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Development and independent testing of a new biotic index of stream macroinvertebrate response to
deposited fine-grained sediment
Iwan Jones, John Murphy, James Pretty, Chas Duerdoth, Adrianna
Hawczak, Amanda Arnold, John Blackburn, Pam Naden, Gareth Old, David Sear, Duncan Hornby, Ralph Clarke and
Adrian Collins
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Erosion and Deposition are Natural Processes
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Human Activities Influence Load, Composition and Retention
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Sources of fine sediment Relative contribution of agriculture to annual sediment load
>50% <50%
National-scale sediment source apportionment for England & Wales Zhang, Collins et al. (2014) Env. Sci. Pol. 42:16-32
Fine sediment is now considered one of the most widespread and detrimental forms of aquatic pollution
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Impact of Fine Sediment Light reduction Bed alteration
Altered hydrodynamics Oxygen depletion
Scouring Burial
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Managing the problem EU Water Framework Directive provides the mandate
UK government requires tools to diagnose where excessive fine sediment is impairing ecological condition
Better targeting of mitigation
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Review Impact of Fine Sediment on WFD BQEs
Fish
[Kemp et al. (2011) Hydrological Processes 25: 1800-1821]
Invertebrates [Jones et al. (2012) River Research and Applications, 28: 1055-1071]
Macrophytes [Jones et al. (2012) River Research and Applications, 28: 1000-1018]
Diatoms [Jones et al. (2014) Hydrological Processes 28, 1226–1237]
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Impacts via
Suspended Sediment Deposited Sediment
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Existing knowledge not always at appropriate spatial scale for management Better understanding of susceptibility of biota required
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Improved Ecological Evidence
Invertebrate response to sediment stress – Correlative field survey – Manipulative experiments
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Objectives
– Establish relationships
– Develop a diagnostic biotic index
– Independently test new index
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Calibration dataset • 230 sites sampled for macroinvertebrates & deposited
fine sediment
• across a gradient of modelled sediment pressure
• across a gradient of stream types
• free from STW and urban area inputs
• upstream of lakes & reservoirs
• predominantly agricultural catchments
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Macroinvertebrate sampling
At each site: – macroinvertebrate sample (RIVPACS protocol) o record physical features of site o acquire map-based data
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Fine sediment sampling
At each site: o remobilisation stilling well sample surface drape and embedded fine sediment
from erosional and depositional areas
Processed in the lab for: mass of sediment organic content particle size
[Duerdoth et al. (2015) Geomorphology 230: 37–50]
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Reach scale measurement Known confidence intervals > 95% variation between rivers Operator < 1% (not sig.)
Fine sediment sampling
[Duerdoth et al. (2015) Geomorphology 230: 37–50]
0
1
2
3
4
5
0 1 2 3 4 5
Sam
ple
log 10
tota
l sed
imen
t (g
m-2
)
Site mean log10
total sediment (g m-2)
•95% c.i. = ±0.269
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• Visual estimates of % cover of fine sediment • 4 visual estimates at 16 sites on three occasions
Assessment of reach-scale fine sediment sampling
Source % Variance
Between river site 94.0*
Operator 2.3*
Replicate sample 3.6
Season 0.1
• Visual estimates affected by operator bias
[Duerdoth et al. (2015) Geomorphology 230: 37–50]
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Comparison with visual estimates of bed composition
surface drape: avera
mean substratum size phi
sedi
men
t m
ass
g/m
2
-8 -4 0 4 8
100
101
102
103
104
105
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Analytical Approach
Partial ordination to relate sediment pressure (predicted/ measured, quantity/quality) to invertebrate community over
a range of sediment loadings within river types
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Unconfounded stress gradients
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Invertebrate response to fine sediment stress comprises two distinct components ToFSIsp index of response to inorganic component of fine sediment oFSIsp index of response to organic component of fine sediment
Index Development
The results of these two indices are then combined CoFSIsp – combined index of
fine sediment stress C
oFS
I sp
[Murphy et al. (2015) Freshwater Biology 60: 2019-2036]
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Independent test 26 sites retained from the survey and 57 stream sites in Wales
[Murphy et al. (2015) Freshwater Biology 60: 2019-2036]
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Independent test PSI (Proportion of sediment sensitive invertebrates)
Expert judgement (habitat preference/morphology)
[Murphy et al. (2015) Freshwater Biology 60: 2019-2036]
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RIVPACS – River Invertebrate Prediction and Classification System
Can predict the community that would be expected in the absence of pollution at any site in the UK
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0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 0.5 1 1.5 2 2.5
Log
10 T
ota
l Sedim
ent
Mass
(g m
-2)
Log10
Slope (m km-1)
y = 3.88 - 0.819 Log10
Slope
R2 = 0.247, p > 0.001
a)
b)
A better descriptor of sediment stress
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CoFSI and WFD classification
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5
EQI CoFSI
EQ
I C
oFS
I
Log10
Total Sediment Mass (g m-2)
R2 = 0.252
p < 0.001
i)EQI CoFSI
Deposited Sediment Mass - Slope Residuals
EQ
I CoF
SI
R2 = 0.204
p < 0.001
i)
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PSI and WFD classification
EQI PSIfam
EQI PSIsp
Deposited Sediment Mass - Slope Residuals Deposited Sediment Mass - Slope Residuals
EQ
I PS
I fam
EQ
I PS
I sp
R2 = 0.126
p < 0.001
R2 = 0.109
p < 0.001
h)g)
i)
PSI is unstable at high levels of pressure
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Sediment Experiments in Artificial Stream Channels
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[Jones et al. (2015) Freshwater Biology 60: 813–826] [Growns et al. (submitted)]
Response variables Turbidity Deposited Sediment Mass Oxygen Penetration Hyporheic Chemistry Interaction with Flow Drift Community Composition Index Values Trait Composition Hyporheic Invertebrates
CONTROL MODERATE HIGH
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CoFSIsp index performs well
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Conclusions Fine sediment has a marked impact on invertebrates
Effects through quantity and quality CoFSI can assess fine sediment stress
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Acknowledgements
Landowners and farmers RivComms staff, Ivor Growns, all others involved