Some Fundamentals of Aqueous Geochemistry

Abstract

Abstract Aqueous geochemistry is the application of chemistry to reactions between rock and natural water. Analytical chemistry, inorganic and organic chemistry, and physical chemistry are used to understand and interpret the dominant processes that effect a redistribution of the elements in man's environment. Examples of these processes are the dissolution and precipitation of minerals, adsorption and desorption of ions, oxidation-reduction or redox reactions, gas uptake or production, transformations involving organic matter, complexation and chelation, evaporation, ion exchange, and anthropogenic changes. In the field of aqueous geochemistry these processes are known to occur in a variety of environments including rain, fog, snow, soils, bedrock weathering, streams, rivers, lakes, estuaries, ground waters, subsurface brines, diagenetic environments, the formation and weathering of mineral deposits, and the global movement of elements and compounds. Aqueous geochemistry is synonymous with low-temperature geochemistry, where the approximate temperature and pressure limits of 0-100°C and 1-500 bars commonly apply. The term environmental geochemistry is often used to emphasize the environmental aspects of geochemistry. Another common term, hydrogeochemistry, is usually applied to the aqueous geochemistry of ground waters. These four terms all refer to the same basic subject matter. In physics and chemistry, great advances are made through theoretical research, experimental research, or optimally through a blend of both. In aqueous geochemistry, a third aspect plays an essential role: field observations. By applying the best that theoretical chemistry and physics can offer to the interpretation of field observations aided by reliable experimental and analytical determinations, the aqueous geochemist is at the crossroads of theory, experiment and the natural environment. Geological phenomena are of a much greater complexity than the carefully controlled systems investigated in physics and chemistry, so that the geochemist has had to expand his knowledge creatively beyond the traditional boundaries of the physical sciences. The challenge of this type of scientific research is not generally appreciated (Alvarez, 1990). There are far more unknown and uncontrolled variables in natural systems than in the typical physicochemical investigation carried out in the laboratory. The hydrological, microbiological, macrobi- ological, and meteorological sciences are all necessary in addition to geology and chemistry.