东非有一个湖泊，面积大得仿佛是一片大海。现在想象一下，一层厚厚的绿色地毯铺满了它的边缘。这在维多利亚湖上真实发生过。根据美国国务院关于凤眼蓝（水葫芦）的案例研究，这种植物已入侵五大洲53个国家。同一案例研究称，它曾覆盖维多利亚湖约90%的湖岸线。一切始于一种因观赏性而被种植的植物。一株漂亮的园艺植物如何成为全球入侵物种美国国家航空航天局（NASA）地球观测站描述了此类入侵通常是如何开始的。
There’s a lake in East Africa that’s so big it feels like a sea. Now imagine a thick green carpet spreading across its edges. That really happened on Lake Victoria. According to a U.S. State Department case study on water hyacinth, this plant has infested 53 countries across five continents. The same case study says it covered some 90 percent of Lake Victoria’s shoreline. It all began with a plant that people grew because it was pretty. How a pretty garden plant became a global invaderNASA's Earth Observatory describes how such invasions usually start.
有人在庭院池塘种植凤眼蓝，因为喜欢它淡紫色的花朵。随后，这种植物开始以每6至18天面积翻倍的速度生长。真正的麻烦始于园丁将其丢弃之时。据NASA称，凤眼蓝原产于南美热带地区。它于1879年前后被引入非洲，约110年后找到了通往维多利亚湖的路径。国务院案例研究称，它于1989年首次在该湖被发现。这种植物威胁渔业、水电生产、农业、人类健康和经济。
Someone plants a water hyacinth in a garden pond because they like its lavender flowers. Then the plant begins to double its area every 6 to 18 days. The real trouble begins when the gardener throws it away. The plant is native to the South American tropics, according to NASA. It was brought to Africa around 1879, and about 110 years later it found its way to Lake Victoria. The State Department case study said it was first spotted on the lake in 1989. The plant threatens fisheries, hydroelectric production, agriculture, human health, and the economy.
凤眼蓝对维多利亚湖造成的影响维多利亚湖是非洲最大湖泊，由坦桑尼亚、肯尼亚和乌干达共享。按面积计算，它是世界第二大淡水湖。案例研究将其描述为凤眼蓝危害的典型案例。厚厚的植被垫与本地植物、鱼类和青蛙争夺氧气，案例研究指出这常导致窒息和大规模死亡。研究还称，小渔船几乎无法在湖面上航行。
What the plant did to Lake VictoriaLake Victoria is the largest lake in Africa and is shared by Tanzania, Kenya, and Uganda. It is the world’s second-largest freshwater lake by surface area. The case study describes it as a major example of the damage water hyacinth can cause. Thick mats compete with native plants, fish, and frogs for oxygen, and the case study says that this often results in suffocation and large die-offs. It also says small fishing boats were nearly impossible to steer across the lake.
NASA还指出，阳光无法穿透植被垫，导致水下本地植物缺乏所需光照。这种植物还会堵塞灌溉运河以及向湖岸城镇和村庄供水的管道。到1998年，NASA估计该植物已蔓延覆盖湖面约20,000公顷，约合77平方英里。
NASA also points out that sunlight does not pass through the mats, so native plants below are missing the light they need. The plant can also clog irrigation canals and the pipes that bring water to cities and villages on the shore. By 1998, NASA estimated the plant had grown to cover some 20,000 hectares of the lake. That’s about 77 square miles.
美国国家航空航天局（NASA）还指出，阳光无法穿透这些植物垫，因此下方的本地植物缺乏所需的光照。NASA 还表示，这种植物会堵塞灌溉渠以及向湖岸城市和村庄供水的管道。到 1998 年，NASA 估计该植物已蔓延覆盖湖面约 20,000 公顷。这大约相当于 77 平方英里。代价与卷土重来该案例研究发现，入侵造成的经济损失估计每年高达 1.5 亿美元。
NASA also points out that sunlight does not pass through the mats, and so native plants below are missing the light they need. NASA also says the plant can clog irrigation canals and the pipes that bring water to cities and villages on the shore. By 1998, NASA estimated the plant had grown to cover some 20,000 hectares of the lake. That’s about 77 square miles. The price tag and the comebackThe case study found that the economic cost of the invasion is estimated at $150 million each year.
这只是一个估算数字，而非精确账单。对于依赖湖泊生存的人们来说，破坏可能非常严重，但故事并未就此结束。NASA 表示，清除行动、以该植物为食的象鼻虫以及其他因素已将其控制在可管理的水平。但 2006 年 12 月的卫星图像显示，该植物再次大量繁殖。2006 年底的暴雨导致注入肯尼亚温纳姆湾的河流泛滥。
That’s one estimate, not a precise bill. The damage can be severe for people who depend on the lake, but the story does not end there. NASA says removal efforts, a weevil that eats the plant, and other factors have cut it down to manageable levels. But satellite images in December 2006 showed the plant was back in business. Heavy rains in late 2006 flooded the rivers that feed Kenya’s Winam Gulf.
洪水将农田径流和富含营养的沉积物冲入湖中，NASA 称这助长了新一轮爆发。给我们的启示植物可以远离原产地传播，其中大多数无害。但有些在错误的地方会造成大麻烦。水葫芦表明，一个微不足道的选择——如随意丢弃一株植物——可能演变成大问题。因此，请避免将不需要的池塘或水族箱植物丢弃在河流或湖泊中。
Floodwaters brought farm run-off and nutrient-rich sediment into the water, and NASA says this contributed to a new outbreak. What this can teach usPlants can travel far from home, and most are harmless. But some can cause big trouble in the wrong spot. Water hyacinth shows how a small choice, like dumping a plant aside, can become a large problem. So, avoid disposing of unwanted pond or aquarium plants in a river or lake.
购买外来植物前，最好先了解当地法规。本案例研究源自一份已归档的美国国务院网站，NASA 的数据截止至 2007 年，因此这些数字仅代表当时的快照。大自然自有其平衡，有时我们无意中就会打破这种平衡。
Before buying exotic plants, it is a good idea to check local rules. This case study is from an archived State Department site and NASA’s account dates to 2007, so the numbers are a snapshot in time. Nature has a balance of its own, and sometimes we can upset that without even meaning to.