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Rethinking Buffer Strips in Three-Dimensions
Marc Stutter1, Mark Wilkinson1, Tom Nisbet2, Jamie Letts3, Rachael Dils3
1The James Hutton Institute, Aberdeen, AB15 8QH, UK; 2Forest Research, Alice Holt Lodge, GU10 4LH, UK; 3Environment Agency, BS1 5AH, UK.
Email: [email protected]
Why a ‘rethink’?
▪ More innovative watercourse margins:
▪ better protect against water quality failures
▪ increase wider environmental benefits
▪ enable alignment of multiple funding sources
▪ increase effort in adoption and space dedicated
▪ Enhancing buffer structure from below ground, surface to canopy can improve functions and these should be tailored landscape pressures
Current issues with watercourse margins
Photos: S Langan, M Stutter, B Kronvang
Common failings of watercourse margins
Sediment and nutrient retention
TP = 19.0ln(width) + 18.5R² = 0.22
diss P= 41.9ln(width) - 71.2R² = 0.09
-400
-350
-300
-250
-200
-150
-100
-50
0
50
100
0 20 40 60
% t
rap
pin
g ef
fici
ency
Buffer width (m)
Total P
Dissolved P
-1900
-1700
-1500
-1300
-1100
-900
-700
-500
-300
-100
100
0 20 40 60
% t
rap
pin
g ef
fici
ency
Buffer width (m)
Nitrate
Sed = 7.4ln(width) + 62.4R² = 0.16
0
20
40
60
80
100
0 20 40 60
% t
rap
pin
g ef
fici
ency
Buffer width (m)
Sediment
Coliforms
Model p Trapping efficiency(Mean ± 95% C.I.)
2 m width 10 m width
Sediment <0.001 67 (62 to 73) 79 (71 to 88)
Total P <0.001 32 (6 to 60) 62 (22 to 103)
Diss P 0.03 -42 (-148 to 64) 25 (-139 to 190)
Stutter et al. In prep.
Margin soils differ to those in the field
Soil moisture
Buffer > Field
Field > Buffer
No significant difference at 5% level
Soil organic matterBuffer > Field
Field > Buffer
No significant difference at 5% level
n=112, 44 sites in NE Scotland
Stutter & Richards (2012). JEQ, 41: 400-409.
NO3
Buffer > Field
Field > Buffer
No significant difference at 5% level
SRP
Buffer > Field
Field > Buffer
No significant difference at 5% level
Nitrate
Soluble reactive P
Narrow riparian buffers do not provide the best riparian habitat
• Recently buffered and degraded sites seemed less stable habitats than established riparian woodland.
Indicator (measure)
Degradedsites
Bufferedsites
Reference-state sites
Functional significance
Canopy (%) 10.7a 14.4a 55.4b Reference sites were mature riparian sites with trees
Carabidae faunal traits:Size (mm)
Dispersal ability (% winged)
Autumn breeders (%)
9.2a
74.4a
65.9a
9.3a
72.1a
64.5a
11.5b
43.0b
85.2b
Larger less mobile species require habitat stability, smaller mobile species are able to respond quickly according to habitat suitability
Autumn breeding is likely to be disturbed by agricultural activities, e.g. ploughing
Stockan et al. (2012). Understanding vegetation patterns and plant-environment relationships along riparian margins. JEQ, 41
Buffer functions and the 3D concept
Key aspects of the 3D buffer structure
6
10
What buffer space exists to build upon?
0
2
4
6
8
10
12
14
16
0 20 40 60 80 100
Bu
ffe
r w
idth
(m)
Percentage exceedence
Arable (n=36)
Pasture (n=8)
National minimum buffer width
% of sites where width is greater
Example measures
Tree planting
▪ Mainly native broadleaved trees
▪ Many benefits
▪ Needs design, establishment time and management
▪ Can use fast-growing biomass species
▪ Present issues with minimum widths of woodland creation schemes
Willow riparian SRC systems in Canada: https://cfs.nrcan.gc.ca/projects/134/2
Riparian wooded buffer, U.S.: USDA, Environmental Quality Incentives Program (EQIP)
Riparian alder for stream shade, NE Scotland
Raised ground features
Examples:
▪ Simple earth banks in floodplains for water (temporary) and sediment /contaminant storage
▪ Small ponded infiltration areas across the slope base e.g. created by a tiled-ridger furrows
(Balruddery magic margins)
Borrowing from the NFM community…
Dealing with artificial soil drainage using saturated buffers
www.transformingdrainage.org
▪ Controlled drainage
▪ Raising and irrigating onto saturated buffers
▪ Breaking/ending drains into small wetlands and ponds
Providing a wider range of public goods
▪ Farm livestock crossings
▪ Public access
▪ Enhancement of visual amenity
e.g. riparian trees, natural channel form
▪ Increased abundance of pollinators
▪ Stream shading and temperature regulation
▪ Alternative harvests
Bottom photo: Fortier et al. Forests 2016, 7(2), 37
A zoned buffer:•Cropping continues on the field slope
•The erosion slope is interrupted by a ditch into which field drains are broken back from the stream
•The ditch increases the residence time of nutrient-rich waters
•Planted trees introduce a bioactive root zone, taking up nutrients into biomass, producing an energy crop, introducing habitat and stream shading
http://www.buffertech.dk/
Integrated buffer designs
Implementing packages of measures
5 measures packages based on a 6 m marginPackage Schematic Cost & effort Acceptance Specific aspects
Vegetated
Buffer
Commonly adopted,
familiar measure for
basic set of outcomes
Wooded
Buffer
Acceptable, benefits
for C, biodiversity,
airborne spray drift,
deep rooting to GW
Designer
vegetation
Specific biodiversity
goals, pollinator
habitat, can use
nutrient mining plants
Raised field
margin
Raised ground for more
extreme erosion
control, fine particles,
flood benefits
Engineered
buffer
Specific options to
tackle drains and bring
wetness diversity.
Includes margin and
cross-ditch measures
Future needs
Planning tools for locating buffers
Thomas et al. Agric. Ecosyst. Environ. 233: 238-252 (2016)
Wilkinson et al. Bunds and planning tools in Tarland, NE Scotland
Control points
Dominant major surface
flowpath
Numerous minor surface
flowpath
Dominant flow through
drain network
No
bu
ffer
Lin
ear
‘su
rfac
e fl
ow
’ bu
ffer
s:
2m
(p
urp
le)
10
m (
gree
n)
Spat
ially
&
flo
wp
ath
op
tim
ised
b
uff
ers
P load reduction scenarios
20 kgP/yr as 60% particulateP, 40% soluble P
20 kgP/yr as 50% PP, 50% SRP
20 kgP/yr as 40% PP, 60% SRP
10% P load reduction in 200m2 (purple) or 60% P load reduction in 1000m2 buffer (green)
20% P load reduction in 200m2 (purple) or 70% P load reduction in 1000m2 buffer (green)
Both basic rules (2 m) and funded buffer (10 m) largely ineffective for subsurface P (<10% removal)
50% P load reduction in additional 200m2 to basic rules (or up to ~90% if 1000m2)
60% P load reduction in additional 300m2
50% P load reduction in 100m2 by cutting back drains to mini-wetland
Support for decision making on right design, right place (SmarterBufferZ, Ireland)
A need for demonstration
▪ Tree planting and grass margins are acceptable to land managers
▪ Features seen as ‘engineered’ are unfamiliar and have negative perceptions unfamiliarity
▪ There’s a negative perception of wet ground on farms
Summary
▪ Current narrow or absent buffers are failing for diffuse pollution and wider benefits; uncertainty in their function leads to a lack of ‘extra effort’
▪ Can build into a riparian space of 6-10 m with packages of options tailored to site requirements
▪ Incorporating 3D structure (canopy to below ground) imparts a range of beneficial processes
▪ Specific strategies are needed for problem erosion situations, subsurface nitrate, soluble P accumulation
▪ Wariness exists of the runoff attenuating measures and saturated buffers; needing demonstration
Resources and activities
▪ EA report forthcoming on 3D watercourse margins
▪ BufferTECH project (www.buffertech.dk/en)
▪ Scientific literature synthesis on riparian management in Journal of Environmental Quality (late 2018; Editors: Stutter
(UK), Kronvang (DK), Rozemeijer (NL), Ó hUallacháin (IRL))
▪ Irish EPA-funded SmarterBufferZ (2018-22)
Acknowledgements
Bottom photo: B. Kronvang
▪ Contributions from Paul Quinn (Newcastle Uni), Adrian Collins (Rothamsted Research), Chris Stoate(GWCT), Dominic Coath (EA) to a project workshop
▪ Environment Agency and Forestry Commission funding for the 3D watercourse margins project
▪ Scottish Government’s RESAS funding for ongoing buffer management investigations
▪ Danish Science Foundation funding for the BufferTech project
