Water Quality and Pollution

During the process of photosynthesis, phytoplankton produces oxygen as a byproduct. Due to their vast and widespread populations, algae and cyanobacteria are responsible for approximately half of all the oxygen found in the ocean and in our atmosphere. During day time they float, due to the accumulation of oxygen. Whereas the reverse happens during the night, which is explained below.
In addition to providing food and oxygen for nearly all life on Earth, phytoplankton help to regulate inorganic carbon (carbon dioxide) in the atmosphere. During photosynthesis, carbon dioxide and water molecules are used to make sugar for energy. The process of incorporating inorganic carbon into organic carbon (glucose and other biologically useful compounds) is called carbon fixation and is part of the biological carbon pump.
As carbon fixation and oxygen production are part of the same process, the extent of phytoplanktons participation is on the same scale. Phytoplankton consumes a similar amount of carbon dioxide as all land plants combined. While phytoplankton can pull carbon dioxide from the atmosphere or the ocean, it will have a similar effect. Carbon dioxide that is taken from the water is replaced by carbon dioxide from the atmosphere.

The function of the reservoir is to meet the deficit which occurs due to meet the deficit which occurs due to imbalance in the rate of influx and efflux.

Thermal pollution is when an industry or other human-made organization takes in water from a natural source and either cools it down or heats it up. They then eject the water back into the natural resource, which changes the oxygen level and can have a disastrous effect on the local ecosystem. 

Fishes respire with the help of gills. Gills are richly supplied with blood capillaries and can readily absorb oxygen dissolved in water. But gills can not absorb gaseous oxygen. Since fishes cannot absorb gaseous oxygen they die soon after they are taken out of the water.

Estuaries are the delicate water bodies where the fresh water from the river and salty water from the sea water meet and mix-up. They are responsible for transporting and mixing the nutrients. The difference in sedimentation of the water of rivers and sea-water, the wind action and the tidal activity allow the trapping and transport of the nutrients. Reefs, deltas and barrier islands protect the estuaries from the ocean forces.

Oxygen is very important for the microorganism to break down and degrade the organic matter which is present in the sewage or the activated sludge. If the oxygen availability of the activated sludge floc is reduced then the degradation rate will slow down.

Water pollution due to organic sources like pollution due to sewage can be prevented by treating sewage before passing into the water course, in sewage or effluent treatment plants (ETP). Domestic sewage primarily contains biodegradable organic matter, which readily decomposes by bacteria and other micro-organisms, which can multiply by using these organic substances as substrates and hence reduce some of the components of sewage. Thus, the correct answer is option A.

Anaerobic digestion is a collection of a process by which microorganism break down biodegradable material in the absence of oxygen and some of these processes are used in the waste Industries to manage the waste. Primary sludge is a result of the capture of suspended solids and organics materials. In the primary process of waste management, the material is treated in a variety of ways. During the biological treatment of the waste a part of activated sludge is used as inoculum and they are passed into the last tank which is known as anaerobic sludge digester. The microorganism present in the sludge gets killed.

Industrial wastewater treatment describes the processes used for the treatment of wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reused or released to a sanitary sewer or to a surface water in the environment.

One of the simplest multicellular organisms is algae. They are seen growing in the freshwater of marine habitats. They are also eukaryotic organisms. Algae can grow rapidly when exposed to stagnant waters. An adequate amount of sunlight, temperature and aquatic habitat leads to the rapid growth of slimy, green patches containing chlorophyll called algae.

Algae are important as primary producers of organic matter at the base of the food chain. They also provide oxygen for other aquatic life. Algae may contribute to mass mortality of other organisms, in cases of algal blooms, but they also contribute to economic well- being in the form of food, medicine and other products. In tropical regions, coralline algae can be as important as corals in the formation of reefs. They may form important constituent of human food (diet) in future. In future when world population will be very much, to provide them all nutritious food, algae will be used as alternate source of energy.

Algae have become significant organisms for self purification of wastewater since they are able to accumulate plant nutrients, heavy metals, pesticides, organic and inorganic toxic substances and radioactive matters in their cells or bodies.

Water makes the major part of an organism's life next to temperature. It s an important factor which influences the life of organisms. The productivity and distribution of land plants are dependent upon availability of water. Water is required for growth and development of plants.