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Lake Mead Science Symposium Concurrent Sessions
LIMNOLOGY AND WATER QUALITY
Session Chairs:
Todd Tietjen and Mike Lico
Tuesday, January 13, 2009 * 1:15 pm to 5:00 pm * Room 2081:20 – 2:40 pm
What Are We Discharging?
Schiefer, Scott H., City of Las VegasSince 1979, the Nevada Division of Environmental Protection has required the wastewater treatment agencies in the Las Vegas Valley to monitor the ambient water quality of the Las Vegas Wash and Lake Mead. In the early days, the dischargers contracted with UNLV to perform the monitoring. In 1991, the dischargers began performing the monitoring themselves. Currently, the monitoring is handled under a cooperative agreement between the City of Las Vegas (CLV), the Clark County Water Reclamation District (CCWRD), and the City of Henderson (CoH). The CLV collects samples and performs field measurements at the Lake, the CCWRD analyzes the samples from the Lake, and the CoH performs all aspects of monitoring the Wash.
The sampling program has changed over the years due to different demands, emerging issues and the lowering lake levels. Recently, to prepare for the Systems Conveyance and Operations Program (SCOP), a pipeline that will take most of the wastewater treatment plant effluent out of the Wash and discharge it deep in Boulder Basin through diffusers near the Boulder Islands, the extent of the monitoring of the Lake has nearly doubled. The purpose for the increased monitoring is to establish background conditions in the Lake, especially around the mixing zone established for the diffusers.
The data that has been collected over the years includes secchi depth, temperature, conductivity, pH, dissolved oxygen, light extinction, zooplankton, phosphorus, total suspended solids, total dissolved solids, ammonia, nitrate, nitrite, coliforms, chlorophyll-a, color.
1:45 – 2:05 pm
The U.S. Geological Survey’s Lake Mead Monitoring Network
Veley, Ronald J.; Fisher, Lawrence H.; and Wiersma, Danelle M., U.S. Geological SurveyStudies are currently underway to determine temporal changes and spatial distributions of natural and anthropogenic chemical compounds in Lake Mead. Water-quality monitoring networks at Lake Mead have been established by several federal, state, and local entities. These networks have focused on common constituents such as major ions, trace metals, nutrients, and selected anthropogenic compounds such as perchlorate. Recently, reservoir models have been developed to gain a better understanding of circulation patterns (hydrodynamics) and associated transport of chemicals in the lake. Moreover, data-collection networks and models for Lake Mead have provided an understanding of areas where baseline data are sparse or areas where additional data on chemical or physical parameters are needed.
To assist with these efforts to better understand the lake’s dynamics, the U.S. Geological Survey (USGS), in cooperation with the National Park Service, Southern Nevada Water Authority, and Clark County Water Reclamation, collects water-quality, water-velocity, and meteorological data as part of its Lake Mead Monitoring Network.
The USGS maintains five platforms on the lake at: Las Vegas Bay, near Sentinel Island, Virgin Basin, Temple Basin, and Overton Arm. At each platform, depth dependent measurements of specific conductance, pH, water temperature, dissolved oxygen, turbidity, and percent fluorescence are collected every six hours. The provisional near-real-time water-quality data are placed online at: http://nevada.usgs.gov/lmqw/index.htm. Quality assured water-quality data for the platforms can also be accessed at this website. In addition, water-velocity and meteorological data are collected hourly at each platform.
2:10 – 2:30 pm
Evaluation of Water Quality Monitoring Instruments with Cooperative Interagency Sampling Events in Lake Mead
Turkett, Warren B., Southern Nevada Water AuthorityEvery year government agencies spend a considerable amount of funds on monitoring programs to determine water quality parameters. In Lake Mead there are at least 8 agencies collecting data with portable water quality instruments. The data collected are used to make important decisions for lake managers, so it is important the data is comparable between agencies. After our first coordinated sampling event on February 13, 2007 the results showed significantly different data between agencies. Two sources of error that were identified were differences between instruments and differences created by operator error. Two additional sampling events were scheduled to further investigate the source of variability. During the investigation we examined the most commonly used multi-probe instruments for water quality monitoring manufactured by Eureka, Hydrolab, and YSI. We examined water column profiles for pH, conductivity, temperature, and dissolved oxygen between the instruments over 3 coordinated sampling events. The results will be presented along with an assessment of some of the most common factors that contribute to variable data. Calibration protocol, maintenance schedules, and operator error will be discussed to help achieve greater data consistency between agencies.
2:35 – 2:55 pm
Long Term Patterns in the Diversity and Composition of Phytoplankton in Las Vegas Bay, Lake Mead
Tietjen, Todd, Southern Nevada Water AuthorityThe Southern Nevada Water Authority has collected integrated, near surface phytoplankton samples from sites along a transect from the confluence with the Las Vegas Wash out into the open waters of Lake Mead since May of 2000. These samples have been analyzed in order to determine the species composition and biovolume of phytoplankton as part of routine monitoring in order to document the occurrence of taste and odor causing algae, to identify the dominant species during periods with algal blooms, and to maintain a record of the species that are present. In this presentation evidence of changes in species diversity that have occurred over this time period will be presented in addition to changes that are observed along the longitudinal gradient from the Las Vegas Wash out into the open water. Additionally these changes will be related to other ecosystem parameters that have been measured simultaneously. While specific events like the Pyramichlamys bloom that occurred in 2001 capture the attention of the public, long term trends can be more informative about changes that are occurring in Las Vegas Bay overall. As the lake enters a period with multiple stressors: continued fluctuation of lake levels, the increasing dominance of the invasive quagga mussel (Dreissena bugensis), and potential shifts in nutrient loading to the lake, it is important to evaluate past patterns in order to be prepared for future changes.
3:15 – 3:35 pm
TDS and Selenium Projections in the Las Vegas Wash post Implementation of the Systems Conveyance and Operation Program (SCOP)
Ryan, Roslyn and Zhou, Xiaoping, Southern Nevada Water AuthorityUrban runoff in the Las Vegas Valley flows into the Las Vegas Wash (Wash) via several major tributaries, contributes approximately 7-10% of the total Wash flow, and has a significant impact on water quality in the Wash and Lake Mead. Urban runoff entering the Wash contains higher total dissolved solids (TDS) and higher selenium (Se). With effluents from three wastewater treatment plants in the valley that significantly dilute the more saline urban runoff and shallow groundwater, TDS concentrations in the Wash are currently suitable for the growth of diverse plants and Se concentrations are below the EPA recommended level (<5g/L) for fish and wildlife. With the population growth and the wastewater effluent increases in the valley, the Systems Conveyance and Operation Program (SCOP) has been implemented to divert the majority of effluent into a pipeline that directly discharges into the Boulder Basin of Lake Mead, effluent flow to the Wash and the resulting dilution factor will be significantly reduced, primarily affecting TDS and Se concentrations. Using the data collected by the SNWA water quality team and a mass-balance model, projections have been made to predict what TDS and Se concentrations can be expected with different effluent flows to the Wash post implementation of the SCOP. These projections will help to develop a management plan to keep TDS concentrations sustainable for the established ecosystems and Se concentrations below the EPA standards for fish and wildlife.
3:40 – 4:00 pm
Characterization of Dissolved Organic Matter from Lake Mead by Liquid Chromatography Quadrupole Time of Flight Mass Spectrometry
Mawhinney, Douglas B.-1; Rosario-Ortiz, Fernando L.-2; Baik, Seungyun-3; Vanderford, Brett J.-1; Snyder, Shane-1
(1) Southern Nevada Water Authority, (2) University of Colorado, (3) University at BuffaloDissolved organic matter (DOM) occurs naturally in surface water due to the decomposition of plant and animal matter. The makeup of DOM can vary based geographical location, as well as seasonal changes in the flora and fauna present in or near the body of water. Such changes are particularly important to understand from a drinking water standpoint, as they can affect the demand for oxidants used in the disinfection process, as well as the profile of by-products formed. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF MS) was employed to characterize DOM standard materials sourced from different locations around the world, as well as samples from Lake Mead and its tributaries. It was found that this technique was most sensitive to the fulvic acid fraction of DOM, and resulted in very complex data. Principle component analysis was employed to simplify the analysis of these data, and it was found that the major differences between samples were related to the relative polarity and nitrogen content of the materials. Specific characterization data for each of the standard materials and samples will be presented, and possible implications will be discussed.
4:05 – 4:25 pm
SCOP Marine Investigations Field Program
MacKinnon, Angela I1 and Orphan, Lynn2
(1) MWH Americas, Inc (2) Clean Water CoalitionThe Marine Investigations Field Program of the Systems Conveyance and Operations Program (SCOP) will be comprised of two tasks: (1) investigation of the sediment thickness in the area of the five diffuser discharge points and (2) investigation of the ability of quagga mussels to attach to HDPE pipe.
The purpose of the sediment thickness task is to investigate the thickness of the post-impoundment sediment at the five outfall discharge locations. Earlier measurements of the thickness of the post-impoundment sediment on the bottom of Lake Mead indicate that the sediment may be 12-inches to as much as 7-feet thick in the area of the proposed pipeline alignment. The sediment thickness task will be developed and implemented whereby a rectangular weight is placed on the lake bottom in these areas. A remotely operated vehicle (ROV) will be utilized to observe post-impoundment sediment thickness and characteristics by capturing underwater video. The purpose of the Quagga Mussel Task is to investigate and observe the potential for quagga mussels to attach to HDPE pipe. The Quagga Mussel Task will be implemented by placing test sections of HDPE pipe on the lake bottom and on the surface.
The results of the Marine Investigation Field Program will be used to make recommendations for the design and operation of the Boulder Islands Outfall pipelines. This paper will discuss preliminary results of the Marine Investigations Field Program.
4:30 – 4:50 pm
EQuIS 5 LakeWatch: The Latest Advances in Lake Data Analysis Software
Weaver, Scot D. and Beard, Mitch, EarthSoft
EQuIS 5 LakeWatch is the latest technology available for effectively managing and analyzing lake or reservoir monitoring data. Based upon the well-known LakeWatch software package designed by one of the world’s preeminent limnologists, Dr. Noel Burns of New Zealand, EQuIS 5 LakeWatch is used to manage Lake Mead monitoring data and designed to display, analyze, and interpret trends in water quality. Using a robust and industry-standard SQL Server or Oracle database backend, EQuIS 5 LakeWatch directly imports data from the previous version of LakeWatch, as well as files from numerous data loggers such as Hydrolab, RUSS, Licor, and Campbell Scientific.
In cooperation with the Southern Nevada Water Authority (SNWA), Lake Mead data will be presented illustrating both characteristics of Lake Mead and highlighting features of the software. In addition to visually depicting sample and profile events and allowing the user to graphically and intuitively establish epi-thermo and thermo-hypo interfaces, EQuIS 5 LakeWatch includes many useful reports including a Trophic Level Index (TLI) report and a Hypolimnetic Volumetric Oxygen Depletion (HVOD) report. New features include enhanced tools for creating vertical profile diagrams as well as isopleths.