Geochemistry of lead contaminated wetland soils amended with phosphorus

To remediate Pb contaminated soils it is proposed that phosphorus can be amended to the soils to transform the Pb into poorly soluble Pb-phosphate mineral phases. However, remediation strategies must account for variable Pb speciation and site-specific factors. In this study soil mineralogy and Pb speciation in soils from P-amended field trials at sites within the Coeur d’Alene River Basin in Idaho, USA were investigated. The soils are contaminated from mining activities and are enriched with Fe and Mn. Selective extraction of the soils indicated that the Fe oxides are poorly crystalline. XRD of the soil clay size fractions identified quartz, muscovite, kaolinite, siderite, lepidocrocite, and chlorite minerals. Amendment with P fertilizer dissolved the siderite. No Pb–phosphate minerals were detected by XRD. Electron microprobe analysis showed direct correlations between Pb, Fe, and Mn in the unamended soils, and negative correlations between Pb and Si. Lead and Mn were strongly correlated. In the amended soils Fe and P were strongly correlated. Results indicate that the Pb is associated with poorly crystalline Fe and Mn oxides, and that added P is primarily associated with Fe oxide phases. Comparisons of pore water Pb concentrations with chloropyromorphite and plumbogummite solubility suggest that in the phosphate-amended soils the pore waters are undersaturated in these phases, whereas several of the control soil pore waters were oversaturated, indicating the added phosphate suppressed the Pb solubility. Results from this research provide insight into the geochemistry occurring in the P-remediated soils that will help in making management and remediation decisions.     

Uranium transport through fractured silicic tuff and relative retention in areas with distinct fracture characteristics

The Nopal I uranium (U) deposit, in the Pefia Blanca District, Chihuahua, Mexico, has been identified as analogous in some regards to the candidate U.S. high-level waste (HLW) repository at Yucca Mountain, Nevada. Uranium transport at the Nopal I deposit has been studied to investigate mechanisms by which HLW components could be transported through silicic tuff over long time periods. This investigation focused on approximately 1400 m2 of essentially continuous bedrock outcrop spanning the Nopal I deposit and surrounding host tuff. Data collected document: (i) the distributions of U within and around the Nopal I deposit, (ii) the distribution and characteristics of the fracture network within and surrounding the deposit, and (iii) the transport of U away from the deposit mainly along fracture paths. Uranium-series isotopic measurements indicate mobilization of U along the margin of the deposit within the last 1 Ma and significant U transport at about 54 Ka. Transport of U away from the Nopal I deposit along a few relatively continuous mesofractures achieved maximum distances at least 20 times greater than transport through the general fracture network composed of thousands of less continuous microfractures within and surrounding the deposit. Uranium transport away from the deposit appears to be largely independent of variations in the general fracture network pattern. Transport of U away from individual micro- and meso-fractures into homogeneous, unfractured tuff matrix appears limited to distances less than 1 mm. At the Nopal I deposit, matrix diffusion does not appear to have been an important factor for retardation of U. This analysis suggests a ranking for U retention: (i) microfracture network retention mesofracture retention, and (ii) individual microfracture retention matrix retention.     

Liquefaction-induced ground deformations at Hotel Sapanca during Kocaeli (Izmit),Turkey earthquake

This paper presents a study of liquefaction-induced ground deformations at the Hotel Sapanca site during the 1999 Kocaeli (Izmit)—Turkey earthquake. The paper discusses: (1) observed ground deformations and displacements after the earthquake, (2) the results of field investigations by means of borings and in situ index tests including standard penetration tests (SPT), static cone penetration tests (CPT) and piezocone (CPTU) tests, (3) analyses of observed ground settlements and lateral deformations by a suite of methods, and (4) comparisons of observed and calculated ground movements.     

A new general circulation model: formulation and preliminary results in a single- and multi-processor environment

This article describes a new general circulation model (GCM) developed jointly by The University of New South Wales (UNSW) and the University of Hamburg. The model is versatile in that it can be run as a medium-range (1 to 15 days) global numerical weather prediction (NWP) model; as an extended range (15 to 30 days) NWP model; and as a GCM for periods extending from seasons, through annual and decadal periods, and beyond. The model can be coupled with ocean models that vary in complexity from simple "swamp" oceans to complex ocean GCMs. The atmospheric GCM also has a number of novel features, particularly in the numerical integration scheme which is a high-order, mass-conserving, semi-implicit semi-Lagrangian scheme, thereby removing the stability restriction on the time-step and allowing efficient long-term integrations. The emphasis here will be on demonstrating that the new model performs effectively on the usual measures of skill (statistics such as mean errors, root-mean-square errors and anomaly correlations) in several standard applications upon which new models usually are assessed. These applications include medium range weather forecasts out to 10 days on a daily basis over a one year period; a limited 10-year simulation climatology, prediction of atmospheric anomalies using SST anomalies in an El Nino year; and an alternative two-way approach to regional modelling (the "down-scaling problem") made possible because the unconditional stability of the semi-implicit, semi-Lagrangian formulation permits large variations in grid spacing without changing the time step size. Finally, the model is run on a variety of parallel computing platforms and it is shown that near-linear speed-up can be attained. This is significant for both medium range NWP and very long-term GCM integrations. Received: 28 February 1996 / Accepted: 30 July 1996     

Soil moisture prediction over the Australian continent

Summary This paper describes an attempt to model soil moisture over the Australian continent with an integrated system of dynamic models and a Geographic Information System (GIS) data base. A land surface scheme with improved treatment of soil hydrological processes is described. The non-linear relationships between soil hydraulic conductivity, matric potential and soil moisture are derived from the Broadbridge and White soil model. For a single location, the prediction of the scheme is in good agreement with the measurements of the Hydrological and Atmospheric Pilot Experiment (HAPEX). High resolution atmospheric and geographic data are used in soil moisture prediction over the Australian continent. The importance of reliable land surface parameters is emphasized and details are given for deriving the parameters from a GIS. Predicted soil moisture patterns over the Australian continent in summer, with a 50 km spatial resolution, are found to be closely related to the distribution of soil types, apart from isolated areas and times under the influence of precipitation. This is consistent with the notion that the Australian continent in summer is generally under water stress. In contrast, predicted soil temperatures are more closely related to radiation patterns and changes in atmospheric circulation. The simulation can provide details of soil moisture evolution both in space and time, that are very useful for studies of land use sustainability, such as plant growth modelling and soil erosion prediction.With 12 Figures     

The effects of bushfires on hydrological processes using a paired-catchment analysis

Summary Several problems associated with capturing the effects of bushfires on hydrological processes in the Goulburn River catchment (6810km²), Hunter Valley, Australia are investigated using a paired-catchment analysis. It is suggested, first, that the within-year-missing data, as defined in this paper, need to be examined carefully when using the double-mass curve of annual total discharge in a paired-catchment analysis. Second, in order to provide an accurate precipitation background, which is one of the most important prerequisites for a paired-catchment analysis, the use of annual average precipitation is strongly recommended together with annual total precipitation when there are large amounts of within-year-missing data. Third, caution is needed in comparing multi-year average precipitation and streamflow data before and after the fire when the data series is not statistically long enough, since the average values for precipitation and streamflow over a different number of years may produce completely contrasting results. Fourth, the analysis of the flow duration curve, which is another useful technique in paired-catchment analysis, needs to be interpreted from the precipitation duration curve. This is because the change of flow duration curve can be caused either from the change of precipitation or the fire. Fifth, the change in streamflow, calculated by subtracting the average streamflow for the non-fire years from the observed streamflow for the years in which fires occurred, is not an efficient way of capturing the fire effects. The problem associated with this approach is not just that the streamflow is strongly dependent on rainfall, as reported elsewhere, but also, it can lead to misinterpretation using the hydrograph when the average streamflow in non-fire years is close to the average streamflow in fire years.By taking into account the above problems there was no effect of fires found on streamflow in the Goulburn River catchment. This result contrasts with the conclusions reported from other studies that have reported an immediate increase in streamflow by experimental analyses, paired-catchment analyses or modelling studies. Instead, it is shown that the spatial pattern of precipitation over the Goulburn River catchment is more important in shaping the hydrograph than the effects of bushfires. The ratio of fire extent to catchment area is approximately 4% in this study, which we suggest is a minimum area required to identify a hydrological response to the fires. The fact that other studies have focused more on capturing the generally expected effect of an immediate increase in streamflow after fire, than on why this effect occurs, makes it highly desirable to undertake micro-meteorological experiments to obtain observed evapotranspiration data before and after fire. Also, it is important to develop a coupled soil-vegetation-atmosphere-transfer dynamic mechanism and high resolution numerical weather prediction model with a distributed hydrological model in order to simulate more realistically the effect of fire on hydrological processes.