Lake Thunderbird algae and water quality 2002 : final report.

              Lake Thunderbird
Algae and Water Quality
2002
for the
Central Oklahoma Master Conservancy District
July 2003
Final Report
Oklahoma Water Resources Board
3800 N. Classen Boulevard
Oklahoma City, OK 73118
Oklahoma Water Resources Board
2
Executive Summary
Chlorophyll-a content, the commonly accepted measure of algae content, was the lowest
in three years of monitoring by the OWRB and well below the goal set in 2000 by the
COMCD and municipalities. Although impressive, Lake Thunderbird continues to be
considered “eutrophic” or having high levels of algal growth. The monitoring years of
2000, 2001 and 2002 show a dramatic reduction of algal growth (Figure 0. 1). The stark
reductions noted imply that in-lake management techniques can be an effective means
of controlling algal growth in Lake Thunderbird.
Figure 0. 1: Percent distribution of trophic state using chlorophyll-a concentration May -
September.
Because abnormal climatic conditions during the spring of 2002 reduced nutrient cycling
within the lake, COMCD should not expect similar chlorophyll-a levels in subsequent
years.
Data was also assessed for algae’s ability to affect water supply, as the organic portions
in algae contribute to the production of disinfection by-products, taste and odor (T&O)
chemicals and toxin production. No clear pattern of algae content and water supply
complaints by City of Norman was seen. The clearest link between lake conditions and
water supply was the concurrence of lake destratification and peak of Norman drinking
water complaints in September. Additional information on the lake and water supply
side is needed to provide a proper evaluation.
Two species of algae identified have the potential to produce toxic chemicals. One
species was only noted in 2001 while the other was present both years. Cell density of
Cylindrospermopsis raciborskii presented a low to moderate risk from direct exposure or
accidental ingestion in 2001 and low risk in 2002. This risk was for recreational
exposure. No evidence of risk was noted for water supply.
2001
23%
46%
31%
Mesotrophic Eutrophic Hypereutrophic
2000
6%
51% 43%
2002
55%
45%
0%
3
Table of Contents
Executive Summary ..........................................................................................................2
Table of Contents ..............................................................................................................3
List of Figures....................................................................................................................4
List of Tables .....................................................................................................................4
Introduction.......................................................................................................................5
Water Quality Evaluation...................................................................................................5
Temperature and Dissolved Oxygen.................................................................................8
Nutrients ..........................................................................................................................10
Algae ...............................................................................................................................15
Chlorophyll-a ...................................................................................................................15
Cell Density .....................................................................................................................18
Biovolume.......................................................................................................................20
Disinfection Byproducts............................................................................................20
Taste and Odor ........................................................................................................21
Toxins.......................................................................................................................23
Summary and Discussion................................................................................................25
Recommendations ..........................................................................................................27
References ......................................................................................................................28
4
List of Figures
Figure 0.1: Percent distribution of trophic state using chlorophyll-a concentration May -
September…………………………………………………………………………………..2
Figure 1: Lake Thunderbird sample sites. ........................................................................6
Figure 2: Temperature and dissolved oxygen profile for a typical eutrophic lake showing
the three distinct layers (epilimnion, metalimnion and hypolimnion). .........................7
Figure 3: 2002 Temperature isopleths for the main body of Lake Thunderbird in degrees
C................................................................................................................................9
Figure 4: 2002 Dissolved oxygen isopleths for the main body of Lake Thunderbird in
mg/L. ........................................................................................................................10
Figure 5: Total dissolved nitrogen species concentrations for Site 1. ............................11
Figure 6: Total dissolved nitrogen species concentrations for Site 2. ............................12
Figure 7: Total dissolved nitrogen species concentrations for Site 4. ............................12
Figure 8: Dissolved ortho-phosphorus concentrations for Site 1....................................13
Figure 9: Dissolved ortho-phosphorus concentrations for Site 2....................................14
Figure 10: Dissolved ortho-phosphorus concentrations for Site 4..................................14
Figure 11: 2001 Chlorophyll-a concentrations for main lake body sites. ........................16
Figure 12: 2002 Chlorophyll-a concentrations for main lake body sites. ........................16
Figure 13: Trophic State using chlorophyll-a concentration for 2000 through 2002
monitoring seasons (May - September). ..................................................................17
Figure 14: 2001 Algae Cell Density................................................................................18
Figure 15: 2002 Algae Cell Density................................................................................19
Figure 16: 2002 Biovolume by site. ................................................................................20
Figure 17: Biovolume of taste and odor algae producing at site 4, 2001. ......................22
Figure 18: Biovolume of taste and odor algae producing at site 4, 2002. ......................22
Figure 19: Cell density of potential toxin producing algae Site 4, 2001..........................24
Figure 20: Cell density of potential toxin producing algae Site 4, 2002..........................25
Figure 21: Percent distribution of trophic state using chlorophyll-a concentration May-
September................................................................................................................26
List of Tables
Table 1: Assessment of human risk to blue-green algae produced toxins. Adapted from
World Health Organization (1998)............................................................................24
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
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Introduction
Lake Thunderbird was constructed by the Bureau of Reclamation and began operation
in 1966. Designated uses of the dam and the impounded water are flood control,
municipal water supply, recreation and fish and wildlife. As a municipal water supply
Lake Thunderbird furnishes raw water for Del City, Midwest City and the City of Norman
under the authority of the COMCD. The Oklahoma Water Resources Board (OWRB)
has provided water quality-based environmental services for the Master Conservancy
District (COMCD) since 2000. The focus of OWRB services is the management of Lake
Thunderbird.
When the OWRB first came aboard in 2000 algae content (as measured by chlorophyll-a
content) was at excessive levels, putting Lake Thunderbird at risk of being placed on
Oklahoma’s 303(d) list. This listing would have required extensive state and local action.
In 2000 the OWRB evaluated lake management practices and facilitated water quality-based
goal setting with the COMCD and its municipal customers. Short-term goals
established were to oxygenate the lake and determine the current capacity of the
reservoir. A long-term goal of reducing summer chlorophyll-a below 20μg/L (the
breaking point for excessive algae growth) was also established (OWRB, 2001). Water
quality monitoring in 2000 confirmed the state’s assessment of excessive algae: over
one-half of the samples were >20 μg/L. Evaluation of lake management practices
concluded that the underpowered aeration system was not oxygenating the lake as
intended and was likely stimulating algae growth. The OWRB recommended
refurbishing or ceasing operation of the aerator for the next year.
For 2001, the COMCD ceased aeration and requested that the OWRB monitor reservoir
water quality and determine lake capacity. 2001 chlorophyll-a data showed a significant
reduction from the previous year with only 31% of the samples greater than 20μg/L
(OWRB, 2002). Cessation of aeration was the primary contributor to the reduction.
Although significant, chlorophyll-a samples still exceeded the 20μg/L level and the lake
bottom lacked oxygen during summer stratification. Conceptual design of a whole lake-mixing
system (to refurbish the current system) was completed; however the cost was
significantly greater than previously estimated. No action was recommended without a
cost effective design to oxygenate the lake. OWRB objectives in 2002 were narrowed to
assisting municipalities in completing a pilot plant study and continuing seasonal water
quality monitoring. Pilot plant testing was delayed until 2003 to allow for a full season of
lake monitoring. Results of routine water quality monitoring have been compiled and
presented in this report. Recommendations for 2003 follow the discussion.
Water Quality Evaluation
Lake Thunderbird was sampled at the sites indicated in Figure 1. Sites 1, 2 and 4
represent the main body of the lake while site 3 represents the Hog Creek arm. Sites 5
and 6 represent the Little River arm of the lake and site 7 represents the Clear Creek
arm. Turbidity, chlorophyll-a, Secchi disk depth, dissolved oxygen, temperature and
oxidation-reduction potential were monitored twice a month from April 22, 2002, through
September 24, 2002, at all sites. Sampling for nutrients (nitrogen and phosphorus
series) occurred three times: April 22, July 15 and September 24. Samples were taken
at the surface and 0.5 meter from the bottom at each site. The diagnostic parameters
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
6
#
Site 6
#
#
#
#
#
#
Site 7
Site 4
Site 3
Site 1
Site 5
Site 2
N
W E
S
Figure 1: Lake Thunderbird sample sites.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
7
for this report are temperature, dissolved oxygen, and dissolved nitrogen, phosphorus
constituents, chlorophyll-a and algae counts. Temperature and dissolved oxygen show
water quality changes and the extent of stratification. Nitrogen and phosphorus are the
primary chemical nutrients for algae growth. Chlorophyll-a serves as an indicator of
algae content while the algae counts serve as direct measures.
Additional parameters were collected during the monitoring period. Surface grab
samples were taken at sites 1,2 and 4 during the 2001 and 2002 monitoring periods and
were sent to a contractor for algae identification (cell density and biovolume) to the
species level as discussed earlier. These parameters have been added to the long-term
database to serve as a diagnostic tool. A brief discussion of lake stratification and its
effects on lake water quality are given before 2002 monitoring data are presented.
In late spring and during summer when temperatures rise, lakes generally stratify
thermally with a warmer, lighter layer of water (epilimnion) overlying a colder, deeper,
and more dense layer of water (hypolimnion). There is usually a transition layer
between the epilimnion and the hypolimnion called the metalimnion or thermocline. The
thermocline isolates the hypolimnion from the epilimnion and the atmosphere (Figure 2).
The water temperature in the metalimnion decreases rapidly with depth. The figure also
shows the depletion of dissolved oxygen in the lower layer of the lake as a result of the
Figure 2: Temperature and dissolved oxygen profile for a typical eutrophic lake showing
the three distinct layers (epilimnion, metalimnion and hypolimnion).
stratification. Decaying organic matter depletes the oxygen in the hypolimnion. Prior to
the onset of stratification, the lake has isothermal conditions throughout the entire depth.
As stratification sets in and strengthens, the epilimnion stays homogenous while the
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
8
metalimnion (often called the “thermocline”) changes radically with depth until the
hypolimnion is reached. This physical structure maintains until surface temperatures
start to decline and epilimnetic temperature match the top of the metalimnion. As
cooling continues the thermocline disappears and fall mixing or “turnover” occurs. Lake
stratification may have a significant effect on water quality by ‘trapping’ nutrients or
chemicals in areas of reduced exchange and water interaction (hypolimnion). This key
feature can have implications for epilimnetic water quality.
Temperature and Dissolved Oxygen
Dissolved oxygen and temperature were used to compare water quality changes and the
extent of lake stratification. Isopleths were prepared to give a three-dimensional picture
of water quality over depth and time. Each line represents a particular temperature or
dissolved oxygen concentration. When the lines are vertical, the dissolved oxygen
and/or temperature are constant throughout the water column, which is completely
mixed at that point in time due to wind or other convective forces. When the lines run
horizontally, a strong temperature (vertical) gradient exists from top to bottom. Strong
vertical temperature gradients indicate stratified water quality conditions. On the
following graphs, Lake Thunderbird’s warmest temperatures are colored dark red. The
red graduates into blue as temperature drops. High oxygen concentrations are colored
blue. The blue graduates into red as the concentration drops to zero.
In 2001 stratification began the beginning of May and ended late September. This was
in contrast to what was seen in 2002 when complete stratification started the end of May
and final destratification the end of September. Unusual climatic features in 2002 can
explain the difference between the two years. On April 22, 2002 the lake was stratified
due to unusually warm weather. Then an unusually cool May caused little heating of the
epilimnion while a strong cold front produced high winds to mix the lake at the end of
May. In short, climatic conditions destratified Lake Thunderbird in late May (Figure 3).
Following these early spring events weather in central Oklahoma was characterized as
cooler than normal, preventing the entire lake (epilimnion and hypolimnion) of Lake
Thunderbird from getting as warm as it was in 2001. Consequently weakening of
stratification occurred later in 2002 than in 2001. The different climatic conditions in
2002 also resulted in a smaller epilimnion and larger hypolimnion in 2002. Although
differences in duration were noted between 2001 and 2002 the magnitude of
stratification was about equal. Strong stratification in 2002 had the largest effect on
water quality by partitioning the hypolimnion from the epilimnion.
Dissolved oxygen at the main lake sites showed a similar pattern to the plots for
temperature for both 2001 and 2002. The key feature for dissolved oxygen is anaerobic
conditions: dissolved oxygen less than 2 mg/L. Low dissolved oxygen is caused by high
organismal (animal and plant) respiration. Bacterial respiration generally depletes
oxygen trapped in the hypolimnion while dead algae feed the bacteria. When anaerobic
conditions are reached at the lake bottom nutrients and other constituents (such as iron
and manganese) are solubulized from the sediment into the water.
In 2001 anaerobic conditions progressed from the deepest site (1) in the beginning of
May towards the shallower sites (5/23/01 at site 2 and 6/1/01at site 4) and extended
from May through September. This fits a pattern of high algae growth in the main lake
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
9
body. The pattern of anaerobic conditions progressing from the deeper sites toward the
shallower sites was not observed in 2002 (Figure 4). Instead, anaerobic conditions
seemed to progress from shallow (started 5/20/02 at site 2 and 6/1/02 at site 4) to deep
(6/8/02 at Site 1). The most likely explanation for the difference between the two years
is the break in stratification noted in late May. This break served to oxygenate the deep
bottom layer of the lake and shorten the duration of anaerobic conditions by one month.
The physical difference between the two years is the most deterministic explanation.
As in 2001, anaerobic conditions eventually encompassed the entire hypolimnion and
portions of the metalimnion in 2002. These low dissolved oxygen levels indicate that
nutrients in the lake sediment dissolve into the hypolimnion. The decreased duration of
anaerobic conditions in 2002 suggest lower dissolved nutrient levels in 2002 compared
to 2001.
Figure 3: 2002 Temperature isopleths for the main body of Lake Thunderbird in
degrees C.
Site 1
-16
-14
-12
-10
-8
-6
-4
-2
0
5/4/02 5/24/02 6/13/02 7/3/02 7/23/02 8/12/02 9/1/02 9/21/02
Site 2
-12
-10
-8
-6
-4
-2
0
5/4/02 5/24/02 6/13/02 7/3/02 7/23/02 8/12/02 9/1/02 9/21/02
Site 4
-10
-8
-6
-4
-2
0
5/4/02 5/24/02 6/13/02 7/3/02 7/23/02 8/12/02 9/1/02 9/21/02
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
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Figure 4: 2002 Dissolved oxygen isopleths for the main body of Lake Thunderbird in
mg/L.
Nutrients
While several measures of nitrogen and phosphorus were made of the water quality
samples taken the dissolved nutrient totals are presented here to yield an estimate of
available nutrients. This indicates the raw materials available for algal growth. High
values in the epilimnion indicate nutrient immediately available for algal growth while
high values in the hypolimnion indicate nutrients available for future algae growth. The
relatively higher dissolved nitrogen values in bottom samples show hypolimnion
accumulation of ammonia. This is to be expected with an anaerobic hypolimnion. The
effect of delayed stratification in 2002 can be shown by the relatively lower maximum
value, 2.6 mg/L, compared to 3.4 mg/L in 2001 (Figure 5).
Site 1
-16
-14
-12
-10
-8
-6
-4
-2
0
5/4/02 5/24/02 6/13/02 7/3/02 7/23/02 8/12/02 9/1/02 9/21/02
Site 2
-12
-10
-8
-6
-4
-2
0
5/4/02 5/24/02 6/13/02 7/3/02 7/23/02 8/12/02 9/1/02 9/21/02
Site 4
-10
-8
-6
-4
-2
0
5/4/02 5/24/02 6/13/02 7/3/02 7/23/02 8/12/02 9/1/02 9/21/02
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
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A close comparison between years for each site and depth showed a key pattern. In
general 2002 dissolved nitrogen levels were comparable to 2001 levels during the first
sample event but then the two years started to diverge. With the exception of the fall
site 1 bottom sample most other samples showed higher levels of dissolved nitrogen in
2002 (Figure 5, Figure 6, Figure 7). Higher epilimnetic dissolved nitrogen suggests
that algae needed less nitrogen for growth: an indicator of phosphorus limitation.
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
01/09/01 04/19/01 07/28/01 11/05/01 02/13/02 05/24/02 09/01/02 12/10/02
Date
mg/L
2001 Surface 2002 Surface 2001 Bottom 2002 Bottom
Figure 5: Total dissolved nitrogen species concentrations for Site 1.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
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0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
01/09/01 04/19/01 07/28/01 11/05/01 02/13/02 05/24/02 09/01/02 12/10/02
Date
mg/L
2001 Surface 2002 Surface 2001 Bottom 2002 Bottom
Figure 6: Total dissolved nitrogen species concentrations for Site 2.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
01/09/01 04/19/01 07/28/01 11/05/01 02/13/02 05/24/02 09/01/02 12/10/02
Date
mg/L
2001 Surface 2002 Surface 2001 Bottom 2002 Bottom
Figure 7: Total dissolved nitrogen species concentrations for Site 4.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
13
Dissolved orthophosphorus is the form of phosphorus most easily used by algae for
growth. As with dissolved nitrogen the relatively higher levels in bottom samples show
the accumulation in the hypolimnion. Anaerobic conditions in the water mediated
release of phosphorus from the sediment. Although both years showed sediment
release of phosphorus, the delay of stratification in 2002 could be shown by the relatively
lower maximum value 0.25 mg/L compared to 0.60 mg/L in 2001(Figure 8).
Aside from this distinct difference of the deep-water samples little year-to-year variation
is noted for the other sites and samples (Figure 9, Figure 10). These indicate utilization
of phosphorus for algal growth. A brief comparison of surface total phosphorus between
years shows lower amounts. All surface samples were above 0.02 mg/L in 2001 while
no sample in 2002 was above 0.02 mg/L.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
01/09/01 04/19/01 07/28/01 11/05/01 02/13/02 05/24/02 09/01/02 12/10/02
Date
mg/L
2001 Surface 2002 Surface 2001 Bottom 2002 Bottom
Figure 8: Dissolved ortho-phosphorus concentrations for Site 1.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
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0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
01/09/01 04/19/01 07/28/01 11/05/01 02/13/02 05/24/02 09/01/02 12/10/02
Date
mg/L
2001 Surface 2002 Surface 2001 Bottom 2002 Bottom
Figure 9: Dissolved ortho-phosphorus concentrations for Site 2.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
01/09/01 04/19/01 07/28/01 11/05/01 02/13/02 05/24/02 09/01/02 12/10/02
Date
mg/L
2001 Surface 2002 Surface 2001 Bottom 2002 Bottom
Figure 10: Dissolved ortho-phosphorus concentrations for Site 4.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
15
Generally, as long as the lake is stratified, surface nutrients are the primary determinant
of algae growth. Stratification conditions were radically different between 2001 and
2002. The delay of stratification in 2002 delayed the duration of anaerobic conditions in
the hypolimnion. Consequently, less phosphorus was released from the sediment into
the water. 2002 nutrient data indicate that phosphorus is the chemical nutrient limiting
algae growth. Dissolved phosphorus serves as an indicator of nutrients available for
growth. When dissolved phosphorus is low total phosphorus can indicate the amount of
algae in the water. These along with the earlier indication of lower dissolved nitrogen use
in 2002 suggest algae levels should be lower in 2002 than in 2001. Chlorophyll-a serves
as a suitable surrogate for direct algae enumeration.
Algae
Several direct and indirect measures are used to indicate algae growth. The most
commonly accepted indirect measure is chlorophyll-a concentration. A more direct
measure of algae growth is the identification and enumeration of species in the algae
community. Perhaps the best measure of algae growth is the determination of primary
production rate. The choice of measure is dependent on the application. In the case of
Lake Thunderbird and the COMCD, the first two measures have the most applicability to
lake management and raw water supply. The use of chlorophyll-a as an indicator of
trophic state in a trophic state index (TSI) allows for quick assessment of water quality
within a lake and across the state. Within the range of TSI for Oklahoma reservoirs
break points have been determined to quantify varying levels of algae production.
Identification of algae density to the species level allows for refinement of the
assessment to estimate impact to raw water supply. For example by identifying species
known to produce objectionable chemicals and estimating organic content the potential
to affect raw water supply can be estimated.
Chlorophyll-a
Chlorophyll-a, the molecule or pigment common to all algae for growth, makes analysis
of its concentration a commonly accepted measure of algae content. In 2001
chlorophyll-a was relatively steady until July when concentration increased into
September (Figure 11). Starting in August chlorophyll-a exceeded the 20 μg/ml goal.
2002 chlorophyll-a showed a pattern of relatively constant concentration while no
sample-exceeded 20μg/ml (Figure 12). By all indications algae growth was
significantly lower in 2002 than any other monitored year. In 2002 the long-term goal of
chlorophyll-a under 20μg/L was achieved.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
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0
5
10
15
20
25
30
35
40
4/12 5/2 5/22 6/11 7/1 7/21 8/10 8/30 9/19
Date
Chl-a (ug/L)
Site 1 Site 2 Site 4 Eutrophic Hypereutrophic
Figure 11: 2001 Chlorophyll-a concentrations for main lake body sites.
0
5
10
15
20
25
30
35
40
4/22 5/6 5/20 6/3 6/17 7/1 7/15 7/29 8/12 8/26 9/9 9/23
Date
Chl-a (ug/L)
Site 1 Site 2 Site 4 Eutrophic Hypereutrophic
Figure 12: 2002 Chlorophyll-a concentrations for main lake body sites.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
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The annual progression of lowered algae growth over the years is most easily expressed
by transforming chlorophyll-a into the three trophic states represented by the red and
blue lines in Figure 13. The red line in Figure 11 and Figure 12 represents the boundary
(at 20 μg/L) between high (eutrophic) and excessive (hypereutrophic) algae growth while
the blue line represents the boundary (7.2 μg/L) between high and lower (mesotrophic)
algal growth. Eutrophic or high algae growth conditions have remained relatively
constant over the three years while hypereutrophic conditions have consistently declined
and mesotrophic conditions consistently increased (Figure 13). In short the quality of
Lake Thunderbird has consistently increased over the last three years. While
chlorophyll-a is a commonly accepted surrogate for algae content surface samples were
taken in 2001 and 2002 as direct measures of algae content. These data are used to
support or refute conclusions based in previous indicators.
0
10
20
30
40
50
60
2000 2001 2002
Percent
Mesotrophic Eutrophic Hypereutrophic
Figure 13: Trophic State using chlorophyll-a concentration for 2000 through 2002
monitoring seasons (May - September).
Algae data are a direct measure of the trophic status and a result of nutrient levels in
Lake Thunderbird. Algae and raw water supply also have a very important relationship
because of the effect compounds created by algae can have on the finished water:
Algae cell contents released into the raw water supply have been documented to affect
the finished drinking water quality whether by increase the level of disinfectant
byproducts (Jack, et. al., 2002), presence of taste and odor compounds (Perrson,
1983) or presence of toxins (Sze, 1986). Lake Thunderbird algae data is presented in
two basic forms: cell density and cellular volume (biovolume). Cell density, the easier
value to determine, is the traditional measure of abundance while biovolume, requiring a
higher level of analysis, is a better measure of cell content. Because of the potential to
estimate impact of algae content to water supply particular attention is given to site 4,
located next to the COMCD raw water intake structure. Algae samples for identification
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
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were taken at the main body sites for both 2001 and 2002. For both 2001 and 2002
algae samples were collected bi-weekly allowing for direct comparison.
Cell Density
In general, cell density was relatively constant over the sample period for both 2001 and
2002 (Figure 14 and Figure 15). This does not match the trends noted for chlorophyll-a
with an increasing trend in 2001 (Figure 11) and relatively flat level in 2002 (Figure 12).
However, the general conclusion comparing chlorophyll-a between years is
corroborated: lower algae content in 2002. Cell density in 2001 varied around the
1,000,000 cells/ml while 2001 density varied around 100,000 cells/ml. Cell counts for
both years were well over 15,000 cells/ml, an indicator of eutrophic or nutrient rich
systems. Hutchinson (1967) describes “eutrophic associations” by the appearance of
the following three species: Aphanizomenon, Anabaena, and Oscillatoria. All three of
these genera occurred in Lake Thunderbird.
1000
10000
100000
1000000
10000000
5/9/01 5/29/01 6/18/01 7/8/01 7/28/01 8/17/01 9/6/01 9/26/01 10/16/01
cells/ml
Site 1 Site 2 Site 4
Figure 14: 2001 Algae Cell Density
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and Water Quality Study 2002 FINAL REPORT
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1000
10000
100000
1000000
10000000
4/14/02 5/4/02 5/24/02 6/13/02 7/3/02 7/23/02 8/12/02 9/1/02 9/21/02 10/11/02
Cells/mL
Site 1 Site 2 Site 4
Figure 15: 2002 Algae Cell Density
As pointed out by Hutchinson, the types of algae can be as important as the amount.
Examination of the algae types showed an abnormal pattern for Oklahoma reservoirs:
blue-green algae throughout the sample season. The generally accepted pattern of
seasonal succession is diatom dominance in the spring followed by dominance of green
algae and finally dominance of blue green algae (Wetzel, 1983). Blue-green algae
dominance throughout the summer season has only been noted in highly eutrophic
Oklahoma reservoirs by the OWRB. In 2001 the primary blue-green species responsible
for overall dominance was Aphanocapsa delicatissima during the beginning of the
sample season with Cylindrospermopsis raciborskii dominating the second half of the
sample season.
In 2002, cell density was again dominated by small unicellular blue-greens with other
divisions represented in varying abundances. Some exceptions were noted. The first
exception occurred at the beginning of the sample season -- all three sites showed the
cryptophytes, miscellaneous microflagellates, chlorophytes, and euglenophytes had
noticeably larger peaks in comparison to the cell density from the rest of the year. The
second noticeable difference was an even larger peak of green algae towards the
beginning of August. Nephroselmis olivacea was the dominant green algae species in
all of these peaks. In 2001, N. olivacea did not even contribute over one percent of the
cell density at any of the three sample sites. This indicates the potential of algae type to
change positively (away from blue-greens) with reduced algal content. While these
results are positive algal biovolume as well as cell density should be examined before
conclusions are drawn.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
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Biovolume
Disinfection Byproducts
Comparing biovolume between the two years showed 2002 to have much higher
biovolume in the spring then in 2001(Figure 16). Interestingly, biovolume for both years
seem to converge in the summer and fall periods. Although cell density counts from
2001 and 2002 showed greatly reduced amounts of algae in 2002 the volume occupied
by algae in the two years seem to have remained the same. This is because algae cells
in 2002 were (on the average) much larger then those in 2001. One conclusion based
on these results is contribution of disinfection byproducts in raw drinking water from
algae should have been about the same in 2002 as in 2001. Examination of biovolume
by species is necessary to compare potential for taste and odor chemical production
between 2001 and 2002.
100,000
1,000,000
10,000,000
100,000,000
4/14 5/4 5/24 6/13 7/3 7/23 8/12 9/1 9/21 10/11
Biovolume (um3/mL)
Site 1 Site 2 Site 4
Figure 16: 2002 Biovolume by site.
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and Water Quality Study 2002 FINAL REPORT
21
Taste and Odor
The most notable difference between cell density and biovolume plots are that blue-greens
were not dominant until the diatoms and dinoflagellates decreased in the
summer. This general pattern occurred in 2001 and 2002 and is closer to the norm for
seasonal succession of algae. The dominant blue-greens were larger, mostly
filamentous forms in comparison to the small, unicellular forms that dominate the
numerical abundance. Blue-green algae have often been recognized as a nuisance in
the drinking waster industry because of the ability of several taxa to produce earthy and
musty smelling compounds. Earthy and musty smells produced by algae are commonly
called taste and odor (T&O) compounds. Geosmin and 2-methyl isoborneol (MIB) are
common T&O compounds that produce musty smells. Aphanizomenon, Microcystis,
Oscillatoria and Anabaena are known geosmin producers (Perrson, 1983) and were
found in Lake Thunderbird. Lyngbya limnetica another cyanophyte in the lake, has also
been known to cause a musty smell in large quantities. Ceratium hirundinella a
dinoflagellate found both years in Lake Thunderbird is known to produce a fishy smell
and bitter taste. The biovolume of the potential taste and odor chemical producers can
serve as indicators of algae contribution to customer complaints regarding finished
drinking water.
Comparing the 2001 reports at site 4 (near the water supply point of diversion) against
total biovolume of algae genera known to produce taste and odor chemicals indicate
potential for T&O reports from June through September; almost the entire sample
season (Figure 17). Ten species of algae were counted distributed in six genera of
potential T&O producers. Fishy smell and bitter taste could be expected from Ceratium
hirundella in June while more traditional T&O complaints such as musty smell are
predicted to predominate July through September due to the presence of Microcystis
aeruginosa, Oscillatoria limnetica and various species of Anabaena. 2002 reports of
T&O algae at Site 4 showed a different distribution of species and amount over time but
indicate the potential for T&O reports from may through September. Compared to 2001
there were one less genus and three less species of potential T&O algae. No new
species of algae were noted in 2002 than were identified in 2001. Of the identified
species the largest difference was for the genus Anabaena and species Ceratium
hirundella. In 2002 Anabaena sp. were noted earlier in the season and at higher levels
than in 2001. Also in 2002 Ceratium hirundella was consistently present from May
through July but at lower levels than the two occasions it was identified in 2001. The
relatively warmer spring season of 2002 may have encouraged earlier growth of
Anabaena while the relatively cooler summer may have extended the growth period of
Ceratium hirundella.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
22
100
1,000
10,000
100,000
1,000,000
10,000,000
4/20 5/4 5/18 6/1 6/15 6/29 7/13 7/27 8/10 8/24 9/7 9/21 10/5
Biovolume (μm^3/ml)
Ceratium hirundinella Anabaena Aphanizomenon
Oscillatoria limnetica Lyngbya sp. Microcystis aeruginosa
Figure 17: Biovolume of taste and odor algae producing at Site 4, 2001.
100
1,000
10,000
100,000
1,000,000
10,000,000
4/20 5/4 5/18 6/1 6/15 6/29 7/13 7/27 8/10 8/24 9/7 9/21 10/5
Date
Biovolume um3/mL
Ceratium Anabaena Aphanizomenon Oscillatoria Lyngbya
Figure 18: Biovolume of taste and odor producing algae at Site 4, 2002.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
23
The purpose of enumerating potential T&O causing species is to relate algae content to
the finished water supply. Understanding algae distribution is a step towards defining
the potential input of T&O chemicals. A measure of T&O quality of the finished product
is also needed to establish a reliable relationship to algae. To date the best measure of
finished water quality is the complaint record maintained by the City of Norman.
Communication with Vernon Campbell of the City of Norman has established that
complaints are due to the quality of water leaving the plant and not due to the distribution
system.
A summary of taste and odor complaints reported to the City of Norman has been
plotted to cross reference to biovolume plots of taste and odor producing algae. During
the 2001 and 2002 sample season Norman received complaints in April of 2001 with a
large peak in August with eight complaints and finally three complaints received in
September (Figure 18). 2002 showed a distinctly different pattern with five complaints
in May, four in June and July, one in August and a large peak of twelve on September.
The water treatment plant superintendent also noted that taste and odor complaints
regularly peak in September almost every year. Although the complaint record
overlapped with the potential for T&O chemical production no clear pattern or
relationship was noted. Recent research in Cheney Reservoir, a water supply for the
City of Wichita, suggested a combined Anabaena and Aphanizomenon biovolume of
300,000 μg/ml as a threshold for an increase of consumer complaints (Smith, et. al.,
2002). Application of this potential threshold to Lake Thunderbird showed no overlap in
2001 and little in 2002. Our initial evaluation does not suggest a determinant factor
between algae content and the quality of water from the treatment plant. Several
analytical and physical factors may obscure any relationship that may exist. Two
physical factors identified were the blending of well water with treated water prior to
distribution and the effect of lake mixing on raw water T&O content. Flow data showed
the amount of lake water reaching customers varied from 95% to 71% in 2001 and 2002.
Varying the percent of treated water would alter concentrations of T&O chemicals in the
distribution system. Mixing of hypolimnetic water into the epilimnion, usually completed
in late September, could account for the consistent peak of complaints noted in
September. While the lake was stratified dying algae cells settled into the hypolimnion.
T&O chemicals released by these dead and dying algae would be stored until the
hypolimnion is eroded in the fall. Two analytical factors identified are the lack of
examination for species level effect and the reliance on customer complaint as the
measure of treatment plant finished water quality. Since general comparisons were not
conclusive the OWRB did not perform species level comparisons. It is possible that this
detailed evaluation would suggest a specific species. Choosing of a more direct
measure of T&O such as taste and odor number, geosmin concentration, MIB
concentration and/or total organic carbon content of water leaving the treatment plant
would enable a more conclusive evaluation.
Toxins
Unfortunately many T&O algae can also produce toxic chemicals. Blue-green algae are
the taxa with the most species documented to produce toxic compounds (Carmicheal,
1985). Microcystis aeruginosa and Cylindrospermopsis raciborskii were the two algae
species identified in collected samples. Microcystis aeruginosa has been documented to
produce a variety of hepatotoxins and was noted in the 2001 but not in 2002.
Cylindrospermopsis raciborskii has been documented to produce a neurotoxin and
cytotoxin (WHO, 1998). Most toxic effects are noted when the particular species is
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
24
present as a scum, indicative of hypereutrophic conditions. No scum formation was
noted in any year the OWRB monitored Lake Thunderbird water quality. The most
common method for toxic effects to be manifested is through direct exposure and NOT
following conventional water plant treatment. The draft guidelines developed by the
World Health Organization (Table 1) assessing relative risk of these toxic chemicals
have been compared against actual levels measured in Lake Thunderbird. Cell
densities showed Microcystis aeruginosa below the low risk level at all times while
Cylindrospermopsis raciborskii was in the low risk level in June and moderate level in
August and September of 2001 (Figure 19). In 2002 only the species
Cylindrospermopsis raciborskii was noted. Cell density fluctuated around the low risk
level from July through September (Figure 20). These risk levels were assessed for
recreational exposure only.
Risk Level Cell density Magnitude of Potential Health Effects
Low 20,000 Short-Term
Moderate 100,000 Short-term and long term
High
Up to millions
(Scum formation)
Poisoning to short term
Table 1: Assessment of human risk to blue-green algae produced toxins. Adapted from
World Health Organization (1998).
100
1,000
10,000
100,000
1,000,000
05/29/01 06/18/01 07/08/01 07/28/01 08/17/01 09/06/01 09/26/01 10/16/01
Cells/mL
Microcystis aeruginosa (colony) Microcystis aeruginosa (single cells) Cylindrospermopsis raciborskii
Figure 19: Cell density of potential toxin producing algae Site 4, 2001.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
25
10
100
1,000
10,000
100,000
1,000,000
05/24/02 06/13/02 07/03/02 07/23/02 08/12/02 09/01/02 09/21/02 10/11/02
Date
Cells/mL
Cylindrospermopsis raciborskii
Figure 20: Cell density of potential toxin producing algae Site 4, 2002.
Over the two-year period that algae identification was performed the presence of toxic
algae seems to have declined. Microcystis aeruginosa, present in 2001 was not
identified in any 2002 samples. Cylindrospermopsis raciborskii was present in both
years but at a significantly lower cell density in 2002. Clearly, the presence of
Cylindrospermopsis raciborskii is disturbing and should bear future investigation. This
species appears to be a newcomer to Oklahoma only reported on one other occasion in
1998 (OWRB, 2002b). In 1998 both Eucha and Spavinaw lakes had this species in the
summer with no subsequent identifications in the following three years: 1999 – 2001. It
is possible that Cylindrospermopsis raciborskii shows an initial peak following
introduction and then declines to more desirable levels.
Summary and Discussion
Monitoring in 2002 showed a set of physical conditions unique to Lake Thunderbird:
abnormal climatic events combined to disrupt stratification and introduce additional
oxygen into the bottom lake layer (hypolimnion). Subsequently the duration of anaerobic
conditions were 1.5 months shorter than in 2001. This shorter period of anaerobic
hypolimnion resulted in less nutrients released from the lake bottom. Nutrient data
suggested lower algae content because of higher amounts of dissolved nitrogen in 2002.
Chlorophyll-a content, the commonly accepted measure of algal content, was the lowest
in OWRB’s three years of monitoring and well below the goal set in 2000 by the COMCD
and municipalities. Although impressive, Lake Thunderbird continues to be considered
“eutrophic” or having high levels of algae growth. The monitoring years of 2000, 2001
and 2002 show a dramatic reduction of algae growth (Figure 21). The stark reductions
noted do imply that in-lake management techniques can be an effect means to control
algal growth in Lake Thunderbird.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
26
Figure 21: Percent distribution of trophic state using chlorophyll-a concentration May-
September.
Because abnormal climatic conditions reduced nutrient cycling within the lake, the
COMCD should not expect similar chlorophyll-a levels subsequent years. However,
2002 monitoring does present a strong argument to evaluate the feasibility of providing
chemical oxidants into the bottom layer of the lake to lower algae growth.
Total algae cell density comparisons confirmed what was suggested by the chlorophyll-a
data: algal cell density was almost ten times less in 2002 than 2001. Algae data was
also evaluated for its ability to affect water supply by examining the biovolume results at
the COMCD point of diversion. Algal biovolume provides an estimate of cellular
contents. Portions of the organic contents contribute to the production of disinfection
byproducts, taste and odor chemicals and toxin production. Comparison of biovolume
suggests about equal contribution towards disinfection byproducts from 2001 and 2002.
Comparison of specific identifications against the complaint record from the City of
Norman did not yield clear pattern. It is possible that short-term storage of dead and
dying algae cells in the hypolimnion released during destratification could account for the
traditional peak of complaints around September. It was also evident that many
complaints were in October or November, after the OWRB’s monitoring period. Two
species of algae identified have the potential to produce toxic chemicals. One species
was only noted in 2001 while the other was present both years. Comparison of cell
density of these species indicated Cylindrospermopsis raciborskii presented a low to
moderate risk in 2001 and low risk in 2002 from direct exposure or accidental ingestion.
Risk was assessed for recreational exposure only. Formation of algae scum in the fall
would indicate a high-risk situation.
2001
23%
46%
31%
Mesotrophic Eutrophic Hypereutrophic
2000
6%
51% 43%
2002
55%
45%
0%
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
27
Recommendations
Determine the feasibility of oxygenating the hypolimnion of Lake
Thunderbird. Concept design of a whole lake mixing device requires a new
compressor and would increase compressor operation and maintenance by a factor of
four. Other options to oxygenate the lake exist such as layered or hypolimnetic aeration.
These and other options should be evaluated for Lake Thunderbird.
Proceed with the pilot plant project. The receipt of algae data has brought the
effect of algae in water supply into tighter focus. More specific data from the
municipalities is needed for an effective evaluation. Addition of test parameters such as
total organic carbon content, Trihalomethane precursor formation potential, haloacetic
acid formation, T&O number, geosmin and 2-methyl isoborneol at Site 4 and the finished
product would provide the necessary data for evaluation. The municipalities have
proposed pilot plant studies to assess economical means to reduce potential impact of
detrimental algae in Lake Thunderbird. This proposal has the potential to provide the
needed data.
Extend water quality monitoring into October and possibly November. This
would allow for monitoring data to overlap municipal complaints better. Chlorophyll-a,
algae identification and basic field parameters are sufficient for extended monitoring.
Engage the Bureau of Reclamation to assess procedures and protocols
necessary to modify the current aeration system. Feasibility results may
indicate a means to meet water quality-based goals with a compressor similar to the
current system. By understanding requirements before action is requested the COMCD
may shorten the time to implementation.
Lake Thunderbird Algae
and Water Quality Study 2002 FINAL REPORT
28
References
Carmichael, W.W., Jones, Cindy L.A., Mahmood, Nik A., Theiss, Winnie C. (1985).
Algal Toxins and Water-Based Diseases. Critical Reviews in Environmental Control 15,
275-313.
Hutchinson, G.E. (1967). Introduction to lake biology and the limnoplankton. A Treatise
on Limnology. Il, 1115.
Jack, J., T. Sellers, P. A. Bukaveckas. (2002). Algal production and trihalomethane
formation potential: an experimental assessment and inter-river comparison. Can. J.
Aquat. Sci. 59: 1882 – 1491.
Oklahoma Water Resources Board (OWRB). (2001). Evaluation of Lake Thunderbird
Water Quality Management Practices for the Central Oklahoma Master Conservancy
District.
Oklahoma Water Resources Board (OWRB). (2002a). Lake Thunderbird Capacity and
Water Quality 2001 for the Central Oklahoma Master Conservancy District.
Oklahoma Water Resources Board (OWRB). (2002b ). Water Quality Evaluation of the
Eucha/Spavinaw Lake System.
Perrson P. E. (1983). Off-flavors in aquatic ecosystems – An Introduction. In: Water
Science Technology 15, pp 1-11.
Smith, V. H., J. Sieber-Denlinger, F. deNoyelles, Jr., S. Campbell, S. Pan, S. J. Randke,
G. T. Blain, V. A. Strasser. (2002). Managing taste and odor problems in a eutrophic
drinking water reservoir. Lake and Reservoir Manage18(4):319-323.
Sze, Philip. (1986). A biology of the algae. 1,24, 179.
Wetzel, Robert G. (1983). Limnology Second Edition. pp 369.
World Health Organization. (1998). Guidelines for Safe Recreational-water
Environments: Coastal and Fresh-waters Draft for Consultation Chapter 7 Freshwater
Algae and Cyanobacteria.