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 opposed 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 .

Lake Pleasant Total Algae Count 12/04/96 60000 50000 Total Algae (cells or colonies/mL) A 40000 B 30000 C D 20000 10000 0 -34.5 -32.2 -30.8 -22 -16 -15.8 -15.6 -10.2 -0.1 Depth (meters)

Algal Divisions with Depth S um of Chlorophy ta A lgal D iv isio ns with D epth 12/04/96 S um of Cy anophy ta S um of Chry s ophy ta 25000 20000 Cells or colonies/mL 15000 10000 5000 0 -22 -10.2 -0.1 -34.5 -15.8 -0.1 -30.8 -15.6 -0.1 -32.2 -16 -0.1 A B C D

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

Sediment Mesocosm Results for Sites B and D Non-Aerated 12 10 8 6 4 2 0 B D 10.03 0.6 M ean Ferrous Iron (mg/L) 5.45 0.65 M ean Ortho P (mg/L) 5.56 0.63 M ean Ammonia-Nitrogen (mg/L)

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 of 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.

0 -5 -10 Depth (m) -15 1996 -20 -25 -30 -35 0 1 2 3 4 5 6 7 8 D.O. (mg/l) 0 -5 -10 Depth (m) -15 1997 -20 -25 -30 -35 0 1 2 3 4 5 6 7 8 D.O. (mg/l)

Mean Hypolimnetic Nutrient Levels in Lake Pleasant by Year Year Ammonia Total P Ortho P 1996 0.06 mg/L 0.21 mg/L 0.18 mg/L 1997 0.01 mg/L 0.14 mg/L 0.06 mg/L

Numbers of Periphytic Algae by Distance from Lake Pleasant During 1996 Pyrrophyta Division by Distance from Lake Pleasant (km) Chlorophyta 70 - 78 Chrysophyta Cyanophyta Pyrrophyta Chlorophyta 6 - 45 Chrysophyta Cyanophyta 0 5000 10000 15000 20000 25000 30000 Mean(Units/cm2)

Numbers of Periphytic Algae in the CAP Canal by Year. Pyrrophyta 1997 Chlorophyta Chrysophyta Cyanophyta Pyrrophyta 1996 Chlorophyta Chrysophyta Cyanophyta 10000 0 20000 Mean(Units/cm2)

Mean Levels of MIB by Distance from Lake Pleasant by Year 70 - 78 1997 0 - 45 70 - 78 1996 0 - 45 0 6 1 2 3 4 5 7 8 9 10 11 Mean MIB (ng/l)

Mean Levels of Geosmin by Distance from Lake Pleasant and Year 70 - 78 1997 0 - 45 70 - 78 1996 0 - 45 2.5 .0 .5 1.0 1.5 2.0 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 oxygen 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 organisms 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 Oneway Analysis of DO_mg_per_L By Sampling_Period 6 5 4 DO_mg_per_L 3 2 1 0 Summer 02 Summer 03 Summer 04 Sampling_Period Oneway Anova Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Prob > F Sampling_Period 2 99.05619 49.5281 44.1519 <.0001 Error 57 63.94067 1.1218 C. Total 59 162.99686 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95% Summer 02 15 3.64400 0.27347 3.0964 4.1916 Summer 03 26 0.45577 0.20771 0.0398 0.8717 Summer 04 19 1.19526 0.24298 0.7087 1.6818 Std Error uses a pooled estimate of error variance

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 occurred 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 other 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 (>24 o C at the surface to <14 o 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.