Spatiotemporal Dynamics Of Soil Erosion And Its Impact On Eco-security

Severe soil erosion, indicative of the deterioration of eco-environment, has become one of the most critical ecological problems in China and a major threat to the nation’s eco-security. Despite the fact that soil erosion is a key factor of eco-security, there are few systematic reports focusing on uncovering their relationship. With a case study in Anji County, Zhejiang Province, south-eastern China, this work monitored the dynamics of soil erosion, analyzed the varions of eco-security, and assessed the impact of soil erosion on eco-security. Thus, a relatively systematic study was conducted into the spatiotemporal dynamics of soil erosion and their responses to eco-security.Firstly, by using Revised Universal Soil Loss Equation (RUSLE) and by integrating remote sensing (RS) and geographic information system (GIS), a quantitative method that separates background factors and dynamic factors in RUSLE was developed to estimate the spatiotemporal dynamics of soil erosion in the study area during1985-2008. The Exploratory Spatial Data Analysis (ESDA) was used to analyze the soil erosion dynamics; Then, a catastrophe theory was employed to generate a grid scale-based model for evaluating eco-security, which was then used to monitor the eco-security dynamics of the study area during1985-2008; At last, based on above results, a Geographically Weighted Regression (GWR) model was utilized to quantify the relationship between soil erosion and eco-security.The major findings of this study are as follows:1. Quantitative monitoring of soil erosion:On the basis of RUSLE, background and dynamic factors were employed to monitor soil erosion in the study area in1985,1994,2003and2008. The results revealed the co-existence of the deterioration and mitigation of soil erosion. There is, however, an overall trend of erosion deterioration, with both the scale and the range of deterioration exceeding that of mitigation.2. Spatiotemporal dynamics of soil erosion:The Moran’s I and Local Indicators of Spatial Association (LISA) were used to identify the spatial and temporal dynamics of soil erosion from the perspectives of quantitative statistics and visualization. The results revealed a trend of erosion deterioration. The hot spots of soil erosion, including areas with serious erosion and deteriorated erosion, were found expanding and clustering. The scale and degree of soil erosion in the area kept going up and erosion became an increasingly critical factor affecting the local eco-environment.3. Spatiotemporal dynamics of eco-security:A system of eco-security assessment indicators, adapted to the grid scale, was established on the basis of the pressure-state-response model. Then catastrophe theory was employed to evaluate the eco-security of the study area. The results showed that the eco-environment in major parts (accounting for over55%) of the study area was relatively secure, indicative of a relatively good eco-environment. However, with the increase of areas featuring insecure and very insecure eco-environment, the overall eco-security was on a trend of deterioration.4. Eco-security responsive to soil erosion:The Geographically Weighted Regression (GWR) model was used to quantify the relationship between soil erosion and eco-security at500m×500m grid scale. The results showed that the change of erosion regulated the change of eco-environment. Continuous erosion deterioration rendered the eco-environment increasingly less safe in the study area, and erosion gradually became the most important threat to the local eco-environment.New methods developed in this study are as follows:1) by separating background factors from dynamic factors, a quantitative method was developed to monitor soil erosion on a long-term basis. And the Exploratory Spatial Data Analysis (ESDA) was introduced to the study of spatial and temporal dynamics of erosion by integrating quantitative statistics and visualization;2) The use of catastrophe theory in eco-security assessment helped avoid the subjectivity in deciding the weight of different factors in a model and made the assessment results more comparable;3) The introduction of GWR to the analysis of the relationship between soil erosion and eco-security made it possible to fully reveal the spatial heterogeneity of the relationship and to get rid of their spatial autocorrelation at its best.With the limitation of data, further research is still required into some methods and theories:The selection of limited number of temporal/spatial scales caused an inadequate analysis of soil erosion change and the temporal/spatial features of eco-security responsive to soil erosion. Further research is to be conducted about the scales of study on the temporal/spatial dynamics of erosion and the responses of eco-security; the selection of indicators for landscape grid-based assessment of eco-security is mainly subject to data availability. A further study could be done on the reasonableness of the indicators and the methods of matching them up with those used in administrative or watershed scale assessment; As GWR model was established mainly with linear interpolation in this study, a further research could be performed to improve the GWR model.