the limnology of lake pleasant arizona and it’s effect on ...introduction impounded water has...

The Limnology of Lake Pleasant Arizona and its Effect on Water Quality in the Central Arizona Project Canal.

by

David Bradley Walker

3

STATEMENT OF AUTHOR

Brief quotations from this work are allowable without special permission, provided that accurate knowledge of source is made.

TABLE OF CONTENTS

Page LIST OF ILLUSTRATIONS 8 LIST OF TABLES 13 ABSTRACT 15 1 INTRODUCTION 16 2 MATERIALS AND METHODS 21 Site Description 21 Hydraulics of Re-Filling and Withdrawing Water from Lake Pleasant 22 Sampling Sites 23 Field Data Collection 24 Lake Pleasant 24 CAP Canal 25 Sediment Mesocosm Experiment 26 Laboratory Methods 28 3 RESULTS 30 Thermal Stratification and Mixing 30 Lake Pleasant Nutrient Data 32 Sediment Mesocosm Data 36 CAP Canal Nutrient Data 39 Lake Pleasant Phytoplankton 42 CAP Canal Periphyton 44 Analysis of MIB and Geosmin in the CAP Canal 46 Relation of Cyanophytes to MIB/Geosmin Levels in the CAP Canal 47 Principal Component Analysis of Lake Pleasant Hypolimnetic Conditions and MIB, Geosmin, and Periphyton Within the CAP Canal 50 4 DISCUSSION 53 5 CONCLUSIONS 58

5

TABLE OF CONTENTS – Continued

Page APPENDIX A - DIGITAL IMAGES 112 LITERATURE CITED 125

6

LIST OF ILLUSTRATIONS

Figure Page

1-1 A generalized model of reservoir zonation from river to dam as proposed by Thornton, Kimmel, and Payne (1990).

61

2-1 Lake Pleasant operational data showing relationship between the

old and new Waddell Dams. 62

2-2 Sampling Sites within Lake Pleasant, Arizona. 63 2-3 Sampling sites within the CAP canal showing approximate

distances from Lake Pleasant. 64

2-4 Image of sediment from Lake Pleasant, Arizona being placed in

polycarbonate containers. 65

2-5 Image of mesocosms in the fiberglass container that was used as

a recirculating water bath. 66

3-1 Mean dissolved oxygen levels (mg/L) by stratified layer in Lake

Pleasant, Arizona. 67

3-2 One-way analysis of hypolimnetic ammonia-N levels (mg/L) in

Lake Pleasant, Arizona by year. 68

3-3 One-way analysis of hypolimnetic total phosphorous levels (mg/L)

in Lake Pleasant, Arizona by year. 69

3-4 One-way analysis of hypolimnetic orthophosphate levels (mg/L)

in Lake Pleasant, Arizona by year. 70

3-5 Rates of dissolved oxygen depletion in non-aerated mesocosms

containing sediments collected from sites B and D in Lake Pleasant, Arizona.

71

3-6 Mean orthophosphate, ammonia-N, and ferrous iron levels (mg/L)

in the non-aerated mesocosms from sites B and D at the end of 17 weeks.

72

7

LIST OF ILLUSTRATIONS - Continued

Figure Page

3-7 Rate of orthophosphate (mg/L) release from sediments in non-aerated mesocosms from sites B and D.

73

3-8 Rate of ammonia-N (mg/L) release from sediments in non-

aerated mesocosms from sites B and D. 74

3-9 Rate of ferrous iron (mg/L) release from sediments in non-

aerated mesocosms from sites B and D. 75

3-10 One-way analysis of nitrate/nitrite-N Levels (mg/L) in the CAP

canal by year. 76

3-11 One-way analysis of ammonia-N levels (mg/L) in the CAP canal

by year. 77

3-12 One-way analysis of total-P levels (mg/L) in the CAP canal by

year. 78

3-13 One-way analysis of orthophosphate levels (mg/L) in the CAP

canal by year. 79

3-14 Mean numbers of algae by division observed in Lake Pleasant,

Arizona during 1996 and 1997. 80

3-15 Mean numbers of phytoplankton (in units/mL) by site in Lake

Pleasant for 1996 and 1997. 81

3-16 Bivariate fit of depth (m) by units/ml while withdrawing water from

Lake Pleasant, Arizona during 1996 and 1997. 82

3-17 Bivariate fit of algal units/mL by depth (m) while pumping water

into Lake Pleasant, Arizona during 1996 and 1997. 83

3-18 Bivariate fit of algal units/mL by depth (m) at site A while pumping

water into Lake Pleasant, Arizona during 1996 and 1997. 84

8


Figure Page

3-19 Bivariate fit of algal units/mL by depth at site B while pumping water into Lake Pleasant, Arizona during 1996 and 1997.

85

3-20 Bivariate fit of algal units/mL by depth at site C while pumping

water into Lake Pleasant, Arizona during 1996 and 1997. 86

3-21 Bivariate fit of units/mL by depth at site D while pumping water

into Lake Pleasant, Arizona during 1996 and 1997. 87

3-22 Divisions of algae (in units/mL) found below 10 meters depth at

sites A, B, and C during the period of re-filling. 88

3-23 Cyanophyte abundance in Lake Pleasant, Arizona by site during

the summers of 1996 and 1997. 89

3-24 One-way analysis of cyanophyte abundance (units/mL) during the

summers of 1996 and 1997 in Lake Pleasant, Arizona. 90

3-25 One-way analysis of periphyton abundance (units/cm2) for all

sites in the CAP canal during 1996 and 1997. 91

3-26 Abundance of algal divisions found within the periphyton of the

CAP canal during the summers of 1996 and 1997. 92

3-27 Cyanophyte abundance by site during the summers of 1996 and

1997. 93

3-28 One-way analysis of numbers of periphytic cyanophytes by year

in the CAP canal at 70-78 km from Lake Pleasant, Arizona. 94

3-29 One-way analysis of numbers of periphytic cyanophytes by year

in the CAP canal at 0-45 km from Lake Pleasant, Arizona. 95

3-30 Mean levels of 2-methylisoborneol in the CAP canal by distance

from Lake Pleasant, Arizona during periods of release for 1996 and 1997 collectively.

96

9


Figure Page

3-31 One-way analysis of mean MIB levels (ng/L) by distance from Lake Pleasant, Arizona during times of release for 1996 and 1997 collectively.

97

3-32 One-way analysis of MIB levels by year (1996, 1997) for all sites

in the CAP canal. 98

3-33 Mean levels of MIB by distance from Lake Pleasant, Arizona

during periods of release into the CAP canal during 1996 and 1997.

99

3-34 Mean levels of geosmin in the CAP canal by distance from Lake

Pleasant, Arizona during periods of release for 1996 and 1997 collectively.

100

3-35 Mean levels of geosmin by distance from Lake Pleasant (km's)

during periods of release into the CAP canal during 1996 and 1997.

101

3-36 Correlations between numbers of Anabaena (units/cm2) to levels

of MIB and geosmin (ng/L) in the CAP canal during 1996. 102

3-37 Correlations between numbers of Anabaena (units/cm2) to levels


3-38 Correlations between numbers of Oscillatoria (units/cm2) to levels


3-39 Correlations Between Numbers of Oscillatoria (units/cm2) to

Levels of MIB and Geosmin (ng/L) in the CAP Canal During 1997.

105

3-40 Correlations between numbers of Lyngbya (units/cm2) to levels of

MIB and geosmin (ng/L) in the CAP canal during 1996. 106

3-41 Correlations between numbers of Lyngbya (units/cm2) to levels of

MIB and geosmin (ng/L) in the CAP canal during 1997. 107

10

LIST OF ILLUSTRATIONS – Continued

Figure Page

3-42 Correlations between numbers of Lyngbya (units/cm2) to levels of MIB and geosmin (ng/L) in the CAP canal during 1997.

108

3-43 Principal component analysis of nutrient and dissolved oxygen

data from the hypolimnion of Lake Pleasant, Arizona and MIB/geosmin data from 70-78 km down-canal during 1997.

109

3-44 Principal component analysis of site B dissolved oxygen levels,

MIB/geosmin and periphyton growth in the CAP canal at 70-78 km down-canal from Lake Pleasant, Arizona during 1996.

110

3-45 Principal component analysis of site B dissolved oxygen levels,

MIB/geosmin and periphyton growth in the CAP canal at 70-78 km down-canal from Lake Pleasant, Arizona during 1997.

111

11

LIST OF TABLES

Table Page

3-1 Table 3-1. Three-way ANOVA testing for effects of site, layer, and year (1996, 1997) on nitrate/nitrite-N levels within Lake Pleasant, Arizona.

33

3-2 Three-way ANOVA testing for effects of site, layer, and year

(1996, 1997) on ammonia levels within Lake Pleasant, Arizona. 34


(1996, 1997) on total phosphorous levels within Lake Pleasant, Arizona.

35


(1996, 1997) on orthophosphate levels within Lake Pleasant, Arizona.

36

3-5 Mean nutrient levels (mg/L) in the aerated and non-aerated

mesocosms at the end of 17 weeks that contained sediments from sites B and D in Lake Pleasant, Arizona.

37

3-6 Mean orthophosphate, ammonia-N, and ferrous iron levels (mg/L)

in the non-aerated mesocosms from sites B and D at the end of 17 weeks.

38

3-7 Two-way ANOVA testing for effects of site and year (1996, 1997)

on nitrate/nitrite-N levels within the CAP canal. 39

3-8 Two-way ANOVA testing for effects of site and year (1996, 1997)

on ammonia-N levels within the CAP canal. 40

3-9 Two-way ANOVA testing for treatment effects on total

phosphorous levels within the CAP canal. 41

3-10 Two-Way ANOVA testing for treatment effects on orthophosphate

levels within the CAP canal. 42

3-11 Overall periphyton abundance (units/cm2) by site including

distance from Lake Pleasant. Means are for 1996 and 1997 collectively.

44

12

LIST OF TABLES - Continued

Table Page

3-12 Table 3-1. Three-way ANOVA testing for effects of site, layer, and year (1996, 1997) on nitrate/nitrite-N levels within Lake Pleasant, Arizona.

49

13

ABSTRACT

Recent changes in the management strategy of water released from Lake

Pleasant into the Central Arizona Project canal have substantially reduced taste

and odor complaints among water consumers. Most of the taste and odor

complaints were likely caused by 2-methylisoborneol (MIB) and geosmin

produced by periphytic cyanobacteria growing on canal surfaces. Most years,

Lake Pleasant consists almost exclusively of water brought in via the CAP canal.

The location of the inlet towers and the old Waddell dam influence sedimentation

of material brought in by the CAP canal. In-coming water was found to contain

large amounts of periphyton of the type commonly found growing on the sides of

the CAP canal. Withdrawal of hypolimnetic water early in the spring of 1997

decreased the time that sediments were exposed to anoxic conditions, potentially

decreasing the amount of nutrients released into the CAP canal and therefore

available for periphytic cyanobacteria. Utilizing this management strategy since

1997 has resulted in a substantial reduction (or elimination) of consumer

complaints of earthy/musty tastes and odors.

14

CHAPTER 1

INTRODUCTION

Impounded water has different physical, chemical, and biological

properties than free-flowing water of rivers, which is primarily defined by climatic

and geologic characteristics of the drainage basin. The impounded water of

reservoirs, however, exhibits spatial variability primarily along 2 axes, latitudinal

variation along the z-axis and longitudinal variation along the y-axis. Water

quality changes with depth (latitudinal variation) in reservoirs is common and

thermal stratification can greatly increase spatial variability in this direction.

Latitudinal variation has been examined and a generalized model

proposed by Thornton, Kimmel, and Payne (1990) has attempted to describe this

variability (Fig. 1-1). This model generally states that there are 3 distinct

longitudinal zones in a reservoir, a riverine, transitional, and lacustrine zone each

with different physical, chemical and biological variables. The riverine zone

usually exerts the greatest initial influence on the reservoir due to in-coming

sediment from the river and this area is usually high in total nutrient levels and

suspended sediments. The transitional zone is where the reservoir opens into a

broader and deeper basin and is usually less turbid and has less suspended

solids than the riverine zone. Within the lacustrine zone the reservoir becomes

more "lake-like" and has lower levels of suspended solids than the riverine or

transitional zone.

15

The continuum of zones, from riverine to lacustrine, within a reservoir

often has a corresponding change in trophic status. The riverine zone is usually

considered more "eutrophic" than the transitional zone, which is often considered

"mesotrophic" while the lacustrine zone is usually considered the most

"oligotrophic" area within the reservoir. This assignment of trophic status to

individual zones can be misleading. While the riverine zone may be considered

eutrophic based on relatively low secchi disk depth readings and total nutrient

concentrations, algal growth may often be light-limited because of the relatively

high levels of suspended sediments. Additionally, while total nutrient levels in

this area may be relatively high, a large amount of these nutrients may not be

bioavailable because they are bound to inorganic materials such as phosphorous

binding to iron to form a ferro-phosphate complex.

Perhaps a better method of assessing the differences between these

zones would be to examine the origin of nutrients within each zone. In the

riverine zone, where suspended solids are usually high, most of the nutrients

come from an allochthonous source e.g., from the surrounding drainage basin. In

the lacustrine zone, and to some degree the transitional zone, the nutrient source

may be highly autochthonous depending on the degree of stratification, reducing

potential, dissolved oxygen levels, pH, and other physico-chemical variables.

Although overall nutrient levels within the lacustrine or transitional zone may be

lower than those found within the riverine zone, they might be more bioavailable

for algal growth. The autochthonous nature and bioavailability of nutrients within

16

the lacustrine zone may have implications upon primary production in this area,

but also on down-stream areas receiving this water. The degree to which the

lacustrine zone affects other areas downstream may be dependant upon where

water is released along the z-axis or, in other words, from the epi-, meta-, or

hypolimnion if thermal stratification is present.

The hypolimnion of thermally stratified reservoirs often becomes anoxic

due to reduced atmospheric aeration and the oxygen-consuming heterotrophic

decay of organic matter "raining" into the hypolimnion from the epilimnion. This

anoxia can have consequences on biogeochemical cycling and solubilize

nutrients that were once stored within sediments into overlying water (Nishri et

al., 2000). If sediments are exposed to these anoxic and reducing conditions for

long periods, nutrients such as ammonia-nitrogen and orthophosphate may

accumulate (Nishri et al., 2000). Therefore, the longer the period of anoxia, the

more these nutrients may accumulate. The N:P ratio, coupled with total nutrient

concentration, may determine the composition of the periphytic community in

those areas downstream of the reservoir receiving this water (Stelzer & Lamberti,

2000).

Knowing which areas of a reservoir are autochthonous, allochthonous, or

some combination of both enables managers to make decisions about which

areas may have the largest effect on water quality not only within the reservoir,

but on receiving waters as well.

17

In the first few years after Lake Pleasant, a reservoir in Central Arizona,

was used to store water from the Colorado River via the Central Arizona Project

canal (CAP), with eventual re-release of this water to several municipalities in the

Phoenix Valley, many consumers complained of earthy or musty tastes and

odors in drinking water (pers. comm. Tom Curry, Central Arizona Water

Conservation District). Earthy or musty tastes and odors often are associated

with certain species of cyanobacteria that are capable of producing 2-

methylisoborneol (MIB) or geosmin (Naes et al., 1988, Izaguirre & Taylor, 1995).

Treatment of this water with powdered activated carbon (PAC) was used

extensively to remove chemicals causing tastes and odors, often at great

expense to utilities.

Anecdotal information suggested that complaints about tastes and odors

decreased dramatically when the CAP canal contained water directly from the

Colorado River as opposed to water that had been stored in Lake Pleasant.

Also, it appeared that complaints of tastes and odors increased among utilities in

the Phoenix Valley that were farthest down-canal from Lake Pleasant.

I studied changes in water release from Lake Pleasant and the

subsequent changes in water quality in the CAP canal for the years 1996 and

1997. Prior to and during 1996, water was released from the surface layer

(epilimnion) of Lake Pleasant during the summer into the CAP canal. Due to

possible nutrient release from anoxic sediments, especially in the area between

the old and new Waddell dams, I recommended release of water from the bottom

18

layer (hypolimnion) in addition to epilimnetic release during the summer of 1997.

I compared water quality and periphyton in the CAP canal during different

release strategies to determine if implementation of my recommendation resulted

in an alleviation of tastes and odors in drinking water supplied by the CAP down-

canal of Lake Pleasant.

Previous studies that have dealt with MIB/geosmin production by

cyanobacteria in source waters have tended to examine the role of reservoirs

(Izaguirre et al., 1982; Berglind et al., 1983; McGuire et al., 1983; Slater & Blok,

1983; Yagi et al., 1983; Negoro et al., 1988; Izaguirre, 1992), or canals

emanating from these reservoirs (Izaguirre & Taylor, 1995) as separate

ecosystems. In contrast, I propose that nutrients released from Lake Pleasant

may promote growth of periphytic taste and odor causing organisms within the

CAP canal.

19

CHAPTER 2

MATERIALS AND METHODS

Site Description

Lake Pleasant is located about 48 km northwest of Phoenix, Arizona and

is used as a storage reservoir for water transported from Lake Havasu on the

Colorado River to central Arizona via the Central Arizona Project (CAP) canal

system. Water is pumped from the canal and into Lake Pleasant during winter

and released back into the canal during summer when it is needed for irrigation

and drinking water. Prior to CAP water being stored in Lake Pleasant, the Agua

Fria River, an intermittent stream entering from the north, was the primary water

source to Lake Pleasant. Smaller, ephemeral streams flowing into the reservoir

are Castle Creek and Humbug Creek. Construction of the new Waddell dam

increased the surface area of Lake Pleasant from 1,497 to 4,168 hectares

(Arizona Game and Fish Dept. unpublished report to U.S. Bureau of

Reclamation, 1990). The old Waddell dam was left submerged within the

reservoir approximately 0.75 km north of the new dam (Fig. 2-1). The primary

water source for Lake Pleasant is now the CAP canal. At maximum capacity,

Lake Pleasant contains about 811,000 acre-feet (324,000 hectare-meters) of

water.

20

The CAP canal is a 541 km, concrete-lined aqueduct that begins at Lake

Havasu, Arizona and terminates 23 km south of Tucson, Arizona. The average

size of the canal between the Waddell forebay and Mesa WTP is 24 m wide

across the top and 7 m wide at the bottom with an average water depth of 6 m

(pers. comm. Steve Rottas, Central Arizona Water Conservation District).

The concrete lining is about 9 cm thick and in several areas, reinforced with

steel. The concrete surface has been roughened to allow small animals to climb

out. The canal is fenced along its entire reach and there is no public access.

Hydraulics of Re-filling and Withdrawing Water From Lake Pleasant

The majority of water now enters or leaves Lake Pleasant via a penstock

pipe that penetrates the new Waddell dam. The reservoir end of the pipe

terminates in a tower with 2 gates at heights approximately 18 m apart (Fig. 2-1).

These gates can be used separately or in combination. The maximum flow that

the Waddell dam forebay and the CAP canal can accommodate is about 1065

cubic meters/second (cms).

Lake Pleasant is unique in that most of the water now enters in the

lacustrine zone of the reservoir instead of the more typical situation of entering

via a river at the farthest upstream reaches of the reservoir (Thornton, Kimmel,

and Payne, 1990). The impact of the Agua Fria River, entering from the north,

on water quality leaving the reservoir is relatively small except possibly during

flood events. The proximity of the old Waddell dam to the CAP inlet/outlet towers

21

(Fig. 2-1) creates an area in the lacustrine zone that enhances sedimentation,

stratification, dissolved oxygen depletion, and primary production. Breaches in

the old Waddell dam, approximately 50 meters wide and 400 meters apart,

allows some mixing of water in this area with the rest of the reservoir however,

the area between the old Waddell dam and the CAP towers may be sufficiently

separated from the rest of the lacustrine zone to have unique water quality

characteristics. This area may have the greatest effect on the quality of water

leaving the reservoir and entering the CAP canal.

Sampling Sites

I established four sampling sites within Lake Pleasant (“A”, “B”, “C”, and

“D”; Fig 2-2), chosen according to the idealized model of reservoir zonation from

upstream to downstream of reservoir as proposed by Thornton, Kimmel, and

Payne (1990). Locations were determined with a Global Positioning System

(GPS) unit. Site A (33o 50’ 57” N and 112o 16’ 18” W) was closest to incoming

CAP water. Site B (33o 51’ 04 N and 112o 17” W) was between the New and Old

Waddell Dams. Site C (33o 51’ 26” N and 112o 16’ 21” W) was about 3 km north

of the old dam and Site D (33o 52’ 20” N and 112o 16’ 11” W) was farthest north

from the CAP inlet and the site most influenced by water entering from the Agua

Fria River. (Fig. 2-2).

22

Five additional sampling sites were established within the CAP canal. The

sites, including approximate distance downstream from Lake Pleasant, were;

Waddell forebay (0 km), 99th Ave (6 km), Scottsdale water treatment plant (45

km), granite reef dam (70 km), and Mesa water treatment plant (78 km)

(Fig. 2-3).

Field Data Collection

Lake Pleasant Samples were collected at each of the four sites every 2 weeks when the

reservoir was stratified (May – November) and monthly when it was de-stratified

(December – April) from May 1996 to March 1998. When the reservoir was

thermally stratified, samples were collected 0.5 m below the surface, immediately

above the thermocline, and 1.0 m above the sediment. When the reservoir was

not thermally stratified samples were collected 0.5 m below the surface, at the

mid-point of the water column, and 1.0 m above the sediment.

Water samples were collected in a 2.2-L Van Dorn-style sample bottle and

transferred to 2, 500-mL, and 1, 100-mL plastic bottles (Nalgene Corp). One of

the 500-mL bottles contained 2 mL of sulfuric acid for preservation of ammonia-

N, nitrate-N, and total phosphorous. The other 500-mL sample was used for

phytoplankton identification and enumeration and contained 25 mL of

formaldehyde. Samples collected for analysis of orthophosphate were field

filtered using a 0.45 µm cellulose acetate sterile syringe filter and a sterile 100-

23

mL syringe and stored in a 100-mL bottle. All samples were kept on ice for

transport to the laboratory. Dissolved oxygen, pH, temperature, specific

conductance, and turbidity levels were recorded through the water column at

each of the 4 sites during every sampling trip using a HydroLab Surveyor 3 data

recorder and sonde (HydroLab Corp).

CAP Canal

Each of the 5 CAP canal sites was sampled approximately every 14 days

when water from Lake Pleasant was the primary source (May – November) and

monthly when Colorado River water directly from Lake Havasu was the

predominant source in the CAP canal (December – April). Samples were

collected in the CAP canal for nutrient analyses in the same manner as those

collected from Lake Pleasant. Water samples collected in 1-L glass amber

bottles for MIB and geosmin analysis were kept on ice for transport back to the

University of Arizona. Periphyton was collected from the sides of the canal at a

depth of 0.5 m. The area scraped was measured and the sample diluted with

250 mL of distilled water and 12 mL of formaldehyde.

24

Sediment Mesocosm Experiment

Sediment samples were collected at sites B and D on 9/11/96 using an

Ekman Grab and placed in 2, 5 gallon stainless steel containers fitted with lids for

transport back to the lab where 3 L of sediment from each site were placed in 4

(8 total), 20 L, polycarbonate Nalgene™ containers. Fifteen liters of water

collected from the hypolimnion of Lake Pleasant was added to each sample

respectively (e.g., sediment collected from site B had water added to it from site

B etc.) (Fig. 2-4). Each container was wrapped in black plastic so that no light

could penetrate. The water and sediment in the containers were allowed to settle

for 24 hours after which time 2 containers from each site were sealed with

polycarbonate lids that had septa affixed to them and the remaining 2 containers

for each site were fitted with lids that had 1.0 cm holes drilled into them. All of

the containers were placed in a 1.6 m diameter X 90 cm tall fiberglass tank filled

with tap water to within 2.0 cm of the surface of each container (Fig. 2-5).

Circulation around the containers was provided by a 0.5 horsepower, 120 volt

end suction centrifugal pump that led to a 0.75 horsepower 115 volt water chiller

that maintained the water temperature at approximately 15o C.

The 4 containers that had the septa attached were sealed around the

edge of the lid with silicone. Water samples were obtained with a hypodermic

syringe and needle inserted through the septa. This allowed analysis of the

water while exposing it to a minimal amount of atmospheric air.

25

The remaining 4 containers had 4.0 mm tubing run into them with a 5.0 X

2.5 cm air diffuser attached to one end and a 2.5 horsepower regenerative

blower attached to the other. In-line air flow meters were attached to the tubing

and the flow was kept at a constant 2.0 L/minute. The diffuser was at an

approximate mid-point in each container so that a minimal amount of sediment

was disturbed.

The 8 containers were labeled as: B1; sediment collected from site B-

aerated, B2; replicate, B3; sediment collected from site B-non-aerated, B4;

replicate, D1; sediment collected from site D-aerated, D2; replicate, D3; sediment

collected from site D-non-aerated, D4; replicate.

I analyzed samples of the overlying water from each container every 7

days for 17 weeks. Sample size collected for each analysis from an individual

container was 150 mL. The volume of water in the containers decreased over

time due to consumption during analysis. The volume of water in Lake Pleasant

also decreases during the summer due to release into the CAP canal. Analysis

included measurements of, dissolved oxygen, temperature, pH, orthophosphate,

total phosphorous, nitrate-N, ammonia-N, and ferrous iron.

26

Laboratory Methods

Water samples were analyzed for NH3-N (Standard Method 417 B), NO3- -

N (Standard Method 4500-NO3-), orthophosphate (Standard Method 4500-P),

total phosphorous (Standard Method 4500-P.5), ferrous iron (Standard Method

3500- Fe D), and total iron (Standard Method 3030 D followed by 3500-Fe D).

Results were determined colorometrically using a Hach DR/890 colorimeter.

Phytoplankton and periphyton were enumerated with a Sedgwick-Rafter

counting chamber with an ocular micrometer (Standard Method 10200 F) on a

calibrated Olympus BH2 phase contrast light microscope (Olympus Corp.) at a

total magnification of 200X. Identifications were made to genus and natural unit

counts were recorded as units/ml for phytoplankton and units/cm2 for periphyton

(Standard Method 10200 F).

MIB and geosmin were determined by GC/MS at the University of

Arizona's Mass Spectrometry Facility. The procedure was:

1) Sorbent and glass fiber filters were washed with 10 mL of CH2CL2 then 3 mL

of methanol.

2) Samples were warmed to room temperature and 100 g of NaCl added to the

1-L sample. Bottles were then capped and rotated to dissolve the NaCl.

Methanol (5-mL) and 10 µL internal standard solution (5 ng/µL 1-chlorodecane in

MeOH) were then added.

27

3) Samples were pulled through the sorbent bed by vacuum. The sample bottle

was rinsed with 5 mL methanol that was then diluted to 50 mL with organic-free

water and pulled through the sorbent bed. The sample volume was recorded.

4) The sorbent bed was eluted with 4 mL of dichloromethane, which was pulled

through a bed of anhydrous sodium sulfate (to remove water). The extract was

concentrated by evaporation under a stream of nitrogen to a volume of ca. 100

µL. Dimethylglutarate was added as a standard to the final concentrate that was

analyzed by GC/MS with selected ion monitoring.

Statistical analyses were performed with JMP 4.0.3 statistical software

(SAS Institute Inc.).

28

CHAPTER 3

RESULTS

Thermal Stratification & Mixing

Thermal stratification was evident at all sites in Lake Pleasant beginning

in May and lasting until mid– to late November of both years. While mean

epilimnetic temperatures were lower in 1996 than 1997 (x = 25.2 and 26.4 oC

respectively, F1,317 = 20.7438, p <0.0001) mean hypolimnetic temperatures were

higher in 1996 (x = 15.8 and 13.5 oC, respectively, F1,578 = 196.4797, p <0.0001).

When the reservoir was not stratified, mean temperatures were lower in 1997

than 1996 (x = 14.25 oC and x = 16.05 oC respectively, F1,912 = 111.6136, p

<0.0001).

Dissolved oxygen (DO) levels were not significantly different among sites

(F3, 1808 = 0.4160, p = 0.7416), but were significantly different among vertical

strata with mean epilimnetic DO levels at 7.5 mg/L, 5.06 mg/L in the metalimnion

and 3.19 mg/L in the hypolimnion (F2, 895 = 433.5019, p <0.0001, Fig. 3-1). The

hypolimnion became anoxic during late summer and early fall 1996.

Mean hypolimnetic dissolved oxygen levels were almost 4 times higher in 1997

(x = 4.6 mg/L) than in 1996 (x = 1.2 mg/L, F1, 578 = 375.1382, p <0.0001).

When the reservoir was stratified, the hypolimnion had significantly lower

mean pH levels (x = 7.94) than shallower strata (epi- and metalimnion x = 8.73

and 8.26 respectively, F1,895 = 938.9329, p <0.0001). Differences in pH values

29

were not significant between sites in either the non-stratified or stratified

condition (F3, 913 = 0.1455, p = 0.9327 and F3, 896 = 0.2682, p = 0.8487

respectively). There were however, significant differences in hypolimnetic pH

values between years with 1996 levels at 7.72 standard units (SU) and 1997

levels higher at 8.04 SU (F1, 578 = 257.8011, p <0.0001).

Turbidity was significantly higher when the reservoir was not stratified than

when thermally stratified (F1,742 = 40.3337, p = 0.0008). When the reservoir was

not stratified, turbidity levels increased with depth (F2, 412 = 23.4621, p <0.0001).

Site B had the highest levels (x = 10.9 NTU) followed by site C (x = 9.12 NTU),

site A (x = 5.85 NTU) and site D (x = 4.17 NTU) (F3, 742 = 18.0206, p <0.0001).

Thermal stratification lasted longer in the fall of 1996 compared to 1997,

especially in the area between the old and new Waddell Dams. In 1997,

de-stratification occurred in October at site B but was evident until late November

during 1996. Mean hypolimnetic dissolved oxygen levels at site B during 1996

and 1997 were 1.19 and 5.28 mg/l respectively. At site B in 1996 the

hypolimnion was often completely anoxic from 16.5 m to the bottom (35 m). At

this site in 1997, the lowest dissolved oxygen level over the sediment was 2.53

mg/l.

30

Lake Pleasant Nutrient Data

Nutrient levels from Lake Pleasant were divided into 3 effects based upon

year (1996 and 1997), site (A, B, C, and D), and layer (epi- meta- and

hypolimnion). Since taste and odor problems primarily occur when water is being

released from Lake Pleasant into the CAP canal, analysis will focus on this

period.

Nitrate and nitrite levels were summed for analysis and showed significant

differences between layers, site, and years as well as for all of the interaction

terms except for site*year (Table 3-1). By layer, the epilimnion had the highest

nitrate levels (x = 0.06 mg/L), followed by the metalimnion (x = 0.05 mg/L) and

hypolimnion (x = 0.03 mg/L) (F2, 103 = 61.7547, p <0.0001). Overall nitrate levels

within Lake Pleasant were higher in 1997 (x = 0.05 mg/L) than in 1996 (x = 0.03

mg/L) (F1, 103 = 70.8291, p <0.0001). There was a significant difference in nitrate

levels for the interaction term layer*site (Table 3-1) and univariate analysis

revealed that the epilimnion of sites A and B collectively had higher levels of

nitrate (x = 0.068 and 0.067 mg/L, respectively) than the epilimnion of sites C and

D collectively (x = 0.052 and 0.048 mg/L respectively) (F1, 103 = 6.9554,

p = 0.0002). Hypolimnetic and metalimnetic nitrate values by site showed similar

trends; site B had the highest levels (x = 0.056 and 0.067 mg/L respectively)

followed by sites C (x = 0.051 and 0.063 mg/L), A (x = 0.047 and 0.061 mg/L),

and D (x = 0.041 and 0.044 mg/L) (F3,103 = 6.2068, p = 0.0004 and F3,103 =

10.9631, p <0.0001 respectively).

31

Table 3-1. Three-way ANOVA testing for effects of site, layer, and year (1996, 1997) on nitrate/nitrite-N levels within Lake Pleasant, Arizona. Effect df SS F-ratio p-value

Site 3,103 0.008399 3.603 0.0051

Layer 2,103 0.030053 12.890 <0.0001

Year 1,103 0.026191 8.024 <0.0001

Site*Year 4,103 0.000723 1.552 0.2160

Site*Layer 5,103 0.005722 6.136 0.0031

Layer*Year 3,103 0.003774 4.403 0.0207

Site*Layer*Year 6,103 0.001787 3.832 0.0533 Residual Error = 0.0800349

Ammonia levels were highest at site B (x = 0.019 mg/L) and lowest at site

D (x = 0.005 mg/L, F3, 103 = 4.0533, p = 0.004) (Table 3-2). The hypolimnion of

all sites had significantly higher levels of ammonia (x = 0.028 mg/L) than did the

meta- (x = 0.005 mg/L) or epilimnion (x = 0.002 mg/L) (F2, 103 = 8.3711,

p = 0.0004). Mean hypolimnetic ammonia levels were higher in 1996 (x = 0.06

mg/L) compared to 1997 (x = 0.01 mg/L) (F 1, 53 = 20.2862, p <0.0001, Fig. 3-2).

32

Table 3-2. Three-way ANOVA testing for effects of site, layer, and year (1996, 1997) on ammonia levels within Lake Pleasant, Arizona. Effect df SS F-ratio p-value

Site 3,103 0.014849 4.478 <0.0001

Layer 2,103 0.030635 14.782 <0.0001

Year 1,103 0.051376 15.494 <0.0001

Site*Year 4,103 0.006623 7.990 0.0006

Site*Layer 5,103 0.003861 4.656 0.0119

Layer*Year 3,103 0.018404 22.201 <0.0001

Site*Layer*Year 6,103 0.002593 6.256 0.0142 Residual Error = 0.113849 Levels of total phosphorous showed no significant differences between

sites (Table 3-3). This trend was carried over to the interaction terms of

site*year, site*layer, and site*layer*year. Mean hypolimnetic total phosphorous

levels were higher in 1996 (x = 0.21 mg/L) than 1997 (x = 0.14 mg/L) (F1,53 =

4.8175, p = 0.03) (Fig. 3-3).

33

Table 3-3. Three-way ANOVA testing for effects of site, layer, and year (1996, 1997) on total phosphorous levels within Lake Pleasant, Arizona. Effect df SS F-ratio p-value

Site 3,103 0.020382 0.8233 0.4426

Layer 2,103 0.065473 5.3033 0.0239

Year 1,103 0.080324 6.8269 0.0147

Site*Year 4,103 0.012819 0.5192 0.5970

Site*Layer 5,103 0.057049 0.9242 0.4697

Layer*Year 3,103 0.204502 16.5647 <0.0001


Dissolved orthophosphate levels followed the same trend as total

phosphorous, with no significant difference between sites or any interaction term

(Table 3-4). The hypolimnetic orthophosphate levels between 1996 (x = 0.18)

and 1997 (x = 0.06) were even more significant than those of total phosphorous

(F1,54 = 22.7184, p <0.0001) (Fig. 3-4). This indicates that most of the

phosphorous in the hypolimnion of Lake Pleasant was in a dissolved and bio-

available form.

34

Table 3-4. Three-way ANOVA testing for effects of site, layer, and year (1996, 1997) on orthophosphate levels within Lake Pleasant, Arizona. Effect df SS F-ratio p-value

Site 3,103 0.011376 0.4607 0.6325

Layer 2,103 0.452959 36.6897 <0.0001

Year 1,103 0.385675 30.5639 <0.0001

Site*Year 4,103 0.004205 0.1703 0.8473

Site*Layer 5,103 0.063453 1.0279 0.4069

Layer*Year 3,103 0.234849 19.0220 <0.0001


Sediment Mesocosm Data

Generally, the aerated mesocosms from both sites had much lower

nutrient levels than the mesocosms that were non-aerated (Table 3-5). The

exception was nitrate-N which had lower levels in the non-aerated mesocosms

(x = 0.01 mg/L) than the aerated mesocosms (x = 0.05). Nitrate is the most

oxidized form of nitrogen and denitrification under anoxic conditions is expected.

35

Table 3-5. Mean nutrient levels (mg/L) in the aerated and non-aerated mesocosms at the end of 17 weeks that contained sediments from sites B and D in Lake Pleasant, Arizona. Analyte Aerated Non-aerated

Orthophosphate 0.04 3.05

Total Phosphorous 0.07 3.39

Ferrous iron 0.05 5.31

Ammonia-N 0.01 3.10

Nitrate-N 0.05 0.01

Rate of dissolved oxygen loss in the non-aerated mesocosms from site B

was over twice that of non-aerated mesocosms from site D (Fig. 3-5). The non-

aerated mesocosms from site B were anoxic during the fifth week and the non-

aerated mesocosms from site D, took 12 weeks to become anoxic (Fig. 3-5).

At the end of 17 weeks, soluble and reduced forms of nutrients (e.g.,

orthophosphate, ammonia-N, and ferrous iron) were much higher in the non-

aerated mesocosms from site B compared to the non-aerated mesocosms from

site D (Table 3-6, Fig. 3-6).

36

Table 3-6. Mean orthophosphate, ammonia-N, and ferrous iron levels (mg/L) in the non-aerated mesocosms from sites B and D at the end of 17 weeks. Nutrient Site B Site D

Orthophosphate 5.45 0.6

Ammonia-N 5.56 0.65

Ferrous iron 10.03 0.6

Non-aerated mesocosms from site B had a higher rate of nutrient release

from the sediment than non-aerated mesocosms from site D. Levels of

orthophosphate in the non-aerated mesocosms from site B, showed a rapid rate

of increase from weeks 1–10 after which, levels of orthophosphate remained

relatively stable (Fig. 3-7). The greatest rate of increase in non-aerated

mesocosms from site D, however, did not occur until weeks 10-13 after which

levels stabilized (Fig. 3-7). Levels of ammonia-N followed the same trend e.g.,

levels in the non-aerated mesocosms from site B increased rapidly between

weeks 1-10 and then tapered but ammonia-N levels in the non-aerated

mesocosms from site D showed the greatest rate of change between weeks 10-

13 (Fig. 3-8). Rate of release of ferrous iron from sediments was similar to

ammonia-N and orthophosphate, however, the greatest rate of change did not

occur until weeks 6-10 in the mesocosm for site B, and weeks 11-13 for site D

(Fig 3-9).

37

CAP Canal Nutrient Data

Nutrient data for water in the CAP canal was divided into 2 effects based

upon site and year (1996, 1997). Analyses focused on periods when water was

being released from Lake Pleasant. For reporting univariate responses, sites

were grouped into 2 categories based upon distance from Lake Pleasant. The 6-

45 km group includes the CAP Canal at 99th Avenue and Scottsdale WTP sites

and the 70-78 km group consisted of the CAP Canal at Granite Reef dam and

Mesa WTP.

During summer 1996, levels of nitrate/nitrite were highest farther away

from Lake Pleasant (70-78 km, x = 0.104 mg/L) compared to sites closer to the

reservoir (6-45 km, x = 0.060 mg/L, F1,32 = 10.2363, p = 0.0039) (Table 3-7). This

trend was still evident in 1997 (6-45 km, x = 0.039 mg/L; 70-78 km, x = 0.058

mg/L, F1,32 = 8.1181, p = 0.0075), however, levels of nitrate/nitrite-N were

significantly lower among all sites during 1997 (x = 0.049 mg/L) as compared to

1996 (x = 0.082 mg/L, F1,63 = 16.3993, p = 0.002, Fig. 3-10).

Table 3-7. Two-way ANOVA testing for effects of site and year (1996, 1997) on nitrate/nitrite-N levels within the CAP canal. Effect df SS F-ratio p-value Site 4,64 0.906977 14.965 <0.0001

Year 1,64 0.418749 27.637 <0.0001

Site*Year 4,64 0.088421 1.4590 0.2247

Residual Error = 0.9697048

38

Spatial trends of ammonia-N were opposite those for nitrate/nitrite during

the summer of 1996 i.e., levels of ammonia-N were higher at sites closer to Lake

Pleasant (6-45 km, x = 0.15 mg/L) than those farther away (40-45 km, x = 0.06

mg/L) (F1,32 = 13.8992, p = 0.0010). This same trend was evident in the summer

of 1997 (6-45 km x = 0.06 mg/L, 40-45 km x = 0.02 mg/L, F1,32 = 12.3682, p =

0.0013). Similar to nitrate/nitrite, levels of ammonia-N were significantly lower at

all sites during 1997 (x = 0.04 mg/L) than 1996 (x = 0.11 mg/L, F1,66 = 22.0415,

p <0.001, Fig. 3-11).

Table 3-8. Two-way ANOVA testing for effects of site and year (1996, 1997) on ammonia-N levels within the CAP canal. Treatment df SS F-ratio p-value

Site 4,66 0.200309 66.451 <0.0001

Year 1,66 0.183651 60.924 <0.0001

Site*Year 4,66 0.060408 40.128 <0.0001


Levels of total phosphorous were much lower during summer of 1997 (x =

0.09 mg/L) compared to summer of 1996 (x = 0.27 mg/L, F1,64 = 135.9570,

p <0.0001, Fig. 3-12). During the summer of 1996, total phosphorous levels

were higher at sites farthest from Lake Pleasant (70-78 km x = 0.31 mg/L)

compared to closer sites (6-45 km x = 0.26 mg/L, F1,31 = 5.1552, p = 0.0342).

39

This trend was not evident during the summer of 1997 and no significant

difference between sites based upon distance from Lake Pleasant was observed

(6-45 km x = 0.09, 70-78 km x = 0.09, F1,32 = 0.0919, p = 0.7636).

Table 3-9. Two-way ANOVA testing for treatment effects on total phosphorous levels within the CAP canal. Treatment df SS F-ratio p-value

Site 4,65 0.200309 66.451 <0.0001

Year 1,65 0.183651 60.924 <0.0001

Site*Year 4,65 0.060408 40.128 <0.0001


In general, orthophosphate levels decreased with increasing distance from

Lake Pleasant during the summer of 1996 (6-45 km, x = 0.16 mg/L, 70-78 km, x

= 0.07 mg/L, F1,29 = 16.1259, p = 0.0005) and 1997 (6-45 km, x = 0.05 mg/L, 70-

78 km, x = 0.03 mg/L, F1,29 = 11.0558, p = 0.0022). Orthophosphate levels were

much lower for all sites in 1997 than 1996 (F1,60 = 38.8166, p <0.001, Fig. 3-13).

40

Table 3-10. Two-Way ANOVA testing for treatment effects on orthophosphate levels within the CAP canal. Treatment df SS F-ratio p-value

Site 4,59 0.081828 25.693 <0.0001

Year 1,59 0.10258 48.313 <0.0001

Site*Year 4,59 0.021045 19.823 <0.0001


Lake Pleasant Phytoplankton

Six divisions of algae were found in the phytoplankton of Lake Pleasant for

1996 and 1997 (Fig. 3-14). Chrysophytes were the most abundant division

followed by chlorophytes, cyanophytes, pyrrophytes, cryptophytes, and

euglenophytes.

Sites B and C had the highest overall mean algal biomass followed by

sites A and D respectively (Fig. 3-15). This same trend was evident during both

1996 and 1997.

When water was being withdrawn from the reservoir (primarily during the

summer and fall), algal numbers decreased with depth at all sites (F1,546 =

83.1356, p <0.0001, Fig. 3-16). This situation was reversed at sites A, B, and C

when water was being pumped into the reservoir, overall algal numbers

increased with depth (F1,285, = 21.4670, p <0.0001, Fig. 3-17). This was noticed

at sites A (Fig. 3-18), B (Fig. 3-19) and C (Fig. 3-20) while site D, the site farthest

41

from the incoming CAP water, had an overall decrease in algal numbers with

depth (Fig. 3-21).

Algal abundance during the period of refilling above and below 10 m at

sites A, B, and C was significantly higher below 10 m (x = 2763 units/mL) than

above 10 m (x = 623 units/mL, F1, 286 = 19.7248, p <0.0001). During this same

period at site D however, there was no difference in algal abundance between

samples collected above or below 10 meters depth (x = 100 and 43 units/mL

respectively, F1, 64 = 3.1630, p = 0.0618).

The division of algae found in highest abundance at sites A, B, and C

below 10 meters during the period of re-filling was (in units/mL) chrysophyta (x =

9439), followed by chlorophyta (x = 4383), pyrrophyta (x = 405), cyanophyta (x =

354), and cryptophyta (x = 105) (Fig. 3-22).

Cyanophyte abundance was highest at site B (x = 373 units/mL) followed

by site A (x = 348 units/mL), site C (x = 293 units/mL), and site D (x = 103

units/mL) (Fig. 3-23). Mean numbers of cyanophytes were significantly greater in

Lake Pleasant during the summer of 1996 (x = 566 units/mL) compared to the

summer of 1997 (x = 152 units/mL, F1, 66 = 16.1537, p <0.0001) (Fig. 3-24).

42

CAP Canal Periphyton

Generally, abundance of periphyton increased with distance from Lake

Pleasant. The exception to this was that periphytic algal abundance was slightly

higher in the Waddell forebay (x = 2805 units/cm2) than it was 6 km down-canal

at the 99th Avenue Bridge (x = 1913 units/cm2, F1, 205 = 11.4276, p = 0.0009).

The remaining sites showed a spatial trend of increasing periphytic biomass with

distance from Lake Pleasant for both years (Table 3-11).

Table 3-11. Overall periphyton abundance (units/cm2) by site including distance from Lake Pleasant. Means are for 1996 and 1997 collectively.

Site Units/cm2 Distance from Lake Pleasant (km)

Waddell Forebay (WFB) 2805 0

CAP at 99th Ave. Bridge 1913 6

CAP at Scottsdale WTP 3205 45

CAP at Granite Reef Dam

4762 70

CAP at Mesa WTP 9098 78

This spatial trend was evident for both years. Examining all sites

collectively however, revealed that 1996 had a significantly higher abundance of

periphyton (x = 6866 units/ cm2) than 1997 (x = 2445 units/cm2, F1, 523 = 10.1582,

p = 0.0015, Fig. 3-25).

43

Periphyton in the CAP canal was comprised of four divisions, chlorophyta,

chrysophyta, cyanophyta and pyrrophyta. During 1996, cyanophytes were the

most abundant member of the periphyton (x = 19,833 units/cm2) followed by

chrysophytes (3377 units/cm2), chlorophytes (2109 units/cm2), and pyrrophytes

(2103 units/cm2) (Fig. 3-26). This hierarchy changed in 1997 with chrysophytes

dominating the periphyton (x = 3132 units/cm2) followed by chlorophytes (2039

units/cm2), cyanophytes (1250 units/cm2), and pyrrophytes (877 units/cm2) (Fig.

3-26).

Spatial and temporal variation in abundance and taxa of periphyton

communities in the CAP canal was large. Cyanobacterial dominance was much

more evident at sites 70-78 km from Lake Pleasant than at sites 6-45 km during

the summer of 1996 (Fig. 3-27). At 6-45 km from Lake Pleasant during the same

period there was no significant difference in abundance between algal divisions

(F3,295 = 1.3736, p = 0.2510). Mean numbers of cyanophytes were over 6 times

greater than the next most abundant division at sites 70-78 km down-canal

during the summer of 1996. Chrysophytes were the most abundant division

found in the periphyton during the summer of 1997, however, there was a much

more equitable distribution among all algal divisions in 1997 compared to 1996.

Periphytic cyanophytes consisted of 5 genera all of which are capable of

producing tastes or odors. In order of abundance these were Lyngbya (x =

17,601 units/cm2), Anabaena (x = 3691 units/cm2), Oscillatoria (x = 3205

44

units/cm2), Phormidium (x = 2387 units/cm2), and Schizothrix (x = 290

units/cm2).

When water was being released from Lake Pleasant into the CAP canal,

periphytic cyanophytes were significantly more abundant at all sites in 1996 than

in 1997 (F1,111 = 9.1036, p = 0.0032). This difference was most pronounced with

increasing distance from Lake Pleasant and the largest change was at sites 70-

78 km down-canal compared to sites 0-45 km (F1,60 = 5.6637, p = 0.0206 and

F1,51, p = 0.0996 respectively) (Figs. 3-28 and 3-29). Cyanophyte abundance at

sites 0-45 km down-canal between 1996 and 1997 was 4503 and 1120 units/cm2

respectively while sites between 70-78 km dropped from 28,156 (1996) to 1335

units/cm2 (1997).

Analysis of MIB and Geosmin in the CAP Canal

Levels of 2-methylisoborneol (MIB) increased with distance from Lake

Pleasant while water from the reservoir was released into the CAP canal

(Fig. 3-30). Levels of MIB were much higher at sites 70-78 km down-canal

compared to sites 0-45 km down-canal (x = 5.52 and 1.68 ng/L respectively, F1,75

= 11.3902, p = 0.0012, Fig. 3-31).

Levels of MIB were much higher in 1996 than in 1997 (F1,75 = 5.3585, p =

0.0234, Fig. 3-32). The biggest difference was at sites 70-78 km from Lake

Pleasant (x = 9.46 ng/L in 1996 and x = 2.67 ng/L in 1997) (Fig. 3-33).

45

Relatively low levels at sites 0-45 km remained unchanged between years with

the mean going from 1.81 ng/L in 1996 to 1.56 ng/L in 1997 (Fig. 3-33).

Overall, levels of geosmin in the CAP canal for both years were lower than

those for MIB (x = 1.19 and 3.39 ng/L respectively) and like MIB, levels of

geosmin decreased with distance from Lake Pleasant (Fig 3-34). Levels of

geosmin did not significantly decrease from 1996 to 1997 (F1, 75 = 0.7263, p =

0.3968). While there was no statistical difference in levels of geosmin between

years, the mean did decrease from 2.50 ng/L in 1996 to 1.51 ng/L in 1997 in

those areas most affected by tastes and odors (e.g., sites 70-78 kilometers from

Lake Pleasant, Fig. 3-35). This difference may represent a significant increase in

water quality to managers, utilities, and consumers.

Relation of Cyanophytes to MIB/Geosmin Levels in the CAP Canal

The majority of taste and odor complaints historically have occurred when

water from Lake Pleasant was being released into the CAP canal. I will focus on

this period only. Because species of Phormidium and Schizothrix were observed

in the periphyton only 5 times, and the mean abundance of each was relatively

low (x = 2387, and 290 units/cm2, respectively), these species are excluded from

this analysis. This leaves 3 taxa of cyanophytes commonly found in the

periphyton of the CAP canal that were analyzed for correlations to MIB and

geosmin; Anabaena, Lyngbya, and Oscillatoria. Because of the apparent

differences in MIB, geosmin, and periphytic cyanophyte levels between 1996 and

1997, each species of cyanophyte is analyzed for these years separately. These

46

data should be interpreted carefully because each genera existed in a matrix of

other potential taste and odor causing taxa within the periphytic community, each

of which are able to produce differing levels of MIB or geosmin depending upon

individual environmental rates of production. Therefore, it is possible that genera

found in low abundance could have produced larger levels of either geosmin or

MIB than those found in higher numbers.

Abundance of Anabaena showed a more positive correlation to geosmin

(R = 0.81) than MIB (R = 0.66) during 1996 (Fig. 3-36). For 1997, numbers of

Anabaena showed no significant correlation to geosmin (R = 0.40) and an

inverse correlation to MIB (R = -0.46, Fig 3-37). The lack of correlation between

Anabaena and geosmin or MIB during 1997 could be due to significantly lower

values for 1997 than 1996. Numbers of Anabaena dropped from 6058 units/cm2

during 1996 to 1482 units/cm2 in 1997 while levels of MIB and geosmin similarly

decreased. Another explanation could be that Anabaena did not have optimum

environmental conditions for the production of taste and odor causing

compounds during 1997.

Abundance of Oscillatoria showed a positive correlation to both MIB (R =

0.89) and geosmin (R = 0.74) during 1996 (Fig. 3-38). Abundance of Oscillatoria

was not correlated to levels of MIB (R = 0.32) or geosmin (-0.41) during 1997

(Fig. 3-39). The lack of correlation between Oscillatoria and MIB and geosmin

during 1997 may be due to environmental conditions not conducive to the

47

production of either compound during 1997. Mean numbers of Oscillatoria

dropped from 5934 units/cm2 in 1996 to 227 units/cm2 in 1997.

There was a positive correlation between amounts of periphytic Lyngbya.

and MIB (R = 0.91, Fig. 3-40) during 1996. This correlation decreased

dramatically during 1997 (R = 0.18, Fig. 3-41). The correlation between Lyngbya

and geosmin was not as pronounced as MIB during 1996 (R = 0.52, Fig. 3-40)

and did not decrease as dramatically during 1997 (R = 0.43, Fig. 3-41).

During 1996, Lyngbya and Anabaena were most closely correlated to

levels of MIB and geosmin, respectively (Table 3-12). During 1997 however,

there were no significant correlations between cyanophyte abundance and MIB

or geosmin.

Table 3-12. Mean numbers of periphytic cyanophytes by year and their correlation to taste and odor producing compounds. Species by Year Mean Units/cm2 Correlation to

MIB (R) Correlation to Geosmin (R)

1996 Anabaena 6058 0.66 0.81 Lyngbya 41,128 0.91 0.52 Oscillatoria 5934 0.89 0.74 1997 Anabaena 1482 -0.46 0.40 Lyngbya 1493 0.18 0.43 Oscillatoria 227 0.32 -0.41

48

Principal Component Analysis of Lake Pleasant Hypolimnetic Conditions and MIB, Geosmin, and Periphyton within the CAP Canal

In order to better view the high-dimensional nature of all the variables

simultaneously, principal component analysis (PCA) was performed on the data

from Lake Pleasant simultaneously with data from the CAP canal. Among Lake

Pleasant sites, site D is lower in nutrients (i.e. N and P) than sites A, B, or C, so

this site was excluded from the PCA analyses. MIB, geosmin, and periphytic

cyanobacterial numbers were much lower closer to Lake Pleasant (0-45 km) than

areas farther removed (70-78 km) therefore, the 0-45 km group was excluded

from PCA analyses. This was done in order to answer the question "what

conditions (if any) within Lake Pleasant contribute most to periphytic

cyanobacterial growth and subsequent MIB/geosmin production within areas of

the CAP canal where taste and odor problems were most pronounced?" PCA

allowed me to determine maximum variability in the data and what the most

important gradients were. I performed standardized principal component

analysis in which the mean was subtracted from the data and divided by the

standard deviation. This sets the centroid of the data cloud to zero and the

standard deviation of all variables to one. This is an eigenanalysis of the

correlation matrix where the covariance of the standardized variables equals the

correlation. The Gabriel (1971) bi-plots associated with each PCA reveal

correlations among chosen variables by examination of the principal component

rays. These rays are orthogonal to one another in the original high dimensional

49

space that defines all of the variables, but as this space becomes forced to

approximate fewer dimensions, it may become evident that not all of the rays are

truly orthogonal. When the higher dimensions are reduced, the correlation

between all variables, even those originally thought to be orthogonal, come

closer together. Those becoming the closest have the greatest correlation.

Variables from the hypolimnion of Lake Pleasant include total

phosphorous ("P"), nitrogen (NO3-N + NH3-N labeled as "N"), and dissolved

oxygen ("D.O."), those from the CAP canal include MIB, geosmin and periphytic

cyanobacteria density ("#/cm2").

For 1996, there was a significant correlation between MIB, total

phosphorous, and nitrogen, with geosmin showing less correlation to both

nutrients (Fig. 3-42). Dissolved oxygen and both N and P levels from the

hypolimnion of Lake Pleasant were inversely correlated. There was also an

inverse correlation between MIB levels within the canal and dissolved oxygen

levels within the hypolimnion of Lake Pleasant. While geosmin had some

relation to hypolimnetic nutrients and MIB, the correlation was less apparent.

The principal component rays for both MIB and geosmin are relatively short

indicating a large degree of variance for 1996.

For 1997, the correlation among nutrient levels from the hypolimnion of

Lake Pleasant and MIB/geosmin production within the CAP canal were less

evident (Fig. 3-43). There was an inverse correlation between dissolved oxygen

and MIB, geosmin, and total phosphorous, but this was not true for nitrogen,

50

which now shows a positive relationship with dissolved oxygen. The only clear

correlation for 1997 was the inverse relationship between dissolved oxygen

within the hypolimnion of Lake Pleasant and MIB and geosmin levels within the

CAP canal. Dissolved oxygen accounted for 45.4 and 41.3% of the total

variation within the data clouds for 1996 and 1997, respectively.

Analyzing the site with the highest hypolimnetic nutrient levels (site B) with

the MIB, geosmin, and periphytic cyanobacterial numbers within the CAP canal

reveals a strong correlation between cyanobacterial numbers and both MIB and

geosmin during 1996 (Fig. 3-44). There was an inverse correlation among these

variables and dissolved oxygen levels. This would indicate that the lower the

dissolved oxygen levels within the hypolimnion of site B, the higher the periphytic

cyanobacterial numbers and MIB/geosmin levels within the CAP canal at those

areas most affected by taste and odor problems.

Analyzing the same sites and variables for 1997 did not show any

correlation and the principal component rays were nearly orthogonal to one

another (Fig. 3-45). Dissolved oxygen levels at site B were higher in summer

1997 than summer 1996 (x = 1.19 and 5.28 mg/l respectively. F1,156 = 178.1413,

p <0.0001). There was an almost completely random scatter of data points

within the cloud. One interpretation of PCA data for 1997 is to say that

conditions within the hypolimnion of site B had no apparent correlation to

numbers of periphytic cyanobacteria or MIB/geosmin levels within those areas of

the CAP that historically had the worst taste and odor problems.

51

CHAPTER 4

DISCUSSION

The correlation between anoxia and nutrient levels within the hypolimnion

of Lake Pleasant and the abundance of periphytic cyanobacteria and

MIB/geosmin production in the CAP canal may be the result of a causal relation.

I propose that nutrients are released from the sediment of Lake Pleasant during

periods of anoxia within the hypolimnion, and when this nutrient-rich water is

released into the CAP canal, it promotes the growth of periphytic taste and odor

causing organisms within the canal. What is less evident is why areas closest to

the reservoir exhibit less severe taste and odor problems and support fewer

periphytic cyanobacteria than areas farther down-canal. This pattern holds even

when there is some detectable level of MIB and geosmin production within Lake

Pleasant (personal observation). I believe that most of the MIB and geosmin

produced within Lake Pleasant was degraded in the turbulent conditions of the

released water and that taste and odor problems farther down-canal were the

result of increased local periphytic cyanobacterial growth. This explanation does

not diminish the role of conditions within Lake Pleasant as the principle cause of

MIB or geosmin production within the CAP canal. My data suggest that the

relationship between MIB and geosmin within the CAP canal is not a direct result

of MIB or geosmin produced within Lake Pleasant. A generalized model of

MIB/geosmin production within the CAP canal is:

52

1) Increased sedimentation of material (mostly periphytic algae from the sides of

the CAP canal upstream of Lake Pleasant) occurs between the old and new

Waddell dams during annual re-filling of Lake Pleasant with CAP canal water.

The lacustrine area between the dams has become the most nutrient rich and

productive zone in the reservoir. Additionally, most of the nutrients found

between the dams at depth during stratification, are in a bioavailable form for

algal growth.

2) Under prolonged anoxia in the hypolimnion, deposited organic material

releases nutrients (especially reduced forms of nitrogen and phosphorous) at a

faster rate than do sediments in other parts of the reservoir.

3) These nutrients accumulate within the hypolimnion. If water is released into

the CAP canal from the top gate of the release tower, the hypolimnion remains

undisturbed for long periods and this stability leads to further nutrient

accumulation within the hypolimnion.

4) Geosmin or MIB formed within Lake Pleasant may be quickly degraded in the

turbulent release water. This may explain why taste and odor has never been a

significant problem at those water treatment plants closest to the reservoir.

Taste and odor problems increase linearly away from Lake Pleasant as a result

of increased periphytic cyanobacterial biomass, which in turn produces MIB or

geosmin.

53

5) Release of nutrient-rich water from the hypolimnion into the CAP canal leads

to the proliferation of taste and odor causing periphytic cyanobacteria within the

canal, especially in areas 70 km or more away from Lake Pleasant.

The linear increase in periphytic cyanobacteria in the CAP canal moving

away from Lake Pleasant may be due to dampening of hydraulic disturbance of

periphyton with greater distance from the site of water release. Many

cyanophytes are not adapted to the turbulent flow found at sites closer to the

reservoir. During 1996, chlorophytes (mostly Cladophora.) and pennate diatoms

were dominant in the CAP canal until 70 km down-canal from Lake Pleasant,

where cyanobacteria began to dominate. During 1997, densities of cyanophytes

were much lower than in 1996 at all reaches of the CAP canal as it crossed the

Phoenix Valley. On average, flow decreases by 400 cfs between areas of the

CAP canal closest to Lake Pleasant and areas 70-78 km away where

cyanobacteria had begun to dominate during 1996 (pers. comm. Tim Kacerak,

Central Arizona Water Conservation District). The higher flows at sites closest to

Lake Pleasant in 1996 may have favored species (e.g., Cladophora, pennate

diatoms) that were adapted to faster-flowing water. Cyanophytes (e.g., Lyngbya,

Anabaena, Oscillatoria) that could not survive in high flow became dominant only

when flow decreased enough to allow establishment.

Tilmans' (1985) resource-ratio theory states that exploitative competition

among taxa with different optimal nutrient ratios will cause changes in plant

community structure. This theory was originally constructed for phytoplankton,

54

and not until recently has it been applied to benthic algae (Bothwell 1983, Stelzer

& Lamberti 2000). Periphytic communities in the southwestern U.S. may be N

limited at ambient levels of 50-90 µg NO3-N L-1 (Grimm & Fisher, 1986). Based

on the Redfield (1958) ratio, Lake Pleasant would be considered N limited with

an average N:P ratio for both years of 9.5:1. This is based upon molecular weight

ratios of NO3-N + NH3-N and total phosphorous levels. Redfield ratios from the

hypolimnion of Lake Pleasant for 1996 and 1997 reveal that N was less limiting in

1997 (N:P = 11.7:1) than in 1996 (N:P = 6:1). Stelzer and Lamberti (2000) found

a strong correlation between intracellular lotic periphyton N:P and N:P of

dissolved nutrients in the ambient stream water. This may mean that the

composition of periphytic communities is determined largely by N:P ratios in the

water. Peterson and Grimm (1992) observed dominance by cyanophytes in

streams that had low N:P ratios because of the ability of cyanophytes to fix

atmospheric N2.

I believe that nutrient ratios alone may be insufficient for identifying limiting

nutrients, and should not be used without quantifying the total nutrient

concentration (TNC). Overall periphyton production may not be as affected by

the N:P ratio as by TNC (Bothwell, 1983). I found that within the CAP canal,

there were differences in both overall periphyton abundance (based upon

numbers/cm2) and assemblage (based upon dominant divisions) between 1996

and 1997. Hypolimnetic TNC (NO3 + NH3 + total P) in Lake Pleasant for 1997

(0.19 mg/L) was less than half of the mean during 1996 (0.32 mg/L)

55

(F1,89 = 142.9567, p <0.0001). Decreased anoxia within the hypolimnion during

1997 as compared to 1996 may have inhibited nutrient release from sediments,

especially in those areas shown to have the greatest amount of nutrient release

during anoxia. I believe that withdrawal of water from the hypolimnion of Lake

Pleasant for delivery to the CAP canal should occur as early as possible during

the season when stratification occurs in order to lower the TNC loading as well

as increase the N:P ratio of water delivered to the CAP canal. This may result in

decreased periphyton abundance and shift periphyton community structure away

from taste and odor-causing organisms (e.g., cyanobacteria) and toward

chlorophytes and diatoms.

56

CHAPTER 5

CONCLUSIONS

I believe that reservoir hypolimnetic withdrawal from Lake Pleasant may

be an effective management tool in controlling nutrient loading and alleviating the

growth of taste and odor causing organisms in those areas of the CAP canal

receiving this released water. This does not mean that hypolimnetic withdrawal

will alleviate taste and odor problems in receiving waters of other reservoirs.

Lake Pleasant is unique for at least 2 reasons.

1) On a year-to-year basis, most of the water enters directly into the lacustrine

zone. This differs from the model proposed by Thornton, Kimmel, and Payne

(1990). In their model, most of the water enters via a river and is released from

the lacustrine zone whereas in Lake Pleasant, water enters and is released from

the same zone.

2) The old Waddell dam serves as a "baffle" for in-coming CAP water during

periods of re-filling and this enhances sedimentation between the old and new

Waddell dams. The CAP canal typically has a low amount of suspended solids

because it emanates from another reservoir (Lake Havasu) and has

sedimentation basins along its length prior to Lake Pleasant. Most of the

suspended solids in the CAP canal are dislodged periphyton from the sides of

the canal and while these numbers may be relatively low, if the majority of them

57

accumulate in a relatively small area (between the 2 dams), it can create

sediments that are different than those found in other areas of the reservoir.

The goal of hypolimnetic withdrawal in Lake Pleasant was not to increase

dissolved oxygen levels throughout the entire reservoir. In most large reservoirs,

without the addition of expensive artificial aeration, this objective is infeasible.

Rather, the goal was two-fold:

1) Increase dissolved oxygen levels over sediments between the 2 dams which

have been proven to contribute the most nutrients to water during periods of

anoxia and,

2) Decrease the length of time these sediments were exposed to anoxic

conditions if the first goal fails.

The hypolimnion of Lake Pleasant has experienced periods of anoxia

since 1996-97 (unpublished data), but anoxia has not been as severe or lasted

as long since water has been released from the lower gates almost exclusively.

Dissolved oxygen depletion within the hypolimnion of thermally stratified

reservoirs is common, however, biologically and chemically there is a large

difference between dissolved oxygen levels of 0.5 and 0.1 mg/L, especially as it

applies to reduction and nutrients and their release from sediment. Generally,

ferric iron (Fe+++) will reduce to soluble ferrous iron (Fe++) only at dissolved

oxygen levels of 0.1 mg/L or less. At this point when phosphorous will lose its

normally close association with iron and solubilize from the sediment and

accumulate within the hypolimnion. The response of periphyton communities in

58

the CAP canal was predicted from resource-ratio theory in that as the N:P ratio

became higher, due to less phosphorous released from Lake Pleasant, any

exploitative competition by species capable of N2 fixation (e.g., cyanobacteria)

was decreased which lead to dominance by chlorophytes and diatoms. Of

course, resource-ratio theory and its use as a management tool are only useful if

total nutrient concentrations are taken into consideration. The management plan

in the CAP canal and Lake Pleasant was to not only change the N:P ratio but

also to lower the total nutrient concentration. I propose that even very subtle

changes of management strategies in reservoirs can change the amount and

type of nutrients released to receiving waters, which may have profound effects

upon not only problems with tastes and odors but issues such as disinfection by-

products, algal toxins, and biodiversity as well. The cost associated with

releasing water from only the lower gates of Lake Pleasant was virtually, nothing.

Since this recommendation was made and its implementation, the taste and odor

problems in the CAP canal have been practically eliminated resulting in

substantial capital savings for municipalities using this water.

59

Figu

re 1

-1. A

gen

eral

ized

mod

el o

f res

ervo

ir zo

natio

n fro

m ri

ver t

o da

m a

s pr

opos

ed

by T

horn

ton,

Kim

mel

, and

Pay

ne (1

990)

.

60

Figu

re 2

-1. L

ake

Ple

asan

t ope

ratio

nal d

ata

show

ing

rela

tions

hip

betw

een

the

old

and

new

Wad

dell

Dam

s

61

Figure 2-2. Sampling Sites within Lake Pleasant, Arizona.

62

Figu

re 2

-3. S

ampl

ing

site

s w

ithin

the

CA

P c

anal

sho

win

g ap

prox

imat

e di

stan

ces

from

Lak

e P

leas

ant.

63

Figure 2-4. Image of sediment from Lake Pleasant, Arizona being placed in polycarbonate containers.

Sediment from site B is on the left and sediment from site D on the right.

64

Figure 2-5. Image of mesocosms in the fiberglass container that was used as a recirculating water bath.

65

Figure 3-1. Mean dissolved oxygen levels (mg/L) by stratified layer in Lake Pleasant, Arizona.

Hypolim nion

Metalimnion

Epilimnion

Laye

r

0 1 2 3 4 5 6 7 8Mean D.O. (mg/L)

66

Figure 3-2. One-way analysis of hypolimnetic ammonia-N levels (mg/L) in Lake Pleasant, Arizona by year. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group.

Amm

onia

-N

0

0.05

0.1

0.15

0.2

1996 1997

Year

Summary of Fit Rsquare 0.280549 Adj Rsquare 0.266714 Root Mean Square Error 0.036197 Mean of Response 0.02763 Observations (or Sum Wgts) 54 Analysis of Variance Source Sum of

Squares Mean Square F Ratio Prob > F

Year 0.02656761 0.026568 20.2774 <0.0001 Error 0.06813098 0.001310 C. Total 0.09469859 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95% 1996 26 0.056550 0.00809 0.04031 0.07279 1997 28 0.010618 0.00621 -0.0018 0.02307 Std Error uses a pooled estimate of error variance

67

Figure 3-3. One-way analysis of hypolimnetic total phosphorous levels (mg/L) in Lake Pleasant, Arizona by year. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group.

Tota

l P

0

0.1

0.2

0.3

0.4

0.5

0.6

1996 1997

Year

Summary of Fit Rsquare 0.112322Adj Rsquare 0.088962Root Mean Square Error 0.109752Mean of Response 0.165875Observations (or Sum Wgts) 54 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Prob > FYear 1 0.05791838 0.057918 4.8083 0.0345Error 52 0.45772600 0.012045C. Total 53 0.51564437 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95%1996 26 0.215000 0.02834 0.15763 0.272371997 28 0.136400 0.02195 0.09196 0.18084Std Error uses a pooled estimate of error variance

68

Figure 3-4. One-way analysis of hypolimnetic orthophosphate levels (mg/L) in Lake Pleasant, Arizona by year. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group.

O

rtho-

P

0

0.1

0.2

0.3

0.4

0.5

1996 1997

Year

Summary of Fit Rsquare 0.299935Adj Rsquare 0.286727Root Mean Square Error 0.094604Mean of Response 0.105273Observations (or Sum Wgts) 55 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Prob > FYear 1 0.20322746 0.203227 22.7073 <.0001Error 53 0.47434345 0.008950C. Total 54 0.67757091 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95%1996 27 0.182619 0.02064 0.14121 0.224031997 28 0.057500 0.01622 0.02496 0.09004Std Error uses a pooled estimate of error variance

69

Figure 3-5. Rates of dissolved oxygen depletion in non-aerated mesocosms containing sediments collected from sites B and D in Lake Pleasant, Arizona.

0

0.5

1

1.5

2

2.5

D.O

.

0 5 10 15Week

B

0

0.5

1

1.5

2

2.5

D.O

.

0 5 10 15Week

D

70

Figure 3-6. Mean orthophosphate, ammonia-N, and ferrous iron levels (mg/L) in the non-aerated mesocosms from sites B and D at the end of 17 weeks.

0

2

4

6

8

10

12

Sediment Mesocosm Results for Sites B and D Non-Aerated

10.03 0.6

5.45 0.65

5.56 0.63

B D

Mean Ferrous Iron (mg/L)

Mean Ortho P (mg/L)

Mean Ammonia-Nitrogen (mg/L)

71

Figure 3-7. Rate of orthophosphate (mg/L) release from sediments in non-aerated mesocosms from sites B and D.

24

68

10121416

2

468

10

121416

BD

Wee

k by

Site

0 1 2 3 4 5 6 7 8 9 10Mean(Ortho-P)

72

Figure 3-8. Rate of ammonia-N (mg/L) release from sediments in non-aerated mesocosms from sites B and D.

24

68

10121416

2

468

10

121416

BD

Wee

k by

Site

0 1 2 3 4 5 6 7 8 9 10Mean(Ortho-P)

73

Figure 3-9. Rate of ferrous iron (mg/L) release from sediments in non-aerated mesocosms from sites B and D.

2468

10121416

2468

10121416

BD

Wee

k by

Site

0 5 10 15 20Mean(Ferrous Iron)

74

Figure 3-10. One-way analysis of nitrate/nitrite-N Levels (mg/L) in the CAP canal by year. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group

Nitr

ate/

Nitr

ite-N

0

0.05

0.1

0.15

1996 1997

Year

Summary of Fit Rsquare 0.21748Adj Rsquare 0.204217Root Mean Square Error 0.031267Mean of Response 0.063115Observations (or Sum Wgts) 64 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Prob > FYear 1 0.01603006 0.016030 16.3974 0.0002Error 62 0.05767813 0.000978C. Total 63 0.07370820 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95%1996 32 0.081923 0.00613 0.06965 0.094191997 32 0.049143 0.00529 0.03857 0.05972Std Error uses a pooled estimate of error variance

75

Figure 3-11. One-way analysis of ammonia-N levels (mg/L) in the CAP canal by year. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group.

Amm

onia

0

0.05

0.1

0.15

0.2

0.25

0.3

1996 1997

Year


76

Figure 3-12. One-way analysis of total-P levels (mg/L) in the CAP canal by year. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group.

T

otal

-P

0

0.1

0.2

0.3

0.4

0.5

1996 1997

Year


77

Figure 3-13. One-way analysis of orthophosphate levels (mg/L) in the CAP canal by year. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group.

Orth

o-P

0

0.05

0.1

0.15

0.2

0.25

0.3

1996 1997

Year


78

Figure 3-14. Mean numbers of algae by division observed in Lake Pleasant, Arizona during 1996 and 1997.

Chlo ro phyta

Cyan ophyta

Chryso phyta

Pyrrop hyta

Crypto phyta

Eugle nop hyta

0 200 400 600 800 100 0 120 0 Mean (U nits /m l)

Division Number Mean Std Error Lower 95% Upper 95%Chlorophyta 198 682.97 156.03 376.7 989.2Chrysophyta 201 1241.92 154.86 938.0 1545.9Cryptophyta 70 46.81 262.41 -468.3 561.9Cyanophyta 194 282.34 157.63 -27.1 591.7Euglenophyta 11 19.36 661.96 -1280.0 1318.7Pyrrophyta 160 260.43 173.57 -80.3 601.1

79

Figure 3-15. Mean numbers of phytoplankton (in units/mL) by site in Lake Pleasant for 1996 and 1997.

D

C

B

A

Site

0 100 200 300 400 500 600 700 800 900 1000 1100Mean(Units/ml)

Site Number Mean Std Error Lower 95% Upper 95%A 212 390.25 151.75 92.39 688.1B 219 1010.06 149.30 717.01 1303.1C 206 720.26 153.94 418.10 1022.4D 197 164.85 157.42 -144.14 473.8

80

Figure 3-16. Bivariate fit of depth (m) by units/ml while withdrawing water from Lake Pleasant, Arizona during 1996 and 1997.

-60

-50

-40

-30

-20

-10

0

Dep

th (m

)

0 1000 2000 3000 4000Units/ml

Linear Fit Linear Fit Depth (m) = -19.76264 + 0.0132913 Units/ml Summary of Fit RSquare 0.132353RSquare Adj 0.130761Root Mean Square Error 14.65224Mean of Response -16.1768Observations (or Sum Wgts) 547 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Model 1 17848.25 17848.2 83.1356 Error 545 117005.11 214.7 Prob > F C. Total 546 134853.36 <.0001

81

Figure 3-17. Bivariate fit of algal units/mL by depth (m) while pumping water into Lake Pleasant, Arizona during 1996 and 1997.

-50

-40

-30

-20

-10

0

Dep

th (m

)

0 10000 20000Units/ml

Linear Fit Linear Fit Depth (m) = -17.01583 - 0.0011781 Units/ml Summary of Fit RSquare 0.070047RSquare Adj 0.066784Root Mean Square Error 15.84388Mean of Response -18.4Observations (or Sum Wgts) 287 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Model 1 5388.823 5388.82 21.4670 Error 285 71543.097 251.03 Prob > F C. Total 286 76931.920 <.0001

82

Figure 3-18. Bivariate fit of algal units/mL by depth (m) at site A while pumping water into Lake Pleasant, Arizona during 1996 and 1997.

-50

-40

-30

-20

-10

0

Dep

th

0 1000 2000 3000 4000 5000 6000 7000 8000Units/ml

Linear Fit Linear Fit Depth = -17.46802 - 0.0047047 Units/ml Summary of Fit RSquare 0.080071RSquare Adj 0.067967Root Mean Square Error 17.07819Mean of Response -19.9705Observations (or Sum Wgts) 78 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Model 1 1929.393 1929.39 6.6151 Error 76 22166.509 291.66 Prob > F C. Total 77 24095.902 0.0121

83

Figure 3-19. Bivariate fit of algal units/mL by depth at site B while pumping water into Lake Pleasant, Arizona during 1996 and 1997.

-40

-30

-20

-10

0

Dep

th

0 10000 20000Units/ml


84

Figure 3-20. Bivariate fit of algal units/mL by depth at site C while pumping water into Lake Pleasant, Arizona during 1996 and 1997.

-50

-40

-30

-20

-10

0

Dep

th

0 10000 20000Units/ml


85

Figure 3-21. Bivariate fit of units/mL by depth at site D while pumping water into Lake Pleasant, Arizona during 1996 and 1997.

-50

-40

-30

-20

-10

0

Dep

th

0 100 200 300 400 500 600Units/ml

Linear Fit Linear Fit Depth = -21.57742 + 0.0556009 Units/ml Summary of Fit RSquare 0.128409RSquare Adj 0.114574Root Mean Square Error 15.50459Mean of Response -16.7769Observations (or Sum Wgts) 65 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Model 1 2231.229 2231.23 9.2816 Error 63 15144.707 240.39 Prob > F C. Total 64 17375.935 0.0034

86

Figure 3-22. Divisions of algae (in units/mL) found below 10 meters depth at sites A, B, and C during the period of re-filling.

Chlorophyta

Cyanophyta

Chrysophyta

Pyrrophyta

Cryptophyta

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000Mean(Units/ml)

87

Figure 3-23. Cyanophyte abundance in Lake Pleasant, Arizona by site during the summers of 1996 and 1997.

0

100

200

300

400

Mea

n(U

nits

/ml)

A B C D

Site

88

Figure 3-24. One-way analysis of cyanophyte abundance (units/mL) during the summers of 1996 and 1997 in Lake Pleasant, Arizona. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group

Uni

ts/m

l

0

1000

2000

1996 1997

Year

Summary of Fit Rsquare 0.199051Adj Rsquare 0.186729Root Mean Square Error 323.2651Mean of Response 226.597Observations (or Sum Wgts) 67 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Prob > FYear 1 1688069.6 1688070 16.1537 0.0002Error 65 6792522.6 104500C. Total 66 8480592.1 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95%1996 32 566.417 93.319 380.05 752.791997 35 152.455 43.589 65.40 239.51Std Error uses a pooled estimate of error variance

89

Figure 3-25. One-way analysis of periphyton abundance (units/cm2) for all sites in the CAP canal during 1996 and 1997. Blue lines represent the standard deviation from the mean at a 95% confidence interval.

Uni

ts/c

m2

0

50000

100000

150000

200000

250000

300000

1996 1997

Year

Summary of Fit Rsquare 0.019089Adj Rsquare 0.01721Root Mean Square Error 15817.42Mean of Response 4461.49Observations (or Sum Wgts) 524 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Prob > FYear 1 2541499212 2.5415e+9 10.1582 0.0015Error 522 1.306e+11 250190684C. Total 523 1.33141e11 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95%1996 239 6866.42 1023.1 4856.4 8876.41997 285 2444.72 936.9 604.1 4285.4Std Error uses a pooled estimate of error variance

90

Figure 3-26. Abundance of algal divisions found within the periphyton of the CAP canal during the summers of 1996 and 1997.

Cyanophyta

Chrysophyta

Chlorophyta

Pyrrophyta

Cyanophyta

Chrysophyta

Chlorophyta

Pyrrophyta

1996

1997

0 10000 20000Mean(Units/cm2)

91

Figure 3-27. Divisions of algae by distance from Lake Pleasant, Arizona during the summer of 1996.

Cyanophyta

Chrysophyta

Chlorophyta

Pyrrophyta

Cyanophyta

Chrysophyta

Chlorophyta

Pyrrophyta

6 - 4

570

- 78

Div

isio

n by

Dis

tanc

e fro

m L

ake

Ple

asan

t (km

)

0 5000 10000 15000 20000 25000 30000Mean(Units/cm2)

92

Figure 3-28. One-way analysis of numbers of periphytic cyanophytes by year in the CAP canal at 70-78 km from Lake Pleasant, Arizona. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group

Uni

ts/c

m2

0

50000

100000

150000

200000

250000

300000

1996 1997

Year

Summary of Fit Rsquare 0.088963Adj Rsquare 0.073255Root Mean Square Error 43038.49Mean of Response 16980.5Observations (or Sum Wgts) 60 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Prob > FYear 1 1.04909e10 1.0491e10 5.6637 0.0206Error 58 1.07434e11 1.85231e9C. Total 59 1.17925e11 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95%1996 35 28156.0 7274.8 13594 427181997 25 1334.8 8607.7 -15895 18565Std Error uses a pooled estimate of error variance

93

Figure 3-29. One-way analysis of numbers of periphytic cyanophytes by year in the CAP canal at 0-45 km from Lake Pleasant, Arizona. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group

Uni

ts/c

m2

0

10000

20000

30000

40000

50000

1996 1997

Year

Summary of Fit Rsquare 0.053304Adj Rsquare 0.03437Root Mean Square Error 6858.744Mean of Response 2397.308Observations (or Sum Wgts) 52 Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Prob > FYear 1 132437765 132437765 2.8153 0.0996Error 50 2352118658 47042373C. Total 51 2484556423 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95%1996 25 4500.53 1573.5 1340.1 7661.01997 27 1186.36 1194.0 -1211.8 3584.5Std Error uses a pooled estimate of error variance

94

Figure 3-30. Mean levels of 2-methylisoborneol in the CAP canal by distance from Lake Pleasant, Arizona during periods of release for 1996 and 1997 collectively.

00

06

45

70

78

Km

's F

rom

Lak

e P

leas

ant

0 1 2 3 4 5 6 7Mean MIB (ng/l)

95

Figure 3-31. One-way analysis of mean MIB levels (ng/L) by distance from Lake Pleasant, Arizona during times of release for 1996 and 1997 collectively. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group.

Mea

n M

IB (n

g/l)

0

5

10

15

20

25

30

0 - 45 70 - 78

Distance from Lake Pleasant (km)

Summary of Fit Rsquare 0.13339Adj Rsquare 0.121679Root Mean Square Error 4.871177Mean of Response 3.244079Observations (or Sum Wgts) 76 Analysis of Variance Source DF Sum of

SquaresMean

SquareF Ratio Prob > F

Distance from Lake Pleasant (km)

1 270.2705 270.270 11.3902 0.0012

Error 74 1755.8994 23.728 C. Total 75 2026.1698 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95%0 - 45 36 1.67889 0.72615 0.2320 3.125870 - 78 40 5.51613 0.87489 3.7729 7.2594Std Error uses a pooled estimate of error variance

96

Figure 3-32. One-way analysis of MIB levels by year (1996, 1997) for all sites in the CAP canal. The horizontal line across each means diamond represents the group mean and the vertical span of each diamond represents the 95% confidence interval for each group.

Mea

n M

IB (n

g/l)

0

5

10

15

20

25

30

1996 1997

Year

Summary of Fit Rsquare 0.067522Adj Rsquare 0.054921Root Mean Square Error 5.052907Mean of Response 3.244079Observations (or Sum Wgts)

76

Analysis of Variance Source DF Sum of Squares Mean Square F Ratio Prob > FYear 1 136.8119 136.812 5.3585 0.0234Error 74 1889.3579 25.532 C. Total 75 2026.1698 Means for Oneway Anova Level Number Mean Std Error Lower 95% Upper 95%1996 34 4.73529 0.86657 3.0086 6.46201997 42 2.03690 0.77968 0.4834 3.5905Std Error uses a pooled estimate of error variance

97

Figure 3-33. Mean levels of MIB by distance from Lake Pleasant, Arizona during periods of release into the CAP canal during 1996 and 1997.

0 - 45

70 - 78

0 - 45

70 - 78

1996

1997

0 1 2 3 4 5 6 7 8 9 10 11 Mean MIB (ng/l)

98

Figure 3-34. Mean levels of geosmin in the CAP canal by distance from Lake Pleasant, Arizona during periods of release for 1996 and 1997 collectively.

00

06

45

70

78

Km

's F

rom

Lak

e P

leas

ant

.0 .5 1.0 1.5 2.0 2.5Mean Geosmin (ng/l)

99

Figure 3-35. Mean levels of geosmin by distance from Lake Pleasant (km's) during periods of release into the CAP canal during 1996 and 1997.

0 - 45

70 - 78

0 - 45

70 - 78

1996

1997

.0 .5 1.0 1.5 2.0 2.5 Mean Geosmin (ng/l)

100

Figure 3-36. Correlations between numbers of Anabaena (units/cm2) to levels of MIB and geosmin (ng/L) in the CAP canal during 1996. Multivariate Correlations Units/cm2 Mean MIB

(ng/l)Mean geosmin (ng/l)

Units/cm2 1.0000 0.6611 0.8058 Mean MIB (ng/l) 0.6611 1.0000 0.7086 Mean geosmin (ng/l)

0.8058 0.7086 1.0000

Scatterplot Matrix

05000

10000150002000025000

05

1015202530

2

4

6

8

10

Units/cm2

05000 15000 25000

Mean MIB (ng/l)

0 5 10 15 20 25 30

Mean geosmin (ng/l)

2 4 6 8 10

101

Figure 3-37. Correlations between numbers of Anabaena (units/cm2) to levels of MIB and geosmin (ng/L) in the CAP canal during 1997. Multivariate Correlations Units/cm2 Mean MIB (ng/l) Mean geosmin

(ng/l) Units/cm2 1.0000 -0.4636 0.3962 Mean MIB (ng/l) -0.4636 1.0000 0.3376 Mean geosmin (ng/l) 0.3962 0.3376 1.0000 Scatterplot Matrix

0

2500

5000

7500

10000

123456

234567

Units/cm2

0 2500 7500

Mean MIB (ng/l)

1 2 3 4 5 6

Mean geosmin (ng/l)

2 3 4 5 6 7

102

Figure 3-38. Correlations between numbers of Oscillatoria (units/cm2) to levels of MIB and geosmin (ng/L) in the CAP canal during 1996. Multivariate Correlations Units/cm2 Mean MIB (ng/l) Mean geosmin (ng/l)Units/cm2 1.0000 0.8899 0.7412Mean MIB (ng/l) 0.8899 1.0000 0.6539Mean geosmin (ng/l) 0.7412 0.6539 1.0000 Scatterplot Matrix

5000

10000

15000

5

10

15

20

25

30

2.5

5

7.5

10

Units/cm2

5000 10000

Mean MIB (ng/l)

5 10 15 20 25 30

Mean geosmin (ng/l)

2.5 5 7.5 10

103

Figure 3-39. Correlations Between Numbers of Oscillatoria (units/cm2) to Levels of MIB and Geosmin (ng/L) in the CAP Canal During 1997. Multivariate Correlations Units/cm2 Mean MIB (ng/l) Mean geosmin (ng/l) Units/cm2 1.0000 0.3226 -0.4067 Mean MIB (ng/l) 0.3226 1.0000 -0.1078 Mean geosmin (ng/l)

-0.4067 -0.1078 1.0000

Scatterplot Matrix

100

200

300

400

500

1

2

3

4

5

0

0.5

1

Units/cm2

100 200 300 400 500

Mean MIB (ng/l)

1 2 3 4 5

Mean geosmin (ng/l)

0 .5 1

104

Figure 3-40. Correlations between numbers of Lyngbya (units/cm2) to levels of MIB and geosmin (ng/L) in the CAP canal during 1996. Multivariate Correlations Units/cm2 Mean MIB (ng/l) Mean geosmin (ng/l)Units/cm2 1.0000 0.9119 0.5221Mean MIB (ng/l) 0.9119 1.0000 0.7388Mean geosmin (ng/l)

0.5221 0.7388 1.0000

Scatterplot Matrix

0

50000

100000

150000

200000

250000

300000

0

5

10

15

20

25

30

0

2

4

6

8

10

Units/cm2

0 100000 250000

Mean MIB (ng/l)

0 5 10 15 20 25 30

Mean geosmin (ng/l)

0 2 4 6 8 10

105

Figure 3-41. Correlations between numbers of Lyngbya (units/cm2) to levels of MIB and geosmin (ng/L) in the CAP canal during 1997. Multivariate Correlations Units/cm2 Mean MIB (ng/l) Mean geosmin (ng/l)Units/cm2 1.0000 0.1853 0.4349Mean MIB (ng/l) 0.1853 1.0000 0.2031Mean geosmin (ng/l)

0.4349 0.2031 1.0000

Scatterplot Matrix

500 1000 1500 2000 2500 3000

1 2 3 4 5 6

0

2 3

5

7

Units/cm2

500 1500 2500

Mean MIB (ng/l)

1 2 3 4 5 6

Mean geosmin (ng/l)

0 1 2 3 4 5 6 7

106

Figure 3-42. Principal component analysis of nutrient and dissolved oxygen data from the hypolimnion of Lake Pleasant, Arizona and MIB/geosmin data from 70-78 km down-canal during 1996.

D.O.

PN

MIBGeosmin

x

y

z

Principal Components EigenValue Percent Cum Percent

2.2695 45.391 45.3911.7580 35.160 80.5500.7309 14.617 95.1680.2339 4.679 99.8460.0077 0.154 100.000

Eigenvectors D.O. -0.41280 0.09699 0.90314 0.04966 0.04538 P 0.64283 -0.06435 0.26385 0.01632 0.71607 N 0.63296 -0.06534 0.32874 0.04692 -0.69629 MIB 0.10132 0.69924 0.01092 -0.70740 -0.01602 Geosmin 0.07391 0.70231 -0.08085 0.70331 0.01051

107

Figure 3-43. Principal component analysis of nutrient and dissolved oxygen data from the hypolimnion of Lake Pleasant, Arizona and MIB/geosmin data from 70-78 km down-canal during 1997.

D.O.

P

N

MIB

Geosmin

x

y

z


2.0665 41.330 41.3301.0071 20.142 61.4710.7440 14.880 76.3520.7349 14.698 91.0490.4475 8.951 100.000

Eigenvectors D.O. -0.49375 0.03727 0.28993 0.67799 0.45945 P 0.34140 0.72941 -0.06904 0.47438 -0.34874 N -0.35736 0.68278 0.04272 -0.54168 0.33295 MIB 0.44340 0.01640 0.87893 -0.13182 0.11505 Geosmin 0.56156 0.01089 -0.36991 0.06709 0.73702

108

Figure 3-44. Principal component analysis of site B dissolved oxygen levels, MIB/geosmin and periphyton growth in the CAP canal at 70-78 km down-canal from Lake Pleasant, Arizona during 1996.

D.O.

#/cm2

MIB

Geosmin

x

y

z


1.8574 46.436 46.4360.9496 23.740 70.1760.9240 23.099 93.2750.2690 6.725 100.000

Eigenvectors D.O. -0.26519 0.94268 -0.14872 0.13750#/cm2 0.33117 0.26258 0.88230 -0.20718MIB 0.67379 0.06719 -0.10177 0.72879Geosmin 0.60498 0.19465 -0.43482 -0.63799

109

Figure 3-45. Principal component analysis of site B dissolved oxygen levels, MIB/geosmin and periphyton growth in the CAP canal at 70-78 km down-canal from Lake Pleasant, Arizona during 1997.

D.O.

#/cm2

MIB

Geosmin

x

y

z


1.4875 37.189 37.1891.0000 25.000 62.1890.9651 24.128 86.3170.5473 13.683 100.000

Eigenvectors D.O. -0.00000 1.00000 0.00000 -0.00000#/cm2 0.68684 0.00000 0.14782 0.71162MIB 0.67765 -0.00000 0.22372 -0.70053Geosmin -0.26276 0.00000 0.96338 0.05349

110

APPENDIX A

DIGITAL IMAGES

111

Digital image 1. CAP inlet towers in relation to the new Waddell Dam in Lake Pleasant, Arizona.

.

112

Digital image 2. CAP inlet towers showing the top gate exposed.

113

Digital image 3. The old Waddell Dam exposed during a time of low water level.

114

Digital image 4. View looking north toward the breach in the old Waddell Dam

115

Digital image 5. View looking south showing the breach in the old Waddell Dam in relation to the CAP inlet towers and the new Waddell Dam.

116

Digital image 6. The Waddell dam forebay from which water in the CAP canal enters Lake Pleasant, or water from Lake Pleasant is released back into the CAP canal.

117

Digital image 7. View looking east at the CAP canal near Granite Reef Dam.

118

Digital image 8. The CAP canal near the city of Mesa water treatment plant intake.

119

Digital image 9. Image of Anabaena, a potential taste and odor causing cyanophtye commonly found growing periphytically on the sides of the CAP canal. Magnification = 200 X

120

Digital image 10. Image of Lyngbya, a potential taste and odor causing cyanophtye commonly found growing periphytically on the sides of the CAP canal. Magnification = 200X

121

Digital image 11. Image of Oscillatoria, a potential taste and odor causing cyanophtye commonly found growing periphytically on the sides of the CAP canal. Magnification = 200X

122

Digital Image 12. Image of the chrysophyte Cocconeis and Gomphonema growing epiphytically on the chlorophyte Cladophora. None of these genera produce tastes or odors and were commonly found in the periphyton of the CAP canal during 1997. Magnification = 250X

123

LITERATURE CITED

American Public Health Association (APHA), American Water Works Association and Water Environment Federation. 1995. Standard Methods for the Examination of Water and Wastewater, 19th Edition, American Water Works Association, Water Environment Federation, and American Public Health Association, Washington, D.C. Arizona Game and Fish Department. 1990. Phase I: Baseline limnological and fisheries investigation of Lake Pleasant. Final report to U.S.Dept. of Interior Bureau of Reclamation. Berglind, L., H. Holtan, and O.M. Skulberg. 1983. Case studies on off-flavors in some Norwegian lakes. Wat. Sci. Tech. 15: p. 99-209. Bothwell, M. L. 1983. All-weather troughs for periphyton studies. Wat. Rsrch. 17: p. 1735-41. Gabriel, K.R. 1971. The biplot graphical display of matrices with applications to principal components analysis. Biometrika. 58: p. 453-477. Grimm, N.B., and S.G. Fisher. 1986. Nitrogen limitation in a Sonoran desert stream. J. North Am. Benthol. Soc. 5: p. 2-15. Izaguirre, G., C.J. Hwang, S.W. Krasner, and M.J. McGuire. 1982. Geosmin and 2-methylisoborneol from cyanobacteria in three water supply systems. App. and Env. Micro. 43: p. 708-714. Izaguirre, G. 1992. A copper-tolerant Phormidium species from Lake Mathews, California, that produces 2-methylisoborneol and geosmin. Wat. Sci. Tech. 25: p. 217-223. Izaguirre, G., and W.D. Taylor. 1995. Geosmin and 2-methylisoborneol production in a major aqueduct system. Wat. Sci. Tech. 31: p. 41-48. McGuire, M.J., S.W. Krasner, C.J. Hwang, and G. Izaguirre. 1983. An early warning system for detecting earthy-musty odors in reservoirs. Wat. Sci. Tech. 15: p. 267-277. Naes, H., H.C. Utkilen, and A.F. Post. 1988. Factors influencing geosmin production by the cyanobacterium Oscillatoria brevis. Wat. Sci. Tech. 20: p. 125-131.

124

Negoro, T., M. Ando, and N. Ichikawa. 1988. Blue-green algae in Lake Biwa which produce earthy-musty odors. Wat. Sci. Tech. 20: p. 117-123. Nishri, A., J. Imberger, W. Eckert, I. Ostrovsky, and Y. Geifman. 2000. The physical regime and the respective biogeochemical processes in the lower water mass of Lake Kinneret. Limnol. Oceanogr. 45: p. 972-981. Peterson, C.G., and N.B. Grimm. 1992. Temporal variation in enrichment effects during periphyton succession in a nitrogen-limited desert stream ecosystem. J. North Am. Benthol. Soc. 11: p. 20-36. Redfield, A.C. 1958. The biological control of chemical factors in the environment. Ameri. Sci. 46: p. 205-221. Slater, G.P., and V.C. Block. 1983. Isolation and identification of odorous compounds from a lake subject to cyanobacterial blooms. Wat. Sci. Tech. 15: p. 228-240. Stelzer, R.S., and G.A. Lamberti. 2000. Effects of N:P ratio and total nutrient concentration on stream periphyton community structure, biomass, and elemental composition. Limnol. Oceanogr. 46: p. 356-367. Thornton, K.W., B.L. Kimmel and F.E. Payne. Reservoir limnology: Ecological perspectives. American Society of Limnology and Oceanography, Waco, TX. Tilman, D. 1985. The resource ratio hypothesis of plant succession. Amer. Nat. 125: p. 827-852. Yagi, M. M. Kajino, U. Matsuo, K. Ashitani, T. Kita, and T. Nakamura. 1983. Odor problems in Lake Biwa. Wat. Sci. Tech. 15: p. 311-321.

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