Comprehensive Watershed Management for the Valley of the

Sun

David WalkerUniversity of Arizona

Environmental Research Laboratorydwalker@ag.arizona.edu

Scope• Analytes

– Physico-chemical– General Chemistry– Nutrients– TOC/DOC– Total and Filtered Metals– Chlorophyll a– Perchlorate– Algae ID and Enumeration– Zooplankton– Aquatic Macroinvertebrates– Algal Toxins– MIB and Geosmin– Sediment Metals– Sediment Nutrients

Issues of Concern

• Eutrophication • Drought• Urbanization• Response to disturbance (e.g.

Rodeo/Chedeski fire)• Perchlorate in Colorado River and

offshoots (CAP canal, Lake Pleasant)

• Algal toxins• Narrative Nutrient Criteria• Biocriteria for reservoirs

Ongoing Drought• According to some climate

experts, the most recent drought began in 1996.

• Dry conditions have been worsening over the past four years; by the summer of 2002 most of Arizona and New Mexico were considered to be in "extreme" drought.

Long-term Climatic Trends and the Pacific Decadal Oscillation

(PDO)• PDO is not a ten-year La Niña. • Regular (20 – 30 year) pattern of

high and low pressure systems over the northern portions of the Pacific Ocean.

• Correlates with relatively wetter or drier periods in the western portion of North America.

What does it mean for Watersheds in the Southwest?

• Positive PDO phases tends to enhance El Niño conditions and weaken the effects of La Niñas.

• Negative PDO phases enhance the effects of La Niñas and weaken the effects of El Niños

• Negative PDO phase starting around 1995.

• This may result in drier La Niña winters.

• An extended period of drier than usual winters would likely produce a decrease in renewable water supplies in the desert southwest.

• Although winter precipitation accounts for only 50 to 60% of our annual precipitation, it is responsible for 80 to 95% of the annual streamflow.

• The UA’s Climate Assessment Project for the Southwest (CLIMAS), conducted an analysis of the effects of prolonged drought in the Phoenix and Tucson Active Management Areas (AMAs).

Impact of Severe Drought on Water Resources

• The research team assumed a ten-year drought of the magnitude that occurred in the 1950s and demand levels projected by ADWR for 2025.

• Even assuming full availability of CAP water, the Phoenix AMA could well exceed its renewable water supply by 39 percent.

• The greater Phoenix metro area has experienced explosive growth in the past 20-30 years, an era when climate has been relatively wet.

Assuming that relatively wet conditions will continue into the indefinite future is unwise given all that we have learned about the climate history of the southwest.

Rodeo/Chedeski Fire and it’s Effect(s) on the Salt River Reservoirs

Salt River Above Roosevelt Nutrient Levels by Sampling Period

Summer02

Fall02

Winter02/03

Spring03

Summer03

Sam

plin

g_P

erio

d

0 10 20 30 40

Y

OverlayChart

Y

Ammonia_N_mgPerL_asN

NitrateNitrite_N_ppm

Total_P_ppm

Total_Kjeldahl_Nitrogen_mgPerl_as_N

Chart

Nutrient Loading via the Salt River by Year (all data from late August/early September)

1999

2000

2002

2003

Year

0 10 20 30 40

Y

OverlayChart

Y

Ammonia_N_mgPerL_asN

NitrateNitrite_N_ppm

Total_P_ppm

Total_Kjeldahl_Nitrogen_mgPerl_as_N

Chart

Summer 02

Summer 03

Sam

plin

g_P

erio

d

0 5 10 15 20

Mean(Chl_a_mgPerm3)

Sampling_Period Summer 02 Summer 03

Chart

Mean Chlorophyll Levels (mg/m3) in Roosevelt for Summer 2002 and Summer

2003.

Components:

Chl_a_mgPerm3

Ammonia_N_mgPerL_asN

NitrateNitrite_N_ppm

Total_P_ppm

TKN_ppm

Prin Comp 1

Prin Comp 2

Prin Comp 3

Prin Comp 4

Prin Comp 5

Chl_a_mAmmonia

Nitrate

Total_PTKN_ppm

x

y

z

1.7365

1.2104

1.0042

0.8146

0.2343

EigenValue

34.730

24.208

20.084

16.291

4.686

Percent

34.730

58.938

79.022

95.314

100.000

Cum Percent

Chl_a_mgPerm3

Ammonia_N_mgPerL_asN

NitrateNitrite_N_ppm

Total_P_ppm

TKN_ppm

Eigenvectors

0.64473

-0.05836

-0.04645

-0.32517

0.68777

0.37632

0.79527

0.00315

0.47121

-0.06230

-0.01135

-0.03050

0.99137

0.06810

0.10721

0.07097

-0.49560

-0.09977

0.81620

0.27057

-0.66146

0.34291

-0.07121

0.03754

0.66212

250 rows not used due to missing values.

Principal Components

Spinning Plot

Correlates of Primary Production in Roosevelt

DO Levels by Depth in Roosevelt for the Summers of 2002 and

2003

-20

-15

-10

-5

0

Dep

th_m

0 1 2 3 4 5 6 7 8 9

DO_mg_per_L

-35

-30

-25

-20

-15

-10

-5

0

Dep

th_m

0 1 2 3 4 5

DO_mg_per_L

Mean D.O. Levels by Year

DO

_mg_

per_

L

0

1

2

3

4

5

6

7

8

9

Summer 02 Summer 03

Sampling_Period

Insert fig 10 from write up

Conclusions• There is no single “slug” of water from

the fire.• Episodic events, especially during

monsoons, will continue to bring heavy nutrient and sediment loads to Roosevelt.

• These events will, hopefully, diminish over time as vegetation becomes established in the watershed.

• The long-term, chronic effects of the fire on downstream water quality are unknown.

Hypolimnetic Anoxia within Lake Pleasant

• Complaints of H2S at Waddell Dam.

• Complaints of dissolved Mn at downstream municipalities.

Why Bottom Release?• Implemented since 1997 to alleviate

taste and odor problems in the CAP canal.

• Recommendation was made not because it was believed that MIB/geosmin produced within Pleasant was problematic to receiving cities.

• Recommended to withdraw anoxic hypolimnetic water as soon as possible in the year.

• Oxygenated water over the sediments as soon as possible in the year = decreased phosphorous, Mn, and H2S accumulation within the hypolimnion.

Did it Work?

• Divisional shift from periphytic cyanobacteria to green filamentous algae and diatoms (non taste and odor producing species).

• Taste and odors are no longer a significant problem in the CAP canal.

• Two things that will hinder the original plan of hypolimnetic withdraw are;– Decreased amount of water

released from the hypolimnion and,

– Increased amount of time sediments are exposed to anoxic conditions.

• Both may occur due to increased amount of bypass pumping of Colorado River water, delay of release from Pleasant until later in the year, etc.

Lake Pleasant Disolved Oxygen-vs-depth Combined Locations

146514751485149515051515152515351545155515651575158515951605161516251635164516551665167516851695

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12Dissolved Oxygen m g/l

Lake

Ple

asan

t Ele

vatio

n

Towers 250yds 1000yds 1mile

Upper Tower Gate

Lower Tower Gate

Lake Level

Questions?