Is Overgrazing Really Influencing Soil Erosion?

Ionut Nicu

doi:10.3390/w10081077

Abstract

Soil erosion is a serious problem spread over a variety of climatic areas around the world. The main purpose of this paper is to produce gully erosion susceptibility maps using different statistical models, such as frequency ratio (FR) and information value (IV), in a catchment from the northeastern part of Romania, covering a surface of 550 km2. In order to do so, a total number of 677 gullies were identified and randomly divided into training (80%) and validation (20%) datasets. In total, 10 conditioning factors were used to assess the gully susceptibility index (GSI); namely, elevation, precipitations, slope angle, curvature, lithology, drainage density, topographic wetness index, landforms, aspect, and distance from rivers. As a novelty, overgrazing was added as a conditioning factor. The final GSI maps were classified into four susceptibility classes: low, medium, high, and very high. In order to evaluate the two models prediction rate, the AUC (area under the curve) method was used. It has been observed that adding overgrazing as a contributing factor in calculating GSI does not considerably change the final output. Better predictability (0.87) and success rate (0.89) curves were obtained with the IV method, which proved to be more robust, unlike FR method, with 0.79 value for both predictability and success rate curves. When using sheepfolds, the value decreases by 0.01 in the case of the FR method, and by 0.02 in the case of the success rate curve for the IV method. However, this does not prove the fact that overgrazing is not influencing or accelerating soil erosion. A multi-temporal analysis of soil erosion is needed; this represents a future working hypothesis.

Highlights

IntroductionSoil erosion became a worldwide issue with regard to the material losses associated (reduction of soil fertility and cultivated areas) with this phenomenon [1]
Soil erosion became a worldwide issue with regard to the material losses associated with this phenomenon [1]
We will refer to the gully erosion susceptibility mapping based on a GIS approach and using two statistical models in a catchment with an area of 550 km2 from the northeastern part of Romania; besides the normal conditioning factors, grazing was added as a conditioning factor

Summary

Introduction

Soil erosion became a worldwide issue with regard to the material losses associated (reduction of soil fertility and cultivated areas) with this phenomenon [1]. One of the most erosive processes acknowledged for water erosion is gullying [7]. We will refer to the gully erosion susceptibility mapping based on a GIS approach and using two statistical models in a catchment with an area of 550 km from the northeastern part of Romania; besides the normal conditioning factors, grazing was added as a conditioning factor. Erosion can be defined as an erosion process in which deep channels are generated by runoff water removing topsoil to a certain depth [8]. Once the gully channels are formed, the process of growing is very fast; this is induced by the local environmental factors, climate, and land use changes [9]

Objectives

Methods

Results

Discussion

Conclusion