AThe fertile land 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.

[p:a]尼罗河三角洲的肥沃土地正沿着埃及地中海沿岸以惊人的速度被侵蚀，部分地区每年估计损失达100米。过去，由地中海海流从海岸带走的陆地，通常会被尼罗河带来的沉积物所取代，但如今这种现象已不再发生。

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BUp 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.

[p:b]迄今为止，人们一直将三角洲土地的流失归因于埃及南部的两座大型阿斯旺大坝。这两座大坝几乎截留了原本沿河流下流而来的全部沉积物。在大坝建成之前，尼罗河自由流淌，将大量泥沙从非洲内陆带向北端，并沉积在尼罗河三角洲地区。这一过程持续了七千年，最终覆盖了超过2.2万平方公里的区域，形成层层肥沃的淤泥层。每年的洪水为三角洲地区带来富含养分的新土壤，取代了被海水冲刷走的部分，也使埃及最富饶的粮食种植区不再需要使用化肥。然而，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免受年复一年的洪水与干旱侵袭后，大部分含天然肥料的沉积物却滞留在大坝上游南侧的纳赛尔湖中，未能流向三角洲地区。

CNow, 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.'

[p:c]然而，事情的真相似乎远不止于此。据观察，在从阿斯旺大坝流出的无泥沙水流在向开罗跋涉800公里的过程中，会侵蚀河床和河岸，从而携带沉积物和沙子。史密森尼学会的丹尼尔·让·斯坦利注意到，在河流进入三角洲前于开罗采集的水样显示，该河有时每立方米水中携带超过850克的沉积物——几乎是建坝前水平的一半。“我惭愧地说，直到读了50到60篇研究之后，我才意识到这一现象的重要性，”斯坦利在《海洋地质学》上写道，“三角洲仍然有大量沉积物流入，但几乎没有任何沉积物被排入地中海以补充海岸线。因此，这些沉积物必定被困在三角洲本身。”

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DOnce 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.

[p:d]一旦进入开罗以北地区，尼罗河的大部分水流被引向超过1万公里的灌溉渠道，仅有少量通过三角洲河流直接汇入大海。斯坦利解释说，灌溉渠道中的水仍然静止或流速极慢，因此无法携带沉积物。这些沉积物会沉到渠道底部，随后由农民倾倒到农田中，或与水一起被抽送到位于三角洲外缘附近的四个大型淡水潟湖里。因此，实际上只有极少部分沉积物能够到达海岸线，以补充被地中海洋流冲刷走的部分。

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EThe 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.

[p:e]三角洲平原上的农场以及泻湖中的渔业和水产养殖，构成了埃及大部分的食物供应。但当沉积物最终沉入农田和泻湖时，其中已积聚了来自开罗地区的大量市政、工业和农业废弃物，而开罗地区拥有超过4000万人口。“污染物正在以越来越快的速度积累，”斯坦利表示。

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·西格尔表示赞同。他说：“以曼扎拉泻湖为例，水银、铅、铜和锌的浓度上升与阿斯旺大坝的建设、廉价电力的普及以及大型电力工业的发展同步发生。” 自此以来，水银的浓度显著增加。使用含铅燃料的发动机及其他工业来源产生的铅也急剧上升。这些毒素容易进入食物链，影响渔业和农业的生产力。另一个问题是，农业废弃物中含有肥料，会促进泻湖中植物生长，破坏当地生态平衡，对渔业造成严重影响。

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FAccording 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.

[p:f]据西格尔称，国际环保组织正开始更加关注该地区，部分原因是尼罗河三角洲面临侵蚀和污染问题，但更重要的是，他们担心这一状况可能对整个地中海沿海生态系统造成影响。然而，目前尚无简单的解决方案。斯坦利认为，在短期内，一种可行的方案是人为引发洪水，以冲刷掉三角洲的水道，就像在大坝修建之前自然洪灾所起的作用一样。但他表示，从长远来看，可能需要采用海水淡化等替代方法来增加可用水资源。斯坦利说：“在我看来，埃及必须想出办法，让更多的水能够流经河流和三角洲。”但在人口快速增长、沙漠化严重的地区，这说起来容易做起来难。