Water Quality and Pollution

The ecological effects of acid rain are most clearly seen in the aquatic environments, such as streams, lakes, etc. Acid rain flows into streams, lakes and marshes after falling on forests, fields, building and roads. Acid rain water primarily decreases the pH of water sources from normal range (6 to 8 pH) Lakes and streams become acidic (i.e., pH values goes down), when water itself and its surrounding soil cannot buffer the acid rain water to neutralize it. In areas where buffering capacity is low, acid rain releases aluminium from soils into lakes and streams, aluminium is highly toxic to many species of aquatic organisms leading to their mortality. Therefore, limiting the survival of aquatic animals. So, the correct answer is 'Lowering of pH in ponds, limiting survival of aquatic organisms'.

Fungi have a well-defined nucleus and membrane-bound organelles and are classified as eukaryotes.

Acid rain will lower down the pH of pond water and will cause an adverse effect on survival of many organisms as the acidic environment does not support the growth and existence of organisms. 

Acid rain is caused by burning of fossil fuels. By reducing the amount of burning of fossil fuel, which is one of the major cause of acid rain, frequency of acid rain can be reduced. Bigger fishes may or may not withstand the acidity. Supply of excess phosphorus and water may not benefit the plants as absorption of these substances by plant is not guaranteed. Likewise, supplying excess sugar and amino acid wont benefit the fungi. Adding alkaline might help but are not eco-friendly.

pH 7 is the neutral pH that does not harm plants and animals. Both plant and fungi will survive. Thus, the correct answer is option D.

Aquatic weeds, such as water hyacinth, are rich in organic matter and nutrients. They are commonly harvested and processed into organic fertilizers or compost to improve soil quality.

Like all green plants, algae produce oxygen during the daylight hours as a by-product of photosynthesis. This is usually a major source of oxygen in fish ponds. In darkness, however, all plants consume oxygen, including algae. Algae blooms in natural water bodies or fish ponds normally produce much more oxygen in the daylight than they consume during the night, but some situations reduce the amount of oxygen a bloom produces without reducing its nighttime oxygen consumption. Trace minerals or nutrients needed by the algae are occasionally used up, causing some or even all, of the bloom to die back temporarily. The resulting bacterial decomposition and loss of normal oxygen production can lead to oxygen depletions and fish kills. Pond water generally changes from a deep green to black, gray, brown or clear after a phytoplankton die-off. 

Freshwater and marine organisms are adapted to specific osmotic environments. Moving them between these environments causes osmotic stress, leading to cell swelling or dehydration, which is fatal.

The primar sludge is formed during primary sewage treatment, while activated sludge is a sludge during secondary sewage treatment, little decomposition occurs during primary sludge formation, while lot of decomposition occurs during activated sludge.

When sewage is discharged into a river, the high organic load increases the biological oxygen demand (BOD) as microorganisms decompose the waste, leading to a drop in dissolved oxygen (DO) and the death of aquatic organisms like fish.

• Biochemical Oxygen Demand (BOD)is defined as the amount of dissolved oxygen needed (i.e. demanded) by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period.
• BOD is an important water quality parameter because it provides an index to assess the effect discharged wastewater will have on the receiving environment. The higher the BOD value, the greater the amount of organic matter or “food” available for oxygen-consuming bacteria.
  
• Hence Measurement of the rate of oxygen utilization by a unit volume of water over a period of time is to measure Biochemical oxygen demand.
• So, the correct answer is 'Biochemical oxygen demand'.

Proper disposal of the domestic waste before it goes in to the lakes and oceans is useful in preventing water pollution. Domestic sewage which is the waste water that goes out into the environment through several routes should be treated before being released. It contains soaps, detergents, toilet paper, household refuse all of which causes water pollution. All this sewage should be properly collected and treated in which contaminants are removed from sewage to produce sludge suitable for discharge into the environment. 

Domestic sewage primarily contains biodegradable organic matter, which readily decomposes by bacteria and other micro-organisms, which can multiply using these organic substances as substrates and hence utilise some of the components of sewage. It is possible to estimate the amount of biodegradable organic matter in sewage water by measuring biochemical oxygen demand (BOD). It can be purified treating with with micro-organisms.

The sewage water can be treated in the treatment plants with the use of microbes. The bacterial cells, fungal cells and algae are the common microbes which are used for the cleaning of the waste. The microbes have the ability to feed and decompose on the organic matter and convert it to simpler non-toxic forms. The organic matter of the wastewater can be reduced and the water can be purified.