Modeling Temperature Regime and Physical Habitat Impacts from Restored Streamflow.

Area of Science:

• Ecology
• Hydrology
• Conservation Biology

Background:

• Bright Angel Creek in Grand Canyon National Park (GRCA) supports endangered humpback chub (Gila cypha) and invasive brown trout (Salmo trutta).
• Water infrastructure updates present an opportunity to increase baseflow by ~20% in Bright Angel Creek.

Purpose of the Study:

• To assess the impact of increased water flow on habitat availability and species' suitability for humpback chub and brown trout.
• To model changes in stream temperature and habitat under restored flow conditions.

Main Methods:

• Physical habitat modeling using the System for Environmental Flow Analysis to quantify habitat area changes.
• Statistical analysis of stream temperature data, including regression modeling relating air and stream temperatures.
• Modeling future stream temperatures based on increased discharge during water system maintenance.

Main Results:

• Increased flow slightly enhanced juvenile habitat for both species but reduced spawning habitat for brown trout.
• Stream temperatures were moderated, leading to fewer extreme high and low temperatures.
• Humpback chub experienced more suitable growth days but fewer suitable spawning days; brown trout showed varied suitability changes.

Conclusions:

• Restored flow may improve juvenile humpback chub rearing conditions in Bright Angel Creek.
• The presence of invasive brown trout complicates the net conservation benefit of increased flow.
• Bright Angel Creek's temperature regime, even with increased flow, remains less favorable year-round compared to other humpback chub habitats.