21.Studies by Hargrave and Geen estimated natural community graz-ing rates by measuring feeding rates of individual zooplankton species in the laboratory and then computing community grazing rates for field conditions using the known population density of grazers.
由哈格雷夫（Hargrave）和吉恩（Geen）所進行的研究，對自然條件下的群落食草比例進行了估計，其手段是通過測量出實驗室內(nèi)單獨的浮游動物種類的結食比例，然后利用已知的食草動物種群密度，計算出實地狀況下的群落食草比例。
22.In the periods of peak zooplankton abundance，that is，in the late spring and in the summer， Haney recorded maximum daily com-munity grazing rates，for nutrient-poor lakes and bog lakes，respectively，of 6.6 percent and 114 percent of daily phytoplankton production.
在浮游動物數(shù)量激增的高峰期，亦即在春季后期以及夏季，哈尼記錄了大程度上的每日群落食草比率，對于營養(yǎng)物不充足的湖和沼澤湖而言，分別為每日浮游植物繁殖量的6.6%和114%.
23.The hydrologic cycle，a major topic in this science，is the complete cycle of phenomena through which water passes，beginning as atmospheric water vapor，passing into liquid and solid form as precipitation，thence along and into the ground surface，and finally again returning to the form of atmospheric water vapor by means of evaporation and transpiration.
水文循環(huán)（hydrologic cycle），作為該學科中的一個主要課題，指的是水所經(jīng)過的諸現(xiàn)象的整個循環(huán)過程，開始時是作為大氣中的水蒸氣，轉而作為雨、雪、露、雹一類的降水量經(jīng)過液體和固體形態(tài)，由此而沿著地層表面分布或進入地層表面，終通過蒸發(fā)和散發(fā)作用再度回復到大氣水蒸氣的形態(tài)。
24.The historian Frederick J. Turner wrote in the 1890's that the agrarian discontent that had been developing steadily in the United States since about 1870 had been precipitated by the closing of the internal frontier——that is，the depletion of available new land needed for further expansion of the American farming system.
史學家弗雷德里克。杰。特納（Frederick J.Turner）于十九世紀九十年代著述道，美國約自18世紀70年代以來一直在持續(xù)不斷發(fā)展的農(nóng)民不滿，由于國內(nèi)邊遠地區(qū)（internal frontier）的封閉而更趨加劇——亦即是說，美國農(nóng)業(yè)系統(tǒng)進一步擴展所必需的可資利用的新土地幾近耗竭。
由哈格雷夫（Hargrave）和吉恩（Geen）所進行的研究，對自然條件下的群落食草比例進行了估計，其手段是通過測量出實驗室內(nèi)單獨的浮游動物種類的結食比例，然后利用已知的食草動物種群密度，計算出實地狀況下的群落食草比例。
22.In the periods of peak zooplankton abundance，that is，in the late spring and in the summer， Haney recorded maximum daily com-munity grazing rates，for nutrient-poor lakes and bog lakes，respectively，of 6.6 percent and 114 percent of daily phytoplankton production.
在浮游動物數(shù)量激增的高峰期，亦即在春季后期以及夏季，哈尼記錄了大程度上的每日群落食草比率，對于營養(yǎng)物不充足的湖和沼澤湖而言，分別為每日浮游植物繁殖量的6.6%和114%.
23.The hydrologic cycle，a major topic in this science，is the complete cycle of phenomena through which water passes，beginning as atmospheric water vapor，passing into liquid and solid form as precipitation，thence along and into the ground surface，and finally again returning to the form of atmospheric water vapor by means of evaporation and transpiration.
水文循環(huán)（hydrologic cycle），作為該學科中的一個主要課題，指的是水所經(jīng)過的諸現(xiàn)象的整個循環(huán)過程，開始時是作為大氣中的水蒸氣，轉而作為雨、雪、露、雹一類的降水量經(jīng)過液體和固體形態(tài)，由此而沿著地層表面分布或進入地層表面，終通過蒸發(fā)和散發(fā)作用再度回復到大氣水蒸氣的形態(tài)。
24.The historian Frederick J. Turner wrote in the 1890's that the agrarian discontent that had been developing steadily in the United States since about 1870 had been precipitated by the closing of the internal frontier——that is，the depletion of available new land needed for further expansion of the American farming system.
史學家弗雷德里克。杰。特納（Frederick J.Turner）于十九世紀九十年代著述道，美國約自18世紀70年代以來一直在持續(xù)不斷發(fā)展的農(nóng)民不滿，由于國內(nèi)邊遠地區(qū)（internal frontier）的封閉而更趨加劇——亦即是說，美國農(nóng)業(yè)系統(tǒng)進一步擴展所必需的可資利用的新土地幾近耗竭。