Effects of poor quality irrigation waters on the nutrient leaching and groundwater quality from sandy soil

Sodium (Na⁺) in poor quality irrigation water participate in ion-exchange processes results in the displacement of base cations into solution and a raised concentration in groundwater. Knowledge of the rate of decrease of nutrients from soils resulting from poor water quality application is essential for long-term planning of crop production while minimizing the impact on groundwater quality. In this study, we examined the effect of sodium adsorption ratio (SAR) of irrigation water on nutrients leaching and groundwater quality in columns of sandy soil. Three types of irrigation waters at three NaCl–CaCl₂ solutions with the following levels of SAR (5, 15, and 30) were synthesized in laboratory. With the application of solutions, exchange occurred between solution Na⁺ and exchangeable cations (Ca²⁺, Mg²⁺, and K⁺), resulting in the displacement of these cations and anions into solution. Increasing the level of SAR from 5 to 15 and 30 resulted in increase in the average exchangeable sodium percentage (ESP) of the soil from 10.4 to 20.3, and 32.5, respectively. Adverse effect of high Na⁺ concentration in the solutions on raising ESP was less pronounced in solution having low SAR. Leaching of Ca²⁺, Mg²⁺, K⁺, and P from soil with the application of solutions represents a significant loss of valuable nutrients. This sandy soil showed the high risk for nutrients transfer into groundwater in concentrations exceeding the groundwater quality standard. Irrigation with poor quality water, which is generally more sodic and saline than regional groundwater, increases the rate of sodification and salinization of shallow groundwater.     

Cycling of calcite and hydrous metal oxides and chemical changes of major element and REE chemistry in monomictic hardwater lake: Impact on sedimentation

The variation of major and rare earth elements and yttrium (REY) in the monomictic hardwater Lake Tiberias during the wet and dry seasons of the hydrological year was studied in two profiles. The average volume and Cl concentration of the known and unknown saline inflows of 1.6 × 10⁷ m³ and 1.2 × 10⁹ mol are derived by closing both balances. This brine corresponds to a mixture of 83% of groundwater from Cretaceous aquifers and 17% of very saline deep brine. Taking cycling of calcite in the hypolimnion into account, the settling rate of authigenic calcite is estimated to be 3.3 mol m⁻² a⁻¹.In the stratified lake of the dry season dissolved inorganic carbon increases by 490 μM at the thermo-/chemocline due to microbial reduction of SO₄²⁻, NO₃⁻, chemical reduction of Fe(III) and MnO₂ colloids, and cycling of calcite in the hypolimnion. REY distribution in the stratified water column is dominantly controlled by coprecipitation with calcite, hydrous ferric oxides and MnO₂ in the epilimnion and cycling of these compounds in the hypolimnion. The positive Ce anomaly in the hypolimnetic water is produced by cycling of MnO₂. The simulation of the increase of REY in the hypolimnion reveals that hydrous ferric and manganese oxides only play a negligible role except Ce. Only about 10% of REY from cycled matter enhance REY in solution. Most of the released REY are adsorbed by particular matter and thus settling on the floor of the lake.Different from Na, U, SO₄²⁻ and SiO₂, the other elements, in particular REY, increase in the mixed water column from the top to the lower third and mostly decrease thereafter toward the bottom in the mixed lake during the wet season. The behavior of REY is caused by some cycling of calcite and pH-dependent re-equilibration of REY bound to hydrous ferric and manganese oxides adsorbed by particular matter.     

湿地生态系统碳循环研究进展

碳在不同类型湿地中储藏量约占地球陆地碳总量的15%。由于全球湿地面积迅速减少,湿地生态系统正常的水循环和碳循环过程产生一定的变化,湿地生态系统的演变也可能是全球大气CO₂含量升高的一个不可忽视的重要因素。气候条件是湿地碳循环生物地球化学过程的重要驱动因素,湿地特殊的生态水文过程和土壤环境条件,使得湿地碳循环具有区别于其它生态系统碳循环的特征。影响湿地中碳积累与分解过程的重要控制因子是温度、水文条件和植物群落,特别是水文条件对湿地碳循环过程影响较大。湿地土壤呼吸通量与根层土壤温度呈正相关关系,并受地表积水深度和地下潜水水位的影响,另外,洪泛作用会增加湿地CO₂的排放率,湿地水文过程决定溶解有机碳的输入与输出过程。     

基于PDCA循环的牛角山隧道光面爆破质量控制与技术改进

光面爆破质量直接关系到隧道施工的质量、安全及成本等,牛角山隧道凿岩爆破开挖施工过程中,采用PD—CA循环质量管理方法,根据TM隧道断面测量系统采集的断面超欠挖数据,进行现场检查、讨论分析,找出影响光面爆破质量的主要因素,通过制定有针对性的改进措施并监督执行,较好地提高了光面爆破效果,一次循环进尺平均光面爆破合格率达到95％,炮眼残留率达到85％,不仅保证了隧道施工质量,而且降低了施工成本,加快了施工进度,获得了良好的质量效果和经济效益。     

A universal nutrient application strategy for the bioremediation of oil-polluted beaches

Biostimulation by nutrient application is a viable technology for restoring oil-contaminated beaches. Maximizing the nutrient residence time is key for achieving a rapid cost-effective cleanup. We considered the nutrient injection strategy through a perforated pipe at the high tide line and we simulated numerically beach hydraulics, which allowed us to estimate the optimal injection flow rate of nutrient solution. Our results indicate that the optimal application is one that starts following the falling high tide and lasts for half tidal cycle. The saturated wet-front of the nutrient solution on the beach surface would move seaward with the same speed of the falling tide keeping a constant distance with the tide line. The numerical results were generalized to beaches of wide ranges of hydraulic and tidal properties using a novel dimensionless formulation for water flow and solute transport in porous media. Nomographs were presented to provide the flow rate based on four parameters: The beach slope and hydraulic conductivity, and tidal amplitude and period.     

岩石节理分级剪切加载-蠕变-卸载的能量与变形特征

为分析岩石节理在剪切加载-蠕变-卸载下的能量演化与变形特征,利用GCTS（RDS?200型）岩石剪切测试系统对人工劈裂岩石节理进行分级剪切加载-蠕变-卸载试验。结果表明：在法向应力小于6.5 MPa和大于7.8 MPa时,滞回环面积与循环级数分别符合线性和指数关系;总变形能和弹性变形能与法向应力呈正相关,与循环级数呈指数关系;塑性变形能与循环级数和法向载荷呈正相关。各级剪切应力加载终止时的剪切位移外包络线与直剪应力-位移曲线变化趋势相同,具有加速上升段、匀速上升段和匀速下降段;累积剪切塑性变形随循环级数增加而增大,但增大速率逐渐变慢;各级剪切加、卸载曲线均能以剪切滑移点为界分为两个阶段;剪切失稳前,加、卸载阶段的法向位移-剪切应力曲线出现在上一循环前方,循环剪切加载和（或）蠕变结束时的累积法向变形出现从增加到减小的现象。     

中国西南岩溶关键带结构与物质循环特征

岩溶关键带调查研究的目标是揭示岩溶生态系统的动态平衡和演化机制,旨在为经济社会提供资源环境服务的可持续管理对策,指出在合理的人为活动下增强岩溶关键带韧性的办法及修复受损部位的有效途径。碳酸盐岩作为可溶岩,赋予了岩溶关键带在结构上及物质循环过程中的岩石圈-生物圈相互作用等方面的若干特殊性。该文以中国西南岩溶区为例,总结了诸多学者的研究成果,揭示了从桂林岩溶区到重庆武隆岩溶区,岩溶关键带发育厚度由几米逐渐增厚至1 000 m的区域差异; 岩溶关键带的垂向物质循环过程以土壤-表层岩溶带为中心环节,而在横向上则呈现“岛屿状”镶嵌分布特征,地表生态具脆弱性; 岩溶关键带碳循环过程包括岩溶碳循环和生态碳循环两部分,碳汇则由植物碳汇、土壤碳汇和岩溶碳汇组成,初步估算其碳汇通量为64.36 t/(km²·a)。     

Organic carbon and nutrient fluxes to the coastal zone from the Sepik River outflow

The Sepik River is a major contributor of water, sediment and associated organic loads to the coastal waters of northern New Guinea and the Bismarck Sea. We compare dissolved and particulate organic carbon data from September 1997 during an extremely dry El Nino year with those from 1996, 1999 and 2000 during La Nina wet season discharges. Estimated Sepik River flux of DOC is 3.2×10¹⁰ mol yr⁻¹ and POC is 1.1×10¹¹ mol yr⁻¹. The estimates for total river nutrient fluxes to the sea are 1.1×10¹⁰ mol yr⁻¹ for nitrogen and 4.6×10⁸ mol yr⁻¹ for phosphorus. The Sepik DOC flux is about equal to that combined from all four major rivers that enter the Gulf of Papua on the south coast of PNG. The Sepik inorganic PIC flux is low (1.4×10⁸ mol yr⁻¹) as the river does not drain carbonate soils. With a narrow continental shelf, and strong coastal currents, much of this exported material is available for long distance transport into the coastal Bismarck Sea and beyond.     

中国生态农业的系统途径(英文)

中国生态农业开始于20世纪70年代末80年代初。中国生态农业的目标是有效地协调农业实践的社会、经济和生态效益。其关键途径包括在景观层面的生态规划,在生态系统层面的循环体系设计,以及重建重要的生物多样性。有利的社会经济环境对于中国生态农业发展至关重要。在社会体系方面,中国的生态农业发展需要通过教育、立法和评估体系建设建立必要的道德标准。在经济环境方面,中国生态农业发展需要有效的政府补助政策,有效的污染排放市场体系,以及生态友好产品销售的成熟市场。