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1.
The 137Cs radioactivity of soils was used as a tracer of soil erosion in a catchment in the Netherlands: 143 samples were analysed to map the 137Cs redistribution using geostatistical interpolation methods. Caesium-137 activities on grassland are significantly higher than on arable land. Also, 137Cs activities on waning slopes are higher and activities on steep slopes are lower. The soil erosion estimates, derived from the 137Cs data, are used to validate the USLE erosion model. The recent Chernobyl nuclear accident also contributed to the 137Cs activity. However, the Chernobyl input of 137Cs, with a constant ratio of 1.765:1 to 134Cs, cannot be used as a tracer of soil erosion. Because of the rapid decay of 134Cs, we will not be possible to separate the sources of 137Cs in the near future in areas significantly influenced by Chernobyl fallout and in these areas 137Cs can no longer be used as a soil erosion tracer.  相似文献   

2.
Inorganic particulate material uptake and release over an oyster reef during a tidal cycle was measured every 11.8 days for one year. There was a net uptake on the flooding tides and a net release on ebbing tides. Particulate uptake was highest in late summer reaching a maximum of 230 g m−2 h−1. Particulate release was also highest in late summer reaching a maximum of 94 g m−2 h−1. On an annual basis, 86.7 kg m−2 y−1 of inorganic particulate material was taken up on flooding tides and 56.5 kg m−2 y−1 was released on ebbing tides. The pattern of uptake on flooding tides and release on ebbing tides was hypothesized to be the result of higher water velocities on ebbing tides.  相似文献   

3.
The status report on metal pollution in tropical estuaries and coastal waters is important to understand potential environmental health hazards. Detailed baseline measurements were made on physicochemical parameters (pH, temperature, redox potential, electrical conductivity, salinity, dissolved oxygen, total dissolved solid), major ions (Na, Ca, Mg, K, HCO3, Cl, SO4 and NO3) and metals concentrations (27Al, 75As, 138Ba, 9Be, 111Cd, 59Co, 63Cu, 52Cr, 57Fe, 55Mn, 60Ni, 208Pb, 80Se, 66Zn) at estuaries and coastal waters along the Straits of Malacca. Principal component analysis (PCA) was employed to reveal potential pollution sources. Seven principal components were extracted with relation to pollution contribution from minerals-related parameters, natural and anthropogenic sources. The output from this study will generate a profound understanding on the metal pollution status and pollution risk of the estuaries and coastal system.  相似文献   

4.
Abstract

Sediment transport capacity is a key concept in determining rates of detachment and deposition in process-based erosion models, yet limited studies have been conducted on steep slopes. We investigated the effects of sediment size on transport capacity of overland flow in a flume. Unit flow discharge ranged from 0.66 to 5.26?×?10-3 m2 s-1, and slope gradient varied from 8.7 to 42.3%. Five sediment size classes (median diameter, d 50, of 0.10, 0.22, 0.41, 0.69 and 1.16 mm) were used. Sediment size was inversely related to transport capacity. The ratios of average transport capacity of the finest class to those of the 0.22, 0.41, 0.69 and 1.16 mm classes were 1.09, 1.30, 1.55 and 1.92, respectively. Sediment transport capacity increased as a power function of flow discharge and slope gradient (R2?=?0.98), shear stress (R2?=?0.95), stream power (R2?=?0.94), or unit stream power (R2?=?0.76). Transport capacity generally decreased as a power function of sediment size (exponent?=??0.35). Shear stress and stream power predicted transport capacity better than unit stream power on steep slopes when transport capacity was <7 kg m-1 s-1. Sediment transport capacity increased linearly with mean flow velocity. Critical or threshold velocity increased as a power function of sediment size (R2?=?0.93). Further studies with fine soil particles are needed to quantify the effects of sediment size on transport capacity of overland flow on steep slopes.

Citation Zhang, G.-H., Wang, L.-L., Tang, K.-M., Luo, R.-T. & Zhang, X.C. (2011) Effects of sediment size on transport capacity of overland flow on steep slopes. Hydrol. Sci. J. 56(7), 1289–1299.  相似文献   

5.
A sampling and measuring device which enables the assessment of atmospheric particulate and gaseous mercury concentrations has been tested on Mount Etna Volcano. Particulate matter is collected on a Whatman GF/C of 1.0 µm pore-size, gaseous mercury species on a Au-column. The analysis is carried out in two steps: (1) the mercury species collected on the filter or the Au-column are transferred to a fixed analytical Au-column; (2) mercury liberated from this column during the second step is detected with a Mercury Vapour Monitor. Average concentrations of gaseous and particulate mercury in ambient sampling sites on Mount Etna are 3.8 ng m?3 and 0.49 ng m?3 respectively. Average concentrations of gaseous and particulate mercury in the plume of Bocca Nuova on Mount Etna are 15 ng m?3 and 24 ng m?3 respectively. An estimation of the total mercury discharge from Mount Etna amounts to 2.5 10?2 tons day?1.  相似文献   

6.
Reference materials are key for assessing inter-laboratory variability and measurement quality, and for placing analytical uncertainty bounds on sample analyses. Here, we investigate four years of data resulting from repeated processing of the CRONUS-N reference material for cosmogenic 10Be and 26Al analyses. At University of Vermont, we prepared a CRONUS-N aliquot with most of our sample batches from 2013 to 2017; these reference material samples were then distributed to four different accelerator mass spectrometry facilities, yielding 73 10Be analyses and 58 26Al analyses. We determine CRONUS-N 10Be concentrations of (2.26 ± 0.14) x 105 atoms g−1 (n = 73, mean, 1 SD) and 26Al concentrations of (1.00 ± 0.08) x 106 atoms g−1 (n = 58, mean, 1 SD). We find a reproducibility of 6.3% for 10Be and 7.7% for 26Al (relative standard deviations). We also document highly variable 27Al and Mg concentrations and a 10Be dispersion twice as large as the mean AMS analytic uncertainty. Analyses of the CRONUS-N material with and without density separation demonstrate that non-quartz minerals are present in the material and have a large impact on measured concentrations of 27Al, 10Be, and impurities; these non-quartz minerals represent only a very small portion of the total mass (0.6–0.8%) but have a disproportionally large effect on the resulting data. Our results highlight the importance of completely removing all non-quartz mineral phases from samples prior to Be/Al extraction for the determination of in situ cosmogenic 10Be and 26Al concentrations.  相似文献   

7.
The radionuclides137Cs,210Pb and7Be have been examined in the alpine Rhoˆne watershed (Switzerland) during a period of two years in order to evaluate their usefulness as tracers of the removal and transport rate of top-soil particles and particle-reactive contaminants of atmospheric origin. The specific activities of the radionuclides in fluvial suspension show a distinct seasonal pattern which depends on the hydrologic regime of the stream and the sources of the suspended matter. Input-output budgets based on the atmospheric deposition and fluvial removal of three radionuclides in the alpine Rhoˆne watershed are used to estimate their erosional residence times. The simplest one box model yields mean residence times of about 800 and 1400 years for137Cs and210Pb, respectively. The removal rate of short-lived7Be suggests that a part of the watershed (0.6–2.3% of the total surface) is exposed to a rapid erosion, in which the mean residence time of the radionuclides is in the range of 1–220 days. This has little influence on the calculated residence time of137Cs but increases the estimated residence time of210Pb in soil to over 1800 years. The use of210Pb-7Be pair in fluvial output may be very helpful in the assessment of the impact of atmospheric pollutants on the water quality in rivers and lakes.  相似文献   

8.
An interpretation of previously reported measurements of the Apollo 15/16 alpha-particle spectrometer on the distribution of 222Rn and 210Po across the lunar surface suggests that continuation of these measurements is a method of monitoring current activity on the moon. Since the two isotopes are relatively short-lived with effective half-lives of 3 days and 21 years, respectively, the activity detected has had to have been released during this current epoch. Changes in the rate of lunar emanation can be measured on three different time scales: (1) of a few days or less by detecting 222Rn at discrete sites such as the crater Aristarchus; (2) of a month by measuring 222Rn activity at the sunrise terminator; (3) of a few years by measuring 210Po activity at various locations. These observations could be carried out very effectively from a lunar polar orbiting satellite.  相似文献   

9.
The occurrence of anomalous (nonthermal) profiles of green emission of oxygen atoms detected with a Fabry-Perot spectrometer in auroras with the effect of a rapid decrease in the intensity of the wings of their dissociative component has been investigated. Based on an analysis of these measured profiles, it has been found that the characteristic time of recombination of a molecular oxygen ion at altitudes of 200–400 km is about 5–7 s. It appears that these molecular ions occur in a horizontally limited region of the auroral ionosphere as a result of ionization by a space localized flux of soft electrons with energies of 0.2–0.4 keV penetrating up to altitudes of 200 km. The estimation of the electron flux produces a value of 1010–1013 electrons cm?2 s?1. They generate the excess concentration n(O 2 + ) ~ 5.6 × 105 cm?3.  相似文献   

10.
The endemic argan woodlands cover large parts of South Morocco and create a characteristic landscape with areas of sparsely vegetated and bare soil surfaces between single trees. This unique ecosystem has been under extensive agrosilvopastoral management for centuries and is now at risk of degradation caused by overgrazing and increasing scarcity and variability of rainfall. To investigate susceptibility to wind erosion, we conducted an experimental–empirical study including wind tunnel tests and a drone-generated digital elevation model and quantified wind-erodible material on five different associated surface types by means of sediment catchers. The highest emission flux was measured on freshly ploughed surfaces (1875 g m–2 h–1), while older ploughed areas with a re-established crust produced a much lower emission flux (795 g m–2 h–1). Extensive tillage may have been a sustainable practice for generations, but increasing drought and uncertainty of rainfall now lead to an acute risk of severe soil erosion and dust production. The typical crusted surfaces characterized by residual rock fragment accumulation and wash processes produced the second highest emission flux (1,354 g m–2 h–1). Material collected from tree-shaded areas (933 g m–2 h–1) was revealed to be a considerable source of organic material, possibly affecting substrate conditions positively on a larger regional scale. The lowest flux was measured on rock fragment-covered surfaces (301 g m–2 h–1). The data show that open argan woodland may be a considerable source for wind erosion and dust production, depending on surface characteristics strongly related to management. An adapted management must include the conservation of argan trees to offer a promising approach to prevent severe wind erosion and dust production and mitigate possible impacts of land-use change and climate change related shifts in wind and rainfall patterns. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

11.
The equations for isotopic evolution in a deforming medium are derived and used to show that the local isotopic composition of the mantle depends primarily on the advection of heterogeneities by the flow field. Various examples of the role of advection are given using a two-scale model of mantle convection. The effect of small-scale flows, which have dimensions smaller than the plates themselves, is to convert any initially localized heterogeneity into thin spiral sheets. The isotopic properties of erupted lavas will depend on the relative size of the zone of partial melt to the spacing between such sheets. An idealized model for87Sr/86Sr variations from Pacific islands and the covariation of143Nd/144Nd-87Sr/86Sr is based on the combined effect of isotopic fluxes at subduction zones and advection by the return flow under the moving lithospheric plates.  相似文献   

12.
The results of 10Be and 9Be measurements in several sections of ten large manganese nodules are presented along with U and Th isotope data on five of them.The 10Be and 10Be/9Be methods yield growth rates (covering a period of 5–10 Ma) which are in excellent agreement with each other. In three cases, these rates are also in very good agreement with those derived from the 230Th methods, whereas in the other two the 230Th-based rates are faster by over a factor of two.Based on the discrepancy between the inventory of 10Be (as well as 230Th) in nodules and the overhead seawater column, it is calculated that the former scavenge their Be and Th isotopes from 2–900 m of the overhead water column. The deduced 9Be concentrations of ocean water based on its 10Be contents and the 10Be/9Be ratios of nodule surfaces are found to be in good agreement with the direct 9Be measurements of seawater implying that 9Be in nodules (like10Be) is mostly authigenic.  相似文献   

13.
This paper studies the effect of drought and pumping discharge on groundwater supplies and marine intrusion. The investigation concerns the Mamora coastal aquifer, northwest of Morocco. A large‐scale groundwater model was established to model (a) the amount of freshwater discharge towards the ocean and the sea water volumes flowing inland as a consequence of the inverse hydraulic gradient, (b) the impact of drought and pumping discharge on the water table level and, as a consequence, on marine water intrusion. In fact, the simulated submarine groundwater discharge (SGWD) would decrease from 864 m3/d/km in 1987 to 425 m3/d/km in 2000. The simulated volumes of sea water intruding the aquifer as a result of inverse hydraulic gradient would increase from 0·25 Mm3/y in 1987 to 0·3 Mm3/y in 2000. As a consequence of a negative rainfall gradient of −5 mm/y, the simulated SGWD would decline to 9 m3/d/km and the sea water intrusion (SWI) would increase to 0·35 Mm3/y since the year 2010. Due to insufficient data on the trend of pumping discharge, a hypothetical increase of this latter from 38·3 Mm3/y to 53·2 Mm3/y is simulated to induce an increase of marine water intrusion from 0·25 Mm3/y to 0·9 Mm3/y. Consequently, to optimally exploit this seemingly fragile coastal aquifer, a plan of future actions to implement is proposed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

14.
Ti-V plots and the petrogenesis of modern and ophiolitic lavas   总被引：10，自引：0，他引：10  
Radioactive and stable cosmogenic nuclides have been determined in the various fragments of the Kirin chondrite (H5). Experimental results obtained from our samples are described and compared with similar data obtained in other laboratories. Cosmogenic54Mn,22Na,60Co,26Al,53Mn,40K (in the metal phase), and light noble gases were measured. Based on these data, the irradiation history of this meteorite can be explained in terms of (1) a multi-stage exposure which involves a first-stage irradiation for 107 years and a second stage for about 4×105 years, and (2) depth effects in the productions of the nuclides in 4π(second stage) and 2π(first stage) geometries. These conclusions are consistent with those of our previous work which was based on a limited number of samples.  相似文献   

15.
《Continental Shelf Research》2007,27(10-11):1600-1615
Multiple box cores were collected on the continental shelf in the Mississippi Deltaic Region adjacent to Southwest Pass and analyzed for particle reactive radionuclides 234Th and 7Be to examine seasonal sediment dynamics associated with variations of river discharge and hydrodynamics. Three stations located along a line west of Southwest Pass were cored and reoccupied in October, November, and December of 2003 and March, April, and May of 2004. High-frequency sampling (∼monthly) comparable to the short half-life of the radiotracers (234Th t1/2=24.1 d; 7Be t1/2=53.3) enabled us to isolate the relative influence that various forcing agents (river discharge, waves, currents) had on sediment inventories of 7Be and 234Th. In addition, the primary source of 7Be (fluvial) differs from 234Th (marine), providing further insight into processes affecting sediment transport and supply. Monthly 7Be inventories showed a significant positive relationship to river discharge (P=0.03) proximal to Southwest Pass. Sites further from Southwest Pass exhibited little to no relationship between 7Be inventories and river flow. At these sites, monthly 7Be inventories demonstrated a significant positive relationship with average wave orbital velocity (P<0.01). During our sampling period, the transport of 7Be-rich sediments to sites located on the middle to outer shelf were dependent on sea conditions not river discharge. Relatively high wave orbital velocities potentially allow particles to remain in suspension longer and travel further distances before initial deposition. In addition, 234Th inventories showed evidence of sediment focusing during periods of high wave orbital velocities.  相似文献   

16.
Bat guano deposits are increasingly used as records of past environmental changes, an approach that requires a precise chronology of the guano layers. This paper presents a comparison between the well-established 14C dating method and methods based on natural 210Pb excesses, (210Pb)ex, and artificial radionuclides 137Cs and 241Am. The studied example is a bat guano deposit from a cave in SW France (the Brantites III cave), which is currently investigated for paleo-environmental reconstructions using stable isotopes. 14C data show that the upper part of the guano deposit accumulated during the last 150 years with a marked increase in accumulation rates after around 1960 AD. While the incorporation of atmospheric 14C in guano is a well-understood process, the origin of 210Pb excesses is more complex. Based on consideration of 137Cs and (210Pb)ex inventories recorded in undisturbed soils in France, and the measured inventories in the guano deposit, we suggest that most of the 210Pb excess is produced by 222Rn decay in the cave air and then adsorbed onto the guano. As Radon concentrations in caves can vary significantly on both short and long-term timescales, one needs to be cautious before applying the often-used CRS (constant rate of supply of 210Pb excess) model to guano dating. Our (210Pb)ex data are best interpreted by two successive periods of roughly constant, but widely different accumulation rates (0.3 cm/y and 2.6 cm/y before and after 1960, respectively) and (210Pb)ex fluxes. We suggest that these relatively abrupt variations result from a change in cave ventilation leading to a more favourable shelter for bats after 1960. The upper 40 cm of the deposit shows evidence of 210Pb mobility, adding a further complexity to the interpretation of (210Pb)ex profiles in guano deposits. However, the existence of well-defined 137Cs and 241Am peaks allows a precise identification of the year of maximum atmospheric fallouts (∼1963–1964). When the ages provided by artificial radionuclides are combined with the 210Pb-derived accumulation rates, an age model can be built, which is in good agreement with the 14C age model. This example shows that the (210Pb)ex method, when associated with 137Cs (241Am) data, can be used to date recent guano deposit, although its application is not as straightforward as the 14C method.  相似文献   

17.
The effect of short-term exposure to high concentration (mg l.?1) of water soluble fraction of aromatic heating oil on subsequent egg production by the estuarine copepod Eurytemora affinis has been studied in laboratory cultures to investigate possibly sublethal biological effects following exposure to hydrocarbon under an oil spill. Significant reduction in subsequent length of life, total number of eggs produced, mean brood size, and rate of egg production was observed. Exposure to naphthalene alone at 1 mg l.?1 for 24 h produced a significant effect on total fecundity of the females. Ingestion rates were significantly lower when measured in the presence of the water soluble fraction, and also naphthalene alone at mg l.?1 concentrations. Exposure to low-levels (10 and 50 μg l.?1) of 14C-naphthalene alone over a period of ten days produced no significant effect on feeding or reproduction despite the high concentrations of hydrocarbon accumulated during this period. The results are discussed in relation to previous work on the fate of hydrocarbons in planktonic copepods, using 14C-1-naphthalene as a model compound.  相似文献   

18.
《水文科学杂志》2013,58(4):655-664
Abstract

Palaeohydraulic modelling is presented for Athabasca Vallis, the youngest known catastrophic flood channel on Mars. This modelling incorporates three significant advantages over previous modelling of Martian channels: a step-backwater hydraulic model; more accurate topography; and improved flood height indicators. The maximum modelled palaeodischarge is between 1 × 106 and 2 × 106m3s?1 depending on the friction coefficient selected. An anomalously high palaeostage indicator suggests a region of ponded backwater in the channel in which streamlined forms were created through deposition, with the additional possibility of post-flood subsidence/lowering of the channel slope due to magma extrusion.  相似文献   

19.
Malachite green (MG), a traditional agent used in aquaculture although is not approved; its low cost and high efficacy make illicit use likely. We developed a small‐scale, simple, and sensitive dispersive liquid–liquid microextraction procedure for the assay of trace amounts of MG in aquatic environment of Trout fish. Fiber optic‐linear array detection spectrophotometry with charge‐coupled device detector benefiting from a microcell was used for this purpose. The method is based on enhancement effect of an anionic surfactant on the extraction of MG in to very fine multidroplets of microextraction solvent which made assisted by disperser solvent. Under the optimum conditions, the enrichment factor 77.5 was obtained from a 5‐mL water sample. The calibration graph was linear up to 5 × 10?7 mol L?1 with detection limit of 1 × 10?8 mol L?1. The relative standard deviation for seven replicate measurements of 4 × 10?7 and 5 × 10?8 mol L?1 of MG were 3.3 and 4.5%, respectively.  相似文献   

20.
The possibility of registering a plasma bubble at altitudes of the topside ionosphere based on its minor species He+ were studied. The characteristic times of the main aeronomic and electrodynamic processes, in which a bubble and its ion component He+ are involved, were calculated and compared. The recombination processes of helium ions in a bubble, the vertical transfer of a plasma bubble as a whole, and the diffusion transfer of the plasma bubble minor constituent (He+) were considered. The characteristic times of ambipolar and transverse (Bohm) diffusion were calculated when the diffusion transfer was estimated. The effect of the photoionization processes on plasma bubble dissipation were estimated based on the He+ bubble ion component. It was shown that the bubble filling characteristic time with an average He+ depletion to the He+ ambient density is ～24 h. It was concluded that such a prolonged bubble lifetime makes it possible to register a plasma bubble reliably over approximately two days. However, it has been noted that only a residual plasma bubble structure, i.e., its trace visible in He+ ions, will apparently be registered during most prolonged observations.  相似文献   

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