Chemistry of surface waters

These processes occur by precipitation through evaporative concentration of a solute in the aqueous medium until its dissolution capacity is exceeded. Then, a solid is formed and deposited either as a sediment or on a nearby surface. These products are called evaporites. A typical example is the deposition and formation of calcium carbonate stalactites and stalagmites. Evaporation is a major process in arid areas and it influences the chemistry of surface waters. That is why in saline lakes, inland seas, or even in estuaries, evaporites of NaCl or NaCl/KCl and deposits of CaS04 and CaC03 are formed. Here, CaS04 generally precipitates first, and then NaCl. 

Kahl J. S., Norton S. A., MacRae R. K., Haines T. A., and Davis R. B. (1989) The influence of organic acidity on the acid-base chemistry of surface waters in Maine, USA. Water Air Soil Pollut. 46, 221-233. 

Over the last several decades, the decline in alkalinity in many streams in Europe and in northeastern USA as a result of acid deposition has been a subject of much concern (Likens et al., 1979). The concentration of bicarbonate, the major anion buffering the water chemistry of surface waters and the main component of dissolved inorganic carbon (DIC) in most stream waters, is a measure of the reactivity of the watersheds and reflects the neutralization of carbonic and other acids by reactions with silicate and carbonate minerals encountered by the acidic waters during their residence in watersheds (Garrels and Mackenzie, 1971). Under favorable conditions, carbon isotopes of DIC can be valuable tools by which to understand the biogeochemical reactions controlling carbonate alkalinity in groundwater and watersheds (MUls, 1988 Kendall et al., 1992 see Chapter 5.14). 

Driscoll C. T., Likens G. E., Hedin L. O., Eaton J. S., and Bormann F. H. (1989) Changes in the chemistry of surface waters 25-year results at the hubbard brook experimental forest. Environ. Sci. Technol. 23, 137-143. 

After a brief description of pollutant sources to surface waters, the physics, biology, and chemistry of surface waters are discussed. The major fate processes for chemicals in surface waters are then presented, including the physical processes of volatilization and sedimentation the chemical processes of reduction-oxidation reactions, hydrolysis, and photodegradation and the biological processes of biodegradation and accumulation in aquatic organisms. 

Aerobic and anaerobic decay and respiration dominate the nighttime chemistry of surface waters, leading to an increase in the CO2 pressure, such as described by line C-D. 

One factor that has been linked with long-term changes in the chemistry of surface waters and soils is the influence of variations in weather, particularly temperature and precipitation. The variability that fluctuations in weather induce in surface water chemistry (Hindar et al. 2003) may obscure the detection of trends resulting from reductions in SO/ deposition. On the other hand, use of long-term data may obscure shorter trends occurring within the series, particularly if the trends are not uni-directional. In this case, the detection of trends may be dependent on the time window used in the analysis, and can affect both the detection of the presence and the direction of a trend (Clair et al. 2002). For example, Clair et al. (1992) found significant decreases in SO/ concentrations in lakes in Nova Scotia, Canada, for the period 1983-1989, but with the addition of two more years of data, many of these trends were reversed (Clair et al. 1995). 

A central problem in the chemistry of natural water systems is the establishment of experimental methods with which to distinguish adsorption from surface precipitation (1-3). Corey ( 2) has written a comprehensive review of this problem which should be read as an introduction to the present essay, particularly for his set of six conclusions that set out general conditions likely to result in adsorption or precipitation. The discussion to follow is not a comprehensive review, but instead focuses on three popular approaches to the adsorption/surface precipitation dichotomy. The emphasis here is on the conceptual relationship of each approach to the defining statements made above To what extent is an approach capable of distinguishing adsorption from surface precipitation ... 

Dissolution and precipitation in the subsurface are controlled by the properties of the solid phases, by the chemistry of infiltrating water, by the presence of a gas phase, and by environmental conditions (e.g., temperature, pressure, microbiological activity). Rainwater, for example, may affect mineral dissolution paths differently than groundwater, due to different solution chemistry. When water comes in contact with a solid surface, a simultaneous process of weathering and dissolution may occur under favorable conditions. Dissolution of a mineral continues until equilibrium concentrations are reached in the solution (between solid and liquid phases) or until all the minerals are consumed. 

Special consideration shonld be given to the transformation of contaminants in sediments and gronndwater. Under saturated conditions, the solid phase may function as a sink, reservoir, and reactor for contaminants. Contaminant presence, persistence, and transformation in the water phase is controlled by the chemistry of the water body, the surface properties of the materials forming the solid phase (sediments or suspended particles), and environmental conditions (temperature and aerobic or anaerobic stams). 

Arnorsson, S., Gunnarsson, I., Stefansson, A., Andresdottir, A. Sveinbjornsdottir, A. E. 2002. Major element chemistry of surface- and ground waters in basaltic terrain, N-Iceland. Geochimica et Cosmochimica Acta, 66, 4015-4046. 

His 40+ publications have dealt with biogeochemical processes that control the alkalinity of surface waters, the geochemisty of dilute seepage lakes, sediment chemistry, the interpretation of water-quality trends, regional analysis of water quality, modeling lake eutrophication, lake management, reservoir water quality, and nonpoint source pollution. He recently joined the faculty of the Department of Civil Engineering at Arizona State University. 

The activities of Mg++ and Ca++ obtained from the model of sea water proposed by Garrels and Thompson have recently been confirmed by use of specific Ca++ and Mg++ ion electrodes, and for Mg++ by solubility techniques and ultrasonic absorption studies of synthetic and natural sea water. The importance of ion activities to the chemistry of sea water is amply demonstrated by consideration of CaC03 (calcite) in sea water. The total molality of Ca++ in surface sea water is about 10 and that of COf is 3.7 x 1C-4 therefore the ion product is 3.7 x 10 . This value is nearly 600 times greater than the equilibrium ion activity product of CaCO of 4.6 x 10-g at 25°C and one atmosphere total pressure. However, the activities of the free 10ns Ca++ and COj = in surface sea water are about 2.3 x 10-3 and 7.4 x 10-S, respectively thus the ion activity product is 17 x 10 which is only 3,7 rimes greater than the equilibrium ion activity product of calcite. Thus, by considering activities of sea water constituents rather than concentrations, we are better able to evaluate chemical equilibria in sea water an obvious restatement of simple chemical theory but an often neglected concept in sea water chemistry. 

The biochemical reduction of sulfate to sulfide by bacteria of the genus Desulfovibrio in anoxic waters is a significant process in terms of the chemistry of natural waters since sulfide participates in precipitation and redox reactions with other elements. Examples of these reactions are discussed later in this paper. It is appropriate now, however, to mention the enrichment of heavy isotopes of sulfur in lakes. Deevey and Nakai (13) observed a dramatic demonstration of the isotope effect in Green Lake, a meromictic lake near Syracuse, N. Y. Because the sulfur cycle in such a lake cannot be completed, depletion of 32S04, with respect to 34S04, continues without interruption, and 32S sulfide is never returned to the sulfate reservoir in the monimolimnion. Deevey and Nakai compared the lake to a reflux system. H2S-enriched 32S diffuses to the surface waters and is washed out of the lake, leaving a sulfur reservoir depleted in 32S. The result is an 34S value of +57.5% in the monimolimnion. 

Efforts to interpret the forms of isotherms in terms of behaviour at molecular level have tended to concentrate on fatty acids and, to a lesser extent, phospholipids. An understanding of the behaviour of films at the air/water interface in terms of the degree of order in the structure of the film is thus largely limited to these materials. Harkins carried out important early work in the detailed study of the isotherms of fatty acids and this work is summarised in his book The Physical Chemistry of Surface films (72J. The nomenclature that he introduced was derived from an attempt to find an analogy with the behaviour of three-dimensional... 

Depending on the chemistry of the water, activated alumina is typically used for one to three months before regeneration or disposal is required (Jekel, 1994, 128). Alumina regeneration begins with a wash of 0.25-1.0 normal (N) NaOH (Clifford and Ghurye, 2002, 221, 229). As shown in the following reaction, hydroxides from the base replace arsenic oxyanions adsorbed onto the surface aluminums ... 

IV sites. A protonated pyridine has never been observed, and the Lewis acid sites on titanium oxides cannot be converted into Br0nsted sites by water vapor adsorption (217). Although Jones and Hockey (216) suggest that the chemistry of surface hydroxyl on rutile corresponds more closely to that of the OH" ion rather than that of the hydroxyl group, no surface reactions similar to that observed with alumina [Eq. (14)] have since been reported. 

Despite its prominent role in atmospheric chemistry [53,54], the hydroxyl radical is considered a minor oxidant in the great majority of surface waters owing to the low formation rates [9] and efficient scavenging by DOM and the bicarbonate/carbonate anions. DOM is at the same time both sensitizer and scavenger of the hydroxyl radical, but CDOM is responsible only for minor formation pathways, which can be summarized as ... 

Environmental Protection Agency, Response of Surface Water Chemistry to the Clean Air Act Ammendments of 1990 (EPA 620/R-03/001, Jan. 2003, p. 18). http //www.epa.gov/ord/htm/CAAA-2002-report-2col-rev-4.pdf... 

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