long term change meaning in English

长期变化

Thirdly , present status of effect of erosion on soil carbon and nutrient has been illustrated in spatial scale of the watershed . based on geographic information system , actuality and process of soil erosion in and between land units were simulated , and actuality and process of annual and long term changing of soil carbon and nutrient in each land unit under erosion were sufficiently calculated and illustrated . results of simulation and illustration showed that , the relative area in which soil carbon , nitrogen , phosphorus and potassium is deceased is 44 . 1 % , 55 . 8 % , 39 . 2 % and 75 . 7 % respectively
三、在流域空间范围内描述了侵蚀影响土壤碳和养分的现状：在地理信息系统的支持下，模拟了流域各地块的侵蚀过程、现状，充分描述了各个地块在侵蚀影响下土壤碳和养分的年变化现状、过程及多年变化过程，得到在现有侵蚀及耕作管理条件下，全流域中土壤碳、全氮、全磷、全钾下降的地块面积分别占流域总面积的44 . 1 、 55 . 8 、 39 . 2 、 75 . 7 ，以及各个地块的碳和养分含量变化趋势，弥补了前人研究在地域华中农业大学2001届硕士研究生学位论文空间联系上的不足。