水质约束条件下确定土壤允许流失量的方法

已有土壤允许流失量（T值）定义多以防止土壤肥力减退、土地生产力下降为目标，考虑的主要因素为成土速度、土层厚度和土壤肥力减退，确定T值的依据是土壤侵蚀速率不大于成土速率，保证土壤资源得到不断更新。然而土壤侵蚀并不完全是人为因素造成的，更是一种客观自然过程，土壤侵蚀除导致土壤养分流失，土壤生产力下降，还可能对侵蚀发生地以外的地区产生一系列环境问题。为保证人类社会可持续发展，制定控制土壤侵蚀目标时，只局限于提高土壤生产力已与时代发展不合拍了，应将视野扩展到保护和改善人类生产、生活和生存环境，引入生态环境影响符合可持续发展的时代要求。因此，在前人研究基础上结合保护水体环境质量要求建立了一种新的确定T值方法，该法体现了多目标特点，可实现既保护土壤资源又维护水环境质量的目标。以随泥沙入湖的TN、TP对湖水养分影响为例，探讨了水质约束条件下确定T值的一般方法。

METHODS FOR DETERMINING SOIL LOSS TOLERANCE UNDER WATER QUALITY RESTRICTION

In order to prevent from the deterioration of soil fertility and the decrease of land productivity, the factors, such as rate of soil forming, the depth of soil layer and the deterioration of soil fertility, are mainly considered in previous definitions of soil loss tolerance (T). In general, the soil loss tolerance is determined on the rate of soil loss which should be less than the rate of soil forming, and under such soil loss tolerance the soil resources could be continuously renewed. However, soil erosion not only lies on human disturbance but also on natural factors. Besides the loss of soil nutrients and the decrease of soil productivity in localities where erosion occurs, a series of environmental problems may be developed far from the (erosion). If the factors for improving soil quality and land productivity are merely considered while determining the soil loss tolerance, it does not suit the need of social evolvement and sustainable development of environment. Protecting and improving productive and existent environment must be regarded as important measures. Therefore, a new concept of soil loss tolerance proposed in the paper is based on the previously mentioned cognition. To determin the soil loss tolerance, ecological and environmental impacts should be taken into account. When sediment, which carried nutrients such as total nitrogen (TN) and total phosphorus (TP), enters into water bodies, the content of TN and TP increase in water and the water is polluted. Based on the contribution of nutrients loss due to soil loss to total input pollutant entering Taihu Lake the method for determining soil loss tolerance is set up under the water quality restriction. Then a general method for determining soil loss tolerance is further discussed.