Freshwater alkalinity

Following detection, alkalinity may be expressed in a number of units including equivalent concentrations of calcium carbonate in units of mg CaCOs micro/milliequivalents, or molarity. Freshwater alkalinity may range from less than -200 to 500 meq 1 whereas in seawater a more consistent concentration of 2.35meql is generally observed. 

If poUed, most aquaculturists would probably indicate a preference for well water. Both freshwater and saline wells are common sources of water for aquaculture. The most commonly used pretreatments of well water include temperature alteration (either heating or cooling) aeration to add oxygen or to remove or oxidize such substances as carbon dioxide, hydrogen sulfide, and iron and increasing salinity (in mariculture systems). Pretreatment may also include adjusting pH, hardness, and alkalinity through the appHcation of appropriate chemicals. 

Freshwater Muds—Dispersed Systems. The pH value of low-pH muds may range from 7.0 to 9.5. Low-pH muds include spud muds, bentonite-treated muds, natural muds, phosphate-treated muds, organic thinned muds (red muds, lignite muds, lignosulfate muds), and organic colloid-treated muds. The pH value of high pH muds, such as alkaline tannate-treated mud, is above 9.5. 

Quebracho-treated freshwater muds were used in drilling at shallow depths. The name of red mud comes from the deep red color imparted to the mud by quebracho. Muds treated with a mixture of lignite and quebracho, or a mixture of alkaline organic polyphosphate chemicals (alkaline-tannate treated muds), are also included in the quebracho treated muds. The quebracho thinners are very effective at low concentrations, and offer good viscosity and filtration control. The pH of red" muds should be 8.5 to 10 mud temperature should be lower than 230°F. 

Rengefors, K., Ruttenberg, K.C., Haupert, L.C., Taylor, C., Howes, B.L. and Anderson, D.M. (2003). Experimental investigation of taxon-specific response of alkaline phosphatase activity in natural freshwater phytoplankton. Limnolology and Oceanography 48 1167-1175. 

Studies of 30 to 60 days duration with three comparatively sensitive species of freshwater fishes demonstrated that concentrations of >1 and <3 pg Cd/L in water of low alkalinity caused reductions in growth, survival, and fecundity of brook trout (Salvelinusfontinalis), the most sensitive species tested (Table 1.3). Under conditions of increasing alkalinity, the maximum allowable cadmium concentration range for brook trout increased to >7 and <12 pg/L a similar case was made for the walleye (Stizostedion vitreum vitreum Table 1.3). 

Zinc ligands are soluble in neutral and acidic solutions, so that zinc is readily transported in most natural waters (USEPA 1980, 1987), but zinc oxide, the compound most commonly used in industry, has a low solubility in most solvents (Elinder 1986). Zinc mobility in aquatic ecosystems is a function of the composition of suspended and bed sediments, dissolved and particulate iron and manganese concentrations, pH, salinity, concentrations of complexing ligands, and the concentration of zinc (USEPA 1980). In freshwater, zinc is most soluble at low pH and low alkalinity 10 mg Zn/L of solution at pH 6 that declines to 6.5 at pH 7, 0.65 at pH 8, and 0.01 mg/L at pH 9 (Spear 1981). Dissolved zinc rarely exceeds 40 pg/L in Canadian rivers and lakes higher concentrations are usually associated with zinc-enriched ore deposits and anthropogenic activities. Marine... 

Distilled water, which equilibrates with CO2 of a non-polluted atmosphere, has a pH of 5.65. At this pH, proton and bicarbonate concentrations are equal and alkalinity becomes zero [9]. We consider freshwaters acidic when [Alk]<0 meq 1 ... 

Because of decreased SO2 emissions, the importance of nitrogen for freshwater acidification becomes more and more determinant. Therefore, uncertainties in the evolution of nitrogen emissions make it difficult to predict future trends in freshwater recovery. On the other hand, climate warming may increase the number of alkaline rain episodes (containing Saharan dust) and enhance weathering reactions, which buffer better acid precipitation, increasing alkalinity and pH. 

Disposal of brine in subsurface wells is probably the most widely used control method, especially in the western and southern oil and gas producing states [23]. For this to be an effective disposal option, two conditions must be met the natural aquifer must be naturally saline and must not leak to freshwater aquifers, and the reinjection pressure must not exceed the fracture pressure of the formation [9]. Produced water is usually pretreated to prevent equipment from being corroded and to prevent plugging of the sand at the base of the well. Pretreatment may include the removal of oils and floating material, suspended solids, biological growth, dissolved gases, precipitable ions, acidity, or alkalinity [27]. A typical system is shown in Fig. 12. 

Freshwater cyanobacterium, Synechocystls aquatllls 1000-10,000 of Sn+2 or Sn- " Inhibited growth and chlorophyll a content in 96 h, but only under alkaline conditions Sn was more toxic than Sn + toxicity of both tin species increased with increased tin concentration, increased exposure, and increased pH of the medium humic acid reduced the toxicity of tin 43... 

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