Coastal East China Sea Research Articles

Polybrominated diphenyl ethers (PBDEs) in sediments of the coastal East China Sea: Occurrence, distribution and mass inventory

Polybrominated diphenyl ethers (PBDEs) of sixty-three sediment samples from the coastal East China Sea (ECS), extending ∼1000 km from the Yangtze River Estuary to the south, were measured. The levels of BDE-209 and ∑PBDE7 (sum of BDE-28, 47, 99, 100, 153, 154, 183) were 0.3–44.6 ng/g (dry weight) and nd-8.0 ng/g, respectively. BDE-209 was the predominant congener, followed by BDE-99/100. This was consistent with the historical and current usage of PBDE mixtures in China. The compositions and distribution of PBDEs suggest that the PBDEs in this area could be mainly from the coastal electronic waste dismantling/recycling and Yangtze River input. The poor correlations between TOC, grain size of sediments with PBDEs imply that the PBDE distribution is more related to their land-based inputs rather than the sediment characters in the area. The coastal ECS is an important sink of PBDEs (7.5 t/yr) in the world.

Distribution and sources of organochlorine pesticides in sediments of the coastal East China Sea

Forty-two surface sediment samples collected from the southern coastal East China Sea (ECS) were analyzed for organochlorine pesticides (OCPs). The results showed high concentrations of DDTs and parent DDT fractions in the nearshore area, suggesting that there is still a fresh input of these species from non-point sources, probably due to the recent usage of relevant products. However, for HCHs, the high concentrations with elevated β-HCH fraction were focused at the local major river estuaries, indicating that soils-released HCH input was mainly from the major river runoffs. The distribution and composition of OCPs in the coastal ECS could be more prominently controlled by the direct regional inputs rather than the general natural sorption process on particulate organic carbon. DDTs and chlordane are more important for their potential ecotoxicological risk on neighboring benthic community in the nearshore region and the local major river estuaries.

The role of shelf mud depositional process and large river inputs on the fate of organochlorine pesticides in sediments of the Yellow and East China seas

[1] The distribution and fate of dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) in sediments from the East China Sea (ECS) and the Yellow Sea (YS) were compared and studied in this work. The ECS has directly large river-dominated inputs of sediment-associated pollutants while the YS does not. The results indicated that these mud deposits of the YS and ECS were the sinks of land-originated DDTs and HCHs. The consistence of these OCP species and total organic carbon (TOC) and the sediment grain size in the YS indicated that the shelf mud depositional process was the dominant factor in controlling the distribution and fate of these organic compounds under the more homogeneous and hydrodynamic-based sedimentary conditions of the YS. The distribution of these chemicals in the coastal ECS, however, showed a much different pattern where the concentrations of DDTs and HCHs decreased with distance from the coast, and the correlations between DDTs and HCHs with TOC were very poor. This indicates that the continuous transferring of organochlorine pesticides (OCPs) into the coastal ECS by the direct riverine inputs and surface runoffs play a key role on the occurrence and fate of OCPs within this more heterogeneous environmental system.

Process-based modeling of morphodynamics of a tidal inlet system

The morphodynamic evolution of an idealized inlet system is investigated using a 2-D depth-averaged process-based model, incorporating the hydrodynamic equations, Englund-Hansen’s sediment transport formula and the mass conservation equation. The model has a fixed geometry, impermeable boundaries and uniform sediment grain size, and driven by shore-parallel tidal elevations. The results show that the model reproduces major elements of the inlet system, i.e., flood and ebb tidal deltas, inlet channel. Equilibrium is reached after several years when the residual transport gradually decreases and eventually diminishes. At equilibrium, the flow field characteristics and morphological patterns agree with the schematized models proposed by O’Brien (1969) and Hayes (1980). The modeled minimum cross-sectional entrance area of the tidal inlet system is comparable with that calculated with the statistical P-A relationship for tidal inlets along the East China Sea coast. The morphological evolution of the inlet system is controlled by a negative feedback between hydrodynamics, sediment transport and bathymetric changes. The evolution rates decrease exponentially with time, i.e., the system develops rapidly at an early stage while it slows down at later stages. Temporal changes in hydrodynamics occur in the system; for example, the flood velocity decreases while its duration increases, which weakens the flood domination patterns. The formation of the multi-channel system in the tidal basin can be divided into two stages; at the first stage the flood delta is formed and the water depth is reduced, and at the second stage the flood is dissected by a number of tidal channels in which the water depth increases in response to tidal scour.

Environmental factors and seasonal dynamics of Prorocentrum populations in Nanji Islands National Nature Reserve, East China Sea

A series of samples were collected from four stations located in Nanji Islands National Nature Reserve (NINNR) from April 2006 to March 2007. During this investigation monthly samples were gathered from July 2006 to March 2007, which delineated summer, autumn and winter conditions. During spring, from April to June 2006, a period that Prorocentrum blooms have occurred previously, water samples were collected every week. Both surface and bottom samples were obtained. Species composition, seasonal variations and vertical distribution of Prorocentrum populations as well as several chemical parameters were determined, as well as the connections between Prorocentrum dynamics and water temperature, salinity, nitrogen and phosphorus concentrations. Four Prorocentrum species were found: P. triestinum Schiller, P. donghaiense Lu, P. micans Ehrenberg and P. sigmoides Bohm. Of these, P. triestinum and P. donghaiense were the dominant species, especially in spring. Large blooms were recorded on 12 and 25 May, respectively. During these blooms Prorocentrum abundances at the surface were far greater than at depth. The temperature and salinity values observed when P. triestinum was at its maximal abundance were 18.5–19.5 °C and 29.58–30.95‰. For P. donghaiense they were 18.5–21.3 °C and 29.03–30.92‰, respectively. Higher Prorocentrum abundances were correlated with both lower inorganic phosphorus and nitrogen concentrations. Using correlation analysis, we found that the dynamics of Prorocentrum population had a strong positive correlation with the N:P ratio, and a negative correlation with absolute phosphorus concentrations. Phosphorus concentrations played a key role in the variations of Prorocentrum populations. The nutrient storage capability of Prorocentrum was greater than that of many diatom species, which may explain how Prorocentrum could grow better and bloom under lower nutrient concentrations in NINNR, as well as in the Yangtze River Estuary, Zhejiang coastal waters and East China Sea.

Atmospheric Deposition of Nutrients and Trace Elements to the Coastal Oceans: A Review

Atmospheric transport and deposition of pollutants to the coastal oceans increase dramatically due to the impacts of climate change and human activities. The paper summarizes a number of researches after 1997 on the atmospheric inputs of nutrients and trace elements to the world coastal oceans with emphasis on the eastern China seas. The atmospheric fluxes of nitrogen and phosphorus to the coastal oceans range from 13 to 73 mmol N /( m2. a) and 0. 11 to 1. 6 mmol P /( m2.a) ,respectively. North Sea appears to be influenced by relatively higher atmospheric flux of nitrogen ( 70 mmol N /( m2.a) ) compared to the eastern coast of North America ( 50 mmol N / ( m2.a) ) and eastern China seas ( 50 mmol N /( m2.a) ). Mediterranean Sea and the Gulf of Aqaba ( Red Sea) receive the lowest fluxes of nitrogen as well as phosphorus from the atmosphere. The deposition fluxes of trace elements vary significantly in both time and space with the highest flux approximately 3 orders of magnitude higher than the lowest one. The flux variations of crustal-dominated trace elements such as Al and Fe are strongly related to the dust transport and agricultural activities of adjacent land,while atmospheric fluxes of non-crustal trace elements like Cd,Zn and Pb are mainly determined by industrial and mobile emissions. Atmospheric inputs of trace elements can partly dissolve into the seawater with the solubility ranging from a few percent to 50% and that portion may become bioavailable and thereby influence the costal ecosystem. For many coastal oceans including East China Sea and Yellow Sea,atmospheric fluxes of nutrients and certain trace elements may exceed their riverine inputs. Atmospheric deposition contributes significantly to the coastal eutrophication,and its episodic nature can enhance primary productivity within a short period,which may induce a harmful algal bloom ( red tide). Trace element deposition may have toxic effects on specific phytoplankton and influence both primary productivity and ecosystem structure of the coastal area. Further studies should be conducted for accurate estimation of atmospheric fluxes of various pollutants to the coastal oceans and for understanding their roles in marine phytoplankton growth.

EVOLUTION OF THE TSUSHIMA WARM CURRENT DURING THE HOLOCENE: SEDIMENTOLOGICAL AND GEOCHEMICAL RECORDS ON THE SOUTHWESTERN SLOPE OF EAST/JAPAN SEA

Synthetic analyses on sedimentology and geochemistry of a sediment core with high deposition rate collected under the Tsushima Warm Current (TWC) axis on the southwestern slope of East/Japan Sea were carried out,in order to discuss the formation and evolution of TWC during the Holocene. Based on them,we got very similar results to those from paleoceanographical method in nearby areas. Thus,sedimentological and geochemical methods were offered for the future study on TWC evolution in the study area. Totally,there were five main evolution periods of TWC recorded in the study core. In the early Holocene,that is 9.6 kaBP,TWC began to weakly enter into the East/Japan Sea,together with the East China Sea Coast Water (ECSCW) enriched in nutrient matter,which led to the transfer of bottom environment from anoxic to oxic. At 6.5 kaBP,the modern current mode dominated by TWC in the southern East/Japan Sea finally formed,whereas the influence of ECSCW almost disappeared. After that,TWC obviously weakened. At 3.0 kaBP,TWC strengthened again to almost reach its present level,since then the circulation structure has been relatively stable,except for a weak depression of TWC during 2.0~0.7 kaBP.

Temporal and spatial variability in nitrogen uptake kinetics during harmful dinoflagellate blooms in the East China Sea

Temporal and spatial variability in the kinetic parameters of uptake of nitrate (NO 3 −), ammonium (NH 4 +), urea, and glycine was measured during dinoflagellate blooms in Changjiang River estuary and East China Sea coast, 2005. Karenia mikimotoi was the dominant species in the early stage of the blooms and was succeeded by Prorocentrum donghaiense. The uptake of nitrogen (N) was determined using 15N tracer techniques. The results of comparison kinetic parameters with ambient nutrients confirmed that different N forms were preferentially taken up during different stages of the bloom. NO 3 − ( V max 0.044 h −1; K s 60.8 μM-N) was an important N source before it was depleted. NH 4 + ( V max 0.049 h −1; K s 2.15 μM-N) was generally the preferred N. Between the 2 organic N sources, urea was more preferred when K. mikimotoi dominated the bloom ( V max 0.020 h −1; K s 1.35 μM-N) and glycine, considered as a dominant amino acid, was more preferred when P. donghaiense dominated the bloom ( V max 0.025 h −1; K s 1.76 μM-N). The change of N uptake preference by the bloom-forming algae was also related to the variation in ambient N concentrations.

Seasonal variations of sediment discharge from the Yangtze River before and after impoundment of the Three Gorges Dam

Over the past decades, > 50,000 dams and reforestation on the Yangtze River (Changjiang) have had little impact on water discharge but have drastically altered annual and particularly seasonal sediment discharge. Before impoundment of the Three Gorges Dam (TGD) in June 2003, annual sediment discharge had decreased by 60%, and the hysteresis of seasonal rating curves in the upper reaches at Yichang station had shifted from clockwise to counterclockwise. In addition, the river channel in middle-lower reaches had changed from depositional to erosional in 2002. During the four years (2003–2006) after TGD impoundment, ~ 60% of sediment entering the Three Gorges Reservoir was trapped, primarily during the high-discharge months (June–September). Although periodic sediment deposition continues downstream of the TGD, during most months substantial erosion has occurred, supplying ~ 70 million tons per year (Mt/y) of channel-derived sediment to the lower reaches of the river. If sand extraction (~ 40 Mt/y) is taken into consideration, the river channel loses a total of 110 Mt/y. During the extreme drought year 2006, sediment discharge in the upper reaches drastically decreased to 9 Mt (only 2% of its 1950–1960s level) because of decreased water discharge and TGD trapping. In addition, Dongting Lake in the middle reaches, for the first time, changed from trapping net sediment from the mainstem to supplying 14 Mt net sediment to the mainstem. Severe channel erosion and drastic sediment decline have put considerable pressure on the Yangtze coastal areas and East China Sea.

The sedimentary fluxes of polycyclic aromatic hydrocarbons in the Yangtze River Estuary coastal sea for the past century

Polycyclic aromatic hydrocarbons (PAHs) in two (210)Pb dated sediment cores from the coastal East China Sea, strongly influenced by the discharge from the Yangtze River, were determined to help to reconstruct the economic development over the past century in East China. The variations in PAH concentrations and fluxes in the sediment cores were primarily due to energy structure change, severe floods and dam construction activities. The impact on PAHs by the river discharge overwhelmed the atmospheric depositions. The profiles of PAH fluxes and concentrations as well as compositions in the cores revealed the transformation from an agricultural economy to an industrial one especially after the 1990s' in the region. PAHs in the study area were dominated by pyrolytic sources.

Paleo-Tsushima Water and its effect on surface water properties in the East Sea during the last glacial maximum: Revisited

The semi-enclosed deep marginal East Sea is known by limited sill flow and low sea-surface salinity during the last glacial maximum (LGM) when sea level was about 130 m lower than the present level. Although three straits (the Tsugaru, the Soya and the Tartar) with shallower than 130 m sills were completely closed, the Korea Strait with a maximum sill depth of 140 m seems to have persisted as a partial connection to the East Sea, allowing a sill flow. The volume transport at the Korea Strait during the LGM is estimated at approximately 0.3–1.1×10 12 m 3/yr, by using bathymetry, seismic reflection profiles and current data. The low sea-surface salinity has been explained by the East China Sea Coast Water (ECSCW) and high precipitation. However, the existing geological observations indicate that precipitation was reduced in the glacial East Sea. The high-resolution numerical simulation results predict that evaporation (2.16 mm/day) exceeded precipitation (1.43 mm/day), further suggesting net evaporation (evaporation minus precipitation) rates (0.2×10 12 m 3/yr) over the LGM East Sea. This signifies that the precipitation was not the factor lowering surface paleosalinity and that the paleo-Tsushima Water carried a huge amount of freshwater from the ECSCW than previously expected. The calculated surplus evaporation (0.2×10 12 m 3/yr) and sill flow (0.3–1.1×10 12 m 3/yr) are not identical, but they could be oceanographically considered as similar. The comparison between both values implies that most of the throughflow ultimately escaped the East Sea through the evaporation process during the LGM. The regional sea level in the almost isolated East Sea might be largely maintained by a rough balance between incoming throughflow and outgoing evaporation during the LGM. The geographic restriction due to lowered sea level and lower surface salinity by limited vertical mixing in the glacial East Sea are analogous to modern oceanographic features in the Black Sea.

Algorithm for HF radar vector current measurements

A new algorithm is proposed, called the stream function method (SFM) for producing vector current maps from radial data measured by dual-site high frequency surface wave radar (HFSWR). In SFM, a scalar stream function is constructed under some oceanographic assumptions. The function describes the two-dimensional (2-D) ocean surface water motion and is used to obtain the distribution of vector currents. The performance of SFM is evaluated using simulated radial data, which demonstrates that SFM has advantages over typical vectorial combination methods (VCM) both in error acceptance and robustness, and excels another method based on least-squares fitting (LSF) in recovering the complicated current models. Furthermore, SFM is capable of providing the total currents based on radials from single-site radar. We also test the assumptions of horizontal non-divergence in the simulation. The new algorithm is applied to the field experiment data of Wuhan University’s ocean state measuring and analyzing radar (OSMAR), collected in the coastal East China Sea during April 11–17, 2004. Quantitative comparisons are given between radar results by three current algorithms and in-situ current meter measurements. Preliminary analysis of the vertical current shear is given based on the current meter measurements.

Coastal upwelling in the East China Sea in winter

The dynamic mechanisms of the upwelling off the East China Sea (ECS) coast in wintertime are studied. First, the upwelling signals off the ECS coast are identified by the observed temperature, salinity, nutrients, and dissolved oxygen data obtained during the cruises in January 1999. The MASNUM wave‐tide‐circulation coupled model is then employed to simulate the hydrography of the ECS. Comparisons between the simulations and observations show that the model performance is satisfactory. On the basis of successful simulation, four numerical experiments are conducted to investigate the upwelling mechanisms. The results suggest that the density (or salinity) front, which separates the inshore Low Salinity Coastal Water and the offshore Taiwan Warm Current (TWC), is the primary inducement for the upwelling. Owing to strong density gradient, the baroclinic pressure gradient force (PGF) is quite large near the frontal zone, and this PGF elicits an upwelling branch along the topography slope. Wind, TWC, and tide affect the density front in extension and intensity, thus exerting subsidiary influences on the upwelling. According to Ekman's theory, the northerly monsoon is downwelling favorable. However, the net effects of wind on the upwelling off the ECS coast in winter are positive because it drives the Changjiang River Diluted Water (CDW) flowing southward and forms the density front. Similarly, the resultant effects of TWC on the upwelling are negative for obstructing the pathway of CDW. Tide contributes to the upwelling because tidal mixing facilitates the expansion of CDW.