Influences of the Fish-Mouth Project and the Groins on the Flow and Sediment Ratio of the Yangtze River Waterway

A depth-integrated two-dimensional numerical model of current, salinity and sediment transport was proposed and calibrated by the observation data in the Yangtze River Estuary. It was then applied to investigate the flow and sediment ratio of the navigati

Abundance and conservation status of the Yangtze finless porpoise in the Yangtze River, China

middle and lower reaches of the Yangtze River, China. It is the only freshwater population of porpoises in the world and is currently listed as Endangered by IUCN. In November and December 2006 we used two boats and line transect methods to survey the entire current range of the population, except for two lakes (Poyang and Dongting). Sighting results were similar for both boats, so we pooled all data and analyzed them using two line transect models and a strip transect model. All models produced similar estimates of abundance (1111, 1225 and 1000). We then added independent estimates of the number of porpoises from the two lakes for a total estimate of approximately 1800 porpoises. Our findings indicate that the population continues to decline and that its distribution is becoming more fragmented. Our current estimate in the main river is slightly less than half the estimate from surveys between 1984 and 1991 (which was probably an underestimate). We also found an apparent gap in the distribution of porpoises between Yueyang and Shishou (similar to 150 km), where sightings had previously been common. Continued threats to Yangtze finless porpoises include bycatch in unregulated and unselective fishing, habitat degradation through dredging, pollution and noise, vessel strikes and water development. Immediate protective measures are urgently needed to ensure the persistence of finless porpoises in the Yangtze River. The survey design and analytical methods developed in this study might be appropriate for surveys of cetaceans in other river systems. (c) 2008 Elsevier Ltd. All rights reserved.

Phosphorus fractions and alkaline phosphatase activity in sediments of a large eutrophic Chinese lake (Lake Taihu)

Spatial, vertical, and seasonal variations in phosphorus fractions and in alkaline phosphatase activity (APA) were investigated in sediments in a large-shallow eutrophic Chinese lake (Lake Taihu) in 2003-2004. The phosphorus content was highest in the most seriously polluted lake area. Iron-bound phosphorus (Fe(OOH)-P) dominated (47% on average) among the phosphorus fractions determined according to Golterman (Hydrobiologia 335:87-95, 1996). Notably, organically-bound P comprised a further significant additional portion (acid-soluble + hot NaOH-extractable organic P = 25%), which was highest at the most polluted sites. The Fe(OOH)-P content was the lowest in spring (April, 2004), suggesting that degradation of organic matter led to the release of iron-bound phosphates. Sediment APA showed a significant positive relationship with both organically-bound P and Fe(OOH)-P. Consequently, organically-bound P is an important portion of the sediment phosphorus in Lake Taihu. It is mainly derived from freshly-settled autochthonous particles and from external discharges. Organically-bound P induces APA and may lead to the release of bioavailable phosphates from the organic sediments, thereby accelerating lake eutrophication.

Estimation of the natural purification rate of a eutrophic lake after pollutant removal

Pollution resulting from increased human activities is threatening Lake Donghu, its effects being characterized by serious eutrophication. A steady increase of phosphorus loading is the most important factor of the lake eutrophication. Pollution external control projects are being implemented and will be accomplished before the year 2010. In order to predict the restoration rate by the lake's self-purification after the projects of external control, a model of predicting the removal rate of total phosphorus (TP) from lake water is developed, and a brief method of estimating the release and export rate of sediment phosphorus is suggested. Results show that, on the premise of external loading fully controlled. The restoration needs about 55 years or more. Obviously, the great P pool in the sediment will be a limiting factor of preventing the improvement of water quality after the external loading is under control. Based on the estimation we conclude that after the external control projects before 2010, in order to restore the lake in a few years, although highly cost, the first step must be the sediment dredging to remove internal loading. The second step is diverting water of River Changjiang into the lake to accelerate the improvement of lake water. Otherwise, removal of pollutant sources will become meaningless. (c) 2006 Elsevier B.V. All rights reserved.

Physical modeling of localized scour for the Yangtze Estuary Waterway Improvement Project, Phase I

In order to examine the effectiveness of engineering protection against localized scour in front of the south groin-group of the Yangtze Estuary Waterway Improvement Project, Phase I, an undistorted physical model on a geometric scale of 1:250 is built in this study, covering two groins and their adacent estuarine areas. By use of rinsing fix-bed model as well as localized mobile-bed model the experiment is undertaken under bi-directional steady flow. According to the experimental results, waterway dredging leads to the increase in steram velocity, the increase being larger during the ebb than during the flood. Construction of the upstream groin has some influence on the flow patterns near the downstream groin. Localized scour in front of the groin-heads is controlled mainly by ebb flow. In the case of a riverbed composed entirely of silt, the depths of localized scour in front of the two groin-heads are 27 m and 29 m, respectively. In reality, the underneath sediment of the prototype riverbed is clay whose threshold velocity is much higher than the stream velocity in the Yangtze Estuary; therefore, the depths of localized scour will not be much larger than the thickness of the silt layer, i. e. 7.4 m and 4.7 m, respectively. The designed aprons covering the riverbed in fron of the groin-heads are very effective in scour control. Aprons of slightly smaller size can also fulfill the task of protection, but the area of localized scour increases significantly.

Trace element composition of peridotites from the southern Mariana forearc: Insights into the geochemical effects of serpentinization and/or seafloor weathering

Peridotites from the southern Mariana forearc were sampled on the landward trench slope of the Izu-Bonin-Mariana (IBM) subduction zone by dredging. These mantle wedge peridotites underwent hydration by fluid derived from a dehydrated descending slab, and later interacted with seawater after emplacement at or near the seafloor. This study investigates how these two different rock-fluid interaction processes influenced trace element distribution in the southern Mariana forearc peridotites. We measured trace element concentrations of peridotites from the southern Mariana forearc. The southern Mariana forearc peridotites are characterized by a distinct seawater-like REE pattern with an obvious negative Ce anomaly, and La shows good correlation with other REEs (except Ce). In addition, there is a great enrichment of U, Pb, Sr and Li elements, which show a distinct positive anomaly relative to adjacent elements in the multi-element diagram. For the seawater-like REE pattern, we infer that REEs are mainly influenced by seawater during peridotite-seawater interactions after their emplacement at or near the seafloor, by serpentinization or by marine weathering. Furthermore, the anomalous behavior of Ce, compared with other rare earth elements in these samples, may indicate that they have undergone reactions involving Ce (IV) when the peridotites interacted with seawater. Positive U, Pb, Sr and Li anomalies are inferred to be related to seawater and/or fluids released during dehydration of the subducting slab.

Impacts of anthropogenic activity on the recent evolution of the Huanghe (Yellow) River delta

Hydrological statistical data, remote sensing images, and bathymetric charts were used to study the recent evolution of the Huanghe (Yellow) River delta under human-induced interventions. It was clear that water and sediment discharge from the Huanghe River had dropped rapidly since 1970, particularly after 1986. The water and sediment discharges for the period of 1986-2000 were found to have been reduced to only 29.2% and 31.2% of those in the period of 1950-69. This was caused by human factors in the upper and middle reaches of the Huanghe River, including water diversion, damming and reservoir construction, and water and soil conservation. Based on the results from visual interpretation of processed Landsat (MSS or TMJETM+) images dated from 1976 to 2001 and two digital elevation models generated from bathymetric charts surveyed in 1976 and 1992, we found that human-induced reduction of water and sediment discharge led to coastline retrogradation, with the maximum mean recession rate of -0.51 km yr-1 over the period of 1976-98, and seabed erosion beyond the -20 m isobath between 1976 and 1992. Other impacts of human activities on the recent evolution of the Huanghe River delta, including tidal flats shrinking, artificial coastline increasing, land surface sinking and so on, were also analyzed. We found that: (i) the whole delta, including subaerial and subaqueous, has turned from a highly constructive period to a destructive phase; (ii) channelization and dredging were two of the main causes of delta destruction; (iii) land loss in the Huanghe River delta caused by submersion will be increased in the near future; (iv) the Huanghe River delta was becoming more fragile and susceptible to natural hazards.

River mouth bar formation, riverbed aggradation and channel migration in the modern Huanghe (Yellow) River delta, China

This paper addresses the recent (1970s-1990s) processes of river mouth bar formation, riverbed aggradation and distributary migration in the Huanghe River mouth area, in the light of station-based monitoring, field measurements and remote sensing interpretation. The results show that the morphological changes of the river mouth bar have been closely associated with the largely reduced fluvial discharge and sediment load. Landforrn development such as bar progradation occurred in two phases, i.e. before and after 1989, which correspond to faster and lower bar growth rates, respectively. Fast riverbed aggradation in the mouth channel was strongly related to river mouth bar progradation. During 1976-1996, about 2.8% of the total sediment loads were deposited in the river channel on the upper to middle delta. Therefore, the river water level rose by a few meters from 1984 to 1996. The frequent distributary channel migration, which switched the radial channel pattern into the SE-directed pattern in the mid-1980s, was linked with mouth bar formation. Marine conditions also constrain seaward bar progradation. Furthermore, the history of river mouth bar formation reflects human impacts, such as dredging and dyking in order to stabilize the coastal area. (c) 2005 Elsevier B.V. All rights reserved.

北极Gakkel超慢速扩张脊大洋橄榄岩的地球化学特征及其意义

Gakkel Ridge in Arctic Ocean is the ulstraslow spreading ridge in the world with a full spreading rate decreasing from 14 mm/yr in the western end to 7mm/yr in the eastern end. To study the histories of partial melting and melt referilization occurred in the oceanic mantle beneath Gakkel Ridge, both extremely fresh and altered abyssal peridotites from two dredge hauls (PS66-238 and HLY0102-D70) have been selected in this research. Major and trace element data of the residual minerals suggest that all samples have been refertilized by late enriched melts after low to moderate degrees (3-12%) of partial melting in the stability field of spinel, whereas some samples also inherited signatures of partial melting in stability field of garnet. Os isotopic compositions of Gakkel samples have not been significantly affected by late processes, e.g., seawater alteration and melt refertilzaiton. Samples from both dredge hauls have similar range of 187Os/188Os, from strongly unradiogenic (~0.114) in the harzburgites to approximating the inferred values of PUM (primitive upper mantle) in some lherzolites (~0.129). Inherited ancient depletion events in the harzburgites with Re-depletion age up to 2 billion years are unrelevant to the recent genesis of MORB (mid-ocean ridge basalts) beneath Gakkel Ridge. Comparisons of highly siderophile elements (HSEs) between the fresh and altered samples suggested both Pd and Re were affected and thus are mobile during seawater alteration, whereas the other HSEs (i.e., Os, Ir, Ru an Pt) are stable. The fractionated HSEs patterns in the harzburgites suggest both PPGEs (Pt and Pd) and Re can be fractionated from IPGEs (Os, Ir and Ru) at low degree of partial melting, which might be due to physical dredging of sulfide melts by silicate melts rather than equilibrium partitioning between residues and silicate melts. Inferred HSEs budget of the PUM confirm the previous study that both Ru/Ir and Pd/Ir are suprachondritic in the PUM. Some modifications of late-veneer hypothesis are required in light of the unique PUM composition. HSEs and Os isotopic compositions of Gakkel abyssal peridotites indicate the oceanic mantle is highly heterogeneous within a scale of one dredge haul (<5 km). Both depleted and fertile mantle domains are likely to be mechanically juxtaposed in the asthenosphere in a state of ‘plum pudding’. Widely distribution of ancient depleted components in the asthenosphere suggests that DMM (depleted MORB mantle) should not be synonymous with the MORB source. The later is just the fertile part of the former, i.e., the depleted components in the DMM do not or contribute little to the genesis of MORB.