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Grand Canyon Monitoring and Research 

Center Water-Quality Program Review

Panelists:

Stephen Hamilton, Professor, Kellogg Biological Station, Michigan State University

Chris Holdren, Environmental Consultant, Littleton, CO.

Edward Stets, Research Ecologist, USGS

Kristin Strock, Assistant Professor, Environmental Science, Dickinson College

Todd Tietjen, Regional Water Quality Manager, Southern Nevada Water Authority

Summary of review panel comments

The panel was impressed with the monitoring program and the dedication of the staff from 

multiple government agencies who have worked together to maintain the program in the 

face of daunting logistical challenges and bare-minimum funding. The long-term data 

record is invaluable for understanding how the linked Lake Powell-Grand Canyon 

Ecosystem functions, how management of the dam may affect ecosystem functions, values 

and services both above and below the dam, and how future changes in climate and runoff 

regimes may impose changes on the ecosystem. 

The justification for the monitoring program, encompassing both the Grand Canyon as well 

as Lake Powell, is clearly articulated in the GCDAMP FY 2017 Knowledge Assessment. The 

major environmental concerns in the Grand Canyon are closely tied to the quality of water 

discharged from the dam, including nutrients as well as temperature and dissolved oxygen

(DO), which in turn reflect limnological conditions in the reservoir. Therefore it is critical to 

understand the Lake Powell ecosystem from the standpoint of maintaining and enhancing 

the Grand Canyon ecosystem as well as protecting environmental values and recreational 

and aesthetic services afforded by the reservoir itself. 

Altered temperature, high salinity and low DO are water quality attributes of particular 

concern, but inorganic phosphorus (measured as soluble reactive phosphorus, SRP) may 

prove to be important as well. There is also increasing concern about high temperature 

fluctuations that can favor non-native fish species. Ongoing study may reveal other 

attributes of concern. The water quality at the penstock depth, and therefore below the 

dam, is determined not only by the rivers that feed Lake Powell but also by a suite of 

incompletely understood, complex drivers including vertical heterogeneity in the water 

column, sediment-water interactions, and planktonic growth in the reservoir. The 

monitoring program also has considerable value for understanding the Lake Powell 

ecosystem in and of itself; this is of interest to the substantial number of boaters and other 

tourists who visit the Glen Canyon National Recreation Area, and to the National Park 

Service who is responsible for stewardship of the lake and its surrounding lands.
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The panel identified areas that are in need of improvement in the Lake Powell monitoring 

program, and a number of these apply as well to monitoring of downstream waters. The 

most important priorities to be addressed can be grouped into these categories:

● Improve data management including metadata.

● Analyze existing data to reveal trends and inform future monitoring

● Increase vertical sampling resolution of the reservoir water column at key sites 

● Use the results of modeling experiments and analysis of previous data to consider 

reducing the spatial extent (number of sites) during quarterly sampling 

● Implement more detailed and formalized sensor calibration and QA/QC of field and 

lab procedures

The four questions posed to the review panel are answered below. We also added a section 

at the end of the report describing recommendations for improved data management, 

which we identified as being a high priority.

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?

The current model, CE-QUAL-W2, seems adequate given its widespread use in reservoirs 

and the heavy investment so far for Lake Powell. The hydrodynamic model seems to be 

working adequately, and we suggest that the greatest improvements to the model will be 

gained from better temperature, meteorological, and bathymetric data. The General Lake 

Model (GLM; see below) is stable and relatively easy to use and could be implemented in 

order to compare its performance alongside CE-QUAL-W2 for Lake Powell. The 

temperature and DO predictions are priorities for improvement, and additional 

temperature data from one or more thermistor strings is recommended because of the 

primacy of temperature and stratification in controlling lake physical and chemical 

properties. Variables such as SRP will require more research before they can be added to 

the model. Finally, while modeling cannot supplant the need for monitoring, it can help 

inform the best use of the limited resources for monitoring. We recommend using CEQUAL-W2 to determine which sampling locations are most critical for model performance 

with the expectation that some of the current 37 quarterly monitoring locations will 

probably be discontinued, leaving fewer stations which can be sampled more intensively.

The current model seems adequate, particularly for hydrodynamics within Lake 

Powell.

CE-QUAL-W2 was developed for large, run-of-the-river reservoirs and has been used on 

those systems for decades. Although it is somewhat cumbersome to use because it is based 
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on Fortran and therefore has very specific requirements for data input, it is also very 

versatile. Small errors in input can create big problems with model output so it is best to 

have someone responsible for the model who is familiar with building and running it. 

One alternative is the GLM model (http://aed.see.uwa.edu.au/research/models/GLM/), 

which has gained wide acceptance because of its versatility, stability, and ease of 

implementation. GLM is a one-dimensional model and so assumptions would need to be 

made about the validity of vertically-averaged model results. Nevertheless, its ease of use 

would make it useful to compare against CE-QUAL-W2 or for exploratory analyses as 

described below.

The current model produces reasonable month-to-month results for predicting 

temperature and salinity. Two factors that can typically improve results for the CE-QUALW2 model are better temperature and meteorological data.

The Lake Powell CE-QUAL-W2 model currently uses meteorological data from the Page, AZ, 

airport. Data from the stations at Hanksville, UT and Bluff, UT were also used in previous 

years, but those stations were discontinued. Placing an additional weather station on a raft 

in Lake Powell could improve modeling results. Meteorological forcing is a primary driver 

of surface temperature and mixing depths, therefore improved meteorological data will 

improve model performance. The proposed meteorologic station should be added at a 

location upstream of the dam to provide the best possible representation of regional 

weather patterns. Bullfrog Marina is recommended because of its distance from the dam 

and because it is a site which should allow for relatively easy maintenance. Because solar 

radiation is not measured at the Page weather station, it should be measured at the new 

site.

The Bureau of Reclamation’s Upper Colorado Regional Office updated Lake Powell 

bathymetry in October 2017 and this data is currently being compiled (personal 

communication, Nick Williams). Improved bathymetry should also further improve the 

accuracy of any modeling efforts.

DO and temperature are priorities for improvement, but improving the predictive 

capability for temperature should also improve results for DO. Better meteorological data 

will improve temperature modeling, as discussed previously. Adding a thermistor string at 

a location upstream of the dam could be used to improve vertical temperature resolution, 

although that also increases the effort required to run the model. A good location for the 

thermistor string would be at Wahweap. That location typically integrates most of the flow 

from farther upstream and additional data at that point could improve predictions for 

water quality leaving the dam. 

Because temperature data are probably the most critical input for the operation of CEQUAL-W2, adding additional thermistor strings at additional upstream locations would 

probably improve modeling results more than adding loggers for DO or other water quality 

variables. Recommended upstream locations would be Bullfrog on the main stem of the 
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lake and Cha Canyon on the San Juan arm. Both of those locations are deep enough to avoid 

undue impacts from suspended sediments. The additional locations may only create 

significant differences in model output during extreme weather events and are not as 

critical as the Wahweap site. 

Another factor that may be adversely affecting current modeling results is high wind 

speeds. The greatest variation between observed and predicted temperatures at the lake 

outlet occurred when wind speeds were greater than 20 m/sec. The potential for adjusting 

model results to account for this observation should be evaluated.

Phosphorus (P) modeling may need to await further information on controls on P 

concentrations in the reservoir; modeling should be a longer term goal. 

While it will take time to incorporate P into Lake Powell modeling efforts, the current 

monitoring program is already collecting much of the data that will be needed to model P 

concentrations (hydrodynamics, nutrients, chlorophyll a, zooplankton, and major algal 

groups). The hypothesized importance of SRP downstream awaits confirmation and may 

influence the effort to be invested in understanding P cycling in the reservoir. Current 

observations suggest that P concentrations are typically low although large overall 

variability has been observed (up to an order of magnitude). Therefore, P modeling can 

wait until after the hydrodynamic modeling is enhanced and the approaches to resolving 

questions of the influence of P on the downstream ecosystem are more formulated more 

completely.

The largest changes in Lake Powell phosphorus levels so far have occurred when flood 

events disturb sediment deltas that are exposed during periods of extended drought and 

lowered water levels. Inclusion of a sediment diagenesis compartment in CE-QUAL-W2 

could potentially be very important in predicting P concentrations at very low lake levels

and how this phosphorus moves through the reservoir. 

GLM may be useful for predicting phosphorus and chlorophyll a concentrations in Lake 

Powell because of its ease of use. It may be advisable to use the GLM model first when P 

modeling is incorporated to evaluate critical factors affecting P levels. That could reduce 

the effort needed to get good nutrient results with CE-QUAL-W2.

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.

Sequentially eliminating stations from model runs and comparing results to runs that 

incorporate all stations should show which stations are the most important. It is likely, 

however, that some of the upstream stations may not be critical when the reservoir is at or 

near full pool but could become increasingly important as water levels drop. Modeling 

cannot supplant the need for field sampling. Although the current sampling program could 

be altered slightly to target specific areas of interest in the future, continued collection of 
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field data is required to understand hydrodynamics and nutrient cycling in Lake Powell 

and should be continued.

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.

In some cases, errors in temperature at the lake outlet are currently larger than desired; 

however, it should be possible to reduce those errors if the above recommendations (i.e., 

adding one or more thermistor strings and an additional weather station at upstream 

locations) are incorporated into the monitoring program.

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?

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.

In the context of the current program review, the analysis of historical records has focused 

largely on phosphorus dynamics in the lake as a potential driver of downstream fish 

productivity. While this is a laudable goal and should be pursued given the current interest 

and need to evaluate drivers of fish productivity, the analysis of historical data, from either 

a historical perspective or at the time of collection, has been a shortcoming of past GCMRC 

activities. While past staff did excellent work to develop and implement a sampling 

program that has provided a wealth of data on Lake Powell, the analysis of these data has 

been minimal at best. The lack of data analysis in the past is a significant driver of the 

management disconnect between the limnology of Lake Powell and its influence on 

downstream conditions. A comprehensive, dedicated analysis of past data is essential for 

rebuilding the link between these systems in the context of the management of this 

regulated river. For example, the reservoir appears to act as a very significant sink for 

phosphorus, an assertion which has been noted here, in the literature, and in discussions 

held during the in-person meeting, but this requires quantification and verification. In 

addition, there is strong support in the literature and in our discussions that organic 
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material transported by the Colorado River through Glen, Marble, and Grand Canyon has 

also been severely reduced. The ramifications of this include both the reduction in organic 

material available to support the food base and a shift toward autochthonous support of 

the food web, which is then more sensitive to changes in phosphorus delivery. Answering 

these and other questions requires dedicated analysis of historical records collected by 

GCMRC, by others, and collected prior to the closing of Glen Canyon Dam. 

While the GCMRC dataset is extensive and has benefitted from consistency of execution in 

the close collaboration of the three partner agencies, it is not the only dataset that should 

be considered in assessing system dynamics. The most recent example of sampling efforts 

that may benefit the understanding of Lake Powell and Colorado River dynamics is the 

work being done to characterize the impact of the Gold King Mine release. While the 

contaminant monitoring will provide information on near and long term health and 

ecosystem impacts, the data should also be considered in the broader context of assessing 

basic ecosystem dynamics. This broader context approach should be expanded to include a 

search for data collected before the impoundment of the reservoir, data collected by other 

agencies (like the Reclamation SLC office) or by other groups within existing agencies. This 

review should include state, tribal and federal agencies, universities, and potentially 

nonprofits or public interest groups that may have focused data collected in the past. Into 

the future there may be value in expanding partnerships that currently exist between 

federal agencies to include university partners or citizen science as sources of focused data. 

These types of partnerships have benefitted efforts in understanding Lake Powell 

(Wildman et al. 2011; Wildman et al. 2017) and the downstream food base (Kennedy et al.

2016) and can have lower costs than more structured long term efforts

Metadata is essential for evaluating data quality, detection limits, analytical methods and 

appropriateness. Analysis of past data can be problematic or ill-advised without this 

information. These problems are particularly vexing for variables like phosphorus in 

systems where concentrations are frequently at or near the limits of detection for even the 

most sensitive methods. The assembly of metadata for all of the data collected in past 

efforts by GCMRC, to the extent possible, should be prioritized. Consistent documentation 

is critical to ensure that future analysis includes the capability to recreate changes in 

analytical methods, detection limits, and sampling techniques and goals. Additionally any 

special conditions (e.g., storm events; algal blooms; flow conditions; etc) that may have 

been observed during the sampling will not be known by those attempting to analyze the 

data in the future. Metadata, particularly for nutrient analyses, chlorophyll concentrations, 

and DO measurements, will be essential if this information is to be included in future 

modeling expansions. For example, knowledge of past phosphorus analytical limitations 

was necessary to modelers developing the Lake Mead 3 Dimensional Water Quality Model 

because updated, lower detection-limit analyses were needed to better predict future 

conditions in Lake Mead.
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Placing past and future data into a curated, publicly available database such as the Water 

Quality Data (WQX) will benefit Colorado River science and management, will make the 

data more broadly available to outside researchers, state, federal, and tribal agencies, and 

will increase the data management requirements and standards. While the broadly defined 

quality of the existing data appears to be high, the collection and incorporation of metadata 

will eventually facilitate its application and use. The benefits of using a system such as 

WQX are: 1) the data infrastructure and public-facing access already exist; and, 2) the 

requirement to adhere to data quality and presentation requirements of an ‘outside‘ 

repository would encourage and require a more proactive approach to data curation. The 

historical Lake Powell data that have been organized into database files in the past have

been integrated into the Lower Colorado River Water Quality Database (LCRWQD) 

maintained by the Southern Nevada Water Authority. While this does encourage the use of 

these data by those who know of its existence, the database does not have the data 

management standards or metadata requirements of databases such as WQX. 

Furthermore, WQX is incorporated into the widely-used Water Quality Portal 

(https://www.waterqualitydata.us/), which is accessible online and through automated 

search routines in the programming language R (https://www.r-project.org/). The 

LCRWQD takes data from outside agencies but does not independently verify, audit, or 

validate the data or require metadata or impose quality standards or evaluation. These 

tasks remain the responsibility of the original agency, and in the case of the Lake Powell 

data the work has largely been restricted to importing the information and gross error 

checking. Incorporation into WQX would bring much higher levels of confidence to the use 

of this data.

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?

The Lake Powell monitoring program was established as part of the Salinity Control Act to 

understand how the lake influences downstream environments with a focus on 

understanding the distribution of salinity (TDS and conductivity), temperature, DO, and 

sediments, and modeling export of water to the river below the dam. The program shifted

in the 1990s to increase spatial coverage of sampling sites and a new focus on nutrients 

and other water quality constituents, but sampling had limited vertical resolution. We 

recommend expanding vertical sampling resolution at sampling sites closest to the dam.

We also suggest options for prioritizing monitoring locations in order to streamline the 

sampling protocol and allow a greater emphasis on vertical sampling resolution. We 

believe this will be beneficial to understanding a number of chemical characteristics of the 

lake, including nutrient dynamics, which may influence downstream fish communities. 
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Other than the Wahweap station, which is sampled at multiple predefined depths during 

quarterly and monthly sampling, other sampling locations are only sampled at 1 m below 

the surface and 1 m above the bottom. Additional samples can be collected throughout the 

water column, but the rules for doing so are not well defined. Profile data and 

presentations shared with the review panel highlight the unique features of Lake Powell, 

including: deep chlorophyll maxima, inflow currents with varying density, and DO minima 

and maxima. Increased vertical resolution in sampling stations near the dam will improve 

the understanding of lake processes that may influence downstream environments. 

Formalizing how these features are monitored will help the monitoring program to 

continue to meet its objectives, as defined in the chemical data summary prepared by 

Vernieu in 2015: “The main objective of the sampling effort was to characterize chemical 

conditions near the surface, near the bottom, and in each major stratum of the water 

column. A secondary objective was to describe unusual phenomena that may occur at 

specific depths such as a metalimnetic DO deficit or an inflow plume flowing into an 

intermediate layer in the reservoir.”

The vertical resolution of sampling should be expanded and formalized. A written protocol 

should be developed and executed which explicitly states when sampling occurs at various 

depths. Currently, additional samples are collected at various depths when stratified 

conditions are observed during quarterly sampling but not during monthly sampling at the 

Wahweap station. It is unclear whether or not there are formal methods or criteria 

outlining when and where this additional sampling occurs (defining what is considered a 

“major stratum” and “unusual phenomena”). It is important to formalize data collection at 

an increased vertical resolution with appropriate scientific justification to ensure these 

data are consistently collected and are useful for discerning long-term trends and the 

effects of sub-surface anomalies on downstream conditions.

As a first step in expanded vertical sampling, the panel suggests sampling at more depths 

based on observed stratification and chemical differentiation (SeaBird profiles) at the 

Wahweap and Crossing of the Fathers stations. Data from these stations can be analyzed 

and may inform expanded vertical sampling at other sites. Ideally, we suggest identifying 

several sampling depths within the epilimnion or euphotic zone and following a specific 

protocol for when and where the samples are collected across all sites. Although the ideal 

representation of surface water chemistry requires collecting an integrated sample from 

the epilimnion or euphotic zone, this is limited from a practical standpoint because the 

euphotic zone can reach 40 m in Lake Powell. Instead, we recommend identifying 

additional sampling depths and developing a formal protocol that defines when these 

samples are collected. 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.
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• 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.

Quarterly sampling of multiple stations in Lake Powell:

As mentioned in section 1 (p. 4), the current quarterly monitoring sites should be evaluated 

in terms of whether they inform the CE-QUAL model. It is possible that some sites could be 

eliminated with little effect on the modeling effort. Deciding which sampling sites to 

maintain should be prioritized based upon whether they are important to model outcomes 

as well as sites with long-term records (pre-1990s) to maintain continuity at high-value 

long-term sites.

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

be incorporated into the routine monitoring program? 

We have a number of specific recommendations about improvements to existing 

observations or additional observations that could be made to further support the goals of 

the monitoring program. Many of the recommendations involve better QA/QC and 

verification of SeaBird data, and these activities should be prioritized because of the central 

role SeaBird data plays in model implementation. We also recommend analyzing historical 

plankton samples and dissolved organic carbon (DOC) data to determine whether sample 

collection is worth continuing. We discuss how additional data from a weather station, 

automated sampling platform, and/or thermistor string would be likely to improve model 

performance and utility, but acknowledge that this expanded data collection would add to 

the expense of sampling and so must be considered carefully. Finally, contaminant 

research does not seem to be a priority for the Lake Powell Monitoring Program and could 

be handled with a lower priority.
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The SeaBird data serve as the backbone of field limnological observations and so we 

recommend prioritizing efforts to ensure that data collection continues and is of the 

highest quality. The SeaBird unit is likely to need replacing soon. It would be wise to 

replace it before it fails and use the current unit as a backup. A primary concern is that the 

annual calibration of the SeaBird does not provide enough temporal resolution to know 

about potential shifts in instrument performance that would affect interpretation of the 

data. We acknowledge that the SeaBird is a complex instrument that is recommended to be 

calibrated only by the manufacturer. However, empirical support from paired samples or a 

paired Sonde, which can be easily calibrated in-house, would allow greater knowledge 

about the rate of drift of the SeaBird and provide independent verification of the data.

Obtaining information from the manufacturer on calibration status when the SeaBird is 

sent in for maintenance but before it is recalbrated would also provide valuable 

information on the rate of drift.

Several measurements collected by the SeaBird should be upgraded or further verified. 

Switching to an optical DO sensor is recommended. The panel acknowledges that the 

response time is longer and varies with temperature and pressure for the optical DO probe. 

However, the Seabird unit should have the instrument lags programmed into data 

interpretation. More importantly, Clarke-type membrane probes are known to be unstable 

and require frequent calibration. The annual calibration by Seabird is not likely to be 

adequate to ensure data quality. The quality of the pH and chlorophyll data are not known 

and so should be treated as estimates only. Recommendations for improving QA/QC of the 

pH and chlorophyll observations are described below.

We recommend the collection of field pH because lab pH measurement occurs after carbon 

dioxide equilibration with the atmosphere and so it may not match the in-situ pH. Consider 

recording field pH at the water sampling depth in addition to lab pH measured much later. 

This can be done in the boat if samples are collected to avoid air equilibration, and 

transferred to the pH electrode using a closed-system method. A recently-calibrated Sonde 

probe or a laboratory-grade pH electrode could be used in the boat. However, we stress 

that the critical piece is the routine calibration of pH because annual calibration is highly 

likely to be inadequate. It is common practice to calibrate pH probes before every field 

sampling trip and to perform daily verification that drift has not occurred. A field pH 

protocol would also provide a means for verifying or correcting the pH data provided by 

the SeaBird.

Unless proven otherwise, SeaBird chlorophyll estimates should be considered approximate 

and not used to replace the “filter-based” lab measurements, nor can they be reliably 

compared with earlier lab measurements. They are critical for relative observations, such 

as identification of a deep chlorophyll maximum or seasonal changes, but the accuracy of 

the absolute concentrations must be verified. Fluorometric measurements of chlorophyll 

with the Welschmeyer non-acidification protocol may be desirable for lab measurements, 

which are subject to their own issues. Earlier practices of working with chlorophyll 

samples in the open sunlight and the current practice of not freezing them in the field raise 

questions about those data. The validity of this method should be tested and documented. 

Tests should be conducted to establish whether these practices affect the measurements 
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and better procedures should be adopted from now on (see below). Conversely, if these 

comparisons have been made, the results should be documented.

Phosphorus measurements could be enhanced by adding a SeaBird HydroCycle-PO4 to 

detect short-term fluctuations. A unit should be obtained on loan and tested against lab 

measurements before considering purchase. The instrument has a relatively high detection 

limit (3 μg l-1) compared to median concentrations in the lake (5 μg l-1) and so its utility 

may be limited in areas other than the inlets where P concentrations are higher. Consider 

total dissolved P (TDP) in addition to Total P to be able to distinguish particulate P, 

dissolved organic P, and acid-extractable P. If after a year of measurements TDP is found to 

be nearly equal to acid-extractable P this could be stopped. However this is unlikely where 

there are significant suspended sediments (i.e., in and near the inflows to the lake).

A thermistor string near the dam boom would be useful for understanding temperature 

and verifying model performance. This recommendation overlaps with recommendations 

made for CE-QUALL W2 modeling improvements (p. 3). The thermistor string could

include DO and conductivity sensors at penstock depth, or better yet a full Sonde, kept in 

place by a subsurface float. A full profiling platform like those in Lake Mead would be ideal. 

A single station at Wahweap would be beneficial and an additional station well upstream 

would be even better to provide advance warning of an DO-depleted plume or unusual 

warming.

Long-term sampling of plankton and DOC should be analyzed and critically evaluated in 

order to decide whether to continue data collection. Plankton data could become 

extremely valuable in light of the Quagga mussel invasion. For example, zebra mussels 

have been implicated in promoting Microcystis in non-eutrophic waters elsewhere. Other 

invasive invertebrate and fish species may change the plankton community in the future. 

The DOC data need to be evaluated. Similar data collection in Lake Mead has not been 

informative.

Sample handling also needs to be improved or demonstrated to be adequate. Nutrient and 

chlorophyll samples should be frozen or at least cooled in the field. Freezers or 

refrigerators for field use on boats are available. Chlorophyll and SRP are especially subject 

to change during storage. Consider using a sample splitter for subsampling, especially 

when suspended sediments or colonial phytoplankton are present. We also stress that if 

any changes are made to protocols, even if they seem to be inconsequential, those changes

should be recorded as metadata that follow the data wherever they end up. Examples 

include sample collection methods, filter type, filtration methods, and sample storage and 

preservation. Furthermore, changes in sampling protocol should be accompanied with a 

period of method comparison in which both methods are used so the comparability 

between the old and updated methods can be evaluated. 

During the face-to-face meeting, several instances of poor replication and possible 

contamination of field samples were given. We strongly recommend formalizing the 

QA/QC procedures in order ensure that the highest quality data are produced. SRP seems 

to show sporadic variation among replicates, suggesting contamination of glassware or 

during sample handling. The source of this potential contamination needs to be 

determined. We recommend testing blank water (i.e. field-preserved DI water) and 
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running 2x reagent blanks in the lab to test the importance of reagents or water as sources

of contamination. Formalizing QA/QC should include duplicates, field blanks, and field 

spikes. Blind standards could be submitted to the lab. Furthermore, inter-laboratory 

comparisons for sample mean and variation between replicates are available for certain 

analyses that are prone to error, such as total P.

Contaminant research does not seem to be a priority for the Lake Powell monitoring 

program. While selenium and mercury have been identified, few options are available for 

management of contaminants within the lake or river system. Trace metals in the anoxic 

plumes may be worth measuring at least synoptically (but see USGS study). The Gold King 

Mine release may be significant but is being handled separately.

5. Recommendations for improving data management and accessibility.

During the face-to-face meeting, the panel noticed that there does not seem to be a central 

repository for data collected as part of the long-term monitoring program. Discussions 

about long-term data resulted in members of the USGS or the Bureau of Reclamation 

learning, on the spot, about methods, what sort of data were available, and the quality of 

some of the data. The panel views improved data management as a primary 

recommendation. The sampling efforts on Lake Powell are unique, high-quality, longterm, and ultimately extremely valuable. The panel worries that without a concerted effort 

to improve data curation, the excellent work done by the group will be lost. Our primary 

recommendation is to use an existing data infrastructure as a repository, a vehicle for 

public access, and motivation to improve data curation, metadata development, and 

documentation. National databases such as the USGS National Water Information System 

(NWIS) or the EPA Water Quality Data (WQX) should be considered. Biological data, such 

as the plankton samples, would be better stored in a database such as BioData.

Proper data management would require dedicated time of a data manager. The first task 

would be to identify where the data are currently located and what curation procedures 

are currently in place. The GCMRC is collaborating with Utah state agencies, so it is 

possible that the data are already being entered into the EPA WQX database. Duplicating 

data would be extremely undesirable, so this step should be taken first. Other steps include 

developing the metadata, identifying all data sources, determining which samples could be 

placed into a database, and documenting the QA/QC procedures. Going through this 

process would be time consuming, but would likely be worth it ultimately. If the NWIS 

system were used, one possibility would be to partner with the USGS Utah or Arizona 

Water Science Center. They have staff who are knowledgeable about NWIS and could be 

contracted to serve as technical assistance in this regard. Either the Utah or Arizona Water 

Science Center would also be the gatekeeper to ultimately decide whether the Lake Powell 

data could be served on NWIS. Whether WQX or NWIS were used, public access to the data 

would be greatly enhanced through web interfaces, the Water Quality Portal, and through 

tools in the R programming language that allow interactive downloads of the data to be 

used by researchers, managers, and the general public.