| Estuarine mixing zone between the land and the ocean has multiple functions. Water properties like salinity and concentration of suspended sediments in the estuary vary in time and space, and alter the element partitioning between solid phase and solution via adsorption and desorption. Seaward element fluxes change considerably in the estuary, and it is important to understand effects of estuarine processes on the phase transformation of elements in order that the flux of dissolved phase can be properly made.Chinese estuaries are shallow with abundant water and high concentration of suspended sediments, and of particularly interest in studying particulate-solution transformation. The Changjiang Estuary serves as an important land-ocean interaction region and can be taken as a natural laboratory for studying estuarine biogeochemical processes. In this study, effects of salinity, pH and SPM on the solid-liquid phase partitioning for some trace elements (Cu, Zn, Cd, Co, Ni) were examined with the samples from Changjing Estuary.Based on the data obtained from in-situ observation and laboratory simulation, some of the results can be summarized below.1. The concentrations of suspended sediments in the Changjiang Estuary vary considerably. Within the maximum turbidity zone, concentration of suspended sediments reaches up to more than 2*103 mg/1. The pH range within the Changjiang estuary is limited to 7.7-8.3. The major ions Changjiang show characteristics of HCO3>C1"+SO42~ for anions and Ca2+>Mg2++Na++K+ for cations independent of variations of sediment concentration and pH. Through salinity gradient, the major cations levels can be predicted with a linear mixing model.2. Simulation results show that pH variation within the Changjiang Estuary has significant effect on solid-liquid partitioning of trace metals. Increasing pH of water samples induces partitioning of metals to solid phases and hence transport of metals with suspended sediments.3. Increase in concentration of sediment promotes adsorption for trace metals onto solid-phase in the estuary, but has little influence on partitioning coefficient for trace metals. The experimental results illustrate that "particle-concentration effects" for trace metals reported in literature are mainly due to the particle dynamics in the estuary.4. The adsorption percentage ratios of adsorptions and partitioning coefficients for trace metals in the Changjiang Estuary decease significantly with higher concentrations of elements. For a given pH condition, adsorption of trace metals on to sediments in theChangjiang Estuary can be described by the Langmuir equation, and implies that increase in trace metal concentrations at natural waters has limited effect on trace metal partitioning coefficients because of high turbidity.5. Changing salinity in the estuary reduces adsorption of Cu, Zn, Cd, Co, Ni on to suspended sediments within the Changjiang Estuary. Among the metals studied, Cd has the obvious salinity depend on Kj due to probably its high affinity for Cl", whereas cations competitive adsorption and compexation of onions should be taken into account for salinity effect on Cu, Zn, Co and Ni. Experimental results show that desorption of particulate trace metals by waters of high salinity is limited due to dynamical processes.6. Based on solid-liquid interface ion exchange model, using in-situ data of pH, sediment concentration, trace metal and salinity in the Changjiang Estuary, solid-liquid phase transformation for metals Cu, Zn, Cd, Co, Ni through salinity gradient was calculated, and the modeling results was compared with in-situ data sets reported in literature. The results show that Cu and Zn tend to be quasi-conservative, whereas Cd, Co and Ni are remobilized over a broad salinity range in the Changjiang Estuary.7. Variation of fluxes for several dissolved trace metals was discussed, using a simple model based on the distributions of SPM, salinity and simulating experiments in the Changjing Estuary, and the results show that disso...
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