Changes in water extractable organic matter during incubation of forest floor material in the presence of quartz, goethite and gibbsite surfaces

The release of dissolved organic matter (DOM) from forest floor material constitutes a significant flux of C to the mineral soil in temperate forest ecosystems, with estimates on the order of 120-500 kg C ha⁻¹ year⁻¹. Interaction of DOM with minerals and metals results in sorptive fractionation and stabilization of OM within the soil profile. Iron and aluminum oxides, in particular, have a significant effect on the quantity and quality of DOM transported through forest soils due to their high surface area and the toxic effects of dissolved aluminum on microbial communities. We directly examined these interactions by incubating forest floor material, including native microbiota, for 154 days in the presence of (1) goethite (α-FeOOH), (2) gibbsite (γ-Al(OH)₃), and (3) quartz (α-SiO₂) sand (as a control). Changes in molecular and thermal properties of water extractable organic matter (WEOM, as a proxy for DOM) were evaluated. WEOM was harvested on days 5, 10, 20, 30, 60, 90, and 154, and examined by thermogravimetry/differential thermal analysis (TG/DTA) and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy. Results indicated significant differences in WEOM quality among treatments, though the way in which oxide surfaces influenced WEOM properties did not seem to change significantly with increasing incubation time. Dissolved organic C concentrations were significantly lower in WEOM from the oxide treatments in comparison to the control treatment. Incubation with goethite produced WEOM with mid-to-high-range thermal lability that was depleted in both protein and fatty acids relative to the control. The average enthalpy of WEOM from the goethite treatment was significantly higher than either the gibbsite or control treatment, suggesting that interaction with goethite surfaces increases the energy content of WEOM. Incubation with gibbsite produced WEOM rich in thermally recalcitrant and carboxyl-rich compounds in comparison to the control treatment. These data indicate that interaction of WEOM with oxide surfaces significantly influences the composition of WEOM and that oxides play an important role in determining the biogeochemistry of forest soil DOM.     

Archaean gold mineralization synchronous with late cratonization of the Western Dharwar Craton,India: 2.52 Ga U–Pb ages of hydrothermal monazite and xenotime in gold deposits

New zircon U–Pb ages for a felsic volcanic rock (2,588 ± 10 Ma) and an intrusive granite (≥2,555 ± 6 Ma) in the Gadag greenstone belt in the Western Dharwar Craton, southern India, are similar to dates for equivalent rocks in the Eastern Dharwar Craton and indicates docking of the two cratons prior to this time. The zircons in the intrusive granite are strongly overprinted, and coexisting titanites yielded two different age populations: the dominant group gives an age of 2,566 ± 7 Ma, interpreted as the emplacement age, whereas the minor group gives an age of 2,516 ± 10 Ma, reflecting a hydrothermal overprint. In situ U–Pb dating of monazite and xenotime in gold reefs of the Gadag (2,522 ± 6 Ma) and Ajjanahalli (2,520 ± 9 Ma) gold deposits reveal a previously undated episode of gold mineralization at 2.52 Ga, substantially younger than the 2.55 Ga Hutti deposit in the eastern Dharwar Craton. The new dates confirm that both the younger greenstone belts and lode gold mineralization in the Dharwar Craton are about 100–120 My, younger than in other well-dated Archaean cratons. Although gold mineralization across the craton postdates most of the magmatic activity and metamorphism at upper crustal levels, widespread thermal reworking of the lower-middle crust, involving partial melting, metamorphism, and lower crustal granitoid intrusion, occurred concurrently with gold mineralization. It is likely that the large-scale hydrothermal fluid flow that produced widespread gold deposition was also part of this tectono-thermal event during the final stages of cratonization of the Dharwar Craton in southern India.     

Simulating the hydrological response to predicted climate change on a watershed in southern Alberta, Canada

The current body of research in western North America indicates that water resources in southern Alberta are vulnerable to climate change impacts. The objective of this research was to parameterize and verify the ACRU agro-hydrological modeling system for a small watershed in southern Alberta and subsequently simulate the change in future hydrological responses over 30-year simulation periods. The ACRU model successfully simulated monthly streamflow volumes (r ²?=?0.78), based on daily simulations over 27 years. The delta downscaling technique was used to perturb the 1961?C1990 baseline climate record from a range of global climate model (GCM) projections to provide the input for future hydrological simulations. Five future hydrological regimes were compared to the 1961?C1990 baseline conditions to determine the average net effect of change scenarios on the hydrological regime of the Beaver Creek watershed over three 30-year time periods (starting in 2010, 2040 and 2070). The annual projections of a warmer and mostly wetter climate in this region resulted in a shift of the seasonal streamflow distribution with an increase in winter and spring streamflow volumes and a reduction of summer and fall streamflow volumes over all time periods, relative to the baseline conditions (1961?C1990), for four of the five scenarios. Simulations of actual evapotranspiration and mean annual runoff showed a slight increase, which was attributed to warmer winters, resulting in more winter runoff and snowmelt events.     

Staying with the system: theoretical consistency and change in Danish geographical work on the Sahel

Scholars have studied the Sahel intensely since major droughts hit the region in the early 1970s. One of the most persistent of these in terms of both volume and time span is Anette Reenberg. In this paper we explore her studies of the Sahel published in peer-reviewed journals and their impact over the last three decades. Reenberg has had a remarkably stable theoretical agenda concerned with the importance of understanding the social and biophysical systems as one coupled human-environmental system. This agenda has influenced contemporary as well as subsequent Danish scholars publishing on the Sahel. Taking papers published in Geografisk Tidsskrift-Danish Journal of Geography as an example we show how scholars have moved from treating aspects of the Sahelian droughts according to the traditional natural-social science divide towards a much more coupled manner. This rise of the coupled human-environmental system framework in the journal may be attributed to Reenberg’s theoretical agenda as well as a new international stream of research joining the human and environmental sciences in an interdisciplinary effort. Hence, it is also shown how Reenberg’s theoretical agenda have influenced scholars trying to grasp contemporary global change. This is especially evident in the land science community.     

Identification of the Fugloyarbanki tephra in the NGRIP ice core: a key tie‐point for marine and ice‐core sequences during the last glacial period

A visible tephra horizon in the NGRIP ice core has been identified by geochemical analysis as the Fugloyarbanki Tephra, a widespread marker horizon in marine cores from the Faroe Islands area and the northern North Atlantic. An age of 26 740 ± 390 yr b2k (1σ uncertainty) is derived for this tephra according to the new Greenland Ice Core Chronology (GICC05) based on multi‐parameter counting of annual layers. Detection of this tephra for the first time within the NGRIP ice core provides a key tie‐point between marine and ice‐core records during the transition between MIS 3 and 2. Identification of this volcanic event within the Greenland records demonstrates the future potential of using tephrochronology to precisely correlate palaeoarchives in widely separated localities that span the last glacial period, as well as providing a potential method for examining the extent of the radiocarbon marine reservoir effect at this time. Copyright © 2008 John Wiley & Sons, Ltd.     

Palaeoceanographic changes in the northern Barents Sea during the last 16 000 years – new constraints on the last deglaciation of the Svalbard–Barents Sea Ice Sheet

The sediment core NP05‐71GC, retrieved from 360 m water depth south of Kvitøya, northwestern Barents Sea, was investigated for the distribution of benthic and planktic foraminifera, stable isotopes and sedimentological parameters to reconstruct palaeoceanographic changes and the growth and retreat of the Svalbard–Barents Sea Ice Sheet during the last ～16 000 years. The purpose is to gain better insight into the timing and variability of ocean circulation, climatic changes and ice‐sheet behaviour during the deglaciation and the Holocene. The results show that glaciomarine sedimentation commenced c. 16 000 a BP, indicating that the ice sheet had retreated from its maximum position at the shelf edge around Svalbard before that time. A strong subsurface influx of Atlantic‐derived bottom water occurred from 14 600 a BP during the Bølling and Allerød interstadials and lasted until the onset of the Younger Dryas cooling. In the Younger Dryas cold interval, the sea surface was covered by near‐permanent sea ice. The early Holocene, 11 700–11 000 a BP, was influenced by meltwater, followed by a strong inflow of highly saline and chilled Atlantic Water until c. 8600 a BP. From 8600 to 7600 a BP, faunal and isotopic evidence indicates cooling and a weaker flow of the Atlantic Water followed by a stronger influence of Atlantic Water until c. 6000 a BP. Thereafter, the environment generally deteriorated. Our results imply that (i) the deglaciation occurred earlier in this area than previously thought, and (ii) the Younger Dryas ice sheet was smaller than indicated by previous reconstructions.     

Enhancement in wind-driven sand transport by electric fields

Aeolian grain transport is a powerful erosion mechanism and a significant factor affecting atmospheric dynamics by the creation of particulate aerosols. Electric fields, both natural and man-made, occur widely at the Earths surface in environments where granular material is found. Such electric fields may induce electrification of granular material and affect the transport dynamics of the grains. In this laboratory study we show that the influence of such electric fields is significant at field strengths well below that at which breakdown occurs and present a simple semi-empirical expression which allows this mechanism to be quantified.     

Temperature and abundance profiles of hot gas in galaxy groups – II. Implications for feedback and ICM enrichment

We investigate the history of galactic feedback and chemical enrichment within a sample of 15 X-ray bright groups of galaxies, on the basis of the inferred Fe and Si distributions in the hot gas and the associated metal masses produced by core-collapse and Type Ia supernovae (SNe). Most of these cool-core groups show a central Fe and Si excess, which can be explained by prolonged enrichment by SN Ia and stellar winds in the central early-type galaxy alone, but with tentative evidence for additional processes contributing to core enrichment in hotter groups. Inferred metal mass-to-light ratios inside r ₅₀₀ show a positive correlation with total group mass but are generally significantly lower than in clusters, due to a combination of lower global intracluster medium (ICM) abundances and gas-to-light ratios in groups. This metal deficiency is present for products from both SN Ia and SN II, and suggests that metals were either synthesized, released from galaxies or retained within the ICM less efficiently in lower mass systems. We explore possible causes, including variations in galaxy formation and metal release efficiency, cooling out of metals, and gas and metal loss via active galactic nuclei (AGN) – or starburst-driven galactic winds from groups or their precursor filaments. Loss of enriched material from filaments coupled with post-collapse AGN feedback emerges as viable explanations, but we also find evidence for metals to have been released less efficiently from galaxies in cooler groups and for the ICM in these to appear chemically less evolved, possibly reflecting more extended star formation histories in less massive systems. Some implications for the hierarchical growth of clusters from groups are briefly discussed.     

Quantification and regionalization of groundwater–surface water interaction along an alluvial stream

In the present study, groundwater seepage to an alluvial stream and two tributary streams was examined at nine field sites using hydrological, geophysical, and geomorphological observations. The data indicate that seepage enters the streams in the following ways: (i) directly through the streambed; (ii) as nearly superficial flow from diffuse discharge areas on the flood plains or; (iii) as a combination of (i) and (ii). At about 40% of the sites more than 50% of seepage flows through the streambed. Moreover, it was found that the ratio C, defined as the width of the wet zone of the flood plain divided by the effective width of the stream, can be used as an indicator of the percentage of water entering the stream directly through the streambed. When C is small streambed seepage is large, while when C is large streambed seepage is small and ground water enters the stream mainly as nearly superficial or over-bank flow from the wet zone.