Regionalization for large area crop estimates by remote sensing

The crop estimates by remote sensing, developing quickly in recent decades, is a up-to-date technique. Regionalization for large area crop estimates by remote sensing, a special applied regionalization, is the foundation of crop estimates in a large area by remote sensing. According to the actual demands of wheat yield estimation by remote sensing and wheat agroclimatic demarcation of China, this paper first puts forward some principles upheld in this regionalization and analyses its main bases. Secondly, it works out the classificatory schemes about the optimum temporal for estimating wheat yield by remote sensing, information sources of space remote sensing and landuse structure in China. Finally, According to the regionalization indices, this study divides the wheat plantable region of China into 14 regions of crop yield estimates and 31 subregions of crop yield estimates.     

Sonar acoustic facies and sediment distribution on an area of the deep ocean floor

Long-range sidescan sonar can be used to map sediment distributions over wide expanses of deep ocean floor. Seven acoustic facies that arise from differing sediment or rock types have been mapped over the low-relief Saharan continental rise and Madeira abyssal plain. These have been calibrated with sampling, profiling and camera studies and the facies can be traced confidently on a regional scale using the sidescan data. The mapping of the sediment distribution shows that a complex interplay of turbidity current and debris flow processes can occur at a continental rise/abysaal plain transition over 1000 km from the nearest continental slope.     

Preservation conditions and the use of sediment pigments as a tool for recent ecological reconstruction in four Northern European estuaries

Down-core sediment pigment concentrations from four Northern European estuaries were measured using high-performance liquid chromatography (HPLC) to investigate phytoplankton community structure and preservation conditions over the last ca. 100 years where all sites have experienced different levels of eutrophication. Phytoplankton pigments have been shown to be useful biomarkers for phytoplankton community structure and abundance due to their taxonomic specificity. The pigment concentrations and sediment pigment inventory showed large variation between the four sites. Concentrations ranged from more than 6000 nmol/g OC to less than 100 nmol/g OC and the inventory integrated over the top 10 cm from more than 300 nmol/cm² to less than 30 nmol/cm² for total identified pigments. Good pigment preservation in Mariager Fjord (Denmark) reflected the almost permanently anoxic conditions. Pigments in Laajalahti (Finland) showed peak concentrations around the time of highest nitrogen loading events known from historical and modelled records over the past 100 years. In contrast, poor down-core preservation of pigments (especially carotenoids) was observed in the Ems-Dollard (The Netherlands) and Himmerfjärden (Sweden) estuaries. The Ems-Dollard site is an intertidal mudflat that experiences daily exposure to light and air, which enhances pigment degradation. In Himmerfjärden, resuspension is an important process affecting both the sedimentation rate and degradation properties. The different preservation conditions at the four sites were supported by the differences in two degradation indicators; the ratio of pheopigment-a to chlorophyll-a and total carotenoids to total pigments. Class-specific carotenoid pigments represented the dominant algal groups reported from each site, however, no distinct down-core changes in the pigment composition were observed at any of the four sites. This indicated that changes in plankton community structure on the group level have been limited over this time period or masked by low preservation of pigments.     

Comparative tolerance of two estuarine annelids to fluoranthene under normoxic and moderately hypoxic conditions

The tolerance of the oligochaete Monopylephorus rubroniveus and the polychaete Streblospio benedicti to sediment-associated fluoranthene was characterized under normoxic (>80% dissolved oxygen saturation) and moderately hypoxic ( approximately 50% dissolved oxygen saturation) conditions. Under both conditions, M. rubroniveus was highly tolerant of fluoranthene. Streblospio benedicti was considerably less tolerant of fluoranthene compared with M. rubroniveus. In addition, S. benedicti was less tolerant to fluoranthene under moderately hypoxic conditions, although no differences in sensitivity between the two oxygen conditions were observed based upon median lethal tissue residues. Bioaccumulation factors were higher for S. benedicti exposed to moderate hypoxia, suggesting that behavioral adaptations to compensate for the lower dissolved oxygen increased its bioaccumulation of fluoranthene. The results of the present laboratory study demonstrate that (1). changes in annelid tolerance to fluoranthene under varying oxygen conditions is a species-dependent phenomenon and (2). the differential tolerance of these two annelids to these combined stressors is consistent with their relative abundances in the field.     

The dimensions of sand ripples in full-scale oscillatory flows

New large-scale experiments have been carried out in two oscillatory flow tunnels to study ripple regime sand suspension and net sand transport processes in full-scale oscillatory flows. The paper focuses on ripple dimensions and the new data are combined with existing data to make a large dataset of ripple heights and lengths for flows with field-scale amplitudes and periods. A feature of the new experiments is a focus on the effect of flow irregularity. The combined dataset is analysed to examine the range of hydraulic conditions under which oscillatory flow ripples occur, to examine the effects of flow irregularity and ripple three-dimensionality on ripple dimensions and to test and improve existing methods for predicting ripple dimensions.The following are the main conclusions. (1) The highest velocities in a flow time-series play an important role in determining the type of bedform occurring in oscillatory flow. Bedform regime is well characterised by mobility number based on maximum velocity in the case of regular flow and based on the mean of the highest one tenth peak velocities in the case of irregular flow. (2) For field-scale flows, sand size is the primary factor determining whether equilibrium ripples will be 2D or 3D. 2D ripples occur when the sand D₅₀ ≥ 0.30 mm and 3D ripples occur when D₅₀ ≤ 0.22 mm (except when the flow orbital diameter is low). (3) Ripple type (2D or 3D) is the same for regular and irregular flows and ripple dimensions produced by equivalent regular and irregular flows follow a similar functional dependence on mobility number, with mobility number based on maximum velocity in the case of regular flow and based on the mean of the highest one tenth velocities in the case of irregular flow. For much of the ripple regime, ripple dimensions have weak dependency on mobility number and ripple dimensions are similar for regular and irregular flows with the same flow orbital amplitude. However, differences in ripples produced by equivalent regular and irregular flows become significant at the high mobility end of the ripple regime. (4) Ripple dimensions predicted using the Wiberg and Harris formulae are in poor agreement with measured ripple dimensions from the large-scale experiments. Predictions based on the Mogridge et al. and the Nielsen formulae show better overall agreement with the data but also show systematic differences in cases of 3D ripples and ripples generated by irregular flows. (5) Based on the combined large-scale data, modifications to the Nielsen ripple dimension equations are proposed for the heights and lengths of 2D ripples. The same equations apply to regular and irregular flows, but with mobility number appropriately defined. 3D ripples are generally smaller than 2D ripples and estimates of 3D ripple height and length may be obtained by applying multipliers of 0.55 and 0.73 respectively to the 2D formulae. The proposed modified Nielsen formulae provide an improved fit to the large-scale data, accounting for flow irregularity and ripple three-dimensionality.     

The Record of an Extreme Flood in the Sediments of Montane Lillooet Lake, British Columbia: Implications for Paleoenvironmental Assessment

Severe rainfall in mid October, 2003 produced the largest floods in almost a century of record on rivers in the Cordillera of southwestern British Columbia. Sediment deposited in Lillooet Lake as a result of this event is clearly distinguished by stratigraphy, colour, texture, magnetic properties, and organic content. Each of these physical properties is related to the lacustrine processes, especially turbid underflow, that distributed the sediment through the lake. The flood, which lasted less than a week, delivered 8–12 times the amount of sediment that accumulates in most entire years in the deepest, central parts of the lake. Recognition of events of this type in the stratigraphic record offers a means of assessing the changing nature of extreme hydroclimatic events, and their relation to more ubiquitous, lower-energy processes.     

Determination of specific yield using a water balance approach – case study of Torla Odha watershed in the Deccan Trap province, Maharastra State, India

Specific yield is an essential parameter for any groundwater management plan. Volumetric analysis in the domain of groundwater budgeting for the non-monsoon months has been undertaken for a typical watershed of the Deccan basalt province. The Torla Odha watershed covers an area of over 22 km² on a third-order tributary of the westerly flowing Bhima River. The watershed receives a normal annual rainfall of 643 mm. The entire water demand is supplied by dug wells, which penetrate a shallow aquifer. The specific yield was estimated by comparing the monthly net volume of water removed from the aquifer, with the volume of aquifer de-saturated, based on monthly water level data. The estimated specific yield ranges from 0.0019 in May to 0.0173 in November with an average value of 0.0093. A correlation of the groundwater levels with the detailed geology suggests that the higher specific yield value (0.017) corresponds to dewatering of the weathered zone within the shallow aquifer. The specific yield of the massive basalt immediately below the weathered zone varies from 0.0089 to 0.0103. The underlying vesicular basalt, which is dissected by sheet joints, has a relatively higher specific yield (0.0121). The massive basalt, which forms the base of the shallow aquifer system, has a lower specific yield from 0.0019 to 0.0022.

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Résumé Le débit spécifique est un paramètre essentiel pour tout plan de gestion des eaux souterraines. Les analyses volumétriques, dans le cadre des bilans hydriques des eaux en dehors des mois de mousson, ont été entreprises pour un bassin-versant typique de la province basaltique du Deccan. Le bassin-versant du Torla Odha couvre une superficie de 22 km², et alimente l’affluent du troisième ordre de la rivière Bhima, qui coule vers l’Ouest. La pluviométrie annuelle atteint 643 mm. Toute la demande en eau es assurée par des puits foncés pénétrant dans l’aquifère phréatique. Le débit spécifique a été estimé en comparant le volume net mensuel d’eau captée dans l’aquifère, avec le volume de l’aquifère dé-saturé, basé sur les données des niveaux piézométriques mensuels. Le débit spécifique estimé s’étend entre 0,0019 en Mai et 0.173 en Novembre; la moyenne se situe à 0,0093. Une corrélation entre les niveaux des eaux souterraines et la géologie, suggère que les débits spécifiques les plus importants (0,017) correspondent aux zones altérées de l’aquifère phréatique. Le débit spécifique du massif basaltique, immédiatement sous la zone altérée, varie entre 0,0089 et 0,0103. Le basalte vésiculaire, situé juste en dessous et traversé par des diaclases parallèles, possède un débit spécifique sensiblement plus élevé (0,0121). Le basalte massif, qui forme la base de l’aquifère phréatique, possède un débit spécifique moins important, compris entre 0,0019 et 0,0022.

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Resumen El rendimiento específico es un parámetro esencial para cualquier plan de manejo de aguas subterráneas. Se ha llevado a cabo el análisis volumétrico, en el entorno de balance de aguas subterráneas, para los meses sin monzón de una cuenca típica de la provincia de basaltos Deccan. La cuenca Rorla Odha cubre un área de 22 km² en un tributario de tercer orden del Río Bhima que fluye al oeste. La cuenca capta una lluvia anual normal de 643 mm. La totalidad de la demanda de agua es abastecida por pozos manuales que penetran un acuífero somero. Se estimó el rendimiento específico al comparar el volumen neto mensual de agua removido del acuífero con el volumen de agua de-saturado estimado a partir de datos de niveles de agua mensuales. Los valores estimados de rendimiento específico varían de 0.0019 en mayo a 0.0173 en noviembre con un valor promedio de 0.0093. La correlación de niveles de agua subterránea con la geología de detalle sugieren que el valor más alto (0.017) de rendimiento específico corresponden con el desaguado de la zona de intemperismo dentro del acuífero somero. El rendimiento específico del basalto masivo que se encuentra inmediatamente debajo de la zona de intemperismo varía de 0.0089 a 0.0103. El basalto vesicular subyacente, el cual está disectado por fracturas laminares, tiene un rendimiento específico relativamente más alto (0.0121). El basalto masivo, que forma la base del sistema de acuífero somero, tiene un rendimiento específico más bajo el cual varía de 0.0019 a 0.0022. Palabras clave: basalto Deccan. India. Rendimiento específico. Recarga de agua subterránea. Balance hídrico.

     

Ammonium regeneration in intertidal sediments of the Yangtze estuary during air-exposure

The influences of exposure to the atmosphere on ammonium cycle in the intertidal surface sediments were in situ studied with a geochemical approach at a typical station in the Yangtze Estuary during three tidal cycles in September 2003. During an about 8-h emersion period of each diurnal tide, six high-resolution vertical profiles of adsorbed and dissolved ammonium were measured. It was observed that both adsorbed and dissolved ammonium generally had an increasing trend in sediment cores during the exposure. The rate of ammonium regeneration in sediments was estimated using the accumulation amount of ammonium including adsorbed and soluble fractions during the daytime emersion. The calculation result showed that there was relatively high ammonification rate (˜500 nmol N cm⁻³ day⁻¹), which reflected that organic nitrogen in sediments was quickly decomposed with a residence time of ˜52.7 days. Due to the dramatic temperature difference observed in sediment profiles, free convection was considered an important mechanism of regulating the efflux of produced ammonium into overlying waters. The total estimated amount of regenerated ammonium was ˜1.35×10⁵ t N year⁻¹ in the intertidal flat of the Yangtze Estuary, which occupied 7.6% of the total inorganic nitrogen annually transported to the estuarine ecosystem.     

Current controlled sediment deposition from the shelf to the deep ocean: the cenozoic evolution of circulation through the SW pacific gateway

 The circulation of cold, deep water is one of the controlling factors of the Earth's climate. Forty percent of this water enters the world ocean through the Southwest Pacific as a deep western boundary current (DWBC) flowing northwards at bathyal to abyssal depths, east of the New Zealand microcontinent. South of latitude 50°S, the DWBC is intimately linked with the Antarctic circumpolar current (ACC), which is the prominent force for the shallow-water circulation. The Pacific DWBC is presently the largest single contributor of deep ocean water, and deciphering its evolution is of fundamental importance to understanding ocean and climate history, and global ocean hydrography. The evolution of the DWBC system, and of related circum-Antarctic currents, has taken place since 30–25 Ma when plate movements created the first oceanic gaps south of Australia and South America. The stratigraphic record preserved in sediment drifts of the Southwest Pacific, in eastern New Zealand, is the best available for deciphering the Neogene history of Southern Ocean water masses, and of the circulation of the ACC, DWBC and their precursor systems. Major current activity commenced on the New Zealand margin in the late Eocene or early Oligocene (Hoiho Drift; early ACC) and was widespread by the mid-late Oligocene (Marshall Paraconformity and Weka Pass Limestone drift; ACC). During the Neogene the eastern South Island continental shelf built seawards by accretion at its outer edge of large Miocene current drifts up to tens of kilometres long and hundreds of metres thick (Canterbury drifts). Also commencing in the mid-Cenozoic, but in depths >2000 m, the DWBC emplaced large deep-water sediment drifts. Rates of drift deposition accelerated considerably in the late Neogene, when climatic change (and particularly glacial sea-level falls) caused the delivery of large volumes of turbiditic sediment into the path of the DWBC via the Bounty and Hikurangi channels. Received: 9 August 1995 / Accepted: 15 January 1996     

某滑坡软弱夹层抗剪强度取值方法的研究

文章主要针对软弱夹层抗剪强度取值所存在的争议，通过对贵州新街子滑坡的软弱夹层分别选择比例极限、屈服极限及峰值作为剪应力值，采用最小二乘法获得比例抗剪强度、屈服抗剪强度和峰值抗剪强度。以参数选取中应用较为成熟的反分析方法推求力学性质参数c、φ值作为判据对以上3种参数进行比较。计算结果表明：本滑坡软弱夹层中由于含泥量较大，而且粘塑性较强，屈服抗剪强度和反分析得到的抗剪强度偏差最小，比例抗剪强度偏差最大，峰值抗剪强度居中。并以此3种抗剪强度进行天然状态下滑坡稳定性验算，结果表明选用比例极限抗剪强度与当前滑坡的地质现象不符，选用峰值极限抗剪强度安全储备较低，而选取屈服极限抗剪强度最为合理。用此参数进行设计，滑坡已经得到了良好的治理。在取值研究中认为采用试验与反分析相结合的方法确定滑坡稳定性计算参数是比较合理的。以上结论为滑坡中软弱夹层抗剪强度取值的选择提供了重要的依据。