Aquatic equilibrium models

Aquatic Equilibrium Model Increased chemistry capability Data intensive, parameters may not be available Models at a developmental stage... 

Hoffman, M. R. (1981). Thermodynamic, kinetic and extra-thermodynamic considerations in the development of equilibrium models for aquatic systems. Environ. Sci. Technol. 15,345-353. 

This paper discusses (1) soil and groundwater and (2) aquatic equilibrium and ranking models. The second category deals with the chemical speciation in soil and groundwater, and with the environmental rating of waste sites, in cases where detailed modeling is not desirable. 

This paper presents a review discussion of soil, groundwater, aquatic equilibrium and ranking modeling concepts including selected documented models. Watershed models are not discussed, since the work of Knisel (1) is one of the most representative watershed computerized packages. 

TT heoretical equilibrium models can be established for oxidation-reduc-- tion systems in natural waters in much the same way that acid-base or solubility models have been developed and found useful in interpreting observed concentrations of ions and other materials. To relate the theoretical models for redox processes to observed conditions and processes in the aquatic environment is, however, much more difficult and cannot be done as rigorously. Primarily this situation occurs because true oxidation-reduction equilibrium is not observed in any natural aquatic system this is partly because of the extreme slowness of most oxidation-... 

Nenes A, Pandis SN, Pilinis C (1998) ISORROPIA a new thermodynamic equilibrium model for multiphase multicomponent inorganic aerosols. Aquat Geochem 4 123-152... 

Thomann, R.V., J.P. Connolly, and T.F. Parkerton. 1992. An equilibrium model of organic chemical accumulation in aquatic food webs with sediment interaction. Environ. Toxicol. Chem. 11 615-629. Thurston, R.V. and P.C. Gehrke. 1993. In Fish Physiology, Toxicology, and Water Quality management. Proceedings of an International Symposium, Sacramento, California, USA, September 18-20,1990. R.C. Russo and R.V. Thurston, Eds., p. 95. Environmental Research Laboratory Office of Research and Development. EPA, Athens, Georgia. EP/600/R-93/157. 

In aquatic ecosystems, complexation to organic and inorganic ligands and competition between toxic metals and Ca or Mg ions for biological adsorption sites reduce the actual amount of metal available for uptake by organisms. Chemical equilibrium models applicable to natural systems include RANDOM (Murray and Linder 1983 ... 

For the matrix extrapolation process for nonpolar organic compounds in most surface waters, the applicability of a first-order, single-compartment equilibrium model means that the total aquatic concentration of the toxicant may be considered... 

Before discussing the chemical dynamics of estuarine systems it is important to briefly review some of the basic principles of thermodynamic or equilibrium models and kinetics that are relevant to upcoming discussions in aquatic chemistry. Similarly, the fundamental properties of freshwater and seawater are discussed because of the importance of salinity gradients and their effects on estuarine chemistry. 

Equilibrium models provide information about the chemistry of the system at equilibrium but will not tell you anything about the kinetics with which the system reached equilibrium state. The basic objectives in using equilibrium models in estuarine/aquatic chemistry is to calculate equilibrium compositions in natural waters, to determine the amount of energy needed to make certain reactions occur, and to ascertain how far a system may be from equilibrium. 

Millero F. J. and Pierrot D. (1998) A chemical equilibrium model for natural waters. Aquat. Geochem. 4, 153-199. 

Natural waters obtain their equilibrium composition through a variety of chemical reactions and physicochemical processes. In this chapter we consider principles and applications of two alternative models for natural water systems thermodynamic models and kinetic models. Thermodynamic, or equilibrium, models for natural waters have been developed more extensively than kinetic models. They are simpler in that they require less information, but they are nevertheless powerful when applied within their proper limits. Equilibrium models for aquatic systems receive the greater attention in this book. However, kinetic interpretations are needed in description of natural waters when the assumptions of equilibrium models no longer apply. Because rates of different chemical reactions in water and sediments can differ enormously, kinetic and equilibrium are often needed in the same system. 

Development of the Nonlinear Fluorescence Quenching Model. The main function of the nonlinear model is to relate aquatic equilibrium considerations based on conventional solution thermodynamics to observed fluorescence intensity changes occurring as metal ion is added at fixed pH. The fundamental relationship equating fluorescence quenching to complexation is present in equation 1. 

Alberts, J. J. and Giesy J.P., Conditional stability constants of trace metals and naturally occurring humic materials Application in equilibrium models and verification with field data. In Aquatic and Terrestrial Humic Materials, R.F. Christman and E.T. Gjessing (Eds.),Ann Arbor Science Publishers, Ann Arbor, Ml, 1983, pp538. 

Quantitative analysis of different reaction pathways for the transformation of aquated sulfur dioxide in atmospheric droplet systems has been a major objective of the research conducted in the principal investigator s laboratory for the last four years. Available thermodynamic and kinetic data for the aqueous-phase reactions of SO2 have been incorporated into a dynamic model of the chemistry of urban fog that has been developed by Jacob and Hoffmann (23) and Hoffmann and Calvert (39). The fog and cloud water models developed by them are hybrid kinetic and equilibrium models that consider the major chemical reactions likely to take place in atmospheric water droplets. Model results have verified that... 

Fortunately, equation (1) is adequate for most solution reactions near room temperature, and several computer equilibrium models make these corrections if the required enthalpy values are available. Unfortunately, enthalpy data for many important solution species (e.g., metal ion species and ion pairs) have not been determined. In a few instances the temperature dependence of a reaction is very well known. A particularily relevant example for aquatic chemistry is log K for water which is given by. 

Thomann RV, Connolly JP, Parkerton TF (1992) An equilibrium model of organic chemical accumulation in aquatic food webs with sediment interaction. Environ. Toxicol Chem 11 615-629. 

Thomann, R.V. 1981. Equilibrium model of fate of microcontaminants in diverse aquatic food chains. Canadian Journal of Fisheries and Aquatic Sciences 38 280-296. 

An ecosystem can be thought of as a representative segment or model of the environment in which one is interested. Three such model ecosystems will be discussed (Figures 1 and 2). A terrestrial model, a model pond, and a model ecosystem, which combines the first two models, are described in terms of equilibrium schemes and compartmental parameters. The selection of a particular model will depend on the questions asked regarding the chemical. For example, if one is interested in the partitioning behavior of a soil-applied pesticide the terrestrial model would be employed. The model pond would be selected for aquatic partitioning questions and the model ecosystem would be employed if overall environmental distribution is considered. 

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