Measuring bluff erosion part 2: pairing aerial photographs and terrestrial laser scanning to create a watershed scale sediment budget

Effectively managing and reducing high suspended sediment loads in rivers requires an understanding of the magnitude of major sediment sources as well as erosion and transport processes that deliver excess fine sediments to the channel network. The focus of this research is to determine the magnitude of erosion from tall bluffs, a primary sediment source in the 2880 km² Le Sueur watershed, Minnesota, USA. We coupled analyses of seven decades of aerial photographs with four years of repeat terrestrial laser scanning (TLS) to determine erosion rates on bluffs. Together, these datasets provide decadal‐scale retreat rates throughout the entire watershed and high‐resolution geomorphic change detection on a subset of bluffs to both constrain erosion rates and document how environmental conditions affect bluff retreat. Erosion rates from aerial photographs and TLS were extrapolated from 243 and 15 measured bluffs, respectively, to all 480 bluffs in the Le Sueur watershed using multiple techniques to obtain estimates of sediment loading from these features at the watershed‐scale. Despite different spatial and temporal measurement scales, the aerial photograph and TLS estimates yielded similar results for bluff retreat rate and total mass of sediment derived from bluffs, with bluffs in the Le Sueur watershed yielding 135 000 ± 39 000 Mg/yr of fine sediment. Comparing this value to the average annual total suspended solids (TSS) load determined from gauging from 2000 to 2010, we determined that bluffs comprise 57 ± 16% of the total TSS load, making bluffs the single most abundant fine sediment source in the basin. Copyright © 2012 John Wiley & Sons, Ltd.     

Kos Plateau Tuff (KPT) on Kalymnos island, Aegean volcanic arc: A geochemical approach

Thirteen pumice samples from the D and E ignimbrite units of Kalymnos Tuff have been analyzed for their biotite and feldspar phenocryst mineral chemistry and for bulk major and 20 trace, including 14 Rare Earth elements, to define and compare their petrochemistry with the Kos Plateau Tuff (KPT). For the same purpose major element analyses were obtained from Kalymnos Tuff and KPT glasses. Both KPT and Kalymnos pumice lapilli are rhyolites characterized by a well-developed ‘silky’ texture and roundish quartz. Phenocrysts of biotite and feldspars (sanidine, oligoclase) from both tuffs display compositional overlap. Crystals are charac-terized by undulatory extinction (quartz), fractures (sanidine, oligoclase) and bent cleavages (biotite) due to the explosive origin of their host. Both tuffs show well-defined petrogenetic trends and extensive compositional overlaps on major and trace element variation diagrams suggesting that they are consanguineous. However, D ignimbrite samples are more evolved than those obtained from E ignimbrite as indicated from major elements, alkali earths (Ba, Rb, Sr), immobile (Zr, Y), compatible (V) and hygromagmatophile trace element (Th) distributions. This evidence indicates a stratified magma chamber under a ～16 Km caldera superstructure which is mostly submarine.     

Katrina and Migration: Evacuation and Return by African Americans and Vietnamese Americans in an Eastern New Orleans Suburb

Hurricane Katrina constitutes the most costly natural as well as technology-induced disaster, in terms of both human suffering and financial loss in the history of the United States. Even years later, it continues to profoundly impact the livelihoods and the mental and physical health of those who have experienced evacuation and return and those who have begun lives anew elsewhere. Our study focuses on these geographical processes associated with the Katrina disaster experiences of African Americans and Vietnamese Americans comprising an overwhelming majority (93.4 percent) of residents in a racially mixed pre-Katrina eastern New Orleans neighborhood. We examine the spatial morphology of routes, volumes, and frequencies of evacuees; their return rates and experiences; and rationales and motivations to return or stay. The conceptual framework is based on the disaster migration, place attachment, and social network literature. Both quantitative and qualitative evidence indicates that the evacuation and return experiences of each minority group substantially differed, especially among African American women, and this was strongly influenced by existing social networks.     

Women in geography in the 21st century. Introductory Remarks: Structure,Agency, and Women Geographers in Academia at the End of the Long Twentieth Century

This paper provides an introduction to the set of articles presented in the focus section Women in Geography in the 21st Century. The paper argues that feminist geographers should view their professional biographies in a structure-agency context. Such a theoretical perspective views events that are commonly thought to be unique and attributable to individual merit or foible as the outcome instead of interactions between actors and social structures. Creating genuinely equal opportunities in geography departments for women and others who are different from the able-bodied, middle-class, white heterosexual male model of “the geographer” depends upon challenges to and transformations of the structures which bear on the discipline, rather than solely upon individual initiative.     

Bio-gentrification: vulnerability bio-value chains in gentrifying neighbourhoods†

In this paper, I develop the concept of “bio-gentrification” as a way to broaden critical theoretical debates on the relationship between gentrification and “social mixing” policies. Bio-gentrification weds urban Marxist political economic insights to the neo-Foucauldian notion of biopower. The former stresses spatial tactics of removal and displacement and value generated through land and property. The latter assesses a wider terrain of spatial tactics, their relationship to knowledge produced about humans as living beings, and their alignment with capitalist urbanization. The Vancouver example illuminates how social mixing “truths” and practices to which they are tied generate value by naturalizing human insecurity in situ and transforming the biological existence of disadvantaged peoples into raw material for profit through a process that can be conceptualized as a “vulnerability bio-value chain.” Bio-gentrification refers to the tension between removal and embedding of disadvantaged peoples and points to the need for a bio-gentrification politics to confront this dynamic.     

Radially truncated galactic discs

We present the first results of a systematic analysis of radially truncated exponential discs for four galaxies of a complete sample of disc-dominated edge-on spiral galaxies.
The discs of our sample galaxies are truncated at similar radii on either side of their centres. With the possible exception of the disc of ESO 416-G25, it appears that the truncations in our sample galaxies are closely symmetric, in terms of both their sharpness and the truncation length. However, the truncations occur over a larger region and not as abruptly as found in previous studies.
We show that the truncated luminosity distributions of our sample galaxies, if also present in the mass distributions, comfortably meet the requirements for longevity. The formation and maintenance of disc truncations are probably closely related to stability requirements for galactic discs.     

Fingerprinting of soil organic matter as a proxy for assessing climate and vegetation changes in last interglacial palaeosols (Veldwezelt, Belgium)

Soil characteristics in palaeosols are an important source of information on past climate and vegetation. Fingerprinting of soil organic matter (SOM) by pyrolysis-GC/MS is assessed as a proxy for palaeo-reconstruction in the complex of humic layers on top of the Rocourt pedosequence in the Veldwezelt-Hezerwater outcrop (Belgian loess belt). The fingerprints of the extractable SOM of different soil units are related to total organic carbon content, δ¹³C and grain-size analysis. Combined results indicate that the lower unit of the humic complex reflects a stable soil surface, allowing SOM build-up, intensive microbial activity and high decomposition. Higher in the profile, decomposition and microbial activity decrease. This is supported by a shift in the isotopic signal, an increased U ratio and evidence of wildfires. Although the chemical composition of the extracted SOM differed greatly from recent SOM, fingerprinting yielded detailed new information on SOM degree of decomposition and microbial contribution, allowing the reconstruction of palaeo-environmental conditions during pedogenesis.     

Long-range transport of Asian emissions to the West Pacific tropical tropopause layer

Journal of Atmospheric Chemistry - Rapid transport by deep convection is an important mechanism for delivering surface emissions of reactive halocarbons and other trace species to the tropical...     

Effects of Bioirrigation and Salinity on Arsenic Distributions in Ferruginous Concretions from Salt Marsh Sediment Cores (Southern Brazil)

Arsenic (As), iron (Fe), and manganese (Mn) contents were measured in sediment nodules and associated pore waters obtained from sediment cores collected from a salt marsh on Pólvora Island (southern Brazil). Sediment cores were obtained when brackish water dominated the estuary, at two different environments: an unvegetated mudflat colonized by crabs (Neohelice granulata), and a low intertidal stand vegetated by Spartina alterniflora. We determined the percentage of nodules in each depth interval of the cores, along with redox potential, and As, Fe, and Mn contents of the nodules. The mineralogy of the nodules was investigated, and results showed they are mainly composed by quartz, phyllosilicates, and amorphous Fe–Mn oxides/oxyhydroxides. Pore water results showed that bioturbation by local crabs supports oxygen penetration to depths of ca. 25 cm below the salt marsh surface, with lower Fe contents in pore water associated with the brackish period. However, S. alterniflora growth appears to have a greater impact on sediment geochemistry of Fe, Mn, and possibly As due to sulfate reduction and the associated decrease in pore water pH. Higher Fe concentrations were observed in the pore waters during the period of brackish water dominance, which also corresponded to the S. alterniflora growth season. The study demonstrates that differences in geochemical conditions (e.g., Fe content) that can develop in salt marsh sediments owing to different types of bioirrigation processes (i.e., bioirrigation driven by crabs versus that related to the growth of S. alterniflora) play important roles in the biogeochemical cycling of As.