黄河三角洲土地利用/覆被变化时空特征研究

黄河三角洲地区受人类活动作用时间相对较短,为土地利用/覆被变化及其驱动力研究提供了难得的条件.以位于黄河入海口处的垦利县为例,通过对1987-2000年土地利用/覆被变化幅度、变化构成以及流向图的分析,得到了该地区土地利用/覆被变化的特点,并应用遥感及GIS空间分析手段分析了黄河、渤海对该区土地利用/覆被变化格局的影响与作用机制.结果表明:(1)位于黄河入海口处的垦利县土地生态环境脆弱,占土地总面积80%的旱地、林草地、盐荒地和滩涂存在状态不稳定,盐荒地是其土地利用/覆被变化的核心类型;(2)黄河淡水和海洋咸水所控制的水文条件变化是该区土地利用/覆被变化的重要驱动因素,基本控制了分布的格局,并影响土地利用/覆被变化的可能性及变化方向.     

Reconceptualising coarse sediment delivery problems in rivers as catchment-scale and diffuse

This paper assesses river channel management activities in the context of the interaction between coarse sediment delivery, climate change, river channel response and flood risk. It uses two main sources of evidence: (1) an intensive instrumentation of an upland river catchment using both traditional hydrometric and novel sediment sensing methods; and (2) a sediment delivery model that combines a treatment of sediment generation from mass failure with a treatment of the connectivity of this failed material to the drainage network. The field instrumentation suggests that the precipitation events that deliver sediment from hillslopes to the drainage network are different to those that transfer sediment within the network itself. Extreme events, that could occur at any time in the year (i.e. they are not dependent on wet antecedent conditions), were crucial for sediment delivery. However, sustained high river flows were responsible for the majority of transfer within the river itself. Application of three downscaling methods to climate model predictions for the 2050s and 2080s suggested a significant increase in the number and potential volume of delivery events by the 2050s, regardless of the climate downscaling scenario used. First approximations suggested that this would translate into annual bed level aggradation rates of between 0.10 and 0.20 m per year in the downstream main channel reaches. Second, the importance of this delivery for flood risk studies was confirmed by simulating the effects of 16 months of measured in-channel simulation with river flows scaled for climate change to the 2050s and 2080s. Short-term sedimentation could result in similar magnitude increases in inundated area for 1 in 0.5 and 1 in 2 year floods to those predicted for the 2050s in relation to increases in flow magnitude. Finally, we were able to develop an alternative approach to river management in relation to coarse sediment delivery, based upon reducing the rates of coarse sediment delivery through highly localised woodland planting, under the assumption that reducing delivery rates should reduce the rate of channel migration and hence the magnitude of the bank erosion problem. Thus, the paper demonstrates the need to conceptualise local river management problems in upland river environments as point scale manifestations of a diffuse sediment delivery process, with a much more explicit focus on the catchment scale, if our river systems are to become more insulated from the impacts of future climate changes.     

Environmental factors controlling spatial variation in sediment yield in a central Andean mountain area

A large spatial variability in sediment yield was observed from small streams in the Ecuadorian Andes. The objective of this study was to analyze the environmental factors controlling these variations in sediment yield in the Paute basin, Ecuador. Sediment yield data were calculated based on sediment volumes accumulated behind checkdams for 37 small catchments. Mean annual specific sediment yield (SSY) shows a large spatial variability and ranges between 26 and 15,100 Mg km^− 2 year^− 1. Mean vegetation cover (C, fraction) in the catchment, i.e. the plant cover at or near the surface, exerts a first order control on sediment yield. The fractional vegetation cover alone explains 57% of the observed variance in ln(SSY). The negative exponential relation (SSY = a × e^{−b C}) which was found between vegetation cover and sediment yield at the catchment scale (10³–10⁹ m²), is very similar to the equations derived from splash, interrill and rill erosion experiments at the plot scale (1–10³ m²). This affirms the general character of an exponential decrease of sediment yield with increasing vegetation cover at a wide range of spatial scales, provided the distribution of cover can be considered to be essentially random. Lithology also significantly affects the sediment yield, and explains an additional 23% of the observed variance in ln(SSY). Based on these two catchment parameters, a multiple regression model was built. This empirical regression model already explains more than 75% of the total variance in the mean annual sediment yield. These results highlight the large potential of revegetation programs for controlling sediment yield. They show that a slight increase in the overall fractional vegetation cover of degraded land is likely to have a large effect on sediment production and delivery. Moreover, they point to the importance of detailed surface vegetation data for predicting and modeling sediment production rates.     

Soil and bedrock distribution estimated from gully form and frequency: A GIS-based decision-tree model for Lebanon

Torrential rainfall and relatively sparse vegetation in the Mediterranean region result in the development of gully systems and land degradation, notably on lands with specific types of soil and bedrock. This paper proposes a decision-tree model to predict the distribution of soil and bedrock susceptible to gully erosion (white Rendzinas and marly rocks) from the form and frequency of gullies. The study area is located in Lebanon and the model is linked to GIS. V-fold cross-validation of the pruned model indicates that gully features including cross-section size and shape, network frequency, types of meandering, and catchment area can explain 80% of variance in soil/rock properties. The overall accuracy of the soil/rock map was estimated to be ca. 87%. The proposed model is relatively simple, and may also be applied to other areas. It is particularly useful when information about soil and rock obtained from conventional field surveys is limited.     

土壤数据集对全球陆面过程模拟的影响

基于通用陆面模式（Common Land Model, CoLM）,首次评估了两套最新的全球土壤数据集GSDE（Global Soil Dataset for Earth System Model）和SG（SoilGrids）对全球陆面过程模拟的影响。比较分析了两套数据中砂粒、粘粒、砾石、有机碳的含量和容重这五个土壤属性在全球分布上的差异以及这种差异造成的对模式估计的土壤特性参数、水力热力变量的影响。结果表明,土壤特性参数在全球的空间分布主要受土壤粒径分布（砂粒、粉粒和粘粒）影响,同时也受砾石、有机碳和容重的影响。土壤资料对全球模拟结果影响主要体现在区域差异,对水文学变量的影响（R_e最大达到±100%）大于对土壤热力学变量的影响（R_e<±10%）,对地表辐射变量的影响较小（R_e<±5%）。其中,土壤体积含水量在加拿大中部及西北部、俄罗斯东南部及中西部和澳大利亚中部地区模拟结果相差较大,总径流在低纬地区模拟结果出现较大的差异,热力学变量在非洲北部、加拿大西北部以及俄罗斯中北部的差异稍大。将模拟的土壤体积含水量与站点观测相比,两套数据的表现接近,与站点观测相比都存在一定的偏差,但SG更接近观测,其中在Molly Caren站点（39°57′N,83°27′W）上SG相比GSDE整体提高约0.01～0.02。本研究表明,模式模拟结果受不同土壤数据集的影响显著,可优先考虑诸如SG较准确的土壤数据。土壤属性对陆面模拟的影响需进一步研究。     

基于陆面模式基准平台ILAMB对陆面模式CoLM的评估

模式评估是模式发展中不可或缺的重要一环。本文利用最新版陆面模式评估软件—ILAMB（International Land Model Benchmarking）对通用陆面模式 (The Common Land Model, CoLM)进行客观评估,并与NCAR陆面模式CLM5(Community Land Model version 5)结果进行比较。作为一个陆面模式评估软件,ILAMB能对参与评估的模式变量自动生成诊断图形并对模式性能进行评分。评估结果表明,CoLM总体性能良好,模拟结果与基准数据较为接近。与CLM5相比,CoLM在总初级生产力及水文方面的表现略微逊色,在辐射方面则表现相当,对部分变量如地表向上长波辐射、地表净辐射等的模拟甚至优于CLM5。通过对比CRUNCEPv7和GSWP3v1两种强迫资料发现,它们在气候平均态上具有一定的差异,模式在GSWP3v1强迫下的表现相对较好。CoLM和CLM5在CRUCNEPv7强迫下模拟的潜热通量在亚马逊平原、亚洲东部和南部地区以及北美东部一带正偏差显著,而在GSWP3v1强迫下的模拟则有明显改善。这两个模式对感热通量的模拟在非洲北部、亚洲中部一带均明显偏高。在辐射方面,CoLM模拟的地表向上短波辐射在全球以偏高为主,这在一定程度上造成了地表净辐射的模拟偏低。各组试验模拟的地表向上长波辐射得分相差不大,但在具体的空间分布上有一定的差别。     

Macroalgal associations of motile epifaunal invertebrate communities on coral reefs

Small grazing motile epifaunal invertebrates play an important ecosystem role on coral reefs, influencing both the abundance and composition of macroalgal communities and acting as a key food source for a range of predatory fishes. The first aim of this study was to investigate the associations between motile epifaunal communities and four common macroalgal species (Lobophora variegata, Dictyota divaricata, Microdictyon marinum and Halimeda opuntia) on fore‐reef environments in the Exuma Cays (Bahamas, wider Caribbean). Secondly, we investigated the implications of the well documented rise of Caribbean macroalgal cover on invertebrate densities by surveying sites inside and outside the Exuma Cays Land and Sea Park (ECLSP), where increases in parrotfish grazing intensity inside the marine reserves have led to reductions in macroalgal cover. Therefore, surveys compared similar reefs with significantly different macrolagal cover. Comparisons between macroalgal species revealed a four to fivefold difference in motile epifaunal densities per unit volume of macroalgae. Post‐hoc tests revealed that this difference was significant only for Lobophora, with no difference observed among the other species. As macroalgae provide both a refuge from predation and a food source for grazing epifauna, the higher densities of epifauna observed in Lobophora may be attributed to either refuge from visual predators through morphological features (high cover of overlapping blades close to the substrate) or lack of palatability for parrotfish grazing, providing a more stable refuge. Our results revealed no significant differences in diversity, density or community structure of motile epifauna per unit volume of macroalgae between sites inside and outside the ECLSP. Since canopy height and invertivore biomass did not vary systematically across reserve boundaries, this suggests that algal cover does not affect the density of epifaunal invertebrates. However, areal cover was consistently higher for all macroalgal species at sites outside the ECLSP than those inside the reserve. Therefore, when scaled by aerial cover of macroalgae, total abundance of epifauna was twofold higher outside the ECLSP. We suggest that the increasing abundance of macroalgae on Caribbean reefs may be having dramatic effects on epifaunal invertebrate populations and potentially their ecological functions.     

无定河上游河道对沙漠化的阻截效应

干旱向湿润转变的过渡区受到风力与水力的交互作用,交互作用形成的风水复合地貌显著区别于单一风力或水力形成的地貌,探究风力与水力的交互作用有助于对干旱-湿润过渡区地貌过程的理解.基于野外考察、遥感影像解译和沉积物粒度分析等手段,分析了无定河上游河道对毛乌素沙地东进的阻截效应,结果表明:(1)无定河上游河道的西侧以流动、半流...     

Monitoring 25 years of land cover change dynamics in Africa: A sample based remote sensing approach

The study examines the changes in sub-Saharan's natural land cover resources for a 25 year period. We assess these changes in four broad land cover classes – forests, natural non-forest vegetation, agriculture and barren – by using high spatial resolution Earth observing satellites. Two sets of sample images, one ‘historical’ targeted at 1975 and a second ‘recent’ targeted at the year 2000, have been selected through a stratified random sampling technique over the study area, targeting a sampling rate of 1% in each of the strata. The results, presented at eco-region level and aggregated at sub-Saharan level, show a 57% increase in agriculture area at the expense of natural vegetation which has itself decreased by 21% over the period, with nearly 5 million hectares forest and non-forest natural vegetation lost per year. The impacts of these changes on the environment on one site and on the socio-economy on the other site are discussed and possible pressures on human well being are highlighted.     

Historical trends affecting accumulation of sediment and phosphorus in Lake Pepin,upper Mississippi River,USA

This study was conducted to collect historical land use information that would help explain the historical patterns in accumulation of sediment and phosphorus in Lake Pepin documented by Engstrom et al. (J Paleolimnol, this issue). A wide range of historical factors including cropping systems, phosphorus applications from fertilizer and manure, human and animal populations, river flows and phosphorus discharges from waste water treatment plants were studied using statistical methods. Results showed that sediment losses from the Minnesota River basin are significantly correlated with historical increases in river flows, row crop production acreage and basin population. Total phosphorus accumulations in the sediments of Lake Pepin are significantly correlated with increased phosphorus discharges from metropolitan area wastewater treatment plants, and increases in row crop acreage and river flows. Total phosphorus inflows to Lake Pepin are significantly correlated with increases in river flows, row crop acreage and phosphorus fertilizer applied to agricultural lands. This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this special issue of the Journal of Paleolimnology. D. R. Engstrom served as guest editor of the special issue.