Connectivity of the Apalachicola River flow variability and the physical and bio-optical oceanic properties of the northern West Florida Shelf

Maps of satellite-derived estimates of monthly averaged chlorophyll a concentration over the northern West Florida Shelf show interannual variations concentrated near the coastline, but also extending offshore over the shelf in a tongue-like pattern from the Apalachicola River during the late winter and early spring. These anomalies are significantly correlated with interannual variability in the flow rate of the Apalachicola River, which is linked to the precipitation anomalies over the watershed, over a region extending 150–200 km offshore out to roughly the 100 m isobath. This study examines the variability of the Apalachicola River and its impacts on the variability of water properties over the northern West Florida Shelf. A series of numerical model experiments show that episodic wind-driven offshore transport of the Apalachicola River plume is a likely physical mechanism for connecting the variability of the river discharge with oceanic variability over the middle and outer shelf.     

Spatial representation in the social interaction potential metric: an analysis of scale and parameter sensitivity

The social interaction potential (SIP) metric measures urban structural constraints on social interaction opportunities of a metropolitan region based on the time geographic concept of joint accessibility. Previous implementations of the metric used an interaction surface based on census tracts and the locations of their centroids. This has been shown to be a shortcoming, as the metric strongly depends on the scale of the zoning system in the region, making it difficult to compare the SIP metric between metropolitan regions. This research explores the role of spatial representation in the SIP metric and identifies a suitable grid-based representation that allows for comparison between regions while retaining cost-effectiveness with respect to computational burden. We also report on findings from an extensive sensitivity analysis investigating the SIP metric’s input parameters such as a travel flow congestion factor and the length of the allowable time budget for social activities. The results provide new insights on the role of the modifiable areal unit problem in the computation of time geographic measures of accessibility.     

Estimating sagebrush cover in semi-arid environments using Landsat Thematic Mapper data

Sagebrush ecosystems of the western US provide important habitat for several ungulate and vertebrate species. As a consequence of energy development, these ecosystems in Wyoming have been subjected to a variety of anthropogenic disturbances. Land managers require methodology that will allow them to consistently catalog sagebrush ecosystems and evaluate potential impact of proposed anthropogenic activities. This study addresses the utility of remotely sensed and ancillary geospatial data to estimate sagebrush cover using ordinal logistic regression. We demonstrate statistically significant prediction of ordinal sagebrush cover categories using spectral (χ² = 113; p < 0.0001) and transformed indices (χ² = 117; p < 0.0001). Both Landsat spectral bands (c-value = 0.88) and transformed indices (c-value = 0.89) can distinguish sites with closed, moderate and open cover sagebrush cover categories from no cover. The techniques described in this study can be used for estimating categories of sagebrush cover in arid ecosystems.     

Comparison and relative quality assessment of the GLC2000, GLOBCOVER,MODIS and ECOCLIMAP land cover data sets at the African continental scale

Land cover dynamics at the African continental scale is of great importance for global change studies. Actually, four satellite-derived land cover maps of Africa now available, e.g. ECOCLIMAP, GLC2000, MODIS and GLOBCOVER, are based on images acquired in the 2000s. This study aims at stressing the compliances and the discrepancies between these four land cover classifications systems. Each of them used different mapping initiatives and relies on different mapping standards, which supports the present investigation. In order to do a relative comparison of the four maps, a preamble was to reconcile their thematic legends into more aggregated categories after a projection into the same spatial resolution. Results show that the agreement between the four land cover products is between 56 and 69%. While all these land cover datasets show a reasonable agreement in terms of surface types and spatial distribution patterns, mapping of heterogeneous landscapes in the four products is not very successful. Land cover products based on remote sensing imagery can indeed significantly be improved by using smarter algorithms, better timing of image acquisition, improved class definitions. Either will help to improve the accuracy of future land cover maps at the African continental scale. Data producers may use the areas of spatial agreement for training area selection while users might need to verify the information in the areas of disagreement using additional data sources.     

An application of spatial filtering techniques for land cover mapping using TM‐images

Land cover classification using satellite imagery is commonly based on spectral information in the individual pixels. The information in neighbouring pixels is ignored. Spatial filtering techniques using information present in neighbouring pixels may however, contribute significantly to an improvement of the classification. In this study different methods of spatial filtering are applied to a part of a TM‐scene of Kenya to assess their relative reliability. The study area is characterized by extended, relatively homogeneous areas of eucalyptus forests and tea estates and by fragmentated areas of agricultural land use. Spectral information was combined with the results of different spatial filtering methods and then classified. The spatial filtering techniques applied were texture calculation by means of variance, “median minus original” filtering and fractal dimension computations using several sizes of templates. The obtained classification accuracy of several image combinations is compared using the percentage correctly classified and using an overall accuracy measure: the Kappa coefficient. It is concluded that in this case the spatial filtering techniques only slightly improve the classification. From the applied filtering methods texture calculation by means of variance yielded the best results.     

A GIS data model for public gardens

An enterprise GIS data model was developed for use in public gardens, which includes botanical gardens, arboreta, and zoos. The data model defines the representation of geographical phenomena, the attributes of each feature, and the relationships between them in order to support information management and analysis within public gardens. The data model was developed using a three‐stage process consisting of conceptual, logical, and physical design, each guided by stakeholder workshops and software testing. The data model includes the attributes of features necessary to create collection maps and perform collection analysis, and is designed to link to existing plant and animal records management systems (BG‐BASE and ZIMS) through a common key. The Public Garden Data Model consists of three modules (Base Map, Facilities and Infrastructure, and Basic Plant Records), unified into one comprehensive spatial data model for public gardens, and contains 59 feature classes and tables connected by 49 relationship classes.     

Natural analogues

Natural analogues, which are occurrences of materials or processes which are analogous to expected materials or processes in a waste repository, are used to clarify the ability of the geologic environment and engineered system to contain the waste. It is hoped that natural analogues can provide data and insight on processes which generally occur on temporal or geometric scales which are too large to be studied in laboratory or field experiments. Natural analogues have been described for the study of transport and migration of radionuclides through the backfill and host rock, and the stability of backfill, shaft seals, waste forms, and waste containers. Natural analogues have also been suggested as an aid in predicting overall repository performance.     

Experimental investigation and application of the equilibrium rutile + orthopyroxene = quartz + ilmenite

Equilibria in the Sirf (Silica-Ilmenite-Rutile-Ferrosilite) system: $${\text{SiO}}_{\text{2}} + ({\text{Mg,Fe}}){\text{TiO}}_{\text{3}} {\text{ + (Mg,Fe)SiO}}_{\text{3}} $$ have been calibrated in the range 800–1100° C and 12–26 kbar using a piston-cylinder apparatus to assess the potential of the equilibria for geobarometry in granulite facies assemblages that lack garnet. Thermodynamic calculations indicate that the two end-member equilibria involving quartz + geikielite = rutile + enstatite, and quartz + ilmenite = rutile + ferrosilite, are metastable. We therefore reversed equilibria over the compositional range Fs_40–70, using Ag₈₀Pd₂₀ capsules with \(f_{{\text{O}}_{\text{2}} } \) buffered at or near iron-wüstite. Ilmenite compositions coexisting with orthopyroxene are \(X_{{\text{MgTiO}}_{\text{3}} }^{{\text{Ilm}}} \) of 0.06 to 0.15 and \(X_{{\text{Fe}}_{\text{2}} {\text{O}}_{\text{3}} }^{{\text{Ilm}}} \) of 0.00 to 0.01, corresponding toK _D values of 13.3, 10.2, 9.0 and 8.0 (±0.5) at 800, 900, 1000 and 1100° C, respectively, whereK _D =(XMg/XFe)^Opx/(XMg/XFe)^Ilm. Pressures have been calculated using equilibria in the Sirf system for granulites from the Grenville Province of Ontario and for granulite facies xenoliths from central Mexico. Pressures are consistent with other well-calibrated geobarometers for orthopyroxeneilmenite pairs from two Mexican samples in which oxide textures appear to represent equilibrium. Geologically unreasonable pressures are obtained, however, where oxide textures are complex. Application of data from this study on the equilibrium distribution of iron and magnesium between ilmenite and orthopyroxene suggests that some ilmenite in deep crustal xenoliths is not equilibrated with coexisting pyroxene, while assemblages from exposed granulite terranes have reequilibrated during retrogression. The Sirf equilibria are sensitive to small changes in composition and may be used for determination of activity/composition (a/X) relations of orthopyroxene if an ilmenite model is specified. A symmetric regular solution model has been used for orthopyroxene in conjunction with activity models for ilmenite available from the literature to calculatea/X relations in orthopyroxene of intermediate composition. Data from this study indicate that FeSiO₃?MgSiO₃ orthopyroxene exhibits small, positive deviations from ideality over the range 800–1100°C.     

Multicomponent reactive transport modeling of uranium bioremediation field experiments

A reaction network integrating abiotic and microbially mediated reactions has been developed to simulate biostimulation field experiments at a former Uranium Mill Tailings Remedial Action (UMTRA) site in Rifle, Colorado. The reaction network was calibrated using data from the 2002 field experiment, after which it was applied without additional calibration to field experiments performed in 2003 and 2007. The robustness of the model specification is significant in that (1) the 2003 biostimulation field experiment was performed with 3 times higher acetate concentrations than the previous biostimulation in the same field plot (i.e., the 2002 experiment), and (2) the 2007 field experiment was performed in a new unperturbed plot on the same site. The biogeochemical reactive transport simulations accounted for four terminal electron-accepting processes (TEAPs), two distinct functional microbial populations, two pools of bioavailable Fe(III) minerals (iron oxides and phyllosilicate iron), uranium aqueous and surface complexation, mineral precipitation and dissolution. The conceptual model for bioavailable iron reflects recent laboratory studies with sediments from the UMTRA site that demonstrated that the bulk (∼90%) of initial Fe(III) bioreduction is associated with phyllosilicate rather than oxide forms of iron. The uranium reaction network includes a U(VI) surface complexation model based on laboratory studies with Rifle site sediments and aqueous complexation reactions that include ternary complexes (e.g., calcium-uranyl-carbonate). The bioreduced U(IV), Fe(II), and sulfide components produced during the experiments are strongly associated with the solid phases and may play an important role in long-term uranium immobilization.     

Friction characteristics of Cd-rich carbonate films on calcite surfaces: implications for compositional differentiation at the nanometer scale

Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO₃) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique. Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms. Friction vs. applied load data acquired on the films and the calcite substrate were successfully fitted to the Johnson Kendall Roberts (JKR) model for single asperity contacts. Following this model, friction differences between film and substrate at low loads were dictated by differences in adhesion, whereas at higher load they reflect differences in contact shear strength. In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0–40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system. Multilayer films of calcian-otavite displayed increasing friction with film thickness, consistent with the expectation that the film surface composition will become increasingly Cd-rich with increasing thickness. Both load- and thickness-dependence trends support the hypothesis that the contact shear strength correlates with the hydration enthalpy of the surface ions, thereby imparting friction sensitivity in the LFM to mineral-water interface composition.