The Thermodynamics and Some Practical Aspects of Zinc Adsorption on Calcite, Dolomite, and Calcian-Magnesite Minerals

Zinc is one of the essential elements required for the normal growth plants. The total amount of zinc commonly occurring in soils is usually many times greater than that necessary to supply the needs of actively growing plants. The ability of the soil to fix zinc in form unavailable for plant use, however, has made the zinc deficiency disease an important plant nutrition problem in the major fruit and nut growing regions of the West. Fixation mechanisms which have been postulated as contributing to zinc deficiency include organic complexes, precipitation of insoluble inorganic salts, and strong zinc-clay interactions. It may be possible that in certain soils naturally occurring soil minerals, other than the clay minerals, may also exert an influence on the capacity of the soil to retain zinc. The accumulation of lime minerals is a distinguishing profile characteristic of soils in arid and semi-arid region and semi-arid regions. These minerals include: calcite (CaCO3), dolomite (CaMg(CO3)2), and magnesite (MgCO3). Despite the widespread occurrence of these minerals in the soil system, relatively few data exist which specifically isolate the interaction between cations in solution and the solid phase of the above-named lime minerals

Development of Procedures to Evaluate Salinity Management Strategies in Irrigation Return Flows

The salinity added irrigation return flows is a major problem in rivers draining agricultural lands throughout the arid regions of the world, and many irrigation water management alternatives have been proposed for reducing downstream salinity problems. The merits of these alternatives, however, can only be judged from reliable information on their actual effects on the salinity in rivers receiving the drainage water and the water withdrawn from the river by downstream users. Hydrosalinity models are widely used to estimate these effects to guide the selection of a policy on management of irrigation return flows. The purpose of this research was to assess the state-of-the-art of hydrosalinity modeling in order to develop a practical management tool for predicting how the salt outflow from irrigated agriculture is affected by various farm management practices. A review of the state-of-the-art of hydrosalinity models identified one of the major gaps in modeling as inadequate understanding and representation of the quantity and quality interrelationships between surface water, drainage water, and groundwater. Most models predict relatively constant levels of salinity over time in surface drains during the irrigation season and an increase in concentration in similar drains at other locations during the nonirrigation season. The study also identified taht a site specific equilibrium threshold conentration (TC) of dissolved solids can be adequately estimated and represented in a model. Salt concentration above the TC would result in precipitation of salts within the soil profile. Higher TC values would, however, exist in the unsaturated soil. Based on these new concepts, salinity in the return flows was modeled as a composite of individual component outflows from the unsaturated zones and the saturated groundwater zone, and represents the interrelationships among surface water, drainage water, and groundwater. The model termed BSAM-SALT was tested using field data from irrigated areas in Grand Valley, Colorado, and the Circleville sub-basin of the Sevier River Basin in Utah. A set of managment runs was made to demonstrate the utility of the model in predicting the salt loading caused by irrigated agriculture in the Grand Valley, Colorado, area

Identification and Modeling the Impact of Marine Shale Bedrock on Groundwater and Stream Salinity: Upper Colorado River Basin

Recent studies have shown that groundwater is a major contributor to stream salinity in the Upper Colorado River Basin. The primary salt sources are the marine shales and shale residuum that underlie the soils of much of the basin. A field site in the Price River Basin, a tributary to the Green and Colorado Rivers, was selected to study the physical and chemical factors that control the interactions between groundwater and these shales. Preliminary data were available at the site as a result of a Bureau of Reclamation study conducted by CH2M Hill. On the basis of the CH2M Hill study and the additional data collected during this study groundwater flow paths, salt transport and weathering processes were identified. Results show that the groundwater evolved from a calcium-bicarbonate water to a sodium-sulfate water with depth and distance along the flow paths. Geochemical equilibrium modeling and mass balance computations were performed using the USGS models PHREEQE and BALANCE. A preliminary saturated-unsaturated two-dimensional flow model (UNSAT) was implemented along the identified groundwater flow path. Once a satisfactory flow calibration was achieved, a solute transport model was then implemented to examine the relative importance of advective, dispersive and diffusive mixing processes along the flow profile. Preliminary management runs were made to study the effect of possible changes in land use practices. Results of these hypothetical cases suggest that water conservation methods (improved irrigation efficiency, canal lining and retiring irrigated land) will reduce return flow salt loads over the short run (about 50 years), when the transport of salts by displacement is most important. However, these salinity control alternatives are much less effective in the long range (\u3e 50 years) because the diffuse salt loading from underlying marine shales is unaffected by groundwater flow rates in the alluvium. Although additional field data must be collected for verification the proposed model is a realistic first step towards a quantitative physically based approach to land use-salinity control issues

Bacterial Absorption on Soils--Thermodynamics

Laboratory studies on the adsorption of bacteria onto soils and activated carbon were undertaken to evaluate the role of the process in removal of bacteria from groundwater. It was hypothesized that removal of bacteria from water passing through soil would be primarily due to adsorption in which case the bacteria would behave in a manner similar to colloidal particles or chemical molecules. The basic kinetics of uptake of Staphylococcus aureus were determined on activated carbon, a highly adsorbing material chemically speaking. Once the technique was worked out and adsorption demonstrated to take place, sand, clay, and Mendon silt loam were studied. Uptake of bacteria was observed microscopically on both activated carbon and clay. Sand showed no measureable uptake of bacteria. Mendon silt loam was also used in competitive adsorption studies. Sodium chloride, sodium lauryl sulfate and peptone were used and their effects on adsorption of the test organism measured. Results clearly showed uptake of the bacteria with equilibrium reached within one hour. Conventional chemical thermodynamics can be applied to bacterial adsorption onto soils with the determination of Langmiur type isotherms and the subsequent evaluation o

1972 Progress Report: Soil as a Factor in Modelling the Phosphorus Cycle in the Desert Ecosystem

The research conducted in 1972 emphasized a nutrient assay of soil from the Curlew Valley site, phosphorus inventory of the vegetation and rabbit droppings, and further chemical characterization of soil phosphorus, which also included determination of the kinetics and energetics of the calcium carbonate-phosphate system