Where does all this nitrogen come from? The answer is farms. The Mississippi River system carries water from 33 American states and part of Canada to the gulf of Mexico. 那么这些氮是从何而来呢?答案就是农场.密西西比河水系将美国33个州以及加拿大部分地区的水带到墨西哥湾. ____________________ Aaron Packman is a professor of Civil and Environmental Engineering at Northwestern University. He says farmers may be able to better control the amount of nitrate fertilizer they put on fields. Aaron Packman美国西北大学土木与环境工程学的教授.他说,农民也许能够更好的控投放到田地里的氮肥总量.
