启德国际教育规划院：托福阅读英文及中文翻译Day 2

启德国际教育规划院：托福阅读英文及中文翻译Day 2

Day 2   Maya Water Problems

To understand the ancient Mayan people who lived in thearea that is today southern Mexico and Central America and the ecologicaldifficulties they faced, one must first consider their environment, which wethink of as "jungle" or "tropical rainforest." This view isinaccurate, and the reason proves to be important. Properly speaking, tropicalrainforests grow in high-rainfall equatorial areas that remain wet or humid allyear round. But the Maya homeland lies more than sixteen hundred kilometersfrom the equator, at latitudes 17 to 22 degrees north, in a habitat termed a"seasonal tropical forest." That is, while there does tend to be arainy season from May to October, there is also a dry season from Januarythrough April. If one focuses on the wet months, one calls the Maya homeland a"seasonal tropical forest"; if one focuses on the dry months, onecould instead describe it as a "seasonal desert."

From north to south in the Yucatan Peninsula, where theMaya lived, rainfall ranges from 18 to 100 inches (457 to 2,540 millimeters)per year, and the soils become thicker, so that the southern peninsula wasagriculturally more productive and supported denser populations. But rainfallin the Maya homeland is unpredictably variable between years; some recent yearshave had three or four times more rain than other years. As a result, modernfarmers attempting to grow corn in the ancient Maya homelands have facedfrequent crop failures, especially in the north. The ancient Maya were presumablymore experienced and did better, but nevertheless they too must have facedrisks of crop failures from droughts and hurricanes.

Although southern Maya areas received more rainfall thannorthern areas, problems of water were paradoxically more severe in the wetsouth. While that made things hard for ancient Maya living in the south, it hasalso made things hard for modern archaeologists who have difficultyunderstanding why ancient droughts caused bigger problems in the wet south thanin the dry north. The likely explanation is that an area of undergroundfreshwater underlies the Yucatan Peninsula, but surface elevation increasesfrom north to south, so that as one moves south the land surface liesincreasingly higher above the water table. In the northern peninsula theelevation is sufficiently low that the ancient Maya were able to reach thewater table at deep sinkholes called cenotes, or at deep caves. Inlow-elevation north coastal areas without sinkholes, the Maya would have beenable to get down to the water table by digging wells up to 75 feet (22 meters)deep. But much of the south lies too high above the water table for cenotes orwells to reach down to it. Making matters worse, most of the Yucatan Peninsulaconsists of karst, a porous sponge-like limestone terrain where rain runsstraight into the ground and where little or no surface water remainsavailable.

How did those dense southern Maya populations deal withthe resulting water problem? It initially surprises us that many of theircities were not built next to the rivers but instead on high terrain in rollinguplands. The explanation is that the Maya excavated depressions, or modifiednatural depressions, and then plugged up leaks in the karst by plastering thebottoms of the depressions in order to create reservoirs, which collected rainfrom large plastered catchment basins and stored it for use in the dry season.For example, reservoirs at the Maya city of Tikal held enough water to meet thedrinking water needs of about 10,000 people for a period of 18 months. At thecity of Coba the Maya built dikes around a lake in order to raise its level andmake their water supply more reliable. But the inhabitants of Tikal and othercities dependent on reservoirs for drinking water would still have been in deeptrouble if 18 months passed without rain in a prolongeddrought. A shorter drought in which they exhausted their stored food suppliesmight already have gotten them in deep trouble, because growing crops requiredrain rather than reservoirs.

参考译文：玛雅的水源问题为了了解生活在今天南墨西哥和中美洲地区的古玛雅人，以及他们所面对的生态困境，我们必须先研究他们生活的环境，也就是今天我们所谓的“丛林”或者“热带雨林”。这种观点并不准确，但是环境因素的意义还是很重要的。严格意义上讲，热带雨林生长在赤道多雨地区，气候常年潮湿。但是玛雅遗址位于北纬17°到22°，距离赤道1 600公里以上，也就是通常所说的“热带季雨林”地区。也就是说，该地区5～510月为雨季，而１～４月为旱季。如果着眼于雨季，可以说玛雅遗址位于“热带季雨林”，如果着眼于旱季，那玛雅遗址就可以被称之为“季节性沙漠”了。

玛雅人所居住的尤卡坦半岛自北向南的年降水量为18到100英寸（457到2540毫米）逐级递增的，而且土壤厚度也是逐渐增加，所以半岛南部的农业生产力相对较高，也就能养活更多人口。不过玛雅遗址每年降雨量变化很大，很难预测。最近一些年份的降雨次数要比其他年份多三四倍。因此，如今农民要在玛雅遗址种植谷物就要面临频繁的作物减产的风险，尤其在半岛的北部地区。古玛雅人也许更有经验也做得更好，但是不管怎么说他们都必须面对旱灾和飓风带来的颗粒无收的风险。

尽管玛雅遗址的南部比北部降水量多，但是在潮湿的南方水资源问题反而更加尖锐。生活在南部地区的人古玛雅人所面临的麻烦，如今也困扰着考古学家，他们想不通为什么湿润的南方比干旱的北方更容易受到旱灾影响。一种可能的解释是，尤卡坦半岛的地下水资源区域是倾斜的，但是地表海拔从北向南递增，所以，越往南地表就会越高于地下水位。而半岛北部海拔非常低，因此古玛雅人可以由深层排水口或者深洞到达地下水位，这种深层排水口叫做“竖井”。在没有排水口且海拔较低的北部沿海地区，玛雅人就需要借助凿井到达75英尺（22米）深的地下水含水层。但在南方若想通过排水口或凿井达到含水层的话，深度就要深得多。更糟糕的是，尤卡坦半岛大部分地区属于喀斯特地貌，多孔状如海绵的石灰岩地形，雨水直接流入地下，几乎没有地表水余留。

那么南部如此密集的玛雅人是如何应对水资源问题的呢？起初最令我们惊讶的是，玛雅的很多城市并没有建在河边而是建在起伏的高地上。有种解释是，玛雅人挖掘或者改造自然的低地，然后在低地的底部涂抹上灰泥来堵住喀斯特地貌的裂口，从而建成水库，收集雨水以备旱季之用。比如说，位于玛雅提卡尔城的水库的蓄水可供一万人饮用18个月。在科巴城，玛雅人围绕湖泊建造堤坝，增加高度从而保障水源供给。但是提卡尔以及其他城市的居民们的饮用水都靠这些水库解决，如果18个月持久干旱滴雨未下，之后他们便要陷入困境。即使是短期的干旱，储存的食物供应的耗费或许已经让他们举步维艰，因为农作物的生长需水量要比水库大得多。

竖井是开挖或清理坎儿井暗渠时运送地下泥沙或淤泥的通道，也是送气通风口。井深因地势和地下水位坎儿井竖井高低不同而有深有浅，一般是越靠近源头竖井就越深，最深的竖井可达90米以上。

喀斯特（KARST）即岩溶，是水对可溶性岩石（碳酸盐岩、石膏、岩盐等）进行以化学溶蚀作用为主，流水的冲蚀、潜蚀和崩塌等机械作用为辅的地质作用，以及由这些作用所产生的现象的总称。由喀斯特作用所造成地貌，称喀斯特地貌（岩溶地貌）。