The soil hydrologic response to forest regrowth: a case study from southwestern Amazonia

As a large and dynamic land‐use category, tropical secondary forests may affect climate, soils, and hydrology in a manner different from primary forests or agricultural areas. We investigated the saturated hydraulic conductivity K_sat of a Kandiudult under different land uses in Rondonia, Brazil. We measured K_sat at four depths (12·5, 20, 30 and 50 cm) under (a) primary forest, (b) a former banana–cacao plantation (SF1), and (c) an abandoned pasture (SF2). At 12·5 cm, all three land uses differ significantly (α = 0·1), but not at the 20 and 30 cm depths. At 50 cm, K_sat was significantly greater in the former pasture than in other land uses. Lateral subsurface flow is expected during intense rainfall (about 30 times per year) at 30 cm depth in SF1 and at 50 cm depth in the forest, whereas the relatively low permeability at shallow 12·5 cm in the SF2 may result not only in lateral subsurface flow, but also saturation overland flow. For modelling purposes, recovering systems seem to have K_sat values distinct from primary forest at shallow depths, whereas at deeper layers (>20 cm) they may be considered similar to forests. Copyright © 2002 John Wiley & Sons, Ltd.     

Analysis of cyclical sedimentation in the lower Permian Mchuchuma coalfield (South-West-Tanzania)

A statistical approach by a modified Markov process model was used to prove that the lower Permian coal measures of the Tanzanian Mchuchuma basin developed distinct cyclicities during deposition. From results the transition path of lithologic states typical for this coal sequence is as follows: (A) coarse sandstone, (B) medium sandstone, (C) fine-very fine sandstone, (D) shale, (E) mudstone, (F) coal or (E+F) and again (A) coarse sandstone. The majority of cycles is are asymmetric (ABCDEF-ABC.)but symmetrical cycles are present as well (ABCDEFED). The statistical results concur with observed sedimentological evidence of depositional environment. Fining upward cycles correspond to the development of basal channel bars, changing into levées, then into back swamps which are topped by coal swamps. Frequent interbedding of coal and mudstone in the upper part of the coal measures calls for periodic flooding and flushing of fine clastics into coal-forming swamps causing interruption of peat formation. Cyclical deposition is explained by wandering channels in response to varying discharge and rate of deposition, their lateral frequent shifting caused the formation of asymmetrical cycles in this fluviodeltaic depositional model.

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Zusammenfassung Das kohleführende untere Perm des Mchuchuma Beckens (SW-Tanzania) wurde statistisch mit Hilfe der Markov Analyse auf Zyklizität innerhalb der Abfolge untersucht. Die statistischen Daten zeigen, daß die bevorzugte und für dieses Kohlebecken typische Sequenz folgende lithologische Abfolge umfaßt: (A) grober Sandstein, (B) mittlerer Sandstein, (C) feiner Sandstein, (D) Siltstein, (E) Tonstein, (F) bzw. (E+F) Kohle und erneut (A) grober Sandstein. Es existieren meist asymmetrische Zyklen (ABCDEF-ABCD...) aber symmetrische Zyklen (ABCDEFED) treten ebenfalls auf. Die Markov Analyse ergänzt sehr gut die Beobachtungen bezüglich des Ablagerungsmilieus in den Aufschlüssen. »Fining up« Zyklen beginnen mit basalen Gerinnesanden, überlagert von levée Ablagerungen, welche ihrerseits übergehen in »back swamps« und Kohlesümpfe. Der obere Teil der Kohleabfolge ist durch häufige Wechsellagerungen von Kohle mit Tonstein charakterisiert, die auf periodische Überflutungen und Verfrachtungen von Feinklastika in die Kohlesümpfe zurückzuführen sind. Wandernde Flußgerinne, ausgelöst durch rasch wechselnde Sedimentfracht und Ablagerungsrate, führten zu zyklischen Ablagerungen. Häufig auftretende laterale Gerinneverlagerungen erklären die asymmetrischen Zyklen in diesem fluvio-deltaischen Ablagerungsmodell.

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Résumé Des analyses statistiques ont été effectuées par la méthode de Markov sur le Permien inférieur charbonnier du bassin de Mchuchuma (Tanzanie du sud-ouest) dans le but de montrer l'existence de cycles sédimentaires. Les résultats font apparaître une séquence, typique de ce bassin, qui s'ordonne ainsi de bas en haut: (A) grès grossier, (B) grès moyen, (C) grès fin à très fin, (F) siltite, (E) pélite, (F) charbon ou (E+F) et de nouveau (A) grès grossier. Les cycles sont pour la plupart assymétriques (ABCDEF-ABC...) mais il en existe aussi de symétriques (ABCDEFED).Les résultats obtenus par la méthode de Markov concordent avec les observations sédimentologiques relatives au milieu de dépôt. Les cycles granoclassés débutent par des sables fluviatiles surmontés par des dépôts de levées suivis à leur tour de »back swamps«, et se terminent par des dépôts de marais tourbeux. La partie supérieure de la série est caractérisée par une stratification alternée de charbon et de pélite due à des inondations périodiques amenant dans les marais des produits clastiques fins qui interrompaient la formation de la tourbe. La sédimentation cyclique s'explique par la migration de chenaux, provoquée par les variations de l'apport sédimentaire et de la vitesse de dépôt. Les fréquents déplacements latéraux des chenaux expliquent l'asymétrie des cycles, dans ce modèle fluvio-deltaïque.

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- Mchuchuma (-). , : (A) ; (B) ; (C) - ; (D) ; (E) ; (F) , (E + F) (A) . (ABCDEF-ABCD), (ABCDEFED). . « » , , , . (). , , , . / .

     

14C age and vertical mixing of deep-sea sediments

Vertical mixing models applied to the radiocarbon age stratigraphy of sediments have to make allowance for the presumably non-vanishing zero-age of the sedimentary particulates freshly arriving at the sediment surface. The appropriate modifications of the simple box model recently presented by Berger and Johnson are outlined. For seven deep-sea cores, zero-age values are found varying between 0.1 and 1.4 kyr. A high zero-age is likely to be indicative for redistribution processes occurring at the sea floor. The box model has been extended to make allowance for a change of sedimentation rate in the depositional interval under study.     

Luminescence-dated aeolian deposits of late Quaternary age in the southern Tibetan Plateau and their implications for landscape history

Aeolian deposits are widely distributed in the interior of the Tibetan Plateau, and their chronology is poorly known. It is not yet clear whether they accumulated only after the last deglaciation, or over a longer time. We applied quartz OSL dating to aeolian samples from the Lhasa area with OSL ages ranging from 2.9 ± 0.2 to at least 118 ± 11 ka. The probability density frequency (PDF) distribution of 24 ages reveals age clusters at about 3, 8, 16–21, 33, and 79–83 ka, indicating enhanced sediment accumulation then. The results show that aeolian deposition occurred throughout most of the last 100 ka. This implies that: 1) an ice sheet covering the whole Tibetan Plateau during the last glacial maximum (LGM) could not have existed; and 2) erosion during the last deglaciation was not as strong as previously proposed, such that not all pre-Holocene loess was removed. The age distribution shown in the PDF indicates that aeolian accumulation is episodic. Sand-formation events revealed by age clusters at 3, 8, and 16–21 ka imply roughly synchronous environmental responses to corresponding global-scale arid events.     

Vorhersage von Niveauänderungen der 500 mb Fläche mittels numerischer Integration der Wellengleichung

Zusammenfassung Es wurde versucht mittels der numerischen Integration der zweidimensionalen homogenen Wellengleichung bei bekannter Phasengeschwindigkeit Niveauänderungen im 500 mb Niveau vorherzusagen. Gleichzeitig wurde das Ergebnis mit der prognostizierten Niveauänderung, die mittels graphischer Integration der barotropen Wirbelgleichung gewonnen wurde, verglichen. Dabei hat es sich gezeigt, dass die Übereinstimmung der beiden vorhergesagten Änderungen sowohl untereinander, als auch mit der tatsächlich eingetroffenen Änderung recht gut ist. Offenbar kann man in einfachen Fällen die physikalischen Vorgänge in der Atmosphäre mittels der homogenen Wellengleichung beschreiben.

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Summary The attempt is made to forecast height changes of the 500 mb contours by a numerical integration of the twodimensional homogenous wave equation provided the phase velocity is known. The result is compared with a forecast obtained by graphical integration of the barotropic vorticity equation. In the case investigated both methods show almost the same accuracy with respect to the contour changes with have actually occured. Appearently in some case it is possible to discribe height variations of an isobaric surface with the aid of the linear twodimensional wave equation with the same success as using the nonlinear vorticity equation.

     

如何写好天文学论文

对如何撰写将要在国际上发表的天文学论文给出一些建议。讲述了论文的每一部分（题目、摘要、引言、主要内容、图表及参考文献等）如何可以写得简洁而又能清晰地表达出观点。这是作者根据在多年的编辑生涯中审阅了许多效果迥异的论文后的经验之谈。     

Increasing levels and biomagnification of persistent organic pollutants (POPs) in Antarctic biota

Representatives of the Antarctic food web (krill, cephalopod, fish, penguin, seal) of the area around Elephant Island and from the Weddell Sea were analysed for the most recalcitrant organochlorine compounds. Due to sorption of the compounds to sinking particles and accumulation in sediments, two benthic fish species (Gobionotothen gibberifrons, Chaenocephalus aceratus) feeding on benthos invertebrates and fish reflected significantly increasing concentrations within a decade (1987-1996), while a benthopelagic species (Champsocephalus gunnari) feeding on krill did not. In the pelagic food chain, lipid normalised concentrations of all compounds increased from Antarctic krill to fish proving that biomagnification of highly lipophilic pollutants (log octanol-water partition coefficient>5) occurs in water-breathing animals. As top predators Weddell and southern elephant seals (Leptonychotes weddellii, Mirounga leonina) biomagnified the persistent organic pollutants relative to krill 30-160 fold with the exception of hexachlorobenzene, the levels of which were lower than in fish indicating its intense specific elimination.     

Mass Diving Tourism – A New Dimension Calls for New Management Approaches

Diving has become a booming branch of the tourism business. The economies of many countries with reef-lined coasts depend on high numbers of tourist divers; the resultant degradation of reefs by mechanical damage is accepted due to the short-term gain from the tourism business. Many activities of recreational diving do not particularly require coral reefs – any varied three-dimensional structure (e.g. a wreck) may be sufficiently attractive. The conflict between the needs of nature conservation and the economic interests of diving tourism can be mitigated by the formation of artificial underwater attractions as reef substitutes. Based on experiments in the northern Red Sea, we propose to deposit calcium minerals from the seawater in situ by electrolysis on a template of any desired shape. After transplantation of living coral fragments, a diverse community will develop. With this method different modules can be designed and formed on the seabed which can serve different needs such as diver training, environmental education and recreation as well as reef rehabilitation. By a combination of such modules, a recreational underwater park can be formed well suited to function as a DAD (diver aggregation device) and therefore, divert diver pressure from the natural reef.