河西走廊西端灌丛沙丘发育过程及其对沙漠化的指示意义

在风沙活动强烈的荒漠地区开展环境变化研究常缺乏符合要求的地质测年材料。灌丛沙丘是干旱区发育的一种特殊生物地貌类型,具有计年和储存环境信息的功能,可以用来重建沙丘的发育过程和过去的环境变化。以河西走廊西端花海盆地发育的灌丛沙丘沉积剖面为研究对象,基于AMS¹⁴C年代学及沉积物粒度、碳酸盐含量、地球化学元素等代用指标的分析,与文献记载、沙漠化监测数据和近几十年的器测气象资料对比分析,试图揭示区域灌丛沙丘的发育过程及其环境指示意义。结果表明：花海盆地灌丛沙丘的发育时间已超过800 年;20世纪60年代中后期至70年代早期人类活动的干扰曾使灌丛沙丘的堆积过程中断,但丰富的物源随后又促使灌丛沙丘再次快速发育。沙丘物源曾发生过剧烈的变化,使得灌丛沙丘沉积物中的粗颗粒组分和中值粒径并不适于作为环境代用指标重建区域的风沙环境变化,而细颗粒组分（<63 μm和<10 μm）和碳酸盐含量的变化,则揭示了研究区在20世纪70-80年代（沙丘高度300~420 cm）时获得了丰富的物质来源。灌丛沙丘沉积物中的Zr/Rb比值,能够作为良好的环境代用指标指示1970-1988年（沙丘高度300~420 cm）区域处在风沙活动较强烈的环境;近几十年花海盆地土地沙漠化明显,尤其是20世纪70年代和80年代。灌丛沙丘可以作为有较高可信度的地质记录载体,在河西走廊西端重建较长时间尺度的、高分辨率的区域气候环境演变历史。     

自由设站起算点可用性的两步判断法研究

目前在地铁隧道结构变形监测中通常采用自由设站极坐标的测量方式,起算点准确是保证监测结果有效性的关键。地铁隧道监测自由设站起算点数量有限,当多点存在变动时通常难以准确判定各点的可用性。本文针对自由设站已知起算点的可用性问题,采用坐标系转换求解各已知点的位移分量完成可用性判断。重点关注坐标系转换关系的求解,提出了两步法的求解思路：采用RANSAC算法计算初值,然后进行迭代权估计计算得到最终结果。最后通过现场实测和模拟测试的方式验证了该算法的探测能力。     

Occurrence of brackish water phytoplankton species at a closed coral reef in Nansha Islands, South China Sea

The phytoplankton assemblage of Zhubi Reef, a closed coral reef in Nansha Islands (South China Sea, SCS) was studied in June 2007. A total of 92 species belonging to 53 genera and four phyla have been identified. The dominant taxa in the lagoon were the diatom Chaetoceros and cyanobacteria Nostoc and Microcystis, while in reef flats were cyanobacteria Trichodesmium erythraeum, dinoflagellates Gymnodinium and Prorocentrum. The species richness and diversity were consistently lower in the lagoon than in reef flats. Classification and nMDS ordination also revealed significant dissimilarity in phytoplankton community structure between the reef flat and lagoon, with statistical difference in species composition and abundance between them (ANOSIM, p = 0.025). Nutrient concentrations also spatially varied, with ammonium-enrichment in the lagoon, while high Si-concentration existed in reef flat areas. Both nutrient levels and currents in SCS may play important roles in determining the composition and distribution of microalgae in Zhubi Reef and SCS.     

IRNSS�������ǵ���ϵͳ�������ܷ���

????IRNSS?????????????????????????????ξ?????????????????IRNSS?????????????λ????????????????????????????????IRNSS???????????Ч???????????????????????????????IRNSS??????????????????????????????????????????????2 000 km????????????????10 m??????λ????????????????????????????????????PDOPС??6????????????????Ч??????????95%???????????     

基于空间模型的全球粮食安全评价

在综合考虑自然、社会和经济等因子对粮食安全影响的基础上,选择了人均粮食占有量和人均GDP两个指标空间显性评价全球粮食安全状况。为此,本研究构建了3个模型,即空间EPIC模型、作物选择模型和IFPSIM模型,分别模拟作物单产、作物播种面积和作物价格。利用构建的评价框架和模型,以网格大小为6分弧度的地理单元为评价对象,选择水稻、玉米、小麦和大豆等4类全球主要作物类型,以2000年为初始年份,对未来2020年的全球粮食安全状况进行了评价。结果表明,到2020年,多数南亚国家和非洲国家,由于其人均粮食占有量和人均GDP两个指标值都显著降低,粮食供应不足和贫困一起将可能导致该区域存在粮食危机和饥饿风险。对于其他区域,日益增长的粮食需求可以通过本区域的粮食生产自给予以满足,或通过外部购买或粮食进口得到满足,总体上不存在粮食安全问题。为保障未来粮食安全,一方面要保护耕地数量和质量、防止土壤退化、增加资本投入、进行技术创新和升级,提高粮食综合生产能力,保障粮食的有效供给;另一方面加大农业补贴,切实提高农民收入,保障农民利益,增强农业购买力。同时,大力改善粮食流通和农产品贸易体制,通过外部市场来调节粮食供给;积极应对气候变化,提高农业生产对气候变化的适应能力,保证粮食生产的稳定。     

Six decades of agricultural land use change in Bangladesh: Effects on crop diversity,productivity, food availability and the environment, 1948–2006

This paper provides a detailed analysis of agricultural land use change in Bangladesh over a 59‐year period (1948–2006) and examines how these have impacted crop diversity, productivity, food availability and the environment. The key findings of the analysis are: first, land use intensity has increased significantly over this period, mainly from the widespread adoption of a rice‐based Green Revolution technology package beginning in the early 1960s; second, contrary to expectation, crop diversity too has increased; third, although land productivity has increased significantly, declines in the productivity of fertilizers and pesticides raise doubts over sustaining agricultural growth; fourth, food availability has improved, with a reversal in the dietary energy imbalance in recent years despite a high population growth rate; and finally, the production environment has suffered with widespread soil nutrient depletion experienced in many agroecological regions. The policy implication points towards crop diversification as a desired strategy for agricultural growth to improve resource economy, productivity and efficiency in farming in Bangladesh.     

地形畸变对偶极-偶极电阻率测深拟断面图的影响

偶极－偶极剖面方法是一种非常流行的物探方法,但就地形对该方法的实质性影响及修正研究得比较少.我们就几种典型的地形畸变情况进行了正演计算,并绘制了拟断面图.通过对这些图形分析,可以看到在地形畸变处的拟断面图不能反映地下地质体的情况,且有效拟断面图是不连续的,需要分段处理,分级解释.     

Modelling potential areas of groundwater development for agriculture in northern Ghana using GIS/RS

Abstract

Groundwater development potential in northern Ghana (108 671 km²) has been assessed by combining spatial layers for five critical factors—recharge rate, regolith thickness, transmissivity, borehole success rate and static water level—through a multi-criteria analysis approach to rank development potential from the viewpoint of groundwater availability and accessibility at a resolution of 1 km². The results indicate a high potential for development in the study area, as about 70% of the area was found to have high to moderate groundwater availability, while 83% has high to medium groundwater accessibility. Comparing the two main hydrogeological environments, the Precambrian Basement rocks (PCB) area was found to generally have a higher groundwater development potential than the Voltaian Sedimentary rocks (VSB). More detailed investigation revealed that the VSB can produce a small proportion of exceptionally high-yielding boreholes that can support large-scale irrigation. A test of the reliability of results showed that generally, the majority of high- and low-yielding boreholes fall in areas predicted by the model as having high and low groundwater availability, respectively.

Editor D. Koutsoyiannis; Associate editor D. Hughes

Citation Forkuor, G., Pavelic, P., Asare, E., and Obuobie, E., 2013. Modelling potential areas of groundwater development for agriculture in northern Ghana using GIS/RS. Hydrological Sciences Journal, 58 (2), 437–451.     

Environmental determinants of leech assemblage patterns in lotic and lenitic habitats

Leeches (Clitellata: Hirudinida) are abundant predators or ecto-parasites inhabiting various freshwater habitats; however many biotic and abiotic drivers of their assemblage patterns have been deduced rather than directly tested. To study species richness and composition changes in leech assemblages, 109 sites of running and stagnant water bodies were sampled in three regions of the Czech Republic in 2007–2010, together with several explanatory variables that are known or expected to be important predictors of leech distribution. In total, 17 species of leeches were recorded, varying between 0–7 and 0–9 species in lotic and lenitic sites, respectively. These differences in species richness of lotic and lenitic sites were highly significant, contrary to the abundances, which varied between 0–283 and 0–295 individuals. The main change in species composition was controlled by water temperature and morphological characteristics (e.g. substrate and cover of macrophytes), mostly reflecting the differences between lotic and lenitic habitats. We found the density of benthos (i.e. prey availability) to be the best predictor of species composition in both lotic and lenitic sites, together with the percentage of canopy cover. However, the other significant predictors (i.e. the substrate and water conductivity found to be significant in lotic sites, and the mean annual temperature and PO₄^3? in lenitic sites), differed between these habitats. Other than mean annual temperature and water temperature, which had different effects on species richness in lotic and lenitic sites, there were no other differences between lotic and lenitic sites in terms of how species richness and abundance responded to all other analyzed predictors. Our results stress the importance of prey availability and canopy for leech distribution patterns. Differences in the significant predictors of leech assemblage patterns between lotic and lenitic sites raise fundamental questions about the underlying mechanisms and ecological constraints to leech distribution in these main types of aquatic systems.     

Assessing strategic water availability using remote sensing,GIS and a spatial water budget model: case study of the Upper Ing Basin,Thailand

Abstract

This paper assesses strategic water availability and use under different development pathways on a basin scale using remote sensing (RS), geographical information systems (GIS) and a spatial water budget model (SWBM). The SWBM was applied to the Upper Ing Basin in northern Thailand to investigate the spatial and temporal variations in the location of streams and water yields from different parts of the basin. The base simulation was carried out for the years 1998–2007 using a DEM and actual land-use data at 100-m resolution. The simulated stream network was compared with topographic maps under different flow conditions, which were successfully represented. The 10-year average simulated river flow rate was 1300 L/s, but it more than doubled during periods of heavy rainfall and decreased below 600 L/s in dry seasons. The total length of the streams (based on flow threshold of 25 L/s) on a typical day in the dry season differed by a factor of approx. 1.5. Agricultural water needs and possible extraction were assessed and presented by dividing the basin into 10 different zones based on the stream network. The results show that there is the potential for harvesting significant quantities of water at different spatial gradients with no initial water supply for irrigation. Monthly water yields for each zone were computed; the results varied from less than 50% to over 137% of the per hectare water yield for the entire basin. This variation was due to differences in topography and land cover. The impact of land use and climate change on streamwater availability was also studied. The basin shows very different hydrological responses. The changes in average river flow relative to the base simulation were +27.6%,??32.1%, +94% and +52.9% under deforestation, changing land use from paddy field to orchard, bare soil and increased rainfall scenarios, respectively.

Citation Bahadur KC, K. (2011) Assessing strategic water availability using remote sensing, GIS and a spatial water budget model: case study of the Upper Ing Basin, Thailand. Hydrol. Sci. J. 56(6), 994–1014.