Indicators of Soil Resilience for Scotland and Northern Ireland
Background to research
Considerable work has been carried out to date in terms of reviewing
and developing indicators of soil quality and to a lesser extent, soil
resilience. However, indicators have yet to be applied routinely to the
assessment of functionality of soils, as determined by physical,
chemical and biological properties. In particular, practical indicators
have not yet been identified to enable assessment of the buffering
function of soil and the interaction between environment and potential
indicators of soil quality. There is increasing awareness of the
threats affecting soils in Scotland and Northern Ireland and a growing
need to be able to measure soil quality, resistance and resilience.
Objectives of research
- To identify and evaluate indicators which are appropriate to use
(with reference to on-going projects commissioned by the UK government
and government agencies).
- To identify thresholds of "good" and "poor" chemical, biological
and physical quality of soil, which may be related to land use in a
range of contexts and functions relevant to agricultural, forestry and
natural systems in Scotland and Northern Ireland.
- To explore whether the characteristics of soil that relate to
resilience and resistance could be potentially captured with indicators.
- To explore whether thresholds for full (healthy) or no
(unhealthy) soil recovery (following a perturbation) could be
established or whether a baseline of resilience is required before
thresholds could be defined.
- To explore how the results could be used to identify soils at
risk and identify barriers to the implementation of concepts of
resilience in policy development.
A set of headline, secondary and tertiary indicators for soil quality
is proposed which included physical, chemical and biological
indicators. Headline indicators are: (physical) soil depth above
impermeable layer, topsoil total porosity/bulk density, subsoil
permeability; (chemical) total soil organic matter (SOM), total soil N,
C:N ratio, pH and Olsen P; (biological) microbial biomass C and
potentially mineralisable N. The advantages and disadvantages of each
indicator are discussed with reference to the soils of Scotland and
Soil resistance is defined as: "the capacity of a soil to continue to
function without change throughout a disturbance". Soil resilience is
defined as "the capacity of a soil to recover its functional and
structural integrity after a disturbance". Sets of headline and
secondary indicators for soil resistance and resilience are proposed.
The headline indicators for soil resistance are: (physical) soil
texture, bulk density and aggregate stability; (chemical) total SOM,
soil pH and buffering capacity; (biological) microbial biomass C,
presence of key microbial groups and soil respiration. The headline
indicators for soil resilience are (physical) aggregate stability and
soil structure; (chemical) buffering capacity; (biological) microbial
biomass C, presence of key microbial groups and soil respiration.
The main sources of data on the soils of Scotland and Northern are
listed in the report. This data allows us to assess the current (or
relatively recent) state of Scotland's soils. However there is a
shortage of soil physical data and an almost complete lack of
biological data for soils in Scotland and Northern Ireland. Almost none
of the available soil property information allows assessment of whether
the status of measured parameters is acceptable or not. Similarly, the
available data provides little indication of the soil’s ability
to resist stresses or recover from them.
The extent or "health" of soil recovery is defined as the extent to
which the functional capacity of the soil is restored or the extent to
which the soil is delivering its full potential. It was not possible to
establish thresholds for full (healthy) or no (unhealthy) soil recovery
following a perturbation at this stage in terms of physical, chemical
or biological indicators. Nor was it possible to define baselines for
soil resilience for the chosen headline indicators with any degree of
confidence given the nature and extent of available data. There may be
some merit in setting preliminary baselines for soil resilience for the
chosen headline indicators using expert group discussion where data
exist (e.g. for some physical and chemical indicators). However,
considerable further work is required before thresholds for soil
recovery/no recovery can be set with confidence for the wide range of
soil types present in Scotland and Northern Ireland.
The relative importance, in the Scottish and Northern Irish context, of
the major threats identified in the EU Soil Framework Directive will
depend on land use, soil types present and on local socio-economic
drivers. It is important that the pressures and risks affecting soils
in Scotland and Northern Ireland are identified and prioritised in
order to facilitate choice of the most appropriate indicators (for soil
quality, resistance and resilience) for use in specific situations and
to optimise their effectiveness in protecting our soil resource.
Development of an interactive tool that quantifies the ability of soils
to deliver identifiable environmental outputs was proposed. Development
of such a tool will necessitate further research to identify the link
between soil properties and the functions that they deliver. In
this report we have highlighted those soil properties that have proved
to be most valuable in this context on the basis of current knowledge.
However, this is a rapidly developing area, and as discussed in earlier
sections there are many areas in which our current understanding is
Recommendations for uptake
A risk-based approach to soil monitoring is proposed as being
appropriate, considering the threats currently facing soils in Scotland
and Northern Ireland. All indicators which are taken forward for
development and/or inclusion in a new minimum dataset for use in
assessing soil quality, resilience and/or resistance should as far as
possible be sensitive, accurate, reproducible, interpretable, capable
of rapid, high throughput and inexpensive. Further refinement of the
proposed set of indicators is required in order to allow us to
implement a programme of monitoring that will allow quantification of
loss of soil quality and the resistance and resilience of soils to
change. The development of indicators for soil resistance and
resilience is considered of greater importance than the development of
indicators for soil quality. Future work on indicators should include
development of new, cheap, rapid throughput chemical and biological
methods which have been shown to be effective in recent studies.
Development of a minimum dataset of soil quality/resistance/resilience
indicators should ideally be linked to a digitised national database
containing reference values for physical, chemical and biological
parameters in terms of good and poor soil quality and the
resistance/resilience of different soil types under different land
capability/land use classifications. Ideally, this database
should be available free or at low cost under licence to anyone wishing
to use it. The availability of linked or stand-alone decision support
tools to enable land managers, scientists, consultants, regulators and
policy-makers to interpret soils data and asses the quality and health
of soils status is vital if maximum use is to be made of the above
digitised national database.
Copies of this report are available from the Foundation, in electronic
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less 20% to FWR members.
N.B. The report is available for download from the SNIFFER Website