Water Quality in Lake Mead and Ups

Influences:

Dissolved Oxygen during 20

Todd Tietjen, Ph.D.Regional Water Quality, SNWAtodd.tietjen@snwa.com
The Southern Nevada Water Aut

 Cooperative Agency founded in 1991

 7 members

 Big Bend Water District, Cities of Boulder City, Henderson, Las Ve

Las Vegas, Clark County Water Reclamation District, and the Las Water District

 Responsibilities

 Managing all water supplies available to Southern Nevada through an 

water budget

 Managing regional water resource management and conservation pro

 Ensuring regional water quality as determined by state and feder

 Allocating and distributing among water purveyors Colorado River wat

other water that becomes available to Southern Nevada 

 Long-term water resource planning  Presenting a unified position on water issues facing Southern Nevada

 Building and operating regional facilities to provide a reliable drinking w

system to all member agencies
Current Lake Elevation: 

SNWA Intake 1&2: SNWA Intake 3: Hoover Dam Upper: Hoover Dam Lower: 

Lake Mead Sampling
Gregg Basin Sampling

Hoover

Dam

~18 miles
Why measure DO?

 We measure dissolved oxygen concentrations for a variety of re

 Important indicator of ecological function

 Most fish will thrive with oxygen concentrations of 4 mg/L (~40% saturatio

 When oxygen concentrations are below 0 and 4 mg/L most fish and aqua

will experience significant physiological stress

 Those that can swim away, will swim away

 If oxygen concentrations drop below 1 mg/L most animals and plants tha

will die (eventually depending on temperature)

 While Lake Mead is only a moderately productive reservoir (in biolo

the extensive bottom waters of the lake collect significant organic mdecomposed by microoorganisms, lowering the oxygen concentratio

 The temperature regime in Lake Mead and Southern Nevada allows Lake 

completely 1 out of every 2 years on average

 When the lake mixes completely “new” oxygen is added back to the botto

 In the past, the conditions in the Colorado River have replenished much o

consumed oxygen during years without complete mixing

 Cold River inflow

 Oxygen is of interest to other stakeholders (LMNRA, NDOW, etc), t

water quality standard to be met, and the SNWA drinking water treaprocess is optimized to treat oxygenated waters.
What makes 2014 interesting?
Gregg Basin 2014

16 C°
Gregg Basin 2014
Gregg Basin 2014
Gregg Basin 2014
Gregg Basin 2014

HFE 

Starts
Metalimnetic DO

EpilimnionMetalimnionHypolimnion
Impact of Inflow temperatures o

Lake Mead DO

EpilimnionMetalimnionHypolimnion

2014

2013
What have we seen in the past?

 USBR Technical Service Center collected data i

region of the lake for most of the 2000’s.

 Low DO concentrations early, increasing later in 

 2002, 2006, 2010

 Similar to this year, likely overflowing CR

 High DO concentrations early, decreasing later 

year

 2001, 2005, 2011

 Opposite of this year, likely cold inflowing CR

 High DO concentrations early and late, lowest m

 2003, 2004, 2007, 2008, 2009

 Partly cold inflow early, warming mid year, cooling late ye
What does this tell us?

 The inflowing Colorado River can have a signific

impact on DO dynamics in Gregg Basin, and the potentially the rest of Lake Mead

 The influence is not simple to predict 

 Need to consider

 Lake Mead Stratification and Temperature Colorado River Temperature Algal Productivity in Gregg Basin Hoover Dam operations Timing

 We made a first attempt at this using the 

data and failed

 Temperature and Discharge were not enough 
What can we expect in the future?

 Warmer river temperatures?

 Drought Regional warming through climate change Ecological flows / experimental manipulation

 Increased organic loading?

 Internal algal production in Lake Mead Colorado River transport

 Lower Lake Mead surface elevations?

 Difficult to assess, but impacts become m

important quickly
Biggest Potential Problem: Phosphorus Releas

Lake Mead TotalPhosphorus Budget
Conclusions

 Upstream temperatures can have significant imp

dissolved oxygen concentrations in Lake Mead

 Cold river temperatures can alleviate or reduce 

dissolved oxygen conditions 

 Higher river temperatures keep the Colorado Riv

higher in the water column

 Unlikely to re-oxygenate lower water column May reinforce “natural” stratification patterns

 Significant, repeated anoxic conditions in upper 

Mead have the potential to significantly alter phodynamics

 Greater phosphorus release Greater algal production Greater anoxia
Questions?

Todd Tietjen, Ph.D.Regional Water Quality, SNWAtodd.tietjen@snwa.com