1. Soil Sensitivity to Wind Erosion in the
Machair Landscape of South Uist, Outer
Hebrides
Elizabeth J. Young1,2
Supervisors: Sue Dawson1 & Blair M. McKenzie2
1Geography (School
of the Environment), University of Dundee
2The James Hutton Institute, Invergowrie
2. Introduction
Machair soils:
• Low aggregate stability
• Organic matter content
generally < 10%
• Sandy texture
• Exposed to highest mean
winds speeds in UK
Figure 1. Field at Cille Pheadair showing cultivation
extending to dune crest, and sand deposition.
Figure 2. Idealised machair cross-section (from Angus, 2001).
3. Methods
Samples rotary sieved at 7 rpm
for 300 s , mesh size = 850 µm.
•Erodible fraction = soil passing
through sieve within 40 s
•Potentially erodible fraction =
soil passing through sieve
between 41-300 s
•Non-erodible fraction = soil
remaining on sieved after 300s
Figure 3. Simplified rotary sieve, after Tisdall et al.
(2012).
Analysis of soil properties:
FTIR, XRF, pH, particle size, water drop penetration time, water repellency.
4. Results
100
90
80
% of 40 g soil sample
70
60
Figure 4. Graph showing % of soil
50 Erodible samples in each class (erodible, non-
40 Potentially erodible erodible, potentially erodible) with
30 Non-erodible distance from the coast.
20
10
0
0 15 30 45 70 130 185 220 260 290
Distance from the coast (m)
100
90
80
70
Figure 5. Graph showing % of 60
soil sample which could pass 50
%
< 850 µm
through the rotary sieve 40 sediment passed through sieve
(particles < 850 µm), and % 30
of sediment which did pass 20
through the sieve. 10
0
0 15 30 45 70 130 185 220 260 290
Distance inland (m)
6. Conclusions
• Machair soils are very susceptible to wind erosion due to
low organic matter content, low aggregate stability, and
exposure to high wind speeds.
•At Cille Pheadair there is a positive correlation between
wind abrasion resistance and distance from the coast.
•pH, water repellency, and the ratio of carbonate:silicate
sand may be correlated with wind abrasion resistance.
7. References
• Angus, S. 2001. The Outer Hebrides: Moor and Machair. The White
Horse Press, Cambridge.
• Moore, H., Wilson, G., Dawson, A.G., Dawson, S. 2005. Western Isles
(South) Coastal Zone Assessment Survey, Grimsay, Benbecula, and
South Uist. Commissioned report for Historic Scotland and Scottish
Coastal Archaeology and the Problem of Erosion. EASE Archaeological
Consultants, Edinburgh.
• Ritchie, W. 1971. The Beaches of Barra and the Uists. A survey of the
beach dune and machair areas of Barra, South Uist, Benbecula, North
Uist, and Berneray. Commissioned report no. 047 for Scottish Natural
Heritage. Aberdeen.
• Seaton, D. 1968. Bornish blow-out: a record of co-operation in
overcoming machair and land erosion. Scottish Agriculture 47, 145-
148.
• Tisdall, J.M., Nelson, S.E., Wilkinson, K., Smith, S., McKenzie, B.M. 2012.
Stabilisation of soil against wind erosion by six saprotrophic fungi. Soil
Biology and Biochemistry 50, 134-141.