A部分

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部分

尼罗河三角洲的肥沃土地正在以惊人的速度被侵蚀，有些地区的侵蚀速度估计每年达到100米。过去，地中海海洋洋流冲刷沿岸带走的土地会得到尼罗河带来的沉积物的补充，但现在这种情况不再发生。

B部分

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.

B部分

到目前为止，人们一直将尼罗河三角洲土地的损失归咎于埃及南部阿斯旺的两座大坝，这些大坝几乎阻断了河流中原本会流下来的所有沉积物。在修建大坝之前，尼罗河自由地流动，从非洲内陆带来大量沉积物北上，堆积在尼罗河三角洲上。这种情况持续了7000年，最终用肥沃的淤泥覆盖了超过2.2万平方公里的地区。每年的洪水给三角洲地区带来新的富含养分的土壤，取代了被海洋冲刷掉的土壤，使埃及最富裕的农田无需使用化肥。然而，在20世纪修建阿斯旺大坝以提供电力和灌溉，并保护开罗及其周边地区的大规模人口中心免受年度洪水和干旱影响时，大部分带有天然肥料的沉积物在南部坝湖纳赛尔湖的上游堆积，而不是流向三角洲。

C部分

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部分

然而，现在看来事情并非如此简单。据史密森尼学会的丹尼尔·让·斯坦利观察到，阿斯旺大坝释放的无沉淀物的水会在800公里的行程中侵蚀河床和河岸，并携带淤泥和沙粒。在进入三角洲之前，开罗的水样本表明，该河流有时每立方米水中携带超过850克的沉积物，几乎是修建大坝之前的一半。斯坦利在《海洋地质》杂志中表示：“我很惭愧，直到我读了50到60份研究报告之后才意识到这个问题的重要性。三角洲仍然有很多沉积物进入，但几乎没有沉积物流入地中海来补充海岸线。因此，这些沉积物必须被困在三角洲上。”

D部分

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部分

一旦过了开罗，大部分尼罗河水被引入10,000多公里的灌溉渠道，只有很少一部分通过三角洲的河流直接流入大海。灌溉渠道中的水是静止或非常缓慢流动的，因此无法携带沉淀物。沉淀物沉降到渠道底部，然后由农民添加到田地中或与水一起泵入位于三角洲外缘附近的四个大淡水泻湖中。因此，很少有沉淀物真正到达海岸线，以取代被地中海洋流冲刷的土壤。

E部分

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.

E部分

三角洲平原上的农场以及泻湖中的捕鱼和水产养殖占据了埃及很大一部分食物供应。但当沉积物停留在田地和泻湖中时，它会携带大约4,000万人口的开罗地区的市政、工业和农业废物，其中包括污染物。斯坦利说：“污染物堆积得越来越快。”根据乔治华盛顿大学的弗雷德里克·席格尔对泻湖沉积物的研究，他表示：“例如，在曼扎拉泻湖中，汞、铅、铜和锌的增加与阿斯旺大坝的修建、廉价电力的供应以及大型电力工业的发展相一致。”自那时以来，汞的浓度显著增加。来自使用含铅燃料的发动机和其他工业来源的铅也大幅增加。这些有毒物质很容易进入食物链，影响渔业和农业的产能。另一个问题是农业废物包括刺激泻湖中植物生长的化肥，扰乱了该地区的生态系统，对渔业产生严重影响。

F部分

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部分

根据席格尔的说法，国际环境组织开始更加关注该地区，部分原因是尼罗河三角洲的侵蚀和污染问题，但主要原因是他们担心这种情况对整个地中海沿岸生态系统的影响。但问题并不容易解决。斯坦利认为，短期内的一个解决方案是人工洪水，以冲刷三角洲的水道，就像在修建大坝之前自然洪水所做的那样。然而，他表示，从长远来看，可能需要使用海水淡化等替代性过程来增加可用水量。斯坦利说：“在我看来，埃及必须想出一种办法让更多的水流经河流和三角洲。”但在这个快速增长的沙漠地区实现这一目标并不容易。