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Matt Johnson and Rob [email protected]
www.mattjohnson.org.uk
Seeing the landscape for the trees: the development of simple metrics to inform riparian zone management
• Rising temperatures due to climate and environmental change will have major consequences for river biota.
• Riparian tree planting to shade rivers is a popular management strategy
• But, in many places planting is currently unfocused
Introduction
LUTEN www.luten.org.uk
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24D1 D2 D3 D4 D5 D6 D9 D1
0D1
1D1
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5D1
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7D1
8D2
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3D2
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Max
imum
15
min
ute
Tw (°
C)Thermal regime
Increasing distance downstream
Potentially harmful to
trout
Water temperature is spatially patchy and temporally variable.
S
WN
E
a)
Sunset
Sunrise
Riparian shade
However, shade is not of equal magnitude
Not all river reaches will benefit from shade to the same degree.
To provide simple metrics to inform where riparian shading will have maximum benefit in mitigating against rising water temperature
Using existing and routinely-collected data.
Aims
4181 J required to heat 1 kg of water by 1 °CHeat capacity and shade length
Predict how long it takes to attain sufficient solar energy to reach heat capacity
Know volume (and therefore weight) of water at a gauge
Which is the length of continuous shade required
Heat capacity and shade length
Shade requirementA river that is 6 m wide, 0.4 m deep and velocity is 0.5 m s-1
requires 1 km of continuous shade - at midday on hottest day- At 52°N latitude
Sensitivity to shade
Landscape
Where shade is lacking
Where is sensitive to riparian shade
Groundwater Inputs
02468
101214161820
Wat
er Te
mp.
(deg
C)
Surface water dominated Groundwater dominated
Groundwater
Groundwater refugeDovedale is an important thermal refuge• Robust Mayfly phenology maintained in
this reach• Substantial changes upstream to a more
vulnerable structure
05
1015202530
0 3 6 9 12 15 18 21 24 27 30
Coun
t
Total length (mm)
05
1015202530
0 3 6 9 12 15 18 21 24 27 30
Coun
t
Total length (mm)
MalesFemales
ConclusionsSensitivity to shading will vary greatly between and along rivers
Riparian planting is likely to be successful on:• Relatively limited regions of catchments• But impacts will be propagated downstream• And there are numerous mutual benefits!
Important to identify and maintain existing thermal refuge, particularly those associated with cool groundwater inputs.• Protect such areas from other adverse pressures.
