Developing a method to estimate the costs of soil erosion in high-risk Scottish catchments: final report

1. Introduction

Soil erosion is a natural process that is dependent on climate, topography, soil type, vegetation cover, land use and land management. Inappropriate land use and land management can trigger accelerated rates of soil erosion that have detrimental impacts both on-site (where the erosion takes place e.g. on agricultural fields) and off-site (away from the erosion site e.g. eroded soil / sediment entering watercourses).

Soil erosion was identified as one of the main threats to Scotland’s soils in the comprehensive ‘State of Scotland’s Soil Report’ (2011). The Scottish Government ‘aims to promote the sustainable management and protection of soils, consistent with the economic, social and environmental needs of Scotland’ (https://www.gov.scot/policies/biodiversity/soils/). The Scottish Soils Framework sets out a vision for soils to be “safeguarded for existing and future generations”. It is recognised that soils provide a range of ecosystem goods and services that support a broad spectrum of human activities and associated benefits (Table 1). The continued provision of benefits from soil depends on successfully maintaining its physical, chemical and biological properties.

However, evidence suggests that the way soils are currently used degrades the resource (e.g. by soil erosion) resulting in loss of soil quantity and quality, along with the functions that soils support, and the ecosystem goods and services delivered by these functions. This can result in significant costs, not only to immediate users of soils but also to society as a whole. Climate change projections for Scotland indicate more heavy rainfall days and an increase in winter rainfall, leading to greater risks of soil erosion in the future, making the status of ‘Soils and agriculture’ in Scotland of ‘high concern’ (Committee on Climate Change, 2019).

Table 1. Millennium Ecosystem Assessment categories of ecosystem services and examples relating to soil (after Haygarth and Ritz, 2009).

Provisioning services i.e. products obtained from ecosystems
Food
Fibre and fuel
Genetic resources

Regulating services i.e. benefits obtained from the regulation of ecosystem processes

• Climate regulation
• Water regulation
• Water purification/detoxification
• Bioremediation of waste

Cultural services i.e. non-material benefits that people obtain through spiritual enrichment, cognitive development, recreation etc.

• Spiritual and religious value
• Inspiration for art, folklore, architecture etc
• Social relations
• Aesthetic values
• Cultural heritage
• Recreation and ecotourism

Supporting services, necessary for the production of all other ecosystem services

• Soil formation and retention
• Nutrient cycling
• Primary production
• Water cycling
• Provision of habitat

The aim of this project is to estimate the financial costs of soil erosion in Scotland. These costs are incurred by land-based businesses where soil erosion occurs, and by society where soil is deposited ‘off-field’ or in-stream. Understanding the impacts and costs of soil erosion will inform policies designed to value the soil resource.

1.1. Approach

A review of the literature was used in an attempt to identify soil erosion rates in Scotland, as well as the impacts of soil erosion and the associated costs of these impacts. At the same time, information on the costs and benefits (effectiveness) of soil erosion control measures was also gathered. A number of representative catchments were selected for the analysis. To estimate the total on-site and off-site costs of soil erosion per annum in those catchments, an updated version of the approach used by Graves et al. (2011; 2015) was used. Once the methodology was applied successfully at the catchment scale, it was then extrapolated to the national scale.

It was agreed that landslips / mass movements were out of scope for the project, as these are different geomorphological processes to those of soil erosion.