The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from human activities. Broad interrelationships among these processes and their effects can be discerned by application of principles of chemical thermodynamics. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibrium, including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the Earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural freshwater. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. Taken together and in application with the further influence of the general circulation of all water in the hydrologic cycle, the chemical principles and environmental factors form a basis for the developing science of natural-water chemistry. Fundamental data used in the determination of water quality are obtained by the chemical analysis of water samples in the laboratory or onsite sensing of chemical properties in the field. Sampling is complicated by changes in the composition of moving water and by the effects of particulate suspended material. Some constituents are unstable and require onsite determination or sample preservation. Most of the constituents determined are reported in gravimetric units, usually milligrams per liter or milliequivalents

Study and Interpretation of the Chemical Characteristics of Natural Water

Inorganic species in geologic fluids: Correlations among standard molal thermodynamic properties of aqueous ions and hydroxide complexes

Quantitative predictions of the effects of acid deposition onterrestrial and aquatic systems require physically based, process-oriented models of catchment soil water and streamwater chemistry. A desirable characteristic of such models is that they include terms to describe the important phenomena controlling a system's chemical response to acidic deposition, yet be restricted in complexity so that they can be implemented on diverse systems with a minimum of a priori data. We present an assessment of a conceptual model of soil water and streamwater chemistry based on soil cation exchange, dissolution of aluminum hydroxide, and solution of carbon dioxide, all processes that occur in catchment soils and that have rapid equilibration times. The model is constructed using an “average” or lumped representation of these spatially distributed catchment processes. The adequacy of the model is assessed by applying it to 3 years of soil water and streamwater chemistry data from White Oak Run, Virginia, a second-order stream in the Shenandoah National Park. Soil properties predicted by the model are in good agreement with presently available measurements of those soil properties. The success of the model suggests that lumped representations of complex and spatially distributed chemical reactions in soils can efficiently describe the gross chemical behavior of whole catchments (e.g., pH, alkalinity, and major ionic concentrations in surface waters). Further assessment of the adequacy of this conceptual approach will require more detailed empirical knowledge of the soil processes being modeled, particularly soil cation exchange and the variability of soil CO2 partial pressures.

Modeling the Effects of Acid Deposition: Assessment of a Lumped Parameter Model of Soil Water and Streamwater Chemistry

The Quantitation of Aqueous Aluminum, P.R. Bloom and M.S. Erich Aqueous Equilibrium Data for Mononuclear Aluminum Species, D.K. Nordstrom and H.M. May Inorganic Aluminum Bearing Solid Phases, B.S. Hemingway and G. Sposito Aqueous Polynuclear Aluminum Species, P.M. Bertsch and D.R. Parker Environmental Chemistry of Aluminum-Organic Complexes, G.F. Vance, F.J. Stevenson, and F.J. Sikora Surface Reactions of Aqueous Aluminum Species, P.M. Jardine and L.W. Zelazny The Surface Chemistry of Aluminum Oxides and Hydroxides, S.R. Goldberg, J.A. Davis, and J.D. Hem The Solubility of Aluminum in Soils, W.L. Lindsay and P.M. Walthall The Chemistry of Aluminum in Surface Waters, C.T. Driscoll and K.M. Postek Aluminum Geochemistry at the Catchment Scale in Watersheds Influenced by Acidic Precipitation, W.H. Hendershot, F. Courchesne, and D.S. Jeffries Index

The Environmental Chemistry of Aluminum

A procedure was developed for the fractionation of aqueous aluminum. This procedure results in the determination of acid-soluble aluminum, non-labile monomeric aluminum and labile monomeric aluminum. Acid-soluble aluminum is thought to include colloidal aluminum and extremely non-labile organic complexes. Non-labile monomeric aluminum is thought to include monomeric alumino-organic complexes. Labile monomeric is comprised of aquo aluminum as well as inorganic complexes of aluminum. The inorganic speciation of aluminum may be calculated by using labile monomeric aluminum, pH, fluoride and sulfate data with a chemical equilibrium model. This procedure was evaluated using synthetic and natural water solutions. In natural waters, levels of labile monomeric aluminum increased exponentially with decreases in solution pH, while non-labile monomeric aluminum was strongly correlated with organic carbon concentration. Non-labile monomeric aluminum was observed to be relatively insensitive to changes in sol...

A Procedure for the Fractionation of Aqueous Aluminum in Dilute Acidic Waters

Gibbsite solubility and thermodynamic properties of hydroxy-aluminum ions in aqueous solution at 25°C

Determination of mononuclear dissolved aluminum in near-neutral waters

Clay minerals. A physico-chemical explanation of their occurrence, vol. 40, developments in sedimentology: B. Velde, 1985, Elsevier, 427 pp., $59.25 (hardcover)

Howard M. May

Papers

Gibbsite solubility and thermodynamic properties of hydroxy-aluminum ions in aqueous solution at 25°C

Determination of mononuclear dissolved aluminum in near-neutral waters

Clay minerals. A physico-chemical explanation of their occurrence, vol. 40, developments in sedimentology: B. Velde, 1985, Elsevier, 427 pp., $59.25 (hardcover)