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    It is said that another acre of the world's forest will be destroyed forever. Why is this happening? There are two reasons — land and wood. In many countries the trees have been cut down because the land was needed for animals or crops. In other parts of the world the trees are cut down because their wood is wanted. This wood is used by local people for firewood or it is used for building. But many people don't know that in most places the trees won't be replaced. The soil in the forests is very thin, but it is protected by the trees. When the trees are cut down, the soil is washed away by the rain or blown away by the wind. Soon nothing can be grown on it. The  forest becomes a desert. Then more land will be needed, and more trees will be cut down.
    When the forest is destroyed, it isn't only the trees that are lost — the homes of millions of animals and plants are destroyed, too. All kinds of animals are in danger — fish,reptiles, birds, mammals, insects, and shellfish — as well as thousands of plants.
    Who is to blame for this? The answer is simple: all of us. There are just too many people in the world. The world's population is now six billion. Of course, it's very easy to blame the local people. We don't cut down trees. They do. But the products are bought by people like you and me — wood houses, beds, tables, chairs, paper… Why are the forests being destroyed? Just look around. You are probably using it right now.

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“沙漠明珠”珠光渐暗

      ①和莫高窟同称为敦煌两大奇观的月牙泉有“沙漠明珠”之称,但由于干旱缺水和人为因素的影响,月牙泉水位在不断下降,这颗“明珠”珠光渐暗,甚至有消失的危险。

      ②敦煌市鸣沙山月牙泉管理处提供的水文实测资料表明,1960年月牙泉水域面积为22.3亩,最大水深7.5米;1986年水域面积为13.3亩,最大水深 4.2米;目前水域面积只有9亩,最大水深仅1米左右。

      ③兰州大学资源环境学院教授张明泉23日在此间举行的干旱气候变化与可持续发展国际学术研讨会上说,月牙泉是敦煌区域地下水在地面的自然露头,是整个地下水系统的一个组成部分,月牙泉接受着区域地下水的补给。然而,由于人类活动等原因,敦煌地下水位不断下降,月牙泉水位也随之下降。

      ④地处中国西北的敦煌曾长期依靠疏勒河、党河等河流的上游来水补给地下水,上世纪50年代以来,随着上游水库的修建,这些河流相继出现断流,敦煌地下水失去了补给来源。随着经济的发展,敦煌需水量在不断增加,目前全市每年要抽取4000多万立方米地下水,造成地下水超采严重。

      ⑤为了保住月牙泉,现在每年需要回灌500余万立方米的河水。尽管如此,根据测量.表水水位每年还在以 15厘米左右的速度下降。

      ⑥专家认为,从长远来说,严格控制地下水开采,使敦煌地下水位得到回升,是解决月牙之水位下降问题的根本途径。同时,有关部门还应考虑进行跨流域调水,以进一步缓解敦煌水源短缺的局面。

      ⑦月牙泉位于敦煌市区以南约5公里处,四面被鸣沙山环抱,流沙与泉相隔仅有数十米。

      ⑧这里地处亚洲中部的大沙漠之中,年均降水量在40毫米左右,但蒸发量高达2480多毫米。在这种极端干旱和强烈蒸发的气候条件下,月牙泉却能保持数千年不干涸,这更增添了她的神奇。