VOA标准英语2011--Species Loss Compromises Earth’s Vital

Species Loss Compromises Earth’s Vital Systems

Scientists have long thought that diverse ecosystems² like forests, lakes and streams are especially good at removing pollutants⁴ that human activities put into the environment.
A new study in the journal Nature, confirms that theory.
University of Michigan ecologist Bradley Cardinale demonstrates how water quality improves in a more diverse ecosystem¹.
In his laboratory Cardinale built 150 meter-long cases that enclosed mock streams. He cultured between one and eight common algae⁵ species in each waterway. The tiny micro-organisms are important actors in removing pollution from the water. He then exposed the streams to nitrate, a common pollutant³ from agricultural run-off and auto⁶ emissions⁷.
Bradley Cardinale
University of Michigan graduate students monitor a water quality experiment.
It took Cardinale three years to set up the experiment, run it and process the data. On average streams with eight species were cleaned four-and-one-half times faster than water with just one species. Cardinale says specific algae species adapt to specific stream habitat.
"As you added more and more species to the stream what happened is that all of these different habitats got filled up and the stream as a whole became a much better bio-filter for this particular nutrient⁸ pollutant."
Cardinale says scientists as far back as Charles Darwin in the 1860s proposed that every species plays a specific role in the ecosystem and compliments each other.
"Basically a diverse world always comes down to having unique niches¹⁰ that allow species somehow to exist with each other. So any system where niche⁹ partitioning is a key biological phenomenon, the results of the study I've shown here and it's implication for water quality should probably apply."
Bradley Cardinale
This sample mock stream contains algae growth after six months and represents between 12 to 15 generations and millions of algae cells.
While Cardinale's study showed that water quality improved in the streams with greater biodiversity, the ecologist notes it did not address how many species would be needed to completely remove the pollutant from soil and water.
"We previously¹¹ expected that somewhere between three and five species was enough to clean nitrate out of soil and water. And my study extends those results to at least to eight species where we didn't even begin to see a plateau."
Cardinale says he expects the number is more than eight, but far less than the several hundred found in a stream. The University of Michigan ecologist hopes future studies will determine that tipping point.

1 ecosystem   

n.生态系统

参考例句：

• This destroyed the ecosystem of the island.这样破坏了岛上的生态系统。
• We all have an interest in maintaining the integrity of the ecosystem.维持生态系统的完整是我们共同的利益。

2 ecosystems   

n.生态系统( ecosystem的名词复数 )

参考例句：

• There are highly sensitive and delicately balanced ecosystems in the forest. 森林里有高度敏感、灵敏平衡的各种生态系统。 来自《简明英汉词典》
• Madagascar's ecosystems range from rainforest to semi-desert. 马达加斯加生态系统类型多样，从雨林到半荒漠等不一而足。 来自辞典例句

3 pollutant   

n.污染物质，散布污染物质者

参考例句：

• Coal itself is a heavy pollutant.煤本身就是一种严重的污染物。
• Carbon dioxide may not be a typical air pollutant.二氧化碳可能不是一种典型的污染物。

4 pollutants   

污染物质（尤指工业废物）( pollutant的名词复数 )

参考例句：

• Pollutants are constantly being released into the atmosphere. 污染物质正在不断地被排放到大气中去。
• The 1987 Amendments limit 301(g) discharges to a few well-studied nonconventional pollutants. 1987年的修正案把第301条（g）的普通排放限制施加在一些认真研究过的几种非常规污染物上。 来自英汉非文学 - 环境法 - 环境法

5 algae   

n.水藻，海藻

参考例句：

• Most algae live in water.多数藻类生长在水中。
• Algae grow and spread quickly in the lake.湖中水藻滋蔓。

6 auto   

n.(=automobile)(口语)汽车

参考例句：

• Don't park your auto here.别把你的汽车停在这儿。
• The auto industry has brought many people to Detroit.汽车工业把许多人吸引到了底特律。

7 emissions   

排放物( emission的名词复数 )； 散发物（尤指气体）

参考例句：

• Most scientists accept that climate change is linked to carbon emissions. 大多数科学家都相信气候变化与排放的含碳气体有关。
• Dangerous emissions radiate from plutonium. 危险的辐射物从钚放散出来。

8 nutrient   

adj.营养的，滋养的；n.营养物，营养品

参考例句：

• Magnesium is the nutrient element in plant growth.镁是植物生长的营养要素。
• The roots transmit moisture and nutrient to the trunk and branches.根将水分和养料输送到干和枝。

9 niche   

n.壁龛；合适的职务(环境、位置等)

参考例句：

• Madeleine placed it carefully in the rocky niche. 玛德琳小心翼翼地把它放在岩石壁龛里。
• The really talented among women would always make their own niche.妇女中真正有才能的人总是各得其所。

10 niches   

壁龛( niche的名词复数 )； 合适的位置[工作等]； （产品的）商机； 生态位（一个生物所占据的生境的最小单位）

参考例句：

• Some larvae extend the galleries to form niches. 许多幼虫将坑道延伸扩大成壁龛。
• In his view differences in adaptation are insufficient to create niches commensurate in number and kind. 按照他的观点，适应的差异不足以在数量上和种类上形成同量的小生境。

11 previously   

adv.以前，先前（地）

参考例句：

• The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
• Let me digress for a moment and explain what had happened previously.让我岔开一会儿，解释原先发生了什么。