%
Prepared By:
United States Environmental Protection Agency
Great Lakes National Program Office
United States
Environmental Protection
Agency
June 2023
905-R-23-004
Great Lakes „
RESTORATION j
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
ACKNOWLEDGMENTS
This work was supported with Great Lakes Restoration Initiative (GLRI) funding to the U.S.
Environmental Protection Agency (EPA) Great Lakes National Program Office (GLNPO) as part of the
task order Scientific and Technical Support for the Great Lakes National Program Office, with General
Dynamics Information Technology (GDIT), under the direction of Kenneth Klewin, Technical Point of
Contact. The United States Geological Survey (USGS) supported this work via the USGS Great Lakes
Deepwater Program supplemented with GLRI funding through Interagency Agreement DW 014
92453901. Special thanks to the captains and crews of the EPA R/V Lake Guardian and the USGS R/V
Muskie for field support. GLNPO gratefully acknowledges the support of the following team members in
the preparation of this Technical Report:
Affiliation
Team Members
EPA GLNPO
Jeffery May, Ken Klewin
GDIT
Kathleen Marshall, Kenneth Miller
Cover photo: Sunrise from coast of Kelleys Island in Lake Erie by Becky Swora.
Citation: U.S. EPA 2023. Lake Erie Dissolved Oxygen Monitoring Program Technical Report: Dissolved
Oxygen and Temperature Profiles for the Open Waters of the Central Basin of Lake Erie during
Summer/Fall of 2021. EPA 905-R-23-004.
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
TABLE OF CONTENTS
Acknowledgments ii
1. Executive Summary 1
2. Introduction 1
3. Methods 2
4. Quality Assurance and Quality Control 5
5. Results and Discussion 6
6. Comparison to Historical Results 7
7. Conclusions 12
8. References 13
Appendix A - Quality Control Results A-l
Table 1. Acceptance criteria for DO and temperature data 6
Table 2. Mean water temperature (± SD) and DO for each survey in 2021 7
Table 3. Generalized linear model (GLM) results for the relationships between SurveyDay and
hypolimnion temperature, thickness and DO concentration 10
Table 3a. Overall GLM results for 2021 10
Table 3b. GLM fit statistics for 2021 10
Table 3c. GLM estimates of deviations in model intercept used to calculate rate of change
in water temperature, thickness and DO concentrations of the hypolimnion for years
2012-2020 compared to 2021 reference year 11
Table A-l. Quality control (QC) scorecard of 2021 CTD-collected temperature and dissolved oxygen
(DO) data not meeting acceptance criteria A-l
Figure 1. Map of GLNPO DO monitoring stations in the central basin of Lake Erie 3
Figure 2. Example of a temperature and DO depth profile from Lake Erie central basin in late summer.... 3
Figure 3. 2021 station means for hypolimnion DO concentrations in the central basin of Lake Erie 6
Figure 4. Survey mean hypolimnion temperatures in the central basin of Lake Erie from 2012-2021 8
Figure 5. Survey mean hypolimnion thicknesses in the central basin of Lake Erie from 2012-2021 8
Figure 6. Survey mean hypolimnion DO concentrations in the central basin of
Lake Erie from 2012-2021 9
Figure 7. Annual DO depletion rate in the central basin of Lake Erie from 1970-2021 12
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
1. EXECUTIVE SUMMARY
The United States Environmental Protection
Agency (EPA) Great Lakes National Program
Office (GLNPO) Lake Erie Dissolved Oxygen
Monitoring Program annually monitors the
oxygen and temperature profiles at 10 fixed
stations in the central basin of Lake Erie during
the stratified season to assess water quality
trends and measure progress made in achieving
water quality improvements.
During the course of the 2021 sampling season
(June 14 - October 7):
• Seven surveys were conducted during the
2021 field season using the USGS R/V
Muskie.
• Surface water temperatures increased from
17.5 °C to 23.1 °C, while hypolimnion
temperatures increased from 10.91 °C to 15.2
°C.
• Hypolimnion DO concentrations during the
sampling season decreased from
approximately 9.0 mg O2/L to 0.36 mg O2/L.
• Low-oxygen conditions (< 6 mg O2/L)
were first recorded on July 28, 2021 (all
stations).
• Anoxic conditions (< 1 mg O2/L) were first
recorded during the August 24-25, 2021
survey (all stations).
• The annual corrected oxygen depletion rate
was 4.32 mg 02/L/month.
2. INTRODUCTION
Lake Erie has been severely impacted by
excessive anthropogenic loadings of
phosphorous resulting in abundant algal
growth and is a factor that contributes to
dissolved oxygen (DO) depletion in the
bottom waters of the central basin. Total
phosphorus loads to Lake Erie reached their
peak in the late 1960s and early 1970s with
annual loads in excess of 20,000 metric tonnes
per annum (MTA) (Maccoux et al.. 2016). In
1978, Canada and the United States signed an
amendment to the 1972 Great Lakes Water
Quality Agreement (GLWQA) that sought to
reduce total phosphorus loads to Lake Erie to
11,000 MTA. In order to determine if the areal
extent or duration of the oxygen-depleted area
was improving or further deteriorating, annual
monitoring of the water column for thermal
structure and DO concentration was needed
throughout the stratified season. The U.S.
Environmental Protection Agency (EPA)
Great Lakes National Program Office
(GLNPO) established the Lake Erie Dissolved
Oxygen Monitoring Program in 1983. This
program was designed to collect necessary DO
concentration data to calculate an annual
normalized rate of DO depletion in the central
basin of Lake Erie. Additionally, these data
could be used by federal and state water
quality agencies to assess the effectiveness of
phosphorus load reduction programs.
Numerous phosphorus reduction programs were
implemented in support of the GLWQA, and by
the early 1980s, the annual phosphorus load to
Lake Erie had been reduced to near targeted
amounts (Dolan. 1993). Correspondingly, the
load reduction resulted in the decrease of the total
area affected by low oxygenated waters
(Makarewicz and Bertram. 1991). By the mid-
1990s, the total extent of the hypoxic area (DO
levels < 2 mg/L) had decreased in size compared
to observations from previous decades. However,
by the 2000s the annual extent of area affected by
hypoxia had increased, returning to the larger
areal extent seen in the late 1980s (Zhou et al..
2013). The annual average hypoxic area in the
central basin since the early 2000s is
approximately 4,500 km2 (1,737 mi2) (U.S.EPA.
2018a). while the largest hypoxic extent recorded
in the past decade - 8,800 km2 (3,398 mi2) -
occurred in 2012, following the record-setting
algal bloom in 2011 (U.S. EPA. 2018a). Hypoxia
in Lake Erie reduces habitat and food supply for
fish and complicates drinking water treatment
(Rowe et al. 2019).
In 2012, the GLWQA was updated to enhance
water quality programs that ensure the "chemical,
physical and biological integrity" of the Great
Lakes (Canada and United States. 2012). As part
of Annex 4 (Nutrients Annex) of this agreement,
the governments of the United States and Canada
adopted the following Lake Ecosystem Objectives:
• minimize the extent of hypoxic zones in the
waters of the Great Lakes associated with
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
excessive phosphorus loading, with
particular emphasis on Lake Erie;
• maintain the levels of algal biomass below
the level constituting a nuisance condition;
• maintain algal species consistent with
healthy aquatic ecosystems in the nearshore
Waters of the Great Lakes;
• maintain cyanobacteria biomass at levels
that do not produce concentrations of toxins
that pose a threat to human or ecosystem
health in the Waters of the Great Lakes;
• maintain an oligotrophic state, relative algal
biomass, and algal species consistent with
healthy aquatic ecosystems, in the open
waters of Lakes Superior, Michigan, Huron
and Ontario; and
• maintain mesotrophic conditions in the open
waters of the western and central basins of
Lake Erie, and oligotrophic conditions in the
eastern basin of Lake Erie.
GLNPO continues to monitor the thermal
structure and DO concentrations in the central
basin of Lake Erie throughout the stratified
season each year. The ongoing monitoring
ensures that data are available to assess the
objectives put forth in the GLWQA, and also
allow for the evaluation of status and trends over
time. This report summarizes the results of the
2021 Lake Erie Dissolved Oxygen Monitoring
Program surveys and places those results within
the context of historical data, where possible.
3. METHODS
Annually, 10 fixed stations (Figure 1) in the
offshore waters of the central basin are sampled
at approximately 3-week intervals, during the
stratified season (June-October). Sampling
usually begins in early June, when the water
column begins to stratify, or separate, into a
warmer upper layer (epilimnion) and a cooler
bottom layer (hypolimnion) and typically
concludes in late September to mid-October just
before the water column seasonally destratifies,
or "turns over," and assumes a uniform
temperature profile. The EPA R/V Lake
Guardian is used as the sampling platform
whenever scheduling and other operating
constraints permit. In the event that the R/V
Lake Guardian is not available for one or more
scheduled sampling times, or additional surveys
are scheduled, alternate vessel support is used to
conduct the sampling. The USGS R/V Muskie
was used to conduct all seven surveys during
2021.
At each station visit, the thermal structure of the
water column is recorded by an electronic
profiling CTD (Conductivity, Temperature,
Depth (pressure) sensor) while DO
concentrations are measured and recorded by an
additional oxygen sensor integrated into the
CTD instrument package. For 2021, a SeaBird
Scientific SBE 19plus V2 SeaCAT Profiler CTD
was used for collecting water temperature data,
and a SBE43 Dissolved Oxygen Sensor was
used for collecting DO data. The resulting
temperature and DO depth profiles, which
provide a visual display of the thermal structure
and DO content of the water (Figure 2). are used
to calculate the annual DO depletion rate (U.S.
EPA. 2018b).
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
Figure 1. Map of GLNPO DO monitoring stations in the central basin of Lake Erie.
Quality Assurance samples were collected at
two of the 10 stations during each survey and
used to confirm the accuracy of the sensor
measurements. DO measurements from the
sensor are compared to those determined by the
Winkler micro-titration method (U.S. EPA.
2018b) for water samples collected at 2 meters
below the surface and at 1 meter above the lake
bottom. Temperature measurements from the
sensor are compared to surface water
thermometer readings obtained from the hull-
mounted transducer on the research vessel.
10
Q.
U
a
15
20
25
Temperature (deg C)
12 15 1£
21
24
27
30
i
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! 1
t
| |
L- ~ ^—* r
r
r - x" —'"" f
— Temperature
' — Dissolved Oxygen
6 9
Dissolved Oxygen (mg/L)
12
15
Figure 2. Example of a temperature and DO depth profile from Lake Erie central basin in late summer.
After each survey, water temperature and DO
concentration data from the CTDs are averaged
for the epilimnion and hypolimnion. A grand
mean of hypolimnion DO concentration is
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
calculated for each station to generate a map of
bottom DO concentrations for the central basin
of Lake Erie at the time of sampling.
To reduce the amount of inter-annual variability
in DO data from Lake Erie, an annual corrected
oxygen depletion rate is calculated using a
Microsoft Access program
(LakeErieDOv05.mdb). This software
statistically adjusts the data for vertical mixing
and seasonable variability and normalizes it to a
constant temperature and hypolimnion thickness
according to the procedures used by Rosa and
Burns (1987). The resultant or "corrected"
annual rate of DO depletion (mg 02/L/month) is
artificial for any given year but permits the
identification of time trends with more precision.
For comparisons between years, results over a
10-year period (2012-2021) were compared
statistically using a general linear model (GLM)
approach to test whether there is a significant
difference in the relationship between time
(expressed as Julian day minus 150 to place the
y-intercept near the beginning of the sampling
period; referred to as SurveyDay in Table 3) and
either hypolimnion temperature, thickness or
DO concentration (Tables 3a. 3b and 3c). This
approach assumes a constant rate of change per
day in the unadjusted measurements (i.e.,
hypolimnion temperature, thickness and DO)
over the full June to October sampling period
within each year, which differs slightly from the
Rosa and Burns (1987) method that only
assumes a constant rate of change between
sampling events, but not across the entire
sampling period. The GLM model includes a
separate factor for the sampling year, and a
Julian day x year interaction term, which is used
to test whether the rate of change in the
hypolimnion temperature, thickness or DO
varies significantly between years (i.e., whether
the estimated slope varies between years).
Statistical significance of the GLM model tests
was set at alpha=0.05. Statistical analysis was
performed using the GLM procedure in SAS
Version 9.4 (SAS Institute, Cary, NC).
4. QUALITY ASSURANCE
AND QUALITY CONTROL
GLNPO's DO monitoring surveys operate under
an approved Quality Management Plan, a
Quality Assurance Project Plan (QAPP), and
standard operating procedures (U.S. EPA. 2020).
The 2021 surveys operated under Revision 11 of
the QAPP (U.S. EPA. 2018b). The overall data
quality objective for this project is to acquire
measurements of DO and temperature at the
central basin stations in Lake Erie that are
representative of the actual conditions present at
the time of sampling.
Acceptance criteria for DO and temperature
(Table 1) are based on the Relative Percent
Difference (RPD) between two independently
derived measurements. By definition, RPD is
the difference between two measurements
divided by the average of both and expressed
as a percent value.
The accuracy criterion for acceptable DO
measurements is an RPD of 10% between sensor
and averaged Winkler values, or an absolute
difference between measurement methods of 0.5
mg/L when DO concentrations are less than 5
mg/L. A maximum RPD of 2% is the acceptable
accuracy for water temperature. Acceptable
levels of precision are defined as a maximum
difference of 0.2 mg/L between Winkler
replicates and agreement within 5% between
sensor measurements for DO. Acceptable
precision for water temperature was defined as
agreement within 2% between sensor
measurements.
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
5. RESULTS AND
DISCUSSION
Table 1. Acceptance criteria for DO and
temperature data
Parameter
Accuracy
criteria
Precision criteria
Temperature
2% RPD
• 2% between sensor
measurements
Dissolved
oxygen
(> 5 mg/L)
10% RPD
• 0.2 mg/L between
Winkler replicates
• 5% between sensor
measurements
Dissolved
oxygen
(< 5 mg/L)
0.5 mg/L
absolute
difference
For this project, completeness is the measure of
the number of samples obtained compared to the
amount that was expected to be obtained under
normal conditions. The completeness goal is to
obtain DO and temperature profiles within
accuracy and precision limits at 90% of all
designated stations during each survey.
During the first survey (June 14-15, 2021), all
stations were stratified with an average
temperature difference of 6.5 °C between the
epilimnion and hypolimnion layers (Table 2).
Over the sampling season, average temperatures
increased in the epilimnion from 17.5 °C to 23.8
°C and in the hypolimnion from 10.9 °C to 15.2
°C. Average DO concentrations during the
sampling season decreased from 10.0 mg O2/L
to 7.8 mg O2/L in the epilimnion and from 9.0
mg O2/L to 0.36 mg O2/L in the hypolimnion.
Low DO concentrations (< 6 mg O2/L) in the
hypolimnion were detected at all 10 stations
during the July 27-28 cruise. By late August, all
stations had become anoxic (< 1 mg O2/L).
During September and early October all stations
that had a hypolimnion present continued to
experience anoxic conditions (Figure 3).
August 25, 2021
October 7, 2021
Dissolved Oxygen Concentrations
^>6mg/l ^ 4-6 mg/L j 2-4 mg/L ^ 1 2 mg/L 0 0-1 mg/L ( ) No Data
September 9, 2021
September 23, 2021
Figure 3. 2021 station means for hypolimnion DO concentrations in the central basin of Lake Erie.
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
Table 2. Mean water temperature (± SD) and DO for each survey in 2021.
CTD
used
Epilimnion
Hypolimnion
zUzi survey
dates
Stations
(#)
Temperature
(°C)
DO
(mg/L)
Temperature
(°C)
DO
(mg/L)
Thickness
(m)
June 14-15
SBE 19+
10
17.45 + 0.78
10.05+0.27
10.91+0.51
9.00 + 0.39
11.33 + 1.80
June 29-30
SBE 19+
10
19.07 + 0.48
9.51+0.43
11.09 + 0.53
7.31+0.45
5.79 + 2.34
July 27-28
SBE 19+
10
22.00 + 0.51
8.99 + 0.23
11.44 + 0.29
3.17 + 0.52
6.42 ± 0.64
August 24-25
SBE 19+
10
23.81+0.37
8.03 + 0.17
11.81+0.18
0.43 + 0.25
5.54+1.98
September 8-9
SBE 19+
10
22.71+0.49
7.78 + 0.10
12.51+0.32
0.36 + 0.10
4.46+1.40
September 20-21
SBE 19+
7
21.49+1.34
7.96 + 0.33
13.31+0.54
0.38 + 0.21
3.76 + 2.89
October 6-7
SBE 19+
1
19.38
8.48
15.22
0.88
3.52
6. COMPARISON TO
HISTORICAL RESULTS
Throughout the 2021 season, the hypolimnion
temperature was significantly warmer than in
2014, 2016, 2018, and 2019 Qable3c). These
were the coolest years over the 10-year period
(Figure 4). Note that the rate of change in
hypolimnion temperature did not vary
significantly between years (Table 3b); however,
since there is no significant interaction, a
significant intercept (as indicated by a p-value
less than alpha = 0.05 in Table 3c) can be
interpreted as an overall difference between
years.
alpha = 0.05 in Table 3c) can be interpreted as
an overall difference between years.
The corrected annual oxygen depletion rate for
2021 was 4.32 mg C^/L/month (Figure 7). This
is the third highest recorded depletion rate since
1970 and the highest seen since 1986. The last
three surveys in 2021 (early September through
early October) were not included in the oxygen
depletion analysis because the average
hypolimnion DO concentration during the
August 24-25 had already reached anoxic
conditions (0.43 mg/L) and thus additional
survey data are not warranted for this
calculation.
Throughout the 2021 season, the hypolimnion
was significantly thicker than in 2012, 2013, and
2019 (Table 3c). These were the years with the
thinnest hypolimnion over the 10-year period
(Figure 5). Note that the rate of change in
hypolimnion thickness did not vary significantly
between years (Table 3b); however, since there
is no significant interaction, a significant
intercept (as indicated by a p-value less than
alpha = 0.05 in Table 3c) can be interpreted as
an overall difference between years.
Throughout the 2021 season, the hypolimnion
unadjusted DO was significantly lower than
throughout the 2014 season (Figure 6. Table 3c).
Note that the rate of change in hypolimnion
unadjusted DO did not vary significantly
between years (Table 3b); however, since there
is no significant interaction, a significant
intercept (as indicated by a p-value less than
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
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245
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Figure 4. Survey mean hypolimnion temperatures in the central basin of Lake Erie from 2012-2021.
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205 225
Julian Day
245
265
285
Figure 5. Survey mean hypolimnion thicknesses in the central basin of Lake Erie from 2012-2021.
JUNE 2023
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
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Figure 6. Survey mean hypolimnion DO concentrations in the central basin of Lake Erie from 2012-2021.
JUNE 2023
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
Table 3. Generalized linear model (GLM) results for the relationships between SurveyDay and hypolimnion temperature, thickness and DO concentration.
In the model, the SurveyDay term is defined as Julian day minus 150 to place the y-intercept near the beginning of the sampling period. The GLM model includes
a separate factor for the sampling year, and a Julian day x year interaction term, which is used to test whether the rate of change in the hypolimnion temperature,
thickness or DO varies significantly between years (i.e., whether the estimated slope varies between years). Statistical significance of the GLM model tests was set
at alpha=0.05.
Table 3a. Overall GLM results for 2021.
T emperature
Thickness
DO concentration
Source
DF
Sum of Squares
Mean
Square
F statistic
p-value
r2+
Sum of Squares
Mean
Square
F statistic
p-value
R2
Sum of Squares
Mean
Square
F statistic
p-value
R2
Model
17
177.4260968
10.4368292
29.74
<.0001
0.945754
124.6945743
7.334975
5.46
<.0001
0.762020
482.6298383
28.3899905
25.65
<.0001
0.93763
Error
29
10.1766074
0.3509175
38.9422967
1.3428378
32.1038171
1.1070282
Table 3b. GLM fit statistics for 2021.
Temperature
Thickness
DO concentration
Source
DF
Type III SS*
Mean Square
F statistic
p-value
Type III SS
Mean Square
F statistic
p-value
Type III SS
Mean Square
F statistic
p-value
SurveyDay5
1
78.90601191
78.90601191
224.86
<0001
50.73168174
50.73168174
37.78
<.0001
303.7905517
303.790552
274.42
<0001
Year
8
19.86699505
2.48337438
7.08
<0001
31.73012688
3.96626586
2.95
0.0152
25.5099903
3.1887488
2.88
0.0173
Interaction
(i.e., SurveyDay x year)
8
4.3799679
0.54749599
1.56
0.1803
18.93500142
2.36687518
1.76
0.126
5.1543147
0.6442893
0.58
0.7842
* Ratio of the Mean Squares to its Error (i.e., overall model significance)
"I" Estimate of the overall variability explained by the model
J Sum of Squares that includes the variation that is unique to the effect listed in that row (e.g., Temperature and SurveyDay) after adjusting for all other effects that are included in the model
§ Julian day minus 150
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
Table 3c. GLM estimates of deviations in model intercept used to calculate rate of change in water temperature, thickness and DO concentrations of the hypolimnion for
years 2012-2020 compared to 2021 reference year.
Parameter
Temperature ( C)
Thickness (m)
DO concentration (mg/L)
Estimate
Standard Error
T statistic"
p-value
Estimate
Standard Error
T statistic
p-value
Estimate
Standard Error
T statistic
p-value
Intercept in 2021
10.03303
0.46322965
21.66
<.0001
9.4433845
0.90616153
10.42
<.0001
8.6312473
0.82276001
10.49
<.0001
Slope in 2021
0.0333851
0.00590161
5.66
<.0001
-0.0525582
0.01154463
-4.55
<.0001
-0.0808456
0.01048208
-7.71
<.0001
Difference in intercept in 2012
1.3996426
0.82486648
1.7
0.1004
-5.7536089
1.613589
-3.57
0.0013
-2.7045558
1.4650771
-1.85
0.0751
Difference in intercept in 2013
-0.2353664
0.81987077
-0.29
0.7761
-3.4801212
1.60381649
-2.17
0.0383
0.109666
1.45620404
0.08
0.9405
Difference in intercept in 2014
-3.2412531
0.7098807
-4.57
<.0001
-0.9237849
1.38865589
-0.67
0.5112
3.3782223
1.26084644
2.68
0.012
Difference in intercept in 2015
-1.1185251
0.75308119
-1.49
0.1483
-1.9138418
1.47316392
-1.3
0.2041
1.7455087
1.33757649
1.3
0.2022
Difference in intercept in 2016
-2.527626
1.13388446
-2.23
0.0337
-2.0805366
2.21808442
-0.94
0.356
3.7104574
2.01393583
1.84
0.0757
Difference in intercept in 2017
0.3628312
0.74430506
0.49
0.6296
-2.4294346
1.4559962
-1.67
0.106
-0.6191409
1.32198887
-0.47
0.643
Difference in intercept in 2018
-2.4222732
0.71539092
-3.39
0.0021
-0.2600131
1.39943489
-0.19
0.8539
1.7022746
1.27063336
1.34
0.1907
Difference in intercept in 2019
-2.3272478
0.68006698
-3.42
0.0019
-4.3523155
1.33033482
-3.27
0.0028
0.5630951
1.20789313
0.47
0.6446
Ratio of the Estimate to its Standard Error
^ Factors are for the difference in the intercept from the reference (i.e., 2021) and the specific year. The tests (i.e., T statistic and p-value) determine if there is a significant difference between the intercept in the reference
year (i.e., 2021) and the specific year. For example, in 2014, the estimated temperature intercept (i.e., estimated value on the 160th Julian day) is 6.7918 °C (10.0330 -3.2413), and it is significantly different from the
estimated temperature intercept in 2021 (i.e., 10.0330 °C) because the p-value is less than alpha = 0.05.
JUNE 2023 PAGE I 11
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
Figure 7. Annual DO depletion rate in the central basin of Lake Erie from 1970-2021.
7. CONCLUSIONS
The U.S. EPA GLNPO Lake Erie Dissolved
Oxygen Monitoring Program monitored the
oxygen and temperature profiles at 10 fixed
stations in the central basin of Lake Erie from June
- October 2021 to assess water quality trends and
measure progress made in achieving water quality
improvements. The long-term observations reveal
that over the course of the summer, DO levels in
the bottom waters of Lake Erie's central basin
steadily decline (Burns et al.. 2005). Variability
in the rate of DO depletion, its severity, and its
duration are related to year-to-year differences
in the thickness and temperature of the bottom
water layer, as well as winter ice coverage.
Year-to-year differences in the hypolimnion
characteristics are determined by the weather
over Lake Erie in the spring (i.e., average air
temperature and wind velocity). Rapidly
climbing air temperature with calm winds will
result in a thinner, warmer epilimnion and a
thicker, cooler hypolimnion that retains more
DO longer into the season. A cooler, windy
spring will permit the entire water column to
warm before the lake stratifies, resulting in a
deeper thermocline depth and a warm, thin
hypolimnion that is more prone to oxygen
depletion earlier in the season (Conrov et al..
2011; Bocaniov. 2020). Furthermore, reduced
ice coverage over the winter can result in earlier
springtime mixing and a longer stratification
period, thus increasing the risk of oxygen
depletion in the hypolimnion (Perello. 2017).
The springtime conditions during 2021 and an
elevated depletion rate, resulted in hypoxic and
anoxic conditions occurring earlier in the season
than on average. This increased the overall
length of time that the bottom waters of Lake
Erie were subjected to these conditions during
this year.
JUNE 2023
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
8. REFERENCES
Bocaniov, S.A., K.G. Lamb, W. Liu, Y.R. Rao, and R.E.H Smith. 2020. High Sensitivity of Lake
Hypoxia to Air Temperature, Winds, and Nutrient Loading: Insights from a 3-D Lake Model.
Water Resour. Res. 56, e2019WR027040. https://doi.org/10.1029/2019WR02704Q.
Bums, N.M., D.C. Rockwell, P.E. Bertram, D.M. Dolan, and J.J. Ciborowski. 2005. Trends in Temperature,
Secchi Depth, and Dissolved Oxygen Depletion Rate in the Central Basin of Lake Erie, 1983-2002. J.
Great Lakes Res. 31 (Supplement 2): 35-49.
Canada and United States. 2012. Protocol Amending the Agreement Between Canada and the United
States of America on Great Lakes Water Quality.
Conroy, J.D., L. Boegman, H. Zhang, W.J. Edwards, and D. A. Culver. 2011. "Dead Zone" Dynamics in
Lake Erie: the Importance of Weather and Sampling Intensity for Calculated Hypolimnetic
Oxygen Depletion Rates. Aquat. Sci. 73:289-304.
Dolan, D.M. 1993. Point Source Loadings of Phosphorus to Lake Erie: 1986-1990. J. Great Lakes Res.,
19: 212-223.
Maccoux, M.J., A. Dove, S.M. Backus, and D.M. Dolan. 2016. Total and Soluble Reactive Phosporus
Loadings to Lake Erie. A Detailed Accounting by Year, Basin, Country and Tributary. J. Great
Lakes Res. 42: 1151-1165.
Makarewicz, J.C. and P.E. Bertram. 1991. Evidence for the Restoration of the Lake Erie Ecosystem - Water
Quality, Oxygen Levels, and Pelagic Function Appear to be Improving. Bioscience. 41(4), 216-223.
Perello, M. M., D. D Kane, P. Golnick, M.C Hughes, M.A Thomas, and J.D. Conroy. 2017. Effects of
Local Weather Variation on Water-Column Stratification and Hypoxia in the Western, Sandusky,
and Central Basins of Lake Erie. Water. 9(4), 279-291. https://doi.org/10.3390/w9040279
Rosa, F. andN.M. Burns. 1987. Lake Erie Central Basin Depletion Changes from 1929-1980. J. Great
Lakes Res. 13(4):684-696.
Rowe, M.D, E.J. Anderson, D. Beletsky, C.A. Stow, S.D. Moegling, J.D. Chaffin, J.C. May, P.D.
Collingsworth, A. Jabbari, and J.D. Ackerman. 2019. Coastal Upwelling Influences Hypoxia
Spatial Patterns and Nearshore Dynamics in Lake Erie. J. of Geophys. Res. Oceans. 124(8), 6154-
6175. 10.1029/2019JC015192.
U.S. Environmental Protection Agency (U.S. EPA). 2020. United States Environmental Protection
Agency Region 5, Quality Management Plan.
U.S. Environmental Protection Agency (U.S. EPA). 2018a. U.S. Action Plan for Lake Erie. Retrieved
from https://www.epa.gov/sites/production/files/2018-Q3/documents/us dap final march l.pdf.
U.S. Environmental Protection Agency (U.S. EPA). 2018b. Dissolved Oxygen and Temperature Profiles
for the Central Basin of Lake Erie Quality Assurance Project Plan. Revision 11, May 2018. U.S.
EPA Great Lakes National Program Office.
Zhou, Y., D.R Obenour, D. Scavia, T.H Johengen, and A.M. Michalak. 2013. Spatial and Temporal
Trends in Lake Erie Hypoxia, 1987-2007. Environ. Sci. Technol. 47(2): 899-905.
JUNE 2023
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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT
APPENDIX A - QUALITY CONTROL RESULTS
A summary of 2021 results not meeting acceptance criteria is provided in the table below.
Table A-l. Quality control (QC) scorecard of 2021 CTD-collected temperature and dissolved oxygen (DO) data not meeting acceptance criteria.
Survey
Issue
Cause
Decision
Corrective Actions
June 15
Winkler precision check
exceeded the QC criterion
(2 of 4 samples)
Analyst error
QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.
Run additional replicate Winkler
analyses until consistency is
achieved.
June 29
Temperature accuracy
check exceeded QC
criterion (1 of 2 samples)
Temperature of the hull may be
affecting the measurement from the
hull-mounted transducer. Samples
may not have been taken at the same
depth.
Average temperature relative
percent difference (RPD) for
survey falls within QC criterion.
Temperature values from CTD
are considered valid.
Re-sample thennometer reading.
Sept. 9
Winkler precision check
exceeded the QC criterion
(1 of 4 samples)
Analyst error
QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.
Run additional replicate Winkler
analyses until consistency is
achieved.
Winkler precision check
exceeded the QC criterion
(1 of 4 samples)
Analyst error
QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.
Run additional replicate Winkler
analyses until consistency is
achieved.
Oct 6-7
For samples with DO < 5
mg/L, the absolute
difference between the
SeaBird values and Winkler
values exceeded the QC
criterion (1 of 1 samples)
Due to a thin hypolimnion
thennocline or epilimnion water may
have been present in the Winkler
sample.
All samples where DO >5.00
mg/L were within QC criteria (3
of 3 samples). CTD DO values
are considered valid.
Not Applicable
JUNE 2023
PAGE | A-l
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