The Icelandic Laki volcanic tephra layer in the Lomonosovfonna ice core, Svalbard

The largest sulphuric acid event revealed in an ice core from the Lomonosovfonna ice cap, Svalbard, is associated with the densest concentration of microparticles in the ice core at 66.99 m depth. Electron microscope analysis of a volcanic ash particle shows it has the same chemical composition as reported for debris from the eruption of Iceland's Laki fissure in 1783 and confirms the identification of the tephra. Most of the particles in the deposit are not ash, but are common sand particles carried aloft during the eruption event and deposited relatively nearby and downwind of the long-lasting eruption. The tephra layer was found 10–20 cm deeper than high sulphate concentrations, so it can be inferred that tephra arrived to Lomonosovfonna about 6–12 months earlier than gaseous sulphuric acid precipitation. The sulphuric acid spike has a significant cooling impact recorded in the oxygen isotope profile from the core, which corresponds to a sudden drop in temperature of about 2°C which took several years to recover to previous levels. These data are the first particle analyses of Laki tephra from Svalbard and confirm the identification of the large acidic signal seen in other ice cores from the region. They also confirm the very large impact that this Icelandic eruption, specifically the sulphuric acid rather than ash, had on regional temperatures.     

Correlation of late Holocene terrestrial and marine tephra markers, north Iceland: implications for reservoir age changes

The tephrochronology of the last 3000 years has been investigated in soil sections in north Iceland and in a marine sediment core from the north Icelandic shelf, 50 km offshore. Tephra markers, identified with major element geochemical analysis of volcanic glass shards, serve to correlate the marine and terrestrial records. Hekla 3, the largest Holocene tephra marker from the volcano Hekla, in south Iceland, dated to 2980 years BP, is used as the basal unit in the tephra stratigraphy. AMS ¹⁴C dating of molluscs in the sediment core shows variable deviation from the tephrochronological age model, indicating that the reservoir age of the seawater mass at the coring site has varied with time. A standard marine reservoir correction of 400 ¹⁴C years appears to be reasonable at the present day in the coastal and shelf waters around Iceland, which are dominated by the Irminger Current. However, values over 500 years are observed during the last 3000 years. We suggest that the intervals with increased and variable marine reservoir correction reflect incursions of Arctic water masses derived from the East Greenland Current to the area north of Iceland.     

高速摄影技术在风沙颗粒测速中的应用研究

通过相邻图像减法获得了清晰的沙粒运动图像。在此基础上,分别提出了通过人工目视解译与计算机追踪相结合进行跃移颗粒数字轨迹追踪的多帧图像匹配算法以及更适用于计算跃移沙粒群运动瞬时速度场的两帧图像匹配算法。结果表明：与前人研究采用的单纯的人工匹配计算相比,多帧图像匹配算法在保证数据准确性的同时,极大的提高了工作效率。两帧图像匹配算法克服了传统的PTV匹配算法对流场内粒子群运动特征的要求,更加适宜于跃移沙粒群的速度测量,不仅拥有较高的匹配率,而且全过程实现全自动计算,具有较高的计算速度,能够为跃移相整体运动特性研究提供具有代表性的数据。因此,此方法有助于高速摄影技术在研究跃移沙粒运动中的优势更加明显。     

Stratigraphy of fossil pigments and Cladophora and its relationship with deposition of tephra in Lake Mývatn,Iceland

Fossil plant pigments and Cladophora fragments were analyzed in a 6.53 m long sediment profile from Lake Mývatn, Iceland, covering most of its history of about 2300 years. A decrease in myxoxanthophyll (produced by Cyanobacteria) with time and an increase in the benthic Cladophora reflects a gradual shift from planktonic to benthic primary production as water depth is reduced (to 3.15 m at the core site) because of sediment accumulation.Two periods of relatively high concentrations of myxoxanthophyll coincided with relatively frequent deposition of tephra (volcanic ash) but did neither conform with tectonic activity which might have changed the water level nor the available climatic record. Sediment depth, tephra content and percent undegraded chlorophyll (an indicator of pigment preservation) together could explain 56.7% of the variation in myxoxanthophyll. It is hypothesized that temporary increases in myxoxanthophyll resulted from periodic nutrient enrichment by fresh tephra deposited in the watershed or because tephra increased the erosion of organic soil in the water catchment area.Fluctuations in Cladophora show an inverse relationship with myxoxanthophyll in the uppermost 4 m of the core, and may result from a shading effect of planktonic Cyanobacteria on the phytobenthos or competition for nutrients released by the bottom sediments.     

The History of Recent Limnological Changes and Human Impact on Upper Klamath Lake, Oregon

Hypereutrophic Upper Klamath Lake has been studied for almost 50 years to evaluate the nature, cause, and effects of its very productive waters. Mitigation of undesirable effects of massive cyanobacterial blooms requires understanding their modern causes as well as their history. Knowledge of the pre-settlement natural limnology of this system can provide guidelines for lake restoration and management of land and water use strategies to maximize the benefits of this aquatic resource. This investigation uses a paleolimnological approach to document the nature and chronology of limnological and biological changes in Upper Klamath Lake for the past 200 years, covering the time when the lake was first described until today. A 45-cm gravity core, dated by ²¹⁰Pb and diatom correlations, was analyzed for diatoms, pollen, akinetes (resting spores) of the cyanobacterium Aphanizomenon flos-aquae, reworked tephra shards, and sediment magnetic characteristics. Pollen profiles show little vegetation change during this time. In contrast, diatoms indicative of increased nutrient fluxes (P and Si) increase moderately, coinciding with the settlement of the region by Euro-Americans. Numerous settlement activities, including draining of lake-margin marshes, upstream agriculture and timber harvest, road construction, and boat traffic, may have affected the lake. Magnetic properties and reworked tephra suggest riparian changes throughout the basin and increased lithogenic sediment delivery to the lake, especially after 1920 when the marshes near the mouth of the Williamson River were drained and converted to agricultural and pasture land. Drainage and channelization also decreased the ability of the marshes to function as traps and filters for upstream water and sediments. Akinetes of Aphanizomenon flos-aquae record progressive eutrophication of Upper Klamath Lake beginning in the 20th century and particularly after 1920 when lake-margin marsh reclamation more than doubled. The coincidence of limnological changes and human activities following European settlement suggests a major impact on the Upper Klamath Lake ecosystem, although ascribing specific limnological changes to specific human activities is difficult.     

Sample preparation methods and replicability in macroscopic charcoal analysis

We explored the use of hydrogen peroxide (H₂O₂) of different strengths (1, 3, 6, and 9%) in the preparation of lake-sediment samples for macroscopic charcoal determination. In previous work we found that soaking sediment samples in 3% H₂O₂ for 24 h disaggregates samples and removes or bleaches some non-charred organic material, making it easier to distinguish macroscopic charcoal particles from dark, non-charred organic matter. To determine whether this procedure alters charcoal particle abundances and size distributions, we tested the procedure on wood and grass samples containing a known number of laboratory-produced charcoal particles from different size classes (250–500, 500–1,000, and 1,000–2,000 μm). For both sample types, we found that post-treatment numbers were not statistically different from pre-treatment numbers. However, application of hydrogen peroxide solutions of 3, 6, and 9% to fossil charcoal assemblages in a sediment core from northwestern Costa Rica reduced charcoal concentrations markedly, by bleaching or removing particles that were not fully charred. We also tested the replicability of charcoal counts by conducting enumerations on multiple samples from the same stratigraphic depths in a core. Horizontally adjacent samples from the same core may vary in charcoal concentration. This finding has implications for establishing sample volume in macroscopic charcoal analysis.     

A model for the retrieval of suspended sediment concentrations in Taihu Lake from TM images

A study was conducted in the Taihu Lake with the aim of deriving a model for the retrieval of suspended sediment (SS) concentrations from Landsat TM images and in situ sampled data. The correlation between suspended sediment concentrations of lake and the reflectance obtained from the TM images is significant. By TM images and in situ sampled data in summer and winter, we obtained a comparative uniform model for the retrieval of suspended sediment concentrations in the Taihu Lake, that is lnSS = a*(R3/R1) + b, where lnSS is the natural logarithm of the suspended sediment concentration, R1 and R3 are the reflectance coincident with the 1st band and the 3rd band in TM images, a and b are the regression coefficients. Furthermore, we analysed the errors particularly to make sure the model is valid. The model is accurate to within 0.33(RMSE), suggesting that this model may be applicable to predict suspended sediment in the Taihu Lake from TM image throughout the year.     

基于TM影像的太湖悬浮物反演模型

1 Introduction Suspended sediment (SS) is the non-dissolved matter in water which reflects the physical and chemical property of water. Suspended sediment plays an important role in water quality management, which influences the total primary productivity…     

Historical change in lake sedimentation in Lake Takkobu, Kushiro Mire, northern Japan over the last 300 years

Environmental degradation, including shallowing, deterioration of aquatic habitat and water pollution, has arisen from the inflow of fine sediment to Lake Takkobu in northern Japan. The lake has experienced gradual environmental degradation due to agricultural development, which has introduced both fine sediment and sediment-associated nutrients into the lake. We have reconstructed the history of sediment yield to Lake Takkobu in Kushiro Mire over the last 300 years and have examined trends with reference to land-use development. Fifteen lake sediment core samples were obtained, and various physical variables of lake sediments were analyzed and dated using ¹³⁷Cs and tephrochronology. The physical variables showed that all points contained mainly silt, except for two points close to the river mouths, where the mean diameter was < 35 μm. The peaks were defined as a “signal” when the physical variables were synchronous in a profile. These were created by floods and engineering works constructing drainage systems. The signal of canal construction in 1898 was detected in all core points. Lake Takkobu core samples contained two tephra layers. From the refractive indices of dehydrated glasses, the lower tephra layer was identified as Ko-c2 (1694) and the upper tephra layer as Ta-a (1739). A clear peak in the ¹³⁷Cs concentration was detected at all the sampling points, except for the site close to the Takkobu River. This site showed two peaks in the ¹³⁷Cs concentration, which was attributed to perturbation from flood events and a drainage project. The maximum ¹³⁷Cs concentration was identified as the sediment surface from 1963, enveloped by the 1962 and 1964 signals. The sediment yield averaged over the last 300 years for Lake Takkobu was reconstructed for four periods using the signal, tephra and ¹³⁷Cs as marker layers. The sediment yield under the natural erosion condition for the first two periods was 226 tons/year from 1694 to 1739 and 196 tons/year from 1739 to 1898. The development of the Takkobu watershed started in 1880s with partial deforestation and channelization in 1898, 1959, and 1962 leading to an increased sedimentation yield of 1016 tons/year from 1898 to 1963. Continued deforestation, channelization works in 1964, road construction in 1980–1990s, as well as agriculture development caused a further increase to 1354 tons/year from 1963 to 2004. Compared to the averaged natural sedimentation yield of 206 tons/year until 1898, initial land-use development in a catchment accelerated lake sedimentation, indicated by the 5-fold sediment yield. With increasing agricultural development since 1960s, sedimentation yields were highest for 1963–2004; a 7-fold increase compared with pre-impact conditions. To reduce sediment yield, riparian buffers along the rivers should be preserved or rebuilt, and sluices may function effectively during short-term periods of flooding. Environmental management policy and laws restricting uncontrolled and inappropriate land-use might help in addition to ensure longer-term environmental health by reducing the sedimentation rate.     

Characteristics of freshly deposited sand and finer sediments along an island-braided, gravel-bed river: The roles of water, wind and trees

Over the past two decades there has been a growing interest in the geomorphological mosaic along large floodplain rivers where channel dynamics are seen to drive habitat-patch creation and turnover and to contribute to high biological diversity. This has required a new perspective on fluvial geomorphology that focuses on biological scales of space and time. This study examines the spatial pattern of surface fine sediment accumulations along a reach of a large gravel-bed river, the Tagliamento River in NE Italy; an area with a moist Mediterranean climate and seasonal flow regime. The study investigates changes in sediment characteristics during the summer low-flow period between April and September. Focussing on five areas representing a gradient from open, bar-braided to wooded island-braided morphologies, the paper demonstrates the importance of riparian vegetation and aeolian–fluvial interactions.Significant contrasts in particle size distributions and organic content of freshly deposited sand and finer sediments were found between sampling areas, geomorphological settings, and sampling dates. In particular, wooded floodplain and established islands supported consistently finer sediment deposits than both open bar surfaces and the lee of pioneer islands, and in September significantly finer sediments were also found in deposits located in the lee of pioneer islands than on open bar surfaces. Overall, the September samples had a greater variability in particle size characteristics than those obtained from the same sites in April, with a general coarsening of the D₅ (φ) (i.e., the coarse tail of the particle size distribution). Also in September, crusts of fine sediment (30 μm < D₅₀ < 64 μm) had formed on the surface of some of the open bar and pioneer island deposits within the more open sampling areas along the study reach. These crusts possessed similar particle size characteristics to aeolian crusts found in more arid environments. They were significantly finer than April samples and September subcrust samples obtained from the same sites and had similar particle size characteristics to some samples taken from wooded floodplain, established island surfaces and the lee of pioneer islands that were not crusted.Local climatological and river level data confirm significant wind and rainfall events during a period of consistently low river levels between the April and September sampling periods. These support deflation, deposition and rain wash of finer sediment during the summer, with windblown sediments being deposited on bar surfaces and in the lee of pioneer islands where wood and young trees provide foci for accelerated sedimentation and island growth as well as on marginal floodplains and established islands. We conclude that along braided rivers in moist settings but with a distinct dry season, aeolian reworking of sediment deposits may have a more important role in driving habitat dynamics than previously considered.     

Discriminating Bio-Induced and Detrital Sedimentary Processes from Particle Size Distribution of Carbonates and Non-Carbonates in Hard Water Lake Sediments

Particle size distribution (PSD) and carbonate content are two of the most frequently used parameters for describing lake sediments. This paper presents a method for rapidly measuring both these parameters using a laser particle-sizer, as well as an original way in which to separately interpret the PSD of the carbonate and non-carbonate fractions. Differential particle size analyses are produced by measuring the PSD of each sample twice. The first PSD is measured using the bulk sample. The second PSD is measured after the carbonate fraction has been completely dissolved by adding hydrochloric acid to the sample. As well as particle size analyses, laser particle-sizers automatically give obscuration values for the samples being analysed. By comparing the obscuration value for the bulk sample with the value for the de-carbonated fraction, the carbonate content of the sediment can be determined. In order to test the accuracy of the method, the results were compared with chemical analyses of carbonate content. This comparison showed that when applied to diatom-rich samples the method underestimates the carbonate content. This is due to the fact that the differential particle size method measures the volume concentrations of the carbonate and non-carbonate fractions, whereas chemical analysis measures the weight concentrations. As diatoms are hollow and have relatively low-densities, differential particle size analyses of diatom-rich samples overestimate the non-carbonate fraction. Despite this limitation, and bearing in mind that laser particle-sizer distributions are expressed in terms of volume percent for each size class and not weight percent, PSDs can provide useful data for interpreting sedimentary processes. One of the main advantages of this method is that it can be used to separate the PSDs of the carbonate (autochthonous) fraction and the non-carbonate (allochthonous) fraction from the PSD of the bulk sample. The value of such an approach was demonstrated by the analysis and interpretation of a 9 m-long core from Lake Bourget in France. An analysis of the bulk sample PSDs plotted as a function of depth showed the consistency of sedimentary processes over the last 7200 years. Amongst these processes, it was possible to identify two modes of clastic material deposition: river-borne fine sedimentation during major floods and gravity reworking of sandy sediment from the lakeshore.     

Interactions between a cushion plant (Azorella selago) and surface sediment transport on sub-Antarctic Marion Island

On sub-Antarctic Marion Island cushions of the dominant vascular plant species, Azorella selago, interact with the geomorphology of fellfield landscapes by affecting sediment distribution and ultimately terrace formation. Here, to understand the consequences of Azorella cushions for substrate movement and sorting, we quantified the size and shape of Azorella cushions and the grain size distribution of sediment surrounding these cushions, using a combination of image analysis approaches. Results show that as cushions become larger, they tend to become more elongated and grow more perpendicular to the slope. Mean and variance of grain size were greater upslope of Azorella cushions, while the number of particles was higher downslope of cushions, although these differences were not significant at all sites studied. Differences between upslope and downslope particle sizes were, however, not related to cushion elongation or growth angle as had been expected. The observed sediment partitioning is likely caused by a combination of frost-related sediment transport and Azorella cushions acting as sediment obstructions. Understanding these interactions between Azorella cushions and the landscape is especially important in the light of recent warming and drying on the island, as particle size affects soil properties such as water-holding capacity and frost susceptibility.     

A feature extraction and similarity metric-learning framework for urban model retrieval

Urban model retrieval has wide applications in the geoscience field, and it is also a very challenging research topic due to the blur and background clutter in query images and the large spatial inconsistencies between query and database images. In this study, a feature extraction and similarity metric-learning framework for urban model retrieval is proposed. In the method, the selective search voting algorithm is presented to automatically localize and segment a query object from an input image with the help of the top-ranked retrieved database images. Then, the local features of object images are extracted via sparse coding, and the global features are learned using the spatial constrained convolutional neural network. We utilize a new similarity metric to match the database images with a query object image. Finally, similar 3D models are retrieved. Both qualitative and quantitative experimental results indicate that the proposed framework can localize and segment a query object from an input image precisely and that the retrieval results are better than those of other related approaches.     

南极普里兹湾沉积物中生物硅对粒度测量结果的影响

为了探讨生物硅对沉积物粒度测量结果的影响, 本文采用两种不同前处理方法对普里兹湾重力柱状样品进行了粒度测试。结果表明, 生物硅对沉积物的平均粒径以及黏土、粉砂、砂组分的影响较小, 而对沉积物的分选、偏态、峰态以及粒度频率分布的影响较显著。结合两组粒度组分相关性分析以及各粒级含量累积减小值, 认为生物硅对沉积物中砂、粉砂、黏土级组分含量的影响逐渐减小, 这也造成未去除生物硅的沉积物粒度测量结果偏粗。另外, 通过对比发现普里兹湾沉积物中生物硅粒径主要分布在<3Φ、5.25Φ—7.25Φ、8.75Φ—9.75Φ的粒径范围。极地研究中, 沉积物粒度结果为重建古环境变化提供重要参考, 本文研究认为在普里兹湾海域沉积物粒度研究中去除生物硅对研究结果有积极作用。     

An inexpensive system for continuous lake core photography

Representative images of split sediment cores document geological records, serve as visual aids for multimedia, and provide samples for image analysis. Existing core imaging systems, often containing integrated hardware and software, are capable of providing excellent images; unfortunately these systems are also bulky and expensive, and are therefore limited to labs that process large volumes of core and those actively involved in image analysis. For most research groups such systems are unfeasible to buy and maintain. Producing good quality core images with a hand-held digital camera is very difficult without a consistent lighting source, and changes in camera angle (in all three spatial dimensions) between photographs may prevent accurate image compositing. Tripods allow for camera stability, but typically do not accommodate downward-facing photography. Presented here is an easily constructed core-imaging system that minimizes many of the drawbacks of personal digital cameras. Software necessary for using this system is readily available and can be run from a personal computer.     

A method for the selective removal of inorganic ash particles from lake sediments

Inorganic ash particles are formed by the fusing of inorganic material present during the high temperature combustion of fossil fuels. As they accumulate in lake sediments, they record the history of atmospheric contamination produced from such sources. A technique has been developed for concentrating these particles from lake sediments involving the stepwise removal of unwanted components of the sediment, including organic material and biogenic silica.When applied to a sediment core taken from Loch Tinker, central Scotland, a particle concentration profile, very similar to that of the carbonaceous particle profile (the other component of fossil-fuel combustion ash) is produced. The concentration of the inorganic ash spheres in the sediment is approximately an order of magnitude higher than the carbonaceous particles and there appears to be a continuous pre-industrial background value. This seems to imply a similar source (i.e. coal combustion rather than oil) for both inorganic ash and carbonaceous particles. This method has also been used with success on peat cores.     

Integrated edge detection and terrain analysis for agricultural terrace delineation from remote sensing images

ABSTRACT

Agricultural terraces are important for agricultural production and soil-and-water conservation. They comprise treads and risers that require manual construction and maintenance. If managed improperly, risers will collapse, causing soil loss, gully erosion, and cultivation threats. However, mapping terrace risers remains a challenge. This study presents a novel approach to automatically map terrace risers by combining remote sensing images and digital elevation models (DEMs). First, a terraced hillslope was extracted via a hill-shading method and edges in the image were detected using a Canny edge detector. Next, the DEM was used to generate the contour direction, and edges along this direction were searched and coded as candidate terrace risers via directional detection. Finally, the results of directional detection and the edge image obtained from the Canny detector were overlaid to backtrack complete terrace risers. The approach was validated using four study areas with different topographic characteristics in the Loess Plateau, China. The results verify that the approach achieves outstanding performance and robustness in mapping terrace risers. The precision, recall, and F-measure were 90.81%–97.57%, 88.53%–94.10%, and 90.13%–95.80%, respectively. This approach is flexible and applicable with freely available images and DEM sources.     

泥石流的结构两相流模型:Ⅱ.应用

本文应用泥石流的结构两相流模型对各类泥石流的运动机理进行探讨,并成功地解释了泥石流运动中的一系列特殊现象,如可能出现的颗粒浓度“上大下小”型分布、泥石流垂线速度的“反Ｓ”型分布、泥石流中颗粒脉动速度分布变化的特殊性、泥石流的输移特性以及在一定条件下出现的“流核”现象,等等。模型计算结果得到了实验资料的验证。     

颗粒分选与有机质因子对复合指纹识别泥沙来源的影响

泥沙来源研究作为土壤侵蚀研究的关键内容之一,对水土保持措施的科学布设具有重要意义.复合指纹识别法是目前研究泥沙来源的较先进方法之一,在泥沙来源研究中具有较大的应用潜力.然而,颗粒分选作用对运用复合指纹识别法判别沉积物来源的准确性有重大影响.加之,有机质等代表的土壤属性(指纹因子)随颗粒分选在不同粒径范围发生富集或贫化也...     

Environmental records of carbonaceous fly-ash particles from fossil-fuel combustion

Analysis of fly-ash particles in lake sediments has become increasingly important in studies of environmental pollution and lake acidification history. Most fly-ash studies have concerned black spheroidal carbonaceous particles (SCP)(>5 m) produced from oil and coal combustion. This review paper provides a summary of this technique and its application, and focusses on our investigations in Sweden between 1979 and 1993. It consists of five parts: i) preparation and analysis methods, ii) historical trends in atmospheric deposition, iii) geographical surveys of atmospheric deposition, iv) sediment dating, and v) studies of sedimentation processes in lakes. Methods for preparation and analyses of SCP have been developed and applied to investigations using sediment, soil and snow samples. Stratigraphic trends of SCP concentrations in lake-sediment cores reflect the consumption history of fossil fuels. A characteristic temporal SCP pattern, with a marked concentration increase beginning after the 1940's and a peak in the early 1970's, has been recognized in most Swedish lakes and elsewhere in Europe. A survey of SCP concentrations in surface sediments of >100 lakes covering Sweden demonstrated that polluted areas in southern Sweden had >100 times higher SCP concentrations than clean areas in the north. The spatial distribution of SCP over Sweden is similar to the deposition pattern of long-range transported airborne pollutants, such as excess sulphate monitored by network stations. SCP also accumulate in soils, and soil analyses can be used for determining the integrated historical deposition of SCP at the local or regional scale. Finally, SCP have been used for indirect dating of sediment cores and as a marker to assess sediment distribution patterns within lake basins.