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

Glossary

Agricultural land
The Scottish Government define this as land used for agriculture for the purposes of trade or business. Scottish National statistics (June 2018) state that the agricultural area in Scotland is around 80 %, which comprises 47% rough/common grazing,17% grass, 7% crops and fallow and 9% ‘other land uses’ (e.g. woodland, ponds or yards).

Accelerated rates of soil erosion
Rates of soil erosion (t ha^-1 yr^-1) that exceed rates of soil formation by natural physical and chemical interactions (geomorphic processes) with the earth surface (Verheijen et al., 2009).

Biodiversity
The variety of plant and animal life in the world or in a particular habitat, a high level of which is usually considered to be important and desirable.

Buffer strips
Vegetated strips of land left uncultivated / ungrazed that control soil erosion by either reducing slope lengths, which reduces the ability of water flowing over the surface to carry soil particles and / or controlling the amount of eroded soil leaving the field by reducing energy to carry soil particles in flowing water resulting in soil particles being dropped within the buffer strip

Catchment
In this report is defined as an area where precipitation that falls inside its boundaries is either held within the area or flows (either overland or via drainage pathways) towards a single point or outlet. Also known as a hydrological area, drainage basin or river basin.

Cohesion
The force that holds together particles (mineral and/or organic) within a soil, which include electrostatic forces between particles and cementing by chemicals (e.g. iron oxide and calcium carbonate)

Cover cropping
Growing crops between main crops to maximise land cover and root development to protect soils

Cultivated land
Land that is worked by ploughing, sowing and raising crops (https://www.thefreedictionary.com)

Cultural services
The non-material benefits people obtain from ecosystems, including aesthetic inspiration, cultural identity, sense of home, and spiritual experience related to the natural environment.

Deposition
The laying down of sediment that has been eroded and transported (moved). It happens when the forces which transported the material become weaker and unable to support the weight of the sediment.

Diffuse pollution
Pollution occurring from multiple points that are often individually minor, but collectively can result in significant environmental damage. Diffuse water pollution is the release of potential pollutants from a range of activities that, individually, may have no effect on the water environment, but, at the scale of a catchment, can have a significant effect. https://www.sepa.org.uk/regulations/water/diffuse-pollution/

Ecosystems goods and services
The benefits arising to humans from the ecological functions of ecosystems. These include provisioning services such as food, water, timber and fibre; regulating services that affect climate, floods, and water quality; cultural services that provide recreational, aesthetic and spiritual benefits and supporting services such as soil formation, photosynthesis and nutrient cycling (Millennium Ecosystem Assessment, 2005)

Erosion event
In the context of this report, is a rainfall event (e.g. storm) of sufficient energy (intensity and duration) to cause soil erosion

Erosion Risk Classes
The risk of a soil being eroded by water under intense or prolonged rainfall. Class divisions are based on factors affecting erosion including soil texture, slope and runoff potential. In this report the erosion risk classes are used to modify the soil erosion rate from 10 simplified land use categories.

Erosive velocity
Water traveling at sufficient speed to detach and entrain soil particles and aggregates. Particle/aggregate size and cohesion determine the critical threshold (amount of energy related to speed of flowing water) at which flow becomes erosive.

Extensive arable
Arable system that uses inputs of herbicides, fertilisers and labour

Geomorph-ological processes
Natural processes of weathering, erosion and deposition that determine the nature and origin of landforms.

Georeferenced
Real world coordinates e.g. Ordinance Survey coordinates, that are used to locate items on a map.

Intensive arable
Arable system that maximises yields through the use of pesticides and fertilisers

Improved Grassland
Land used for grazing where over one third of the sward comprises, singly or in mixture, ryegrass, cocksfoot or timothy, or land that has been improved by management practices such as liming and top dressing, where there is not a significant presence of sensitive plant species indicative of native unimproved grassland https://www2.gov.scot/Topics/farmingrural/SRDP/RuralPriorities/Options/Biodiversitycroppinginbye/DefinitionsofLandTypes

Humic soils
Humic soils are soils with a dark coloured, organic-rich topsoil (typically >7% organic carbon in the uncultivated state).

Land-based businesses
Relates to farming and industries connected to the land and environment, including horticulture, food production and forestry

Land use
The dominant activity taking place on an area of land. Within this report land use areas include arable and horticultural fields, grassland, forestry, woodland, wildscapes and urban

Mitigation measures
Measures to control soil erosion: grouped into agronomic (i.e. use of vegetation to control erosion), structural (e.g. use of field structures such as terraces and bunds) or soil management (e.g. reduced tillage) measures.

National Forest
The National Forest Inventory (NFI) is a rolling programme designed to provide accurate information about the size, distribution,

Inventory of Scotland

composition and condition of forests and woodlands within Great Britain. It is essential for developing and monitoring the policies and guidance that support the sustainable management of woodland (https://www.forestresearch.gov.uk/tools-and-resources/nationalforest-inventory/about-the-nfi/)

Natural capital
The world’s stocks of assets from the natural environment, which include geology, soil, air, water and all living things. https://naturalcapitalforum.com/about/

Off-site impacts of soil erosion
The consequences of soil erosion that occur away from the site of the erosion event (e.g. dredging of eroded soil (sediment) from watercourses; water treatments needed to remove sediment from water for subsequent use such as for drinking water)

On-site impacts of soil erosion
The consequences of soil erosion where the erosion event occurs (e.g. loss in crop yield due to reduced soil depth or damage to the crop; the need to apply more fertiliser to compensate for nutrients lost in the eroded soil). Also includes the need for installation of mitigation measures.

Organic soils
Organic soils are formed under waterlogged conditions or where the natural decomposition rates of organic material are significantly slower than the rates of accumulation. These soils have more than 60% organic matter and exceed 50cm in thickness. (https://www.hutton.ac.uk/learning/soilshutton/soil-classification).

Organo-mineral soils
Soils with topsoil organic carbon concentrations greater than 35% and less than 50cm thick.

Organomineral and peat soils
A blanket term used in this report to include both organo-mineral (peaty and humic soils) and peat soils

Particle size
The size of soil particles (categorised as sands, silt and clays). This affects soil erodibility (susceptibility to detachment, transport and deposition), depending on the energy of the eroding agent. Particle size also affects specific surface area which determines the capacity of soil to adsorb nutrients, contaminants etc., which are eroded with the sediment.

Peat soils
Peat soils are formed under waterlogged conditions or where the natural decomposition rates of organic material are significantly slower than the rates of accumulation. These soils have more than 60% organic matter and exceed 50cm in thickness. (https://www.hutton.ac.uk/learning/soilshutton/soil-classification).

Provisioning services
Ecosystem services that provide materials or energy from the ecosystems (e.g., food, fibre, timber)

Reduced tillage <
Cultivations that minimise soil disturbance. Usually non - inversion tillage with the use of shallow tines, chisels and discs

Regulating services
The benefits obtained from the regulation of ecosystem processes (e.g., climate regulation, water regulation, pest and disease regulation)

Rill erosion
Small eroded channels of intermittent, concentrated flow that can be removed by cultivations or the next rainfall event

Risk
A probability or threat of damage, injury, liability, loss, or any other negative occurrence that is caused by external or internal vulnerabilities, and that may be avoided through preemptive action (http://www.businessdictionary.com/definition/risk.html)

Rough grassland
(https://www2.gov.scot/Topics/farmingrural/SRDP/RuralPriorities/Options/Biodiversitycroppinginbye/DefinitionsofLandTypes)

Rough grazing
Land that is either steep, very poorly drained, has very acid or shallow soils and occurs in wet, cool or cold climates zones. https://www.hutton.ac.uk/learning/exploringscotland/land-capabilityagriculturescotland/rough-grazing

Sediment
Solid materials and particles that are detached, transported and deposited by the processes of erosion. Sediment may include mineral fractions (clays, silts, sands) and / or organo-mineral materials (e.g. peats).

Sediment concentration
The sediment load per unit of flow volume (e.g. mg l^-1)

Sediment load
Solid particles (e.g. sands, silts and clays) produced by soil erosion processes that are part of the transport flow (e.g. by water).

Sediment transport
The movement of eroded material (sediment load) from the original site of the erosion event.

Sediment yield
The amount of sediment reaching or passing a point of interest in a given period of time

Soil degradation
The physical, chemical and biological decline in soil quality

Soil erosion
Detachment and transport of soil particles / aggregates by agents of erosion. These are rainfall; runoff; wind; co-extraction with harvested crops; adhesion to agricultural vehicles and implements. However, for this report the focus is on soil erosion by water. Units are usually tonnes per hectare per year (t ha^-1 yr^-1) i.e. soil mass lost per unit area per unit time.
Mass movements (e.g. deeper seated slope failures) are excluded from the analysis. (Morgan, 2005)

Soil erosion by coextraction on harvested crops, vehicles, farm machinery
Soil adhering on crop roots, tyres, tracks, vehicles, which then leaves the field, causing loss of soil.

Soil formation rate
The rate at which soil is formed naturally by biological, physical and chemical processes (Alexander, 1988; Verheijen et al., 2009; Egli et al., 2018)

Soil functions
Capabilities of soil (e.g. infiltration, carbon storage) associated with the delivery of a range of ecosystem goods and services (e.g. flood control, regulation of greenhouse gases)

Soil quality
“the capacity of soil to function, within natural or managed ecosystem boundaries, to sustain plant or animal productivity, maintain or enhance water quality, and support health and human habitation” ….or more simply “the capacity of soil to function” or “fitness for use”.
(Karlen et al., 1997)

Soil texture
Defined by the proportion of soil distributed over specified particle size ranges (categorised as sands, silt and clays) (Brady and Wyle, 1990)

Soil type
Soil type is based on soil properties (for example, colour, texture) and on the arrangement and nature of the different horizons (layers) within the soil. (https://soils.environment.gov.scot/maps/soil-maps/national-soil-mapof-scotland/)

Supporting services
Ecosystem services that are indirect services, as they are necessary for the production of provisioning, regulating or cultural services (e.g., soil formation, nutrient cycling, photosynthesis)

Tillage erosion
Movement of soil downslope, caused by preferential displacement of soil by tillage implements, both on the contour as well as up / downslope

Tolerable rate of soil erosion
Any actual soil erosion rate at which a deterioration or loss of one or more soil functions does not occur (Verheijen et al., 2009)

Topography
The shape and features of the land surface

Unimproved grassland
Land used for grazing or mowing which is not normally treated with mineral fertiliser or lime and does not constitute either improved grassland or rough grazings (https://www2.gov.scot/Topics/farmingrural/SRDP/RuralPriorities/Options/Biodiversitycroppinginbye/DefinitionsofLandTypes)

Water quality
The physical, biological and chemical properties of waterbodies that determine its ecological status and treatment requirements (e.g. to meet drinking water standards).

Wildscape
Area of largely semi-natural landscape with minimal signs of human influence. (https://www.nature.scot/professional-advice/landscape/landscapepolicy-and-guidance/landscape-policy-wild-land)