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  3. Fertilizer use has exploded, overloading plants worldwide, likely altering ecosystems for decades to centuries, scientists repor

Fertilizer use has exploded, overloading plants worldwide, likely altering ecosystems for decades to centuries, scientists repor

admin2016-12-18  93
问题     Fertilizer use has exploded, overloading plants worldwide, likely altering ecosystems for decades to centuries, scientists report Thursday. In the journal Science, a review led by Donald Canfield of the University of Southern Denmark found that fertilizer use worldwide increased 800% from 1960 to 2000. "Given the rising costs of synthetic fertilizer production, this overuse is not only economically expensive, but also initiates a series of large-scale environmental impacts," says the review.
    Fundamentally, nitrogen from fertilizers has led to an explosion in "dead zones" in seas and oceans, upsetting a cycle of nutrients balanced with growth that has lasted for billions of years, the authors find.
    As well, the excess nitrogen is forming large amounts of nitrous oxide(一氧化二氮), a powerful greenhouse gas in wetlands, adding to climate change. Agriculture today produces about a quarter of the nitrous oxide in the atmosphere.
    "The effects of humans have been profound. In the last few decades we have doubled the worldwide biological availability of nitrogen, an element that often limits growth of plants and algae," says Thomas Jordan of the Smithsonian Environmental Research Center in Eclgewater, Md., who was not part of the review. The review, "is a very careful analysis of the nitrogen cycle by three of the world authorities in this area," says biochemist Robert Blankenship of Washington University in St. Louis, who also was not part of the review. "The concerns they raise for how the nitrogen cycle is now significantly out of balance are important and need to be addressed by changing agricultural practices. The world’s food supply depends directly on nitrogen application in the form of fertilizer, but current practices are such that much of the applied nitrogen ends up in rivers and eventually in the ocean where it causes serious problems."
    "Natural feedbacks driven by microorganisms will likely produce a new steady state over time scales of many decades," say the review authors. "However, because of the projected increase in human population through at least 2050, there will be demand for an increase in fixed nitrogen for crops to feed this population." And that will mean a lot more dead zones, they warn, like the one that blooms yearly, in 2010 about the size of New Jersey, in the Gulf of Mexico.
    "Several new approaches and a much wider use of more sustainable time-honored practices, however, can decrease nitrogen use substantially," they conclude. The rising cost and environmental toll of fertilizers will increase demand for less use on farms, they add. "However, even with management, the future cycle will likely be different from the one that preceded the Industrial Revolution."
According to Robert Blankenship, the nitrogen cycle is out of balance because______.
选项 A、nitrogen is applied in the form of fertilizer
B、much nitrogen ends up in seas and oceans
C、food supply depends directly on nitrogen
D、much nitrogen is applied in agriculture
答案B
解析 第3段倒数第2句末尾的并列句and need to be addressed by changing agricultural practices表明氮循环的不平衡是因为agricultural practices不当所致，最后一句中的but current practices are such that…可知问题在于“大多数的氮渗入了河流中，最后流入大海”，这就是导致氮循环失衡的原因。因此，本题应选B．
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