The Transport Of Inorganic And Organic Carbon In The Yellow River Estuary And Its Effect On Laizhou Bay

The transport of carbon by rivers is an important component of the global carbon cycle. Of the well-documented 0.9 Gt carbon carried by world rivers each year, about 40% is organic and the remaining 60% is inorganic. Despite the large quantities of carbon delivered from rivers, only a small fraction of it is transported to the adjacent shelf and open ocean. Estuaries are the primary fresh-salt water interface. They are extremely dynamic systems, characterized by strong physico -chemical gradients, enhanced biological activity (both heterotrophic and autotrophic) and intense sedimentation and resuspension. Estuaries play an important role in transportation of dissolved and particulate material from the continent to the marine system, however very little is known about the estuarine processes that control the fate of riverine inorganic and organic carbon. The Yellow River, as one of the high turbid river, has important effect on carbon cycle of North -west Pacific Ocean, to better understand the effect of estuarine processes on riverine inorganic and organic carbon, during this study, the distributions of DOC, DIC, POC and PIC in Yellow river estuary were investigated during both dry (April, 2004; April, 2006) and wet (September, 2004; September,2005) seasons. Estuarine processes controlling carbon transport in the estuaries were discussed, and net carbon flux was calculated. Moreover, the effects of Yellow River carbon transport on Laizhou Bay were estimated by July and September 2005 cruises.DOC and DIC concentrations of Yellow river during dry seasons were higher than during wet seasons. The effective concentrations of DOC (CDOC*) were higher than the observed DOC at zero salinity. This input of DOC in the Yellow River estuary was due to sediment de-sorption processes in low salinity region. In contrast to DOC, the effective concentrations of DIC were 10% lower than the DIC measured at freshwater end, the loss of DIC was caused by CaCO3 precipitation in low salinity region.POC and PIC content of the particles stabilized to a constant value ( 0.51% and 1.75% respectively ) within the turbidity maximum zone (TMZ) and showed no noticeable seasonal variations . A rapid drop of PIC and rose of POC occurred simultaneously dropped of PIC% and rose of POC% outside the TMZ. POC% increase with decreasing particles size, more than 80% POC concentrate onΦ<16μm size particles and POC inΦ<32μm size particles account to 95% flux from Yellow river estuary to Bohai sea. When TSS=455mg/l, the ratio of DOC/POC is 1, which indicate that organic carbon transport in Yellow river is in the form of POC. They are due to an intense dilution of riverine inorganic-rich particles into a pool of aquatic organic-poor particles outside TMZ. Annually, the Yellow River transported 4.13×105 t of DIC, 3.84×104 t of DOC, 1.21×106 t of PIC and 3.54×104 t of POC to the ocean.With the dramatically sediment of POC in upper estuary, the partial pressure of CO₂ (pCO₂), which is derived from biogenic respiration, swiftly decrease and lead to CaCO3 precipitation in low salinity regions, the pH value will simultaneously increase in this area. Instant increasing pH value can be used as index of CaCO3 precipitation in Yellow river estuary, during dry season, photosynthesis will enlarge CaCO3 precipitation to salinity of 18. According to dissolved matter mixing model in estuary, the observation of 1-to-1 removal of TA and DIC provide just evidence that DIC removal we observed in the field is a result of HCO3- removal. The process can clean 10%(4.59×104 tons)DIC which is transported by freshwater both in dry and wet weathers, and ten percent of CO₂ (8.40×104t) which is absorbed by chemical weathering process in drainage basin will release to atmosphere in Yellow river estuary.The distribution of DOC and DIC in Laizhou Bay were controlled by Yellow river during the test of water-sediment regulation of the Yellow river (July,2005), however, with runoff of Yellow river decreasing and Xiaoqing river increasing in September 2005, DOC and DIC from Xiaoqing river will influence Southwest Laizhou Bay. According to the analysis of chlorophyll-a and mineral in TSS, when TSS is less than 30mg/l, phytoplankton increase but sediment from Yellow river decrease in TSS. Simultaneously,∑C20-/∑C20+ and CPI of n-alkane respectively increase and decrease. TSS=30mg/l can be regarded as effective boundary between allochthonous TSS and autochthonous TSS. Sediment from the Yellow river diffuse to southern river-mouth in surface layer; However in bottom layer, sediments diffusion range concentrate at northern and southern river-mouth of Yellow river, the central section of Laizhou Bay is possible habitation of sediment from the Yellow river.