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Lesson 5�

Industrial Water Pollution

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Sources of pollution with nitrogen

Farmers, foresters, homeowners, and business people can pollute water by improperly using chemical fertilizers. For example, in urban areas, homeowners often apply more than the recommended amounts of fertilizer to lawns, gardens, and flowers. Farmers applying too much manure or fertilizer at the wrong time can cause similar problems. For instance, it is not good to apply fertilizer during the rainy season. After heavy rains, fertilizer can wash into rivers and lakes and supply the aquatic plants with too many nutrients. As a result, algae can multiply faster and cause algae blooms. Algae blooms can reduce the supply of oxygen in the water because oxygen is required for algae respiration and growth. During the day, algae photosynthesize and produce more oxygen than they can use. But at night when photosynthesis ceases, algae may use more oxygen to grow than may be available. This can deplete the supply of dissolved oxygen in the water. When the algae dies, oxygen is required to break down or decompose the dead algae. Both respiration and decomposition can make oxygen unavailable to fish and other aquatic life and may cause fish kills. When plants and animals die, they settle to the bottom. Under normal conditions this causes the water body to gradually fill with sediment and organic material. This process is called eutrophication. This process is accelerated when excess nutrients and sediment are added to a water body.

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