Neogene fluvial landscape evolution in the hyperarid core of the Atacama Desert

Dating of extensive alluvial fan surfaces and fluvial features in the hyperarid core of the Atacama Desert, Chile, using cosmogenic nuclides provides unrivalled insights about the onset and variability of aridity. The predominantly hyperarid conditions help to preserve the traces of episodic climatic and/or slow tectonic change. Utilizing single clast exposure dating with cosmogenic 10Be and 21Ne, we determine the termination of episodes of enhanced fluvial erosion and deposition occurring at ~19, ~14, ~9.5 Ma; large scale fluvial modification of the landscape had ceased by ~2–3 Ma. The presence of clasts that record pre-Miocene exposure ages (~28 Ma and ~34 Ma) require stagnant landscape development during the Oligocene. Our data implies an early onset of (hyper-) aridity in the core region of the Atacama Desert, interrupted by wetter but probably still arid periods. The apparent conflict with interpretation that favour a later onset of (hyper-) aridity can be reconciled when the climatic gradients within the Atacama Desert are considered

Folgen des Tourismus. Tourismuspolitik im Zeitalter der Globalisierung. Bd. 2

Für den Tourismus als globales Geschehen werfen die Strukturveränderungen im Zuge des Globalisierungsprozesses eine Vielzahl neuer Fragen auf. Dazu zählen das weltweit anwachsende Volumen der Reiseströme, die noch ungeklärte Rolle der global players der Branche, der Wettkampf der Destinationen um alte und neue Quellmärkte, die Gefahr von Überkapazitäten und ruinösem Wettbewerb sowie der Beitrag des Tourismus zur globalen Umweltproblematik. Auf der anderen Seite versprechen Wachstum und neue Märkte Arbeitsplätze und wirtschaftliche Prosperität. Gesucht wird eine Balance zwischen den Chancen weiterer Liberalisierung und Deregulierung und den ökonomischen, sozialen und ökologischen Risiken des Tourismus. Neben einer Analyse der Globalisierungstendenzen im Tourismus ist die zentrale Thematik dieses zweiten Bandes "Folgen des Tourismus" die Frage, wie eine intelligente und kooperative Tourismusaußenpolitik zu konzipieren wäre und wie sie auf die Ursachen und Phänomene einer weltweiten Umbruchsituation reagieren könnte. "Folgen des Tourismus", Band 1: Gesellschaftliche, ökologische und technische Dimensionen, ist bereits 1998 erschienen

Biogeochemical factors affecting mercury methylation rate in two contaminated floodplain soils

An automated biogeochemical microcosm system allowing controlled variation of redox potential (EH) in soil suspensions was used to assess the effect of various factors on the mobility of mercury (Hg) as well as on the methylation of Hg in two contaminated floodplain soils with different Hg concentrations (approximately 5 mg Hg kg(-1) and > 30 mg Hg kg(-1)). The experiment was conducted under stepwise variation from reducing (approximately -350 mV at pH 5) to oxidizing conditions (approximately 600 mV at pH 5). Results of phospholipid fatty acids (PLFA) analysis indicate the occurrence of sulfate reducing bacteria (SRB) such as Desulfobacter species (10Me16:0, cy17:0, 10Me18:0, cy19:0) or Desulfovibrio species (18:2 omega 6,9), which are considered to promote Hg methylation. The products of the methylation process are lipophilic, highly toxic methyl mercury species such as the monomethyl mercury ion [MeHg+], which is named as MeHg here. The ln(MeHg/Hg-t) ratio is assumed to reflect the net production of monomethyl mercury normalized to total dissolved Hg (Hg-t) concentration. This ratio increases with rising dissolved organic carbon (DOC) to Hg-t ratio (ln(DOC/Hg-t) ratio) (R-2 = 0.39, p < 0.0001, n = 63) whereas the relation between ln(MeHg/Hg-t) ratio and lnDOC is weaker (R-2 = 0.09; p < 0.05; n = 63). In conclusion, the DOC/Hg-t ratio might be a more important factor for the Hg net methylation than DOC alone in the current study. Redox variations seem to affect the biogeochemical behavior of dissolved inorganic Hg species and MeHg indirectly through related changes in DOC, sulfur cycle, and microbial community structure whereas EH and pH values, as well as concentration of dissolved Fe3+/Fe2+ and Cl-seem to play subordinate roles in Hg mobilization and methylation under our experimental condition

Evidence for multiple Plio-Pleistocene lake episodes in the hyperarid Atacama Desert

Cosmogenic nuclide exposure dating of ancient shoreline terraces of the Quillagua-Llamara Soledad Lake in the central Atacama Desert of northern Chile provides new insights in the paleohydrology of the driest desert on Earth. The lake developed in a paleo-endorheic drainage system in the Central Depression prior to draining into the Pacific due to incision of the Río Loa canyon. The durations of lake stages were sufficiently long to form wave-erosion induced shoreline terraces on the wind-exposed slopes of former islands. Successively younger shoreline levels are preserved over an elevation range of 250 m due to progressive uplift of the islands coeval with the lake stages. Cosmogenic 10Be- and 21Ne-derived exposure ages of the shorelines reveals that the hyperarid conditions in the Río Loa catchment were interspersed by several pluvial stages during the Pliocene and Pleistocene, which generated a large and persistent lake in the Quillagua-Llamara basin. The exposure ages of the final lake stage provide the maximum age for the incision of the Río Loa canyon (274 ± 74 ka) and the subsequent breaching of the Coastal Cordillera