92 resultados para CHANGJIANG
Resumo:
To analyze and evaluate the status of organochlorine pollutants in the Changjiang (Yangtze River) estuary and adjacent waters, the concentrations of hexachlorocyclohexane (HCHs) and dichlorodiphenyltrichloroethane (DDTs) in shellfish collected in study area from 2006 to 2007 were determined with gas chromatography (GC). The concentration range of HCHs was (ND-12.13)x10(-3) mg/kg wet weight and averaged at 0.54x10(-3) mg/kg while the concentration of DDTs was in the range of (4.06-281.73) x10(-3) mg/kg with a mean of 57.52x10(-3) mg/kg in the survey areas. The concentrations of DDTs in the shellfish were higher than HCHs', so that DDTs could be considered as typical organochlorine pollutants in the areas. The concentrations of DDTs in the shellfish were higher than HCHs', so that DDTs could be considered as typical organochlorines pollutants. The HCHs in all the shellfish conformed to the first level of criterion (0.02 mg/kg) of the Marion Biology Quality (GB 18421-2001), and that of DDTs in most samples were beyond the first level (0.01 mg/kg) but conformed to the second level (0.10 mg/kg). On average, alpha-HCH and delta-HCH occupied the most part of HCHs, while O,P'-DDT and P,P'-DDT occupied the most part of DDTs. The concentrations of organocholorine pesticides in shellfish samples varied in site and in species. The highest level occurred at the Shengsi (SS), followed by Yangkougang (YKG), Lvsi (LS), Dongyuan (DY) and Beibayao (BBY), low concentrations were observed at Changsha (CS), Beidaodi (BDD), and Gouqi (GQ). The concentration of HCHs and DDTs in most sites decreased clearly from 2006 to 2007 except for YKG, DY, BDD, LYS, and SS. All of above results suggested that the study area was slightly affected by organochlorine pesticide, special by DDTs.
Resumo:
Eutrophication has become increasingly serious and noxious algal blooms have been of more frequent occurrence in the Yangtze River Estuary and in the adjacent East China Sea. In 2003 and 2004, four cruises were undertaken in three zones in the estuary and in the adjacent sea to investigate nitrate (NO3-N), ammonium (NH4-N), nitrite (NO2-N), soluble reactive phosphorus (SRP), dissolved reactive silica (DRSi), dissolved oxygen (DO), phytoplankton chlorophyll a (Chl a) and suspended particulate matter (SPM). The highest concentrations of DIN (NO3-N+NH4-N+NO2-N), SRP and DRSi were 131.6, 1.2 and 155.6 mu M, respectively. The maximum Chl a concentration was 19.5 mg m(-3) in spring. An analysis of historical and recent data revealed that in the last 40 years, nitrate and SRP concentrations increased from 11 to 97 mu M and from 0.4 to 0.95 mu M, respectively. From 1963 to 2004, N:P ratios also increased from 30-40 up to 150. In parallel with the N and P enrichment, a significant increase of Chl a was detected, Chl a maximum being 20 mg m(-3), nearly four times higher than in the 1980s. In 2004, the mean DO concentration in bottom waters was 4.35 mg l(-1), much lower than in the 1980s. In comparison with other estuaries, the Yangtze River Estuary was characterized by high DIN and DRSi concentrations, with low SRP concentrations. Despite the higher nutrient concentrations, Chl a concentrations were lower in the inner estuary (Zones 1 and 2) than in the adjacent sea (Zone 3). Based on nutrient availability, SPM and hydrodynamics, we assumed that in Zones 1 and 2 phytoplankton growth was suppressed by high turbidity, large tidal amplitude and short residence time. Furthermore, in Zone 3 water stratification was also an important factor that resulted in a greater phytoplankton biomass and lower DO concentrations. Due to hydrodynamics and turbidity, the open sea was unexpectedly more sensitive to nutrient enrichment and related eutrophication processes.
Resumo:
Both nitrate (NO (3) (-) ) and soluble reactive phosphate (PO (4) (3-) ) concentration in the freshwater end-member at the mouth of the Changjiang River have increased dramatically since the 1960s. Within the same period in the sea area, with surface salinity > 30, NO (3) (-) concentration has shown an obvious increase, PO (4) (3-) has not changed greatly and dissolved reactive silica (SiO (3) (2-) ) has deceased dramatically. An examination of the elemental ratio of NO (3) (-) to PO (4) (3-) at the mouth of the Changjiang River did not show a systematic trend from the 1960s to 2000s largely because both nutrients increased simultaneously. In comparison, the elemental ratio of dissolved inorganic nitrogen (DIN) to PO (4) (3-) in surface seawater, with salinity > 22, has shown a clearly increasing trend. Furthermore, an overall historical change of the SiO (3) (2-) :PO (4) (3-) ratio has undergone a reverse trend in this area. Based on the changes of SiO (3) (2-) :PO (4) (3-) and DIN:PO (4) (3-) ratios, we can conclude that an overall historical change of SiO (3) (2-) :DIN ratio has decreased in this area from the 1950-1960s to 2000s. The argument that phytoplankton productivity in the Changjiang estuary has been enhanced by increasing nutrient input from the riverine transport was supported by these results. A comparative study analyzing the shift of phytoplankton composition from the mid-1980s to 2000s was also made. The results indicated that the average yearly percentage of diatom species in the Changjiang estuary has decreased from 84.6% during 1985-1986 to 69.8% during 2004-2005. Furthermore, the average yearly percentage of diatom abundance in the Changjiang estuary decreased from 99.5% during to 75.5% over the same time period, while the abundance of dinoflagellates has increased dramatically, from 0.7% to 25.4%.
Resumo:
On the basis of data collected in the summer of 2006 from 27 sampling stations in the Changjiang Estuary and its adjacent waters, the ecological characteristics of macrobenthos and the relationship between the macrobenthos and the environmental factors were studied using hierarchical cluster and non-metric multidimensional scaling ( MDS). The biomass, abundance, Shannon - Wiener's and Margalef' s indices of the macrobenthos were presented. The results showed that a total of 253 maerobenthic species were found in the research region, and most. of them belong to mollusks and polychaetes. The dominant species were Cossurella dimorpha, Eocylichna cylindrella, Episiphon kiaochowwanense, Nassarius semiplicatus, Ocstergrenia variabilis and Sternaspis scutata. The average abundance of the macrobenthos was (313.15 +/- 233.4) ind. / m(2), and the average biomass was (15.2 +/- 11.2) g/ m(2). The distribution patterns of the abundance and biomass of the macrobenthos were similar. The abundance and biomass in the area close to the estuary were lower than those from the area more distant to the estuary; the central part of the research region had higher abundance and biomass than other parts of the research region. In accordance with the results, four macrobenthic communities with distinct spatial differences were identified. The low abundance and biomass in the area close to the estuary should be caused by the high sedimentation rate. The statistical analysis indicated that the depth is the most important factor affecting the distribution of macrobenthos.
Distributions of dissolved rare earth elements during estuarine mixing at the Changjiang River mouth