Name: Stable Community and Biodiversity Conservation
Uploaded: 2019-07-19
Duration: 9 min 44 s
Description: Our planet has millions of species of plants, animals, and other living organisms. What happens if one of them becomes extinct? Learn more about a stable com...

Question

Explain how pollution by sewage causes dissolved oxygen levels to decrease in the following graph.

Accepted Answer

Farmers and horticulturists used fertilizers to increase the yield of their crops. The fertilizers usually contain nitrates and phosphates. Nitrates were very soluble in water. Nitrate fertilizer was put onto the soil, these were called leaching. The leached nitrates were to run into streams and rivers.

Algae and green plants in the river were growing faster when they were supplied with extra nitrates. They had grown so much that they completely covered the water. In the $19$ th century, sewage from the city drained directly into the river.

Chemical waste may contain heavy metals, such as lead, cadmium, or mercury. These substances were very poisonous (toxic) to living organisms because heavy metals stop enzymes from working. They got into streams, rivers, or the sea, they killed almost every living thing in that area of water.
Untreated sewage got into rivers, microorganisms decomposed it. They used oxygen from the water for aerobic respiration. As a result, there was less oxygen dissolved in water, so aquatic organisms such as fish and insects may be unable to survive.

Explain how pollution by sewage causes dissolved oxygen levels to decrease in the following graph.

Important Questions on Humans and the Environment

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