Benthic Macroinvertebrates Index Development and Physical Habitat Evaluation for Truckee River, Carson River, and Walker River

Prepared for: NDEP, Prepared by: Tetra Tech.
September 2007

Executive Summary
The objective of this project is two-fold; to develop a benthic macroinvertebrate multimetric
index using existing data to apply to the main stems of the rivers of west central
Nevada (the Truckee River, the Carson River, and the Walker River) and to evaluate
physical habitat measurements for the main stem of the Truckee River as a potential
assessment tool.

A multimetric benthic macroinvertebrate index was developed for the area of interest that
integrated data from three river systems and two agencies (Nevada Division of
Environmental Protection and Pyramid Lake Paiute Tribe). Data used for the index were
collected during low flow periods (late June to early November) to minimize the effects
of flow on the calibration of the index. Samples were collected from riffles and were
subsampled to 500 organisms, identified to genus level.

The calibrated benthic macroinvertebrate index consists of five metrics each scored 0-100
(100 being closest to reference or optimal) with the final index value calculated as an
average of the five metric scores. The metrics are: number of Ephemeroptera, Plecoptera,
+ Trichoptera (EPT) taxa, number of filterer taxa, number of burrower taxa, percent
sprawlers, and percent dominant taxon. Using the newly developed index and the
proposed narrative assessments, 7% of samples from all the three rivers rated as
Exceptional, 14% as Good, 62% as Fair, and 17% as Poor.

The second goal was to develop a suite of measurements that could be used to easily and
effectively assess the physical habitat at various locations on the Truckee River. A
number of physical habitat assessment methods were evaluated as applicable to these
Nevada rivers. The EMAP protocols were used as a template and then investigated for
minimizing the amount of field data needed to ascertain reliable reachwide values.
It was determined that the relative bed stability (RBS) was the single parameter best
suited to measuring the physical habitat of the rivers in this study. Modifications of the
method were investigated that would get similarly meaningful results with reduced effort
in the field. It was found that coarser measurements for bankfull height and thalweg
depth could be employed given the homogenous nature of the rivers. The Truckee River,
measured with RBS, tends toward stable habitat above Reno and again in the lower river
on the Pyramid Lake Paiute Reservation above Nixon.

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