剑桥雅思5 Test 3阅读Passage 2原文翻译 Disappearing Delta 消失的三角洲
剑桥雅思5 Test 3 Passage 2阅读原文翻译
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.
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 natural fertilizer accumulated up above the dam in the southern, upstream half of Lake Nasser, instead of passing down to the delta.
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.’
但是，现在，事实证明故事还不止于此。从阿斯旺水坝涌出的不含沉积物水在前往开罗的800公里的行程中，冲走了淤泥和沙子，侵蚀了河床和河岸。史密森尼学会（Smithsonian Institute）的丹尼尔·让·斯坦利（Daniel Jean Stanley）注意到，在河流进入三角洲之前，在开罗采集的水样表明，河流每立方米水中有时携带850克以上的沉积物-几乎是大坝修建之前沉积量的一半。“我羞于承认，直到读了50或60篇研究之后才意识到这一发现的重要性”，斯坦利在Marin Geology上说，“仍有大量沉积物进入三角洲，但实际上没有沉积物进入地中海以补充海岸线。因此，这些沉积物一定被困在了三角洲自己身上”。
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.
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.
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.
根据他对三角洲泻湖沉积物的调查，乔治华盛顿大学的弗雷德里克·西格尔（Frederic Siegel）赞同上述观点。“例如，Manzalah泻湖中水银，铅，铜和锌增长的时间恰好与阿斯旺大坝的建造，廉价电力的提供，以及主要电力基础产业发展建设的时间相同，” 他说。自那时以来，水印的浓度已大大增加。来自使用含铅燃料的发动机和其他工业来源的铅也急剧增加。这些有毒物质很容易进入食物链，影响渔业和农业的生产力。另一个问题是，农业废物中包含的肥料会刺激泻湖中植物的生长并破坏该地区的生态，对渔业产生严重影响。
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.