Lake Pleasant Limnology and Down-Canal Water Quality Implications - - PowerPoint PPT Presentation

Lake Pleasant Limnology and Down-Canal Water Quality Implications

Spatial Variation in Reservoirs

Thermal stratification (latitudinal

variation)

Longitudinal variation from incoming

river to the dam

A priori Information

Taste and odor complaints decreased

dramatically when the CAP canal contained water directly from the Colorado River as

• pposed to water that had been stored in

Lake Pleasant.

Taste and odor complaints increased among

utilities in the Phoenix Valley that were the farthest from Lake Pleasant.

Thermal Stratification

Nutrient Loading

Allochthonous (from canal into

reservoir) during periods of annual refilling of reservoir.

Autochthonous (from reservoir into

canal) during periods of release into the canal.

10000 20000 30000 40000 50000 60000 Total Algae (cells or colonies/mL)

• 34.5
• 32.2
• 30.8
• 22
• 16
• 15.8
• 15.6
• 10.2
• 0.1

Depth (meters)

Lake Pleasant Total Algae Count 12/04/96

A B C D

Algal Divisions with Depth

5000 10000 15000 20000 25000 Cells or colonies/mL

• 22

A

• 10.2
• 0.1
• 34.5

B

• 15.8
• 0.1
• 30.8

C

• 15.6
• 0.1
• 32.2

D

• 16
• 0.1

A lgal D iv isio ns with D epth 12/04/96

S um of Chlorophy ta S um of Cy anophy ta S um of Chry s ophy ta

Algal Speciation During Filling With Water From CAP Canal

Between dams at depth

mostly periphytic species that are usually found growing along the side of the CAP canal

Sites to the north of the old dam

more planktonic (true lacustrine) species

Preliminary data from 1996 suggested an

increase in dissolved and/or reduced forms of algal nutrients within the hypolimnion

Hypolimnion Metalimnion Epilimnion .0 .1 .2 mg/L Y Mean(Total P) Mean(Nitrate/nitrite-N) Mean(Ortho P) Mean(Ammonia-N)

y

2 4 6 8 10 12

Sediment Mesocosm Results for Sites B and D Non-Aerated

M ean Ferrous Iron (mg/L) 10.03 0.6 M ean Ortho P (mg/L) 5.45 0.65 M ean Ammonia-Nitrogen (mg/L) 5.56 0.63 B D

Recommendation

Prior to 1996, water was released from the

top gate (epilimnion) into the canal.

This left the hypolimnion intact to become

anoxic and accumulate nutrients.

These nutrients were slowly released into the

canal when stratified and in a large pulse during turn over.

Hypolimnetic Withdrawal

Recommended for the Spring/Summer

• f 1997 to try and siphon off the

hyplominion as early in the year as possible.

Done to increase dissolved oxygen over

the sediments especially in the area between the old and new Waddell dams.

• 35
• 30
• 25
• 20
• 15
• 10
• 5

Depth (m) 1 2 3 4 5 6 7 8 D.O. (mg/l) 1996

• 35
• 30
• 25
• 20
• 15
• 10
• 5

Depth (m) 1 2 3 4 5 6 7 8 D.O. (mg/l) 1997

Mean Hypolimnetic Nutrient Levels in Lake Pleasant by Year

0.06 mg/L 0.14 mg/L 0.01 mg/L 1997 0.18 mg/L 0.21 mg/L 0.06 mg/L 1996 Ortho P Total P Ammonia Year

Numbers of Periphytic Algae by Distance from Lake Pleasant During 1996

Cyanophyta Chrysophyta Chlorophyta Pyrrophyta Cyanophyta Chrysophyta Chlorophyta Pyrrophyta 6 - 45 70 - 78 Division by Distance from Lake Pleasant (km) 5000 10000 15000 20000 25000 30000 Mean(Units/cm2)

Numbers of Periphytic Algae in the CAP Canal by Year.

Cyanophyta Chrysophyta Chlorophyta Pyrrophyta Cyanophyta Chrysophyta Chlorophyta Pyrrophyta 1996 1997 10000 20000 Mean(Units/cm2)

Mean Levels of MIB by Distance from Lake Pleasant by Year

0 - 45 70 - 78 0 - 45 70 - 78 1996 1997 1 2 3 4 5 6 7 8 9 10 11 Mean MIB (ng/l)

Mean Levels of Geosmin by Distance from Lake Pleasant and Year

0 - 45 70 - 78 0 - 45 70 - 78 1996 1997 .0 .5 1.0 1.5 2.0 2.5 Mean Geosmin (ng/l)

Generalized Model of MIB and Geosmin Production in the CAP Canal

1) Increased sedimentation of material between the old and new Waddell dams during re-filling of Lake Pleasant with CAP water. 2) This sedimentation may lead to increased

• xygen demand and anoxia within the

hypolimnion during thermal stratification.

3) Under anoxic (and reducing) conditions, this sediment may release nutrients at a faster rate than other areas of the reservoir. 4) These nutrients accumulate within the

• hypolimnion. If water is released from the top

gate, the hypolimnion remains undisturbed for long periods and this may lead to further nutrient accumulation. 5) Geosmin or MIB may be quickly degraded in the turbulent release water

6) Release of nutrient-rich water from the

hypolimnion into the CAP canal may lead to the proliferation of taste and odor causing

• rganisms in the canal, especially in areas 70

km or more away from Lake Pleasant.

Current Problems

Increased biomass of periphyton growing

alongside the CAP canal (not this summer).

Hydrogen sulfide emissions upon release

during mid-late summer.

Iron and manganese in canal water from

Lake Pleasant.

Spikes in tastes and odors during late

summer/early fall 2004.

Hypolimnetic DO Levels by Year

DO_mg_per_L 1 2 3 4 5 6 Summer 02 Summer 03 Summer 04 Sampling_Period Sampling_Period Error

• C. Total

Source 2 57 59 DF 99.05619 63.94067 162.99686 Sum of Squares 49.5281 1.1218 Mean Square 44.1519 F Ratio <.0001 Prob > F

Analysis of Variance

Summer 02 Summer 03 Summer 04 Level 15 26 19 Number 3.64400 0.45577 1.19526 Mean 0.27347 0.20771 0.24298 Std Error 3.0964 0.0398 0.7087 Lower 95% 4.1916 0.8717 1.6818 Upper 95% Std Error uses a pooled estimate of error variance

Means for Oneway Anova Oneway Anova Oneway Analysis of DO_mg_per_L By Sampling_Period

Taste and Odor Increases During Late October of 2004.

Probably attributable to earlier-than-normal

de-stratification.

Huge pulses of mib and/or geosmin have

• ccurred in the past when water was

switched from the lower to the upper gate and occurred even when there was little or no mib/geosmin production within the lake itself.

The majority of the mib spike downstream of

Pleasant is probably due to lysing of periphyton growing alongside the canal.

Lysing of periphytic cells occurs when there

are large, sudden changes in temperature, or

• ther parameters, in the canal.

Tastes and odors greatly diminished when

release was once again switched back to the lower gates.

Numbers of periphytic species capable of mib

and geosmin production growing periphytically alongside the CAP are less than what we find growing in the Salt and Verde Rivers below the reservoirs.

However, if large amounts are suddenly

lysed, it will result in large mib or geosmin hits.

Why Earlier-Than-Normal De-stratification?

Profile data on 9/24/04 indicated strong

stratification (>24o C at the surface to <14o C at the bottom of the hypolimnion).

Samples taken by Steve Rottas and Al

Grochowski of CAP on 10/19, showed that almost the entire reservoir was de-stratified.

They also noticed a strong smell of hydrogen

sulfide in the open water, an indication of recent turnover.

USGS data from the Agua Fria River near

Rock Springs, showed a significant flooding event on 9/19 and 9/20/04.

The Agua Fria approached 2000 cfs and this

pulse of water could have aided in an earlier- than-normal de-stratification.

We have no data on other drainages into

Pleasant such as Humbug Creek, Castle Creek, or Cole’s Wash.

However, it appears that the lake level

actually rose slightly while water was being released from Waddell Dam.

Summary

Most of the water quality problems down-

canal of Lake Pleasant are dependant upon dissolved oxygen and ORP levels within the hypolimnion which are, in turn, dependent upon other limnological processes.

Operational changes in the release of water from Lake Pleasant will address several of these water quality issues.