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1.
Fluvial sediments are subject to cyclic submersion during changes in stream flow, which can affect their phosphorus (P) sorptive capacity. As fluvial sediments play a major role in determining P concentrations in stream flow, we compared the P chemistry of exposed stream bank and submerged bed sediments from an agricultural catchment in central Pennsylvania, USA. Total P concentration was greater in bank (417 mg kg-1) than bed sediments (281 mg kg-1), but because bed sediments contained more sand-sized material, they could release more P and support a higher solution P concentration (0.043 mg l-1) than bank sediments (0.020 mg l-1). Phosphorus release was a function of Mehlich-3 soluble Fe in stream sediments (r > 0.65), reflecting redox processes in the fluvial system. In contrast, P sorption maxima of bank and bed sediments were related to Mehlich-3 soluble Al (r > 0.78) and organic matter concentration (r > 0.79). Overall, our research suggested that erosion of bank sediments should contribute less P and may be a sink for P in the stream system compared with resuspension of bed sediment. However, bank sediments may have the potential to be a large source of P in downstream reservoirs or lakes, where increased microbial activity and reducing conditions may solubilise sediment-bound P.  相似文献   

2.
This paper examines the long-term field performance of the check-dams in mitigation of soil erosion in the Duozhao catchment of Jiangjia stream, southwest China. Since their construction between 1979 and 1982, the check-dams have been functioning effectively. The examination is made via comparisons between the environmental conditions of the Duozhao catchment with its adjacent Menqian catchment in the stream, because no check dams were constructed in the Menqian catchment. The examination is based on recent field investigations and aerial photograph analyses, and covers four aspects: (a) bed gradients of catchment channels; (b) stability of bank slopes; (c) rates of land erosion; and (d) vegetations on bank slopes. The field data demonstrate that the check-dams have had the following good functions for mitigation of soil erosion: (1) restricting the channel depth and lateral erosions, (2) protecting the channel erosion base, (3) reducing the bed gradients of debris-flow channels, (4) fixing the channel bed, (5) stabilizing the bank slopes, as well as (6) facilitating the growth of vegetations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

3.
Geochemical methods (major elements and Sr, Nd isotopes) have been used to (1) characterize Lake Le Bourget sediments in the French Alps, (2) identify the current sources of the clastic sediments and estimate the source variability over the last 600 years. Major element results indicate that Lake Le Bourget sediments consist of 45% clastic component and 55% endogenic calcite. In addition, several individual flood levels have been identified during the Little Ice Age (LIA) on the basis of their higher clastic content (> 70%).Potential sources of Lake Le Bourget clastic sediments have been investigated from Sr and Nd isotope compositions. The sediments from the Sierroz River and Leysse River which are mainly derived from the Mesozoic Calcareous Massifs are characterised by lower 87Sr/86Sr ratios and slightly lower ?Nd(0) ratios than the Arve River sediments which are derived from the Palaeozoic Mont-Blanc External Crystalline Massifs. The Rhône River appears to have been the main source of clastic sediments into the lake for the last 600 years, as evidenced by a similar Sr and Nd isotopic compositions analyzed in core B16 sediments (87Sr/86Sr = 0.719, ?Nd(0) = − 10) and in the sediments of the Rhône River (87Sr/86Sr = 0.719, ?Nd(0) = − 9.6).The isotopic signatures of flood events and background samples from core B16 in Lake Le Bourget are also similar. This indicates that prior to ∼ 1800, the inputs into the lake have remained relatively homogeneous with the proportion of clastic component mainly being a function of the palaeohydrology of the Rhone River. Early human modification (deforestation and agriculture) of the lake catchment before the 1800s appears to have had little influence on the source of clastic sediments.  相似文献   

4.
We have collected ∼500 stream waters and associated bed-load sediments over an ∼400 km2 region of Eastern Canada and analyzed these samples for Fe, Mn, and the rare earth elements (REE + Y). In addition to analyzing the stream sediments by total digestion (multi-acid dissolution with metaborate fusion), we also leached the sediments with 0.25 M hydroxylamine hydrochloride (in 0.05 M HCl), to determine the REE + Y associated with amorphous Fe- and Mn-oxyhydroxide phases. We are thus able to partition the REE into “dissolved” (<0.45 μm), labile (hydroxylamine) and detrital sediment fractions to investigate REE fractionation, and in particular, with respect to the development of Ce and Eu anomalies in oxygenated surface environments. Surface waters are typically LREE depleted ([La/Sm]NASC ranges from 0.16 to 5.84, average = 0.604, n = 410; where the REE are normalized to the North America Shale Composite), have strongly negative Ce anomalies ([Ce/Ce∗]NASC ranges from 0.02 to 1.25, average = 0.277, n = 354), and commonly have positive Eu anomalies ([Eu/Eu∗]NASC ranges from 0.295 to 1.77, average = 0.764, n = 84). In contrast, the total sediment have flatter REE + Y patterns relative to NASC ([La/Sm]NASC ranges from 0.352 to 1.12, average = 0.778, n = 451) and are slightly middle REE enriched ([Gd/Yb]NASC ranges from 0.55 to 3.75, average = 1.42). Most total sediments have negative Ce and Eu anomalies ([Ce/Ce∗]NASC ranges from 0.097 to 2.12, average = 0.799 and [Eu/Eu∗]NASC ranges from 0.39 to 1.43, average = 0.802). The partial extraction sediments are commonly less LREE depleted than the total sediments ([La/Sm]NASC ranges from 0.24 to 3.31, average = 0.901, n = 4537), more MREE enriched ([Gd/Yb]NASC ranges from 0.765 to 6.28, average = 1.97) and Ce and Eu anomalies (negative and positive) are more pronounced.The partial extraction recovered, on average ∼20% of the Fe in the total sediment, ∼80% of the Mn, and 21-29% of the REEs (Ce = 19% and Y = 32%). Comparison between REEs in water, partial extraction and total sediment analyses indicates that REEs + Y in the stream sediments have two primary sources, the host lithologies (i.e., mechanical dispersion) and hydromorphically transported (the labile fraction). Furthermore, Eu appears to be more mobile than the other REE, whereas Ce is preferentially removed from solution and accumulates in the stream sediments in a less labile form than the other REEs + Y. Despite poor statistical correlations between the REEs + Y and Mn in either the total sediment or partial extractions, based on apparent distribution coefficients and the pH of the stream waters, we suggest that either sediment organic matter and/or possibly δ-MnO2/FeOOH are likely the predominant sinks for Ce, and to a lesser extent the other REE, in the stream sediments.  相似文献   

5.
The paper discusses the geochemical and Sr–Nd–Pb-isotope data on ice-rafted sediments (IRS) from different areas of the Arctic Ocean. Samples were collected during the Cruise of R/V Polarstern between Spitsbergen and North Pole, Yermak Plateau, as well as in Fram Strait. It is shown that the studied IRS samples in terms of LaN/YbN and εNd values are close to the composition of suspended particulate matter (SPM) from the mouth parts of large rivers and rivers transporting the sedimentary erosion products. This also follows from their Th/Sc, Th/Co, La/Sc, La/Sm, Sc/Th ratios and Sc content and from the position of their data points in the Sc–Th/Sc, La/Sc–Th/Co, and La/Sm–Sc/Th diagrams between the average SPM compositions of the Ob and Lena rivers. The values of 207Pb/206Pb and εNd in IRS samples give grounds to suggest that the rock complexes of the European, North American, and Asian continental margins could be potential sources for this sedimentary material. In the 207Pb/206Pb–εNd diagram, the IRS samples from all three studied areas define a compact cluster and are mainly confined to the triangle with corners represented by the Mackenzie River, Okhotsk–Chukotka volcanic area, and Lena River, being closer to the latter. In the Sm/Nd–εNd diagram, IRS points also form a compact field, being located almost in the middle between the average SPM compositions of the Yenisei and Ob rivers, on the one hand, and Lena River, on the other. In all diagrams, IRS samples from the different West Arctic areas show no significant scatter. With allowance for the fact that sediments are not subjected to significant homogenization during ice rafting, sediments from all three areas were obtained from a common source. As seen from the position of IRS data points in the 87Sr/86Sr–εNd diagram, this source was the Asian continental margin.  相似文献   

6.
Lanthanoids were studied in a boreal landscape where an abundance of acid sulfate soils and Histosols provide a unique opportunity to increase the understanding of how these metals behave in acidic soils and waters and interact with soil and aqueous organic matter. In the acid sulfate soils lanthanoids are mobile as reflected in high to very high concentrations in soil water and runoff (typically a few mg l−1 but up to 12 mg l−1) and abundant release by several relatively weak extractants (ammonium acetate EDTA, sodium pyrophosphate, hydroxylamine hydrochloride) applied on bulk soil. Normalisation with the lanthanoid pool in the underlying parent materials (sulphide-bearing sediments deposited in brackish-water) and soil water showed that the extensive release/retention in the acidic soil was accompanied by large, and variable, fractionation trends across the lanthanoid series. In low-order streams draining these soils, the lanthanoid concentrations were high and, as indicated by frontal ultrafiltration and geochemical modelling, largely dissolved (<1 kDa) in the form of the species LnSO4+ and Ln3+. In other moderately acidic stream waters (pH 4.3-4.6), organic complexation was predicted to be important in the <1 kDa fraction (especially for the heavy lanthanoids) and strongly dominating in the colloidal phase (1 kDa-0.45 μm). Along the main stem of a stream in focus (catchment area of 223 km2), lanthanoid concentrations increased downstream, in particular during high flows, caused by a downstream increase in the proportion of acid sulfate soils which are extensively flushed during wet periods. The geochemical models applied to the colloidal Ln-organic phase were not successful in predicting the measured fractionation patterns.  相似文献   

7.
Characterizing stream erosion in any steep mountain landscape is arduous, but the challenge level increases when the stream flows through a glaciated catchment frequently modified by hillslope debris.Glacial landforms and stochastic mass wasting in alpine systems may interfere with sediment delivery to downstream sites where detrital sediments are often collected to represent upstream bedrock sources.To use detrital sediments as indicators of erosion, we need to understand potential sediment accumulation in flat glaciated reaches or behind rockfall barriers. This study investigates the stream channel in Garnet Canyon, a glaciated catchment located in the central Teton Range, to describe hillslope coupled channel morphology and the subsequent effects on sediment transport throughout the catchment.Stream cross-section surveys and sediment size measurements of the surface bedload were collected in the field within a glacially flattened segment of Garnet Canyon. Calculations of shear stress conditions allowed evaluation of the importance of mineral densities on potential grain entrainment. The length of the Garnet Canyon stream observed in this study was coupled with hillslope deposits. Critical shear stresses were sufficient to move gravel-sized sediments through all sections when calculated with quartz mineral density and through most sections when applying apatite mineral density. These results verify the application of detrital sediments to evaluate erosion rates or spatial bedrock sources because snowmelt stream flow efficiently moves entrained sediment past glacially reduced slopes and potential talus barriers.  相似文献   

8.
A new method is proposed for the identification and apportionment of contemporary source soils contributing to estuarine sediments. The method uses compound-specific isotopic analysis of naturally occurring biomarkers (fatty acids) derived from plants to link source soils to land use within a single catchment. For identification and apportionment of source soils in the estuarine samples, the method uses the isotopic mixing model, IsoSource. The feasible proportions obtained from IsoSource are then scaled to allow for the percent organic carbon in the source soils. With this approach, the estimation of each source soil contribution to a location in the estuary is independent of any degradation of the biomarkers through microbial or biogeochemical processes. Identification relies on the evaluation of the sediment sample relative to a “library” of reference source soils from different land use within the catchment. Selection of potential sources is geographically constrained by the requirement for a natural linkage between each source soil and the sediment site sampled. A case study, using this method, mapped the distribution of three main land use source soils (pasture, native forest, and pine forest) across the river delta in a small estuary fringed with mangroves. Rather than being uniformly distributed, the results indicated that the source soil contributions varied markedly across the delta, raising concerns about the validity of taking single cores to characterize the sediments of an estuary. Coupling the source apportionment results with land use data indicated that the mean percent contribution of pine forest soil in the river delta sediments was almost three times greater than the percent land use area of pine forest in the catchment. Furthermore, isotopic signatures indicated that most of the pine forest soil came from the much smaller areas exposed to erosion by clear cut harvesting and that the soil contribution from recently harvested areas of pine forest could be as much as 20 times greater than that land use area in this catchment. This is the first method that can identify and apportion, by land use on a catchment scale, the sources of soil contributing to the sediment at a location of an estuary. The results are given as a “best estimate”, within definable limits, of the proportional contribution of each potential source soil. Information obtained using this method will allow development of management strategies to alter land use practices to reduce the sediment load to rivers, and thus, the impact on the aquatic ecosystem downstream in estuaries.  相似文献   

9.
Over the last few years there has been growing concern over the mobilisation of anthropogenically derived, atmospherically deposited Pb from upland blanket peat soils to receiving surface waters. The near-surface layer of blanket peat soils of the Peak District, southern Pennines, UK, is severely contaminated with high concentrations of Pb. Erosion of peat soils in this upland area may be releasing large quantities of previously deposited Pb into the fluvial system. Samples of fluvial sediments (suspended, floodplain, streamside fan, trash-line and channel bed) were collected from a severely eroding blanket peat catchment in the Peak District in order to investigate Pb contamination of fluvial sediments, to determine the mechanism for fluvial Pb transport and to determine if erosion of contaminated peat soils in the catchment is releasing Pb into the fluvial system. Concentrations of Pb associated with fluvial sediments are considerably higher than those in the catchment geology, but not as high as those in peat soils in the catchment. Intra- and inter-storm variability in the Pb content of suspended sediments can be explained by differences in organic matter content of these sediments and differences in erosion processes operating within the catchment. High Pb concentrations are associated with suspended sediments that have a high organic matter content. The results of this study suggest that organic matter is the principle vector for sediment-associated Pb in the fluvial system. Erosion of contaminated peat soils in the Peak District is releasing Pb into the fluvial system. The extent to which this is a problem in other peatland environments is an area requiring further research.  相似文献   

10.
《Applied Geochemistry》2001,16(3):387-396
The concentration variations of 16 trace elements were determined along the main stem of a medium-sized stream (catchment area=107 km2), which drains areas covered with acid sulphate soils developed on sulphide-bearing marine sediments. During high flows in autumn, there was a strong downstream increase in the concentrations of Al, Cd, Co, Cu, Mn, Ni, Se, U and Zn and a moderate increase in those of Cr and Tl, related to extensive leaching of the acid sulphate soils, which increase in abundance from the headwater towards the basin outlet. During high flow in early summer, the downstream increase in the concentrations of these elements was not as strong as in autumn, due to decreased amounts of available mobile element fractions in the acid sulphate soils. Under baseflow conditions, the runoff from areas with acid sulphate soils is low in comparison to that in areas covered with other soils/sediments, resulting in relatively small loads of trace elements throughout the stream. The concentration variations of As, Pb, Sb, Ti and V were unrelated to catchment cover and did not vary along the stream in a regular manner. These 5 elements are, therefore, in contrast to the others, not leached more abundantly from the acid sulphate soils than from other soils/sediments. Based on the identified hydrogeochemical features and controls, it is suggested that water-quality improvement measures should include methods that primarily aim at reducing the leaching of hazardous chemical elements in the source areas (acid sulphate soils).  相似文献   

11.
Geochemical variations in stream sediments (n = 54) from the Mahaweli River of Sri Lanka have been evaluated from the viewpoints of lithological control, sorting, heavy mineral concentration, influence of climatic zonation (wet, intermediate, and dry zones), weathering, and downstream transport. Compositions of soils (n = 22) and basement rocks (n = 38) of the catchment and those of <180 μm and 180–2000 μm fractions of the stream sediments were also examined. The sediments, fractions, soils and basement rocks were analyzed by X-ray fluorescence to determine their As, Pb, Zn, Cu, Ni, Cr, V, Sr, Y, Nb, Zr, Th, Sc, Fe2O3, TiO2, MnO, CaO, P2O5 and total sulfur contents. Abundances of high field strength and ferromagnesian elements in the sediments indicate concentration of durable heavy minerals including zircon, tourmaline, rutile, monazite, garnet, pyriboles, and titanite, especially in <180 μm fractions. The sediments show strong correlation between Ti and Fe, further suggesting presence of heavy mineral phases containing both elements, such as ilmenite and magnetite. The basement rocks range from mafic through to felsic compositions, as do the soils. The river sediments lack ultrabasic components, and overall have intermediate to felsic compositions. Elemental spikes in the confluences of tributary rivers and high values in the <180 μm fractions indicate sporadic inputs of mafic detritus and/or heavy minerals to the main channel. Al2O3/(K2O + Na2O) and K2O/Na2O ratios of the sediments and LOI values of the soils correlate well with the climatic zones, suggesting intense weathering in the wet zone, lesser weathering in the intermediate zone, and least weathering in the dry zone. Low Sr and CaO contents and Cr/V ratios in stream sediments in the wet zone also suggest climatic influence. Fe-normalized enrichment factors (EFs) for As, Pb, Zn, Cu, Ni and Cr in stream sediments in the main channel are nearly all <1.5, indicating there is no significant environmental contamination. The chemistry of the sediments, rocks and the soils in the Mahaweli River are thus mainly controlled by source lithotype, weathering, sorting, and heavy mineral accumulation.  相似文献   

12.
Strontium and neodymium isotopes, measured on diverse mud and sand fractions of sediment in transit along all major Nile branches, identify detritus sourced from Precambrian basements, Mesozoic strata, and Tertiary volcanic rocks exposed along the shoulders of the East African rift and in Ethiopian highlands. Sr and Nd isotopic ratios reflect the weighted average of detrital components generated in different catchments, allowing us to discriminate provenance, calculate sediment budgets, and investigate grain-size and hydraulic-sorting effects.87Sr/86Sr and 143Nd/144Nd range, respectively, from as high as 0.722 and as low as 0.5108 for sediment derived from Archean gneisses in northern Uganda, to 0.705 and 0.5127 for sediment derived from Neoproterozoic Ethiopian and Eritrean basements. 87Sr/86Sr and 143Nd/144Nd, ranging 0.705-0.709 and 0.5124-0.5130 for Blue Nile tributaries, are 0.704-0.705 and 0.5127-0.5128 for largely volcaniclastic sediments of River Tekeze-Atbara, and 0.705-0.706 and 0.5126-0.5127 for main Nile sediments upstream Lake Nasser.Model mantle derivation ages (tDM), oldest in Uganda where sediment is principally derived from the Congo Craton (3.4-3.0 Ga for Victoria and Albert Nile), progressively decrease northward across the Saharan Metacraton, from 2.6 Ga (Bahr el Jebel in South Sudan), to 2.4-2.2 Ga (Bahr ez Zeraf across the Sudd), and finally 1.6-1.3 Ga (White Nile upstream Khartoum). Instead, tDM ages of Sobat mud increase from 0.9 to 1.5 Ga across the Machar marshes. TDM ages are younger for sediments shed by Ethiopian (1.2-0.7 Ga) and Eritrean basements (1.5-1.2 Ga), and youngest for sediments shed from Ethiopian flood basalts (0.3-0.2 Ga).Integrated geochemical, mineralogical, and settling-equivalence analyses suggest influence on the Nd isotopic signal by volcanic lithic grains and titanite rather than by LREE-rich monazite or allanite. Because contributions by ultradense minerals is subordinate, intrasample variability of Sr and Nd ratios is minor. In Blue Nile, Atbara and main Nile sediments of mixed provenance, however, the Nd ratio tends to be higher and tDM ages lower in largely volcaniclastic mud than in mixed volcaniclastic/metamorphiclastic sand.The complete geochemical database presented here, coupled with high-resolution bulk-petrography and heavy-mineral data, provides a key to reconstructing erosion patterns and detrital fluxes across the whole Nile basin, and to investigate and understand how sources of sediment have changed in the historical and pre-historical past in relation to shifting climatic zones across arid northern Africa.  相似文献   

13.
The present research tests the application of geochemical atlas of soils and stream sediments in the investigation of weathering and erosion processes on volcanic islands. The composition of surface soils collected in six catchments from Santiago Island (Cape Verde) are compared with bedload stream deposits sourced by these catchment areas in order to evaluate the spatial variability of these exogenous processes. The geochemistry of bedload stream deposits is between that of the fresh rocks and the topsoils of their source areas. Relative to average soil composition, bedload deposits are depleted in most of less-mobile elements (e.g., Al, Fe, La, Sc) and strongly enriched in Na and, usually, Ca. When the topsoil weathering intensity in the catchment areas is highly variable and the composition of bedload deposits is substantially different from the average soil composition, bedload deposits should incorporate significant amounts of poorly-weathered rocks and sectors from erosion occur within the drainage basin. Ratios of non-mobile elements allow the identification of highly vulnerable and erosion-protected sectors within the catchments. It is proposed that the catchments of the rivers in the SW flanking side of Santiago Island include sectors where lava shields formed during the post-erosional eruptive phases are capable of an effective protection to erosion. Conversely, the NE-facing part of the island is highly dissected and any younger post-erosional cover was either completely eroded away, or never existed in the first place. Simple compositional parameters derived from the databases of geochemical maps of soil and stream sediments provide important information for the analyses of weathering, erosion and denudation processes at the catchment scale.  相似文献   

14.
Specific surface area (SSA) of headwater stream bed sediments is a fundamental property which determines the nature of sediment surface reactions and influences ecosystem-level, biological processes. Measurements of SSA – commonly undertaken by BET nitrogen adsorption – are relatively costly in terms of instrumentation and operator time. A novel approach is presented for estimating fine (<150 μm) stream bed sediment SSA from their geochemistry – after removal of organic matter – for agricultural headwater catchments across 15,400 km2 of central England, UK. From a regional set of 1972 stream bed sediment sites with common characteristics for which geochemical data were available, 60 samples were selected – based on maximising their variation in Al concentrations – and their BET SSA measured by N2 adsorption. After careful selection of potential regression predictors following a principal component analysis and removal of a subset of samples with the largest Mo concentrations (>2.5 mg kg−1), four elements were identified as significant predictors of SSA (ordered by decreasing predictive power): V > Ca > Al > Rb. The optimum model from these four elements accounted for 73% of the variation in bed sediment SSA (range 6–46 m2 g−1) with a root mean squared error of prediction – based on leave-one-out cross-validation – of 6.3 m2 g−1. It is believed that V is the most significant predictor because its concentration is strongly correlated both with the quantity of Fe-oxides and clay minerals in the stream bed sediments, which dominate sediment SSA. Sample heterogeneity in SSA – based on triplicate measurements of sub-samples – was a substantial source of variation (standard error = 2.2 m2 g−1) which cannot be accounted for in the regression model.  相似文献   

15.
A number of rivers have been found to transport highly aged organic matter [OM]; however, the sources of this aged material remain a matter of debate. One potential source may be erosion and weathering of headwater lithologies rich in ancient sedimentary OM. In this study, waters, suspended particulates, streambed sediments, rocks and soils from fourteen small headwater watersheds of a mid-size, temperate, passive margin river were sampled and characterized by Δ14C, δ13C, and POC/TPN ratios to identify sources of particulate and dissolved OM delivered to the river mainstem. These headwater sites encompass a range in lithology (OM-rich shales, OM-lean carbonate/mudstone facies, and OM-free crystalline rocks) and land use types (forested and agricultural), and allow investigation of the influence of agriculture and bedrock types on stream OM characteristics. Streams draining large areas of both agricultural land use and OM-rich lithology contain particulate OM [POM] that is more 14C-depleted than streams draining forested, shale-free watersheds. However, this is not sufficient to account for the significantly lower Δ14C-POC measured in the river mainstem. Dissolved OM [DOM] Δ14C are in all cases enriched compared to POM from the same stream, but are otherwise highly variable and unrelated to either land use or lithology. POC/TPN ratios were likewise highly variable. POC and DOC δ13C signatures were similar across all watersheds. Based on isotope mass balance, 14C-free fossil OM sources contribute 0-12% of total stream POM. Although these results do not unequivocally separate the influences of land use and lithology, watershed coverage by shale and agriculture are both important controls on stream Δ14C-POC. Thus export of aged, particle-associated OM may be a feature of river systems along both passive and active continental margins.  相似文献   

16.
Here the hydrogeochemical constraints of a tracer dilution study are combined with Fe and Zn isotopic measurements to pinpoint metal loading sources and attenuation mechanisms in an alpine watershed impacted by acid mine drainage. In the tested mountain catchment, δ56Fe and δ66Zn isotopic signatures of filtered stream water samples varied by ∼3.5‰ and 0.4‰, respectively. The inherent differences in the aqueous geochemistry of Fe and Zn provided complimentary isotopic information. For example, variations in δ56Fe were linked to redox and precipitation reactions occurring in the stream, while changes in δ66Zn were indicative of conservative mixing of different Zn sources. Fen environments contributed distinctively light dissolved Fe (<−2.0‰) and isotopically heavy suspended Fe precipitates to the watershed, while Zn from the fen was isotopically heavy (>+0.4‰). Acidic drainage from mine wastes contributed heavier dissolved Fe (∼+0.5‰) and lighter Zn (∼+0.2‰) isotopes relative to the fen. Upwelling of Fe-rich groundwater near the mouth of the catchment was the major source of Fe (δ56Fe ∼ 0‰) leaving the watershed in surface flow, while runoff from mining wastes was the major source of Zn. The results suggest that given a strong framework for interpretation, Fe and Zn isotopes are useful tools for identifying and tracking metal sources and attenuation mechanisms in mountain watersheds.  相似文献   

17.
《Applied Geochemistry》2003,18(2):283-309
International agreements (e.g. OSPAR) on the release of hazardous substances into the marine environment and environmental assessments of shelf seas require that concentrations and bioavailability of metals from anthropogenic sources can be distinguished from those originating as a result of natural geological processes. The development of a methodology for distinguishing between anthropogenic and natural sources of metals entering the Irish Sea through river inputs is described. The geochemistry of stream, river and estuarine sediments has been used to identify background geochemical signatures, related to geology, and modifications to these signatures by anthropogenic activities. The British Geological Survey (BGS) geochemical database, based on stream sediments from 1 to 2 km2 catchments, was used to derive the background signatures. Where mining activity was present, the impact on the signature was estimated by comparison with the geochemistry of sediments from a geologically similar, but mining free, area. River sediment samples taken upstream and downstream of major towns were used respectively to test the validity of using stream sediments to estimate the chemistry of the major river sediment and to provide an indication of the anthropogenic impact related to urban and industrial development. The geochemistry of estuarine sediments from surface samples and cores was then compared with river and offshore sediment chemistry to assess the importance of riverine inputs to the Irish Sea. Studies were undertaken in the Solway, Ribble, Wyre and Mersey estuaries. The results verify that catchment averages of stream sediments and major river samples have comparable chemistry where anthropogenic influences are small. Major urban and industrial (including mining) development causes easily recognised departures from the natural multi-element geochemical signature in river sediment samples downstream of the development and enhanced metal levels are observed in sediments from estuaries with industrial catchments. Stream sediment chemistry coupled with limited river and estuarine sampling provides a cost-effective means of identifying anthropogenic metal inputs to the marine environment. Investigations of field and laboratory protocols to characterise biological impact (bioaccumulation) of metals in sediments of the Irish Sea and its estuaries show that useful assessments can be made by a combination of surveys with bioindicator species such as clams Scrobicularia plana, selective sediment measurements that mimic the ‘biologically available’ fractions, and laboratory (mesocosm) studies.  相似文献   

18.
Bed sediment-associated trace metals in an urban stream, Oahu, Hawaii   总被引：78，自引：0，他引：78  
 Of the 117 stream and lake systems sampled nationwide, fish from Manoa Stream on Oahu, Hawaii, have consistently shown the highest Pb concentrations. Therefore a detailed study was conducted to examine total metal contents in bed sediments from a 5.8-km stretch of Manoa Stream. A total of 123 samples (<63 μm) were examined for 18 elements and 14 samples for 21 elements. Selected samples were also examined using different leach solutions to examine metal phase associations. All trace metal data, computations of enrichment ratios and the modified index of geoaccumulation point to mineralogical control for Cr and Ni; minor anthropogenic contamination for Ba, Cd, Cu, Hg and Zn; and a very strong contamination signal for Pb. Maximum Pb contents (up to 1080 mg kg−1) were associated with anthropogenic material dumping in minor tributaries, storm sewer sediments and sediments in the “lower” section of the basin. Proportionally Pb had the highest non-residual component of elements examined; dominantly in the reducible phase associated with Mn and amorphous Fe oxyhydroxides. The contamination signal was typically lowest in the “undisturbed” headwater reach of the basin (above 5.1 km) with significant increases throughout the “residential” and “commercial-institutional” zones of the mid-basin. The spatial pattern of bed sediment contamination and evidence from storm sewer-outlet sediments strongly indicates that Pb, and to a lesser degree some other metals, is still being transported to the stream and the primary agent is soil erosion and transport of metals sorbed to sediments. The primary source of sediment-associated metals is considered to be the automobile, though other minor sources can not be ruled out. Received: 3 November 1998 · Accepted: 26 January 1999  相似文献   

19.
Environmental geochemistry plays an important role in understanding the distribution of major cations (Ca2+, Mg2+, Na+, K+) in Helwan catchment, south Cairo, Egypt. Evaluation of soil mechanical erosion rate, depletion rate, exchangeable rates of base cations and sodium adsorption ratios are essential for understanding soil degradation problems in the representative Helwan catchment. Soil erosion is a natural process. It often becomes a problem when human activity causes it to occur much faster than under natural conditions. The results of the mechanical erosion rate of soil and the exchangeable rates of base cations are 1845 and 80.3 kg ha−1 yr−1, respectively. The high intensity of the mechanical erosion rate is probably attributed to the high specific surface area of the studied type of Vertisol, intensive application of fertilizer and industrial activities. Mechanical erosion of soil, exchangeable rate of base cations and the depletion rate of base cations are almost inexhaustible sources of sodium, and all these increase the problem of sodic soils and may affect plant productivity in Helwan catchment.  相似文献   

20.
Relative contribution of different diffuse sources to the sediment and phosphorous (P) budgets in the Ben Chifley Reservoir was estimated using a multivariate mixing model and geochemical indices and tracers. The influence of the underlying geology on land use characteristics and the dynamics of sediment and P in the catchment were discussed. Sediments currently in transport to the reservoir are derived mainly from areas underlain by Quaternary alluvium, accounting for 33% of the reservoir sediment budget. A major portion of the sediments from the Quaternary alluvium originates from pasture land which also contributes about 60% of sediment-bound P in the reservoir, followed by cropland (30%) and forest area (10%). Phosphorus-based fertiliser contributes more than 50% of the soil P in pasture and cropland and more than 60% in forest plantation area. The remaining P reaching the reservoir originates from natural soils (native sources). Phosphate from both fertiliser and native sources are transported to the water courses and ultimately the reservoir as a consequence of gully, stream bank and surface erosion. Erosion control, trapping of fertiliser runoff, establishing riparian vegetation and reducing application of P-based fertiliser by increasing native pasture cultivation in the risk areas should be considered as management options for controlling the impact of P and sediment in the reservoir.  相似文献   

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