作物相对水分利用效率与理论节水潜力

作物水分利用效率是评价农业用水效率的重要指标,由于气候差异,采用作物水分利用效率评价不同区域的用水效率可能存在一定误差,尚缺乏深入研究。基于潜在水分利用效率指标和气象数据,计算了2014年中国小麦、玉米和水稻在充分灌溉条件下的潜在水分利用效率,分析了区域气候差异对作物水分利用效率的影响,提出了相对水分利用效率和理论节水潜力的概念和计算方法,并进行了实例研究。结果表明:各类作物在不同站点的潜在水分利用效率的标准差为0.49~1.01 kg/m3,多数作物潜在水分利用效率的空间差异大于实际水分利用效率的空间差异;主要作物的平均相对水分利用效率为50.7%,其理论节水潜力为884.8~4 064.5 m3/hm2;作物水分利用效率和广义节水潜力指标可能高估或低估作物的用水效率和节水潜力。研究认为在比较区域间作物的水分利用效率时不能忽略气候差异的影响;由于考虑了区域气候差异,相对水分利用效率和理论节水潜力指标更合理。     

Fragmented subfossil <Emphasis Type="Italic">Chaoborus</Emphasis> mandibles reveal periods of cyprinid presence in lake histories

Cyprinid fish have pharyngeal teeth that mash ingested food. Here we show that roach (Rutilus rutilus L.), a common cyprinid in Swedish boreal lakes, often break the mandibles of ingested Chaoborus larvae into smaller fragments. The presence/absence of roach in historic fish communities could therefore possibly be determined from the proportion of fragmented Chaoborus mandibles in lake sediments, which we assessed using the following three approaches. (1) Roach that were fed Chaoborus larvae in laboratory aquaria evacuated a significantly higher fraction of fragmented prey mandibles than perch (Perca fluviatilis L.). (2) Surface sediments from lakes in an acidified region in southwestern Sweden showed significantly higher proportions of fragmented mandibles for lakes containing roach compared to lakes devoid of cyprinid fish. (3) A paleo-study in Lake Lysevatten, into which roach were introduced in the 1880s and were extirpated in the 1960s, showed significantly higher proportions of fragmented mandibles in sediment layers from the roach period. We conclude that mandible fragmentation was related to roach presence, and propose that the proportion of fragmented Chaoborus mandibles in lake sediments may provide important information when historical cyprinid alterations are of interest, as in paleo-studies on acidification, eutrophication, or fish introductions.     

Reading the climate record of the martian polar layered deposits

The martian polar regions have layered deposits of ice and dust. The stratigraphy of these deposits is exposed within scarps and trough walls and is thought to have formed due to climate variations in the past. Insolation has varied significantly over time and caused dramatic changes in climate, but it has remained unclear whether insolation variations could be linked to the stratigraphic record. We present a model of layer formation based on physical processes that expresses polar deposition rates of ice and dust in terms of insolation. In this model, layer formation is controlled by the insolation record, and dust-rich layers form by two mechanisms: (1) increased summer sublimation during high obliquity, and (2) variations in the polar deposition of dust modulated by obliquity variations. The model is simple, yet physically plausible, and allows for investigations of the climate control of the polar layered deposits (PLD). We compare the model to a stratigraphic column obtained from the north polar layered deposits (NPLD) (Fishbaugh, K.E., Hvidberg, C.S., Byrne, S., Russel, P.S., Herkenhoff, K.E., Winstrup, M., Kirk, R. [2010a]. Geophys. Res. Lett., 37, L07201) and show that the model can be tuned to reproduce complex layer sequences. The comparison with observations cannot uniquely constrain the PLD chronology, and it is limited by our interpretation of the observed stratigraphic column as a proxy for NPLD composition. We identified, however, a set of parameters that provides a chronology of the NPLD tied to the insolation record and consistently explains layer formation in accordance with observations of NPLD stratigraphy. This model dates the top 500 m of the NPLD back to ～1 million years with an average net deposition rate of ice and dust of 0.55 mm a^?1. The model stratigraphy contains a quasi-periodic ～30 m cycle, similar to a previously suggested cycle in brightness profiles from the NPLD (Laskar, J., Levrard, B., Mustard, F. [2002]. Nature, 419, 375–377; Milkovich, S., Head, J.W. [2005]. J. Geophys. Res. 110), but here related to half of the obliquity cycles of 120 and 99 kyr and resulting from a combination of the two layer formation mechanisms. Further investigations of the non-linear insolation control of PLD formation should consider data from other geographical locations and include radar data and other stratigraphic datasets that can constrain the composition and stratigraphy of the NPLD layers.     

Were last glacial climate events simultaneous between Greenland and France? A quantitative comparison using non‐tuned chronologies

Several large abrupt climate fluctuations during the last glacial have been recorded in Greenland ice cores and archives from other regions. Often these Dansgaard–Oeschger events are assumed to have been synchronous over wide areas, and then used as tie‐points to link chronologies between the proxy archives. However, it has not yet been tested independently whether or not these events were indeed synchronous over large areas. Here, we compare Dansgaard–Oeschger‐type events in a well‐dated record from southeastern France with those in Greenland ice cores. Instead of assuming simultaneous climate events between both archives, we keep their age models independent. Even these well‐dated archives possess large chronological uncertainties that prevent us from inferring synchronous climate events at decadal to multi‐centennial time scales. If possible, comparisons between proxy archives should be based on independent, non‐tuned time‐scales. Copyright © 2009 John Wiley & Sons, Ltd.     

On the Scale-dependence of the Gradient Richardson Number in the Residual Layer

We present results of a technique for examining the scale-dependence of the gradient Richardson number, Ri, in the nighttime residual layer. The technique makes use of a series of high-resolution, in situ, vertical profiles of wind speed and potential temperature obtained during CASES-99 in south-eastern Kansas, U.S.A. in October 1999. These profiles extended from the surface, through the nighttime stable boundary layer, and well into the residual layer. Analyses of the vertical gradients of both wind speed, potential temperature and turbulence profiles over a wide range of vertical scale sizes are used to estimate profiles of the local Ri and turbulence structure as a function of scale size. The utility of the technique lies both with the extensive height range of the residual layer as well as with the fact that the sub-metre resolution of the raw profiles enables a metre-by-metre ‘sliding’ average of the scale-dependent Richardson number values over hundreds of metres vertically. The results presented here show that small-scale turbulence is a ubiquitous and omnipresent feature of the residual layer, and that the region is dynamic and highly variable, exhibiting persistent turbulent structure on vertical scales of a few tens of metres or less. Furthermore, these scales are comparable to the scales over which the Ri is less than or equal to the critical value of Ri _c of 0.25, although turbulence is also shown to exist in regions with significantly larger Ri values, an observation at least consistent with the concept of hysteresis in turbulence generation and maintenance. Insofar as the important scale sizes are comparable to or smaller than the resolution of current models, it follows that, in order to resolve the observed details of small Ri values and the concomitant turbulence generation, future models need to be capable of significantly higher resolutions.     

Predicted wavelengths of coronal transitions in the configurations 3s 23p 2, 3s 23p 3 and 3s 23p 4

The level intervals in the ground configurations 3s ²3p ^k(k = 2, 3, 4) have been studied through the isoelectronic sequences up to Ni. Semiempirical expressions for the parameters F ₂(pp) and _p, are derived from observed data and the intervals are recalculated from interpolated or extrapolated values of the parameters. As a result, predicted wavelengths of magnetic-dipole transitions within the configurations are obtained with an estimated uncertainty of one or two Å.     

Chloride retention in forest soil by microbial uptake and by natural chlorination of organic matter

Inorganic chlorine (i.e. chloride; Cl_in) is generally considered inert in soil and is often used as a tracer of soil and ground water movements. However, recent studies indicate that substantial retention or release of Cl_in can occur in soil, but the rates and processes responsible under different environmental conditions are largely unknown. We performed ³⁶Cl tracer experiments which indicated that short-term microbial uptake and release of Cl_in, in combination with more long-term natural formation of chlorinated organic matter (Cl_org), caused Cl_in imbalances in coniferous forest soil. Extensive microbial uptake and release of Cl_in occurred over short time scales, and were probably associated with changes in environmental conditions. Up to 24% of the initially available Cl_in within pore water was retained by microbial uptake within a week in our experiments, but most of this Cl_in was released to the pore water again within a month, probably associated with decreasing microbial populations. The natural formation of Cl_org resulted in a net immobilization of 4% of the initial pore water Cl_in over four months. If this rate is representative for the area where soil was collected, Cl_org formation would correspond to a conversion of 25% of the yearly wet deposition of Cl_in. The study illustrates the potential of two Cl_in retaining processes in addition to those previously addressed elsewhere (e.g. uptake of chloride by vegetation). Hence, several processes operating at different time scales and with different regulation mechanisms can cause Cl_in imbalances in soil. Altogether, the results of the present study (1) provide evidence that Cl_in cannot be assumed to be inert in soil, (2) show that microbial exchange can regulate pore water Cl_in concentrations and (3) confirm the controversial idea of substantial natural chlorination of soil organic matter.     

四川黄龙沟景区钙华的起源和形成机理研究

对四川黄龙沟钙华景区的水化学测试发现，形成黄龙沟钙华的泉水具有很高的Ca^2 和HC03^-离子浓度，相应地，泉水的C02分压显著高于大气和土壤生物成因所能产生的C02分压。结合泉水出露的地质条件和泉口C02气体碳稳定同位素组成(δ^13C＝—6．8‰)的分析，进一步发现，高C02分压与深部成因的C02有关。可见，黄龙沟钙华属于热成因类钙华，而非原来普遍认为的“是气候岩溶作用的产物”。此外，黄龙沟钙华的大量出现与水中方解石的迅速沉积、Ca^2 和HC03^-浓度的大量降低有关。随着地下水自泉口出露，由于水的C02分压远高于大气，水中C02大量释放于大气，结果水的pH值迅速升高，方解石饱和指数由泉口的负值很快转变为高的正值，为方解石的沉积奠定了必要的物理化学基础。放置于水中的大理岩石片观测表明，流速较快的边石坝处的方解石沉积速率是其附近水池内的2—5倍，这清楚地显示了水动力条件对沉积速率的控制。进一步根据DBL理论模型分析发现，水动力条件对方解石沉积速率的控制在于其对固液界面间扩散边界层(DBL)厚度的影响，流速愈快，DBL厚度愈薄。且DBL厚度最终制约着沉积表面的化学组成浓度，即厚度愈小，表面H^ 浓度愈低(或pH愈高)、方解石饱和指数愈高，进而方解石沉积愈快。