21.Studies by Hargrave and Geen estimated natural community graz-ing rates by measuring feeding rates ofinpidual zooplankton species in thelaboratory and then computing1 community grazing rates for field conditionsusing the known population density2of 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率進行了估計，其方法是通過測量出實驗室內單獨的浮游動物類型的結食比率，然后借助已知的食草動物種群密度，計算出實地情況下的群落食草比率。
22.In the periodsof peak zooplankton abundance，that is，in the late spring and in the summer，Haney recorded maximum daily com-munity grazing rates，for nutrient-poorlakes and bog3 lakes，respectively，of 6.6 percent and 114 percent of daily phyTOPlankton production.
在浮游動物數目激增的高峰期，亦即在春天后期與夏天，哈尼記錄了最大程度上的每天群落食草比率，對于營養物不充足的湖和沼澤湖而言，分別為每天浮游植物繁殖量的6.6%和114%.
23.The hydrologic cycle，a major TOPic in this science，is the complete cycle of phenomena4 through which water passes，beginning as atmospheric5 water vapor6，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 evaporation7 and transpiration8.
水文循環（hydrologic cycle），作為該學科中的一個主要課題，指的是水所經過的諸現象的整個循環過程，開始時是作為大方中的水蒸氣，轉而作為雨、雪、露、雹一類的降水量經過液體和固體形態，由此而沿著地層表面分布或進入地層表面，最后通過蒸發和散發用途再度回復到大方水蒸氣的形態。
24.The historian Frederick J. Turner wrote in the 1890's that the agrarian9 discontent that had been developingsteadily10 in the United States since about 1870 had been precipitated11 by theclosing of the internal frontierthat is，the depletion12 of available new landneeded 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不斷進步的農民不滿，因為國內邊遠區域（internal frontier）的封閉而更趨加劇亦即是說，美國農業系統進一步擴展所必需的可資借助的新土地幾近耗竭。