Environment and Rural Affairs Monitoring & Modelling Programme ERAMMP report-70: The use of remote sensing to assess soil erosion, poaching and disturbance features

Soil is a finite resource. Within the concepts of natural capital and ecosystem services, the erosion and compaction of soil are considered to be major threats to both ‘soil stock’ and ‘soil function’. Principal drivers of erosion include slope angle and length, precipitation quantity and intensity and vegetation coverage. Soil compaction (primarily caused by repeated movements by vehicles or poaching by animals leading to exposed soils) may reduce soil function in terms of water and gaseous movement and exacerbate N2O emission, as well as potentially creating pathways for erosion to occur. However, producing national scale assessments of soil erosion is expensive and difficult, whilst soil compaction, or disturbance remains largely unconsidered in assessments. Soil erosion is a compliance issue, however, the work outlined in this report is not aligned with any regulatory or compliance process such as outlined in Good Agriculture and Environmental Conditions 5 (Welsh Govt, 2022); it is purely a research project for the monitoring and assessment of soils. Many methods for measuring soil erosion exist and are used over a range of different spatial scales. These include plot experiments, field or catchment studies. However, widespread quantification of erosion rates are time consuming and still remain spatially restricted. Other approaches are more suited to national scale assessments. Modelling approaches, usually based on the ‘Universal Soil Loss Equation’ or its variants can provide an indication as to where long-term erosion is most likely to occur under certain land-use and climatic conditions and are useful for looking at potential change. Walk-over-surveys have the potential to measure area and sometimes volumes of soil erosion, but are also time consuming to undertake. However, they do provide the most repeatable basis for widespread or national scale monitoring. The use of earth observation presented here, combined with field survey, may be an effective and less time-consuming approach for the assessment of national scale soil erosion, but its benefits and limitations need to be explored. This study reports on (i) a desk-based soil erosion and disturbance survey undertaken using high resolution aerial images (0.25 m); and (ii) a subsequent ground survey of the aerial photo survey undertaken as part of the 2021 ERAMMP field survey.