Temporal trends in agricultural water use and the relationships to hydroclimatic factors in the High Plains aquifer region

The High Plains aquifer (HPA) is the primary water source for agricultural irrigation in the US Great Plains. The water levels in many locations of the aquifer have declined steadily over the past several decades because the rate of water withdrawals exceeds recharge, which has been a serious concern to the water resources management in the region. We evaluated temporal trends and variations in agricultural water use and hydroclimatic variables including precipitation, air temperature, reference evapotranspiration, runoff, groundwater level, and terrestrial water storage across the HPA region for different periods from 1985 to 2020 at the grid, county, or region scale. The results showed that water withdrawals decreased from 21.3 km³/year in 1985 to 18.2 km³/year in 2015, while irrigated croplands increased from 71,928 km² in 1985 to 78,464 km² in 2015 in the entire HPA. The hydroclimatic time-series showed wetting trends in most of the northern HPA, but drying and warming trends in the southern region from 1985 to 2020. The groundwater level time-series indicated flat trends in the north, but significant declining in the central and southern HPA. Trends in irrigation water withdrawals and irrigation area across the HPA were controlled by the advancement of irrigation systems and technologies and the management of sustainable water use, but also were affected by dynamical changes in the hydroclimatic conditions.     

基于井口涌水量变化类型判断岩溶含水层厚度

针对含水相对均匀的溶洞-裂隙水含水岩组,为判断岩溶含水层厚度,通过对空气潜孔锤钻进工艺施工钻孔井口涌水量变化进行分析,结果发现:利用该工艺施工的钻孔井口涌水量一般会出现稳定型、降低型和增长型三种变化类型;井口涌水量变化类型反映了岩溶含水层是空间尺度上发育的垂向地下水系统,具有分层特征,其厚度与碳酸盐岩岩溶化程度的不均一性耦合,体现了碳酸盐岩岩体内不同空隙的发育规模、密度及其相互间的联系程度;明确了地下水埋深状况以及含水层的构成条件。故采用空气潜孔锤钻进工艺施工的钻孔,在非干孔情形下,可以利用井口涌水量的变化类型判断岩溶含水层厚度。     

带压开采陷落柱突水影响因素数值模拟

为研究承压水压与煤层陷落柱位置这两种因素对陷落柱突水的影响,在分析固流耦合数学模型的基础上,利用数值模拟软件FLAC3D,以双柳矿地质条件为背景,分别对3 MPa和5 MPa承压水压下开采上、下两组煤4种情况进行模拟,分析陷落柱及其周边围岩的渗流-塑性破坏耦合场、应力场和位移场的变化.结果表明:随着工作面推进至接近陷落柱,工作面前方集中应力场与柱体周边应力场发生耦合,并出现应力集中,当水压为5 MPa开采上组煤时应力集中系数最大,最容易形成突水危险区域;当上组煤工作面距离陷落柱为30 m时,陷落柱渗流场与集中应力场开始连通,在开采下组煤时这一距离比上组煤扩大15 ～ 20 m;煤层底板随工作面推进发生压缩-膨胀周期变化,引起拉伸、剪切破坏.     

Direct Effects of Cattle on Grassland Birds in Canada

Effects of grazing on grassland birds are generally thought to be indirect, through alteration of vegetation structure; however, livestock can also affect nest survival directly through trampling and other disturbances (e.g., livestock‐induced abandonment). We extracted data on nest fates from 18 grazing studies conducted in Canada. We used these data to assess rates of nest destruction by cattle among 9 ecoregions and between seasonal and rotational grazing systems. Overall, few nests were destroyed by cattle (average 1.5% of 9132 nests). Nest destruction was positively correlated with grazing pressure (i.e., stocking rate or grazing intensity), but nest survival was higher in more heavily grazed areas for some species. Because rates of destruction of grassland bird nests by cattle are low in Canada, management efforts to reduce such destruction may not be of ecological or economic value in Canada. Efectos Directos del Ganado sobre las Aves de Pastizales en Canadá     

Considering climate change and regional differences: An efficiency assessment of coal mine use and land restoration

China is the country with the largest coal mining production and consumption in the world, but due to a large amount of coal burning, air pollution and climate change are exasperating related problems. The previous literature mainly has discussed coal mine production and environmental pollution, but failed to take into account external factors such as climate change and seldom discussed the relationship between coal mine land use and land restoration. Therefore, this study uses the meta-Epsilon-Based Measure two-stage Data Envelopment Analysis under the exogenous model and incorporates coal mine land use and land restoration use into the model to explore the relationship between the two under climate change. The research results are as follows. (1) If the external climate factors are not considered, then the phenomenon of overestimation or underestimation of the technology gap arises. (2) The efficiency value of the coal mining stage in most provinces is generally higher than the land restoration efficiency value.     

大口径未爆弹销毁安全距离研究

为保证大口径未爆弹销毁作业中人员的安全,从理论上研究了未爆弹销毁安全距离。根据破片的理论初速、破片杀伤判据、杀伤破片的飞散距离,得到防破片安全距离的计算公式;根据冲击波理论,得到防冲击波安全距离的计算公式;根据防破片安全距离和防冲击波安全距离,从理论上确定未爆弹销毁时的警戒安全距离和防护掩体设置距离。以某大口径未爆弹为例进行实例分析,确定了其相应的警戒安全距离和防护掩体设置距离。研究结果表明:该未爆弹销毁时警戒安全距离主要考虑破片,与GJB5120—2002的结果进行比较,认为GJB5120—2002的结果过于保守。     

基于景观中性模型的不同竞争力外来种入侵对栖息地毁坏的响应

栖息地毁坏和生物入侵被认为是全球物种多样性的两大威胁,也是当前研究的热点。同时,两者的共同作用将比单独作用所带来的物种多样性丧失更大。本文基于竞争-扩散均衡机制,考虑了外来种的不同竞争力,结合景观中性模型和元胞自动机模型,模拟了外来种入侵对栖息地毁坏（栖息地破碎和面积丧失）的响应。研究结果表明：1）外来种入侵成功将首先威胁竞争力与其相邻的弱物种;2）栖息地毁坏与种间竞争共同决定着外来种入侵的成功与否。当栖息地破碎促进了与外来种竞争力相邻的本地强物种时,将会抑制入侵;当其抑制了与外来种竞争力相邻的本地强物种时,则会促进入侵。当栖息地丧失促进了外来种相邻的本地强物种时,将会抑制入侵;当栖息地丧失抑制了外来种相邻的本地强物种,将一定程度地促进入侵,但随着丧失面积的增加,则转为抑制。因此,为了抑制不同竞争力的外来种入侵,应采取不同的栖息地保护策略,并保护和促进其竞争力相邻的本地强物种。     

Seawater Intrusion and Sustainable Yield of Basal Aquifers1

Liu, Clark C.K. and John J. Dai, 2012. Seawater Intrusion and Sustainable Yield of Basal Aquifers. Journal of the American Water Resources Association (JAWRA) 48(5): 861‐870. DOI: 10.1111/j.1752‐1688.2012.00659.x Abstract: Basal aquifers, in which freshwater floats on top of saltwater, are the major freshwater supply for the Hawaiian Islands, as well as many other coastal regions around the world. Under unexploited or natural conditions, freshwater and the underlying seawater are separated by a relatively sharp interface located below mean sea level at a depth of about 40 times the hydraulic head. With forced draft, the hydraulic head of a basal aquifer would decline and the sharp interface would move up. It is a serious problem of seawater intrusion as huge amounts of freshwater storage is replaced by saltwater. Also, with forced draft, the sharp interface is replaced by a transition zone in which the salinity increases downward from freshwater to saltwater. As pumping continues, the transition zone expands. The desirable source‐water salinity in Hawaii is about 2% of the seawater salinity. Therefore, the transition zone expansion is another serious problem of seawater intrusion. In this study, a robust analytical groundwater flow and salinity transport model (RAM2) was developed. RAM2 has a simple mathematical structure and its model parameters can be determined satisfactorily with the available field monitoring data. The usefulness of RAM2 as a viable management tool for coastal ground water management is demonstrated by applying it to determine the sustainable yield of the Pearl Harbor aquifer, a principal water supply source in Hawaii.     

非水相硝基苯在含水层中的迁移释放规律

通过室内模拟实验,探讨了在非水相硝基苯污染含水层的条件下,其在含水层中的迁移及释放规律。迁移规律表明,非水相硝基苯并非在含水层中直接进行垂向迁移,而是一方面在自身重力作用下向含水层下部迁移,另一方面在地下水流的作用下随地下水同向运移,整体表现为随地下水流的侧向运移,并最终迁移至含水层底部。释放规律表明,非水相硝基苯在含水层迁移的过程中会向地下水大量释放,释放出的硝基苯在水流的作用下随地下水同向运移,污染源及迁移至含水层底部的非水相硝基苯均存在再次释放。