Relationship between biogeochemical features of biogenic elements and flocculation in the Changjiang Estuary

This paper reports the relationship between the biogeochemical characteristics of C.N.P and flocculation and settling of suspended materials in the Changjiang Estuary.Regional activities of bacteria and the plankton and biogeochemical processes at the water-particle interface under some environmental conditions are quite variable.This leads to the transition of material phase with speciation variation of elements C.N.P.in the transfer processes.Therefore, the composition and reactivity of particle surface and dissolved constituent are modified, affecting the stability of the particulate dispersion system.In summer, the concentration of NO₃^- and PO₄^3- are positively correlated with turbidity, while the weight percentage of PON, POC and PP are negatively correlated with turbidity.When particles in the river move seaward, two zones can be distinguished:ⅰ) zone with maximum flocculation speed, in salinity 0.1-2.0;ⅱ)zone with huge coagulating particles netting and high turbidity at the bottom, in salinity 2-11.The highest values of C/N in particles (or the low valley of C.E.C.of particle surface) appear in the two zones.These results demonstrate that the biogeochemical action is one of the major factors and mechanisms to dominate the flocculation of particles in the Changjiang Estuary.