Element geochemistry of Holocene sediment and paleoenvironmental change in the Changjiang Estuary

Analyses of 41 elements reveal that Holocene sediments in the Changjiang Estuary bear regular elemental compositions in different sedimentary environments, and Holocene sediments came mainly from the Changjiang River based on compositions of REEs and most trace elements. Some heavy metals are more enriched in the surface sediment than in the deltaic sediments, reflecting human impact. Elemental compositions of the river channel sediment are related to the influence of proximal sediments. Sedimentary environments exert some influences on elemental compositions. Some chemical indices can be used to record chemical weathering undergone by the Changjiang sediment and environmental change.     

Field measurements of bottom boundary layer processes and sediment resuspension in the Changjiang Estuary

A field observation of the hydrodynamics and the sediment resuspension in a bottom boundary layer was carried out in the Changjiang Estuary, during July-August 1997. Using bottom field research facilities, detailed measurements of near-bottom currents and suspended sediment concentration distribution within 1.0 m above bed have been obtained in the Changjiang Estuary——a high concentration estuary. An Acoustic Suspended Sediment Monitor (ASSM) wasused to observe near bed sediment resuspension processes. In addition, the log-profile method was applied to estimating hydraulic roughness Z0 and bottom shear stress values (or friction velocities u). Further understanding of sediment suspension mechanics and hydrodynamic characteristics will require the long-term measurements of near bed processes.     

Fluid mud transportation at water wedge in the Changjiang Estuary

In situ data show that fluid mud of the Changjiang Estuary consists of fine sediment ranging from 8 to 11.5μm (median grain-size) including 28.8%-36.4% of clay. The composition of the clay is illite, chlorite, kaolinite and montmoillonite. The FM is a layer of high sediment concentration near the bed and results from flocculation under the environment of salt and fresh water mixing. Three kinds of FM have been identified under typical dynamic conditions: the first one is formed at slack water of ebb tide during the flood season, with the characteristics of extended area and low thickness; the second one is formed following a storm, characterized by large area and larger thickness; the third one is formed around the front of the saltwater wedge, characterized by small area but large thickness. In the dredged channel, the FM can be accumulated up to 1 m thick. In general, FM will change with the alternation from spring to neap tides, flood and dry seasons. Drastic change can happen during storms. At the s     

Transformation and source of nutrients in the Changjiang Estuary

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.     

Types of saltwater intrusion of the Changjiang Estuary

The Changjiang Estuary is characterized by multi-order bifurcations, unsteady submerged sandbars, mid-channel sandbars, creeks and riffles. The following four types of saltwater intrusion are found: (1) direct intrusion from the sea; (2) intrusion during tidal flooding; (3) intrusion from tidal flats overflow; and (4) salt water coming upstream through other waterways. These result in a complicated temporal and spatial salinity distribution. A high chlorinity concentration zone exists from the Liuhekou to the Sidongkou along the South Branch. The salinity during neap tide or ordinary tide is higher than during spring tide.     

Seasonal, neap-spring variation of sediment concentration in the joint area between Yangtze Estuary and Hangzhou Bay

An analysis of variations in suspended sediment concentration (SSC) over one year is presented for the joint area between the Yangtze Estuary and the Hangzhou Bay. Results suggest that daily SSC presents periodic variations, which correspond with seasonal and neap-spring tidal cycle. SSCs are higher during the winter season and during spring tides when compared with summer and neap-tide conditions. Furthermore, data indicate that wave and tidal currents are the two dominant factors affecting SSC. Although the Yangtze River discharges abundant sediments to the study area, it does not directly affect concentration variations. But the changing path of the Yangtze River plume plays a certain role in the seasonal variations of SSC. Finally, the calculation of bottom stresses suggests that SSC is a function of both wave and tide-induced resuspension.     

Progradation of the Changjiang River delta since the mid-Holocene

Subaqueous deltaic deposits with approximately 30 radiocarbon ages show that the Changjiang River delta was strongly affected by tides and that the delta progradation rate after 2 kaBP was almost double the rate before 2 kaBP. This change in the progradation rate correlates well with the active extension of the subaerial delta plain shown by previous work. Widespread human activities, such as farming, deforestation, and dike construction, probably resulted in an increase in sediment discharge to the river-mouth area.     

The change of characteristics of tidal wave in the Changjiang River mouth area since the post-glacial transgression maximum

During the period of the post-glacial transgression maximum (PGTM), there was a huge trumpet estuary in the modern Changjiang River Delta area. The location and the shape of the Paleo-Changjiang River Estuary (PCRE) were much different from those of the present Chang-Jiang River Estuary. The study on the change of characteristics of tidal wave in the Changjiang River mouth area since the PGTM can help to understand better the dynamic development of the Changjiang River Delta. The course curves of tidal level and tidal current velocity during a single tidal cycle for 35 points are calculated, and characteristics of tidal waves in the PCRE and its adjacent area are compared with those of tidal waves in the modern Changjiang River mouth area. The results show that the tidal waves within the PCRE and in its adjacent area during the period of the PGTM belonged to standing wave or a mixture of standing wave and progressive wave. Since then, the tidal wave in the Changjiang River mouth become gradually to be pr     

Field measurements of bottom boundary layer processes and sediment resuspension in the Changjiang Estuary

2,4-Bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5-triazine(bpt) has been synthesized by using a new, simple and general method with high yields. Reactions of bpt with Ni(ClO₄)₂·6H₂O and Zn(ClO₄)₂·6H₂O in methanol gave mononuclear complex [Ni(bpt)₂]· (ClO₄)₂·H₂O and ternary complex [Zn(mpt)₂(dmp)](ClO₄)₂ respectively, where mpt (2,4-dimethoxy-6-(3,5-dimethyl- pyrazol-1-yl)-1,3,5-triazine) and dmp(3,5-dimethylpyrazole) are the alcoholysis products of bpt in the presence of Zn²⁺ ion. A possible mechanism for this catalytic reaction was proposed. X-ray crystal structure for ligand bpt, Ni and Zn complexes are reported. The protonated form of the ligand bpt crystallizes as its perchlorate salt including one molecule of water, [Hbpt·H₂O·ClO₄]. The proton is located on one pyrazole N-atom. [Hbpt·H₂O·ClO₄], in which [Hbpt]⁺ is in cis-cis conformation, are packed in slipped stacks of approximately parallel layers. The Π -Π overlap interactions between the non-protonized pyrazoles of the adjacent layers give a zigzag arrangement of the planar aromatic [Hbpt]⁺ molecules. In [Ni(bpt)₂](ClO₄)₂·H₂O, bpt are meridionally three-coordinated with Ni²⁺. The coordination sphere around Ni²⁺ is a slightly distorted square bipyramid, where four pyrazole nitrogen atoms occupy the basal positions and two triazine nitrogen atoms the apical one. In [Zn(mpt)₂(dmp)](ClO₄)₂, the Zn atom is coordinated with a pair of bidentate mpt ligands and one monodentate dmp ligand, forming a distorted trigonal bipyramid, where the two triazine nitrogen atoms of mpt and one nitrogen atom of dmp occupy the basal positions, and the two pyrazole nitrogen atoms of mpt the apical one.     

Climates and Environments of the Holocene Mega thermal Maximum in China

Based on data from palynology, paleosols, paleolimnology, ice core, archeology, sea levels, etc. , we reconstructed climates and environments of the Holocene Megathermal maximum (7. 2-6. 0 ka B. P. ), particularly vegetation zones, temperatures, precipitation and sea-level fluctuations. Annual mean temperature during that period was estimated at 1 ℃ higher than today for South China, 2 ℃ higher for the Changjiang River Valley, about 3℃ higher for North China, Northeast China and Northwest China and up to 4 - 5 ℃ higher for southern Qinghai-Xizang Plateau. Relative winter temperatures increased much more than average annual temperatures. The centennial-scale warming was accompanied by the expansion of summer monsoon and recession of winter cold currents as well as northward and westward shift of vegetation zones. Higher lake levels registered in all inland lakes of Inner Mongolia, Xinjiang, Qinghai and Xizang indicated that precipitation increased to a certain extent. The Holocene highest sea level i     

Seasonal changes in coastal dynamics and morphological behavior of the central and southern Changjiang River delta

Seasonal changes in sea level, tidal range, wind, riverine discharges, nearshore SSC (suspended sediment concentration) and bed-level of intertidal flat at 4 different sites were shown. In addition, the statistical relationships between the dynamics and the behavior of the sediment surface were examined. The average intertidal elevation seems negatively correlated to sea level while positively correlated to nearshore SSC. The effect of wind on seasonal cycle of average intertidal elevation is not evident although wind is an important factor governing short-term erosion/accretion events. The influence of riverine discharges on seasonal cycle of deltaic intertidal flats is masked by other factors. It is concluded that seasonality on mudflats is more complicated than on beaches.     

Preservation potential of individual couplet and deposition rates on mudflats in the Changjiang Estuary

Non-barrier mudflats in the Changjiang Estuary is examined to obtain preservation potentials and deposition rates over different time scales. The preservation potential of couplet is ca. 46.6% within daily scale and decreases as the time-interval extending, with 9.2% on a semi-lunar scale and 3.7% on a seasonal scale. In the long term, only 1.6% of daily deposition can potentially be preserved in the tidal flat sequence and other 98.4% have been eroded and leave sedimentary discordances, discernable or un-discernable, in the mudflat deposits. A negative log-linear relationship is examined between sedimentation rates and the time spans. The length of sedimentary hiatuses on the mudflat deposition were estimated with considerable uncertainty, but it can provide from an actualistic base some further insights into the nature and origin of ancient mudflat deposits with emphasis on the sedimentary discordances.     

Distribution and forms of phosphorus in tidal flat sediments of the Yangtze Estuary and coast

The distribution and forms of phosphorus (P) were investigated in the tidal flat sediments of the Yangtze Estuary and coast. The total P contents in surface sediments range from 18.0 to 31.4 μmol · g-1 along the southern coast. The spatial and temporal distribution of P in tidal flats is closely related to the location and pollution resources, especially in association with the variation of hydrodynamic conditions. Significant variations in the forms of P in different sites were observed. P bonded with Ca(Ca-P) is the dominant mineral form in all surface sediments, organic P(Org-P) is lower. Most P is of unstable form, suggesting that P has larger potential activity. P accumulation is the main behavior process between water and sediment in the coastal environment of the Yangtze Estuary.     

Heavy metal distribution in the sediment profiles of the Sauípe River Estuary, north seashore of the Bahia State, Brazil

The distribution of the elements Al, Fe and selected heavy metals (Pb, Zn, Cd, Cu and Cr) plus the organic matter in the sedimentary substratum of the mangrove ecosystem that surrounds the estuary of the Sauípe River (Bahia, Brazil) is presented. Mangrove sediments were collected from six stations from where each sample was collected from the interface water-sediment till the depth of 50 cm and its location was in accordance to the inter-tidal transection in order to characterize the three mangrove stands (proximal, intermediate and distal spatial position in relation to the main river channel). The results are important to subsidize any further studies in this region that require local geochemical references. The substratum of the Sauípe River's mangrove is in accordance with the other mangroves that occur in the Bahia State where there is no evidence of anthropic source of pollution.     

Estimation of dissolved inorganic nutrients fluxes from the Changjiang River into estuary

Because the estuary acts as either a trap or a source or both for nutrient elements and will modify greatly the riverine transport to the ocean, it is necessary to calculate the flux from river into estuary and that from estuary into sea, respectively. The present work aims to use a long-term record of nutrients concentrations and runoff discharges on H.e Datong section (625 km inland from the Changjiang River mouth) to identify the variability of nutrients concentrations and to estimate nutrients fluxes from the Changjiang River into the estuary.     

Behavior of Zn, Cu, Pb and Cd in biota of Yangtze Estuary

The contents of zinc, copper, lead and cadmium were measured in the dominant species (plants: Scripus triquetor and Phrgrmites australis, macrobenthos: llyoplax deschampsin, Helice tridens tientsinensis, Bullacta exarata and Corbicula fluminea, and migrating waders: Calidris ruficollis and C. alpina) of the ecosystem of Yangtze Estuary, China, from 1995-1998. Results show that:     

Tidal changes in the Yellow/East China Sea caused by the rapid sea-level rise during the Holocene

Two-dimensional numerical simulations of M2 and K1 tides were performed in order to assess the effect of the rapid sea level change occurring during the last 20000 years in the Yellow/East China Sea (YECS). Results were interpreted by utilizing the difference of the dynamical nature inherited in diurnal and semi-diurnal tides. M2 tides at the coastal region south of Korea exceeded 2 m in amplitude when the sea-level was low, and decreased as the water depth become larger. In the Yellow Sea, on the other hand, tidal amplitudes were small at the low sea-level stages and increased along with the sea-level rise. The way of the increase was not monotonic but with fluctuations, which was due to the movement of the standing wave nodes. An additional experiment with closing the Taiwan Strait revealed that changing the sill depth of the strait not only affects the M2 tides around the southeastern Chinese coast, but also modifies the tides around the southwestern coast of Korea. This result recall us the significa     

The Climatic Fluctuation and Important Events of Holocene Megathermal in China

Data from various sources including the ice core, inland lakes , paleosols in loess and eolian sands, sea level fluctuations, paleozoological, archeological evidences especially palynology and bontanical studies of China are reviewed . Holocene Megathermal mainly appeared during 8. 5-3 ka BP and lasted for 5. 5 ka. There were several strong climatic fluctuations and cooling events during this period, e. g. it was an unstable temperature fluctuation phase during 8. 5-7. 2 ka BP and was accompanied with the increase of the precipitation as well as the northward and westward migration of the vegetation zone ; the rapid development of Neolithic Culture happened in this phase. It was a stable warm and wet phase from 7. 2 to 6 ka BP, i. e. Megathermal Maximum, when monsoon was rainfall almost throughout China, plants were unprecedentedly flourished, and the Yangshao Culture reached its climax. It is characterized by strong climatic fluctuation and adverse environment during 6-5 ka BP and the impact of strong     

Magnetic normalization of particle size effects in a heavy metal pollution study of intertidal sediments from the Yangzte Estuary

Magnetic, granulometric and geochemical analyses were conducted on an intertidal sediment core from the Yangtze Estuary to evaluate the possibility of normalizing samples for particle size effects in a heavy metal pollution study by means of magnetic proxies. It has been found that the magnetic parameter XARM, indicating fine grained ferrimagnetic minerals, correlates well with the clay content and organic matter concentration of the sediments. XARM also shows significant relationship with heavy metals. Therefore XARM is proposed as a proxy for clay content in the sediments, and can be used to compensate for the particle size effect in sedimentary heavy metal records, where magnetic minerals are not subject to significant post-depositional alteration.     

A Study of Impacts of Global Sea Level Rise on Salt Water Intrusion Into the Changjiang Estuary

Using the methods of empirical correlation and numerical analogue computation of the longitudinal distribution of two-dimensional chlorinity and combined with the actual situation of water supply in the Changjiang Estuary, a calculation and analysis have been made in this paper of the impacts of sea level rise of 0.5—1.0 m in the Changjiang Estuary in the next century on the probabilities of hourly chlorinity of more than 100×10~(-6), 200×10~(-6) and 250×10~(-6) during the dry season st Wusong station and on the intrusion distance of the isohalines of 1×10~(-3) and 5×10~(-3) during the ebb tide stand of the dry season in the South Branch as well as on the longitudinal distribution of the chlorinity of the South Branch in the most unfavorable situation with the minimum monthly mean discharge during the special dry year.