Geochemical and mineralogical impacts of H2SO4 on clays between pH 5.0 and −3.0

Natural and constructed clay liners are routinely used to contain waste and wastewater. The impact of acidic solutions on the geochemistry and mineralogy of clays has been widely investigated in relation to acid mine drainage systems at pH > 1.0. The impact of H₂SO₄ leachate characterized by pH < 1.0 and potentially negative pH values on the geochemistry and mineralogy of clays is, however, not clear. Thus, laboratory batch experiments were conducted on three natural clay samples with different mass ratios of smectite, illite and kaolinite to investigate the impact of H₂SO₄ on the geochemistry and mineralogy of aluminosilicates from pH 5.0 to −3.0. Batch testing was conducted at seven pH treatments (5.0, 3.0, 1.0, 0.0, −1.0, −2.0 and −3.0) using standardized H₂SO₄ solutions for four exposure periods (14, 90, 180, and 365 d). Aqueous geochemical and XRD analyses showed: increased dissolution of aluminosilicates with decreasing pH and increasing exposure period, that smectite was more susceptible to dissolution than illite and kaolinite, precipitation of an amorphous silica phase occurred at pH ? 0.0, and anhydrite precipitated in Ca-rich clays at pH ? −1.0. In addition, global dissolution rates were calculated for the clays and showed good agreement to literature smectite, illite and kaolinite dissolution rates, which suggests global dissolution rates for complex clays could be determined from monomineralic studies. A stepwise conceptual model of the impact of H₂SO₄ on aluminosilicate geochemistry and mineralogy between pH 5.0 and −3.0 is proposed.     

Concentration and spatial variability of mercury and other heavy metals in surface soil samples of periurban waste mine tailing along a transect in the Almadén mining district (Spain)

Mercury (Hg) is one of the elements with increasing environmental significance. A total of 22 samples (soils, rocks and gels) were collected along a 6 km transect around the Valdeazogues River valley in the southwest of the Iberian Peninsula (Almadén, Spain). Samples were characterized by different soil types of depositional sequences associated with mining tailings, type and system tracts: 15 surface soil samples included in the transect; 3 of a Haploxerept soil profile developed on slates; 2 of quartzite and slates rocks (reference rocks in the area). Moreover, two of a gel substance (in the lower tract of the river). Soil samples were analyzed for Hg, Cu, Ni, Cr, V, Pb, Cd and As, as well as for organic matter, pH abrasion and calcium carbonate content. All samples were collected from the Almadén mining district. The level of occurrence of the elements (especially Hg) and the effect of some properties on its concentration distributions were investigated. The total mercury contents varied in the range 7,315–3.44 mg kg⁻¹. The mean concentration of total mercury in soils and rocks was 477.03 mg kg⁻¹dry mass. This value is very high compared to the regional background value of other areas. Only rarely is it higher than 1%: in one sample (7,315 mg kg⁻¹) it was almost eight times in comparison with the affected zones, with a high value of 1,000 mg kg⁻¹. Significant differences between samples were found in the total content of mercury. A large percentage of the samples registered detectable levels of V, Cr, Ni, Pb, As and Cu. Cd readings were below the detectable range for all samples tested. Cr mean concentration was 216.95 mg kg⁻¹ (minimun concentration 86, maximun 358); V mean concentration was 119.09 mg kg⁻¹ (minimun concentration 69, maximun 1,209); As mean concentration was 51.24 mg kg⁻¹ (minimun 13.3 and maximun 319.4); Ni mean concentration was 45.64 mg kg⁻¹ (minimun concentration 21.2 and maximun 125.6); Cu mean concentration was 33.25 mg kg⁻¹ (minimun concentration 19.3 and maximun 135); Pb mean concentration was 15.19 mg kg⁻¹ (minimun 1.12 and maximun 1013). Metal distribution generally showed spatial variability ascribed to significant anthropogenic perturbation by mining tailing type. Hg showed vertical profile characterized by surface enrichment, with concentrations in the upper layer (93.7–82.2 mg kg⁻¹ in front of 3.4 of the rock value) exceeding, in several occasions, the background value. The results obtained denote a potential toxicity of some heavy metals in some of the studied samples. Water-soluble mercury could enter the aquatic system and accumulate in sediments. Mercury and other heavy metals contamination depended on the duration and intensity of mining activities.     

Anatomical variation of five plant species along an elevation gradient in Mexico City basin within the Trans-Mexican Volcanic Belt,Mexico

Change in environmental conditions with altitudinal gradients induces morpho-anatomical variations in plants that have been poorly documented in intertropical regions. Five species with three life forms, cryptophyte (Alchemilla procumbens, Geranium seemannii), hemicryptophyte (Acaena elongata, Lupinus montanus), and phanerophyte (Symphoricarpos microphyllus), distributed along an altitudinal gradient in the Sierra Nevada of central Mexico, were studied. The aims were to identify and evaluate their morpho-anatomical modifications under the hypothesis that the sizes of individuals and of their wood and leaf cell types decrease as elevation increases. Three individuals per species per site were collected at seven locations along the altitudinal gradient (2949-3952 m). Their morpho-anatomical characters were analyzed through multiple regression analyses. Elevation was the variable that best explained anatomical changes in the leaf and wood of the five species. Canopy density and potassium content in the soil also contributed to explain the variation in anatomical variables along the gradient. As elevation increased a bimodal pattern was observed in various anatomical characters as in the leaf width of A. elongata, A. procumbens and G. seemannii and in the vessel diameter of A. procumbens, G. seemannii, and L. montanus. Other features as the vessel diameter of A. elongata, the fiber length of S. microphyllus, and the ray width of A. elongata increased as the elevation increased. Anatomical traits have a tendency to decrease in size but just toward the end of the gradient, which is probably related to changes in canopy density. The plant response to the altitudinal gradient is more focused on anatomical adaptations than morphological variation; it is also species dependent.     

Symmetries and Bifurcations in the Sitnikov Problem

We present some qualitative and numerical results of the Sitnikov problem, a special case of the three-body problem, which offers a great variety of motions as the non-integrable systems typically do. We study the symmetries of the problem and we use them as well as the stroboscopic Poincarée map (at the pericenter of the primaries) to calculate the symmetry lines and their dynamics when the parameter changes, obtaining information about the families of periodic orbits and their bifurcations in four revolutions of the primaries. We introduce the semimap to obtain the fundamental lines l ₁. The origin produces new families of periodic orbits, and we show the bifurcation diagrams in a wide interval of the eccentricity (0 0.97). A pattern of bifurcations was found.This revised version was published online in October 2005 with corrections to the Cover Date.     

Sustainability in a materials world

Many adverse impacts on the environment can be directly related to the materials dispersed to the environment during processing or use, or after use as refuse and waste. Some materials, such as toxic wastes, are a major concern because they create immediate problems with longerterm effects. Gases released by major manufacturing industries can contribute to long-term regional and global problems such as acid rain or increased carbon dioxide in the atmosphere. The use of other materials, however, appears to be more benign or strictly localized in their impacts. If the current per capita level of material consumption in the United States was achieved worldwide, it would create major stresses on both resource adequacy and the environment. In fact, stresses have been created and will continue from this consumption style (developed countries) even if others don't achieve them.Correspondence should be directed to Earle B. Amey, U.S. Geological Survey, National Center 983, Reston, Virginia 20192.     

Forces and ionic transport between mica surfaces: implications for pressure solution

Using a surface forces apparatus (SFA), we have studied the interactions between mica surfaces in pure and mixed NaCl and CaCl₂ solutions at relevant geological conditions of pressure and electrolyte composition. Our results show that the short-range (0-50 Å) colloidal forces, including attractive van der Waals and ion-correlation forces, repulsive electrostatic forces, and oscillatory or monotonically repulsive hydration (surface-induced water structure-dependent) forces are involved in different stages of pressure solution. These forces depend on the type (Na⁺, Ca²⁺, and H⁺) and concentration (6-600 mM) of the cations present in the solution. Equilibrium water film thicknesses were measured as a function of the applied (normal) pressure up to 50 MPa (500 atm) and ranged from 30 to 0 Å at pressures above 10 MPa (100 atm). Measurements were also made of the rates of diffusion and exchange of ions into and out of such ultrathin films, and on the nucleation and growth of ionic crystallites on and between the surfaces, which occurred only in the presence of calcium ions. Diffusion of ions into and out of structured water films as thin as one to five water molecules (3 to 15 Å) were found to be surprisingly rapid and never less than two orders of magnitude below the diffusion in bulk water. In contrast, the rates of binding and exchange of ions to the surfaces were found to be the rate-limiting steps to adsorption and crystal formation. These findings imply that, for certain systems or conditions, pressure solution rates could be limited by surface reactions rather than by ion diffusion in thin fluid films.     

Variations of the Treescape in Relation to Urban Development in a Chinese City: The Case of Nanjing*

Urban trees, as prominent and pertinent landscape elements of cities, are increasingly studied by both practitioners and academics. Trees in Chinese cities have hitherto received little detailed analysis from the viewpoint of urban forestry or landscape analysis. This study attempts a comprehensive evaluation of the tree population in Nanjing, focusing on the association between urban development and treescape attributes. Six districts, covering the main built‐up area of 130 km², formed the study area. Nine land‐use types with varied urban morphology and three urban zones with different development history were identified, within which subareas and trees were sampled for field study of tree dimensions, tree performance, and site characteristics. Statistical analyses on the 6,527 surveyed trees verify that tree performance is significantly associated with land use, site condition, and related human activities. Treescape is associated with housing ownership, town planning, and the history of urban expansion. The relationship between treescape and urban landscape units can furnish hints for improved urban forest planning and management and better coordination between planners and landscape professionals.     

Structure and dynamics of mangrove forests along a flooding gradient

The zonation patterns ofAvicennia bicolor andRhizophora racemosa were studied in a mangrove forest on the Pacific Coast of Costa Rica. Comparisons were made between the establishment, survival, and growth of both species in three plots, 1 ha each, located along the flooding gradient. Based on cohort analysis and reciprocal planting observations, it was concluded that species zonation was primarily regulated by the depth of tidal inundation and the differential ability of the propagules to become established. However, tidal sorting was not the only operative factor related to inundation. Drought and probably high soil salinities limited the survival and growth ofR. racemosa in the landward sections of the forest. Tidal sorting, however, confined propagules to zones where they probably had the highest likelihood of contributing to another generation.     

Downscaling Landsat-8 land surface temperature maps in diverse urban landscapes using multivariate adaptive regression splines and very high resolution auxiliary data

ABSTRACT

We propose a method for spatial downscaling of Landsat 8-derived LST maps from 100(30?m) resolution down to 2–4?m with the use of the Multiple Adaptive Regression Splines (MARS) models coupled with very high resolution auxiliary data derived from hyperspectral aerial imagery and large-scale topographic maps. We applied the method to four Landsat 8 scenes, two collected in summer and two in winter, for three British towns collectively representing a variety of urban form. We used several spectral indices as well as fractional coverage of water and paved surfaces as LST predictors, and applied a novel method for the correction of temporal mismatch between spectral indices derived from aerial and satellite imagery captured at different dates, allowing for the application of the downscaling method for multiple dates without the need for repeating the aerial survey. Our results suggest that the method performed well for the summer dates, achieving RMSE of 1.40–1.83?K prior to and 0.76–1.21?K after correction for residuals. We conclude that the MARS models, by addressing the non-linear relationship of LST at coarse and fine spatial resolutions, can be successfully applied to produce high resolution LST maps suitable for studies of urban thermal environment at local scales.