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Which of the following could result from an algal bloom in a river?

A). The algae purify the water

B). The local plants produce flowers early

C). Fish and other aquatic life die off

D). Plant and animal populations increase

Of the following, which is most likely to happen after a farmer sprays his crops with pesticides?

A). The crops die

B). Insect population increases

C). The soil dries up and blows away

D). A neighbor's well tests positive for pesticides

The rapid growth of algae in the river results in algal bloom and is acknowledged by the water discoloration due to their pigments. It is harmful to aquatic life and leads to fish die-offs as well as for human consumption.

A neighbor’s well might test positive for pesticide if the farmer sprays his crop with pesticides.

Further Explanation:

An algal bloom can occur in marine or freshwater ecosystems. It is caused due to the accumulation of a large number of nutrients such as nitrogen and phosphorus in the water bodies. These nutrients support the enhanced growth of green plants and algae. The color of the algal bloom is determined by the photosynthetic pigment in the algal cells and therefore, can be greenish, brown, red, or yellow in color.

The presence of an excess of nutrients results in a freshwater algal bloom. The fertilizers used in the agricultural land may result in the excess nutrients which are drained into the water bodies along with rainwater. The nutrients may also drain off from the household wastes. The high concentration of nutrients speeds up the growth of the algae in the water system. The algae live for a brief period of time and result in the accumulation of dead organic matter. This matter starts decaying and uses the oxygen dissolved in the river. The hypoxic conditions develop which leads to the death of the fishes and plants in large numbers due to unavailability of oxygen.

The algal bloom also causes odor and taste problems in water which is used for drinking. It can make the aquatic life devoid of sunlight by blocking its passage due to the over-accumulation of algae.

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Answer Details:

Grade: High School

Subject: Biology

Topic: Algal bloom

Keywords:

Algae, algal bloom, excess of nutrients, fish die-offs, marine ecosystem, freshwater ecosystem, photosynthetic pigments, fertilizers, dissolved oxygen, hypoxic condition, dead organic matter, aquatic life.