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Spatial and temporal distributions of nutrients (N and P) and heavy metals (Cu, Zn, Pb and Cd) in the intertidal sediments at Dongtan wetland of the Changjiang River (Yangtze River) Estuary were examined by laying one transect running seaward to landward during January, April, June, August and October of 2005. Total nitrogen (TN) and heavy metal concentrations in the intertidal sediment showed an increasing trend from open bare flat to the high marsh, with the maximum concentrations in the high marsh and the minimum values in open bare flat. In contrast, sediment total phosphorus (TP) concentrations changed little among sampling sites. One-way ANOVA found that there were significantly temporal variations of nutrients and heavy metals concentrations in the intertidal sediment (P <0.05). The concentrations of heavy metals generally showed an increasing trend from January to October. As compared with other large estuaries, heavy metal contamination in the intertidal sediment of the Changjiang River Estuary was relatively low.

In this paper, the acute toxicity of four fuel oils including F120, F180, F380 and No.-20 was evaluated by exposing the marine microalgae Chlorela spp. (Chlorophyta) and Skeletonema costatum (Bacillariophyta) in the fuel oil water accommodated fractions (WAF). The bioassay showed that F180 WAF was the most toxic to both microalgae. The 96 h EC(50) value of F180 WAF for Skeletonema costatum and Chlorela spp. was 9.41 and 13.63 mg/L expressed in concentration of total petroleum hydrocarbons, respectively. WAFs of F120, F180 and F380 were more toxic to Skeletonema costatum than to Chlorela spp. In contrast, No.-20 WAF did not show significant toxicity for both Skeletonema costatum and Chlorela spp.

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The lethal and sublethal effects of aquatic organisms by crude or fuel oils has been widely investigated, but the potential impacts of crude oils and fuel oils in the Yangtze River Estuary and East China Sea aquatic environments remain unclear. The toxicity of oils and compounds were measured in the sensitive embryonic development of the Large Yellow Croaker (Larmichthys crocea). The EC 50 of hatching rate of embryos of the Large Yellow Croaker by TJ014 and -20 were 112.4 mg/L and 510.8 mg/L, respectively; The LC 50 of after hatched of larvae by TJ014 and -20 were 8.5 mg/L and 156.2 mg/L, respectively. Acute exposures lead to the developmental abnormalities such as bradycardia, spinal curvatures, and reducing somite which is convenient and useful to evaluate the toxicity of oil. According to Values of LC 50 /EC 50 and the degree developmental abnormalities could explain the toxicity of TJ014 was larger than -20. Therefore, these results may be provided some useful proofs to analysis the aquatic environmental risk.

Algal bloom has been a subject of much research, especially the occurrence of blue-green algae (cyanobacteria) blooms and their effects on aquatic ecosystems. However, the interaction between green algae blooms and zooplankton community was rarely investigated. In the present study, the effects exerted by Scenedesmus dimorphus (green alga) bloom on the community structure of zooplankton and the top-down control of the bloom process mediated by the zooplankton were evaluated using a series of laboratory cultures. The results showed that a dense S. dimorphus bloom could change the zooplankton community structure by decreasing its diversity indices, leading to the enrichment of a particular zooplankton species, Brachionus calyciflorus. In the presence of mixed species of zooplankton, the density of S. dimorphus in the culture was decreased as determined by a change in total chlorophyll a (Chl a) concentration, which was about 200 μg L-1 lower than that of the zooplankton-free culture. Furthermore, the number of species belonging to Cladocera, Copepoda and Rotifera all decreased, with all the cladocerans disappeared in the co-culture within 2 weeks of culturing, while the density of rotifers increased from 818 (±243) ind L-1 at the time of inoculation to 40733 (±2173) ind L-1 on the 14th day post-inoculation. Grazing of S. dimorphus by the rotifer B. calyciflorus neutralized its growth, and the gradual increase in B. calyciflorus density eventually led to the collapse of the bloom. Furthermore, grazing by B. calyciflorus also led to a decrease in the maximal photochemical efficiency (Fv/Fm) of photosystem II (PSII). The combined changes occurring in the zooplankton community structure during the process of S. dimorphus bloom and the negative effects of grazing on algal growth, morphology and photosynthetic activities confirmed the key role of zooplankton in the control of algal bloom. The results of the study therefore indicated that dense algal blooms caused by non-toxic algae could still remain a threat to aquatic ecosystems.

Abstract:The lethal and sublethal effects of oils on aquatic organisms have been widely investigated, but the potential molecular impacts of oils on aquatic organisms are remaining unclear now. In order to realize the effects of diesel oil on the Zhe oyster, the RAPD (random amplified polymorphic DNA) technique was used. RAPD is a useful assay procedure for the detection of genotoxin-induced DNA damage and mutations. In the present study, the Zhe oysters were exposed to diesel oil at different concentrations and for different exposure periods. The results showed that the DNA band change in RAPD profiles of oysters following diesel oil treatment included loss of normal DNA bands, the appearance of new DNA bands and variations in DNA intensity compared to oysters not exposed to diesel oil. The effects of changes to GTS (genome template stability) were time-and concentration-dependent, the GTS of 10 mg/L was 82.46%, 80.70% and 63.15% in the 8, 16 and 32 days, the GTS of 20 mg/L was 75.44%, 71.93% and 56.14% in the 8, 16 and 32 days, the GTS of 40 mg/L was 73.68%, 70.18% and 56.14% in the 8, 16 and 32 days, respectively. The DNA polymorphisms detected by RAPD analysis could be used as a useful biomarker assay for the detection of genotoxic effects in diesel oil pollution on the oysters, and may be useful for environmental contamination risk assessment.

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