Southern Bohai Sea Research Articles

DISTRIBUTION OF CaO AND SMECTITE IN SURFACE SEDIMENTS OFF THE YELLOW RIVER MOUTH AND IN THE NEARBY BOHAI SEA AND THE IMPLICATIONS FOR DISPERSION OF THE RIVER SEDIMENTS TO THE SEA

A large-scale investigation of surface sediments was carried out off the Yellow River mouth and in the nearby Bohai Sea during August-September 2007. Approximately 250 samples were selected to determine CaO and smectite content using X-ray fluorescence spectrometry and X-ray diffraction. The analyzed data show that the CaO content distribution has similar occurrence to the smectite,which decreases seaward gradually from the Yellow River mouth. The study area can be classified into three provinces in terms of CaO and smectite contents. Provinces Ⅰfrom the river mouth to the central part of Laizhou Bay,is characterized by high contents of CaO and smectite,7.30% and 12.3% respectively. In contrast,the contents of CaO and smectite are as low as 5.62% and 10.8% in province Ⅲ,which covers the eastern and southern Laizhou Bay. Province Ⅱ is distributed between provinces Ⅰand Ⅲ,where the contents of CaO and semctite range from 5.62% to 7.30% and from 10.8% to 12.3% respectively. The results demonstrate that the CaO and semctite contents in surface sediments of southern Bohai Sea can not only be used as indictors to trace the dispersion of the Yellow River sediments to the sea in the study area,but also has important implications of hydrodynamical conditions off the river mouth.

Phase-transfer of nitrogen species within the water column of the Bohai Sea

Biogeochemical constituents, especially the different phases of nitrogen, were investigated in the central and southern Bohai Sea, China, during fall 1998 and spring 1999 by repeatedly sampling a regular station grid. Apart from at the area off the Huanghe River, dissolved organic nitrogen dominated the nitrogen fraction, indicating the seasonally maturated stage of the ecosystem. Inputs of dissolved inorganic nitrogen from the Yellow Sea (by the “Yellow Sea Warm Current”) as well as by the Huanghe River fuelled primary production and led to high primary production at the entrance of the Bohai Sea during both seasons and in the shallow areas, especially at the Huanghe River mouth, during spring. Beside the nitrogen import, resuspension and remineralisation processes of nitrogen contributed to the ongoing phytoplankton blooms and, thus, to the conversion of nitrogen. In spite of the high variability indicated by strong changes within a fortnight, seasonal differences could be detected, such as specific contribution of phytoplankton to suspended matter. Correlations of particulate nitrogen with total suspended matter as well as changes in concentrations of the different nitrogen species as well as in primary production rates helped in distinguishing between conversion and transport/diffusion processes. Overall, the Bohai Sea was revealed as a huge “bioreactor” for the conversion of nitrogen, and—due to permanent nitrogen input and extensive water–sediment interaction processes—as a possible important sink on a global scale for nitrogen via denitrification processes.

Phytoplankton dynamics in the Bohai Sea—observations and modelling

A Sino–German cooperative project (AMBOS/AMREB) was carried out to improve the understanding of the nutrient–phytoplankton dynamics with processes and governing factors through observation and modelling. Two cruises in April/May 1999, September 1998 and two 15-month coastal monitoring stations were completed and a three-dimensional model for the nutrients–phytoplankton cycle was established. During the cruises in spring and autumn, increased phytoplankton concentrations were found in the southern Bohai Sea characterized by high biomass in spring and higher production in autumn. The annual cycle of nutrients and chlorophyll a concentrations was monitored at Changdao and Penglai. A sudden depletion of nutrients occurs after spring bloom and is replenished by river discharges from summer to autumn and mixing up from bottom in winter. The concentrations in coastal areas were higher than that in the Central Bohai Sea. The Laizhou Bay and the Central Bohai Sea had the maximum annual mean biomass and primary production, while the Bohai Bay had the lowest values. The Huanghe River, the most turbid one in the world, with large sediment load enters the Bohai Sea and causes the low transparency around its mouth especially during strong wind mixing time. This influences the annual cycle of phytoplankton significantly in that area. Comparing with the historical data of 1982/1983, 1984/1985 and 1992/1993, the annual cycle and horizontal distribution pattern did not change much within two decades. Diatoms and dinoflagellates are the major components of the phytoplankton community in the Bohai Sea and the ecotype of these phytoplankters is temperate and neritic. Nanophytoplankton is a major component and the picophytoplankton is also not negligible. In spring, the phytoplankton community is mainly composed of small cell diatoms and in autumn of big cell diatoms and dinoflagellates. The replacement of diatoms by dinoflagellates is the main feature of phytoplankton changes in recent years. Using DIN, phosphate, phytoplankton and bottom detritus biomass as state variables, a three-dimensional ecosystem model (ECOHAM) is established coupled with the hydrodynamic model (HAMSOM). The simulation was carried out for the year 1982 because hydrodynamic model simulations and meteorological data were available. The simulated nutrients (dissolved inorganic nitrogen [DIN], phosphate), phytoplankton biomass and primary production variability are in reasonable agreement with the observations. Using model results of 1982, the phytoplankton processes could be discussed by model sensitivity studies. The variation of the phytoplankton was controlled by temperature, nutrient and especially by available light, which was strongly influenced by transparency. The annual phytoplankton cycle was sensitive to the basic respiration rate, mortality rate and grazing rate and to the limitation of light. The net primary production of phytoplankton is 7469 kt C. Respiration of phytoplankton take great role in the regeneration of nutrients and it can compensate 62% of the nutrients consumed by algal growth while bottom remineralization, another important source for nutrients regeneration, can add 23%. The influences of horizontal advection, river loads and different biological processes are also discussed based on this model simulation. The maximum of biomass without horizontal advection in summer is two times higher than that with advection and the high biomass area locates along the shore. Transported by horizontal advection, the high biomass area extends to the east in the Laizhou Bay, to the southeast in the Liaodong Bay and concentrates at north in the Bohai Bay. The variation of the river load only has regional influences to the evolution of the system. The increasing of the proliferation of industries, agriculture and domestic sewage compensates the drop of the DIN concentration induced by river load shutdown. If only the phosphorous cycle is considered, the simulated biomass is six times higher and the situation of the Bohai Sea cannot be adequately reproduced.

Forms of phosphorus and silicon in the natural grain size surface sediments of the southern Bohai Sea

The forms of phosphorus and silicon in the natural grain sizes surface sediments of the southern Bohai Sea were studied. In sediments, the organic matter bound form of phosphorus was the main form of transferable phosphorus and ranged from 0.37 μmol/g to 1.57 μmol/g, accounting for 10.7% of the total phosphorus, others were the carbonate bound form, iron-manganese oxide bound form and ion-exchange able form; the transferable form of phosphorus accounted for 19.2% of the total phosphorus. Silicon’s carbonate bound form was predominant over others among its transferable forms, and content ranged from 1.55 μmol/g to 8.94 μmol/g, accounting for 0.05% of the total silicon; the total amount of transferable silicon forms accounted for only 0.12% of the total silicon. Therefore, 19.2% of the total phosphorus and 0.12% of the total silicon contained in the surface sediments of the southern Bohai Sea could participate in the biogeochemical cycling.

Biogeochemical processes of phosphorus and silicon in southern Bohai Sea surface sediments

Based on the author's previously obtained results on P and Si forms in southern Bohai Sea surface sediments, this study mainly foucusing on the controlling factors, existence forms, and biogeochemical processes of P and Si showed that the transferable forms of phosphorus in sediments were mainly controlled by the mineralization of organic matters and the reduction of high-valence iron; whereas the transferable forms of silicon were possibly controlled by the dissolution and precipitation as well as biochemical processes of living organisms.

Mass physical properties of Huanghe delta and Southern Bohai Sea near‐surface deposits, China

Abstract The Huanghe or Yellow River is the second largest river in the world in respect to sediment load, debouching approximately 1.1 × 109 tons annually into the Bohai Sea. Owing to the predominance of silt‐size material, 80–90% of the sediment is deposited within 20 km of the estuary mouth with only about 36% getting out beyond the delta front. Gross annual lateral growth of the delta may be as much as 4.5 km. The delta presents a complex depositional setting with considerable disruption of the deposits taking place because of the dynamics of this environment, where wave action, rapid loading‐induced mass failure, and underflows predominate. The upper 2 m of the delta front deposits are classified as clayey silts whose median diameters commonly range from 5 to 8⊘ (0.031–0.004 mm), with wet bulk densities of 1.52–1.98 Mg/m3, water contents of 26–98% dry weight, shear strengths of 1.6–8 kPa, and sensitivities of 2 to 6. As expected, these properties vary considerably both laterally and with depth. Within the delta front, areas of disturbed and thoroughly homogenized sediment are common. These deposits, relative to those not showing disturbance, frequently are characterized by slightly lower percentages of clay‐size material, lower water contents, higher bulk densities, and slightly higher shear strengths distributed uniformly with depth. Because of the shallow nature of the Bohai Sea and the high winter‐induced waves, the upper intervals of the bottom sediments are annually reworked and considerable erosion of the delta front takes place. This unique dynamic setting tends to result in a greater degree of uniformity in time of the Bohai bottom sediments.