Question

How can the pH of an acidic lake be increased?

Answer 1

The pH (also known as potential of hydrogen or power of hydrogen) is a scale used to specify the acidity or basicity of an aqueous solution. Generally, acidic solutions have low pH and basic solutions have high pH. Hence, pH can be increased by making the solution alkaline or addition of alkaline substances

Complete answer:
The pH of water expresses its acid or base content. The pH scale ranges from 0 (strongly acidic) - 14 (strongly basic). Most natural lake waters have a pH range from 6.2 to 8.9 and are slightly basic due to the presence of carbonates and bicarbonates in it. Fish production is generally observed higher in alkaline (pH= 7.1 - 9) waters. We also know that the alkalinity of water refers to its capacity to neutralize acids or to resist changes in pH range. It is a measure of the concentrations of three basic ions: carbonates, bicarbonates, and hydroxides in water.
Acid lake is the result of a mixture of carbonic acid, nitric acid, and sulfuric acid. Many acidic lakes (i.e., pH below 4) often are devoid of fish, frogs, crayfish, insects, and planktons. This is because very acidic surface waters can have toxic concentrations of aluminum in solution due to which aquatic animals may be subjected to a potentially lethal double dose of poisonous acid and metals.
We can increase the pH of the acidic lakes through “liming”. The addition of limestone, primarily calcium carbonate ($CaC{{O}_{3}}$ ), to neutralize acid waters and buffer them from fluctuations in pH is known as Liming.
Liming is one of the most inexpensive methods (also non-toxic and easy to dissolve). It slows down the effects of acidification, helps in restoring acidic waters and enhancing the abundance of aquatic life. It also reduces the toxic effects of metals especially aluminum, copper, cadmium, lead, nickel, and zinc, which can threaten aquatic life and human health. By neutralizing acid waters and reducing toxic dissolved metals, liming not only improves the reproduction and survival rate of aquatic animals and organisms but also promotes healthy, balanced fish populations.

Note:
Liming of acidic water to increase the pH is only a temporary solution. Another alternative is “Continuous Laminar Flow Inversion and Oxygenation”, a process of continuous lake inversion and lake aeration from surface to bottom. In this process, carbon dioxide in carbonic acid is liberated to the atmosphere and nitric acid is reduced facultatively by bacteria called pseudomonas, using nitric acid as an electron donor and carbon in the sediment to produce nitrogen gas and carbon dioxide along with water. Sulfuric acid is reduced to elemental sulfur by a variety of aerobic bacteria.