Geoscience Reference
In-Depth Information
Table 26.5
The 2009 status of resources that represent the main focus of the Glen Canyon Dam Adaptive Management
Program (from Hamill, 2009).
Environmental Impact
Statement prediction (1995)
Resource
Status (2009)
NATURAL RESOURCES
Water quality
(water temperature). (Goal:
Establish water temperature, quality,
and flow dynamics to achieve Program
ecosystem goals).
No effect.
Since 2003, downstream water
temperatures have increased in response
to drought conditions (http://pubs.
ugs.gov/ds/2007/251/).
Specific conductance
(salinity).
No effect.
Drought conditions, prevalent since 1999,
generally result in increases in specific
conductance (http://pubs.usgs.gov/
ds/363/).
Sediment
(sandbars and related physical
habitats). (Goal: Maintain or attain
levels of sediment storage within the
main channel and along shorelines.)
Modest improvement.
Sandbars erode during periods between
high flows. Increases in total sandbar
area and volume are only possible when
high-flow releases follow large tributary
floods that enrich sand supplies in the
main channel (http://pubs.usgs.
gov/fs/2007/3020/).
Aquatic food web
(Goal: Protect or
improve the aquatic food base.)
Potential major increase.
Increases were apparent in Glen Canyon
Dam tailwater reach, but the trend is
unclear along downstream reaches.
Unlikely that quagga mussels (
Dreissena
bugensis
) will become well established
in the mainstem Colorado River below
Lees Ferry or its tributaries
(http://pubs.usgs.gov/of/2007/1085).
Native fish
(humpback chub) (Goal:
Maintain or attain viable populations
of existing native fish.)
Potential minor increase.
The population of adult humpback chub
(
Gila cypha
) decreased between 1989
and 2001; however, adult abundance has
increased more than 50% since 2001
(http://pubs.usgs.gov/of/2009/1075/).
Trout
(Goal: Maintain a naturally
reproducing population of rainbow
trout above the Paria River.)
Increased growth potential,
dependent on stocking.
Rainbow trout (
Oncorhynchus mykiss
)
numbers have decreased in the Lees
Ferry reach until 2008 when increased
recruitment was detected in response to
the March 2008 high-flow experiment.
Riparian vegetation
(Goal: Protect or
improve the biotic riparian and spring
communities.)
Modest increase.
Native and non-native woody vegetation
continues to expand in the river corridor.
Non-native tamarisk (
Tamar ix
ramosissima
) is the dominant species,
making up 24% of vegetation
(http://pubs.usgs.gov/of/2008/1216/).
Kanab ambersnail
(Goal: Maintain or
attain viable populations of Kanab
ambersnail.)
Some incidental take.
Snail habitat increased since 1998 (Chapter
6 at http://www.gcmrc.gov/
products/score/2005/).
(
Continued
)
