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1.
《Applied Geochemistry》1996,11(3):409-423
Determining metal bioavailability is critical in assessing the necessity to remediate contaminated sediments. In the Halls Brook Holding Area Pond (HBHAP) sapropel, As (3000 mg/kg), and Cr (1400 mg/ kg), are sequestered by amorphous Fe(OH)3 (KdAs=560; KfCr=59,0001/kg), while Pb solubility is limited by PbS(am). Fillet As concentrations in detritivorous and omnivorous fish were similar in the HBHAP (1.19 mg/kg), and the adjacent unimpacted Phillips Pond (1.18 mg/kg). Cr and Pb in both HBHAP and Phillips Pond fish were below analytical detection limits, except for one (0.73 mg/kj Pb), in the HBHAP. The low sediment bioaccumulation factors for As, Cr, and Pb (6.5 × 10−4, < 1.1 × 10, and 1.8 × 10−6, respectively in HBHAP) suggest that the sediment acts to sequester metals, rendering them non-bioavailable due to precipitation of solids, and sorption to iron phases. 相似文献
2.
Sediment cores were collected from deep-water areas of Lake Chenghai, China in June 1997. The vertical profile of 137Cs activity gives reliable geochronological results. The results also indicate that sediment accumulation rates in deep-water areas of Lake Chenghai were relatively constant in recent decades, averaging 0.43 g cm− 2 y− 1, despite a variable organic carbon influx. 210Pbeq (= 226Ra) activity was relatively constant also, with an average value of 54.3 ± 3.2 Bq kg− 1. Vertical profiles of 210Pbex (= 210Pbtotal − 226Ra) decreased exponentially, resulting in somewhat lower sediment accumulation rates (0.3 g cm− 2 y− 1). These lower rates are likely less reliable, as the relatively large fluctuations in 210Pbex activities correlate closely to the organic carbon (Corg) content of the sediments. For example, the vertical profile of 210Pbex activity displays peaks at mass depths of 3.7-4.7 g cm− 2 (10-12 cm) and 10-11 g cm− 2(25-28 cm), similar to the maxima in the vertical profile of Corg. This phenomenon must be related to the delivery of particulate organic matter (POM) from the water to the sediments, or to watershed soil erosion. Since the mean atomic ratios of Horg / Corg and Corg / Norg in Lake Chenghai sediments are 5.5 and 7.0, respectively, indicating that POM was predominantly derived from the remains of authigenic algae, this eliminates watershed erosion rates as a primary control on lake sedimentation rates as resolved by 210Pbex. Sedimentation fluxes (F(Corg)) of particulate organic carbon since 1970 varied between 60 to 160 g m− 2 y− 1, and appeared to closely influence variations in 210Pbex concentrations. For example, sedimentation fluxes of 210Pbex (F(210Pbex)) showed maxima in the years 1972-1974 and 1986-1989, likely reflecting historical variations of lake biological productivity or carbon preservation. 相似文献
3.
The distribution of 210Pb, 137Cs, and Ambrosia (ragweed) pollen in two sediment cores from Lake Ontario and in three cores from Lake Erie provides independent estimates of sediment accumulation rates. Geochronology with 210Pb is based on radioactive decay of the isotope following burial in sediments. The method can reveal with precision changes in sedimentation occurring over the past 100 yr or so. Geochronologies with 137Cs and Ambrosia are based on the occurrence of a horizon corresponding, respectively, to the onset of nuclear testing 25 yr ago and to regional forest clearance in the middle 1800s. These methods provide estimates of long-term average sediment accumulation rates. In all but one core, the distributions of 137Cs and 210Pb indicate no physical mixing of near-surface sediments. In two cores, including one from central Lake Erie collected by diver, all three estimates of sedimentation rates are in excellent agreement. In two other cores, rates based on 210Pb are significantly higher than those inferred from Ambrosia pollen profiles. Lower average rates appear to result from occasional massive losses of sediments. Such events, apparent in the distribution of 210Pb but not in pollen records, correlate with the occurrence of major storm surges on the lakes during this century. In one core from western Lake Erie, exponential distributions of both 210Pb and Ambrosia appear to be artifacts which may result from extensive biological or physical reworking of sediments in shallow water (11 m). Previous indications of increased sedimentation in Lake Erie since about 1935 based on Castanea (chestnut) pollen data are not substantiated. 相似文献
4.
Triplicate porewater lead concentration profiles were determined on six occasions in a Canadian Shield lake. Total Pb concentrations were also measured in a dated core obtained at the same site. This information, as well as an extensive dataset comprising ancillary geochemical measurements on porewaters and sediment and the population densities of benthic animals, is used in a one-dimensional transport-reaction diagenetic model to investigate the transport and mobilization of Pb in these sediments. Application of the model consistently indicates the presence of a zone of Pb production to the porewaters that lies above a zone of Pb consumption. The profiles of various porewater constituents and thermodynamic calculations indicate that Pb is mobilized in the zone of production by the reductive dissolution of iron oxyhydroxides, whereas it is removed in the zone of consumption by precipitation as a solid sulfide. Rate constants are estimated for reductive iron dissolution (kdFe(III) = 2.0 ± 0.5 × 10−1 cm3 mol−1 s−1), Pb adsorption on iron oxyhydroxides (kadsPb = 98 ± 55 cm3 mol−1 s−1), and Pb precipitation (kpptPb = 8 × 10−20 mol cm−3 s−1 to 16 ± 13 × 10−22 mol cm−3 s−1, depending on the solubility product assumed for the precipitation of PbS). According to model calculations, diagenetic processes, such as remobilization, molecular diffusion, bioturbation, and bioirrigation have a negligible influence on the solid phase Pb profile. In agreement with this finding, the present-day fluxes of dissolved Pb by diffusion (JDPb = −6.5 × 10−11 mol cm−2 yr−1), bioturbation (JBPb = −1.1 × 10−13 mol cm−2 yr−1), and bioirrigation (JIPb = −1.5 × 10−11 mol cm−2 yr−1) are small compared to the flux of Pb deposited with settling particles (JSPb = 5.3 × 10−9 mol cm−2 yr−1). 相似文献
5.
《Applied Geochemistry》2004,19(3):323-334
In the present study the distribution of TBT between solid and water phase as a function of several parameters was determined. Two types of clay minerals (Na-montmorillonite SWy and kaolinite KGa) and quartz sand were used as sorbents in conventional batch experiments. Sorption coefficients (Kd) followed the order montmorillonite (89 l/kg) > kaolinite (51 l/kg) > quartz (25 l/kg), while for sorption coefficients normalized to the surface area (Kd′) an opposite trend was observed, with the lowest value determined for montmorillonite (2.79 × 10−3 l/m2) and the highest for quartz sand (8.04 × 10−2 l/m2). The results demonstrate that numerous environmental parameters influence the adsorption process of TBT, such as solid/solution ratio, clay content and salinity. Another important factor governing TBT adsorption is pH, because it affects both the TBT species in the water phase as well as the surface properties of the mineral phase. The maximum of TBT adsorption onto clays was always around pH 6–7. According to the data, it is evident that the content of organic matter in the solid phase plays an important role on TBT adsorption, either as particulate organic matter (POM) or organic matter adsorbed to mineral particles (AOM). Experiments were carried out with well characterized organic matter and the results showed a linear increase of Kd from 51 up to 2700 l/kg upon the addition of 5% of particulate organic matter to pure phased kaolinite. TBT adsorption onto mineral surfaces, which were previously enriched with adsorbed organic matter, was investigated at different pH. The present study points to the importance of identifying and characterizing sorbents and envrionmental conditions, in order to predict and model TBT distribution in natural systems. 相似文献
6.
210Pb具有百年时间尺度沉积计年的重要价值。210Pbex计年假设：沉积物是封闭系统；进入水体的210Pb能有效地转移到沉积物中并不发生沉积后迁移；非过剩210Pb与其母体226Ra保持平衡。210Pbex计年可用稳定输入通量-稳定沉积物堆积速率模式、常量初始浓度模式或恒定补给速率模式。沉积物柱芯必须保持原态并以0．5～1cm间隔分截；用相应层节226Ra校正。沉积物表层混合作用及222Rn的丢失可能导致顶部210Pbex异常。季节性缺氧湖泊沉积物顶部可能存在210Pb及210Po的再迁移。210Pb与137Cs两种计年方法原理上具有根本差别。210Pb，137Cs与沉积纹理方法对比是准确计年的重要保证。 相似文献
7.
《Resource Geology》2018,68(3):244-257
Alternation layered lake sediment that had accumulated over a period of 22 years, from 1990 to 2012, was collected from the Tamagawa Dam Lake, which is located in the northeastern part of Akita Prefecture. The lake water is acidified (pH = 4.1) by the inflow of high‐acidic thermal water (pH = 1.2) from the Obuki Hot Spring, the main hot spring in the Tamagawa Hot Spring area. The vertical variations in Si, Al, Fe, Ti, and Pb contents of the sediment were determined by XRF, EPMA, and LA‐ICP‐MS in order to clarify the sedimentation processes of the lake sediment. The layers consisting of the sediment could be mostly classified into three types: dark brown, yellowish brown, and reddish layers. The contents of Si, Al, Fe, and Ti corresponded to the variation in color of each layer in the sample. Based on the Si, Al, and Fe contents in the sediment of Tamagawa Dam Lake, the sources of these elements were classified as detrital origin in dark brown and yellowish brown layers (Si, Al, and Ti) and chemical precipitate origin in reddish layers (Fe). Detrital components were derived from volcanic rocks in the watershed of Tamagawa Dam Lake. The variation of Pb content did not accord with the color of layers. The content of Pb in the sediment of Tamagawa Dam Lake ranges from 45 to 522 ppm. The vertical variation of Pb content in sediment corresponded to the temporal variation of Pb content in thermal water from the Obuki Hot Spring from 1990 to 2012. A large influence of hydrothermal activity of the Tamagawa Hot Spring on the vertical distribution of Pb was found during the active period of the Obuki Hot Spring, resulting in high Pb content within layers at 5–8 cm from the bottom of the sample. T‐Fe2O3‐rich reddish layers were also found in this range. Therefore, it is assumed that T‐Fe2O3 and Pb originated from Obuki Hot Spring and precipitated in Tamagawa Dam Lake. However, no correlation was found between T‐Fe2O3 and Pb contents for any of the dark brown, yellowish brown, and reddish layers. Some layers with high Pb content were also found to have high SiO2 and Al2O3 contents. These findings indicate that there are several possibilities for the sedimentation process of Pb. The sedimentation of Pb as well as that of T‐Fe2O3 in Tamagawa Dam Lake provides a good example of the accumulation of elements by chemical precipitation away from the source of elements. 相似文献
8.
Weathering and anthropogenic influences on the water and sediment chemistry of Wular Lake,Kashmir Himalaya 总被引：1，自引：1，他引：0
Javid A. Sheikh Gh. Jeelani R. S. Gavali Rouf Ahmad Shah 《Environmental Earth Sciences》2014,71(6):2837-2846
This paper presents a study on the Wular Lake which is the largest fresh water tectonic lake of Kashmir Valley, India. One hundred and ninety-six (196) water samples and hundred (100) sediment samples (n = 296) have been collected to assess the weathering and Anthropogenic impact on water and sediment chemistry of the lake. The results showed a significant seasonal variability in average concentration of major ions being highest in summer and spring and lower in winter and autumn seasons. The study revealed that lake water is alkaline in nature characterised by medium total dissolved solids and electrical conductivity. The concentration of the major ion towards the lake central showed a decreasing trend from the shore line. The order of major cations and anions was Ca2+ > Mg2+ > Na+ > K+ and HCO3 ? > SO4 2? > Cl?, respectively. The geochemical processes suggested that the chemical composition lake water is mostly influenced by the lithology of the basin (carbonates, silicates and sulphates) which had played a significant role in modifying the hydrogeochemical facies in the form of Ca–HCO3, Mg–HCO3 and hybrid type. Chemical index of alteration values of Wular Lake sediments reflect moderate weathering of the catchment area. Compared to upper continental crust and the post-Archean Shale, the sediments have higher Si, Ti, Mg and Ca contents and lower Al, Fe, Na, K, P, Zn, Pb, Ni, Cu content. Geoaccumulation index (Igeo) and US Environmental Protection Agency sediment quality standards indicated that there is no pollution effect of heavy metals (Zn, Mn, Pb, Ni and Co).The study also suggested that Wular Lake is characterised by both natural and anthropogenic influences. 相似文献
9.
Robert W Talbot 《Geochimica et cosmochimica acta》1984,48(10):2053-2063
The vertical distribution of 210Pb and 210Po in the dissolved (<0.4 μm) and the paniculate (>0.4 μm) phases was measured in Crystal Lake, Wisconsin, to examine the spatial and temporal variability during the seasonal cycle of this oligotrophic lake. The concentration of unsupported 210Pb in the water column is maintained principally by atmospheric input. However, most of the 210Po in Crystal Lake is produced in situ from radioactive decay of 210Pb.Mass balance considerations indicated that the removal rates of 210Pb and 210Po from the water column to the sediment varied temporally by nearly an order of magnitude. During transient periods of high biological productivity, a large net flux of these nuclides into the sediment occurred. In addition, 210Pb was rapidly stripped from the water column during fall turnover. It was during these short-lived events that most of the annual net removal of 210Pb and 210Po occurred. The mean removal residence time was estimated to be 0.095 yr for 210Pb and 0.26 yr for 210Po. These residence times suggest that there is a difference between 210Pb and 210Po in the extent of their recycling in the water column. Calculations indicated that there was a cyclic response of the water column 210Po inventory corresponding to successive time periods where there was a net loss or net gain. This cycling is attributed to rapid biological removal and subsequent release from the sediment of freshly deposited 210Po. For 210Pb, replenishment of the water column appeared to occur mainly from atmospheric input. 相似文献
10.
Françoise Elbaz-Poulichet Attila Nagy Tibor Cserny Piroska Pomogyi 《Aquatic Geochemistry》1996,2(4):379-402
Mn, Sr, Ba, Rb, Cu, Zn, Pb and Cd concentrations have been measured seasonally in the water and deposited sediments of the system comprising: Zala river (main input) — Lakes Kis-Balaton 1 and 2 (small artificial lakes created in a former bay of Lake Balaton) — Keszthely bay (hypertrophic part of Lake Balaton). The concentrations of the trace elements together with pH, alkalinity, dissolved cations (Ca2+, Mg2+, Na+, and K+), dissolved inorganic ligands (Cl–, SO4
2–), particulate Al, Ca, inorganic and organic carbon are used to assess the contamination of the study area and biogeochemical processes controlling trace element concentrations. Thermodynamic speciation calculations have also been utilized to enhance our understanding of the system. In the sediments Rb, Ba, Cu and Zn concentrations were mainly controlled by the abundance of the aluminosilicate fraction. Strontium was mainly associated with the calcium carbonate fraction. The aluminosilicate fraction constitutes a major sink for Mn and Cd but the concentration of these elements are also strongly related to calcite precipitation. The main processes that control the dissolved distribution of trace elements in the Balaton system were: solid phase formation (carbonate) for Mn; coprecipitation with calcite for Sr, Ba, Rb and possibly Mn and Cd; adsorption/desorption processes (pH dependent) for Zn and Pb; solubilization of Mn and precipitation of Cd and Cu in reed covered wetland areas where anoxic conditions were probably existing during the warm season. A preliminary budget of atmospheric and river input to Lake Balaton has also been outlined. Although Lake Balaton, is subjected to anthropogenic inputs mainly from agricultural and domestic activities, their impact on trace element concentrations in the Balaton system is very limited due to the efficiency of removal processes (i.e. adsorption and co-precipitation) and to high sedimentation rates and strong sediment re-suspension. Anthropogenic inputs are only detected for Pb. 相似文献
11.
To test the relative effectiveness of stream water and sediment as geochemical exploration media in the Rio Tanama porphyry copper district of Puerto Rico, we collected and subsequently analyzed samples of water and sediment from 29 sites in the rivers and tributaries of the district. Copper, Mo, Pb, Zn, SO42?, and pH were determined in the waters; Cu, Mo, Pb, and Zn were determined in the sediments. In addition, copper in five partial extractions from the sediments was determined. Geochemical contrast (anomaly-to-background quotient) was the principal criterion by which the effectiveness of the two media and the five extractions were judged.Among the distribution patterns of metals in stream water, that of copper most clearly delineates the known porphyry copper deposits and yields the longest discernable dispersion train. The distribution patterns of Mo, Pb, and Zn in water show little relationship to the known mineralization. The distribution of SO42? in water delineates the copper deposits and also the more extensive pyrite alteration in the district; its recognizable downstream dispersion train is substantially longer than those of the metals, either in water or sediment. Low pH values in small tributaries delineate areas of known sulfide mineralization.The distribution patterns of copper in sediments clearly delineate the known deposits, and the dispersion trains are longer than those of copper in water.The partial determinations of copper related to secondary iron and manganese oxides yield the strongest geochemical contrasts and longest recognizable dispersion trains. Significantly high concentrations of molybdenum in sediments were found at only three sites, all within one-half km downstream of the known copper deposits. The distribution patterns of lead and zinc in sediments are clearly related to the known primary lead-zinc haloes around the copper deposits. The recognizable downstream dispersion trains of lead and zinc are shorter than those of copper. 相似文献
12.
Juanle Wang Eryang Chen Ge Li Lu Zhang Xiaoming Cao Yongjie Zhang Yujie Wang 《Environmental Earth Sciences》2018,77(16):590
Concentrations of suspended solids in lakes can affect the latter’s primary productivity and reflect changes in sediment deposition. Determining the temporal and spatial distribution of suspended solid concentrations has important significance in lake water environmental management; this is particularly urgent for Poyang Lake, the largest freshwater lake in China. In this study, suspended solid concentration inversion models for Poyang Lake were created using a semi-empirical method with regression analysis between continuously measured suspended solid concentration data and multi-band moderate-resolution imaging spectroradiometer images for spring, summer, autumn, and winter from 2009 to 2012. The coefficient of determination (R2) is from 0.6 to 0.9 and the average relative error for the accuracy verification was between 10 and 30%. The seasonal distributions of suspended solid concentrations in Poyang Lake from 2000 to 2013 were then obtained using optimal reversal models. The results showed that the seasonal variation in suspended solid concentrations had a “W” shape in which high spring and autumn and low summer and winter values. The suspended solid concentrations increased annually from 2000 to 2013 and were mainly distributed in the northern and central portions of the lake, with lower values along the shorelines. Further analysis indicated that the large difference in water level between the wet and dry seasons is an important factor in explaining these seasonal variations. Moreover, the suspended solid concentrations were poorly correlated with water temperature and chlorophyll-a concentration but more highly correlated with the deferred chlorophyll-a concentration. 相似文献
13.
Yinian Zhu Bin Huang Zongqiang Zhu Huili Liu Yanhua Huang Xin Zhao Meina Liang 《Geochemical transactions》2016,17(1):2
Background
The interaction between Ca-HAP and Pb2+ solution can result in the formation of a hydroxyapatite–hydroxypyromorphite solid solution [(PbxCa1?x)5(PO4)3(OH)], which can greatly affect the transport and distribution of toxic Pb in water, rock and soil. Therefore, it’s necessary to know the physicochemical properties of (PbxCa1?x)5(PO4)3(OH), predominantly its thermodynamic solubility and stability in aqueous solution. Nevertheless, no experiment on the dissolution and related thermodynamic data has been reported.Results
Dissolution of the hydroxypyromorphite–hydroxyapatite solid solution [(PbxCa1?x)5(PO4)3(OH)] in aqueous solution at 25 °C was experimentally studied. The aqueous concentrations were greatly affected by the Pb/(Pb + Ca) molar ratios (XPb) of the solids. For the solids with high XPb [(Pb0.89Ca0.11)5(PO4)3OH], the aqueous Pb2+ concentrations increased rapidly with time and reached a peak value after 240–720 h dissolution, and then decreased gradually and reached a stable state after 5040 h dissolution. For the solids with low XPb (0.00–0.80), the aqueous Pb2+ concentrations increased quickly with time and reached a peak value after 1–12 h dissolution, and then decreased gradually and attained a stable state after 720–2160 h dissolution.Conclusions
The dissolution process of the solids with high XPb (0.89–1.00) was different from that of the solids with low XPb (0.00–0.80). The average K sp values were estimated to be 10?80.77±0.20 (10?80.57–10?80.96) for hydroxypyromorphite [Pb5(PO4)3OH] and 10?58.38±0.07 (10?58.31–10?58.46) for calcium hydroxyapatite [Ca5(PO4)3OH]. The Gibbs free energies of formation (ΔG f o ) were determined to be ?3796.71 and ?6314.63 kJ/mol, respectively. The solubility decreased with the increasing Pb/(Pb + Ca) molar ratios (XPb) of (PbxCa1?x)5(PO4)3(OH). For the dissolution at 25 °C with an initial pH of 2.00, the experimental data plotted on the Lippmann diagram showed that the solid solution (PbxCa1?x)5(PO4)3(OH) dissolved stoichiometrically at the early stage of dissolution and moved gradually up to the Lippmann solutus curve and the saturation curve for Pb5(PO4)3OH, and then the data points moved along the Lippmann solutus curve from right to left. The Pb-rich (PbxCa1?x)5(PO4)3(OH) was in equilibrium with the Ca-rich aqueous solution.Graphical abstractLippmann diagrams for dissolution of the hydroxypyromorphite–hydroxyapatite solid solution [(PbxCa1?x)5(PO4)3OH] at 25??C and an initial pH of 2.00.
14.
The Onyx River (Wright Valley, Antarctica) is a dilute meltwater stream originating in the vicinity of the Wright Lower Glacier. It acquires a significant fraction of its salt content when glacial meltwaters contact Wright Valley soils at Lake Brownworth and the concentrations of all ions increase with distance along the 28-km channel down to Lake Vanda. Average millimolar concentrations of major ions at the Vanda weir during the 1980–1981 flow season were: Ca = 0.119; Mg = 0.061; Na = 0.212; K = 0.033; Q = 0.212; SO4 = 0.045; HCO3 = 0.295; and SiO2 = 0.049. Based on the flow measurements of Chinn (1982), this amounts to an annual flux (in moles) to Lake Vanda of: Ca = 0.238 × 106; Mg = 0.122 × 106; Na = 0.424 × 106; K = 0.066 × 106; Cl = 0.424 × 106; SO4 = 0.09 × 106; HCO3 = 0.59 × 106; SiO2 = 0.098 × 106.In spite of the large salt input from this source, equilibrium evaporation of Onyx River water would have resulted in early calcite deposition and in the formation of a Na-Mg-Cl-HCO3 brine rather than in the Ca-Na-Mg-Cl waters observed in Lake Vanda. The river alone could not have produced a brine having the qualitative geochemical features of the lower saline waters of Lake Vanda.It is proposed that the Vanda brine is instead the result of past ( > 1200 yrs BP) mixing events between Onyx River inflows and calcium chloride-rich deep groundwaters derived from the Don Juan Basin. The mixing model presented here shows that the Onyx River is the major contributor of K, HCO3, SO4, and (possibly) Mg found in the lake and a significant contributor (approximately one half) of the observed Na. Calcium and Cl, on the other hand, came largely from deep groundwater sources in the Don Juan Basin. All concentrations except Mg are well predicted by this model. The chemical composition of the geologically recent upper lake is explained in terms of ionic diffusion from the pre-formed brine, coupled with Onyx River inflow. Ionic ratios calculated from this latter model are in very good agreement with those observed in the lake at 35 meters. 相似文献
15.
Bernd Kober 《Contributions to Mineralogy and Petrology》1987,96(1):63-71
The internal precision of Pb isotope analyses using single-zircon evaporation in a double-filament solid source mass spectrometer (Kober 1986) can be improved combining the evaporation of Pb directly from the single grain with a suitable Pb+ emitter-bedding technique. This is most easily done by step-wise evaporating the investigated grain at temperatures of 1700–1800 K generating on the ‘cold’ ionization filament a deposit of radiogenic Pb together with further elements and compounds derived directly from the crystal. The heating of the deposit on the ionization filament to 1400–1500 K results in long-lived and stable Pb+ ion beams. The ‘activating reagents’ in the deposit are HfO2 and SiO2. Their release from the zircon grain together with the radiogenic Pb, which presumably is sited in the crystalline zircon domains as Pb4+, is probably due to disintegration reactions of trace-element silicates hosted in the grain. In the bedding deposited on the ionization filament thermally stable Pb/Hf/SiO2 compounds are formed (PbHfSiO5(?)). They retain the Pb isotopes on the (Re) filament up to 1400 K–1500 K and are highly efficient Pb+ ion emitters similar to the ‘Si-gel’-method (Cameron et al. 1969). The combined evaporation/emitter-bedding technique has been applied to natural zircons of different genesis and to isotope standards. Routinely, a Pb+ ion yield of 2*10?4-1*10?3 and a relative standard deviation of the 207Pb/206Pb ratio in the order of 1% have been obtained for sub-ng- to ng-amounts of Pb from standards and samples. The method rapidly can yield Pb isotope information on the ‘concordant’ zircon phases with a standard deviation of ±15–20 Ma of the derived ages also in the case of Paleozoic zircon populations. 相似文献
16.
The solubilities of PbCO3(s), 2PbCO2·Pb(OH)2(s), and of 3PbCO3 2Pb(OH)2(s) have been studied at 25°C ± 0.1°C in solutions of the constant ionic strength I = 0.3 mol/dm3, consisting primarily of sodium perchlorate. A few experiments with hydrocerussite were performed in solutions of 0.1 M KNO3. The concentrations of lead and hydrogen ions have been determined in solution in contact with the solid phase. From experimental data the following values for equilibrium constants are obtained: log [Pb2+]·pCO2·[H+]?2 = 5.20log [Pb2+]·pCO0.672·[H+]?2 = 6.80log [Pb2+]3·[CO2?3]2·[OH?]2 = ?44.08 (and ?44.8 forI = 0.1 M)log [PbCO03]·[Pb2+]?1·[CO2?3]?1 = 5.40log [Pb(CO3)2?2]·[Pb2+]?1·[CO2?3]?2 = 8.86 The data indicate that hydrocerussite is the most stable solid phase in natural waters. Comparison with the literature and needs for further research are also presented. 相似文献
17.
Vertical distribution and feeding types of nematodes from Chetumal Bay, Quintana Roo, Mexico 总被引：1，自引：0，他引：1
The vertical distribution and feeding type of nematodes in sediments of Chetumal Bay, Mexico, were studied in five intertidal transects along the urbanized zone in June and December 1995. Sediments were collected with a PVC corer to 6-cm sediment depth and cut immediately into three equal 2-cm depth fractions. Nematode density varied from 7.4 × 103 to 5.3 × 105 m?2 in June and from 1.7 × 104 to 7.2 × 105 m?2 in December. In June, the epistrate feederPseudochromadora sp. was the most abundant in the deepest sediment fraction (4–6 cm), whereas epistrate feeders,Neotonchoides sp.,Desmodora sp., and the deposit feederBathylaimus australis were dominant in the top most sediment (0–2 cm). In December, deposit feeders,Desmolaimus zeelandicus, Parodontophora sp., and the epistrate feederOncholaimus oxyuris were the most abundant in the deepest sediment, whereasNeotonchoides sp. andPseudochromadora sp. dominated the first 2 cm of sediments. Highest nematode density was recorded in the uppermost sediment layer (0–2 cm). Feeding types showed different abundance among transects and between months. There was a seasonal change in vertical distribution of nematodes, with the highest abundance in the deepest sediment layer in December, possibly due to the effect of wind waves on sediments of Chetumal Bay. The trophic composition of the nematode fauna in Chetumal Bay showed a dominance of deposit feeders and epistrate feeders, most likely in response to organic enrichment that is typical of eutrophic environments. 相似文献
18.
Characterizing the dynamics of fluvial sediment sources over space and time is often critical in identifying human impacts on fluvial systems. Upland interfluve and subsoil sources of suspended sediment at Loco Bayou, Texas, were distinguished using 226Ra/232Th, 226Ra/230Th and, 228Ra/232Th. Source contributions were apportioned at three stations during within-bank and flood flows. 137Cs and 210Pbxs (excess 210Pb) were used to determine floodplain sedimentation; suspended sediment 210Pbxs/137Cs data mirrored results of Ra/Th, showing dominance of subsoil sources during within-bank flows, changing to interfluve sources during flood. This trend corresponds spatially to influx of sediment from ephemeral tributaries, reflecting mobilization of stored interfluvial sediments during flood stage. Upper basin sedimentation was similar but markedly less at the lowermost station. These results indicate (1) modified ephemeral tributaries store sediment derived from sheet wash, discharging them during flood, and (2) southernmost Loco Bayou is episodically re-worked, resulting in significantly reduced local rates of sedimentation. 相似文献
19.
The dissolved silica concentration in waters of Lake Superior probably is in a steady state because it is not influenced significantly by man, and the climate, topography and vegetation in the drainage area of the lake have been stable for the past 4000 years. Therefore the rate at which dissolved silica is introduced to the lake should equal the output rate.The primary inputs are: tributaries (4.1–4.6 × 108kgSiO2/yr), diffusion from sediment pore waters (0.21?0.78 × 108kgSiO2/yr) and atmospheric loading (0.26 × 108kgSiO2/yr). Silica is lost from the lake waters by: outflow through the St. Marys River, diatom deposition, adsorption onto particulates in the sediments, and authigenic formation of new silicate minerals. Tributary outflow accounts for less than one half the annual input of silica, and diatom deposition and silica adsorption withdraw less than 10% of the annual input. Therefore the formation of new silicate phases must be the dominant sink for dissolved silica in Lake Superior. The specific phases formed are not identified in the bottom sediments. X-ray diffraction studies suggest that smectite is one product, and amorphous ferroaluminum silicates may be another product.Mathematical modeling of the dissolved silica response to lake eutrophication suggests that the phosphate loading to Lake Superior would have to increase by about 250-fold to cause a silica depletion rate equal to that reported for Lake Michigan, assuming no change in the rate of upwelling of deep waters. 相似文献
20.
S. M. Kim T. I. Jang M. S. Kang S. J. Im S. W. Park 《Environmental Earth Sciences》2014,71(5):2155-2165
The objective of this study was to assess the lake sediment budget of land use changes using the Universal Soil Loss Equation (USLE), sediment delivery ratio (SDR), and trap efficiency (TE). The geographic information system was combined with the USLE to estimate the soil erosion of the Lake Asan watershed. Spatial data for each of the USLE factors were obtained from the land use, soil, and 1/25,000 scale digital contour maps. Landsat-5 TM images were selected for analyzing soil erosion changes due to land use changes. The sediment yield to Lake Asan was estimated using the SDR and TE. The estimated sediment budget was compared with observed data from the Lake Asan watershed between 1974 and 2003. The total estimated annual mean sediment budgets from Lake Asan in 1986, 1992, and 2000 were 0.267, 0.301, and 0.339 × 106 ton, respectively, with an average of 0.302 × 106 ton. The average measured sediment budget was 3.15 × 106 ton year?1. The average estimated value shows reasonable agreement with the observed sediment balance. The average estimated and measured sediment budgets contain uncertainties due to both the methods and the approach used by the observers. The simulated results indicated that soil erosion in the Lake Asan watershed increased at a rate of approximately 2 % per year from 1986 to 2000 due to land use change. This study may be useful for managers to identify reservoir rehabilitation management methods for stable irrigation water supply. 相似文献