11. Recommendations for future research
The estimates of the total annual costs of soil erosion in Scotland have been calculated from land uses based on LCM 2007. Land use would be more accurate if based on LCM2015, but this dataset was not available to the team.
No information on current use of soil erosion mitigation measures in the case study catchments (or in Scotland as a whole) was available at the time of the project. If the type (Appendix 11) and location of soil erosion mitigation measures were known, this would improve the accuracy of the estimate of total costs of soil erosion in Scotland. Installation and maintenance of these measures would add to the costs of soil erosion (i.e. costs of controlling soil erosion). However, by controlling soil erosion rates and probabilities (and on-site and off-site impacts), these measures would also reduce the associated costs of these impacts. This identifies another gap in knowledge: how effective those mitigation works would be in controlling soil erosion. It is likely their effectiveness would vary over space and time (Maetens, Poesen and Vanmaercke, 2012; Rickson, 2014). This needs to be better understood if this additional information is to be incorporated into models estimating the total costs of soil erosion. Given the predicted increase in soil erosion rates due to climate change (Boardman et al., 1990; Boardman and Favis-Mortlock, 2001; Hough, Towers and Aalders, 2010; IPCC, 2019; Mullan, 2013a, 2013b; Favis-Mortlock and Mullan, 2011; Nearing, Jetten and Stone, 2005; Nearing, Pruski and O’Neal, 2004), the environmental and economic need for soil erosion mitigation measures is likely to increase.
The current analysis has included organo-mineral soils and peats into one ‘soil erosion risk class’. It is recognised that most soils in this category are organo mineral soils, but have been given the same erosion risk class as peats. The results may be different if these 2 soil types were separated (see Section 10.4).
The present study is likely to have underestimated some off-site costs. The figures do not include the costs of P in watercourses (only in freshwater lakes / lochs). This is on the assumption that most P is moved with the sediment and becomes a cost when deposited in still waters (i.e. lakes). The load and concentration of P in rivers and canals is not accounted for (although N is included). Further investigation of the loads, concentrations and impacts of P in watercourses would improve the costs estimates associated with soil erosion.
Better understanding of the partitioning, loads, concentration and impacts of soil carbon losses (including DOC and POC), that are specifically associated with soil erosion would improve the accuracy and reliability of the estimates. Similarly, the present study found no data on methane or nitrous oxide emissions specifically linked to soil erosion, yet these will have environmental and economic impacts, and associated costs.
Future soil research should explore the annual costs of other soil degradation processes (e.g. soil compaction, loss of soil organic matter, loss of soil biodiversity), as was attempted by Graves et al. (2011) for England and Wales. The correlations, trade-offs and synergies amongst different soil degradation processes (e.g. soil erosion and loss of organic matter, compaction and loss of biodiversity) and their economic and other effects should be recognised, particularly where these are cumulative and integrated. Similarly, the multiple beneficial effects of mitigation measures should also be recognised (e.g. measures that control soil compaction will also reduce erosion risk).
The links between soil quality and ecosystem services are best developed for provisioning (mainly agricultural production) and regulating services (water quality, GHG emissions and flooding). Information to reflect the contribution of soils to supporting cultural services, such as landscape, biodiversity, recreation and heritage is less developed. The condition of soils can make a difference to the quality of important and highly valued habitats. They are important in the preservation of archaeological artefacts. They affect the condition of footpaths that provide access to the countryside, and the visual appearance of landscapes. The extent to which this affects the value of services has not been explored to any great extent to date, and has not been developed here. It is recommended that the cultural dimension of soils are assessed to provide a more complete assessment of soil value.