1. Monitoring the impacts of peatland
drain blocking.
LIFE-Nature Active Blanket Bogs in Wales
Lorraine Wilson, J. Wilson, J. Holden,
A. Armstrong, I. Johnstone & M. Morris
2. The study site
Lake Vyrnwy catchment:
- 10,000 ha
- approx. 4,800 ha blanket bog
- upland areas were drained in 1950-70s
- SAC, SPA, SSSI.
- blanket bog in ‘unfavourable’ condition due to
drainage & historic overgrazing & burning
- Lake is the water supply to Liverpool
-Upland areas are hill farmed by the Royal Society
for the Protection of Birds (low levels, April-Oct only)
3. The project aims
• Restore damaged blanket bog to ‘favourable’ condition
– Blocking drainage ditches across a large upland catchment
• Structure restoration to provide experimental conditions
– 4 sub-catchments, blocked sequentially 1 per winter
– Longitudinal (before/after) data per sub-catchment
– Experiment/Control data between sub-catchments
• Research targeted to address stakeholder concerns & project
priorities.
– Recovery of vegetation?
– Recovery of conditions for vegetation (higher, stable water tables)?
– Effects on organic carbon release & discharge water colour?
– Implications for flood risk management?
– Effects on hill sheep farming?
4. Field methods: Hydrology
•Dipwell & Creststage
tubes at: 0.5, 1, 5, 10,
20m from drains.
•Water grab samples
from drains & streams.
•Automatic pressure
transducers in 4 drains,
3 streams & 3 dipwells.
•Nov 2007 – ongoing.
5. Water tables
5
0
Water table depth (cm)
0 100
-5
Unblocked
-10
Blocked
-15
-20 % Time water table was below given depth
Water tables and surface water increased within 5m of drains, especially
downslope.
Surface water also increased much more widely.
Water tables less variable after blocking, particularly during the summer.
6. Peak flow events
600 1
Total discharge (m3 s-1)
Unblocked 0.8
400
Blocked 0.6
0.4
200
0.2
0 0
Baseflow Runoff Efficiency Flashiness
Based on 20-25 events from 4 drains and 3 streams.
Also: peak flow rates declined & recession duration increased
Response in streams less marked than in drains, but still significant.
Blocking leads to less flashy peak flow events, with slower release of rainwater &
more water being held in the bog.
7. Drought events
0
0.5m 1m 5m Unblocked
Adjusted drain flow rate
-2
0.E+00 Blocked
Water table (cm)
-4
-6
-8 -5.E-04
-10
Unblocked
-12 Blocked
-1.E-03
-14 Dist. to drain 1 5 9 13
Days
Based on data from 17 drought events (of 5-18 days) from 4 drains, 3 streams
and 78 dipwells.
Blocking reduces the degree of water table drawdown during droughts, and
maintains more constant flow rates in both drains and streams.
8. Water colour
0.1
2.37
Absorbance 400nm
Flow weighted Abs400
Absorbance Units
0.05
0
Unblocked Blocked Unblocked Blocked
Grip Stream
Models show no significant changes in absolute Absorbance at 400nm
Flow weighted absorbance declined in streams, and stayed stable in grips.
9. Organic carbon
100.00 10.00
DOC POC
Concentration 769 38.2
(mg/L)
80.00 8.00 Concentration (mg/L)
Load (mg/s)
Load (mg/s)
60.00 6.00
4.00
40.00
2.00
20.00
0.00
0.00 Unblocked Blocked Unblocked Blocked
Unblocked Blocked Unblocked Blocked
Grip Stream
Grip Stream
DOC levels increased in grips after blocking.
DOC concentrations in streams did not change & reductions in flow led to
very large reductions in load.
POC concentrations were unaffected by blocking. Loads declined in both grips
and streams.
10. Organic carbon
Drought water colour and organic carbon release showed slight declines after
blocking.
Post drought ‘flushes’ of water colour and organic carbon were significantly
reduced.
11. Organic carbon
Estimating total annual organic carbon fluxes from the study site:
• Variable POC levels during baseflow = possible overestimation
• Extrapolated high resolution datasets:
– Rating equations for baseflow, rising limb and falling limb flow periods per sub-catchment.
R2 values = 0.30-0.67
• Flux estimation using Method 5 (Walling & Webb, 1985)
– Accurate but imprecise = large error margins
– Per sub-catchment stream, per full year blocked/unblocked
– Averaged across all sub-catchments & total peatland area of catchment
Before blocking: 554 - 927 t/km2/yr
After blocking: 22 - 37 t/km2/yr
12. Hydrology Summary
1. Has drain blocking allowed water tables to recover adjacent to drains.
– YES. Although recovery is still underway.
– Water tables also become more stable & more ‘drought resistant’.
2. Has drain blocking reduced water colour & fluvial organic carbon loss?
– YES.
3. Does drain blocking have the potential to mitigate downstream flood
risk?
– YES.
14. Vegetation recovery
60 0.68
Sedges & rushes
50 Sphagnum spp.
Condition score
40 0.64
% cover
30
20 0.6
10
0 0.56
Control Unblocked Blocked Control Unblocked Blocked
Wet specialist species have increased in blocked areas & dry tolerant species
have declined.
Statutory ecological condition is improved by drain blocking.
Implications for gaseous flux trends but further study needed to model this.
15. Hill sheep farming
Local farming community initially unwilling to consider drain blocking.
Research through meetings, talks, open & demonstration days identified main
areas of concern:
1. Decrease in grazing quality.
2. Decreased access to blocked areas.
3. Increased stock entrapment in blocked drains.
4. Increased prevalence of parasite-borne diseases.
Vegetation survey data & targeted basic field surveys carried out to attempt
to address each point.
16. Hill sheep farming
100
Control
Unblocked
75
Blocked
50
25
0
Grass Sedge Dwarf shrub Sheep
Preferred fodder species (grasses) showed no change after blocking.
Sheep accessed wet areas more widely after blocking, probably due to increased
availability of crossing points.
17. Hill sheep farming
0.2
Ticks /km
0.15
Carcasses /km/yr
0.1
0.05
0
Control Unblocked Blocked
Parasite surveys hampered by very low local abundances, but suggest that
ticks decline after drain blocking.
Stock loss in blocked drains significantly less than prior to blocking.
18. Vegetation & farming summary
1. Has drain blocking allowed vegetation condition to recover?
– YES.
– Change is still ongoing, current communities are not the end point.
2. Does drain blocking reduce sheep farming viability?
– NO. It may even be a positive management tool.
– Grazing is unchanged and access to wet grazing increases.
– Stock entrapment in drains declines.
– Parasite abundances may decline.
3. Regular communication of these studies has led to the LIFE project &
CCW entering into 12 private landowner agreements to carry out drain
blocking on 2500ha of blanket bog.
19. Conclusions
• Drain blocking at Lake Vyrnwy appears to be delivering for several key
‘ecosystem services’, ranging from habitat conservation to drinking water
quality.
• Fluvial organic carbon fluxes, and changes to vegetation communities will have
profound impacts on overall carbon balances from restored peatlands. More
research is needed to model the role of vegetation change in gaseous fluxes.
• Peatland restoration is at least a neutral agricultural management tool & thus
has potential to be spread beyond protected sites with appropriate advocacy
and research.
Ongoing research:
• Study of vegetation responses to tree removal and experimental grazing.
• Study of vole and passerine trends on blanket bogs, testing for responses to
drain blocking, using RSPB survey data.
20. Acknowledgements
M. Morris, F. Walker & J. Lane for help with fieldwork. The study site is owned
by Severn Trent Water.
LIFE-Nature fund & project partners:
