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In the spring of 1996, a nine-day test flood from Glen Canyon Dam involved the deepest and largest hypolimnetic withdrawals from the penstocks and the river outlet works (ROW) since 1986, interacting with ongoing hydrodynamic and stratification patterns to enhance freshening of the hypolimnion of Lake Powell reservoir and its tailwaters. Prior to the test flood, a six-year drought had produced a pronounced meromictic hypolimnion that was weakening from high inflow events in 1993 and 1995. Hypoxia, however, had continued to increase in the deepest portions of the reservoir. Over the course of the test flood, 0.893 km3 were released from the ports located at and below the hypolimnetic chemocline. The increased discharge...
Blackbrush is a dominant shrub species in the transition zone between North American warm and cold deserts. Its seeds are dormant at dispersal and lose dormancy in response to moist chilling. Seeds from warmer low-elevation habitats have shorter chilling requirements and a higher optimum chilling temperature than those from colder habitats where winter snow regularly occurs. This ecotypic variation functions to time germination optimally in habitats with contrasting chilling regimes. Regulation of germination phenology is an important feature of the life history of this ecotonal species, which must be able to migrate elevationally through recruitment from seed in response to long-term climatic shifts in order to...
Streamflow prediction in ungauged basins provides essential information for water resources planning and management and ecohydrological studies yet remains a fundamental challenge to the hydrological sciences. A methodology is presented for stratifying streamflow regimes of gauged locations, classifying the regimes of ungauged streams, and developing models for predicting a suite of ecologically pertinent streamflow metrics for these streams. Eighty-four streamflow metrics characterizing various flow regime attributes were computed along with physical and climatic drainage basin characteristics for 150 streams with little or no streamflow modification in Colorado, Washington, and Oregon. The diverse hydroclimatology...
The hydrography of the shallow (<30 m) Upper Gulf of California was mapped during a rare Colorado River fresh water discharge, which occurred during March and April, 1993. This provided (a) an opportunity to observe what may have been the hydrographic conditions before the damming of the river, and (b) a data base that can be used to calibrate numerical models with a view to simulating those conditions for ecological applications. In opposition to the now normal inverse estuarine situation, salinity and density decreased toward the head. Dilution was detectable in a coastal band flowing to the right-hand side of the river discharge, up to some 70 km from the river mouth. Tidal mixing maintained vertical homogeneity...