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1.
We developed light requirements for eelgrass in the Pacific Northwest, USA, to evaluate the effects of short- and long-term reductions in irradiance reaching eelgrass, especially related to turbidity and overwater structures. Photosynthesis-irradiance experiments and depth distribution field studies indicated that eelgrass productivity was maximum at a photosynthetic photon flux density (PPFD) of about 350–550 μmol quanta m−2 s−1. Winter plants had approximately threefold greater net apparent primary productivity rate at the same irradiance as summer plants. Growth studies using artificial shading as well as field monitoring of light and eelgrass growth indicated that long-term survival required at least 3 mol quanta m−2 day−1 on average during spring and summer (i.e., May-September), and that growth was saturated above about 7 mol quanta m−2 day−1. We conclude that non-light-limited growth of eelgrass in the Pacific Northwest requires an average of at least 7 mol quanta m−2 day−1 during spring and summer and that long-term survival requires a minimum average of 3 mol quanta m−2 day−1.  相似文献   

2.
The size-fractionated phytoplankton biomass and primary production were investigated in four contrasting areas of Hong Kong waters in 2006. Phytoplankton biomass and production varied seasonally in response to the influence of the Pearl River discharge. In the dry season, the phytoplankton biomass and production were low (<42 mg chl m−2 and <1.8 g C m−2 day−1) in all four areas, due to low temperatures and dilution and reduced light availability due to strong vertical mixing. In contrast, in the wet season, in the river-impacted western areas, the phytoplankton biomass and production increased greater than five-fold compared to the dry season, especially in summer. In summer, algal biomass was 15-fold higher than in winter, and the mean integrated primary productivity (IPP) was 9 g C m−2 day−1 in southern waters due to strong stratification, high temperatures, light availability, and nutrient input from the Pearl River estuary. However, in the highly flushed western waters, chl a and IPP were lower (<30 mg m−2 and 4 g C m−2 day−1, respectively) due to dilution. The maximal algal biomass and primary production occurred in southern waters with strong stratification and less flushing. Spring blooms (>10 μg chl a L−1) rarely occurred despite the high chl-specific photosynthetic rate (mostly >10 μg C μg chl a −1 day−1) as the accumulation of algal biomass was restricted by active physical processes (e.g., strong vertical mixing and freshwater dilution). Phytoplankton biomass and production were mostly dominated by the >5-μm size fraction all year except in eastern waters during spring and mostly composed of fast-growing chain-forming diatoms. In the stratified southern waters in summer, the largest algal blooms occurred in part due to high nutrient inputs from the Pearl River estuary.  相似文献   

3.
Cinnabar (α-HgS) and metacinnabar (β-HgS) dissolved at environmentally significant rates in oxygenated slurry experiments simulating a low-flow fluvial system. Based on SO42− production, cinnabar dissolution rates were 2.64 to 6.16 μmol (SO42−) m− 2 day− 1, and metacinnabar dissolution rates were 1.20 to 1.90 μmol (SO42−) m− 2 day− 1. Monodentate-bound thiosulfate (S2O32−) was identified as an oxidation product on the HgS surface by ATR-IR spectroscopy based on strong infrared absorption bands in the 1140–1145 cm− 1 and 1006–1014 cm− 1 regions. The presence of sulfide oxidation intermediates on the HgS surface indicates that SO42− concentration underestimates α-HgS and β-HgS dissolution in this setting. Mercury release rates during dissolution were more than two orders of magnitude less than SO42− production, but were significant: 0.47 mg (Hg) m− 2 y− 1 from cinnabar [6.45 nmol (Hg) m− 2 day− 1], and 0.17 mg (Hg) m− 2 y− 1 from metacinnabar [2.29 nmol (Hg) m− 2 day− 1]. The Hg mobilized during α-HgS and β-HgS dissolution is sufficient to form natural Au–Hg amalgam in downstream placer settings. The proportion of mercury that is not remobilized during α-HgS and β-HgS dissolution likely adsorbs to the dissolving mercuric sulfide. Adsorption of Hg2+ to cinnabar was detected in situ by anodic stripping voltammetry using a cinnabar-modified carbon paste electrode following accumulation of Hg2+ on the electrode at open circuit potential.  相似文献   

4.
In order to determine time-dependent changes in estuarine pore-water chemistry and flux variations across the sediment-water interface, sediment cores of an intertidal mud flat in the Weser Estuary were taken monthly over a one-year period. Sediment temperature, pH, Eh, Cl–, O2, NO 3 – , and SO 4 2– pore-water concentrations were measured and showed variations that relate to the changes of surface temperature and estuarine water composition. Fick's first law was applied to quantify diffusive fluxes from concentration gradients in the diffusive boundary layer and in the pore water. Total nitrate fluxes were calculated from flux chamber experiments. Diffusive oxygen fluxes increased from 5 mmol m–2 d–1 in winter to 18 mmol m–2 d–1 in early summer, while nitrate fluxes into the sediment increased from 3 mmol m–2 d–1 in winter to 60 mmol m–2 d–1 in early summer. Oxygen and nitrate fluxes into the sediment correlated linearly to sediment temperature. Sulfate fluxes increased from 0.5 mmol m–2 d–1 in winter to 10 mmol m–2 d–1 in August and September. Converted into carbon fluxes, the sum of these oxidants ranged from 10 mmol m–2 d–1 in winter to 80 mmol m–2 d–1 in summer. An estimation of the upper limit of the annual nitrate flux into the sediment showed that about 10% of the 250,000 t of nitrate discharged annually by the river may be decomposed within the inner Weser Estuary.  相似文献   

5.
The 25th cruise of R/FAkademik Knipovitch conducted in January–April of 1990 comprised investigations of total organic carbon (TOC) at the following sections: through the Polar Frontal Zone (PFZ) along 40° W, made in January and April; from the PFZ to the South Orkney Islands, and on the South Georgia shelf. The measurements made comprised TOC, organic nitrogen, nitrate, nitrite, ammonium nitrogen, phosphate and silicate.The surface waters of the region were characterized by high heat content, which influenced the Antarctic phytosynosis function. The data obtained showed low content of organic matter (OM); high content of TOC, rising up to 3,5 mg m–3, was recorded at the photic layer and in the layer of OM accumulation, at the upper boundary of the Antarctic Deep Waters and the vertical boundaries of the Antarctic Intermediate Waters. The South Georgia shelf waters showed even distribution of TOC, about 0,2 mg m–3, being under the influence of the south periphery of the ACC waters.  相似文献   

6.
Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO3 type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ18O of − 8.3‰, δD of − 48.2‰,δ11B of 1.5‰, and 87Sr/86Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO4 type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ18O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ11B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and 87Sr/86Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO4 type water with the highest TDS (249.1 g/l, brine) and has δ18O of − 2.8‰, δD of − 45.8‰,δ11B of 21.2‰, and 87Sr/86Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ11B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.  相似文献   

7.
The GALO system is applied to the numerical reconstruction of burial and thermal histories of the West Bashkirian lithosphere from the Riphean to the present. An analysis of the variation in tectonic subsidence of the basin during its development is utilized to estimate approximately the mantle heat flow variations. Our variant of basin evolution suggests that after cooling in the Early Riphean, the rather weak thermal reactivations have not led to considerable heating of the lithosphere in the study region. Surface heat flow decreased from relatively high values in the Early Riphean (60–70 mW/m2 in the eastern area and 40–50 mW/m2 in the western part) to present-day values of 32–40 mW/m2. In spite of the relatively low temperature regime of the basin as a whole, a syn-rifting deposition of more than 10 km of limestone, shale and sandstone in the Riphean resulted in rather high temperatures (180–190 °C) at the base of present-day sedimentary blanket in the eastern area. In agreement with the observed data, computed present-day heat flow through the sediment surface increases slightly from 32 to 34 mW/m2 near the west boundary of the region to 42 mW/m2 near the boundary of the Ural Foldbelt, whereas the heat flow through the basement surface decreases slightly from 28–32 to 24–26 mW/m2 in the same direction. The mantle heat flow is only 11.3–12.7 mW/m2, which is considerable lower than mean heat flow of the Russian Platform (16–18 mW/m2) and comparable with the low heat flow of Precambrian shields.  相似文献   

8.
The oxygen isotope record of planktonic foraminifera from tropical core MD77194 (Eastern Arabian Sea) exhibits a clear two-step deglaciation with a brief δ18O transient event. In the tropics, this δ18O maximum could correspond to a cooling or to a change in the δ18O content of sea water. In this study, past sea-surface temperature (SST) and primary production (PP) are reconstructed from foraminiferal transfer functions and compared to values estimated from alkenone measurements. SST and PP records from both proxies indicate a 1.5–2.5°C deglacial warming, coupled with a PP decrease, and a 0.5–1°C cooling during the Younger Dryas (YD). A detailed comparison between independent micropaleontological and geochemical proxies helps us identify potential biases and thus strengthen the paleo-reconstructions.  相似文献   

9.
This paper reviews the geochemical, isotopic (2H, 18O, 13C, 3H and 14C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO3 type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ2H and δ18O suggest a common meteoric origin and that the Mg–HCO3 type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO3 to Mg–HCO3 waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO2 (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of 14C and 13C values, which is in agreement with the 3H concentrations being below the detection limit.  相似文献   

10.
During a semi-lunar tidal cycle from full moon till new moon, tide is characterized by the periodic change in spring and neap tide. Under the in situ conditions of light and temperature, the influence of a semi-lunar spring and neap tidal cycle on nutrient cycling in intertidal flat of the Yangtze estuary was simulated in the laboratory in July 2002. Lab experiments showed that NH4+ and PO43– were always released into overlying waters, while NO3– was directed into sediments in the permanently waterlogged systems, suggesting that the long-term waterlogged sediment acts as a significant source for NH4+ and PO43–, and a sink for NO3– in water columns. In contrast, reflooding of intertidal sediments after long-term desiccation promoted the considerable effluxes of NH4+, NO3– and PO43– into overlying waters, reflecting that the long-term exposed sediment is an important source for nutrients in overlying waters. In addition, the semi-lunar tidal cycle led to the intricate depth distribution patterns of nutrients in intertidal sediments. During long-term exposure, NH4+ in sediments was quickly transformed into NO2– and NO3–, while organic P pool might be converted to slightly adsorbed and iron-bound P. Therefore, it is considered that the semi-lunar tidal circulation has the significant influence on the biogeochemical cycle of nutrients in intertidal systems.  相似文献   

11.
Eleven new estimates of heat flow (q) from the southern Altai-Sayan Folded Area (ASFA) have provided update to the heat flow map of Gorny Altai. Measured heat flow in the area varies from 33 to 90 mW/m2, with abnormal values of >70 mW/mq at four sites. The anomalies may have a deep source only at the Aryskan site in the East Sayan (q = 77 mW/m2) while high heat flows of 75–90 mW/m2 obtained for the Mesozoic Belokurikha and Kalguty plutons appear rather to result from high radiogenic heat production in granite, which adds a 25–30 W/m2 radiogenic component to a deep component of 50–60 mW/m2. The latter value is consistent with heat flow estimates derived from helium isotope ratios (54 mW/m2 in both plutons). Heat flow variations at other sites are in the range from 33 to 60 mW/m2. The new data support the earlier inferences of a generally low heat flow over most of ASFA (average of 45–50 mW/m2) and of a “cold” Cenozoic orogeny in the area (except for southeastern ASFA), possibly driven by shear stresses associated with India indentation into Eurasia.  相似文献   

12.
Stable isotope compositions (18O and 2H), determined for underground and surface waters from the watershed of a hill reservoir and downstream from the reservoir, suggest that (i) the reservoir water, which is more or less evaporated, represents a mixture between surface waters (rainfall, runoff) and the upstream alluvial groundwater meteoric in origin; (ii) the downstream alluvial groundwater have a stable isotope composition of a previously infiltrated reservoir water. The 18O isotope enrichment modelling of the mixed reservoir water shows that an input flux of 50 m3 day−1 is balanced by an output flux of 300 m3 day−1 when the reservoir water level is above 4.5 m, and by an output flux of 170 m3 day−1 when water levels are lower. The contribution of hill reservoirs to local groundwater movements must be considered in any regional scale hydrological investigations of areas that contain hill reservoirs. To cite this article: O. Grünberger et al., C. R. Geoscience 336 (2004).

Résumé

La composition isotopique (18O et 2H) d'eaux souterraines et superficielles, déterminée pour le bassin versant d'une retenue collinaire et sa partie aval, suggère (i) que l'eau de la retenue, qui est plus ou moins évaporée, représente un mélange entre les eaux de surface (pluie, ruissellement) et la nappe alluviale amont d'origine météorique et (ii) que la nappe alluviale aval a la composition isotopique d'une eau de la retenue anciennement infiltrée. La modélisation de l'enrichissement en isotope 18O pour l'eau mélangée de la retenue montre qu'un flux entrant de 50 m3 j−1 est compensé par un flux sortant de 300 m3 j−1, lorsque le niveau d'eau de la retenue est supérieur à 4,5 m, et par un flux sortant de 170 m3 j−1 en dessous. La contribution des lacs collinaires aux écoulements souterrains doit être prise en compte pour de futures études hydrologiques à l'échelle régionale. Pour citer cet article : O. Grünberger et al., C. R. Geoscience 336 (2004).  相似文献   

13.
遥感技术根据植被光谱特征可以有效地估算植被的净初级生产力(NPP).利用遥感数据估算植被NPP,是近10年来NPP的模型研究和估算方法最为突出的特点.文章借鉴了CASA,GLO-PEM,VPM等光能利用率NPP模型的优点,同时充分考虑了研究区域其植被光能利用率和环境因素的典型特点,建立了针对研究区域基于光能利用率原理的...  相似文献   

14.
The carbonate system of waters of the inner, middle, and outer shelves was studied for a long period in the eastern part of the Laptev Sea. It is shown that the inner and middle shelves is a heterotrophic province and is a source of CO2 to the atmosphere during August–September. The average CO2 flux is 7.9 mmol m–2 day–1 and during one month waters of inner and middle shelves release into the atmosphere up to 0.7 Tg of carbon (C). The outer part of the shelf absorbs up to ~0.1 Tg C at an average rate of 3.9 mmol m–2 day–1 during the month. Generally, the ice-free zone of the eastern shelf of the Laptev Sea is a source of CO2 in the studied season: the amount of C released into the atmosphere within a month is ~0.6 Tg.  相似文献   

15.
We present original heat flow determinations carried out during the Flumed surveys by the CEPM along three transects of the Provençal Basin (Gulf of Lions-West Sardinia; Toulon-Ajaccio; Nice-Calvi). A total of 121 thermal gradients and 37 conductivities are examined together with previous heat flow determinations along depth sections based on previous geophysical investigations. The mean observed heat flows are clearly shown to increase from NW to SE along the profiles (expect for the Toulon-Calvi transect, where results are ambiguous). The observed heat flow increases from 55–65 mW m−2 (Gulf of Lions) to 85 ± 14 mW m−2 (West Sardinia) and from 55–65 mW m−2 (Var Basin) to 103–108 mW m−2 (lower Corsican margin), suggesting an asymmetrical distribution of the observed heat flow. We examine whether this asymmetry could be caused by thermal refraction above salt structures or by any other superficial cause (sedimentation, topography, etc.) and conclude that an asymmetrical distribution of the subcrustal heat flow is probably the cause of this thermal regime. The elevated heat flows observed to the east in the abyssal plain, corrected for sedimentation, cannot be accounted for by the standard age/heat flow relations established for oceanic or attenuated continental lithosphere. The geodynamic significance of this speculative subcrustal origin remains poorly constrained, but could be related to post-rifting magmatic activity. Further investigations are necessary to elucidate the apparent high local variability of the heat flow on the upper margin of the Gulf of Lions and on the Provençal margin of the Ligurian Sea.  相似文献   

16.
About 500 well and spring waters were collected on an approximately 1-km spacing in an area centered on six small U and Cu-U occurrences near Monticello, N.Y., as an orientation survey in the NURE program. Rocks of the area belong to the Devonian Catskill Group and are predominantly red sandstones and shales of fluvial origin. The sediments dip 0–5° in the main part of the area, but steepen to 45° in the east. The ground waters were analyzed for 46 elements plus several other water properties.An R-mode factor analysis extracted 10 factors. The strongest factor, termed “Dissolved solids”, has heavy loadings on most major elements, plus U, B, Li, Sr, and Zn. This factor is attributed to varying degrees of interaction between original rainwater and rocks. Recognition of anomalies for elements loaded on this factor is aided by evaluation of ratios or plots against total dissolved solids or conductivity. Three weaker factors apparently represent admixtures with two types of deep brine and with waters of enhanced Fe-Mn resulting from reducing conditions. Other factors include an assemblage of insoluble trace metals and a Zn-Cu-P factor, both possibly related to contamination and/or analytical problems, a rare earth group, and an Se-As-Ag factor. The waters are clearly complex mixtures of effects.The geographic distribution of high U values shows some correlation with the distribution of U occurrences, but many equally high values occur outside the known mineralized area. When the data are projected to a vertical section normal to the strike, high U values define two gently dipping aquifers. The upper anomalous aquifer contains the known occurrences but extends downdip. Samples within this aquifer show patterns in U, dissolved O2, and conductivity, apparently related to influx of fresh water from updip, along major rivers, and along possible fractured zones. High He values are also most numerous near the occurrences and define the deeper U-rich aquifer. The interpretation of the data is greatly clarified by separation of individual aquifers.Saturation indices are generally −3.4 to −5 and show patterns similar to dissolved U, except for values of −6 to −9 in a few samples with high phosphate. Predominant U species are usually UO2(CO3)22−, or less commonly UO2CO30 or UO2(HPO4)22−.  相似文献   

17.
Aerobic mineralisation of Corg in surface sedimentsof the deep (>2000 m water depth) eastern Mediterranean Sea has been quantified by analysis of detailedbox core Corg concentration versus depth profiles and the modelling environment for early diageneticproblems MEDIA. The reactive fraction comprises 60–80% of the total Corg reachingthe sediments and is largely oxidised within the surficial 10 cm. A non-reactive C orgfraction (GNR) dominates at depths >10 cm, and makes up20–40% of the total C org flux to the sediments. First-order rateconstants for decomposition of the reactive fraction calculated from theC org profiles range from 5.4 × 10-3 to8.0 × 10-3 y-1 to 8.0 × 10-3 y-1. Total mineralization rates in thesurface sediment are between 1.7 and 2.6 mol C cm-2 y-1 and thus are typical for oligotrophic, deep-seaenvironments. The low fluxes and rapid remineralisation of C org are accompanied by210Pbexcess surface mixed layers which are only 2 cm deep, among the thinnest reported for oxygenated marine sediments.Model results indicate a mismatch between the C org profiles and O2 microprofileswhich were measured onboard ship. This can be attributed to a combination of decompression artefactsaffecting onboard measurement of the O2 profiles or the leakage ofoxygen into the core during handling on deck. Furthermore, the used Db values, based on 210Pb, may not befully appropriate; calculations with higher Db values improve the O2 fits. The surficial sediment13C org values of -22 become less negative with increasing depth and decreasing C orgconcentrations. The major 13C change occurs in the top 3 to 4 cm and coincides with the interval weremost of the organic carbon oxidation takes place. This indicates that the reactive fractionof organic matter, commonly assumed to be marine, has a more negative 13C orgthan the refractory fraction, usually held to be terrestrial. Palaeoproductivity estimates calculated from thesediment data by means of literature algorithms yield low surface productivities(12–88 gC m-2 y-1), which are in good agreement with field measurements of primary productivity in otherstudies. Such values are, however, significantly lower than those indicated by recent productivitymaps of the area derived from satellite imagery (>100 gC m-2 y-1).  相似文献   

18.
《Applied Geochemistry》1997,12(4):347-366
The research site at Otis Air Base, Cape Cod, Massachusetts, has been developed for hydrogeological and geochemical studies of sewage-effluent contaminated ground water since 1982. Research of hydrologic properties, transport, and chemical and biological processes is ongoing, but the origin of background water chemistry has not been determined.The principal geochemical process giving rise to the observed background water chemistry is CO2-controlled hydrolysis of Na feldspar. Geochemical modeling demonstrated that CO2 sources could vary over the project area. Analyses of unsaturated zone gases showed variations in CO2 which were dependent on land use and vegetative cover in the area of groundwater recharge. Measurements of CO2 in unsaturated-zone gases showed that concentrations of total inorganic C in recharge water should range from about 0.035 to 1.0 mmoles/L in the vicinity of Otis Air Base. Flux of CO2 from the unsaturated zone varied for 4 principal land uses, ranging from 86 gC/m2/yr for low vegetated areas to 1630 gC/m2/yr for a golf course. Carbon dioxide flux from woodlands was 220 gC/m2/yr, lower than reported fluxes of 500 to 600 gC/m2/yr for woodlands in a similar climate. Carbon dioxide flux from grassy areas was 540 gC/m2/yr, higher than reported fluxes of 230 to 490 gC/m2/yr for grasslands in a similar climate.  相似文献   

19.
This paper describes the distribution of Fe and Ni between the octahedral and tetrahedral sites in pentlandite (Fe,Ni)9S8. The dependence of the distribution on pressure and temperature and the activation energy of the cation exchange reaction were determined through annealing experiments. Synthetic crystals were annealed at 433–723 K and pressures up to 4 GPa, and natural crystals were annealed at 423, 448 and 473 K in evacuated silica capillary tubes for various durations. The cation distributions in the synthetic crystals were determined with an X-ray powder method employing the anomalous dispersion effect of CuK. and FeK radiations, while those of natural crystals were calculated from the cell dimensions. The values of U, S and V for the Fe/Ni exchange reaction are –6818 J mol–1, 20.52 J K–1 mol–1, and 6.99 × 10–6 m3 mol–1, respectively. The dependence of the Fe/Ni distribution on pressure (Pa) and temperature (Kelvin) was determined as lnK = 2.47+8.20 × 102 T –1+8.41 x 10–7 T –1 P, where K = (Fe/Ni)octahedral /(Fe/Ni)tetrahedral. The activation energy of the cation exchange reaction was 185 kJ mol–1.  相似文献   

20.
A regional lithostratigraphic and hydraulic interpretation is presented for the upper 0–300 m of the Benin Formation where groundwater is abstracted in the Rivers State, Nigeria.The aquifers are predominantly sand beds with minor clays, lignite, and conglomerate intercalations. The sands are very fine to coarse grained, subangular to subrounded, poor to fairly well sorted and mostly lithic arenites. A maximum thickness greater than 50 m is developed in places and vertical stacking is common. Most of the conglomerate beds have a matrix support fabric and appear restricted to the east as the lignite beds. An east-west trending belt, about central to the state, seems to contain more clay interbeds.The transmissivity values for the aquifers range from 1.05 × 10–2 to 11.3 × 10–2 m2/sec, while the coefficient of storage varies between 1.07 × 10–4 and 3.53 × 10–4 and specific capacity values lie between 19.01 and 139.8 m3/h/m drawdown. These values suggest that the aquifers have very good capacity to transmit groundwater. The static water level map shows a north-to-south regional groundwater flow pattern except in the northeast (Imo River catchment area) where the flow is northeast to southwest. The groundwater quality is very good and compares favorably with WHO standards for drinking water. However, relatively high iron and chloride values are localized in time and space.Deposition of the aquifer materials is thought to have occurred in alluvial fan, fluvial channel, tidal channel, intertidal flat, beach, and related microenvironments.  相似文献   

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