Alkalinity surface water

The practical significance of such competition evolves from the experience that silicate and (anionic) humics can increase the efficiency of phosphate fertiliser because these compounds occupy sites suitable for phosphate adsorption (Kingston et ak, 1968 Schwertmann, 1995). Hydroxyl is another anion that competes effectively with adsorbing anions, owing to its location in the inner Helmholz layer. The release of adsorbed phosphate after liming a soil or after inflow of acidic surface soil into weakly alkaline surface waters due to erosion, can be considered as the result of competition between OH and phosphate ions. 

From the selective extraction analysis of sediment, chemical equilibrium calculations, and seeded crystallization measurements, several conclusions can be reached concerning the behavior of phosphate in alkaline surface waters. 

Assuming saturation with natron at atmospheric CO2 pressure (10" bar) and 25°C, MINTEQA2 computes pH = 10.14. Highly alkaline surface water pH s are also caused by photosynthetic depletion of dissolved carbonic acid. 

Ortho-phosphate dose range (mg/i P) Percentage of high alkalinity ground waters Percentage of high alkalinity surface waters Percentage of low alkalinity surface waters... 

Deposition of a protective layer of crystalline CaCO has been proposed for protection of metallic surfaces against corrosion by using the natural calcium and alkalinity in water (36). 

Consider a lake with a smaU watershed in a forest ecosystem. The forest and vegetation can be considered as an acid concentrator. SO2, NO2, and acid aerosol are deposited on vegetation surfaces during dry periods and rainfalls they are washed to the soil floor by low-pH rainwater. Much of the acidity is neutralized by dissolving and mobilizing minerals in the soil. Aluminum, calcium, magnesium, sodium, and potassium are leached from the soil into surface waters. The ability of soils to tolerate acidic deposition is very dependent on the alkalinity of the soil. The soil structure in the... 

An increase in seawater alkalinity (for example, by the dissolution of CaCOa) would decrease pC02 in seawater and decrease the Revelle factor (10), Thus CaCOa dissolution would provide a a strong negative feedback in response to an increased level of CO2 in the atmosphere and ocean. However, the surface water of temperate and tropical oceans is supersaturated with respect to CaCOa by several fold. It is not likely that the dissolution of CaCOa would provide a negative feedback to the air-sea CO2 transfer process in the near future. 

The elements Na, K, Cl, SO, Br, B, and F are the most conservative major elements. No significant variations in the ratios of these elements to chlorine have been demonstrated. Strontium has a small (< 0.5%) depletion in the euphotic zone (Brass and Turekian, 1974) possibly due to the plankton Acantharia, which makes its shell from SrS04 (celestite). Calcium has been known since the 19th century to be about 0.5% enriched in the deep sea relative to surface waters. Alkalinity (HCOf") also shows a deep enrichment. These elements are controlled by the formation... 

Figure 6-8 shows how the partial pressure of carbon dioxide in equilibrium with surface water oscillates in phase with the fluctuations in precipitation rate, saturation state, and temperature. The oscillations in alkalinity and bicarbonate concentrations have shifted in phase by about 90° because these quantities decrease when precipitation and evaporation are removing carbon from the system at above-average rates. 

Fig. 3. Schoeller diagrams, with pH (inset), showing the average compositions for ground water and surface water from sites 1 (A) and 2 (B). Abbreviations Aik - alkalinity AGW -Atikokan ground water.

Nickel (8) calculated the thickness of the proposed "residual layer" on albite from the mass of dissolved alkalis and alkaline earths released during laboratory weathering and the measured surface area, and determined that the thickness ranges from 0.8 to 8.0 nm in the pH range of natural surface waters. Although he interpreted his results differently, they anticipate later findings on the pH dependence of residual layer compositions (see below). 

Surface water concentrations of (a) total alkalinity ( ji,mol/kg) and (b) dissolved inorganic carbon (ljumol/kg). Source After Key, R. M., et al. (2004). Global Blogeochemical Cycles 18, GB3011. (See companion website for color version.)... 

The initial decrease in ocean uptake rate will eventually be reversed once enough time has passed (millennia) for meridional overturning circulation to recycle the subsurface waters. This will serve to inject CO2 below the mixed layer. Once the surface waters have been sufficiently acidified and are transported into the deep sea, they will eventually start dissolving sedimentary calcium carbonate. The resupply of alkalinity via this route will provide sufficient enhancement to ocean carbon uptake capacity to... 

The primary ozonation by-products of atrazine (15 mg/L) in natural surface water and synthetic water were deethylatrazine, deisopropylatrazine, 2-chloro-4,6-diamino-s-triazine, a deisopropylatrazine amide (4-acetamido-4-amino-6-chloro-5-triazine), 2-amino-4-hydroxy-6-isopropylamino-5-triazine, and an unknown compound. The types of compounds formed were pH dependent. At high pH, low alkalinity, or in the presence of hydrogen peroxide, hydroxyl radicals formed from ozone yielded 5-triazine hydroxy analogs via hydrolysis of the Cl-Cl bond. At low pH and low alkalinity, which minimized the production of hydroxy radicals, dealkylated atrazine and an amide were the primary byproducts formed (Adams and Randtke, 1992). 

Cadmium is found naturally deep in the subsurface in zinc, lead, and copper ores, in coal, shales, and other fossil fuels it also is released during volcanic activity. These deposits can serve as sources to ground and surface waters, especially when in contact with soft, acidic waters. Chloride, nitrate, and sulfate salts of cadmium are soluble, and sorption to soils is pH-dependent (increasing with alkalinity). Cadmium found in association with carbonate minerals, precipitated as stable solid compounds, or coprecipitated with hydrous iron oxides is less likely to be mobilized by resuspension of sediments or biological activity. Cadmium absorbed to mineral surfaces (e.g., clay) or organic materials is more easily bioaccumulated or released in a dissolved state when sediments are disturbed, such as during flooding. 

Figure 8.35 shows the redox state and acidity of the main types of seawaters. The redox state of normal oceanic waters is almost neutral, but they are slightly alkaline in terms of pH. The redox state increases in aerated surface waters. Seawaters of euxinic basins and those rich in nutrients (eutrophic) often exhibit Eh-pH values below the sulfide-sulfate transition and below carbonate stability limits (zone of organic carbon and methane cf figure 8.21). We have already seen (section 8.10.1) that the pH of normal oceanic waters is buffered by carbonate equilibria. At the normal pH of seawater (pH = 8.2), carbonate alkalinity is 2.47 mEq per kg of solution. 

In order to verify whether atmospheric deposition directly affects surface water chemistry of high-altitude Alpine lakes, trend analyses were performed for 20 mountain lakes with low alkalinity on the key variables involved in acidification and recovery alkalinity (Gran alkalinity), pH, sulphate, nitrate, base cations (calcium + magnesium). The analysis covers the period 1980-2004 and allows a comparison between atmospheric inputs and surface water quahty. 

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. 

---