Spatial and temporal variation of natural recharge in the semi-arid valley of Aguascalientes,Mexico

The investigation involves a temporal and spatial analysis to characterize recharge in the Aguascalientes valley in central Mexico. The results are based on a two-part methodological strategy using a geospatial and numerical analysis. Results from the geospatial analysis are based on the analytical hierarchical process (AHP) method, which involves developing a zoning map that qualifies the conditions for groundwater recharge in the valley. In addition, one-dimensional numerical modeling based on the van Genuchten equation was applied for various soil column configurations to estimate the transit time of recharge through the vadose zone. The analysis was performed over a 20-year period from 1995 to 2015. The results of the geospatial analysis indicate that the optimal area for groundwater recharge is the lower zone of the valley, particularly the portion influenced by surface discontinuities. The shortest estimated period of recharge for water to pass through the vadose zone is approximately 4.25 years.     

Sorting of bivalve populations in a beach environment

Size sorting of shells and valves of transported death assemblages of Mytilus edulis is shown to have taken place, and greatly affected size-frequency distributions of shell accumulations deposited in a beach environment. Selective transport and deposition of different size grades gives histograms which may be strongly skewed or multimodal, and include numerous small shells. The usually predicted bell-shaped distributions for sorted assemblages are not always produced. Little evidence of growth and mortality rates can be deduced with confidence from the transported assemblages.     

半干旱区内陆湖泊透明度高光谱估测模型研究——以松嫩平原查干湖为例

通过实测查干湖高光谱数据,建立透明度(Secchi Disk Depth,SDD)单波段估测模型、比值估测模型以及神经网络高光谱估测模型,并以确定性系数R2以及剩余残差RMSE为指标进行了验证.通过对单波段估测模型和比值估测模型进行比较发现,单波段模型估测结果与比值模型相差无几,而水体透明度经对数处理有利于模型精度提高,但是神经网络模型是三者中最优的.查干湖透明度高光谱定量估测模型的建立,有利于今后利用遥感影像,对查干湖水体透明度进行全面估测,对于研究和监测查干湖水体水质状况有重要意义.     

Spatial variation of selenium in Appalachian coal seams

Selenium (Se) is a trace element that can cause human physical deformations due to selenosis, and mutagenic changes on a range of sensitive macro-organisms. Previous studies indicated that Se enrichment is significantly greater in coal than in other rock units, suggesting a correlation between Se and coal bed proximity. Since coal extraction can cause a release of Se, some regulatory authorities have responded by requiring sampling of coal seams and adjacent rock for Se prior to issuing coal mining permits. This sampling is done under the assumption that Se in a small number of samples will be correlated to the Se concentrations throughout the strata they represent. For example, in one case a single continuous deep rock core was sampled for Se to estimate the concentrations of Se across a 2.52 km² proposed surface coal mine. This project examined the adequacy of such an approach using univariate statistics and variograms to determine the spatial variability and correlation of Se concentrations collected from six Appalachian coal seams. The results from all analyses showed no significant spatial correlation of Se within any coal seam examined. Given this lack of measured Se spatial correlation in Appalachian coal seams for scales as small as 0.10 km, it is unlikely that a Se spatial correlation exists in adjacent rock units at similar scales either, which is currently the assumption being made for sampling to minimize Se pollution from surface coal mining.     

Weathering rates of sandstone in a semi-arid environment (Hunter Valley,Australia)

The rate of sandstone weathering in the semi-arid climate of the Hunter Valley, New South Wales, Australia has been estimated from observations of gravestone weathering in the area. The gravestone data points to two distinct stages in the weathering process. The first stage covering the first century of exposure is characterised by a relatively low recession rate of 0.5 mm/100 years. This is followed by a second stage in which the rate of weathering increases sharply to ca 2.5 mm/100 years. The non-linear nature of the weathering trends over time suggests that during the first century of exposure, structural changes took place within the sandstone material, which lay the foundation for accelerated weathering after further exposure. Laboratory trials were also conducted to identify the effectiveness of different weathering processes in the decay of sandstone in this region. Of the four processes examined, only the freeze–thaw cycle produced a significant degree of mass loss and is therefore most likely a strong contributor to the weathering of sandstone in this region.     

Long-term variation of fiddler crab populations in North Carolina salt marshes

Estuaries and Coasts - Total biomass of the fiddler crabsUca pugnax andU. minax in fourSpartina marshes in the lower Cape Fear River estuary, North Carolina, declined by 65 to 70% between the...     

Genetic variation in two populations of blue crab,Callinectes sapidus

Genetic variability of the blue crab,Callinectes sapidus, was estimated for populations in Chesapeake and Chincoteague Bays. Genetic similarity between these populations was attributed to larval intermixing in the mid-Atlantic Bight.     

岩溶区土壤有机质空间变异性分析

采用GIS和地统计学研究土壤有机质（SOM）的空间分布、影响因素和预测是指导农业生产、环境治理和土壤碳储计量的重要手段。基于广西马山县北部岩溶区表层土壤 (0~20 cm)的441个SOM数据,建立普通克里格(OK)、回归克里格（RK）,以及结合辅助变量的地理加权回归克里格(GWRK)、残差均值（MM_OK）和中值（MC_OK）均一化克里格的5种模型,并比较其预测精度,旨在探讨岩溶区SOM制图中地统计学方法的适用性。结果表明：（1）SOM的变异系数为37.30%,属于中等空间变异;（2）岩溶区SOM空间变异受土地利用方式、土壤类型和地形因子等因素共同影响,SOM高值区分布在西北部、西部和东部等石灰土分布的岩溶区和水田,低值区位于北部红水河沿岸的冲积土地带;（3）RK、GWRK、MM_OK和 MC_OK对SOM解释能力均较优,可用于岩溶区SOM预测制图。结合辅助变量因子的GWRK预测模型能有效消除空间变异因素的影响,克服岩溶区SOM含量的空间非平稳性,从而提高SOM含量模型的稳定性和精度,同时MC_OK模型能提高预测的准确度。     

Quaternary lacustrine deposits in a high-energy semi-arid mountain environment,Karakoram Mountains,northern Pakistan

Impressive Quaternary lacustrine deposits are present as terrace remnants throughout the Karakoram Mountains, northern Pakistan. They are mainly the result of damming of drainage systems during glacial advances or by catastrophic mass movement deposits. The longevity of most lakes is relatively short, in the order of years to tens of years, but sedimentation rates are extremely high as a consequence of the high sediment loads within the rivers. This results in deposits that frequently exceed 10 m in thickness. The sediments comprise dominantly planar bedded, massive and, less commonly, planar laminated, silts, comprising detrital quartz, feldspar, mica, calcite, chlorite and illite. A facies model for lacustrine sedimentation in a high-energy semi-arid high mountain region is presented, using case studies from a glacially dammed palaeolake (Glacial Lake Gilgit) and a debris-flow dammed palaeolake (Lake Serat). The rapid deposition and absence of organic material restricts the usefulness of these lacustrine sediments as proxies for palaeoenvironmental reconstruction, but they are helpful in reconstructing the former extent of glaciers and illustrating the importance of high-magnitude–low-frequency events, such as landsliding, as formative processes contributing to the evolution of the Karakoram landscape.     

Village water supply in Botswana: assessment of recommended yield for production boreholes in a semi-arid environment

More than 90% of the rural villages and settlements throughout Botswana have water supplies based on groundwater. The annual increase in water demand is about 0.3 × 10⁶ m³ and on average around 60 new boreholes are needed annually. In parallel with construction of new production boreholes for rural villages, there is an on-going rehabilitation of existing boreholes which have lost their original yield due to clogging, corrosion, encrustation, etc. The total annual cost of siting, drilling and testing of around 100 new production boreholes for rural villages water supply is estimated at around US$7.5 million (1997 price).Modelling of every groundwater resource for rural village water supply in Botswana is currently not feasible due to a lack of relevant and detailed information. A modelling exercise will assess the resource of the aquifer being studied, but can not give an assessment of the yield of each production borehole. Groundwater supply to rural villages is therefore currently based on the abstraction possible from established production boreholes. Test pumping data from these boreholes are the prime information in such an assessment. However safety factors and the fact that drought periods of longer duration are common in a semi-arid environment must also be considered. A computer program package TESTCURV developed by the Department of Water Affairs is a most useful tool in the assessment of yields for production boreholes for village water supply in Botswana, based on the performance of the well and the aquifer. No replenishment is assumed and the question of sustainable yield is not addressed by the program.     

Spatial information of soil hydraulic conductivity and performance of cokriging over kriging in a semi-arid basin scale

Unlike the studies in small parcels by systematic measurements, the spatial variability of soil properties is expected to increase in those over relatively large areas or scales. Spatial variability of soil hydraulic conductivity (K _h) is of significance for the environmental processes, such as soil erosion, plant growth, transport of the plant nutrients in a soil profile and ground water levels. However, its variability is not much and sufficiently known at basin scale. A study of testing the performance of cokriging of K _h compared with that of kriging was conducted in the catchment area of Sarayköy II Irrigation Dam in Cank?r?, Turkey. A total of 300 soil surface samples (0–10 cm) were collected from the catchment with irregular intervals. Of the selected soil properties, because the water-stable aggregates (WSA) indicated the highest relationship with the hydraulic conductivity by the Pearson correlation analysis, it is used as an auxiliary variable to predict K _h by the cokriging procedure. In addition, the sampling density was reduced randomly to n = 175, n = 150, n = 75 and n = 50 for K _h to determine if the superiority of cokriging over kriging would exist. Statistically, the results showed that all reduced K _h was as good as the complete K _h when its auxiliary relations with WSA were used in cokriging. Particularly, the results of the “Relative Reduction in MSE” (RMSE) revealed that the reduced data set of n = 75 produced the most accurate map than the others. In this basin-scaled study, there was a clear superiority of the cokriging procedure by the reduction in data although a very undulating topography and topographically different aspects, two different land uses with non-uniform vegetation density, different parent materials and soil textures were present in the area. Hence, using the statistically significant auxiliary relationship between K _h and WSA might bring about a very useful data set for watershed hydrological researches.     

Quantitative technique for assessing the geomorphic thresholds for floodplain instability and braiding in the semi-arid environment

For the semi-arid environment of southern California, a reach-scale classification system and conceptual model were created to synthesize the observed floodplain forms into three basic floodplain continuums: armored, non-armored, and active-regional alluvial fan. These continuums are comprised of three to five alluvial floodplain forms (cascade, step-pool, plane-coarse-bed, plane-mixed-bed, plane-fine-bed, pool-riffle, braided, and dune-ripple). For the non-armored floodplain continuum, a floodplain state diagram has been generated to quantitatively describe the natural downstream progression of floodplain forms and geometry, using specific stream power and the width-to-depth ratio as the state and shape metrics, respectively. Based on field data for 91 cross sections along 14 watercourses, this floodplain state diagram provided the basis to define geomorphic thresholds for floodplain instability and braiding using logistic regression analyses. This method for defining floodplain instability thresholds provides a unique management tool by providing both a systematic and a quantitative means to assess the stability state of watercourses and, thereby, provide a means for assessing the potential for the hazards associated with watercourse instability.     

Spatial and temporal variation of heavy metals in a tropical estuary

The lower part of the Coatzacoalcos River has great industrial development in which high pollution has been reported. Surface sediments of this area were studied over a year to observe spatial and seasonal sedimentological and chemical variations. Higher metal concentrations were found during the dry season, Pajaritos Dock and Teapa sampling points showing the highest values. Ni (182 ppm) and Co (37 ppm) concentrations are elevated relative to other estuarine areas. Metal normalization against Al₂O₃ content shows contaminant input in areas where urban and industrial discharges exist. A cluster analysis of the data separates sediment samples from the different sampling trips, suggesting the dynamic nature of the sediments. Through the statistical t-test, metal enrichment of Cd, Cu, Cr, Ni, Pb, and Zn was evaluated and compared with metal concentration in sediments of the river higher parts. The percentage of bioavailable metals is a function of the physicochemical characteristics of the system.     

寒旱环境草本植物根系护坡的时间尺度效应

为研究植物护坡效应的可持续性,选取芨芨草、细茎冰草、垂穗披碱草、赖草4种草本植物,分别对生长时间为1~4年的上述草本进行了野外现场拉拔试验。试验结果表明:4种草本其平均抗拔力、平均须根数、平均根径和平均根长随生长时间的增加,均呈增加趋势。芨芨草的平均抗拔力与生长时间之间存在显著幂函数关系,垂穗披碱草、细茎冰草和赖草之间均存在指数函数关系;4种草本的平均须根数与生长时间之间均存在较显著的对数函数关系;芨芨草的平均根径与生长时间之间呈显著的幂函数关系,垂穗披碱草和细茎冰草之间均呈指数函数关系,赖草的根径与生长时间之间呈对数函数关系;芨芨草的平均根长与生长时间之间呈显著的对数函数关系,细茎冰草和赖草之间均呈线性函数关系,垂穗披碱草的平均根长与生长时间之间呈幂函数关系。     

Spatial dynamics of soil salinity under arid and semi-arid conditions: geological and environmental implications

Salinity is a highly important problem in arid and semi-arid regions. Consequently, the analysis of soil salinity plays a crucial role in environmental sciences. Environmental variables show spatial variability and statistical tools able to analyze and describe the spatial dependence and quantify the scale and intensity of the spatial variation are needed. Moreover, the spatial prediction has special importance for agricultural transformation of the land or for environmental restoration (selection of the most appropriate species adapted to soil salinity). In this paper we propose a methodological framework based on geostatistics to model the spatial dynamics of soil salinity measurements to further analyze the case of a region in southeastern Spain.     

Spatial simulation of evapotranspiration of semi-arid Inner Mongolian grassland based on MODIS and eddy covariance data

In semi-arid regions of Central Asia, water shortage results from low annual precipitation (P) with high interannual variability. Evapotranspiration (ET) dominates water balance losses entirely. Previous studies showed large differences between individual grassland sites in the partitioning of ET into evaporation and transpiration, but only little difference in the evaporative ratio ET/P. The hydrological model BROOK90 was applied to the Xilin river catchment in Inner Mongolia (China) in combination with data from moderate resolution imaging spectroradiometer (MODIS) and ET measurements. The ET part of the model was parameterised using several years of eddy covariance (EC) measurements over grasslands differing in grazing intensity and leaf area index (LAI). Using a relatively well-established relationship of LAI and P as well as LAI and temperature derived from MODIS, the water balance components of a 16 km2 sample area in the catchment were modelled with a 1 km2 resolution for the vegetation period of 2006. All pixels were modelled assuming a similar ET control as at the EC sites. Spatial variation in ET as well as in the partitioning of ET between transpiration and evaporation could be identified. The results indicate the potential of using MODIS data and BROOK90 to upscale ET of semi-arid grasslands from site to larger grass dominated catchments.     

断陷湖泊水下扇类型与分布模式*

水下扇是断陷湖泊中一种重要沉积类型,近年来受到关注度越来越高。海洋和湖泊中与重力流有关的各类扇体的术语很多,诸如深水扇、盆底扇、湖底扇、斜坡扇、滑塌扇和浊积扇等,而它们都是不同类型的水下扇。国内沉积学界对湖泊水下扇这一术语的合理性一直有争议,与之相关的术语有水下冲积扇、近岸水下扇和远岸浊积岸等。文中梳理了有关水下扇的一些术语的含义异同,进而明确了断陷湖泊水下扇的基本类型;明确提出了湖泊外部物源体系与内部物源体系,并由此建立了湖泊水下扇的沉积分布模式;最后讨论对比了水下扇、冲积扇及扇三角洲之间的沉积差异,以期为今后深入研究这一类型沉积体提供借鉴。