Questions
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How does our ability to model dissolved oxygen, temperature, nutrients, and conductivity in both Lake Powell and in its outflow compare to predictive capability in other systems using the same or different modeling approaches? What, if any, improvements can we make on our current modeling techniques?
- The current model seems adequate, particularly for hydrodynamics within Lake Powell.
- Phosphorus (P) modeling may need to await further information on controls on P concentrations in the reservoir; modeling should be a longer term goal.
- The current model could inform which Lake Powell sampling stations are critical to water quality prediction at the dam intake and in the main body of the lake.
- Linking the lake temperature predictions to downstream water temperatures immediately below the dam and in the downstream river reaches should already be possible with current information and models.
How should analysis of the historical dataset be prioritized to improve our understanding of how management actions and natural mechanisms affect phosphorus dynamics in Lake Powell?
- Analysis of historical records is important not only to show past trends but also to determine whether measurements should continue in future.
- There may be undiscovered data of value, for example from the Bureau of Reclamation’s Boulder City lab.
- Metadata records need improvement for P (and other measurements). Changes in methods including detection limits present a challenge to interpretation of the data.
- Ultimately, placing past and future data into USGS National Water Information System (NWIS) would be a good goal.
Is current monitoring being conducted at an appropriate number of depths and/or sites and at an appropriate temporal frequency to give accurate information on the current status and trends of water-quality conditions and to inform predictions using either the current modeling approach or a potentially improved model?
The recommended changes to the discrete sampling depths are:
- The deep chlorophyll maximum (DCM) when it exists. Included within this recommendation is a formal definition of a DCM. Our suggestion is to define a DCM as a layer which has a chlorophyll concentration > 2 x the surface concentration, based on the SeaBird chlorophyll profile.
- Any apparent interflow layer. The SeaBird conductance profile could be used to objectively define the interflow layer. For example, a > 100 µS cm-1 change in mid water column could be used as the threshold to indicate a chemically distinct interflow layer.
- The current routine includes sample collection at 1 m above the bottom. This collection method risks disturbing the sediments and contaminating the sample. We recommend collecting deep water from the middle of the hypolimnion, as defined by the SeaBird profile. A trial using paired samples from 1 m above the bottom and the middle of the
hypolimnion could be conducted and if the samples compare well, the deeper samples should be discontinued.
- In addition, we recommend that the current sampling scheme at 1 m below the surface, a deep water sample, and at the penstock depth for the forebay site, should be maintained for long-term continuity. Therefore, the recommendations would result in an increase in the number of samples collected at each monitoring location.
Are there additional types of measurements or newer methodologies that should be incorporated into the routine monitoring program?
Recommendations for improving data management and accessibility.
The panel views improved data management as a primary recommendation. [1]
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Agenda and Prospectus
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Links and Information
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Reading List
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Adaptive Management
Calcite Coprecipitation
CE-QUAL Modeling
Contaminants
- Hart et al. 2005. Physical and chemical characteristics of Knowles, Forgotten, and Moqui Canyons, and effects of recreational use on water quality, Lake Powell, Arizona and Utah: U.S. Geological Survey Scientific Investigations Report 2004–5120, 43 p.
- Schonauer. 2014. The presence and distribution of polycyclic aromatic hydrocarbons and inorganic elements in water and lakebed materials and the potential for bioconcentration in biota at established sampling sites on Lake Powell, Utah and Arizona: U.S. Geological Survey Open-File Report 2013–1299, 28 p.
- Waddell and Wiens. 1993. Reconnaissance study of trace elements in water, sediment, and biota of Lake Powell.
- Walters. 2015. Mercury and selenium accumulation in the Colorado River food web, Grand Canyon, USA. Environmental Toxicology and Chemistry, Vol. 34, No. 10, pp. 2385–2394, 2015
General Lake Powell Limnology
- Gloss. 1980. Advective control of nutrient dynamics in the epilimnion of a large reservoir. Limnol. Oceanogr., 25(2), 1980, 219-228
- Johnson and Page. 1981. Oxygen depleted waters: Origin and distribution in Lake Powell, Utah - Arizona. Proceedings of the Symposium on surface water impediments. American Society of Civil Engineers, NY.
- Johnson and Merritt. 1979. Convective and Advective Circulation of Lake Powell, Utah-Arizona, During 1972-1975. Water Resources Research. 15:4
- Stanford and Ward. 1990. Limnology of Lake Powell and the Chemistry of the Colorado River. Colorado River Ecology and Dam Management: Proceedings of a Symposium May 24-25, 1990 Santa Fe, New Mexico. Chap 5.
- Wildman and Vernieu. 2017. Turbid releases from Glen Canyon Dam, Arizona, following rainfall-runoff events of September 2013, Lake and Reservoir Management
Long-term Water Quality Trends
P Biogeochemistry
USGS Data Series, Circulars, and other Reports
Water Quality and Glen Canyon Dam Management
Water Quality and Metabolism in the Colorado River below Glen Canyon Dam
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Other Stuff
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