRE area.The average concentration of detrital P(De-P)was 0.45 ± 0.1 ?M,accounting for 18.8 ± 4.5% of TPP content.Exchangeable or loosely sorbed P(Ex-P)and authigenic apatite-bound P(Ca-P)accounted for a lower proportion,and were 15.7 ± 8.9% and 8.6 ± 2.8%,respectively.De-P was the main form of PIP in SPM in the QRE area,and the average De-P content was 0.43 ± 0.13 ?M,accounting for 28.8 ± 9.7% of TPP.The average content of Fe-P was 0.27 ± 0.18 ?M,accounting for 15.9 ± 6.3% of TPP,and the proportions of Ex-P and Ca-P were relatively lower,accounting for 12.8 ± 11.0% and 11.6 ± 4.9%,respectively in the QRE area.The average contents of TP in surface sediments of the MRE and QRE area were 12.15 ± 7.67 ?mol/g and 9.78 ± 5.14 ?mol/g,respectively.Inorganic phosphorus(IP)was the main form of TP in surface sediments of the MRE and QRE area,accounting for 64.4% and 65.9%,respectively.Organic P(OP)accounted for a lower proportion of TP.Fe-P was main form of IP in different estuaries,accounting for 31.2% and 28.1% respectively.(4)The distribution of different P species in SPM were influenced by riverine inputs,water environment characteristics,biological activities and other governing factors in different estuaries of the Maowei Sea,and the distribution of different P species in surface sediments was also related to the sediment environmental characteristics and grain size.The complex environment promoted the migration and transformation of different P species between SPM and surface sediments.This shows that Fe-P and Ca-P may migrate between SPM and surface sediments,and Ex-P in SPM can transform into Ca-P in surface sediments.There was a significant transformation relationship between Fe-P in SPM and Ca-P or De-P in surface sediments.The mineralization and decomposition process of OP can also promote the transformation of other P species.(5)The sum of Ex-P,Fe-P and OP was taken as the potential bioavailable P(BAP),and the average concentration of BAP was 1.85 ± 0.79 ?M and 0.97 ± 0.49 ?M in SPM of the MRE and QRE area,which accounted for 72.6 ± 4.3% and 58.6 ± 13.8% of the TPP,respectively.The average concentration of BAP was 9.10 ± 6.44 ?mol/g and 6.92 ± 4.19 ?mol/g in surface sediment of the MRE and QRE area,which accounted for 73.9 ± 11.8% and 68.8 ± 5.8% of the TP pool,respectively.This shows that there is a higher bioavailability of P within the P pool,as well as high potential capacity for phosphorus release,especially in the estuaries. |
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