Sewage treatment to the environment can lead to a buildup of nutrients, called eutrophication, which can in turn encourage the overgrowth of weeds, algae, and cyanobacteria (blue-green algae). This may cause an algal bloom, a rapid growth in the population of algae. The algae numbers are unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses up so much of the oxygen in the water that most or all of the animals die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins that contaminate drinking water
Artificial reproduction Artificial reproduction Artificial reproduction/propagation is the creation of new life by other than the natural means available to an organism. Examples include artificial insemination, in vitro fertilization, cloning and embryonic splitting, or cleavage. Cutting plants' stems and placing them in compost is also a form of artificial reproduction. We can grow many plants from one plant by using the man-made methods. The process of growing many plants from one plant by man-made methods is called artificial propagation of plants. A number of methods of artificial propagation of plants are used in agriculture (for raising crops), and horticulture (cultivation of vegetables,