铀水冶尾矿库地下水流特征与模拟分析：以某矿为例

铀水冶尾矿库中地下水流动特征控制了核素向周围环境扩散与迁移。本文以某矿山谷型尾矿库为例,运用二维有限元模拟了库内地下水分布及流动,结合水文地质条件进行了分析与讨论。     

Radiometric dating of recent lake sediments from a highly eroded area in semiarid Tanzania

Semiarid regions are vulnerable environments with a series of important and often discussed problems such as land degradation, water scarcity and desertification. These regions are dynamic and respond quickly to climatic and environmental changes. Unlike lakes in temperate zones, lakes in semiarid regions are yet poorly utilized as climatic and environmental indicators. In this study aquatic deposits are used to uncover the environmental history of a severely degraded area in central Tanzania. The ²¹⁰Pb and ¹³⁷Cs chronologies date a 360 cm long sediment sequence to 155 years. The sediments show that lake Haubi basin changed from a seasonally waterlogged depression to a lake at the turn of the century. Calculated sedimentation rates show that the catchment of the lake has been subject to varied and enhanced soil erosion during the last 155 years.     

Modern sediment yield compared to geologic rates of sediment production in a semi‐arid basin,New Mexico: assessing the human impact

An Erratum has been published for this article in Earth Surface Processes and Landforms 29(13) 2004, 1707. In the semi‐arid Arroyo Chavez basin of New Mexico, a 2·28 km² sub‐basin of the Rio Puerco, we contrasted short‐term rates (3 years) of sediment yield measured with sediment traps and dams with long‐term, geologic rates (～10 000 years) of sediment production measured using ¹⁰Be. Examination of erosion rates at different time‐scales provides the opportunity to contrast the human impact on erosion with background or geologic rates of sediment production. Arroyo Chavez is grazed and we were interested in whether differences in erosion rates observed at the two time‐scales are due to grazing. The geologic rate of sediment production, 0·27 kg m^?2 a^?1 is similar to the modern sediment yields measured for geomorphic surfaces including colluvial slopes, gently sloping hillslopes, and the mesa top which ranged from 0·12 to 1·03 kg m^?2 a^?1. The differences between modern sediment yield and geologic rates of sediment production were most noticeable for the alluvial valley ?oor, which had modern sediment yields as high as 3·35 kg m^?2 a^?1. The hydraulic state of the arroyo determines whether the alluvial valley ?oor is aggrading or degrading. Arroyo Chavez is incised and the alluvial valley ?oor is gullied and piped and is a source of sediment. The alluvial valley ?oor is also the portion of the basin most modi?ed by human disturbance including grazing and gas pipeline activity, both of which serve to increase erosion rates. Copyright © 2004 John Wiley & Sons, Ltd.     

Potential radionuclide transport pathways from seafloor dumpsites: Kamchatka region of the North Pacific Ocean

Encapsulated nuclear waste materials, dumped by Russia, are present at two deepwater seafloor locations in the offshore north-west Pacific Ocean, south-east of the Kamchatka Peninsula. This paper assesses potential pathways by which these wastes might, if released from their containers, disperse away from the dumpsites and through the surrounding ocean. A review of large-scale ocean circulation theory and of field and model results suggests that mean abyssal currents are north-eastward to eastward from the dumpsite locations and would advect leaking materials toward the north-eastern Pacific. Results of advective and diffusive horizontal plume transport models are consistent with this sense of flow. Trajectory speeds are, however, subject to considerable uncertainty. Our results suggest that as little as 5 years or as long as 100 years might be required for material to be transported from the dump sites to the north-east Pacific. Dilution by 4 or 5 orders of magnitude is predicted during this transit. Vertical mixing or upwelling are necessary in order to transport contaminants upward from north-east Pacific abyssal waters to the near-surface layers before they can potentially impact productive coastal regions, such as those off Alaska. Information concerning such upwelling mechanisms is inadequate for estimation of rates or to identify geographical areas that might be at risk.     

中国煤中的铀、钍和放射性核素

中国煤中的铀平均含量为3mg/kg,在某地富铀煤中检测到的最高值达25660mg/kg,其赋存状态主要是与有机质相结合的方式;钍平均含量6 mg/kg,没有发现异常现象.南方一些地区的石煤中含有较多的放射性核素,并且容易在灰渣中富集,综合利用时应加强监控,以避免产生危害.     

Mapping gamma radiation and its uncertainty from weathering products in a Tasmanian landscape with a proximal sensor and random forest kriging

The radionuclides of potassium (⁴⁰ K), uranium (²³⁸U) and thorium (²³²Th) emit from the land surface gamma radiation that is characteristic of the underlying rocks and the distribution of their weathering products in the landscape. We measured the radiation along widely separated transects using a mobile proximal sensor over a 10 000‐ha region of Tasmania. We supplemented the transect data with information from soil and geological maps and dense data from LandSat and SPOT imagery, a digital elevation model and terrain attributes on a grid at 30‐m intervals so as to map the radionuclides. We used a sequence of steps, starting with a spatial bootstrap and random forests to predict emissions across the study area and at sampling points excluded from the bootstrap samples. The predictions at the sampling points were compared with the observed values to obtain residuals, which were then used to krige them at all points on the 30 m grid. We combined the random forest and kriging predictions on the 30‐m grid to obtain our random forest kriging predictions. Repeating the procedure 100 times provided confidence limits on our results and predictions. The resulting maps of the radionuclides accord well with what we know of the soil, lithology and topography of the region from other sources. Alluvial deposits with large amounts of potassium extend from the foot slopes of the Great Western Tiers and along the flood plains of the Meander River, providing evidence of previous widespread weathering and deposition of the material. The fertile Red Ferrosols (roughly equivalent to Ferralic Nitisols in the World reference base (WRB) classification) on the extensive Tertiary basalt plateau emit little gamma radiation as a result of deep weathering and of potassium movement and accumulation down its talus slopes. The maps show the complexity of the region in terms of soil, lithology and terrain, and they show the merits of gamma radiometry for mapping and understanding the distribution of materials in such regions. Copyright © 2013 John Wiley & Sons, Ltd.     

Joint isotopic mass balance: a novel approach to quantifying channel bed to channel margins sediment transfer during storm events

The important role of floodplains and the broader riparian zone in providing temporary storage for a large fraction of the annual sediment load of rivers is well established, but this understanding is largely based on observations of the long‐term average behavior of the catchment. Here we combine measurements of the fallout radionuclides ⁷Be and ²¹⁰Pb and the stable isotopes of hydrogen in water to quantify fine sediment mobilization and storage in a stream and its channel margins during individual intermediate‐sized storm events with recurrence intervals of a few months or less. We demonstrate this method using five storm events in a small (~15 km²), undeveloped, gravel‐bedded tributary of the Connecticut River (USA). We estimate that in each storm, the mass of sediment deposited onto the margins accounts for almost 90% of the sediment mobilized from the bed, with the remainder of the mobilized bed sediment transported downstream as suspended load. The result that the bed is a net source of sediment to the stream and the margins a net sink is robust, but estimates of the mass of material eroded from the bed and deposited on the margins are less certain. The source of sediment to the bed remains unclear as, consistent with earlier studies, we observe only limited deposition of sediment to the bed during the storm events. The suspended sediment is organic‐rich and thus its source may be associated with in‐channel organic decay between storm events. Understanding the coupled interactions between discharge magnitude and frequency and sediment resupply at the event time scale has important implications for stream restoration efforts seeking to connect the channel and the broader riparian zone, and for the development of accurate sediment budgets and predictions of sediment flux from a watershed. Copyright © 2015 John Wiley & Sons, Ltd.     

Late Pleistocene Glaciations in the Northwestern Sierra Nevada, California

Pleistocene fluvial landforms and riparian ecosystems in central California responded to climate changes in the Sierra Nevada, yet the glacial history of the western Sierra remains largely unknown. Three glacial stages in the northwestern Sierra Nevada are documented by field mapping and cosmogenic radionuclide surface-exposure (CRSE) ages. Two CRSE ages of erratic boulders on an isolated till above Bear Valley provide a limiting minimum age of 76,400±3800 ¹⁰Be yr. Another boulder age provides a limiting minimum age of 48,800±3200 ¹⁰Be yr for a broad-crested moraine ridge within Bear Valley. Three CRSE ages producing an average age of 18,600±1180 yr were drawn from two boulders near a sharp-crested bouldery lateral moraine that represents an extensive Tioga glaciation in Bear Valley. Nine CRSE ages from striated bedrock along a steep valley transect average 14,100±1500 yr and suggest rapid late-glacial ice retreat from lower Fordyce Canyon with no subsequent extensive glaciations. These ages are generally consistent with glacial and pluvial records in east-central California and Nevada.