Grand Canyon Monitoring and Research Center 

Water-Quality Program Review

September 2017

The U.S. Secretary of the Interior established the Glen Canyon Dam Adaptive Management 

Program (GCDAMP) in early 1997 to implement the Grand Canyon Protection Act of 1992

(US Department of the Interior, 1992). The GCDAMP advises the Secretary on the effects of 

Glen Canyon Dam operations and management actions on the values for which Grand 

Canyon National Park and Glen Canyon National Recreation Area were established. 

Programs focus on key resources in and alongside the Colorado River and its tributaries in 

Glen, Marble, and Grand Canyons, Arizona, between the Glen Canyon Dam (GCD) forebay 

and Lake Mead. The Glen Canyon Dam Long-Term Experimental and Management Plan 

(LTEMP) is the most recent adaptive management plan for the Colorado River ecosystem

(U.S. Department of Interior, 2016a). The selected alternative identified in the LTEMP 

Record of Decision (ROD) (U.S. Department of Interior, 2016b) describes various data 

collection, analysis, modeling, and interpretation efforts to be conducted by the U.S. 

Geological Survey’s (USGS) Grand Canyon Monitoring and Research Center (GCMRC). 

The GCMRC is the primary science support agency for the GCDAMP. As the lead science 

provider, the USGS was required to develop a science plan for implementation of the 

LTEMP (Vanderkooi and others, 2017). In accordance with the science plan, the GCMRC 

periodically convenes independent review panels to assess the quality, 

comprehensiveness, and need for various research and monitoring programs. Periodic 

reviews of various areas of GCMRC’s work, including the water-quality program, have been 

conducted in the past. The last water-quality review was completed in 2001. A review of 

the water-quality program was recommended as a work element in the FY 2015-2017 

triennial work plan of the GCMRC and funding for it was provided under the GCDAMP. The 

work proposed herein satisfies this recommended work element.

Ongoing Water-Quality Monitoring Program

Water-quality data have been collected in various areas of Lake Powell and the Colorado 

River by the USGS and the U.S. Bureau of Reclamation (BOR), with assistance from the 

National Park Service (NPS), since 1964. Early analyses of water quality data emphasized 

the role of advective mixing in determining the distribution of solutes within the reservoir 

(Gloss and others, 1980) and the development of oxygen minima in the reservoir 

metalimnion (Johnson and Page, 1981). Since the mid-1990s, the GCMRC and the BOR have 

continued water quality monitoring under a cooperative agreement funded via the Water 

Quality group in the Upper Colorado Regional Office of the BOR. The water-quality 
monitoring program is currently designed to address the status and trends in the quality of 

water in Lake Powell and of water released from the GCD. 

The ongoing Lake Powell water-quality monitoring program consists of monthly surveys of 

the forebay and tailwater (conducted by GCMRC and NPS) and quarterly surveys of the 

entire reservoir, including the Colorado, San Juan, and Escalante arms of the reservoir to 

the inflow areas (conducted by BOR, GCMRC, and NPS). The GCD forebay station is located 

approximately 2.4 km upstream from the dam. Two tailwater sites are located downstream 

from the dam, one immediately downstream and one at Lees Ferry, approximately 25 km 

downstream. Depending on reservoir elevation, 21-37 established sites, including the 

forebay and tailwater stations, are sampled during the quarterly surveys. At each site, 

initial surface observations (for example, bottom depth, Secchi depth, weather 

observations) are recorded, after which a depth profile of temperature, specific 

conductance, dissolved oxygen, pH, redox potential, turbidity, and chlorophyll florescence 

is collected using a Seabird SBE19plusV2. The data are downloaded immediately after 

collection and viewed in the field to determine stratification patterns. At each site, chemical 

samples for major ionic constituents and nutrient concentrations are collected one meter 

below the surface and one meter above the lake bed. Under stratified conditions, samples 

are also collected from above and below the thermocline and additional depths are 

sometimes sampled if other chemically distinct layers are observed. Dissolved organic 

carbon samples are collected at the forebay, tailwater, and tributary inflow sites. Biological 

samples for chlorophyll concentration as well as samples for phytoplankton and 

zooplankton species identification are also collected at selected sites. Samples are filtered 

and preserved in the field for subsequent laboratory analysis.

Analyses for major ion, nutrient, and chlorophyll concentrations are performed by BOR’s

Lower Colorado Regional Laboratory in Boulder City, NV. Phytoplankton and zooplankton 

samples are analyzed under contract by BSA Environmental, Inc. Processing of the Seabird 

profile data is performed in the office after the field survey. All field and analytical data 

have historically been entered into a database (referred to as WQDB) for analysis and longterm storage. Details of the monitoring program, a description of the WQDB database, and 

physicochemical data from 1965-2013 are available in a USGS Data Series report (Vernieu, 

2015).

Water quality monitoring data from Lake Powell have been used to develop a CE-QUAL-W2

model of water column temperature, conductivity, total dissolved solids (TDS), and 

dissolved oxygen (Williams, 2007). This model is run in forecasting mode monthly by the 

BOR and results are reported to the BOR Upper Colorado Region Water Resources group. 

Model results are also shared with the GCDAMP and can be used to inform management 

decisions. The water-quality monitoring program has also supported, to varying degrees, a 

host of work by both GCMRC researchers and independent scientists. Topic areas include, 

but are not limited to; the role of HFEs in altering downstream water quality (Hueftle and 

Stevens, 2001; Vernieu, 2010), the role of storms in changing the clarity of Lake Powell 

outflows (Wildman and Vernieu, 2017), and the potential role of deltaic sediments as a 

source of phosphorus loading to Lake Powell (Wildman and Hering, 2011).
Current work being conducted by GCMRC on Lake Powell water quality focuses on analysis 

of historic data with the eventual goal of constructing a model of outflow soluble reactive 

phosphorus concentrations from the dam. Historical data analysis will ideally inform new

work to identify factors that control phosphorus cycling in Lake Powell such as the role of 

deltaic sediments, inflows, water level, wind regime, and quagga mussel establishment. 

The current interest in Lake Powell phosphorus dynamics is driven largely by evidence that 

soluble reactive phosphorus availability at the GCD outflow controls rates of primary 

production, aquatic insect availability, and native fish condition in the Colorado River 

downstream of the dam (Yackulic, 2017). There is also a growing appreciation for the 

important of interactions between temperature and food availability in ultimately 

determining fish responses (Dodrill and others, 2016). This makes temperature predictions 

from the Lake Powell outflow also relevant to downstream work on fish ecology conducted 

by GCMRC.

Finally, there has been some effort to characterize contaminants in Lake Powell. This work 

has focused on hydrocarbons, mercury, and selenium. A survey of polycyclic aromatic 

hydrocarbons in Lake Powell from 2010-2011 revealed dissolved concentrations of phenol 

>5 μg/L (Schnonauer and others, 2014). Phenol is an EPA primary pollutant but the 

concentrations documented in Lake Powell are still well below aquatic life criteria (600 

μg/L as a 24 hour average) and human health criteria (3.4 mg/L, (U.S. Environmental 

Protection Agency, 1978). Mercury and selenium were also sampled in organic matter, 

invertebrates, and fish in the Colorado River and concentrations of these contaminants 

were found to be relatively high compared to other large rivers (Eagles-Smith and others, 

2014; Walters and others, 2015). These contaminants can be toxic to fish and wildlife, 

appear to biomagnify through the food web, and likely have sources far removed from the 

observed sinks. Utah and Arizona have issued a mercury consumption advisory for Striped

Bass (Morone saxatilis) in Lake Powell downstream of Dangling Rope Marina.

Purpose of Water-Quality Program Review 

The purpose of this water-quality review is to satisfy requirements under the GCDAMP that 

the science work of the GCMRC receive periodic independent review. Some important 

questions that should be addressed by this water-quality review include: 1) what is the 

status of water quality in Lake Powell and the Colorado River downstream of the GCD and 

how does it vary over time, 2) how might water quality in Lake Powell and the Colorado 

River downstream of the GCD change in the future, and 3) how might management of the 

GCD affect water quality in Lake Powell and the Colorado River downstream of the GCD 

both now and in the future. The GCDAMP has historically been focused on these questions 

as they pertain to water in the GCD forebay and outflow from the reservoir. This focus is 

due to the obvious effects that the dam has on tailwater resources. However, the GCDAMP 

is also interested in understanding how management decisions regarding GCD impact 

water quality downstream of the dam. Some management actions that might water quality 

include: seasonal timing of discharge, variation in reservoir storage, and height of water 

withdrawal. These research questions must be balanced by the broader water-quality goals 

of the BOR which include: a mandated biennial progress report on the water quality of the 
Colorado River Basin (via the Colorado River Storage Project Act) and an understanding of 

salinity dynamics in Lake Powell as they relate to the Salinity Control Act. 

In order to satisfy GCDAMP requirements, the panel selected as part of this water-quality 

review is asked to address the 5 questions posed by the GCMRC below. These questions 

address various characteristics of the program including: the spatio-temporal resolution of 

monitoring activities, modeling capabilities, data analysis and experimental research 

priorities, and field sampling methodology. The aim of this review is to provide the GCMRC

with the guidance they need to ensure that the science information produced is of the 

highest quality. The results of the panel and its recommendations will help to inform future 

water-quality work of the GCMRC as it implements the next Triennial Work Plan for fiscal 

years 2018-2020 (US Bureau of Reclamation, 2017).

Key Questions

1. 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?

In the past, the Bureau of Reclamation has employed several models to predict waterquality conditions in the Colorado River system including RiverWareTM for modeling 

salinity and CE-QUAL-W2 for modeling water surface elevations, velocities, temperatures, 

and water quality constituents (US Bureau of Reclamation, 2006; Williams, 2007). These 

models have been very helpful to managers and scientists as they provide water quality

projections and also support visualizations of water quality from the inlet to the outlet of 

the reservoir. For future work, there is general interest in developing a model that can 

predict phosphorus export at the Glen Canyon Dam outlet. A recent water quality 

knowledge assessment for Lake Powell and the Colorado River downstream of the GCD 

highlighted some uncertainty associated with our ability to predict temperature and 

dissolved oxygen at the Lake Powell outflow (Braun, 2017). The CE-QUAL-W2 model 

predicts temperature and dissolved oxygen with a mean accuracy of 0.5oC and 1.15 mg/L 

dissolved oxygen (Williams, 2007), but there is often more error at the height of the 

penstock given that it is frequently located within the reservoir metalimnion. For example, 

we sometimes observe differences between predicted and observed values that exceed 3 

mg/L dissolved oxygen and 2 oC. We are interested in obtaining guidance concerning the 

best modeling approaches moving forward. Specifically, this over-arching question 

includes the following additional questions:

a. Should phosphorus dynamics be modeled via CE-QUAL-W2, or some 

other modeling platform? The open source General Lake Model

(http://aed.see.uwa.edu.au/research/models/GLM/), for example, could 

be coupled with the Framework for Aquatic Biogeochemical Models

(Bruggeman and Bolding, 2014) to simulate P dynamics, but such a model

would require more vertically resolved data. We would like guidance
regarding the most appropriate modeling platforms to: 1) predict 

phosphorus concentrations at the Lake Powell outflow, and 2) better 

identify the mechanisms that control or influence phosphorus

concentrations.

b. Do we have sufficient data to create mechanistic models for water quality 

parameters in Lake Powell? If not, what additional data should be 

collected?

c. Should a model be developed that would link temperature between the 

lake and the river? This type of predictive capability would be especially 

important if temperature control methods are employed in the dam 

intakes as is recommended under the LTEMP ROD.

d. CE-QUAL-W2 provides an excellent modeling platform for predicting 

whole-lake temperature and dissolved oxygen profiles, especially given 

the advection-based hydrodynamics in Lake Powell. However, is this 

model the best choice for estimating temperature and dissolved oxygen at 

a single point such as the dam outflow? More specifically, is the degree of 

accuracy of CE-QUAL-W2 in predicting outflow temperature and 

dissolved oxygen comparable to that attainable via other modeling 

approaches?

2. 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?

While both nitrogen (N) and phosphorus (P) are known to be important limiting nutrients 

in freshwater ecosystems, exceptionally high N:P ratios in the Colorado River ecosystem 

suggest that P is the most limiting in this system. Soluble reactive phosphorus (SRP), the 

most bioavailable phosphorus, is an important driver of whole-ecosystem dynamics. 

Preliminary data suggest that declines in SRP availability at the outflow from Glen Canyon 

Dam over the last five years have propagated through the entire aquatic food web. This 

decline in SRP has constraining rates of primary production, invertebrate production, and 

ultimately suppressing the recruitment of rainbow trout (Oncorhynchus mykiss) at Lees 

Ferry and the condition of adult humpback chub (Gila cypha) near the Little Colorado River 

(LCR) confluence (Yackulic, 2017). In addition, rainbow trout recruitment since 2001 

(when the detection limit for monitoring SRP was lowered to allow for tracking of trends) 

can be better explained statistically by models that include SRP concentration than by 

models that include flow variables alone. An improved understanding of phosphorus 

dynamics in Lake Powell could inform conditions under which higher concentrations of 

SRP are exported from the reservoir.

Reservoirs behind dams are often sinks for biologically relevant nutrients like nitrogen and 

silica (Harrison and others, 2012; Harrison and others, 2009). With respect to 
phosphorous, individual reservoirs can either be sinks or sources of phosphorus depending 

on their individual characteristics (Powers and others, 2015); however, they often retain 

phosphorus and contribute to significant reductions in the downstream transport of 

phosphorus at the global scale (Maavara and others, 2015). Available evidence suggests 

Lake Powell is functioning as a net phosphorous sink given higher concentrations of 

phosphorous in the reservoir inflows than in the outflow. In particular, Lake Powell 

outflows often have very low concentrations of SRP that also vary substantially through 

time. The recent water-quality knowledge assessment highlighted the importance of an 

enhanced understanding of the mechanisms that control or influence nutrient 

concentrations in Lake Powell.

Given the large volume of historical nutrient data available for Lake Powell, the river outlet 

works, and Lees Ferry, and given that there has been relatively little analysis of that data, 

GCMRC plans to spend time assessing spatial and temporal trends in nutrient 

concentrations and potential environmental drivers of nutrient availability. We then plan 

to follow up with targeted experimental work as informed by this historical data analysis. 

Below we have summarized some ideas pertaining to analysis and experimental work.

The Colorado and San Juan Rivers deliver large amounts of total phosphorous to Lake 

Powell; however, much of this phosphorous is bound to fine sediments and is deposited in 

the deltaic sediments. As the elevation of Lake Powell drops, these deltaic sediments can 

become repeatedly exposed and re-inundated. It has been hypothesized that inundation of 

these sediments may lead to surges of SRP flowing out of the deltas into Lake Powell 

(Wildman and Hering, 2011). In many systems, P release during re-inundation is driven by 

shifting redox conditions, wherein iron-bound P is released as water becomes anoxic 

(Boström and others, 1988; Kinsman-Costello and others, 2014). In Lake Powell, this 

mechanism is not likely to be very important since iron-bound P makes up only a very 

small fraction of the total P in deltaic sediments (Wildman and Hering, 2011). Instead, the 

mineralization of organic P under dry conditions (when sediments are more aerobic) may 

produce a sizeable, loosely bound, and easily exchangeable SRP pool that can be mobilized 

into the water column upon re-inundation. In fact, previous characterization of sediment P 

fractions in Lake Powell’s sediment delta show that a sizeable fraction of P is bound to 

organic material (Wildman and Hering, 2011). P mobilized from deltaic sediments is most 

likely to be transported towards the dam in spring when there is less biological uptake of 

SRP within the reservoir and inflow waters tend to flow under the Lake Powell epilimnion. 

This hypothesis suggests that the interaction of season, low lake elevation, and high inflows 

should lead to increased SRP in metalimnion and hypolimnion waters, leading to increased 

SRP discharge at Glen Canyon Dam. However, an alternative hypothesis is that high inflow 

nutrient loading itself may bring high concentrations of SRP into Lake Powell. 

Distinguishing between the potential sources of SRP is important for predicting how 

climate, water policy, or both may affect overall phosphorous cycles in Lake Powell.
To understand the fate of nutrient loading to Lake Powell’s inlets, GCMRC is currently using 

the USGS program LOADEST in combination with historic discharge and nutrient 

concentrations (records generally exist from 1990-2000) from the NWIS stations: Green 

River at Green River, Colorado River near Cisco Utah, and San Juan River at Bluff. Modeled 

riverine nutrient loading for this decade will be compared to nutrient measurements in the 

Lake Powell dataset to look for an advective signal of riverine nutrient loading and to 

create a reservoir-wide phosphorus budget. Given the capacity for co-precipitation of 

phosphorus with calcite in other lake ecosystems (Hamilton and others, 2009) and given 

that the geochemistry of Lake Powell appears to favor calcite formation (Reynolds and 

Johnson, 1974), GCMRC plans to use the long term dataset to look for relationships 

between phosphorus concentrations and factors that control, or are influenced by, calcite

deposition including: chlorophyll a, pH, bicarbonate [HCO3-

], conductivity, alkalinity, 

turbidity, and secchi depth. Finally, we will look for spikes in Lake Powell phosphorus 

concentrations during years where a high inflow event follows particularly low water level 

conditions. After mining the historical database, targeted field incubations could be 

conducted to better understand within-lake phosphorus cycling.

In addition to exploring in-reservoir drivers of phosphorus cycling, the potential for 

experimental flows, as recommended by the GCDAMP, to modify downstream nutrient 

regimes will further be examined by conducting targeted nutrient sampling before, during,

and after experimental flows. Previous sampling efforts have documented the capacity for 

changes in flow at GCD outlets to affect the chemistry of water below the dam. For example, 

work by Hueftle and Stevens showed that the 1996 spring high flow event diminished 

bottom water hypoxia in Lake Powell as far as 100 km uplake while also resulting in high 

salinity, high oxygen concentrations, and damped dissolved oxygen (DO) and pH 

fluctuations in the dam tailwater (Hueftle and Stevens, 2001). Nutrient data collected 4 

days before and 2 days after the high flow event showed drops in phosphorus 

concentration at both the penstock and river outlet works, although the magnitude of this 

drop is difficult to determine given the detection limit of the analyses used at that time. 

Monitoring during the 2008 high flow experiment also showed elevated DO concentrations 

downstream of the dam (at maximum 120% of saturation), but relatively minimal effects 

on the structure of the water column upstream of the dam (Vernieu, 2010).

3. 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?

With respect to nutrients, the current monitoring program places more emphasis on 

horizontal spatial resolution (e.g. >10 sites sampled for nutrients and ions) than on vertical 
resolution. For example, nutrients are collected only from the surface and bottom DEPTHS 

with an additional sample or two collected mid-water column during stratified conditions. 

Will the current vertical data resolution allow us to effectively model SRP concentrations at 

the Lake Powell outflow? In addition, is the current laboratory reporting level of SRP 

sufficiently low to detect changes associated with changes in the management of GCD?

4. Are there additional types of measurements or newer methodologies that should 

be incorporated into the routine monitoring program? 

The current water quality monitoring program conducts a series of 21-37 profiles 

quarterly using a Seabird Electronics SBE19plus-V2 equipped with sensors for 

temperature, pressure, conductivity, pH, oxidation reduction potential, DO (SBE 43 

membrane-type sensor), chlorophyll a (WET Labs Fluorometer ECO-AFL/FL), and turbidity 

(WET labs ECO-NTU). At a subset of these sites, filtered and unfiltered water samples are 

collected and preserved for analysis of a suite of nutrients and major ions (TSS, TDS, Ca, Mg, 

Na, K, CO32-

, HCO3-, Cl-, SO42-, SiO2, CaCO3, TP, SRP, NH3, NO3-+NO2-, and TKN ). Dissolved 

organic carbon samples are collected at the forebay, tailwater, and tributary inflow sites. 

Samples for analysis of dissolved metals are collected at least once yearly (usually in the 

summer) from the major inflows, confluences, sites where previous anomalies have been 

noted, and from near the outflow. With the exception of the inflow sites (which are sampled 

1m below the surface) metal samples are collected from one meter off the bottom of the 

lake bed. Net tows and surface water sampling at these sites support analysis of 

phytoplankton and zooplankton assemblage and abundance as well as filter-based 

quantification of surface water chlorophyll a concentrations. Currently, the most utilized 

measurements in this dataset are those that the CE-QUAL-W2 model requires including; 

temperature, salinity, DO, TDS, and phytoplankton. Dissolved solute data, however, could 

support hydrodynamic and geochemical models that would likely improve our 

understanding of nutrient cycling in the system. 

The quarterly sampling effort consumes a significant amount of time (5+ days) and 

resources and thus the relative cost/benefit of additional measurements should be 

considered. In addition to the whole-reservoir quarterly sampling, more targeted monthly 

sampling at the dam forebay, penstocks, and below the dam is also conducted. Below, we 

list some additional methodological questions for the panel to consider:

a. Should we switch the current membrane-type DO sensor for an optical DO 

sensor? Currently the SeaBird is only calibrated once a year, so an optical DO 

sensor may provide for more stable calibration. 

b. With the recent interest in reservoir phosphorus cycling (as well as nutrient 

availability more broadly), should grab nutrient sampling be supplemented 

and/or modified in any way? In particular, would the use of a HydroCyclePO4 (http://wetlabs.com/hydrocycle) wet chemistry phosphate sensor (2.3 

ug P/L detection limit) be feasible and informative towards efforts to model 
P availability in reservoir outflows? Also, should we add total dissolved 

phosphorus to the current suite of analyses conducted?

c. The BOR installed a thermistor string at the GCD forebay in 2012, but the 

string was lost in 2016 and has not yet been replaced. Could the installation 

of thermistor and conductivity loggers help inform Lake Powell modeling 

efforts? If so, at how many sites and depths should these be deployed?

d. Are continued filter-based measurements of chlorophyll a concentrations 

necessary or are they redundant with newer probe-based estimates of 

chlorophyll a concentrations?

e. Should the program consider periodic collection of data on any additional 

contaminants in water from sites above and below the Glen Canyon Dam? If 

so, which contaminants would be most relevant to examine? 

f. The analysis of plankton data has been extremely limited up to this point. 

The 2001 PEP recommended that plankton sampling be limited to quarterly 

samples at Wahweap, a mid-lake site, and an up-lake site (Jones and others, 

2001), but this sampling reduction was not incorporated. Should the 

program consider cutting the amount of plankton sampling? Or is the current 

quagga mussel invasion grounds to continue with the current sampling 

regime?

g. Are DOC samples giving us valuable data? Should this sampling be expanded 

or discontinued? Similarly, should we explore the utility of adding a CDOM 

(colored dissolved organic matter) sensor to the SeaBird?

h. Currently there is no detailed protocol for QA/QC. Typically one QA/QC 

sample is collected for every 20 field samples which includes a duplicate of 

the field sample and a trip blank, field blank, or equipment blank. Reagent 

spikes have also been created in the past. Are these current QA/QC practices 

adequate?

i. The previous water-quality review panel recommended a weather station be 

setup from a dock at the Wahweap site and suggested that ancillary wind 

speed and direction data be collected from the roofs of the floating restrooms 

spread throughout Lake Powell (Jones et al. 2001). This recommendation 

was not followed, so we do not have a good understanding of how 

representative the weather station at the Page airport is for over-lake 

conditions. Should we consider installing a weather station?

j. The previous water-quality review panel suggested that nutrient data should 

be collected at the gaging stations for Lake Powell’s primary inflows (on the 

San Juan, Green, and Colorado Rivers). This would provide a stationary 

inflow site given that the inflow sites within the reservoir move each trip (as 

they are dependent on water levels). Should we consider adding this 

sampling?
Suggested Priority Reading List

Braun, D.P., 2017, GCDAMP FY 2017 Knowledge Assessment--final report from the executive coordinator for the 

Science Advisors Program: Glen Canyon Dam Adaptive Management Program (GCDAMP), Science 

Advisors Program, Technical Work Group (TWG): 36 p., 

http://gcdamp.com/images_gcdamp_com/2/26/GCDAMP_FY_2017_Knowledge_AssessmentScience_Advisor_Program_Final_Report_2017-04-30.pdf

Gloss, S.P., Mayer, L.M., and Kidd, D.E., 1980, Advective control of nutrient dynamics in the epilimnion of a large 

reservoir: The American Society of Limnology and Oceanography, v. 25, no. 2, p. 219-28.

US Bureau of Reclamation, Glen Canyon dam Adaptive Management Program Triennial Budget and Work Plan –

Fiscal Years 2018-2020, accessed on September 15, 2017 at URL 

https://www.usbr.gov/uc/rm/amp/amwg/mtgs/17sep20/TWP.pdf

Vernieu, W.S., Hueftle, S.J., and Gloss, S.P., 2005, Water quality in Lake Powell and the Colorado River, in Gloss, 

S.P., Lovich, J.E., and Melis, T.S. eds., The state of the Colorado River ecosystem in Grand Canyon: U.S. 

Geological Survey Circular 1282, 69-85 p., http://pubs.usgs.gov/circ/1282/

Vernieu, W.S., 2015, Historical physical and chemical data for water in Lake Powell and from Glen Canyon Dam 

releases, Utah-Arizona, 1964-2013: U.S. Geological Survey Data Series 471, 23 p., 

http://dx.doi.org/10.3133/ds471

Williams, N.T., 2007, Modeling dissolved oxygen in Lake Powell using CE-QUAL-W2: Provo, Utah, Brigham Young 

University, M.S. in Science, 120 p. p., https://deercreek.groups.et.byu.net/Papers/Models/W2-

MODEL/DO_ModelingPowell_WilliamsThesis.pdf

Expanded Reading List

Hueftle, S.J., and Stevens, L.E., 2001, Experimental flood effects on the limnology of Lake Powell reservoir, 

southwestern USA: Ecological Applications, v. 11, no. 3, p. 644-656, 

http://www.jstor.org/stable/pdfplus/3061107.pdf

Johnson, N.M., and Page, F.W., 1981, Oxygen depleted waters: origin and distribution in Lake Powell, Utah-Arizona: 

Proceedings of teh Symposium on Surface Water Impoundments, p. 1631-1637.

Jones, J., Kennedy, R.H., Nestler, J., Robertson, D., Ruane, R.J., and Schladow, S.G., 2001, Final report of the 

Protocol Evaluation Panel (PEP) for the Grand Canyon Monitoring and Research Center Integrated Water 

Quality Program (IWQP): Flagstaff, Ariz., 39 p. plus appendices, available at 

http://www.usbr.gov/uc/rm/amp/twg/mtgs/09mar16/Attach_11.pdf.

Vernieu, W., 2015, Biological data for water in Lake Powell and from Glen Canyon Dam Releases, Utah and Arizona, 

1990-2009, U.S. Geological Survey Data Series 959: 12 p. p., http://dx.doi.org/10.3133/ds959

Walters, D.M., Rosi-Marshall, E., Kennedy, T.A., Cross, W.F., and Baxter, C.V., 2015, Mercury and selenium 

accumulation in the Colorado River food web, Grand Canyon, USA: Environmental Toxicology and 

Chemistry, v. 34, no. 10, doi: 10.1002/etc.3077, p. 2385-2394, http://dx.doi.org/10.1002/etc.3077

Wildman, R.A., Jr., and Hering, J.G., 2011, Potential for release of sediment phosphorus to Lake Powell (Utah and 

Arizona) due to sediment resuspension during low water level: Lake and Reservoir Management, v. 27, no. 

4, p. 365-375.

References Cited

Boström, B., Andersen, J.M., Fleischer, S., and Jansson, M., 1988, Exchange of phosphorus across the sedimentwater interface: Hydrobiologia, v. 170, no. 1, doi: 10.1007/bf00024907, p. 229-244, 

http://dx.doi.org/10.1007/BF00024907
Braun, D.P., 2017, GCDAMP FY 2017 Knowledge Assessment--final report from the executive coordinator for the 

Science Advisors Program: Glen Canyon Dam Adaptive Management Program (GCDAMP), Science 

Advisors Program, Technical Work Group (TWG): 31 p., 

http://gcdamp.com/index.php?title=2017_Knowledge_Assessment

Bruggeman, J., and Bolding, K., 2014, A general framework for aquatic biogeochemical models: Environmental 

Modelling & Software, v. 61, doi: http://dx.doi.org/10.1016/j.envsoft.2014.04.002, p. 249-265, 

http://www.sciencedirect.com/science/article/pii/S1364815214001066

Dodrill, M.J., Yackulic, C.B., Kennedy, T.A., and Hayes, J.W., 2016, Prey size and availability limits maximum size of 

rainbow trout in a large tailwater--Insights from a drift-foraging bioenergetics model: Canadian Journal of 

Fisheries and Aquatic Sciences, v. 73, no. 5, p. 759-772, http://dx.doi.org/10.1139/cjfas-2015-0268

Eagles-Smith, C.A., Willacker, J.J., and Flanagan Pritz, C.M., 2014, Mercury in fishes from 21 National Parks in the 

Western United States-- Inter- and Intra-Park Variation in Concentrations and Ecological Risk, U.S. 

Geological Survey Open-File Report 2014-1051: https://pubs.usgs.gov/of/2014/1051/pdf/ofr2014-1051.pdf

Gloss, S.P., Mayer, L.M., and Kidd, D.E., 1980, Advective control of nutrient dynamics in the epilimnion of a large 

reservoir: The American Society of Limnology and Oceanography, v. 25, no. 2, p. 219-28.

Hamilton, S.K., Bruesewitz, D.A., Horst, G.P., Weed, D.B., and Sarnelle, O., 2009, Biogenic calcite–phosphorus 

precipitation as a negative feedback to lake eutrophication: Canadian Journal of Fisheries and Aquatic 

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