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  • 生态系统中的氮循环

    Aerial view of a coastal area showing discolored water due to nutrient runoff.

     

    Why are these fish dead?
    ::为什么这些鱼死了?

    In a  dead zone , there is so little oxygen that fish can't live. What causes the oxygen to disappear? Indirectly, it's nitrogen.
    ::在死区,有如此少的氧气 鱼类无法生存。是什么导致氧气消失?间接地,它是氮。

    The Nitrogen Cycle
    ::氮循环

    Living things need nitrogen. Nitrogen is a key  element  in  proteins . Like carbon, nitrogen cycles through  ecosystems . The  nitrogen cycle  is pictured below ( Figure   ).
    ::生命需要氮。 氮是蛋白质中的一个关键元素。 与碳一样,氮在生态系统中循环。 氮循环的图示如下( 图 ) 。

    The nitrogen cycle, showing nitrogen's movement through air, soil, and living organisms.

     

    The nitrogen cycle includes air, soil, and living things.
    ::氮循环包括空气、土壤和生物。

    Fixing Nitrogen
    ::固化氮

    Air is about 78 percent nitrogen.  Decomposers  release nitrogen into the air from dead organisms and their wastes. However,  producers  such as plants can’t use these forms of nitrogen. Nitrogen must combine with other elements before producers can use it. This is done by certain bacteria in the  soil . It’s called “fixing” nitrogen.
    ::空气约为78%的氮。 分解器将死亡生物及其废物的氮释放到空气中。 但是,植物等生产者不能使用这些氮。 氮必须与其他元素相结合,生产者才能使用氮。 这是由土壤中某些细菌完成的。 它被称为“固定”氮。

    Human Actions and the Nitrogen Cycle
    ::人类行动和氮循环

    Nitrogen is one of the most important  nutrients  needed by plants. That’s why most plant fertilizers contain nitrogen. Adding fertilizer to soil allows more plants to grow. As a result, a given amount of land can produce more food. So far, so good. But what happens next?
    ::氮是植物需要的最重要养分之一。 这就是为什么大多数植物肥料都含有氮。 将肥料添加到土壤中可以让更多的植物生长。 结果,一定数量的土地可以生产更多的粮食。 到目前为止,这已经是好事。 但接下来会发生什么呢?

    Rain  dissolves fertilizer in the soil.  Runoff  carries it away. The fertilizer ends up in bodies of  water , from  ponds  to oceans. Nitrogen is a fertilizer in the water. Since there is a lot of nitrogen, it causes algae to grow out of control. Pictured below is a pond covered with algae ( Figure   ). Algae use up carbon dioxide in the water. After the algae die, decomposers break down the dead tissue. The decomposers use up all the oxygen in the water. This creates a dead zone. A  dead zone  is an area in a body of water where nothing grows because there is too little oxygen. There is a large dead zone in the Gulf of Mexico ( Figure   ). The U.S. states outlined on the   have  rivers  that drain into the Gulf of Mexico. The rivers drain vast agricultural lands. The water carries fertilizer from these areas into the Gulf.
    ::雨水会溶解土壤中的肥料。 雨水会将肥料运走。 肥料最终会进入水体, 从池塘到海洋。 氮气是水中的肥料。 由于氮气很多, 它会使藻类生长失控。 下面是藻类覆盖的池塘( Figore ) 。 藻类死后, 分解器会分解死亡组织。 分解器会消耗水中的所有氧气。 这造成了一个死亡区。 死亡区是水体中的一个地区, 水体里没有生长任何东西, 因为氧气太少。 墨西哥湾( Figore ) 存在一个巨大的死亡区 。 在墨西哥湾( Figore ) 所描述的美国州有河流排入墨西哥湾的河流。 河流排出大量的农业用地。 水会从这些地区将肥料输送到海湾。

    A pond covered with algae and a map showing the Gulf of Mexico dead zone.

     

    The pond on the left is covered with algae because there is too much nitrogen in the water. The red-shaded area in the map on the right is a dead zone in the Gulf of Mexico. It’s called the hypoxic (“low oxygen”) zone in the figure.
    ::左边的池塘被藻类覆盖,因为水中的氮过多。 地图右边的红色阴影区是墨西哥湾的一个死区。 图中称为缺氧区(低氧区 ) 。

    This very thorough video on the nitrogen cycle with an aquatic perspective was created by high school students.
    ::这是由中学生制作的关于氮循环与水生观点的非常彻底的录像。

    Summary
    ::摘要

    • Nitrogen is an essential part of many molecules needed by living organisms.
      ::氮是活生物体需要的许多分子的重要组成部分。
    • Nitrogen is fixed when it is changed into a form that organisms can use.
      ::氮在改变为生物可以使用的形态时是固定的。
    • Dead zones come about when excess nitrogen in the water causes algae to grow out of control. Decomposers use oxygen to decompose the algae when they die. The lack of oxygen makes it impossible for other organisms to live in that zone.
      ::当水中的过量氮导致藻类生长失控时,就会产生死亡区。 分解者在藻类死亡时使用氧气进行分解。 缺氧使得其他生物无法生活在该区。

    Review
    ::回顾

    1. What is nitrogen fixing?
      ::什么是氮固化?
    1. Why is nitrogen fixing important?
      ::为什么固氮很重要?
    1. How do dead zones come about?
      ::死区是如何形成的?
    1. Why does the Gulf of Mexico contain such a large dead zone?
      ::为什么墨西哥湾有这么大的死区?

    Explore More
    ::探索更多

    Use the resource below to answer the questions that follow.
    ::利用以下资源回答以下问题。

    1. What percentage of the air is nitrogen?
      ::氮气占空气的百分比是多少?
    1. How is nitrogen removed from the air?
      ::如何从空气中去除氮?
    1. What contributes nitrogen to the soil?
      ::氮在土壤中的成分是什么?
    1. What happens to soil nitrites?
      ::土壤亚硝酸盐怎么办?
    1. How is nitrogen released from the soil?
      ::氮是如何从土壤中释放出来的?
    1. Why is this called the nitrogen cycle?
      ::为什么这叫氮循环?