单选题 Recalculating the global use of phosphorus, an important fertilizer element of modem agriculture, a team of researchers warns that the world's stocks may soon be in short supply and that overuse in the industrialized world has become a leading cause of the pollution of lakes, rivers and streams.
Writing in the Feb. 14 edition of the journal Environmental Research Letters, Stephen Carpenter of the University of Wisconsin-Madison and Elena Bennett of McGill University report that the human use of phosphorus, primarily in the industrialized world, is causing the widespread eutrophication of fresh surface water. What's more, the minable global stocks of phosphorus are concentrated in just a few countries and are in decline, posing the risk of global shortages within the next 20 years. "There is a finite amount of phosphorus in the world," says Carpenter, one of the world's leading authorities on lakes and streams. "This is a material that's becoming rarer and we need to use it more efficiently."
Phosphorus is an essential element for life. Living organisms, including humans, have small amounts and the element is crucial for driving the energetic processes of cells. In agriculture, phosphorus mined from ancient marine deposits is widely used to boost crop yields. The element also has other industrial uses.
But excess phosphorus from fertilizer that washes from farm fields and suburban lawns into lakes and streams is the primary cause of the algae blooms that destroy freshwater ecosystems arid degrade water quality. Phosphorus pollution poses a risk to fish and other water life as well as to the animals and humans who depend on clean fresh water. In some instances, excess phosphorus sparks blooms of toxic algae, which pose a direct threat to human and animal life.
"If you have too much phosphorus, you get eutrophication," explains Carpenter, of the cycle of excessive plant and algae growth that significantly degrades bodies of fresh water. "Phosphorus stimulates the growth of algae and weeds near shore and some of the algae can contain cyanobacteria, which are toxic. You lose fish. You lose water quality for drinking." The fertilizer-fueled algae blooms themselves amplify the problem as the algae die and release accumulated phosphorus back into the water.
Complicating the problem, says Carpenter, is the fact that excess phosphorus in the environment is a problem primarily in the industrialized world, mainly Europe, North America and parts of Asia. In other parts of the world, notably Africa and Australia, soils are phosphorus poor, creating a stark imbalance. Ironically, soils in places like North America, where fertilizers with phosphorus are most commonly applied, are already loaded with the element. Bennett and Carpenter argue that agriculture practices to better conserve phosphate within agricultural ecosystems are necessary to avert the widespread pollution of surface waters. Phosphorus from parts of the world where the element is abundant, they say, can be moved to phosphorus deficient regions of the world by extracting phosphorus from manure, for example, using manure digesters. (490 words)

单选题 We learn from Paragraph 1 that the pollution of lakes, rivers and streams is mainly caused by ______.

单选题 The word "eutrophication" (Line 3, Para. 2) most probably means ______.

单选题 Which of the following is not correct about the use of phosphorus?

单选题 What is the result if the algae blooms?

单选题 According to the last paragraph, we learn that ______.