Water Quality and Pollution

Chlamydomonas, Scenedesmus, Chlorella, Pondorhina, Euridina, etc. live in sewage water. 

One of the most beneficial factors from live plants in the aquarium is the supply of oxygen. Oxygen is very essential to the survival of the biological system and inhabitants of any aquarium. Through a process known as “photosynthesis,” live plants utilise the carbohydrates from inorganic substances such as water and carbon dioxide (which is respired by fish) as a food source and in turn, release oxygen as a by-product.

Eutrophication is the process by which a body of water acquires a high concentration of nutrients, especially phosphates and nitrates. Eutrophication is a phenomenon observed in ponds and wells.

The presence of fecal coliform in water may indicate that the water has been contaminated with fecal material of humans or other animals. Groundwater in a properly constructed well should be free of coliform bacteria. Fecal coliform bacteria can be found in wells through direct discharge of waste from mammals and birds, agricultural and human sources. This could also happen due to poor construction or cracks in the well or through runoffs from wooded areas, pastures, feedlots, septic tanks and sewage plants into streams or groundwater. Regular monitoring of the microbial quality of drinking water is an essential step in ensuring the safety of drinking water. Thus, Option 2 is correct.

In a lake polluted with pesticides, water fowls will contain the maximum amount of pesticides. Waterfowl are members of the family Anatidae. They are strong swimmers with medium to large bodies. They have historically been an important food source, and continue to be hunted as game, or raised as poultry for meat and eggs. 

Some ponds look green from a distance because of the excessive growth of algae. The excessive growth of algae being green in color gives a false impression that the pond is green from a distance. 

'A lot of carbon dioxide is used in the process of decomposition and its decreasing level kills aquatic organisms' is an incorrect statement. Phosphorus and nitrogen combined with carbon dioxide are the main supplies that can turn your pond from clean to green very quickly. All aquatic plants and algae make their own energy through photosynthesis which uses sunlight and carbon dioxide to create energy and oxygen as the byproducts. Carbon dioxide released in the process of photosynthesis is used in aerobic decomposition. 

A river said to be ‘dead’ when the river becomes highly polluted to sustain aquatic life. 

Such microbes help to degrade the organic wastes present in water, reducing their BOD or polluting potential. This feature is made use of in STP's (sewage treatment plants).

Oxygen is an abiotic factor in aquatic ecosystems. While oxygen levels can be influenced by plants and algae, oxygen itself is a dissolved gas - a non-living chemical component. Plants, fish, and algae are all biotic (living) factors.

Freshwater floods add nutrients to lakes and rivers. This leads to improved fisheries for a couple of years. 

This option is correct because Chlamydomonas, Scenedesmus, Chlorella, Pondorhina, Euridina, etc. are living in sewage water. 

The green patches on stagnant water bodies or ponds depict algae.

Chlorination is the process which is used to kill certain bacteria and other microbes in water as chlorine is highly toxic. Thus, the given assertion is true, but reason is not correct.

Eutrophication is the ecosystem response to the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system. One example is the "bloom" or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Negative environmental effects include hypoxia, the depletion of oxygen in the water, which induces reductions in specific fish and other animal populations.