The joint application of digital modeling and field soil survey data for improvement of the accuracy in soil erosion mapping

We used the data from field surveys with more than 2500 soil sampling points at 4 research sites in various regions of Russia. The study sites are located in the European part of Russia in the most contrasting physical-geographical and socio-historical conditions of soil erosion: in the Moscow, Kursk, Belgorod regions and in the Republic of Bashkortostan. The digital modeling was carried out with using of the WATEM / SEDEM model based on digital elevation models of detailed scale (1:10 000) on a total area more than 2000 km². An analysis of the sediment balance in small catchments showed, that the digital modeling of soil erosion (in case of a certain quality level of input parameters) at an acceptable level reflects on the average long-term erosion rates in the valley-beam relief. The authors developed an original method in soil erosion mapping. It consists in revealing statistical relationships between the calculated erosion rates by WATEM / SEDEM model and the actual data of soils humus horizons thicknesses. Based on these dependencies, the probability of participation of soils with varying degrees on erosion in each pixel is calculated.

The specific in formation of soil erosion at the Moscow region is largely due to the complex stage history of agricultural land development. For this key site, a detailed study of historical maps was carried out (with digitization in the GIS of the sites boundaries with a different land use history) for 8 periods, starting from 1797 to the present. Also, the history of crop rotation was studied in detail. Based on the analysis of maps and digital modeling of erosion-accumulation processes in this territory, a very high dynamics of arable land and soil erosion over the past few centuries was revealed, which significantly influenced on the formation of soil cover. At research sites in the Belgorod and Kursk regions, the features in formation of erosion-accumulative soil cover structures are due to the large area of agricultural land development. The comparison of soil cover erosion maps produced in accordance to the traditional method and the author’s approach is revealed a high convergence of results and the perspective of digital modeling using. The indisputable advantage of the digital method is the ability to formalize the procedure for assessing soil erosion, minimizing the contribution of subjective factors. Detailed studies in the Republic of Bashkortostan revealed the features in the formation of soil erosion  due to the developed denudation processes and karst microrelief. A detailed mapping of the soil cover and topographic mapping of the relief in key areas was carried out. It was revealed, that the using of a digital elevation model with very high accuracy (scale 1: 1000 and higher) allows to qualitatively simulate and estimate the rates of erosion and accumulation even in conditions of pronounced karst microrelief.

Acknowledgement
This research was supported by the Russian Foundation for Basic Research (RFBR) within the scientific project No. 18–35–20011.