Aijun Wang

The source of natural and anthropogenic heavy metals in the sediments of the Minjiang River Estuary (SE China): implications for historical pollution.

Two sedimentary cores in the Minjiang River estuary (SE China) are documented for grain size, clay minerals, heavy metals, magnetic parameters and Pb isotopes to investigate the source and historical variation of heavy metals. The MJK9 core was collected outside of the Minjiang River estuary, and the core is composed of mixed sediments, of which ~70% from the Yangtze River and 30% from the Minjiang River. It is thus difficult to be used for tracing the human activity along the Minjiang River. In contrast, the sediments of MJK16 core which was collected in a nearshore area are primarily from the Minjiang River. The enrichment factors of the sediments were <1.5, indicating minor pollution. The results indicate that the sediments of the MJK16 core have Cu and Pb concentrations increasing since 1980, associated with the increase of magnetic mineral concentration and (206)Pb/(207)Pb and (206)Pb/(208)Pb of the sediments. We compared the Pb isotopic compositions between our results and those for the deposit mining in the Minjiang River basin, and aerosols and coal dust in south China, and considered that Pb in the sediments of the MJK16 core was derived primarily from weathered rocks as well as industrial emission (e.g. coal combustion). The sediments have anthropogenic Pb concentrations ranging from 6% in 1950 to 23.7% in 2010, consistent with the impact of rapid urban and industrial development in China.

Seasonal variation of water column structure and sediment transport in a mud depo-center off the Zhejiang-Fujian coast in China

Two surveys were conducted in December, 2008, and August, 2009, in the mud depo-center off the Zhejiang-Fujian coast (MDZFC) in the inner shelf of East China Sea to depict the seasonal variation of the water column structure and analyze the factors responsible for the variation. The results were also used to discuss the sediment transport process and formation mechanism of the MDZFC. The water column structures varied significantly between the two surveys, with respect to the temperature, salinity, and turbidity. The summer water body, with relatively high temperatures and salinities, was evidently stratified with respect to the temperature, whereas the salinity remained constant throughout the water column. The stratification restricts sediment resuspension and transport. From the north to the south, the temperature in the middle-bottom water layer slightly increased, whereas the salinity remained mostly constant. In winter, the water body, with relatively low temperatures and salinities, was well mixed vertically. The temperature and salinity both increased from the surface to the bottom toward the east (deep water) and the south. A wedge-shaped water mass, which appears as a coastal upwelling, with relatively low temperature and high salinity in summer and relatively high temperature and high salinity in winter, spread landward along the sea floor, from the sea deeper than 50xa0m, whereas the extension was relatively stronger in winter. The water turbidity in winter was clearly higher than in summer. In the surface layer, the turbidity was generally greater than 5 FTU in winter and less than 1 FTU in summer. In the bottom layer, the turbidity was much greater than 200 FTU in winter and slightly greater than 50 FTU in summer. Moreover, the turbid water layer close to the sea floor in winter can reach into an area deeper than 50xa0m with a thickness of over 10xa0m; however, it was only limited to only 30-m-deep water with a thickness of 5xa0m in summer. The differences of marine sedimentary environment in the MDZFC were attributed to the seasonal variations of hydrodynamics environment, weather conditions, sediment supplies, and seasonal circulations. The results suggest that winter is the key season for particle transportation and deposition. The bottom turbid layer is the primarily channel of sediment transport, and the upwelling currents and the oceanic front systems play an important role in the sediment deposit processes and the formation of the MDZFC.

Heavy metal accumulation during the last 30 years in the Karnaphuli River estuary, Chittagong, Bangladesh

Heavy metal contamination of aquatic environment has attracted global attention owing to its abundance, persistence, and environmental toxicity, especially in developing countries like Bangladesh. Five heavy metals, namely chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) were investigated in surface and core sediments of the Karnaphuli River (KR) estuary in Chittagong, Bangladesh, in order to reveal the heavy metal contamination history in estuarine sediments and its response to catastrophic events and human activities. The surface sediment was predominantly composed of silt and sand, and the surface sediment was contaminated with Cr and Pb. Based on the 210Pb chronology, the sedimentation rate in the inter-tidal zone of KR estuary was 1.02xa0cm/a before 2007, and 1.14xa0cm/a after 2008. The core sediment collected from 8 to 20xa0cm below the surface mainly originated from terrestrial materials induced by catastrophic events such as cyclone, heavy rainfall and landslides in 2007 and 2008. The values of contamination factor (CF) showed that the sediment became moderately contaminated with Cr and Pb in the last 30xa0years. The variation and accumulation of heavy metals in core sediment before 2000 was mainly related to natural variations in sediment sources; however, in subsequent years, the anthropogenic inputs of heavy metals have increased due to rapid physical growth of urban and industrial areas in the Chittagong city. In general, the accumulation pattern of heavy metals after normalization to Aluminum in sediments of KR estuary indicated an accelerated rate of urbanization and industrialization in the last 30xa0years, and also suggested the influence of natural catastrophic event on estuarine environment.

Geochemical analysis of sediments from a semi-enclosed bay (Dongshan Bay, southeast China) to determine the anthropogenic impact and source

The geochemical compositions of sediments in the Dongshan Bay, a semi-enclosed bay on the southeast coast of China, were obtained to identify pollutant sources and evaluate the anthropogenic impacts over the last 100 years. The results indicated that the metal flux had been increasing since the 1980s. Enrichment factor values (Pb, Zn and Cu) suggested only slight enrichment. The proportion of anthropogenic Pb changed from 9% to 15% during 2000-2014. Coal combustion might be an important contamination source in the Dongshan Bay. The historical variation in the metal flux reflected the economic development and urbanization in the Zhangjiang drainage area in the past 30 years. According to the Landsat satellite remote sensing data, the urbanization area expanded approximately three times from 1995 to 2010. The δ13C values (-21‰ toxa0-23‰) of the organic matter (OM) in the sediments indicated that the OM was primarily sourced from aquatic, terrigenous and marsh C3 plants. Nitrogen was mainly derived from aquatic plants and terrigenous erosion before the 1980s. However, the total organic carbon (TOC) contents, total nitrogen (TN) contents and δ15N had been increasing since the 1980s, which suggested that the sources of nitrogen were soil erosion, fertilizer and sewage. In addition, the TOC and TN fluxes in the Dongshan Bay had significantly increased since the 1980s, which reflected the use of N fertilizer. However, the TOC and TN fluxes significantly decreased in the past decade because environmental awareness increased and environmental protection policies were implemented.

Hydrodynamic and Biological Mechanisms for Variations in Near-Bed Suspended Sediment Concentrations in a Spartina alterniflora Marsh—a Case Study of Luoyuan Bay, China

Near-bed suspended sediment concentration (SSC) was measured at the margin and in the interior of a Spartina alterniflora marsh in Luoyuan Bay, a semi-enclosed embayment sheltered from the East China Sea, in January and July 2008. Variations in SSC at the two stations correlated to the tidal cycle: high SSC occurred in the early stage of the flood tide and the later stage of the ebb tide, while SSC was significantly lower at all other times. The SSC increased from the neap tide to the spring tide in both winter and summer. The high SSC in winter was primarily a result of stronger hydrodynamic processes, whereas the high SSC in summer was primarily attributable to biological activity. The particulate organic carbon (POC) in the S. alterniflora marsh of Luoyuan Bay primarily originates from freshwater and marine algae and phytoplankton, while the contribution of marsh detritus is limited. The contribution of POC to near-bed SSC is less than 5% in both winter and summer. During winter, the near-bed SSC was closely related to the bottom shear stress; therefore, variations in SSC were controlled by hydrodynamic processes. However, the correlation between bottom shear stress and near-bed SSC was poor in summer because of the interference of burrowing organisms during the late stage of the ebb tide. The maximum estimated contribution of turbid water flowing out of caves due to the biological activity of burrowing organisms was approximately 30.3xa0mgxa0L−1 or 20.2 to 50.5% with a mean value of 34.9% of total SSC at the late stage of the ebb tide. Our findings also suggest that the relative importance of hydrodynamic processes and biological activity can vary considerably between seasons.

Impact of Rapid Urbanization on the Modern Sedimentary Environments in a Semi-Enclosed Embayment: Tong'an Bay, Southeast China Coast

ABSTRACT Tong’an Bay (TAB) is a semienclosed embayment in the north of Xiamen Island. The sea area of TAB was mainly used for aquaculture in enclosed areas before 2003. Since 2003, the districts surrounding TAB have been undergoing a rapid urbanization process, and the scale of land used for urban construction in these districts has been continuously increasing. Under the backdrop of rapid urbanization, the coastline of TAB has largely been transformed into an artificial coastline. Due to the large scale of land reclamation and, dredging activities and the opening of the Gaoqi-Jimei (GJ) Seawall, there have been relatively significant changes in the coastal and submarine geomorphology in central northern, western, and southern TAB and Wuyuan Bay as well as a significant increase in the area where artificial submarine geomorphologies are distributed; the number of surface sediment types in the TAB has increased, and sediments in the sea area surrounding engineering projects have been coarsening; the sediment transport pattern has not significantly changed at the mouth of TAB and in central northern TAB, but the suspended sediment transport direction near the GJ Seawall has changed to a certain extent.

SUSPENDED SEDIMENT CONCENTRATIONS IN SHALLOW SEA: COMPARATIVE STUDY OF METHODS: SUSPENDED SEDIMENT CONCENTRATIONS IN SHALLOW SEA: COMPARATIVE STUDY OF METHODS

Various methods were used to measure the suspended sediment concentrations(SSCs) in the Jiulong Estuary in March,2010 and in the North Branch of Yangtze Estuary in February,2011.The synchronous acoustics and optical data including OBS,LISST-100X,ADCP,ADP and ADV were obtained by profiling and seabed tripod measurements.During these surveys,water samples were collected from the water columns form the sea surface down to the bottom,and then the SSC was retrieved by filtration in the lab.Distinctions were discerned among the above methods.Firstly,the seawater filtration is a benchmark method.Secondly,SSCs could be successfully and accurately estimated from acoustic and optical instruments installed at the same height above the seabed,with small measurement errors.Hence,they can be replaced each other,as a case of complementary measurement.Finally,the settling method may overestimate the SSCs,comparing to the filtration method due to the saline substance remained in the sediments.Thus,in order to estimate better SSCs,a suitable method should be selected according to the study purpose and local SSC background.