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Elucidation of causal chains and restoration applying agricultural engineering approaches for watershed degradation to the Lam Phachi River, Thailand

阐明泰国 Lam Phachi 河流域退化的因果链和恢复应用农业工程方法

基本信息

批准号：
12575020
负责人：
MAITA Hideji
金额：
$ 9.41万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

We conducted a case study in the Lam Phachi River Basin, Thailand in order to clarify causal chains for watershed degradation using many types of field survey techniques, and satellite image analysis etc. Main results are as follows.1) The Lam Phachi River Basin was almost covered by forests until the beginning of the 1970's, however they were not natural forests but secondary forests due to the sustainable shifting cultivation conducted by mountain tribes. The forests has decreased to 50-60 percent in area until 1990 because of widespread conversion of the forests to cultivated lands caused by settlers since the 1970's. Recently pineapple fields are expanding to the sloping area of the target area of the basin due to a shift to a more profitable cash-crop culture since the 1990's.2) The forestlands had higher final infiltration rates (44-160 mm/hr) than the pineapple and cassava fields (5-39 mm/hr). Such low infiltration capacities of cultivated lands and strong rainfall intensities of tropical region caused severe soil erosion (69, 163 t/ha/yr) in some pineapple fields on the sloping areas. Thus the conversion to cultivated lands during the last three decades, particularly the expansion of pineapple fields to the sloping areas during the last decade, increased the susceptibility to accelerated erosion.3) Through this study, we understood the vicious cycle of watershed degradation as follows. If the critical point in deterioration is exceeded by inappropriate agricultural practices, accelerated erosion becomes self-sustaining, that is, the more surface runoff occurs, the more soil is removed and the less water and nutrients remain to support the plant growth, therefore the site cannot recover natural processes.4) Dynamic changes in cultivation during the last decade might have already caused the vicious cycle of watershed degradation in some areas of the basin (e.g., pineapple fields on the sloping areas).

本文以泰国Lam法基河流域为例，运用多种实地调查技术和卫星图像分析等手段，对流域退化的原因链进行了研究。主要结果如下：1）Lam法基河流域在20世纪70年代初之前几乎被森林覆盖;然而，由于山区部落进行的可持续轮垦，它们不是天然林，而是次生林。由于自1970年代以来定居者将森林广泛转化为耕地，森林面积减少到1990年的50- 60%。最近，由于从20世纪90年代开始转向更有利可图的经济作物种植，菠萝田正在向盆地目标区域的斜坡区域扩展。2）林地的最终渗透率（44-160 mm/hr）高于菠萝和木薯田（5-39 mm/hr）。耕地的这种低渗透能力和热带地区的强降雨强度造成了严重的土壤侵蚀（69，163吨/公顷/年），在一些菠萝领域的斜坡。因此，在过去的三十年中，耕地的转换，特别是在过去的十年中，菠萝田的扩大到坡地，增加了加速侵蚀的敏感性。如果不适当的农业做法超过了恶化的临界点，加速的侵蚀就会自我维持，也就是说，地表径流越多，土壤被移走的就越多，留下来支持植物生长的水和养分就越少，因此，该网站无法恢复自然过程。过去十年中种植的动态变化可能已经在该流域的某些地区造成了流域退化的恶性循环（例如，斜坡上的菠萝田）。