Aimin Long

Chemical speciation of 12 metals in surface sediments from the northern South China Sea under natural grain size.

pling programme, the calculated dilution suggested that even a substantial bulk water release was highly unlikely to pose a significant threat to the surrounding environment. However, if the results had suggested much higher levels of toxicity (precisely how toxic would have been determined by producing a median lethal effect, LC50, value from a dilution series) this would have alerted the salvage team to take specific precautions to minimise the release from the holds into the environment and may have informed alternative control operations such as the removal of the hold water to a tanker or via a controlled release. It is in this way that this approach could play an important part in understanding the potential effects of shipping accidents and in informing the salvage and mitigation activities. In the context of the MSC Napoli incident the use of this approach provided important assurance to the environment group, conservationists and the general public that the release of the hold contents (58,000 tonnes of water was pumped overboard during the refloating of the vessel) was unlikely to result in significant detriment to the surrounding biota. The opportunity to deploy a toxicity test method to the assessment of cargo-mediated hazard assessment in a real incident has allowed the value of such an approach to be confirmed. This approach could be applied to the hazard assessment of water within any enclosed or semi-enclosed vessel in the event of an incident at sea provided that access is available for sampling. This clearly has applications to shipping accidents but may also be applied to other scenarios. It is recommended that the approach be developed into a more standardised methodology for deployment at short notice in emergency response situations. A range of other short-term bioassays or screening tests (e.g. to assess endocrine disruption, genotoxicity etc.) could be used in this context dependent on the perceived nature of the hazard. For optimum value the method should be used in conjunction with appropriate hydrodynamic models to assess dilution factors in the vicinity of the incident.

Bacterioplankton dynamics along the gradient from highly eutrophic Pearl River Estuary to oligotrophic northern South China Sea in wet season: Implication for anthropogenic inputs

Bacterioplankton abundance (BA) and biomass (BB) from the eutrophic Pearl River Estuary (PRE) to the oligotrophic northern South China Sea (NSCS) were studied in the wet season. BA was significantly higher (p < 0.05) in PRE (12.51 ± 3.52 x 10⁸ cells L⁻¹), than in the continental shelf neritic province (CSNP, 4.95 ± 2.21 x 10⁸ cells L⁻¹) and in the deep oceanic province (OP, 3.16 ± 1.56 x 10⁸ cells L⁻¹). Nutrient-replete PRE waters (DIN > 100 μM and PO₄ > 1 μM) resulted in high chl a and BB, whereas nutrient-depleted offshore waters (DIN < 5 μM and PO₄ < 0.5 μM) had low biomass. Temperature (> 26 °C) was not the controlling factor of BA. BB was significantly correlated with chl a biomass both in PRE and NSCS. The bacteria to phytoplankton biomass (BB/PB) ratio increased clearly along the gradient from near-shore PRE (0.15) to offshore CSNP (0.93) and deep OP (2.75), indicating the important role of small cells in the open ocean compared to estuarine and coastal zones.

Composition and sources of organic matter and its solvent extractable components in surface sediments of a bay under serious anthropogenic influences: Daya Bay, China.

Organic matter of nine surface sediments from the Daya Bay was Soxhlet-extracted with a mixture of 2:1 (v/v) dichloromethane-methanol and separated into five fractions: non-aromatic hydrocarbons, aromatic hydrocarbons, ketones, alcohols, and fatty acids and asphaltenes, and analyzed to determine their bulk and biomarker composition. Marine autogenic input appears to be a major source of organic matter. Generally, non-aromatic hydrocarbons are the most dominant fraction of solvent-extractable organic matter (EOM) followed by the other four fractions in decreasing amounts: fatty acids and asphaltenes, ketones, alcohols and aromatic hydrocarbons. On average, both non-aromatic hydrocarbon fraction and fatty acid and asphaltene fraction account for approximately 40% of EOM. The sources of acyclic methyl ketones, alkanols and fatty acids were examined. For n-alkan-2-ones, allochthonous input is a more important source than marine autogenetic input; the reverse is true for n-fatty acids; for n-alkanols, allochthonous and autogenetic inputs seem comparable. Both n-alkan-2-ones and n-fatty acids in the surface sediments of different areas appear to be derived from common sources.

Spatial-temporal variability of total and size-fractionated phytoplankton biomass in the Yangtze River Estuary and adjacent East China Sea coastal waters, China

The spatial and seasonal dynamics of total and size-fractionated phytoplankton biomass (chlorophyll- a) as well as physical and chemical factors in the Yangtze River Estuary and adjacent East China Sea coastal waters were investigated from April 2002 to February 2003. Average surface total and water column integrated chlorophyll a biomass showed a clear seasonal variation in response to the Yangtze River discharge, with the highest in summer (∼4 mg m−3 and >60 mg m−2), intermediate in spring and autumn (∼1 mg m−3 and 26–28 mg m−2), and the lowest in winter (0.5 mg m−3 and <20 mg m−2). Summer maximum chlorophyll a concentrations (>10 mg m−3) occurred at intermediate salinities (∼20–30) region beyond the front zone between 112.5°E and 123°E with sufficient nutrients replenishment for phytoplankton growth. Generally, spatial distribution of size-fractionated phytoplankton showed that phytoplankton biomass was dominated by the large size fraction (>20 μm) in the turbid eutrophic estuarine and near-shore waters, while the small-sized phytoplankton (<5 μm) were dominant in the offshore stations. Phosphate was the main limiting nutrient of phytoplankton biomass in river diluted water and most near-shore stations, while dissolved inorganic nitrogen became the potential limiting nutrient in some offshore stations, except for summer when phosphate limited almost all in the whole investigation region. Controlling the inputs of phosphate loading from the Yangtze River is one of the most effective strategies for reducing the increasing eutrophication and occurrences of harmful algal blooms in Yangtze River Estuary and adjacent East China Sea coastal waters.

Saltwater Intrusion Induced by a Complete Neap Tide and Its Effect on Nutrients Variation in the Estuary of Pearl River, China

ABSTRACT Long, A.; Sun, L.; Shi, R.; Zhou, W., and Dang, A.,2013. Saltwater intrusion induced by a complete neap tide and its effect on nutrients variation in the estuary of Pearl River, China. Temporal and spatial variations of water temperature, salinity, dissolved oxygen (DO), and dissolved inorganic nutrients (, , and ) were investigated over a complete neap tide in the estuary of Pearl River, China. Obvious saltwater intrusion was observed at the lower reaches of our survey section: surface water salinity varied from 2.00‰ to 17.80‰, and bottom water salinity varied from 5.59‰ to 22.13‰. The calculated stratification index indicated that the lower reaches had intense stratification during the present neap tide. Obvious dilution of and was observed in the course of saltwater intrusion. Due to intensive decomposition and desorption-releasing action, and concentration increased with increasing water salinity. Investigation results revealed that saltwater intrusion had a significant effect on nutrient structure and probably alleviated a phosphorus-limiting situation in the estuary ecosystem. All these changes were induced to some degree by tidal currents and their associated sediment-agitation process and had a profound effect on the estuary ecosystem.

Characteristics of Phytoplankton Biomass, Primary Production and Community Structure in the Modaomen Channel, Pearl River Estuary, with Special Reference to the Influence of Saltwater Intrusion during Neap and Spring Tides

In recent decades, increasing frequency and intensity of saltwater intrusion in the Modaomen Channel has threatened the freshwater supply in the surrounding cities of the Pearl River Estuary, and ulteriorly changed the environmental conditions of the estuarine waters. Phytoplankton biomass, primary production (PP) and species composition, as well as hydrological and chemical parameters were examined along a downstream transect in the Modaomen Channel during neap tide (NT) and spring tide (ST), when a strong saltwater intrusion event occurred in late September, 2011. A total of 46 species phytoplankton were identified, including Bacillariophyta (25 species), Dinoflagellate (14 species), Chlorophyta (4 species), Cyanophyta (2 species) and Euglenozoa (1 species). The dominant species were shifted from freshwater diatoms (e.g., Melosira granulata and Melosira granulata var. angustissima) in the upper reaches to saline water diatoms (e.g., Skeletonema costatum and Coscinodiscus sp.) in the river mouth. Generally, phytoplankton density, biomass (chl-a) and PP decreased from the upper to lower reaches along the channel, and were significantly higher in NT than those of ST. There was a shift from large-sized phytoplankton (>20 μm) in the upper reaches to relative small-sized cells (5–20 μm) in the lower reaches. Compared to NT, low discharge and flow velocity, coupled with strong easterly winds during ST specially aggravated saltwater intrusion further to the upstream (~50 km from the estuary). The intruded saltwater diluted nutrients, N/P ratios, chl-a, and phytoplankton abundances, and thereby led to a decline in PP during ST.

Coupling Effects of Silicate, Iron and Other Various Abiotic Variables on Growth of Two Diatoms, Phaeodactylum Tricornutum and Thalassiosira Weissflogii and Their Silicon Utilization

The effects of various Abiotic factors, including concentrations of silicate and iron, temperature, light intensity and salinity of media on two purebred red tide diatoms, Phaeodactylum tricornutum and Thalassiosira weissflogii were investigated through single and full factorial experiments. The single-factor experiments showed diatom Phaeodactylum tricornutum had the fastest growth rate with initial silicate concentration of 200 μmol•L-1, initial iron content of 10 μmol•L-1, environmental temperature of 20oC, and light intensity of 231.25 μmol photons•m-2•s-1 respectively. Thalassiosira weissflogii grew fastest when initial silicate concentration was 250 μmol•L-1, initial iron concentration was 10 μmol•L-1, temperature of 30 o C light intensity of 231.25 μmol photons•m-2•s-1. From full factorial experiments, the main factors affecting Phaeodactylum tricornutum were iron concentration, temperature, the coupling effect of temperature and light intensity, and the coupling effect of temperature and iron concentration. The main factors affecting Thalassiosira weissflogii were temperature, the coupling effect of temperature and iron concentration, and the coupling interaction of silicate and iron. Silicates, iron ions and the coupling effects of temperature and silicate are the main factors affecting the production of biosilicon in Phaeodactylum tricornutum; and temperature, iron and the coupling effect of silicate and iron ions were the main factors influencing biosilicon produced by Thalassiosira weissflogii.