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  Disappearing Delta

  日益消失的三角洲

  A The fertile land of the Nile delta is being eroded along Egypt’s Mediterranean coast at an astounding rate,in some parts estimated at 100 metres per year.In the past,land scoured away from the coastline by the currents of the Mediterranean Sea used to be replaced by sediment brought down to the delta by the River Nile,but this is no longer happening.

  A 尼罗河三角洲在地中海沿岸的肥沃土地正以惊人的速度遭到侵蚀。在某些地段,估计侵蚀速度会达到100米/年。过去,由地中海洋流冲刷掉的沿岸土地会得到由尼罗河带到三角洲的土壤的补充,但是现在情况却发生了改变。

  B Up to now, people have blamed this loss of delta land on the two large dams at Aswan in the south of Egypt,which hold back virtually all of the sediment that used to flow down the river. Before the dams were built,the Nile flowed freely carrying huge quantities of sediment north from Africa’s interior to be deposited on the Nile delta.This continued for 7,000 years,eventually covering a region of over 22,000 square kilometres with layers of fertile silt.Annual flooding brought in new, nutrient-rich soil to the delta region,replacing what had been washed away by the sea,and dispensing with the need for fertilizers in Egypt’s richest food-growing area.But when the Aswan dams were constructed in the 20th century to provide electricity and irrigation,and to protect the huge population centre of Cairo and its surrounding areas from annual flooding and drought,most of the sediment with its naturaI fertilizer accumulated up above the dam in the southern, upstream half of Lake Nasser, instead of passing down to the delta.

  B 到目前为止,人们一直在指责埃及南部阿斯旺的两座大坝,认为它们造成了三角洲土地的流失,这两座大坝几乎将所有原来顺尼罗河直下的淤泥都阻挡住了。在建坝之前,尼罗河可以自由地流动,携带非洲北部内陆地区的大量泥沙、淤积到尼罗河三角洲地区,这种情况一直持续了 7000年,最终将这个22,000多平方公里的土地覆盖上了一层又一层肥沃的淤泥。每年的洪水泛滥都会给尼罗河三角洲地区带来新的富有营养的淤泥,补充那些被海水冲刷走的土壤。这样一来,尽管这个地区是埃及粮食产量最高的地区,却不需施加肥料。但是,到了 20世纪,人们建造了阿斯旺水坝来提供电力和进行灌溉,并保护开罗这个人口大城及其周边地区免遭洪水和干旱。自那时起,大多数淤泥连带其中的丰富养分都在大坝南部,Nasser湖的上游淤积起来,而没有被带入尼罗河三角洲。

  C Now, however, there turns out to be more to the story.It appears that the sediment-free water emerging from the Aswan dams picks up silt and sand as it erodes the river bed and banks on the 800-kilometre trip to Cairo.Daniel Jean Stanley of the Smithsonian Institute noticed that water samples taken in Cairo,just before the river enters the delta,indicated that the river sometimes carries more than 850 grams of sediment per cubic metre of water — almost half of what it carried before the dams were built. ‘I’m ashamed to say that the significance of this didn’t strike me until after I had read 50 or 60 studies,’ says Stanley in Marine Geology.‘There is still a lot of sediment coming into the delta, but virtually no sediment comes out into the Mediterranean to replenish the coastline.So this sediment must be trapped on the delta itself.’

  C 然而,现在看来,情况似乎不这么简单。从阿斯旺水坝流出的无沉淀物的河水在到达开罗前的800公里的路程当中,似乎在不断地侵蚀其流经的河床和河岸,泥沙含量在不断增加。Smithsonian学院的Daniel Jean Stanley注意到,从河水流人三角洲前的开罗河段中采集的水样表明,尼罗河携带的泥沙含量有时会多于850g/m3,差不多相当于建坝前的一半。Stanley在《海洋地质学》杂志上说:“说起来有些羞愧,我读了 50到60项研究才惊讶地发现这一重大情况,仍然有大量淤泥流入三角洲地区,但却几乎没有淤泥由此处流入地中海来补充海岸线,这就说明这些淤泥肯定淤积在了三角洲地区。”

  D Once north of Cairo, most of the Nile water is diverted into more than 10,000 kilometres of irrigation canals and only a small proportion reaches the sea directly through the rivers in the delta.The water in the irrigation canals is still or very slow-moving and thus cannot carry sediment, Stanley explains. The sediment sinks to the bottom of the canals and then is added to fields by farmers or pumped with the water into the four large freshwater lagoons that are located near the outer edges of the delta.So very little of it actually reaches the coastline to replace what is being washed away by the Mediterranean currents.

  D 从前在开罗北部,尼罗河水大部分被引入长达1,000公里的灌溉渠道,只有一小部分通过三角洲地区的河流直接汇入海洋。Stanley解释说,因为灌溉渠道中的河水是不流动的或流速很慢,所以不会携带泥沙。泥沙会沉积到灌溉渠的底部,然后由农民施加到田里,或者和河水一起被抽人三角洲外缘附近的四大淡水泻湖中。所以,事实上只有很小的一部分泥沙到达海岸线,补充被地中海洋流冲刷走的土壤。

  E The farms on the delta plains and fishing and aquaculture in the lagoons account for much of Egypt’s food supply.But by the time the sediment has come to rest in the fields and lagoons it is laden with municipal, industrial and agricultural waste from the Cairo region, which is home to more than 40 million people.’Pollutants are building up faster and faster,’ says Stanley.

  E 三角洲平原的农业和泻湖地区的渔业和水产养殖业为埃及提供了大部分食物。但当淤泥开始逐渐在田里和泻湖沉积的时候,淤泥中已经含有大量来自开罗这个人口超过4000万城市的工业和农业废弃物。Stanley说:“污染物增加的速度越来越快。”

  Based on his investigations of sediment from the delta lagoons, Frederic Siegel of George Washington University concurs. ‘In Manzalah Lagoon, for example, the increase in mercury, lead, copper and zinc coincided with the building of the High Dam at Aswan, the availability of cheap electricity, and the development of major power-based industries,’ he says. Since that time the concentration of mercury has increased significantly. Lead from engines that use leaded fuels and from other industrial sources has also increased dramatically. These poisons can easily enter the food chain, affecting the productivity of fishing and farming. Another problem is that agricultural wastes include fertilizers which stimulate increases in plant growth in the lagoons and upset the ecology of the area, with serious effects on the fishing industry.

  乔治华盛顿大学的Frederic Siegel根据自己对尼罗河三角洲地区泻湖沉积物的调查,对Stanley的说法表示赞同。他说:“以Manzalah泻湖为例,随着阿斯旺高坝的建设、廉价电力的使用和大型耗电工业的发展,湖中汞、铅、铜和锌的含量也增多了。”从那时起,汞的浓度便大幅上升。使用含铅燃料的发动机产生的铅和其他工业源产生的铅也大幅度增加。这些有害物质很容易就会进入到食物链中,从而影响渔业和农业的产量。另一个问题就是包括化肥(残留物)在内的农业废弃物会刺激泻湖中植物的迅速生长,扰乱该地区的生态平衡,进而对渔业产生严重的影响。

  F According to Siegel, international environmental organisations are beginning to pay closer attention to the region, partly because of the problems of erosion and pollution of the Nile delta, but principally because they fear the impact this situation could have on the whole Mediterranean coastal ecosystem. But there are no easy solutions. In the immediate future, Stanley believes that one solution would be to make artificial floods to flush out the delta waterways, in the same way that natural floods did before the construction of the dams. He says, however, that in the long term an alternative process such as desalination may have to be used to increase the amount of water available. ‘In my view, Egypt must devise a way to have more water running through the river and the delta,’ says Stanley. Easier said than done in a desert region with a rapidly growing population.

  F 据Siegel说,国际环保组织开始日益关注这一地区,一部分原因是因为侵蚀问题和尼罗河三角洲污染的问题,但主要原因还是他们害怕这种情况会影响到整个地中海沿岸的生态系统。可是对于这个问题并没有简单的解决方案。Stanley认为,在不远的将来,使用人工洪水,像建造大坝前自然洪水那样冲刷三角洲的水道可能会是一种解决方案。但是,他又说,从长远角度来看,可能需要采取其他的作法(如海水淡化)来增加可用水的数量。Stanley说:“我认为,埃及必须设计出一种方案,使更多的水流入尼罗河,流经三角洲地区。”在这样一个人口迅速增长的沙漠地区,做到这一点的确不是一件容易的事。

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