Benthic Macroinvertebrate Index for the Truckee, Carson, and

Walker RiversErik W. Leppo

January 5, 2009Reno, Nevada

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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

Study Area

California Nevada

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TRUCKEE R

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CARSON R

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WALKER R

California Nevada

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TRUCKEE R

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CARSON R

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WALKER R

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

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

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)

USGS Gage data, monthly means, 1980-2005

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

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

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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NevadaCalifornia

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Truckee River

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Walker River

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Carson River

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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TruckeeCarsonWalker

Shaded Relief MapTruckee, Carson, and Walker River basins

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)

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200 0 200 400 Miles

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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.

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

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.

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

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.

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.

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

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

Metric Selection

• 19 metrics were considered as candidate metrics for inclusion in the overall index.

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

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

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).

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.

Metric Scoring Formula

• Metrics that decrease with decreasing stress:

• Metrics that increase with decreasing stress:

100*min95

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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

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.

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

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

Final Index

• Index alternative 5 was selected.– Ephemeroptera, Plecoptera, and Trichoptera (EPT)

Taxa– Filterer Taxa– Burrower Taxa– Percent Sprawlers– Percent Dominant 01 Taxon

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

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.

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

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Nevada Multimetric Index, Narrative Assessment Ratings

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Nevada Multimetric Index, Narrative Assessment Ratings

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Multi-Metric Index Scores

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.

Average MMI Scores by Site

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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

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.

Programs Used

• Data Management– Excel, Acccess

• Spatial Data– ArcView 3.x, ArcMap 9.2

• Statistics– PC-ORD, R, Excel

Contact Information

• Nevada DEP– Karen Vargas

• kvargas@ndep.nv.us

• Tetra Tech– Erik Leppo

• Erik.Leppo@tetratech.com

– Michael Paul• Michael.Paul@tetratech.com