|
1. Definition
| Name |
ACIDIFIED
AREA |
| Brief definition |
% area acidified |
| Unit of measure |
% area of surface
soil with pH below 6.0 |
| Spatial scale |
Local to watershed. |
| Temporal
scale |
Little
overall change over time, but note that pH can change by up
to 1 unit during the growing season depending on temperature
and moisture conditions. |
2. Position
within the logical framework DPSIR
| Type of Indicator |
Driving Force/State |
3. Target and
political pertinence
| Objective |
Determination
of the acidified area provides an indicator of both soil quality
and restriction to vegetation growth. Most plants grow best
in soils with a pH range of 6 to 7. |
| Importance
with respect to desertification |
pH is a measure of soil
quality and can indicate how well the soil will support vegetation
cover. A soil pH lower than 6 can reduce the activity of micro-organisms
breaking down organic matter and reduce the availability of
essential plant nutrients such as calcium, magnesium and phosphorous.
Many potentially toxic heavy metals are more soluble in acidic
conditions, becoming concentrated in plants/crops, soils,
groundwater, aquifers, etc. Aluminium is toxic to plants and
soil organisms and has a limiting effect on plant growth and
breakdown of soil organic matter in soils of low pH where
aluminium is more soluble and exchangeable (FAO, 1970).
pH is affected by mineralogy,
climate and weathering in natural systems. The balance can
easily be changed by management practices. Nitrogen fertilisers
can be acid-forming. If there are sulphur-forming minerals
in the soil, these can promote acidity when exposed to air.
This can happen on tidal flats or where recent mining activity
has been drained.
|
| International
Conventions and agreements |
ISRIC, the
International Soil and Reference Information Centre, is accredited
to the UNCCD. |
| Secondary
objectives of the indicator |
Acidified
area as an indicator is related to desertification in terms
of soil quality, and also to biodiversity in terms of the limits
to vegetation growth. The acidity may be natural or related
to contamination from e.g. minewaste, sewage, agricultural chemicals,
and industrial chemicals. |
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
pH is a measure
of the hydrogen ion activity [H+] in an aqueous solution, or
for soil, in a paste or suspension of soil particles. |
| Benchmarks
Indication of the values/ranges of value |
The USDA Natural Resources
Conservation Service (1998) recognises the following soil
pH classes:
- Extremely acid 3.5-4.4
- Very strongly acid
4.5-5.0
- Strongly acid 5.1-5.5
- Moderately acid 5.6-6.0
- Slightly acid 6.1-6.5
- Neutral 6.6-7.3
- Slightly alkaline 7.9-8.4
- Moderately alkaline
7.9-8.4
- Strongly alkaline 8.5-9.0
|
| Methods of
measurement |
The soil paste
or suspension is made with water or calcium chloride solution,
and the chosen method must be recorded. Measurements of pH can
be made with dyes, paper strips, or glass electrodes. Chemical
activity is affected by temperature so pH should be corrected
to a standard temperature of 25ºC (77ºF). |
| Limits of the
indicator |
pH can vary
suddenly spatially due to factors that are not expected or are
forgotten. Examples include: from ploughing in of minewaste
or contaminated soil, from irrigation water, or from excess
ammonia fertiliser application. |
| Linkages
with other indicators |
Vegetation
cover type, Soil type, Soil organic matter in surface soil. |
5. Evaluation
of data needs and availability
| Data required
to calculate the indicator |
pH classes
recognised over a given area. |
| Data sources |
Local, National
and Regional soil survey and mapping. |
| Availability
of data from national and international sources |
European
Soil Bureau http://ies.jrc.cec.eu.int/Projects/ESB/International
Soil and Reference Information Centre http://lime.isric.nl/index. |
6. Institutions
that have participated in developing the indicator
| Main institutions
responsible |
King's College
London. |
| Other contributing
organizations |
This indicator
was suggested by stakeholders. |
7. Additional
information
| Bibliography
|
USDA Natural Resources
Conservation Service Soil Quality Information Sheet: Soil
quality Indicators: pH. (1998) http://soils.usda.gov
European Soil Bureau http://ies.jrc.cec.eu.int/Projects/ESB/
International Soil and
Reference Information Centre http://lime.isric.nl/index
Prosoil. Problem soil
database
http://www.fao.org/ag/agll/prosoil/acid.htm
|
| Other references |
United States Department
of Agriculture Natural Resources Conservation Service. http://www.nrcs.usda.gov
FAO 1970. Physical and
chemical methods of soil and water analysis by Dewis, J and
Freitas F, FAO Soils Bulletin No. 10, Rome.
Peirce, FJ and WE Larson,
1996. Quantifying indicators for soil quality. In Berger AR
and WJ Iams (eds) Geoindicators:assessing rapid environmental
changes in earth systems: 309-321 Rotterdam: AA Balkema.
|
| Contacts
Name and address |
Dr Nichola Geeson
DESERTLINKS Office,
1 St Lukes Drive, Bembridge, Isle of Wight, PO35 5XA, UK
desertlinks@medalus.demon.co.uk
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