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1.
黄钾铁矾是酸性矿山废水（AMD） 中常见的次生矿物,能有效吸附AMD中Cu、Pb、Zn、Gd、As等重金属元素。不 同条件下形成的黄钾铁矾微形貌不同,其吸附能力也不同。文章通过化学法和微生物法合成了黄钾铁矾,并在粤北大宝山 矿酸性矿山废水中采集了含黄钾铁矾的泥样。利用扫描电镜-能谱分析（SEM） 和X光衍射（XRD）,对三种不同条件下形 成的黄钾铁矾进行鉴定和微形貌特征观察,并分析黄钾铁矾的形成条件。结果表明,常温条件下,pH值2.0~2.5时能够化 学合成黄钾铁矾,其晶体粒径约2~10 μm,且晶形呈板状;而在65℃时,可在pH2.0~3.0之间化学合成黄钾铁矾,但晶形 差。微生物法合成黄钾铁矾pH范围是2.0~5.0,其晶形完好,呈菱面体且晶体大小比较均匀,而约为2~4 μm。酸性矿山废 水中的黄钾铁矾形成的pH值为2.5~3.5,晶形为菱面体形,单个晶体大小多为1~2 μm。根据其形成条件和微形貌特征,文 章推测酸性矿山废水中形成的黄钾铁矾可能是微生物成因。  相似文献   

2.
黄钾铁矾是酸性矿山废水（AMD） 中常见的次生矿物，能有效吸附AMD中Cu、Pb、Zn、Gd、As等重金属元素。不 同条件下形成的黄钾铁矾微形貌不同，其吸附能力也不同。文章通过化学法和微生物法合成了黄钾铁矾，并在粤北大宝山 矿酸性矿山废水中采集了含黄钾铁矾的泥样。利用扫描电镜-能谱分析（SEM） 和X光衍射（XRD），对三种不同条件下形 成的黄钾铁矾进行鉴定和微形貌特征观察，并分析黄钾铁矾的形成条件。结果表明，常温条件下，pH值2.0~2.5时能够化 学合成黄钾铁矾，其晶体粒径约2~10 μm，且晶形呈板状；而在65℃时，可在pH2.0~3.0之间化学合成黄钾铁矾，但晶形 差。微生物法合成黄钾铁矾pH范围是2.0~5.0，其晶形完好，呈菱面体且晶体大小比较均匀，而约为2~4 μm。酸性矿山废 水中的黄钾铁矾形成的pH值为2.5~3.5，晶形为菱面体形，单个晶体大小多为1~2 μm。根据其形成条件和微形貌特征，文 章推测酸性矿山废水中形成的黄钾铁矾可能是微生物成因。  相似文献   

3.
Jarosite [KFe3(SO4)2(OH)6] is a mineral that is common in acidic, sulphate-rich environments, such as acid sulphate soils derived from pyrite-bearing sediments, weathering zones of sulphide ore deposits and acid mine or acid rock drainage (ARD/AMD) sites. The structure of jarosite is based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, made up from slightly distorted FeO6 octahedra and SO4 tetrahedra. Batch dissolution experiments carried out on synthetic jarosite at pH 2, to mimic environments affected by ARD/AMD, and at pH 8, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)2), suggest first order dissolution kinetics. Both dissolution reactions are incongruent, as revealed by non-ideal dissolution of the parent solids and, in the case of the pH 8 dissolution, because a secondary goethite precipitate forms on the surface of the dissolving jarosite grains. The pH 2 dissolution yields only aqueous K, Fe, and SO4. Aqueous, residual solid, and computational modelling of the jarosite structure and surfaces using the GULP and MARVIN codes, respectively, show for the first time that there is selective dissolution of the A- and T-sites, which contain K and SO4, respectively, relative to Fe, which is located deep within the T-O-T jarosite structure. These results have implications for the chemistry of ARD/AMD waters, and for understanding reaction pathways of ARD/AMD mineral dissolution.  相似文献   

4.
Major, trace and rare earth element concentrations were measured in porewater, surface water and sediments at an acid sulfate soil site. The concentrations of La and Ce in porewater are up to 1-3 ppm. There is a strong correlation between REE concentration and acidity, except that the maximum concentrations were consistently found below the horizon of maximum acidity, associated with an increase in pH (to ca. 4) and change in mineralogy from jarosite-dominated to goethite-dominated mottles. Jarosite replacement by goethite is as expected with the rise in pH, which in turn is due to the occurrence of a fossil shell bed just below. The rare earth element patterns in the porewaters are enriched in the MREE with respect to Post-Archaean Australian Shale (PAAS). Measurements and calculations show that this is in accord with experiments on low-degree partial dissolution of jarosite, even when the jarosite itself is highly enriched in LREE. There is a clear fractionation in the patterns between the clay-rich soil matrix, which is slightly depleted in the LREE when normalized to PAAS (La/YbPAAS ∼0.5), and the secondary mineral phase jarosite, which is enriched in the LREE (La/YbPAAS = 15-50). The REE pattern in the porewater changes with the transition from jarosite- to goethite-rich mottles, becoming relatively more enriched in the LREE compared to the HREE, which is consistent with the incongruent dissolution of jarosite to form goethite and the release of greater amounts of jarosite REE to solution, including proportionately more of the jarosite-compatible LREE.Maximum surface water REE concentrations in acidic water were 100-200 ppb La and Ce. REE patterns in surface water were very similar to the porewater transition zone, enriched in the MREE, but asymmetric, relatively enriched in the LREE compared to the HREE.  相似文献   

5.
The natural alteration products developed on mattes from lead metallurgy were determined: oxides and hydroxides (HFO, Cu(OH)2), sulphates (thenardite, gypsum), hydroxysulphates (jarosite, beaverite, brochantite) and carbonates (cerussite, malachite, NaOH·2 PbCO3). The large range of stability of newly formed phases confirms a significant variety of Eh–pH conditions of natural weathering of matte. Jarosite is stable at pH<3, but some hydroxides and carbonates typically form in neutral and alkaline environments. Consequently, the best dumping conditions for metallurgical mattes are difficult to determine. Such materials can have severe environmental effects and should be dumped in controlled waste-disposal sites. To cite this article: V. Ettler et al., C. R. Geoscience 335 (2003).  相似文献   

6.
This paper focuses on characterizing the current status of physical and chemical characteristics of King Talal Dam (KTD) sediments. The quality of sediments was investigated based on several international sediment quality guidelines. The volume of sediment and sedimentation rate in (KTD) was also estimated. Five types of granulometric textural facies were observed for the sediments of KTD reservoir bed, with an average grain size distribution of gravel (1.38%), sand (32.38%), silt (32.35%) and clay (32.38%). The fraction of <63 micron showed that the total mean size was 8.0 micron. Other sediment parameters in KTD were 7.0% for total organic matter (TOM), 7.3 for pH, 35.9% for CaCO3 and 100.5 meq/100 g for cation exchange capacity, with dominant mineralogical constituents of quartz, calcite, dolomite, clay minerals and minor feldspar. The total concentrations of F, Cl, NO2, NO3, PO4 and SO4 in sediment samples were lower inward for KTD. The vast majority of trace metals in sediments were generally within the standard limits recommended for soils. TOM and grain size of sediment are major factors governing the trace metal concentrations. The calculated geoaccumulation index (I geo) and enrichment factor of metals in bottom sediments showed that the metals were in the following order: Cd > Pb > Zn > Co > Cr > Ni > Fe > Cu > Sr > Mn and Cd > Zn > Pb > Co > Cr > Ni > Cu > Sr > Mn, respectively. Based on the sonic survey of KTD reservoir, the annual sedimentation rate was about 0.4061 MCM/year, in which about 18.66% of the reservoir initial storage capacity was lost to sediments and a projected lifespan of about 198 years.  相似文献   

7.
Ferrihydrite (2.5 Fe2O2-4.5 H2O) is an unstable colloidal mineral. It dissolves in highly alkaline solutions and is precipitated from them in the form of goethite. Jarosite is stable at very low pH but is decomposed at higher values of pH with separation of iron oxides. Experiments show that in rapid decomposition of jarosite a protohematite substance, ferrihydrite, is formed. This transformation occurs at moderate pH values when solutions percolate through the aggregates of jarosite. Ferrihydrite, an unstable colloidal hydrated oxide of ferric iron, changes spontaneously to stable hematite with time. Very slow decomposition of jarosite results in its replacement by iron hydroxide, goethite. Under laboratory conditions in alkaline solutions lepidocrocite may be obtained from jarosite. The synthesis of this iron hydroxide passes through a stage of intermediate products: ferrihydrite and hydrated ferric oxide - ferriprotolepidocrocite, formed by solution of ferrihydrite in strongly alkaline solutions. The transformation of ferriprotolepidocrocite into lepidocrocite may be regarded as a topotactic reaction. —Authors.  相似文献   

8.
The importance of the discovery of jarosite at the Meridiani Planum region of Mars is discussed. Terrestrial studies demonstrate that jarosite requires a unique environment for its formation, crystallizing from highly acidic (pH < 4) S-rich brines under highly oxidizing conditions. A likely scenario for jarosite formation on Mars is that degassing of shallow magmas likely released SO2 that reacted with aqueous solutions in shallow aquifers or on the martian surface. This interaction forms both H2SO4 and H2S. A martian oxidant must be identified to both oxidize H2S to produce the required acidity of the fluid, and to oxidize Fe2+ to Fe3+. We suggest that reactions involving both sulfur and the reduction of CO2 to CO may provide part of the answer. The jarosite crystal structure is truly remarkable in terms of its tolerance for the substitution of a large number of different cations with different ionic radii and charges. The structure accommodates hydrogen, oxygen, and sulfur, the stable isotope systematics of which are strong recorders of low-temperature fluid-rock-atmosphere interactions. Jarosite has been proven to be a robust chronometer for Ar-Ar and K-Ar dating techniques, and there is every reason to believe that U-Pb, Rb-Sr, and Nd-Sm techniques for older jarosite from Mars will also be robust. Although the discovery of jarosite on Mars alone, with no other analytical measurements on the phase, has given us insights to martian surficial processes, the true power of jarosite can not be exploited until jarosite is sampled and returned from Mars. Mars sample return is a long way off but, until then, we should be vigilant about examining martian meteorites for alteration assemblages that contain jarosite. A suite of jarosite samples representing a significant time span on Mars may hold the key to reading the record of martian atmospheric evolution.  相似文献   

9.
Most efforts in the study of sea-marginal sabkhas have concentrated on the Persian Gulf, but little is known about the sediments and mineralogy of sabkhas marginal to other seas. The purpose of this paper was to present some geochemical and mineralogical observations in a recent sabkha on the coast of Sinai along the Gulf of Suez. The sabkha is composed of coarse clastic sediments with marine-derived groundwater at depth of about 1 m. The general morphology, climate and water salinity of the Gulf of Suez resemble those of the Persian Gulf, despite the fact that the content of authigenic evaporites in this sabkha is more sparse. The evaporite minerals accumulated only in the upper 30–40 cm of the sabkha, below that and down to the groundwater table, there is no accumulation of evaporites. Laterally, the salinity of the groundwater in the sabkha and the concentration of evaporites in the sediments above it increase constantly with distance from the shore. In contrast to the Persian Gulf where anhydrite is a major evaporite mineral, in Belayim gypsum is the only calcium sulphate mineral in the recent sabkha. Anhydrite is found only in an old elevated sabkha where it recrystallized from gypsum. The gypsum occurs as interstitial crystal concentrations or lithified horizons almost exclusively at the depth of 20–40 cm below the sabkha surface. Above that, in the uppermost horizons, there is in situ accumulation of interstitial halite crystals. The total concentrations of gypsum and halite are almost equal in this sabkha. The sea water recharge in El Belayim is almost exclusively by seepage through the sabkha sediments and not by flooding. The groundwater under this sabkha is only slightly more saline than the Gulf water, thus, not heavy enough for extensive downward refluxing. The major hydrodynamic process must be upward migration of the brines from the groundwater, precipitating on the way gypsum and later halite with some magnesite. Since the sediments of the sabkha are too coarse to support extensive capillary movement, the brines must, therefore, migrate upwards due to ‘evaporative pumping’.  相似文献   

10.
氧化亚铁硫杆菌作用下形成的黄钾铁矾的SEM研究   总被引：29，自引：3，他引：26  
黄钾铁矾是金属硫化物在酸性条件下氧化形成的主要次生矿物。很多研究表明,金属硫化物矿区广泛发育的氧化亚铁硫杆菌会影响金属硫化物的氧化分解和次生矿物的形成。为讨论氧化亚铁硫杆菌在黄钾铁矾形成过程中的作用,设计了两组平行实验制备黄钾铁矾：一种采用化学方法合成黄钾铁矾,另一种在相同条件下接种氧化亚铁硫杆菌合成黄钾铁矾。利用X-射线衍射仪(XRD)、扫描电子显微镜(SEM)和能谱分析仪(EDS)等技术对两种实验获得的黄钾铁矾进行定性分析和形貌观察。结果表明：在氧化亚铁硫杆菌充分繁殖的条件下,细菌的参与更利于黄钾铁矾的形成;Fe^2+的氧化速率可能是影响黄钾铁矾结晶的主要因素,氧化亚铁硫杆菌通过提高Fe^2+的供应速度促使黄钾铁矾快速结晶,细菌作用下形成的黄钾铁矾结晶程度好于纯化学方法制备的黄钾铁矾。  相似文献   

11.
The increasing anthropogenic activities (e.g., constructing touristic resorts) have led to notable changes in the Yemeni Red Sea coastal regions. In this context, recent sediments have been investigated to infer possible natural and man-induced processes on these coastal areas. The target area lies between longitudes 43°13′–43°30′E and latitudes 13°15′–13°55′N. It extends about 90 km along the coastline as a part of the Tihama plain. Geomorphologically, it forms a long-curved stretch with pronounced headlands, embayments and bays. Generally, it is covered by recent sediments (wadi, lagoon, beach and spit deposits along with sabkha, coastal dunes and mangrove). Textural studies reveal that most of the studied sediments are mainly poorly to moderately sorted and are composed mainly of sandy fractions with few gravel and mud, mostly bimodal with minor unimodal patterns. The igneous (granites) as well as basic (basalt, andesite and andesitic pyroclastics) and acidic (dacite and rhyolite) volcanic rocks of Tertiary age, which are exposed to the east of the study area, are believed to be the source of pyroxenes, amphiboles, epidotes, biotite, sphene, zircon, tourmaline and rutile, in a decreasing order of abundance. Moreover, smectite, kaolinite, chlorite, illite and palygorskite are the predominant clay minerals, mainly of detrital origin. The total carbonate content fluctuates from 37.41% (lagoon sediments) to 53.74% (sabkha sediments). The high amount of sea grasses, which covers the tidal flat zone and relates to the fine-grained sediments, accounts for the high organic matter content. The mineralogy of the source rocks has controlled the general distribution of major elements (Fe, Mg, Na, K and Mn) in the beach sediments. In such sediments, the concentrations of the heavy metals (Cu, Zn, Cd, Ni, Pb and Co) may reflect the sediment pollution using different approaches. The enrichment factors (EFs) of the trace metals for most samples reveal values that are greater than 1, referring to three groupings, which are: moderate to moderately severe (Zn, Cu and Mn), minor to moderate (Pb and Co) and zero to minor (Cd and Ni) enrichment. The EFs for Pb, Cd, Ni and Co metals (<5) may be attributed to the crustal materials and/or natural weathering processes. But, those for Zn, Cu and Mn (>5), especially in Al-Khowkhah–Abu-Zahr, Moushij–Zahari–Ruays, Yokhtol and Mokha localities, are possible of anthropogenic contributions.  相似文献   

12.
Upper reaches of the Arabian Gulf consist of different types of fine sediments including the vast Mesopotamia Plain sediments, tidal flat sediments and estuarine sabkha sediments. The height of the plain starts from zero meter and increases northwards to three meters with extremely gentle gradient. The vast plain to the north of the Arabian Gulf is drained by Shat Al-Arab (Shat means river in Iraqi slang language) and Khor Al-Zubair (Khor means estuary). The former drains the extreme eastern part of the plain; whereas, the latter drains the western part. Shat Al-Arab is the resultant of confluence of the Tigris and Euphrates rivers near Al-Qurna town; about 160 km north of the Arabian Gulf mouth at Al-Fao town; whereas, the length of Khor Al-Zubair is about 50 km; as measured from Um Qasir Harbor. The drainage system around Khor Al-Zubair is extremely fine dendritic; whereas around Shat Al-Arab is almost parallel running from both sides of the river towards the river; almost perpendicularly. The fine dendritic drainage around Khor Al-Zubair shows clear recent erosional activity, beside water divides, abandoned irrigation channels and dislocated irrigational channels and estuarine distributaries; all are good indication for a Neotectonic activity in the region. These may indicate the presence of subsurface anticlines, which may represent oil fields; since tens of subsurface anticlines occur in near surroundings, which are oil fields.  相似文献   

13.
This study examined the chemical speciation and mobility of As and heavy metals in a tailings impoundment in Samsanjeil mine located in Gosung, Korea, as well as the factors affecting them. XRD, SEM, and 5-step sequential extraction were used to examine the samples at two sampling sites (NN and SN sites). The pH of the tailings decreased with increasing depth at the NN site (from 7.2 to 2.8), whereas no significant differences were observed at the SN site (8.1–8.8). The samples at the SN site showed a larger amount of calcite than those at the NN site, indicating that calcite plays an important role buffering the pH in the study sites. Jarosite was found only at the lower part of the NN site, where calcite was not found. The mineralogical observation of jarosite and calcite was also confirmed by SEM. The concentrations of As and heavy metals in the tailings were as follows: Cu > As > Zn > > Pb > Co > Cr > Ni > Cd. The total concentrations of Ni, Zn, Co, and Cd were higher at the SN site than those at the NN site. On the other hand, the concentrations of As and Cr existing as oxyanions were higher at the NN site, which can be explained by the mobility changes of those elements affected by pH variations. At the NN site, the fractions of heavy metals bound to the Fe/Mn oxides, except for As and Cr, decreased, and Cu, Zn, and Co showed an increasing fraction of exchangeable metals with increasing depth. This suggests that the pH and resulting surface charge of minerals, such as goethite and jarosite, are the dominant factors controlling the chemical speciation of metals. These results highlight the importance of mineralogy in controlling the mobility and possible bioavailability of heavy metals in tailings.  相似文献   

14.
Nabq sabkha exists 16 km north of Sharm El Sheikh City occupying the low land topography in the alluvial fan zone along the coastal area, Gulf of Aqaba, Sinai, Egypt. The long axis of the sabkha trends NW–SE receiving water from two different sources: meteoric water drained from the surrounding mountainous area and seawater seepage. Field observations help to divide the area into raised beach, hill slopes, sabkha basin, and coastal area. The sabkha basin can be subdivided from its center outward into (1) basin center hypersaline lake flourished with microbial mat and precipitation of halite as rafts, cumulates, and chevrons, (2) saturated saline sand and/or mud flat zone with the extensive growth of gypsum and halite crystals growing displacively as well as different forms of petee structures, and (3) an elevated marginal dry zone with tepee structures. Mineralogical analysis reveals that quartz, halite, and gypsum are the dominant minerals with subordinate amount of aragonite, anhydrite, thenardite, and/or polyhalite. In addition, clay minerals in the mudflat zone are presented by illite and smectite, indicating derivation of soil from the surrounding basement rocks. Chemical analysis of the collected brine samples reveals alkali character in the saline lake (pH?=?7.6) and high concentrations of Na+ (680 meq/l), Cl? (940 meq/l), Mg2+ (208 meq/l), Ca2+ (70 meq/l), SO 4 2+ (30 meq/l), and HCO 3 ? (6 meq/l). The high salinity values are due to the aridity of the area, which favors precipitation of halite. Using comparative sedimentological, chemical, and mineralogial methods between such modern and ancient evaporitic environments and by detailed field, petrographic and mineralogical studies of modern evaporite environments help to interpret paleo-depositional environments of ancient evaporites sequences still in debate.  相似文献   

15.
Sulfur biogeochemical cycling and associated Fe-S mineralization processes exert a major influence over acidity dynamics, electron flow and contaminant mobility in wetlands, benthic sediments and groundwater systems. While S biogeochemical cycling has been studied intensively in many environmental settings, relatively little direct information exists on S cycling in formerly drained wetlands that have been remediated via tidal re-flooding. This study focuses on a tidal wetland that was drained in the 1970s (causing severe soil and water acidification), and subsequently remediated by controlled re-flooding in 2002. We examine reduction rates and Fe-S mineralization at the tidal fringe, 7 years after the commencement of re-flooding. The initial drainage of the wetland examined here caused in-situ pyrite (FeS2) oxidation, resulting in the drained soil layers being highly acidic and rich in -bearing Fe(III) minerals, including jarosite (KFe3(SO4)2(OH)6). Tidal re-flooding has neutralized much of the previous acidity, with the pore-water pH now mostly spanning pH 5-7. The fastest rates of in-situ reduction (up to ∼300 nmol cm−3 day−1) occur within the inter-tidal zone in the near-surface soil layers (to ∼60 cm below ground surface). The reduction rates correlate with pore-water dissolved organic C concentrations, thereby suggesting that electron donor supply was the predominant rate determining factor. Elemental S was a major short-term product of reduction, comprising up to 69% of reduced inorganic S in the near-surface soil layers. This enrichment in elemental S can be partly attributed to interactions between biogenic H2S and jarosite - a process that also contributed to enrichment in pore-water Fe2+ (up to 55 mM) and (up to 50 mM). The iron sulfide thiospinel, greigite (Fe3S4), was abundant in near-surface soil layers within the inter- to sub-tidal zone where tidal water level fluctuations created oscillatory redox conditions. There was evidence for relatively rapid pyrite re-formation within the re-flooded soil layers. However, the results indicate that pyrite re-formation has occurred mainly in the lower formerly drained soil layers, whereas the accumulation of elemental S and greigite has been confined towards the soil surface. The discovery that pyrite formation was spatially decoupled from that of elemental S and greigite challenges the concept that greigite is an essential precursor required for sedimentary pyrite formation. In fact, the results suggest that greigite and pyrite may represent distinct end-points of divergent Fe-S mineralization pathways. Overall, this study highlights novel aspects of Fe-S mineralization within tidal wetlands that have been drained and re-flooded, in contrast to normal, undisturbed tidal wetlands. As such, the long-term biogeochemical trajectory of drained and acidified wetlands that are remediated by tidal re-flooding cannot be predicted from the well-studied behaviour of normal tidal wetlands.  相似文献   

16.
A two-dimensional, vertically integrated, nonlinear numerical model was applied to investigate the tide-driven bed load transport of sediments and morphodynamics in the shallow coastal lagoon of Yavaros, located in the southeastern part of the Gulf of California, Mexico. Satellite imagery exposes strong sediment dynamics in this coastal region. The dynamics in the lagoon were forced by 13 tidal constituents at the open boundary. Tides are of a mixed character and they are predominantly semidiurnal. The calculations showed areas of intense tidal currents and considerable water exchange with the Gulf of California. Numerical experiments revealed an ebb-dominant tidal distortion and a net export of sediment from the lagoon to the Gulf of California. A simulation of 20 years showed that the lagoon exported about 1,600 m3 of sediment; however, the daily oscillating exchange of sediment reached values of around 8 m3. The daily averaged flux of export–import sediments oscillates principally with semiannual, monthly and fortnightly periods. By applying a threshold velocity, a variable friction coefficient and the calculated amplitude of tidal velocities, it was possible to determine that morphological changes occur in zones of sharp topographic gradients and to explain the effect of friction on the export–import process of sediments. A 10-year simulation revealed that accumulation of sediment (~20 cm) occurred in small areas, whereas erosion occurred in larger areas but with less intensity (~8 cm). Besides the importance for the morphodynamics, these kinds of erosion–accretion processes may be relevant for the marine ecology.  相似文献   

17.
This study addresses the distribution of total phosphorus (TP) and its inorganic (IP) and organic (OP) fractions, grain-size and organic matter of surface and recent sediments, coupled to the behavior of total and dissolved inorganic phosphorus (TP and DIP) of the water column, of the semi-pristine Guaratuba Bay estuary, SE Brazil. Surface sediment samples were taken at 43 sites spread along the estuarine gradient and recent sediments from 3 short (35 cm long) cores from the upper, central and lower portions of the estuary, respectively. Highest TP and IP concentrations of surface sediments were detected within the upper sector and the transition zone between the upper and central sectors, all characterized by fine sediments, low salinities and water depths. In contrast, the lower sector and its narrow and deep tidal channel, subject to more intense tidal forcing, exhibited a higher fraction of sandy sediments with lower TP, IP and OP contents. In spite of the spatial variability in sediment grain size, IP corresponded to the major fraction of TP in all estuarine sectors and both TP and IP correlated significantly with the fine sedimentary (silt + clay) grain-size fraction. The fine surface sediments acted as a trap for IP at the fresh water–low salinity interface, which also corresponded to the region of a DIP sink in surface waters. In general, the short sediment cores showed that TP and IP contents increased from 15 cm depths to the top layer. Published sedimentation rates from additional cores taken at the sites of the short cores of this study, implied that depositional alterations of TP and IP increased during the early 1970s, which corresponded to the onset of anthropogenic disturbances from crop plantations in the lowland plains of the river end-member and urbanization at the estuary’s mouth and along the adjacent coast.  相似文献   

18.
The clay mineral content of the < 2 µm fraction in tidal flat sediments in the former Harle Bay on the Lower Saxony coast has changed considerably since the thirteenth century up to the present time. The proportion of smectite has decreased from 29 to 11 wt%, whereas the proportion of illite has increased by about 10 wt% and those of chlorite and kaolinite by about 3 wt% each. The chemical composition of the major clay mineral illite has also changed: Al2O3 has decreased by about 2 wt%, K2O by about 1·5 wt% and SiO2 by about 3 wt%. It can be concluded that the changes in the clay mineral content are mainly influenced by dike construction and sea level rise, modifying flow pattern, submarine morphology, sedimentation and tidal range. These processes cause smectite to settle less rapidly because of its small grain size and low density resulting from interlayer water, so that the sediment becomes impoverished in this mineral.  相似文献   

19.
Mapping the occurrence and thickness of layers within a soil profile is a prerequisite for soil characterization. The objective of this paper is to compare the applicability of two statistical methods—discriminant analysis (DA) and logistic regression (LR)—used to calculate the thickness of Quaternary sediments in a formal way and to identify parameters controlling the occurrence of these sediments. The investigations were carried out in southern Bavaria in an area of about 150 ha presenting a large variability in relief and parent material (Tertiary material, Pleistocene loess, colluvial/alluvial sediments). Comparisons between the two statistical methods were carried out with a training dataset and an evaluation dataset. The results show that DA was preferable under the assumptions of normality and equal variance/covariance matrices. The analyses produced models with 80 % and 79 % correctly reclassified assignments and a canonical correlation coefficient of approximately 0.60. From the simulations, it was found (i) that the determining predictors were altitude, slope, and upslope catchment area (partly expressed as topographical wetness index), SAGA wetness index and specific catchment area; and (ii) that a disadvantage of LR was that trial and error was frequently necessary to find the optimal composition of variables. In this study, a hierarchical combination of binary and ordinal LR was used and revealed (iii) that when the probabilities in LR between adjacent categories were similar, the possibility of incorrect calculations increased and (iv) that visual inspections as well as RMSE showed that DA with weighted depths (5 cm-stepwise DA) provided the best prediction accuracy. This information can help improve soil surveys and the predictability of the spatial heterogeneity in landscapes.  相似文献   

20.
A new occurrence of Recent stromatolites different from those known up to now has been discovered on tidal flats of the Bay of Saint-Jean (near Cape Timiris). Their most remarkable features are predominance of quartz sand instead of carbonate, characteristic surface-contouring by grazing fish, absence of cementation, intensive reworking by crabs, and connection with saline sabkha deposits. Entrapment of sand grains and great resistance of the algal sheaths are most important for stromatolitic growth, although today destruction appears to prevail over accretion. Quartz sand of aeolian dunes and carbonatic pellets of aragonitic ooze feeders are the main constituents of the stromatolitic sediments. According to the tidal range the following zonation of the algal mat exists: (A) knoll and cuspate zone, (B) flat zone, (C) gas-domed zone, and (D) crinkle zone.  相似文献   

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