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Class Level and Curriculum Links
Leaving Certificate Geography Ordinary and Higher Levels
Core Unit 3: Geographical Investigation and Skills
Investigating the Effects of Turf Cutting on the Vegetation, Hydrology and Peat Soil Properties of a Bog
Turf is used as a solid fuel in homes for heating and cooking in Ireland. Turf cutting is a feature of the midland and western regions of Ireland where bogs occur. For 400 years turf has been cut form the edge of the bogs using an implement called a sleán. Individual sods of turf are cut vertically or horizontally from a turf bank. They are then spread out in small stacks to dry on the bog surface before being transported home. The process of turf cutting has been mecahinised in modern times. Today it is more common to see a JCB working at the edge of the bog scooping huge chunks of peat from the bank and feeding this into a hopper machine which extrudes long lengths of wet peat on the bog surface. As they dry the long lengths split into pieces the length of a sod. These are stacked by hand on the bog surface to dry. Peat is also used as an energy source, generating 14% of our electricity. Large scale commercial peat milling is carried out by Bord na Móna. The milled peat crumb produced is dried naturally on the bog and is taken by rail to the peat-fired power stations. To date 568,000ha of peatland has been cut away by hand and 84,000ha have been cut mechanically.
Effects of Turf and Peat Extraction
on Bogs
In its natural state a bog is
95-98% water. Drainage removes water and increases the dry matter
content of the peat. This causes shrinkage of the peat. The bog
sinks. Sometimes the bog can even implode, like a big bubble
bursting. Studies undertaken by the National Parks and Wildlife
Service at Clara Bog in Co. Offaly have shown that the bog has
subsided by as much as 5-6m depth alongside a main drain and
the effects of the subsidence are in evidence at a distance of
500m from the drain itself. Cracking of the peat is commonly
associated with subsidence. Subsidence of the peat and cracking
increases the slope of the bog surface and this increases the
discharge of water from the bog.
Drainage removes water from the peat lowering the water table.
Studies at Wedholme Flow in the UK by English Nature showed that
each drain inserted, had the effect of lowering the water table
over the entire bog surface from 10cm to 30cm or more. This destroys
the upper living layer of the bog which contains the living carpet
of Sphagnum mosses, the peat forming community. As a result
the bog loses its peat forming capacity. The vegetation changes
form a Sphagnum dominated community to a vegetation type
dominated by dry bog species such as heaths, and sometimes the
colonisation by birch trees follows.
Once peat is exposed to air by drainage, it begins to break down. Oxygen in the air makes it possible for bacteria to digest the peat. Carbon is released during decomposition. Drying of the peat and decomposistion changes it structurally, making it difficult to re-wet and therefore unsuitable for re-colonisation with Sphagnum mosses.
This investigation looks at the effects of turf cutting on bogs.
Hypothesis
The extraction of turf from
bogs alters the physical structure of the peat in the bog, its
water content and peat forming vegetation community. Specifically
this investigation will determine whether
1. there is a difference in the height of the water table between
the margin and the centre of the bog.
2. there is a difference in the moisture content, humus content
and acidity or pH, of the peat in the two areas.
3. there is a difference in the topography of the bog surface
in the two areas.
4. there will be differences in Sphagnum moss cover and
other wet bog species between the two areas.
5. there will be a difference in the height and density of Ling
Heather and other dry bog species between the two areas.
Planning and Preparation
Reserach from Secondary Sources
Teachers might encourage students
to do research from books and web sites into the effects of turf
cutting on bogs.
Choosing a Site
Use an ordnance survey map combined with a peat distribution
map to identify a suitable peatland study site.
Equipment Needed
Bamboo rods and string, tape measure, spirit level, metre stick,
1m lengths of 2.5cm diameter wavin tubing drilled with holes
in the sides, sample bag and trowel, half meter squared quadrat,
recording sheet (see below), bog moss and ling heather identification
photographs and a pH meter.
Gathering Information in the Field
Use a belt transect set up from the cut margin towards the centre
of the bog. Each member to record a half metre distance along
the transect on the work sheet provided below.
1. Lay a tape measure along the bog surface to show position
of the transect.
2. Write a general description of the transect.
3. Insert a series of bamboo rods at 1m intervals along the transect,
using the tape measure as a guide.
4. Tie string between each rod. Make sure it is level across
the transect.
5. Measure the distance between the string and the bog surface
at 25cm intervals. Record the results. This gives a profile of
the transect and describes the topography of the bog.
6. Measure the percentage cover of ling heather and Sphagnum
moss, in a series of 50cm squared quadrats laid consecutively
along the transect.
7. Measure the depth of the water table below the bog surface,
at 10m intervals along the transect. This can be done by inserting
wavin tubes drilled with holes into the bog. The tubes should
be protrude 10cm above the bog surface. The tubes are left for
an hour to allow the water table to settle within them and a
meter stick is then inserted into the tube to record the depth
of the water below the bog surface.
8. Take peat soil samples at 10m intervals along the transect
for laboratory analysis of their % water content, % humus content
and pH.
Results, Conclusions and Evaluation
1. Plot the profile of the bog surface, draw histograms
to show the distribution of Sphagnum moss and ling heather.
Plot the water table depth below the bog surface and the soil
data.
2. Interpret the results. What are the effects of drainage on
bogs? How might these effects be reversed?
Effects of Turf Cutting on Bogs: Data Recording Sheet
This table can be modified depending on the length of the transect you choose to set up.
Site: Date: Recorded By:
Description of Belt Transect
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| Section Number |
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| Distance (m) | ||||||||||||
| Distance between bog surface and string (cm) | ||||||||||||
| Water Table Depth (cm) | ||||||||||||
| Peat: (a) fresh weight | ||||||||||||
| (b) dry weight | ||||||||||||
| % moisture content (b/a)x100 |
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| (c) ash weight | ||||||||||||
| % Humus (c/b)x100 | ||||||||||||
| pH | ||||||||||||
| % cover of Ling Heather | ||||||||||||
| % cover of Sphagnum or Bog Moss |
