Section 3: Water Pollution Read the passage below and answer the questions that follow. The natural process of eutrophication is accelerated when inorganic plant nutrients, such as phosphorus and nitrogen, enter the water from sewage and fertilizer runoff. Eutrophication caused by humans is called artificial eutrophication. Fertilizer from farms, lawns, and gardens is the largest source of nutrients that cause artificial eutrophication. Phosphates in some laundry and dishwashing detergents are another major cause of eutrophication. Phosphorus is a plant nutrient that can cause the excessive growth of algae. In bodies of water polluted by phosphorus, algae can form large floating mats, called algal blooms. As the algae die and decompose, most of the dissolved oxygen is used and fish and other organisms suffocate in the oxygen-depleted water. IDENTIFYING MAIN IDEAS One reading skill is the ability to identify the main idea of a passage. The main idea is the main focus or key idea. Frequently, a main idea is accompanied by supporting information that offers detailed facts about main ideas. In the space provided, write the letter of the term or phrase that best completes each statement or best answers each question. 1. Which of these are examples of inorganic plant nutrients? a. eutrophication and oxygen c. oxygen and algal bloom b. phosphorus and nitrogen d. farms