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)

5. Human resilience to
environmental change?
Ploughing close to the dune crest
exposes soil with very low wind abrasion
resistance to high wind speeds.
Wind erosion in the dunes can be locally
severe (Ritchie, 1971), leading to
blowouts, agricultural disruption
(Seaton, 1968; Angus, 2001) and can
threaten archaeological remains (Moore
et al., 2005). Figure 6. Photo of exposed machair front at
Staoinebrig, where there is no protective dune cordon.
Figure 6. Machair profile at Cille Pheadair showing the decrease in elevation from the dune crest (at left of image).
Profile from LiDAR dataset © SNH on behalf of the Western Isles Data Partnership.

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.