WhatDoes aNaturalStreamLookLike?ByEmmaMarris孙大明选注【选注者言】自然的溪流应该是什么样子?是我们印象中的那种“小河弯弯”吗?并不尽然。美国研究者认为，到18世纪后期，美国东部的溪流已经建了很多水坝，由于砍伐森林造成了水土流失，在水底存有厚厚的沉积物；后来因为蒸汽机的使用取代水力发电，很多水坝被打开缺口，湍急的流水冲开积淀物，才形成了今天蜿蜒曲折的形状，这恰恰是人工改造的结果。Ecologists working to restore streams in the easternUnitedStates have been using a misguided ideal，according to new research．The picturesque④notion，supported by many ecologists。that a stream untouched by human hands meanders②in a singleS-shaped channel with high vertical banks seems tO be wrong．Instead。this shape iS an artefact of the thousands of small mill dams built on eastern streams bet访een the seventeenth and nineteenth centuries． sayRobertWalter andDorothyMerritts ofFranklin andMarshallCollege inLancaster，Pennsylvania．The team poured over old maps，looked at historical documents， visited hundreds of streams and used light detection and ranging(LIDAR)④techniques to get a sense of the lay of the land underneath modern vegetation@．In some places。they used a backhoe⑤to expose sedimentary⑩layers and check on the geological history．女弋七女女电电七电七弋电七七女电电七七女电电七女弋女电女专 research also shows that most people consider themselves happy most of the time，’’saysUniversity ofEdinburgh’SBates．“We’re wired to be optimistic．Most people think they’re happier than mostEother]people．’’And even if you aren’t part of that lucky majority，Bates says，there’S always that other50％of overall life satisfaction that，according tO his research，iS not genetically predetermined．To feel happier，he recommends mimicking@the personality traits of those who are：Be social，even if it’S only with a few people；set achievable goals and work toward them；and concentrate on putting setbacks and worries in perspective④．Don’t worry，as the saying goes．Be happy．■2008年第5期总第329期圈凰The researchers conclude that streams in thePiedmont region of the easternUnitedStates—j ust to the eastOi theAppalachian mountains——were more like swamps than streams whenEuropeans first arrived．The water didn’t run in a single channel，but rather was in branching streams，pools and mud，they report inScience．By the1ate eighteenth century，many streams had been dammed(with dams as wide as whole valleys，because the streamsWereSO sDread ont)，and they turned into a necklace of mill ponds，One everv four kilometres or so．Meanwhile．deforestatiod川on the high ground increased the water supply and inflow of soil．Mill ponds collected thick layers of sediment on their bottoms．When steam power started to displace④hydropower凹for milling．forging and mining，many of these dams were breached。．The resulting bursts of fast—flowing water cut a channel through the sediment in the old ponds，creating the meandering shape thought of as‘natural’today．“These characteristic meandering streams in wide valley bottoms with steep—cut banks are not normal，”saysWalter．Muddied watersSimilar work has been done in thePacificNorthwest，and the team adds that they think the same process might have taken place inEurope．“By the1700s．there were80，000 mills inFrance，”saysWalter．If this reconstruction of events is true，then millions of dollars have been spent trying to return streams to an artiticial state：their condition after old dams came down，rather than before they went up．In a project tentatively@planned for summer2008 inPennsylvania，Walter andMerritts are working with restorers to try to remove all that modern sediment and strip valleys down to theHolocene wetlands beneath．They think this will allow old marshlands to return．decreasing sediment and nutrient load in the streams and preventing some of the problems seen today from excessive sediment①picturesque：奇特有趣的．②meander：(河流和小溪)蜿蜒曲折地流．③light detection and ranging(I。IDAR)：激光探测及测距系统．④vegetation：植被，植物．⑤backhoe：(有伸缩挖掘装置的)锄耕机．⑥sedimentary：沉积的，沉淀性的．⑦deforestation：采伐森林．⑧displace：取代，置换．⑨hydropower：水力发的电．⑩breach：打开缺口．⑩rentalively：试验性地，暂时地．⑩viable：能自行生长发育的．硎籍骟

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