8172

• UCREFRP Catalog Number: 8172
• Author: Jacobi, G. Z., J. E. Sublette, S. J. Herrmann, D. E. Cowley and M. D. Hatch.
• Title: Final Report
• USFW Year: 1998.
• USFW - Doc Type: Investigations of an Index of Biotic Integrity in New Mexico.
• Copyright Material: NO

upper Rio Grande drainage included five of
the variables important in the Swedish
study.
Lang and Reymond (1993) found that the
inverse relation between organic pollution
and elevation was useful in. a study of 56
rivers in western Switzerland. Their results
indicated that invertebrate diversity
increased -as -elevation-. -increased. In
contrast, analysis of the number of
chwonomid species versus elevation in the
upper Rio Grande showed no significant
relationship with elevation. Lang and
Reymond (1993) noted that the total number
of taxa was not correlated with elevation in
the Alps where the harsh environment
presumably limited the number of taxa
present.
The superiority of aquatic ecoregion
classifications, as opposed to Hydrologic
Units, has been demonstrated for the upper
Rio Grande drainage of New Mexico.
Aquatic ecoregion classification resulted in
significant differences between Aquatic
Ecoregions 1 and 2 in 10 of the 22
environmental variables. In contrast,
Hydrologic Unit classification provided a
landscape subdivision with significant
differences in only 4 environmental
attributes. Thus, elevational segregation of
sites accomplished with aquatic ecoregions
was superior to the subdrainage-level
classification provided by Hydrologic Units.
By separating sites with greater degrees of
environmental variation, aquatic ecoregions
may be superior for development and
application of IBIS.
The aquatic ecoregions described in this
report (Figure 6) for the upper Rio Grande
drainage suggest that two IBI's might be
warranted, i.e., one for high altitude (above
-7400') Aquatic Ecoregion 1 and one for
lower altitude sites in Aquatic Ecoregion 2.
Sites in Aquatic Ecoregion 1 have few fish
species. It is observed commonly that
headwater systems, even when they are
relatively undisturbed and pristine, have a
depauperate fish fauna (Stewart and Loar,
1994). In contrast, Aquatic Ecoregion 1
sites have a proportionally richer benthic
macroinvertebrate fauna. As a result, an
.. EBI - for --aquatic - -Ecoregion 1 should be
based on anacrobenth invertebrates. The
sites in Aquatic Ecoregion 2 are typical
"trout stream" sites that have more fish
species than sites in Aquatic Ecoregion 1.
However, these sites have few enough fish
species that an IBI for these sites might need
to include statistics for invertebrates and
fish.
With the results obtained for the upper Rio
Grande drainage and considering the
general ' physiography of northern New
Mexico, it is anticipated that the two aquatic
ecoregion classifications will be applicable
to sites at similar elevations in other
drainages . of northern New Mexico.
However, when analyses are extended to
include additional low elevation sites, it is
anticipated that a third aquatic ecoregion
will be necessary for sites below about 5400
feet in elevation. Statewide, there should be
considerable heterogeneity in freshwater
environments. It remains to be determined
if analysis of environmental data for sites at
many locations in New Mexico will yield
ecoregions consistent with the five
ecoregions proposed for the state by
Omernik (1986, 1987; Figure 7).
Faunal Regions
The faunal regions for chironomid species
in the upper Rio Grande suggests that sites
3r
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