benthic macroinvertebrate index for the truckee, carson, and walker rivers
DESCRIPTION
Benthic Macroinvertebrate Index for the Truckee, Carson, and Walker Rivers. Erik W. Leppo January 5, 2009 Reno, Nevada. Study Area. Truckee, Carson, and Walker Rivers in western Nevada Mainstem only All flow east from the Sierra-Nevada Mountains in California into Nevada - PowerPoint PPT PresentationTRANSCRIPT
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Benthic Macroinvertebrate Index for the Truckee, Carson, and
Walker RiversErik W. Leppo
January 5, 2009Reno, Nevada
Reference Other Stressed
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Reference Class
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Reference Other Stressed
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Reference Class
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Exceptional
Good
Fair
Poor
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Study Area
• Truckee, Carson, and Walker Rivers in western Nevada– Mainstem only– All flow east from the Sierra-Nevada Mountains in
California into Nevada
• Fixed station network (N=47)– Total of 377 samples– Not all stations sampled every year
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Study Area
California Nevada
#
TRUCKEE R
#
CARSON R
#
WALKER R
California Nevada
#
TRUCKEE R
#
CARSON R
#
WALKER R
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Index Development Steps
• Gather and organize data• Reference and stressed identification• Site classification• Calculate biological metrics for all samples• Determine metric sensitivity to stressors• Combine metrics into index alternatives• Select the most appropriate index• Evaluate the performance of the selected index
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Data - Providers & Extent
• Truckee, Carson, and Walker Rivers– Stateline to outlets
• Nevada DEP and Pyramid Lake Paiute Tribe– PLPT data only on lower reach of Truckee River
where NDEP data missing
• Years of data, 1981 to 2005– NDEP, 2000-2005– PLPT, 1981-2005
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Targeted Sample Period
• Low Flow– July – October, based on USGS Gage data
• Post 1997– Extreme flood conditions in winter 1997/8, river
changed course in some locations– Used 1998 – 2005
• Data Sources– NDEP (all 3 rivers but not lower Truckee)– PLPT (lower Truckee)
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USGS Gage data, monthly means, 1980-2005
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MethodsNDEP PLPT
Sampling Gear D-frame kicknet Modified kicknet
Mesh Size (µ) 500 500
Habitat Sampled Riffle Riffle
Field Effort 9 combined replicates 1-4 (kept separate)
Subsampling (Laboratory) 500 organisms Total pick
Organism Identifications (non-midges)
Genus Genus
Organism Identifications (midges)
Species Genus
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Data Differences• Field replicates
– NDEP – 9 combined in field– PLPT – 1-4 separate
• Combined 3 random replicates.• Only used samples with at least 3 replicates
• Lab Sorting– NDEP – 500 org– PLPT – entire sample
• Used computer to randomly subsample 500 org (± 20%).
• Identifications– NDEP – genus (midges to species)
• Used computer to group to genus– PLPT – genus
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Data Merge
• PLPT replicates “combined” and then subsampled to 500 organisms (± 20%).
• All identifications lumped to genus level.• Restricted time of collection to July to October
(low flow).• 377 total samples. After removing samples
outside of index period, less than target number of organisms, and field duplicates had 222 samples.
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Basins (Study Area)State BoundaryWater (RF1)Mainstem Rivers (Study Area)
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Combining Rivers & Reaches
• Used non-metric multidimensional scaling (NMS) plots to show relationships of sampling points.– Statistical technique to evaluate similarity of
samples based on the organisms present.– Points closer together are more similar. Points
farther apart are more dissimilar.– Can then code points by different grouping
variables and look for reasons for why points are close or distant.
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Axis 1
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s 3
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Axis 1
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s 3
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1.9E+03Elev_m
Axis 1r = -.236 tau = -.224
Axis 3r = .035 tau = .028
0 1.9E+03
River
TruckeeCarsonWalker
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Shaded Relief MapTruckee, Carson, and Walker River basins
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Ecoregions (Level 3)
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Central Basin and Range
Northern Basin and Range
Mojave Basin and Range
Sierra Nevada
NevadaRiver Basins (Study Area)Water (RF1)Rivers (Study Area Mainstems)
# Stations
200 0 200 400 Miles
N
EW
S
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Reference and Stressed
• These assessment models are built using least disturbed reference and know stressed.
• Model is built to discriminate between the two.• Reference and stressed are identified without
biological data to avoid circularity.• Water quality standards are used.• A variety of physical/chemical measures are
used to identify sites.
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Reference and StressedType Parameter Criteria
Chemical Dissolved Oxygen (mg/L)
> 6
Conductivity (µS/cm) < 300
pH < 9
Total Phosphorus (mg/L)
< 25
Water Temperature (°C)
< 20
Physical Habitat
Embeddedness (surrogate for percent
fines)
≥ 15
Channel Alteration ≥ 15
Total Score > 150 (75%)
Other Natural Hydrograph Not immediately below a dam
• A priori– Reference
• Pass 100% of parameters
– Stressed• Pass < 50% of
parameters
– Other• Fail < 50% or • Insufficient data
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Site Classification
• Did not see enough difference in NMS plots to separate out the 3 river basins.
• Within the Truckee River did not see enough differences to separate the upper and lower reaches.
• Looked at a range of physical and grouping variables.
• Looked at Reference sites but also all sites.• Included all sites as a single bioregion.
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Site Classification
• Reserved 20% of data set for model validation (N=46).
• Multimetric index created using the development dataset (N=176).
River Basin
Reference Other Stressed Total
Truckee
11 105 34 150
Carson 6 25 19 50
Walker 7 19 4 22
Total 24 141 57 222
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Metrics
• A metric is a measure of some attribute or element of the structure of, in this case, the bottom-dwelling (benthic) macroinvertebrate assemblage.
• Metrics that change in some predictable way to increasing stress are looked at.
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Metric Calculation
• A suite of 64 metrics were calculated for each sample.
• Metrics were calculated for multiple groups– habit, feeding, tolerance, richness, and
composition.
• Metrics were then evaluated for response to perturbation, discrimination ability, and ecological significance.
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Metric Calculation Method
• Calculations performed in EDAS, an Access database.
• Use of a database reduces random error and puts a system in place to limit systematic error.– Use of master taxa list– Saved queries to reproduce calculations
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Metric Evaluation
• All metrics were evaluated for their ability to provide ecologically meaningful data.
• Included metrics from the candidate pool– Sufficient range of detection
• Range > 3
– Discrimination Efficiency (DE); number of sites assessed correctly divided by total number of sites being evaluated.
• ≥ 50%
– Variability• Coefficient of Variation (CV) (std dev / mean) of Ref < 0.9
– Response to increasing perturbation• Respond in anticipated direction
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Metric Selection
• 19 metrics were considered as candidate metrics for inclusion in the overall index.
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Candidate Metric TestsCategory Metric DE CV
Feeding % Collectors 62.2 .59
Collector Taxa 82.2 .58
Filterer Taxa 62.2 .43
Predator Taxa 66.7 .48
Scraper Taxa 64.4 .77
Habit % Burrower 71.1 .69
% Sprawler 53.3 .70
Burrower Taxa 77.8 .48
Swimmer Taxa 71.1 .40
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Candidate Metric TestsCategory Metric DE CV
Richness Chironomidae Taxa 57.8 .65
Coleoptera Taxa 64.4 .67
Diptera Taxa 68.9 .57
Ephemeroptera Taxa 73.3 .40
EPT Taxa 77.8 .47
Tanytarsini Taxa 88.9 .86
Total Taxa 82.2 .42
Tolerance Beck’s Biotic Index 62.2 .64
Percent Dominant 01 Taxon
68.9 .42
Percent Dominant 05 Taxa
77.8 .19
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Candidate Metric Correlations
• Metrics that are strongly correlated are not used in the same index.– This can result in not using a metric since it is
correlated with so many other metrics.
• Strongly correlated metrics are not used together in the same index as they are most likely responding to the same stressor(s).
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Metric Scoring
• Need to translate metric values to a common scale for scoring and inclusion in an index.
• Each metric value is converted to a 0-100 score where values closer to 100 are considered optimal.
• Used 95th and 5th percentile of reference sites as “best” values.
• Index is an average of the component metric scores.
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Metric Scoring Formula
• Metrics that decrease with decreasing stress:
• Metrics that increase with decreasing stress:
100*min95
min
XX
XXScore
100*5max
max
XX
XXScore
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Metric Scoring ExampleMetric Response to
PerturbationPercentile
for Standard Best Value
Standard Best Value
Measured Metric Value
Standardized Metric Value
EPT Taxa Decrease 95th 18.3 20 100
Filterer Taxa Decrease 95th 5.0 5 100
Burrower Taxa Decrease 95th 7.0 4 57.1
Percent Sprawlers
Decrease 95th 34.5 10.2 29.6
Percent Dominant 01 Taxon
Increase 5th 17.9 26.5 89.5
Overall MMI Score 75.2
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Index Selection• Targeted
– 4-6 metrics with 1 from each of the metric categories. Candidate pool of metrics included only 4 categories (no composition metrics).
– Metrics with a high discrimination efficiency.– A final index with a high discrimination efficiency.
• Avoided– Pairs correlated at greater than |0.80|.– Pairs measuring the same group (i.e., percent and taxa
richness).• Final index score an average of component metrics.• Developed 5 index alternatives.
– Not every metric was combined into one of the metric alternatives.
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Index AlternativesMetric Category
Candidate Metrics
Index01 Index02 Index03 Index04 Index05
Feeding % Collectors X X
Collector Taxa
Filterer Taxa X X X
Predator Taxa
Scraper Taxa
Habit % Burrowers X
% Sprawlers X X
Burrower Taxa X X X
Swimmer Taxa
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Index AlternativesMetric Category
Candidate Metrics Index01 Index02 Index03 Index04 Index05
Richness Chironomidae Taxa
Coleoptera Taxa
Diptera Taxa X
Ephemeroptera Taxa X
EPT Taxa X X X
Tanytarsini Taxa X
Total Taxa X
Tolerance Beck’s Biotic Index
% Dominant 01 Taxon X X X X X
% Dominant 05 Taxa
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Final Index
• Index alternative 5 was selected.– Ephemeroptera, Plecoptera, and Trichoptera (EPT)
Taxa– Filterer Taxa– Burrower Taxa– Percent Sprawlers– Percent Dominant 01 Taxon
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Index PerformanceDataset Index01 Index02 Index03 Index04 Index05
Development 80.0 77.8 80.0 80.0 84.4
Validation 75.0 75.0 75.0 66.7 75.0
Combined 78.9 77.2 78.9 77.2 82.5
Discrimination efficiency calculated using stressed samples
• Index alternative 5 was selected.– Ephemeroptera, Plecoptera, and Trichoptera (EPT) Taxa– Filterer Taxa– Burrower Taxa– Percent Sprawlers– Percent Dominant 01 Taxon
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Narrative Assessments
• Assessment thresholds with narrative descriptions are intended to translate the numerical score into something that is more easily communicated to managers and the public.
• Use the range of values of the reference sites to set thresholds.
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Narrative Assessment Categories• Exceptional
– ≥ 75th percentile of reference– 71.9 - 100
• Good– ≥ 25th percentile of reference– 60.2 – 71.8
• Fair– upper bisection of 25th percentile of
Reference– 30.1 – 60.1
• Poor– lower bisection of 25th percentile of
Reference– 0 – 30.0
Reference Other Stressed
02
04
06
08
01
00
Reference Class
Ne
vad
a M
ulti
me
tric
Inde
x
Reference Other Stressed
02
04
06
08
01
00
Reference Class
Ne
vad
a M
ulti
me
tric
Inde
x
Exceptional
Good
Fair
Poor
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Exceptional Good Fair Poor
Nevada Multimetric Index, Narrative Assessment Ratings
Num
ber
of S
ampl
es
02
04
06
08
01
00
12
0
Exceptional Good Fair Poor
Nevada Multimetric Index, Narrative Assessment Ratings
Num
ber
of S
ampl
es
02
04
06
08
01
00
12
07%
14%
62%
17%
Reference Other Stressed
02
04
06
08
01
00
Reference Class
Ne
vad
a M
ulti
me
tric
Ind
ex
Reference Other Stressed
02
04
06
08
01
00
Reference Class
Ne
vad
a M
ulti
me
tric
Ind
ex
Exceptional
Good
Fair
Poor
Multi-Metric Index Scores
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Narrative Assessments
• Preliminary• Categories
– Could have 5 categories (tri-sect area under 25th percentile of reference).
• Names– Want to use names that convey meaning to both
managers and the public.
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Average MMI Scores by Site
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TRUCKEE R
#
CARSON R
#
WALKER R
NevadaCalifornia
River Basins (Study Area)State BoundaryWater (RF1) Rivers (Study Area)
Biological Sites, Average NV MMI Score#S Exceptional%U Good#Y Fair$T Poor
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Conclusions
• Have a tool to assess the biology of the mainstem rivers of the Truckee, Carson, and Walker Rivers.
• Work in progress– As more data become available, can refine index
(metrics or thresholds) and/or expand its spatial scope. Could be viewed as a building block for a state-wide index.
– Narrative assessment categories can be modified to match agency goals.
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Programs Used
• Data Management– Excel, Acccess
• Spatial Data– ArcView 3.x, ArcMap 9.2
• Statistics– PC-ORD, R, Excel
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Contact Information
• Nevada DEP– Karen Vargas
• Tetra Tech– Erik Leppo
– Michael Paul• [email protected]