The extensive growth of planktonic (free-floating) algae in water bodies due to the presence of organic matter in water (cnitrogen and phosphores) that acts as a food source is called an algal bloom. This imparts a distinct colour to the water bodies.

Biomagnification refers to the increase in the concentration of the toxic substances at successive trophic level Is in the food chain.

This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted and when this organism is eaten up by another animal of higher trophic level, it is passed on to this and then to the next higher trophic level and so on.

The three major kinds of impurities in domestic waste water are

(i) Dissolved salts such as nitrates, phosphates, other nutrients, toxic, metal ions and organic compounds.

(ii) Biodegradable organic matter.

(iii) Pathogenic microorganisms.

Reforestation is the process of restoring a forest that had once existed but was removed at some point of time in the past. Though, it can occur naturally in a deforested area but we can expedite it by planting trees with due consideration to biodiversity that earlier existed in that area.

The best solution for the treatment of electronic wastes is to recycle it. Electronic waste recycling facilities have advanced considerably and now they can be recycled 95-98\% by weight.

Recycling has two fold benefits

(i) It prevents the toxic components of computers from entering the delicate environment and ground water via landfill.

(ii) It also slows the use and mining of primary raw materials.