| The Loess Plateau, located in the middle reaches of the Yellow River, is the cradle of Chinese civilization. It is well known in the world for its deep loess deposits and serious soil erosion. Due to the unreasonable land use, this region has become one of the places with fragile eco-system. People in this region have struggled long and hard against soil and water loss. The government has increasingly paid attention to the region, especially in the past 50 years. A lot of efforts have been used to prevent soil and water loss. As a result, the conditions of soil erosion and environment have changed greatly.The common issues that policy makers and scientific researchers concerned are how to analyze the spatio-temporal characters and difference of soil loss and how to distinguish the impacts on environment from natural effects and human being. Though hydrologic observation stations can supply some data of runoff and sediment at present, the data just can reflect the overall situation of area observed by station and the effects of climate and soil conservation together. It could not tell the impacts on environment from soil and water conservation. In this paper we choose Yanhe Basin as research area to develop a method for assessing impacts of soil and water conservation on environment using GIS technology and professional model in order to supply scientific base for massive work of soil and water conservation and environment construction. The research is supported by the Program 973. Yanhe Basin is very representative for its special situation, such as climate including two kinds of climate type, three types of geomorphology, serious soil erosion, long-term action to prevent soil erosion and some research achievements.Based on involved scientific theory of soil and water conservation, soil science, hydrology, ecology and ecological economics, this research analyzed spatio-temporal changes of natural and human activity factors that affected soil erosion, calculated soil loss and runoff of Yanhe Basin from 1986 to 2006, brought forward the model of assessing impacts of soil and water conservation on environment and used this model to assess the impacts of soil and water conservation on environment. The main results are as following.(1) To establish the spatio-temporal-scenic database of Yanhe Basin. The database mainly consists of precipitation, runoff, vegetation cover, land use, topography map, DEM, soil, thematic maps, remote sensing image, field landscape pictures, and investigated data of practices of soil and water conservation.(2) To develop a method to quantify regional engineering practice factor of soil and water conservation in order to use the Chinese Soil Loss Equation (CSLE). The regional engineering practice factor of soil and water conservation was defined as the ratio of soil loss with engineering practice to without engineering practice when other situation was the same. We collected engineering practice data with township as unit because it's impossible to get engineering practice data by fieldwork for such a large area and we can't get information of engineering practice by TM image. However the collected data of engineering practice had no spatial information and we planned to average the impacts of engineering practice to the whole collected unit with spatial information to get the map of regional engineering practice factor. The equation is as follows.(3) To calculate all factors of soil erosion and the loss of soil and runoff. The factors include rainfall erosivity, soil erodibility, slope length and slope steepness factors, biological measure factor, engineering measure factor and tillage measure factor. It also simulated to calculate runoff and soil loss in the beginning year of soil and water conservation. All the results had the corresponding maps with the same projection and the same grid size.(4) To calculate the ecological value of different years in different state of soil and water conservation based on GIS with the data of climate, soil, topography and land use and obtained all the map of Yanhe Basin.(5) To develop a method for quantitatively assessing the impacts of soil and water conservation on environment. Practices of soil and water conservation changed the situation of the earth surface of this basin and also changed the structure and function of eco-system. This research chose one kind of ecological service respectively from hydrosphere, soil sphere, biology sphere and atmosphere to assess impacts of soil and water conservation on environment according the progress of ecological service research. However the ecological service can't be added together for different dimensions, it was necessary to use the concept of ecological service value to make them with the same dimension. Index of impacts on environment from soil and water, which was ratio of ecological service value of the end state to the beginning state of soil and water conservation, was put forward based on ecological service value. This index is 106.55 and 110.24 in 1997 and 2006 respectively and could reflect that soil and water conservation improved the quality of environment. The equation of calculating this index is as follows.Main new progresses: (1) To develop a method of assessing impacts of soil and water conservation on environment. (2) To develop a method to quantify the regional engineering practice factor of soil and water conservation.
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