The concentrations of phosphate(PO43-),ammonium,nitrite,nitrate,silicate,dissolved organic nitrogen(DON),dissolved organic phosphorus(DOP),particulate phosphorus(PP)and particulate nitrogen(PN)along the salinity gradient were measured in the Changjiang Estuary in April 2007.The behavior of nutrient species along the continuum from the freshwater to the coastal zone is discussed.In the mixing zone between the riverine and marine waters,nitrate and phosphate behave non-conservatively,while silicate behaves conservatively.Nutrient import was quantified from the river load.Nutrient export to the sea was quantified from river discharge and from the salinity-nutrient gradient in the outer estuary.Using these data,a nitrogen and phosphorus budget was made.The internal estuarine fluxes played an important role in the nutrient estuarine fluxes,which accounted for approximately 41%of the nitrogen flux and 45%of the phosphorus flux.The mixing experiments in the laboratory generally reproduced well the inorganic process affecting nutrient dynamics in the Changjiang Estuary,indicating that the primary P and N transformation processes were phosphate and nitrate desorption along the salinity gradient.
YAO QingZhenYU ZhiGangLI LingLingCHEN HongTaoMI TieZhu
Suspended particulate matter (SPM) collected in the Changjiang (Yangtze River) estuary in June 2006 was separated into five fractions via water elutriation:clay-very fine silt (<8 μm),fine silt (8-16 μm),medium silt (16-32 μm),coarse silt (32-63 μm) and sand (>63 μm).The SPM and fractionated particles were sequentially analyzed by a modified SEDEX sequential extraction method to obtain six species of phosphorus:exchangeable or loosely-sorbed P,organic P,Fe-bound P,authigenic P,detrital P and refractory P.The results indicated that all particulate phosphorus species except for detrital P were negatively correlated to particle size;a high detrital P content was found in coarse silt and very coarse silt.From the inside of the river mouth to the gate of the river mouth,organic P,Fe-bound P and refractory P in the suspended particles decreased and a higher amount of exchangeable P appeared around the gate of the river mouth.From the gate of the river mouth to the sea,exchangeable P and organic P in suspended particles increased distinctly.The total particulate P flux into the estuary from the Changjiang River was about 45.45×108 μmol/s during sampling.Of this,about 8.27×108 μmol/s was associated with the "truly suspended" fraction.The bio-available particulate P flux was about 13.58×108 μmol/s.Of this,about 4.24×108 μmol/s was transported by "truly suspended" particles.
