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1.
Forests in the Southeastern United States are predicted to experience future changes in seasonal patterns of precipitation inputs as well as more variable precipitation events. These climate change‐induced alterations could increase drought and lower soil water availability. Drought could alter rooting patterns and increase the importance of deep roots that access subsurface water resources. To address plant response to drought in both deep rooting and soil water utilization as well as soil drainage, we utilize a throughfall reduction experiment in a loblolly pine plantation of the Southeastern United States to calibrate and validate a hydrological model. The model was accurately calibrated against field measured soil moisture data under ambient rainfall and validated using 30% throughfall reduction data. Using this model, we then tested these scenarios: (a) evenly reduced precipitation; (b) less precipitation in summer, more in winter; (c) same total amount of precipitation with less frequent but heavier storms; and (d) shallower rooting depth under the above 3 scenarios. When less precipitation was received, drainage decreased proportionally much faster than evapotranspiration implying plants will acquire water first to the detriment of drainage. When precipitation was reduced by more than 30%, plants relied on stored soil water to satisfy evapotranspiration suggesting 30% may be a threshold that if sustained over the long term would deplete plant available soil water. Under the third scenario, evapotranspiration and drainage decreased, whereas surface run‐off increased. Changes in root biomass measured before and 4 years after the throughfall reduction experiment were not detected among treatments. Model simulations, however, indicated gains in evapotranspiration with deeper roots under evenly reduced precipitation and seasonal precipitation redistribution scenarios but not when precipitation frequency was adjusted. Deep soil and deep rooting can provide an important buffer capacity when precipitation alone cannot satisfy the evapotranspirational demand of forests. How this buffering capacity will persist in the face of changing precipitation inputs, however, will depend less on seasonal redistribution than on the magnitude of reductions and changes in rainfall frequency. 相似文献
2.
Chris Yakymchuk Adrian Rehm Zhuoheng Liao John M. Cottle 《Journal of Metamorphic Geology》2019,37(6):839-862
Sapphirine–quartz granulites from the Cocachacra region of the Arequipa Massif in southern Peru record early Neoproterozoic ultrahigh‐temperature metamorphism. Phase equilibrium modelling and zircon petrochronology are used to quantify timing and pressure–temperature (P–T) conditions of metamorphism. Modelling of three magnetite‐bearing sapphirine–quartz samples indicates peak temperatures of >950°C at ~0.7 GPa and a clockwise P–T evolution. Elevated concentrations of Al in orthopyroxene are also consistent with ultrahigh‐temperature conditions. Neoblastic zircon records ages of c. 1.0–0.9 Ga that are interpreted to record protracted ultrahigh‐temperature metamorphism. Th/U ratios of zircon of up to 100 reflect U‐depleted whole‐rock compositions. Concentrations of heavy rare earth elements in zircon do not show systematic trends with U–Pb age but do correlate with variable whole‐rock compositions. Very large positive Ce anomalies in zircon from two samples probably relate to strongly oxidizing conditions during neoblastic zircon crystallization. Low concentrations of Ti‐in‐zircon (<10 ppm) are interpreted to result from reduced titania activities due to the strongly oxidized nature of the granulites and the sequestration of titanium‐rich minerals away from the reaction volume. Whole‐rock compositions and oxidation state have a strong influence on the trace element composition of metamorphic zircon, which has implications for interpreting the geological significance of ages retrieved from zircon in oxidized metamorphic rocks. 相似文献
3.
4.
Zhi-gen Yang Wen-yao Zhu C. K. Shum Feng-chun Shu 《Chinese Astronomy and Astrophysics》2002,26(4):303-502
The vertical deformation rates (VDRs) and horizontal deformation rates (HDRs) of Shanghai VLBI station in China and Kashima and Kashima34 VLBI stations in Japan were re-analysed using the baseline length change rates from Shanghai to 13 global VLBI stations, and from Kashima to 27 stations and from Kashima34 to 12 stations, based on the NASA VLBI global solution glb1123 (Ma, 1999). The velocity vectors of the global VLBI stations were referred to the ITRF97 reference frame, and the Eulerian vectors of different models of plate motion were used for comparative solutions. The VDR of Shanghai station is estimated to be −1.91±0.56 mm/yr, and those of Kashima and Kashima34 stations, −3.72±0.74mm/yr and −8.81±0.84mm/yr, respectively. The difference between the last two was verified by further analysis. Similar estimates were also made for the Kokee, Kauai and MK_VLBA VLBI stations in mid-Pacific. 相似文献
5.
对"数字地球"的几点认识 总被引:7,自引:0,他引:7
自“数字地球”的概念被提出以来,已引起全球的广泛关注和积极响应。然而,数字地球在目前还仅仅是一个概念。为了逐步建立“数字地球”,需要就“数字地球”的理论、技术以及实现进行深入地探讨。从“数字地球”的产生背景、基本概念、研究内容、构成框架、关键技术、实施难点和发展战略等方面谈了对“数字地球”的一些认识。 相似文献
6.
利用 12年的Lageos 1卫星激光测距资料 (1990 - 2 0 0 1)解算得到了地球定向参数 (EOP) ,将该序列的结果与同期的EOP(IERS)C0 4进行比较 ,其外符精度为 :极移XP— 0 .4 0mas,YP— 0 .4 2mas ,日长变化Dr— 0 .0 35ms。 相似文献
7.
超基性岩中含铜、钴块状硫化物矿床——德尔尼铜矿成因新认识 总被引:1,自引:0,他引:1
长期以来对德尔尼铜矿的成因存在着不同认识。从矿石组成和结构、构造来看,应属典型的块状硫化物矿石,矿床亦应属于含铜黄铁矿型矿床。但从其地质产状来看又与一般的黄铁矿型矿床大不相同,与一般的岩浆熔离铜镍硫化物矿床也有较多差异。这就是本矿床类型独特之处。近年来通过工作又取得一些新资料,特别是超基性岩和矿石的同位素年龄数据。本文在综合新老资料基础上,提出新看法,认为该矿床形成于上地幔,再就位于地壳浅部。其成因类型暂定为:“深部熔离—构造侵位矿床”。鉴于本矿床与一般块状硫化物矿床相比有其独特性,建议命名为“德尔尼型”。 相似文献
8.
月日潮汐摩擦和地球惯量矩变化是日长长期变化的主要原因.在本文中,利用最新的地球物理和古生物钟数据,对过去15亿年以来的月日潮汐摩擦、地球惯量矩变化和日长长期变化等作了数值对比研究.由此得到二个重要结论:一是仅利用地球的自转形变不能解释J2的变化,这说明地球的重力分异现象至今仍存在着;其二是在几亿年前的潮汐摩擦比现在大得多,若取潮汐耗散与距离的立方成反比时,理论结果与由古生物钟得到的回归年日数和朔望月日数数据较为符合。 相似文献
9.
The uranium deposits in the basin of Franceville (Gabon) host the only natural fission reactors known in the world. Unique
geological conditions favoured a natural fission reaction 2 Ga ago. This was detected by anomalous isotopic compositions of
uranium and rare earth elements (REE), which are produced by the fission reaction. In total, 16 reactor zones were found.
Most of them are mined out. The reactor zone of Bangombé, is only 10–11 m below the surface. This site has been influenced
by surface weathering processes. Six drill cores have been sampled at the site of the reactor zone of Bangombé during the
course of the study and only one drill core (BAX 08) hit the core of the reactor. From these data and previous drilling campaigns,
the reactor size is estimated to be 10 cm thick, 2–3 m wide and 4–6 m long. The migration of fission products can be traced
by the anomalous isotope ratios of REE because of the fission process. The 149Sm/147Sm ratio close to the reactor zone is only 0.28 (normal: 0.92) because of the intense neutron capture of 149Sm and subsequent transmutation, whereas 147Sm is enriched by the fission reaction. Similar changes in isotopic patterns are detectable on other REE. The isotope ratios
of Sm and Nd of whole rock and fracture samples surrounding the reactor indicate that fission-genic REE migrated only a few
decimetres above and mainly below the reactor zone. Organic matter (bitumen) seems to act as a trap for fission-genic REE.
Additional REE-patterns show less intense weathering with increasing depth in the log profile and support a simple weathering
model.
Received: 26 November 1999 · Accepted: 2 May 2000 相似文献
10.
在社会发展的层面上认识“数字地球” 总被引:1,自引:0,他引:1
本文讨论了“数字地球”的有关问题。指出“数字地球”是人类社会及其活动在网络空间的延伸和拓展,是信息技术带来的社会发展趋势。关于“数字地球”的讨论不应局限在空间信息技术领域,而应该在社会发展的层面上认识它 相似文献