Evapotranspiration from citrus trees growing in sandy soilunder drip irrigation with saline water

An experiment on evapotranspiration from citrus trees under irrigation with saline waterwas carried out for 4 months. Two lysimeters planted with a citrus tree in the green house wereused. One lysimeter was irrigated with saline water (NaCl and CaCl2 of 2000 mg/L equivalence,EC = 3.8 dS/m, SAR = 5.9) and the other was irrigated with freshwater using drip irrigation. Theapplied irrigation water was 1.2 times that of the evapotranspiration on the previous day.Evapotranspiration was calculated as the change in lysimeter weight recorded every 30 minutes.The lysimeters were filled with soil with 95.8% sand. The results of the experiment were as follows.(i) The evapotranspiration from citrus tree was reduced after irrigation with saline water. Theevapotranspiration returns to normal after leaching. However it takes months to exhaust the saltfrom the tree. ( ii ) To estimate the impact of irrigation with saline water on the evapotranspirationfrom citrus trees, the reduction coefficient due to salt stress (Ks) was used in this experiment.Evapotranspiration under irrigation with saline water (ETs) can be calculated from evapotranspira-tion under irrigation with freshwater (ET) by the equation ETs = Ks× ET. Ks can be expressed as afunction of ECsw. (iii) The critical soil-water electrical conductivity (ECsw) is 9.5 dS/m, beyondwhich adverse effects on evapotranspiration begin to appear. If ECsw can be controlled at below9.5 dS/m, saline water can be safely used for irrigation.     

δO of carbonate, quartz and phosphate from belemnite guards: implications for the isotopic record of old fossils and the isotopic composition of ancient seawater

Belemnite guards of Cretaceous and Jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum. The oxygen isotopic composition of coexisting carbonate, quartz and phosphate from the same rostrum was measured according to well-established techniques. None of these compounds showed isotopic values in equilibrium with one another. Assuming δ¹⁸O values of the diagenetic water within the range of meteoric waters, the δ¹⁸O(SiO₂) yield temperatures in agreement with the apparent secondary origin of this phase. The δ¹⁸O(CO₃²⁻) range, with a certain continuity, between −10.8 and +0.97 PDB-1 with most of the intermediate values being within the range of the carbonate isotopic values of Mesozoic fossils. The most positive isotopic results obtained from phosphate are close to +23/+24‰ (V-SMOW). They can hardly be related to a secondary origin of the phosphate, or to the presence of diagenetic effects, since these results are among the most positive ever measured on phosphate. As far as we know there is no widespread diagenetic process determining an ¹⁸O enrichment of phosphate. The very low concentration of phosphate did not allow the determination of its mineralogical composition. All the available δ¹⁸O(PO₄³⁻) values from belemnite and non-belemnite fossils of marine origin of Tertiary and Mesozoic age are reported along with the newly measured belemnites. The following conclusions may be drawn from the data reported: (1) the pristine oxygen isotope composition of fossil marine organisms (either carbonate or phosphate) may easily undergo fairly large changes because of oxygen isotope exchange processes with diagenetic water; this process is apparent even in the case of geologically recent fossils; (2) the δ¹⁸O(PO₄³⁻) of belemnite rostra seems to be, at least in the case of the most positive results, in isotopic equilibrium with environmental water because of the similarity between the results from Cretaceous belemnites and the results from Cretaceous and Lower Tertiary pelecypods and fish teeth; 3) if so, the only feasible interpretation that can be suggested for the ¹⁸O enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from Jurassic to recent time.     

川滇地区地震(Ms≥5.0)破裂类型与前兆异常分布的关系

对川滇地区 31次 (组 ) 5 .0级以上地震与余震次数的关系进行了统计 ,结合“强地震分为走滑型地震和断错型地震”的理论 ,确定了各次 (组 )地震的破裂类型。从物理机制上对地震破裂类型与震前前兆异常分布关系进行了讨论 ,由此进一步探讨了 5 .0级以上地震震后趋势预测     

北京建设世界城市模式与政策导向的初步研究

结合世界城市同经济增长、科技创新以及区域基础这间的关系，世界城市结构演化及其成长过程等的一般规律，在内外部环境综合分析基础上，提出北京建设世界城市的基本经济模式与空间结构模式。加大开放程度，推进产业价值链分工，提高高级生产者服务以及高科技产业在经济结构中的比重，积极吸引跨国公司总部与研发机构，增强对全球经济资源的配置能力，为基本经济模式；而在首都圈与环渤海地区形成合理的空间分工，以及改北京单中心结构为近、远程多中心圈域型结构，为基础空间结构模式，并进一步提出了北京建设世界城市的六大政策导向。     

长江巨洪前期物理因子的配置

提出了长江巨洪前期物理因子配置的概念，在每一次巨洪发生之前，影响巨洪的主要物理因子之间一般都会表现出相似的特征，即出现一些固有的配置，这些配置正是长江发生巨洪的强信号，对长江巨洪的预测研究具有重要的指示作用。     

河北南部地区资源、环境、发展初析

河北南部地区山前平原区农业气候条件适于夏玉米的生长 ,黑龙港地区适于棉花的生长。本区水资源匮乏 ,地下水超采严重。浅层地下水超采模数为 8.0 1× 1 0 4 m3/( km2 ·a) ,深层地下水为 2 .5 8× 1 0 4 m3/( km2·a)。全区水资源利用的综合边际效益以廊坊市最高 ( 2 6.68元 /t) ,保定市最低 ( 1 4.85元 /t) ,两者之比为 1 .80。区内地下水降落漏斗与地面沉降等环境地质灾害频繁 ,1 998年浅层地下水漏斗区面积为 0 .5 4× 1 0 4 km2 ,深层地下水为 1 .5 9× 1 0 4 km2。地下水、粮食和蔬菜受到农药残留、过量化肥的污染。本区 2 0 1 0水平年外流域调水将占可供水量的 2 3.9% ,但缺水率仍达 36.2 %。若全区通过发展工程节水 (提高综合节水率 3.2 % )、实施适水种植 (冬小麦播种面积下调 7% ) ,利用水分胁迫处理 (减少一次灌溉 )等节水措施 ,则比 1 999年节水 1 7.2 %。     

21世纪黄河系统工程方略

该文指出 :王化云的治黄思想 ,“上拦下排、两岸分滞、蓄水拦沙、宽河固堤、除害兴利、综合利用” ,实际上是治理黄河的系统工程 ,2 1世纪应该继承和发展黄河系统工程的方略。黄河地处中国腹地 ,是中华民族的摇篮 ,当今高新科技的发展 ,足以从更大的范围 ,以全国的水资源、土资源为核心来考虑黄河的建设。统一计算水资源中的大气水、地表水、地下水、壤中水、生态水、环境水、生产水、生活水 ;统一计算土资源中的土壤资源、沙资源、沙石资源 ,真正按照地理系统工程来建设黄河。     

分布式侵蚀预报模型中网格面积的选定——以黄土高原丘陵沟壑区为例

在分布式土壤侵蚀过程模型中 ,承载数据以及进行运算的最小单元 ,即基本地块的选取是非常关键的 ,它直接关系到模型的模拟精度和运算数据量。目前大多数分布式模型都采用平均布设矩形网格的方法 ,这种方法在基本网格的大小选取上存在着盲目性和不统一性。本文以黄土高原丘陵沟壑区为例 ,利用GIS和SPSS分析了黄土高原丘陵沟壑区属性均一的基本地块在面积上的统计规律 ,给出了基本地块选取的合理依据 ,以促进建立更好的分布式模型     

青藏高原土壤水热分布特征及冻融过程在季节转换中的作用

利用GAME-Tibet期间所取得的高分辩率土壤温度和含水量资料，对青藏高原（主要是藏北高原）土壤水热分布特征及冻融过程在季节转换中的作用进行了分析。指出藏北高原4cm学深处土壤在10月份开始冻结，次年4-5月份开始消融，冻结持续时间长达5-7个月。冻结过程有利于土壤维持其水分，因此，在刚刚开始消融时土壤含水量仍然很高。从而为夏季风爆发前土壤通过蒸发向大气提供水分打下了基础。指出土壤冻融过程可能在高原季节转换中起着重要作用。