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 2017-2019


LAKE ERIE DISSOLVED OXYGEN
MONITORING PROGRAM

TECHNICAL REPORT

I-	^

^ *- m «*

Dissolved Oxygen and Temperature Profiles for the Open Waters of the
Central Basin of Lake Erie during Summer/Fall of 2017-2019

vvEPA

United States
Environmental Protection
Agency

December 2022
EPA 950-R-21-003

Great Lakes
RESTORATION

p\

Prepared By:

United States Environmental protection Agency
Great Lakes National Program Office

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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 EPA
Contract No. EP-C-15-012, Technical, Analytical, and Regulatory Mission Support for the Water Security
Division, with CSRA LLC, a General Dynamics Information Technology company (hereinafter referred
to as "CSRA"), under the direction of Louis Blume, Project Manager. 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, Louis Blume

CSRA

Kathleen Marshall, Kenneth Miller

Cover photo: Sunset over Lake Erie. Photo by Katiefish via Pixabav

Citation: U.S. EPA 2022. 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 2017-2019. EPA 95O-R-21-003.

DECEMBER 2022

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

TABLE OF CONTENTS

Acknowledgments ii

Table of Contents iii

List of Tables iii

List of Figures iv

1. Executive Summary 1

2. Introduction 2

3. Methods 3

4. Quality Assurance and Quality Control 5

5. Results and Discussion 5

6. Conclusions 20

References 21

Appendix A - Quality Control Results A-l

Table 1. Acceptance criteria for DO and temperature data 5

Table 2. Mean water temperature (± SD) and DO for each survey in 2017 6

Table 3. Mean water temperature (± SD) and DO for each survey in 2018 8

Table 4. Mean water temperature (± SD) and DO for each survey in 2019 9

Table 5. Generalized linear model (GLM) results for the relationships between SurveyDay and

hypolimnion temperature, thickness and DO concentration 14

Table 5a. Overall GLM results for 2017 14

Table 5b. GLM fit statistics for 2017 14

Table 5c. GLM estimates of deviations in model intercept and slope used to calculate rate of change in
water temperature, thickness and DO concentrations of the hypolimnion for years 2008-2016
compared to 2017 reference year 15

Table 5d. Overall GLM results for 2018 16

Table 5e. GLM fit statistics for 2018 16

Table 5f. GLM estimates of deviations in model intercept and slope used to calculate rate of change in
water temperature, thickness and DO concentrations of the hypolimnion for years 2009-2017
compared to 2018 reference year 17

Table 5g. Overall GLM results for 2019 18

Table 5h. GLM fit statistics for 2019 18

Table 5i. GLM estimates of deviations in model intercept and slope used to calculate rate of change in
water temperature, thickness and DO concentrations of the hypolimnion for years 2010-2018
compared to 2019 reference year 19

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Table A-l. Quality control (QC) scorecard of 2017 CTD-collected temperature and dissolved oxygen

(DO) data not meeting acceptance criteria	A-l

Table A-2. Quality control (QC) scorecard of 2018 CTD-collected temperature and dissolved oxygen

(DO) data not meeting acceptance criteria	A-4

Table A-3. Quality control (QC) scorecard of 2019 CTD-collected temperature and dissolved oxygen

(DO) data not meeting acceptance criteria	A-6

LIST OF FIGURES

Figure 1. Map of GLNPO dissolved oxygen (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.... 4

Figure 3. 2017 station means for hypolimnion DO concentrations in the central basin of Lake Erie	6

Figure 4. 2018 station means for hypolimnion DO concentrations in the central basin of Lake Erie	8

Figure 5. 2019 station means for hypolimnion DO concentrations in the central basin of Lake Erie	9

Figure 6. Survey mean hypolimnion temperatures in the central basin of Lake Erie from 2010-2019	12

Figure 7. Survey mean hypolimnion thicknesses in the central basin of Lake Erie from 2010-2019	12

Figure 8. Survey mean hypolimnion dissolved oxygen concentrations in the central basin of Lake Erie

from 2010-2019	'	13

Figure 9. Dissolved oxygen depletion rate in the central basin of Lake Erie from 1970-2019	20

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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 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.

Hypoxic and anoxic conditions (< 2 mg O2/L
and < 1 mg O2/L, respectively) were observed in
all three sampling seasons (2017-2019) by our
ship-based observations of dissolved oxygen
(DO) concentrations. However, seasonal
variations can cause annual differences in the
onset, extent and duration of these low-oxygen
conditions in a given year. For example, 2017
had one of the higher annual DO depletion rates
observed in the last two decades, which led to
the presence of anoxic conditions much earlier
in the season than on average over the time
series. On the other hand, 2018 and 2019
exhibited two of the lowest DO annual depletion
rates, and anoxia was not seen until almost a
month later during these seasons. Seasonal
synopses for 2017-2019 are as follows:

During the course of the 2017 sampling season
(June 8 - October 3):

•	Six surveys were conducted during the 2017
field season using the EPA R/V Lake
Guardian. Four additional surveys were
conducted using the USGS R/V Muskie.

•	Surface water temperatures increased from
14.0 °C to 19.7 °C, while hypolimnion
temperatures increased from 9.8 °C to 13.9 °C.

•	Hypolimnion DO concentrations during the
sampling season decreased from
approximately 9.2 mg O2/L to 0.04 mg O2/L.

•	Low-oxygen conditions (< 6 mg O2/L)
were first recorded at one station on June
27, 2017.

•	Hypoxic and anoxic conditions were first
recorded during the August 13-14, 2017
survey. Hypoxia was present at two stations,
while anoxia was present at an additional
seven stations.

•	The annual corrected oxygen depletion rate
was 3.71 mg 02/L/month.

During the course of the 2018 sampling season

(June 7 - October 3):

•	Six surveys were conducted during the 2018
field season using the EPA R/V Lake
Guardian. Two additional surveys were
conducted using the USGS R/V Muskie.

•	Surface temperatures during the field season
increased from 14.1 °C to 24.0 °C, while
hypolimnion temperatures increased from
8J2 °C to 12.4 °C.

•	Hypolimnion DO concentrations during the
field season decreased from approximately
11.9 mg O2/L to 0.12 mg O2/L.

•	Low-oxygen conditions (< 6 mg O2/L)
were first recorded at four stations on July

19.2018.

•	Hypoxic and anoxic conditions were first
recorded during the September 6,2018
survey. Hypoxia was present at two
stations, while anoxia was present at one
additional station.

•	The annual corrected oxygen depletion rate
was 2.88 mg 02/L/month.

During the course of the 2019 sampling season

(June 5 - October 8):

•	Five surveys were conducted during the
2019 field season using the EPA R/V Lake
Guardian. Four additional surveys were
conducted using the USGS R/V Muskie.

•	Surface water temperatures increased from
12.3 °C to 23.5 °C, while hypolimnion
temperatures increased from 7.8 °C to 14.5 °C.

•	Hypolimnion DO concentrations during the
sampling season decreased from
approximately 9.8 mg O2/L to 0.10 mg O2/L.

•	Low-oxygen conditions (< 6 mg O2/L)
were first recorded at five stations on July

17.2019.

•	Hypoxic and anoxic conditions were first
recorded during the August 26, 2019 survey.
Hypoxia was present at two stations, while
anoxia was present at one additional station.

•	The annual corrected oxygen depletion rate
was 2.87 mg 02/L/month.

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

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 such that the
total impacted area was smaller in area than had
been observed in 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.
2018). 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. 2018). 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
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
2017, 2018, and 2019 Lake Erie Dissolved
Oxygen Monitoring Program surveys and places
those results within the context of historical
data.

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

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 10 additional surveys
during 2017-2019 (four surveys in 2017, two in
2018 and four in 2019). 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 instalment package. For
all three years, a SeaBird Scientific SBE 91 lplus
CTD and SBE 19plus V2 SeaCAT Profiler CTD
were used for collecting water temperature data,
and a SBE43 Dissolved Oxygen Sensor
integrated into each of the SBE CTDs was used
for collecting DO data. Comparison analyses
using the standard Quality Control (QC) criteria
for the DO program are conducted to ensure
comparable data are being collected between
different instrumentation whenever more than
one SBE CTD is used during a given season.
Samples from each instrument are assessed. 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. 2018).

Figure 1. Map of GLNPO dissolved oxygen (DO) monitoring stations in the central basin of Lake Erie.

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Quality Assurance samples are 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.
2018) 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.

In 2017, additional Winkler titration and
temperature measurements were collected
during several surveys as part of a separate
project. These supplementary samples were also
included as QC samples for this year.

Temperature (deg C)
12 15 IE

| H

— Temperature

— Dissolved Oxygen

6 9

Dissolved Oxygen (mg/L)

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
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 (2008-2017, 2009-2018 and
2010-2019) 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 5) and either hypolimnion
temperature, thickness or DO concentration
(Tables 5a-5i). 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

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

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 2017 surveys operated under Revision 10 of
the QAPP (U.S. EPA. 2017). and the 2018 and
2019 surveys operated under Revision 11 of the
QAPP (U.S. EPA. 2018). 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 criteria 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.

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.

5. RESULTS AND
DISCUSSION

2017 Synopsis

During the first survey (June 8, 2017), all
stations were stratified with an average
temperature difference of 4.2 °C between the
epilimnion and hypolimnion layers (Table 2).
Over the sampling season, average temperatures
increased in the epilimnion from 14.0 °C to 19.7
°C and in the hypolimnion from 9.8 °C to 13.9
°C. Average DO concentrations during the
sampling season decreased from 10.3 mg O2/L
to 8.0 mg O2/L in the epilimnion and from 9.2
mg O2/L to 0.04 mg O2/L in the hypolimnion.

Low DO concentrations (< 6 mg O2/L) in the
hypolimnion were first detected at the south,
western-most sampling station (ER43) during
the late June cruise. By late July, all stations had
DO concentrations below 6 mg O2/L and by
mid-August, seven stations had become anoxic
(< 1 mg O2/L). During mid-September and early
October all stations that had a hypolimnion
present were experiencing anoxic conditions
(Figure 3).

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Dissolved Oxygen Concentrations

^>6 mg/L Ijp 4-6 mg/L 0 2-4 mg/L ^1-2 mg/L £ 0-1 mg/L Q> No Data

Figure 3. 2017 station means for hypolimnion DO concentrations in the central basin of Lake Erie.
Table 2. Mean water temperature (± SD) and DO for each survey in 2017.



CTD

used



Epilimnion

Hypolimnion

2UI / survey
dates

Stations
(#>

Temperature
(°C)

DO

(mg/L)

Temperature
(°C)

DO

(mg/L)

Thickness
(m)

June 8

SBE911+

10

14.04 ±0.52

10.34 ± 0.11

9.81 ±0.26

9.20 ± 0.55

6.24 ± 1.60

June 27

SBE911+

10

18.45 ± 1.09

9.53 ±0.20

10.56 ±0.20

7.96 ± 1.20

6.74 ± 1.88

July 24-25

SBE91R

10

21.68 ±0.85

8.54 ±0.24

11.95 ± 1.18

3.87 ± 1.20

4.91 ±2.32

August 13-14

SBE911+

10

21.68 ± 1.19

8.29 ±0.54

13.04 ± 1.54

0.96 ± 1.07

3.22 ± 1.92

September 11-12

SBE911+

6

19.61 ±0.32

8.62 ±0.21

12.82 ± 1.11

0.04 ±0.01

3.72 ±2.17

October 2-3

SBE911+

5

19.69 ±0.22

7.98 ± 0.24

13.86 ± 1.24

0.09 ±0.11

2.07 ±0.62

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Two reoccurring data quality issues were present
during the 2017 sampling season (Table A-l).
The temperature accuracy checks exceeded the
acceptance criteria for 27% of the samples
collected. Additionally, the temperature values
from the hull-mounted transponder were higher
than the CTD temperature values for 34 of the 44
readings (which includes all but one of the
samples that exceeded the QC criteria). Heat
transfer from the hull to the surrounding water
may be one cause of this general bias seen in the
data. As such, this thermometer may not be an
appropriate instrument for assessing the accuracy
of the CTD temperature values. Therefore, an
independent temperature sensor was used during
the 2018 sampling season to collect temperature
values to assess whether the high exceedance rate
for temperature accuracy was associated with the
hull transducer or an issue with the CTD (e.g.,
calibration factor, sensor).

Winkler precision checks exceeded the
acceptance criteria for nearly 30% of the
samples collected. However, 96% of the
Winkler-CTD accuracy checks for values above
5.0 mg/L were still within acceptance criteria
(Appendix A). Inexperienced technicians or
improper laboratory procedures may have
contributed to the high exceedance rate in 2017.
As such, additional training and/or a longer
observational period will be required for any
inexperienced individual planning to participate
in a DO survey during that year.

2018 Synopsis

During the first survey (June 7-8, 2018), all
stations were stratified with an average
temperature difference of 5.9 °C between the
epilimnion and hypolimnion layers (Table 3). By
the late September survey, the hypolimnion was
so thin that only the deepest portion of the basin
still had distinct water layers. As such,
hypolimnion conditions could only be measured
at the five southern and southeastern stations
during this survey and the following survey in
early October. During the sampling season,
average temperatures increased in the epilimnion
from 14.1 °C to 24.0 °C by mid-August, before

decreasing to 19.2 °C by early October. Average
temperatures in the hypolimnion increased from
8.2 °C to 12.6 °C. Average DO concentrations
during the sampling season decreased from 11.2
mg O2/L to 7.9 mg O2/L in the epilimnion and
from 11.9 mg O2/L to 0.12 mg O2/L in the
hypolimnion.

Low-oxygen concentrations (< 6 mg O2/L) in the
hypolimnion were first detected at the north and
western-most sampling stations (ER30, ER38,
ER42 and ER43) during the mid-July cruise.
The first station to become anoxic (< 1 mg O2/L)
was observed during the early-September
survey, and by early-October all stations that
had a hypolimnion present were experiencing
anoxic conditions (Figure 4).

Winkler precision checks exceeded the
acceptance criteria for approximately 27% of the
samples collected (Appendix A). However, all
Winkler-CTD accuracy checks for values above
5.0mg/L were within acceptance criteria.

In response to the data quality issues observed in
2017 associated with the temperature sensors, an
independent handheld thermometer was used
instead of the hull-mounted transducer for the
QC checks during this year. This method
reduced the overall bias seen with the hull-
mounted transducer (75% of all samples in 2017
had a negative relative percent difference versus
45% in 2018). However, this method does not
appear to be a completely viable solution to this
ongoing issue. Because this new probe was
lightweight and on the end of a long cable, any
surface current or movement of the vessel made
it increasingly difficult for the sensor to sink to
the same depth as the CTD temperature sensor
(in some instances greater than 2 meters depth).
As such, the two sensors were often not
sampling at the same depth. Any temperature
gradient in these surface waters might therefore
result in an exceedance of the QC criteria simply
due to position in the water column, instead of
any problems with the sensors or their
calibrations (Appendix A).

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

September 24-26, 2018

i

October 3-4, 2018

• ••••

Dissolved Oxygen Concentrations

Q >6 mg/L £ 4-6 mg/L (J) 2-4 mg/L ^1-2 mg/L £ 0-1 mg/L (_) No Data

Figure 4. 2018 station means for hypolimnion DO concentrations in the central basin of Lake Erie.

Table 3. Mean water temperature (± SD) and DO for each survey in 2018.







Epilimnion



Hypolimnion



zulo survey
dates

t ID

used

Stations

m

Temperature
(°C)

DO
(mg/L)

Temperature
(°C)

DO

(mg/L)

Thickness
(m)

June 7-8

SBI911+

10

14.15 ± 0.50

9.27 ± 0.65

8.21 ±0.68

9.70 ±0.48

8.84 ± 1.64

June 26-27

SBI911+

10

18.48 ±0.45

9.26 ±0.17

9.02 ± 1.27

8.43 ±0.97

8.11 ±2.59

July 19-20

SBB911+

10

22.49 + 0.32

9.02 ±0.16

9.04 ±0.59

6.62 ± 1.20

5.91 ± 1.60

August 12

SBE911+

10

22.69+ 1.76

8.24 ± 0.44

9.50 ±0.36

5.33 ± 1.48

7.70 ± 2.06

August 21-22

SBB19+

10

23.52 + 1.81

7.94 ±0.68

10.19 ±0.79

4.32 ± 1.79

5.76 ± 1.24

September 5-6

SBI911+

9

23.34 + 0.62

8.40 ±0.31

11.41 ± 1.20

2.37 ± 1.25

2.84 ±2.85

September 24-26

SBE19+

5

20.15 ±0.43

7.88 ±0.13

12.64 ±1.28

0.39 ±0.54

2.18 ± 1.36

October 3-4

SBE911+

5

19.24 ±0.45

8.30 ±0.16

12.39 ±0.93

0.12 ±0.08

3.59 ± 0.66

DECEMBER 2022

PAGE | 8

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

2019 Synopsis

During the first survey (June 5, 2019), all
stations were stratified with an average
temperature difference of 4.5 °C between the
epilimnion and hypolimnion layers (Table 4).
Over the sampling season, average epilimnion
temperatures increased from 12.3 °C to 23.5 °C
(June to early August) and then began to
decrease, reaching 20.8 °C by the end of the
sampling period. The hypolimnion temperature
increased from 7.8 °C to 14.5 °C. Average DO
concentrations during the sampling season
decreased from 11.4 mg O2/L to 8.0 mg O2/L in
the epilimnion and from 9.8 mg O2/L to 0.1 mg
O2/L in the hypolimnion.

Low DO concentrations (< 6 mg O2/L) in the
hypolimnion were first detected at the western
and eastern-most sampling stations during the
mid-July cruise. By the next survey (late July),
the low oxygenated waters (< 6 mg O2/L) had
shifted westward; only the south eastern-most
stations (ER31 and ER32) had DO
concentrations > 6.0 mg O2/L. Additionally, this
was the first survey where DO concentrations <
4.0 mg O2/L were observed (at ER42). While

there were equipment issues (Table A.3)
halfway through the August 26 survey, two of
the sampled stations had hypolimnion DO
concentrations < 2 mg O2/L and one station
(ER42) had a DO concentration < 1 mg O2/L.
By the beginning of September, half of the
stations were hypoxic (< 2 mg O2/L) and the
other half were anoxic (< 1 mg O2/L). Anoxic
conditions were observed at all stations where
data were available for the last two surveys of
the season (Figure 5).

Winkler precision checks exceeded the
acceptance criteria for approximately 18% of the
samples collected (Appendix A). However, all
Winkler-CTD accuracy checks for values above
5.0mg/L were within acceptance criteria.

An alternative method for assessing the quality
of the CTD temperature measures was not able
to be piloted in 2019. As a result, the QC
temperature measurements were measured from
the hull mounted transducer during this year.
Use of a temperature sensor that can be attached
directly to the CTD is planned to be piloted
during the 2020 field season.

DECEMBER 2022

PAGE | 9

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

June 5, 2019

June 27, 2019

• ® , •

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•

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July 17, 2019

July 31, 2019

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• ° ©

•

•

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August 9, 2019

August 26, 2019

•

• •

.Ml ° ©

Q o #

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• • g

September 5, 2019

September 26, 2019

•

• •

.• • •
• • •

•

•

• • •

•

October 8, 2019



. 	M • • •

• • •

•

Dissolved Oxygen Concentrations

Q >6 mg/L

0 4-6 mg/L O 2-4 mg/L 0 1-2 mg/L % 0-1 mg/L 0 No Data

Figure 5. 2019 station means for hypolimnion DO concentrations in the central basin of Lake Erie.
Table 4. Mean water temperature (± SD) and DO for each survey in 2019.







Epilimnion



[Ivpolimnion



2019 Survey
dates

CTD

used

Stations
(#)

Temperature
(°C)

DO

(mg/L)

Temperature
(°C)

DO

(mg/L)

Thickness
(m)

June 5

SBE 911+

10

12.29 + 0.64

11.35 + 0.43

7.76 + 0.61

9.8 + 0.54

6.04+1.49

June 27

SBE 911+

10

16.40 + 0.47

10.23 + 0.13

8.47 + 0.60

8.15 + 0.70

4.28+1.57



SBE 911 +

10

20.78 + 0.61

8.90 + 0.36

9.46 + 0.99

5.70 + 0.69

3.57+ 1.90

July 31

SBE 19+

10

21.97 + 3.51

8.07+1.03

11.21 + 1.36

5.24 + 0.92

4.82 + 2.27

August 9

SBE 911+

10

23.52+ 1.81

7.94 + 0.68

10.46 + 0.99

4.59+ 1.29

5.27+1.99

August 26

SBE 19+

5

22.81 + 1.17

8.17 + 0.39

10.95 + 0.81

1.90 + 0.83

5.58+1.20

September 5

SBE 911+

10

21.71 + 1.26

7.76 + 0.71

11.78 + 0.87

0.83 + 0.53

5.01+2.49

September 26

SBE 19+

8

21.86 + 0.21

8.53 + 0.07

12.20 + 0.84

0.10 + 0.07

3.94 + 1.51

October 8

SBE 19+

7

20.81+0.20

7.99 + 0.11

14.49 + 2.96

0.10 + 0.27

2.19 + 2.01

DECEMBER 2022

PAGE | 9

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Comparison to historical results
2017 Comparison

At the start of the 2017 season, the hypolimnion
was significantly warmer than in 2011 and 2014-
2016 (Table 5c). but still significantly cooler
than in 2012 (Table 5 c). The rate of change in
hypolimnion temperature varied significantly
between years (Table 5b). with the hypolimnion
temperature increasing more slowly in 2017 than
in 2013 and 2016 (Table 5b. 5c).

At the start of the 2017 season, the hypolimnion
was significantly thicker than in 2009 and 2012,
and thinner than in 2010 (Table 5c). The
hypolimnion thickness approximated the
previous 10-year average through most of the
season. A slight increase in thickness occurred
during the mid-September survey
(approximately 0.5 m), but decreased to the
second thinnest average hypolimnion by mid-
October (Figure 7). The rate of change in
hypolimnion thickness varied significantly
between years (Table 5b). with the hypolimnion
thickness decreasing more slowly in 2017 than
in 2010, and faster than in years during which
the thickness increased overtime (i.e., 2009,
2011 and 2012) (Table 5c).

Throughout the 2017 season, the hypolimnion
unadjusted DO concentration was significantly
higher than throughout the 2012 season and
significantly lower than in the 2008, 2014 and

2016	seasons. Furthermore, DO concentrations
reached hypoxic conditions (< 2 mg O2/L) by
August 7, the second earliest date for this time
period.

The corrected annual oxygen depletion rate for

2017	was 3.71 mg 02/L/month (Figure 9). This
is the second highest depletion rate since 2005.
The last two surveys in 2017 (mid-September
and early October) were not included in the
oxygen depletion analysis. The average
hypolimnion DO concentration during the mid-
August survey was <1.0 mg O2/L with five
stations <0.3 mg O2/L. Additionally, two of the
three stations which had oxygen levels >1.0 mg
O2/L (ER30 and ER38) did not have a
hypolimnion present during the mid-September
survey, and therefore a depletion rate could not
be calculated over that time period for those

stations. Hypolimnion DO concentrations did
not change between the mid-September and
early October surveys. Of the four stations that
had a hypolimnion present during both surveys,
oxygen levels at two stations did not change
between both surveys, while the oxygen
concentration at the other two stations increased
slightly over that time period (by 0.25 mg O2/L
and 0.01 mg O2/L, respectively). As such, the
inclusion of these surveys in the 2017 annual
oxygen depletion rate calculation would
artificially reduce the rate by dividing a static
concentration (as no additional depletion
occurred during this time period) by an
additional 20 days (the time period of the last
two survey.

2018 Comparison

At the start of the 2018 season (June 1), the
hypolimnion was significantly warmer than in
2014, the coolest year over the 10-year period
(Table 5f). but was still significantly cooler than
the warmer years (2009, 2010, 2012, 2013 and
2017, Table 5f). The rate of change in
hypolimnion temperature varied significantly
between years (Table 5e). with the hypolimnion
temperature increasing more slowly in 2018 than
in 2013 and 2016 (Table 5f).

At the start of the 2018 season, the hypolimnion
was significantly thicker than in 2009, 2011-
2013 and 2017 (Table 5f). The rate of change in
hypolimnion thickness varied significantly
between years (Table 5e). with the hypolimnion
thickness decreasing more slowly in 2018 than
in years during which the thickness increased
overtime (i.e., 2009, 2011 and 2012) (Table 5f).

Throughout the 2018 season, the hypolimnion
unadjusted DO was significantly higher than
throughout the 2009 and 2012 seasons (Table
5f). Note that the rate of change in hypolimnion
unadjusted DO did not vary significantly
between years (Table 5e); however, since there
is no significant interaction, a significant
intercept (as indicated by a p-value less than
alpha = 0.05 in Table 5f) can be interpreted as
an overall difference between years.

The corrected annual oxygen depletion rate for
2018 was 2.88 mg 02/L/month (Figure 9). This
is the fourth lowest depletion rate since 2005 at

DECEMBER 2022

PAGE | 10

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

approximately 0.32 mg 02/L/month below the
average for that time period.

2019 Comparison

Throughout the 2019 season, the hypolimnion
temperature was significantly warmer than in
2014, the coolest year over the 10-year period
(Table 5i). but still significantly cooler than in the
warmer years (2010, 2012, 2013 and 2017, Table
5i). Note that the rate of change in hypolimnion
temperature did not vary significantly between
years (Table 5h); however, since there is no
significant interaction, a significant intercept (as
indicated by a p-value less than alpha = 0.05 in
Table 5i) can be interpreted as an overall
difference between years.

At the start of the 2019 season, the hypolimnion
was significantly thicker than in 2012 and
significantly thinner than in 2010, 2014, 2016
and 2018 (Table 5i). The rate of change in
hypolimnion thickness varied significantly
between years (Table 5h). with the hypolimnion
thickness decreasing more slowly in 2019 than
in 2010, 2016 and 2018 (Table 5i).

Throughout the 2019 season, the hypolimnion
unadjusted DO was significantly higher than
throughout the 2012 season and significantly
lower than throughout the 2014 season (Table
5i). Note that the rate of change in hypolimnion
unadjusted DO did not vary significantly

between years (Table 5h); however, since there
is no significant interaction, a significant
intercept (as indicated by a p-value less than
alpha = 0.05 in Table 5i) can be interpreted as an
overall difference between years.

The corrected annual oxygen depletion rate for
2019 was 2.87 mg 02/L/month (Figure 9). This
was the third lowest depletion rate since 2005, at
approximately 0.33 mg 02/L/month below the
average for that time period. The August 26
survey was not included in the 2019 depletion
rate analysis because data were only recorded at
half of the stations. A subsequent survey
(September 5-6) was conducted approximately
one week later in which all stations were able to
be sampled which enabled depletion rates to be
calculated at all stations during the August 9 -
September 5 time interval. The final survey
(October 8) was not included in the annual
depletion rate calculation for 2019. All stations
where hypolimnionic data were available, had
reached anoxic conditions by the previous
survey on September 26 (average DO
concentration for the September 26 survey was
0.10 mg O2/L). No further oxygen depletion
occurred between the September 26 and October
8 surveys (average DO concentration for the
October 8 survey was 0.10 mg O2/L), and
therefore this last survey was not included in the
depletion rate calculation for this year.

DECEMBER 2022

PAGE | 11

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

p
oj

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145

165

185

205 225

Julian Day

245

265

285

••••2010
••¦••2011
••¦••2012
••¦••2013
••¦••2014
•*•• 2015
•A*" 2016
•*••2017
•A*** 2018
•*••2019

Figure 6. Survey mean hypolimnion temperatures in the central basin of Lake Erie from 2010-2019.

0
"S
E

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

CuO °

£_

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••2010
••2011
••2012
••2013
••2014
2015
*••2016
2017
Ar** 2018
A»«« 2019

145 165 185 205 225

Julian Day

245

265

285

Figure 8. Survey mean hypolimnion dissolved oxygen concentrations in the central basin of Lake Erie from
2010-2019.

DECEMBER 2022

PAGE | 13

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Table 5. 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 5a. Overall GLM results for 2017.

T emperature

Thickness

DO concentration

Sum of Squares

Mean Square

F statistic*

p-value

R2t

Sum of Squares

Mean Square

F statistic

p-value

Sum of Squares

Mean Square

F statistic

p-value

Model

225.65

11.88

70.06

<.0001

0.98

157.22

8.27

10.7

<.0001

0.88

667.61

35.14

67.77

<0001

0.97

Error

4.92

0.17

22.44

0.77

15.04

0.52

Table 5b. GLM fit statistics for 2017.

Temperature

Thickness

DO concentration

Source

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

101.20

596.95

<0001

43.61

56.37

<.0001

463.72

655.52

<.0001

Year

27.06

3.01

17.74

<.0001

57.47

6.39

8.25

<.0001

33.22

3.69

5.22

0.0003

Interaction

(i.e., SurveyDay x year)

5.35

0.59

3.51

0.0048

44.91

4.99

6.45

<.0001

9.16

1.02

1.44

0.2175

* 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

DECEMBER 2022

PAGE | 14

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Table 5c. GLM estimates of deviations in model intercept and slope used to calculate rate of change in water temperature, thickness and DO concentrations of the
hypolimnion for years 2008-2016 compared to 2017 reference year.

Temperature (°C) Thickness (m) DO concentration (mg/L)

Parameter

Estimate

Standard Error

T statistic*

p-value

Estimate

Standard Error

T statistic

p-value

Estimate

Standard Error

T statistic

p-value

Intercept in 2017

9.7863

0.3216

30.43

<.0001

6.9925

0.6871

10.18

<.0001

9.4262

0.6570

14.35

<.0001

Slope in 2017

0.0336

0.0042

8.1

<.0001

-0.0380

0.0089

-4.28

0.0002

-0.0870

0.0085

-10.25

<.0001

Difference in intercept in 2008"]""f

-0.6860

0.4508

-1.52

0.1389

0.1997

0.9631

0.21

0.8372

2.0441

0.9209

2.22

0.0344

Difference in intercept in 2009

-0.2903

0.4524

-0.64

0.5262

-2.2916

0.9665

-2.37

0.0246

-0.8675

0.9242

-0.94

0.3557

Difference in intercept in 2010

-0.8190

0.4684

-1.75

0.0909

3.4977

1.0006

3.5

0.0015

0.5721

0.9568

0.6

0.5545

Difference in intercept in 2011

-2.3808

0.4821

-4.94

<.0001

-0.1398

1.0300

-0.14

0.893

1.2433

0.9849

1.26

0.2169

Difference in intercept in 2012

1.2988

0.4719

2.75

0.0101

-3.7021

1.0081

-3.67

0.001

-2.1560

0.9640

-2.24

0.0332

Difference in intercept in 2013

-0.4482

0.4677

-0.96

0.3458

-1.4719

0.9991

-1.47

0.1515

0.9421

0.9554

0.99

0.3322

Difference in intercept in 2014

-3.6884

0.4469

-8.25

<.0001

1.3765

0.9548

1.44

0.1601

2.9493

0.9130

3.23

0.0031

Difference in intercept in 2015

-1.3572

0.5686

-2.39

0.0237

0.9738

1.2147

0.8

0.4292

1.9154

1.1615

1.65

0.1099

Difference in intercept in 2016

-2.0056

0.5128

-3.91

0.0005

1.9394

1.0956

1.77

0.0872

2.4917

1.0476

2.38

0.0242

Difference in slope in 2008JJ

-0.0034

0.0062

-0.54

0.5921

0.0157

0.0133

1.18

0.2495

-0.0170

0.0128

-1.33

0.1927

Difference in slope in 2009

0.0057

0.0065

0.89

0.3826

0.0391

0.0138

2.83

0.0084

0.0069

0.0132

0.52

0.6064

Difference in slope in 2010

0.0123

0.0072

1.69

0.1014

-0.0458

0.0155

-2.96

0.0061

-0.0176

0.0148

-1.19

0.2436

Difference in slope in 2011

0.0034

0.0092

0.37

0.7162

0.0539

0.0196

2.76

0.01

-0.0019

0.0187

-0.1

0.9185

Difference in slope in 2012

0.0033

0.0064

0.52

0.605

0.0492

0.0136

3.61

0.0011

0.0126

0.0130

0.97

0.3413

Difference in slope in 2013

0.0180

0.0063

2.88

0.0074

0.0081

0.0134

0.61

0.548

-0.0174

0.0128

-1.36

0.1855

Difference in slope in 2014

0.0082

0.0065

1.26

0.217

0.0067

0.0139

0.48

0.6321

0.0127

0.0133

0.96

0.3454

Difference in slope in 2015

0.0149

0.0076

1.96

0.0595

-0.0057

0.0162

-0.35

0.7296

-0.0095

0.0155

-0.61

0.5439

Difference in slope in 2016

0.0285

0.0068

4.17

0.0003

-0.0216

0.0146

-1.48

0.1498

-0.0140

0.0140

-1

0.326

# Ratio of the Estimate to its Standard Error

H Factors are for the difference in the intercept from the reference (i.e., 2017) 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., 2017) and the specific year. For example, in 2008, the estimated temperature intercept (i.e., estimated value on the 150th Julian day) is 9.1003 °C (9.7863 -0.6860), and it is not significantly different from the
estimated temperature intercept in 2016 (i.e., 9.7863 °C) because the p-value is greater than alpha = 0.05.

J J Factors are for the difference in the slope from the reference (i.e., 2017) and the specific year. The tests (i.e., T statistic and p-value) determine if there is a significant difference between the slope in the reference year (i.e.,
2017) and the specific year. For example, in 2009, the estimated thickness slope is 0.0011 m/day (-0.0380 + 0.0391), and it is significantly different from the thickness slope in 2016S (i.e., -0.0380 m/day) because the p~
value is less than alpha = 0.05.

DECEMBER 2022

PAGE | 15

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Table 5d. Overall GLM results for 2018.

T emperature

Thickness

DO concentration

Source

Sum of
Squares

Mean
Square

F statistic*

p-value

R2t

Sum of
Squares

Mean
Square

F statistic

p-value

Sum of
Squares

Mean
Square

F statistic

p-value

Model

242.13

12.74

61.08

<0001

0.97

186.62

9.82

10.48

<0001

0.87

678.50

35.71

54.74

<.0001

0.97

Error

6.47

0.21

29.06

0.94

20.22

0.65

Table 5e. GLM fit statistics for 2018.

T emperature

Thickness

DO concentration

Source

Type III SSJ

Mean Square

F statistic

p-value

Type III SS

Mean Square

F statistic

p-value

Type III SS

Mean Square

F statistic

p-value

SurveyDay§

107.60

515.71

<.0001

55.28

58.98

<0001

455.90

698.87

<.0001

Year

29.10

3.23

15.49

<.0001

68.07

7.56

8.07

<0001

31.30

3.48

5.33

0.0002

Interaction

(i.e., SurveyDay x year)

4.46

0.50

2.37

0.0356

50.64

5.63

<0001

7.85

0.87

1.34

0.259

* 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

DECEMBER 2022

PAGE | 16

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Table 5f. GLM estimates of deviations in model intercept and slope used to calculate rate of change in water temperature, thickness and DO concentrations of the
hypolimnion for years 2009-2017 compared to 2018 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 2018

7.5253

0.3437

21.89

<.0001

9.5363

0.7285

13.09

<.0001

10.8485

0.6077

17.85

<.0001

Slope in 2018

0.0379

0.0041

9.15

<.0001

-0.0536

0.0088

-6.1

<.0001

-0.0846

0.0073

-11.54

<.0001

Difference in intercept in 2009

1.9708

0.4927

0.0004

-4.8353

1.0442

-4.63

<.0001

-2.2897

0.8711

-2.63

0.0132

Difference in intercept in 2010

1.4420

0.5107

2.82

0.0082

0.9539

1.0824

0.88

0.3849

-0.8501

0.9030

-0.94

0.3537

Difference in intercept in 201 Iff

-0.1197

0.5262

-0.23

0.8215

-2.6835

1.1153

-2.41

0.0223

-0.1789

0.9305

-0.19

0.8488

Difference in intercept in 2012

3.5598

0.5147

6.92

<.0001

-6.2458

1.0908

-5.73

<.0001

-3.5782

0.9100

-3.93

0.0004

Difference in intercept in 2013

1.8128

0.5099

3.56

0.0012

-4.0156

1.0808

-3.72

0.0008

-0.4801

0.9016

-0.53

0.5982

Difference in intercept in 2014

-1.4274

0.4865

-2.93

0.0062

-1.1672

1.0310

-1.13

0.2663

1.5271

0.8601

1.78

0.0856

Difference in intercept in 2015

0.9038

0.6235

1.45

0.1572

-1.5699

1.3214

-1.19

0.2438

0.4932

1.1024

0.45

0.6577

Difference in intercept in 2016

0.2554

0.5608

0.46

0.652

-0.6043

1.1886

-0.51

0.6148

1.0695

0.9916

1.08

0.2891

Difference in intercept in 2017

2.2610

0.4954

4.56

<.0001

-2.5437

1.0501

-2.42

0.0215

-1.4222

0.8760

-1.62

0.1146

Difference in slope in 2009JJ

0.0014

0.0069

0.21

0.8359

0.0547

0.0146

3.74

0.0007

0.0046

0.0122

0.37

0.7112

Difference in slope in 2010

0.0080

0.0078

1.02

0.3145

-0.0303

0.0165

-1.83

0.0764

-0.0200

0.0138

-1.45

0.1573

Difference in slope in 2011

-0.0009

0.0100

-0.09

0.9253

0.0695

0.0211

3.29

0.0025

-0.0043

0.0176

-0.24

0.8102

Difference in slope in 2012

-0.0010

0.0068

-0.14

0.8876

0.0647

0.0144

4.5

<.0001

0.0103

0.0120

0.86

0.3986

Difference in slope in 2013

0.0137

0.0067

2.06

0.0476

0.0237

0.0141

1.68

0.1026

-0.0197

0.0118

-1.67

0.1043

Difference in slope in 2014

0.0039

0.0069

0.56

0.5776

0.0223

0.0147

1.52

0.1386

0.0104

0.0122

0.85

0.4023

Difference in slope in 2015

0.0106

0.0082

1.29

0.2049

0.0099

0.0173

0.57

0.5713

-0.0119

0.0145

-0.82

0.4186

Difference in slope in 2016

0.0242

0.0073

3.31

0.0024

-0.0060

0.0155

-0.39

0.7002

-0.0163

0.0129

-1.26

0.2173

Difference in slope in 2017

-0.0043

0.0062

-0.69

0.493

0.0156

0.0131

1.19

0.2446

-0.0023

0.0110

-0.21

0.8328

# Ratio of the Estimate to its Standard Error

ll Factors are for the difference in the intercept from the reference (i.e., 2018) 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., 2018) and the specific year. For example, in 2011, the estimated temperature intercept (i.e., estimated value on the 150th Julian day) is 7.4056 °C (7.5253 -0.1197), and it is not significantly different from the
estimated temperature intercept in 2018 (i.e., 7.5253 °C) because the p-value is greater than alpha = 0.05.

J J Factors are for the difference in the slope from the reference (i.e., 2018) and the specific year. The tests (i.e., T statistic and p-value) determine if there is a significant difference between the slope in the reference year (i.e.,
2018) and the specific year. For example, in 2009, the estimated thickness slope is 0.0011 m/day (-0.0536 + 0.0547), and it is significantly different from the thickness slope in 2018 (i.e., -0.0536 m/day) because the p-
value is less than alpha = 0.05.

DECEMBER 2022

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Table 5g. Overall GLM results for 2019.

Temperature

Thickness

DO concentration

Source

Sum of

Squares

Mean
Square

F statistic*

p-value

r2+

Sum of

Squares

Mean
Square

F statistic

p-value

Sum of

Squares

Mean
Square

F statistic

p-value

Model

262.17

13.80

53.87

<0001

0.97

192.94

10.15

10.62

<0001

0.85

735.32

38.70

61.57

<.0001

0.97

Error

8.97

0.26

33.46

0.96

22.00

0.63

Table 5h. GLM fit statistics for 2019.

T emperature

Thickness

DO concentration

Source

Type III SSJ

Mean Square

F statistic

p-value

Type III SS

Mean Square

F statistic

p-value

Type III SS

Mean Square

F statistic

p-value

SurveyDay§

115.93

452.59

<.0001

63.81

66.75

<0001

478.73

761.59

<.0001

Year

29.66

3.30

12.87

<.0001

62.55

6.95

7.27

<0001

26.31

2.92

4.65

0.0004

Interaction

(i.e., SurveyDay x year)

4.51

0.50

1.95

0.0759

47.32

5.26

5.5

0.0001

7.86

0.87

1.39

0.2302

Ratio of the Mean Squares to its Error (i.e., overall model significance)
f 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

DECEMBER 2022

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Table 5i. GLM estimates of deviations in model intercept and slope used to calculate rate of change in water temperature, thickness and DO concentrations of the
hypolimnion for years 2010-2018 compared to 2019 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 2019

7.3469

0.3564

20.61

<.0001

5.6162

0.6886

8.16

<.0001

10.1378

0.5583

18.16

<.0001

Slope in 2019

0.0462

0.0043

10.85

<.0001

-0.0148

0.0082

-1.8

0.0798

-0.0824

0.0067

-12.36

<.0001

Difference in intercept in 2010"]""f

1.6204

0.5497

2.95

0.0057

4.8740

1.0620

4.59

<.0001

-0.1395

0.8611

-0.16

0.8722

Difference in intercept in 2011

0.0586

0.5674

0.1

0.9183

1.2366

1.0962

1.13

0.267

0.5317

0.8889

0.6

0.5536

Difference in intercept in 2012

3.7382

0.5543

6.74

<.0001

-2.3257

1.0708

-2.17

0.0367

-2.8676

0.8683

-3.3

0.0022

Difference in intercept in 2013

1.9912

0.5488

3.63

0.0009

-0.0955

1.0603

-0.09

0.9287

0.2305

0.8598

0.27

0.7902

Difference in intercept in 2014

-1.2490

0.5220

-2.39

0.0222

2.7529

1.0085

2.73

0.0099

2.2377

0.8178

2.74

0.0097

Difference in intercept in 2015

1.0822

0.6777

1.6

0.1193

2.3502

1.3092

1.8

0.0813

1.2038

1.0616

1.13

0.2645

Difference in intercept in 2016

0.4338

0.6067

0.71

0.4794

3.3158

1.1722

2.83

0.0077

1.7801

0.9505

1.87

0.0695

Difference in intercept in 2017

2.4394

0.5323

4.58

<.0001

1.3764

1.0284

1.34

0.1894

-0.7116

0.8339

-0.85

0.3993

Difference in intercept in 2018

0.1784

0.5216

0.34

0.7344

3.9201

1.0077

3.89

0.0004

0.7106

0.8171

0.87

0.3904

Difference in slope in 2010 J J

-0.0003

0.0085

-0.03

0.9753

-0.0690

0.0163

-4.23

0.0002

-0.0222

0.0132

-1.67

0.103

Difference in slope in 2011

-0.0092

0.0109

-0.84

0.4059

0.0307

0.0210

1.46

0.1535

-0.0065

0.0171

-0.38

0.7068

Difference in slope in 2012

-0.0092

0.0073

-1.26

0.2171

0.0260

0.0141

1.84

0.0745

0.0081

0.0115

0.7

0.4862

Difference in slope in 2013

0.0055

0.0072

0.77

0.4476

-0.0150

0.0138

-1.09

0.2846

-0.0219

0.0112

-1.95

0.0591

Difference in slope in 2014

-0.0043

0.0075

-0.58

0.566

-0.0165

0.0144

-1.14

0.2615

0.0082

0.0117

0.7

0.4887

Difference in slope in 2015

0.0024

0.0089

0.27

0.7914

-0.0288

0.0172

-1.68

0.1023

-0.0141

0.0139

-1.01

0.3198

Difference in slope in 2016

0.0160

0.0079

2.02

0.0516

-0.0448

0.0153

-2.93

0.006

-0.0185

0.0124

-1.49

0.1448

Difference in slope in 2017

-0.0125

0.0066

-1.88

0.0678

-0.0232

0.0128

-1.81

0.0796

-0.0045

0.0104

-0.44

0.6655

Difference in slope in 2018

-0.0082

0.0063

-1.31

0.1977

-0.0388

0.0121

-3.2

0.0029

-0.0022

0.0098

-0.22

0.8234

# Ratio of the Estimate to its Standard Error

H Factors are for the difference in the intercept from the reference (i.e., 2019) 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., 2019) and the specific year. For example, in 2011, the estimated temperature intercept (i.e., estimated value on the 150th Julian day) is 7.4056 °C (7.3469 +0.0586), and it is not significantly different from the
estimated temperature intercept in 2019 (i.e., 7.3469 °C) because the p-value is greater than alpha = 0.05.

J J Factors are for the difference in the slope from the reference (i.e., 2019) and the specific year. The tests (i.e., T statistic and p-value) determine if there is a significant difference between the slope in the reference year (i.e.,
2019) and the specific year. For example, in 2010, the estimated thickness slope is -0.0839 m/day (-0.0148 -0.0690), and it is significantly different from the thickness slope in 2019 (i.e., -0.0148 m/day) because the p-
value is less than alpha = 0.05.

DECEMBER 2022

PAGE | 19

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Figure 9. Annual dissolved oxygen depletion rate in the central basin of Lake Erie from 1970-2019.

6. CONCLUSIONS

U.S. EPA GLNPO Lake Erie Dissolved Oxygen
Monitoring Program 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).

In 2017-2019, hypoxic and anoxic conditions
were observed in all three sampling seasons by
our ship-based observations. However, seasonal
variations led to annual differences in the onset,
extent, and duration of these low-oxygen
conditions during each year. 2017 exhibited one
of the higher annual dissolved oxygen depletion
rates observed in the last two decades, which led
to the presence of anoxic conditions much
earlier in the season than had been recorded in
recent preceding years. On the other hand, 2018
and 2019 exhibited two of the lowest annual
dissolved oxygen depletion rates, and anoxia
was not seen until almost a month later during
these seasons compared to 2017.

DECEMBER 2022

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

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.

Bouffard, D., J.D. Ackerman, and L. Boegman. 2013. Factors Affecting the Development and Dynamics
of Hypoxia in a Large Shallow Stratified Lake: Hourly to Seasonal Patterns. Water Resour. Res.
49(5): 2380-2394.

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.

Charlton, M.N. 1980. Hypolimnion Oxygen Consumption in Lakes: Discussion of Productivity and
Morphometry Effects. Can. J. Fish. Aquat. Sci. 37(10): 1531-1539.

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 forthe 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). 2017. Dissolved Oxygen and Temperature Profiles
forthe Central Basin of Lake Erie Quality Assurance Project Plan. Revision 10, June 2017. U.S.
EPA Great Lakes National Program Office.

DECEMBER 2022

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

U.S. Environmental Protection Agency (U.S. EPA). 2018. 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.

U.S. Environmental Protection Agency (U.S. EPA). 2018. U.S. Action Plan for Lake Erie. Retrieved from
https://www.epa.gov/sites/production/files/2018-03/documents/us dap final march l.pdf.

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.

DECEMBER 2022

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

APPENDIX A - QUALITY CONTROL RESULTS

A summary of 2017 results not meeting acceptance criteria is provided in the table below.

Table A-l. Quality control (QC) scorecard of 2017 CTD-collected temperature and dissolved oxygen (DO) data not meeting acceptance criteria.

Survey

Issue

Cause

Decision

Corrective Actions

June 8

Temperature accuracy
check exceeded QC
criterion (1 of 2 samples)

Temperature of the hull may be
affecting the measurements from the
hull-mounted transducer.

Suspected issue with QC sample
methodology and does not affect
quality of CTD data. CTD
temperature values are
considered valid.

Independent temperature sensor will
be used for 2018 surveys.

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.

Additional training and/or
observational period will be required
for inexperienced analysts. Run
additional replicate analyses until
consistency is achieved.

June 27

Temperature accuracy
check exceeded QC
criterion (5 of 10 samples)

Temperature of the hull may be
affecting the measurements from the
hull-mounted transducer.

Suspected issue with QC sample
methodology and does not affect
quality of CTD data. CTD
temperature values are
considered valid.

Independent temperature sensor will
be used for 2018 surveys.

Winkler precision check
exceeded the QC criterion
(6 of 17 samples)

Analyst error

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Additional training and/or
observational period will be required
for inexperienced analysts. Run
additional replicate analyses until
consistency is achieved.

July 24-25

Temperature accuracy
check exceeded QC
criterion (2 of 10 samples)

Temperature of the hull may be
affecting the measurements from the
hull-mounted transducer.

Suspected issue with QC sample
methodology and does not affect
quality of CTD data. CTD
temperature values are
considered valid.

Independent temperature sensor will
be used for 2018 surveys.

DECEMBER 2022

PAGE | A-l

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Survey

Issue

Cause

Decision

Corrective Actions

Winkler precision check
exceeded the QC criterion
(5 of 14 samples)

Analyst error

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Additional training and/or
observational period will be required
for inexperienced analysts. Run
additional replicate analyses until
consistency is achieved.

SeaBird vs. Winkler for
<5.00 mg/L Accuracy
differences exceeded the
QC criterion (2 of 6
samples)

Due to a thin hypolimnion.
thermocline or epilimnion water may
have been present in the Winkler
samples.

All samples where DO
>5.00mg/L were within QC
criteria (9 of 9 samples). CTD
DO values are considered valid.

Not Applicable

Aug 13-14

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.

Additional training and/or
observational period will be required
for inexperienced analysts. Run
additional replicate analyses until
consistency is achieved.

SeaBird vs. Winkler for
<5.00 mg/L Accuracy
differences exceeded the
QC criterion (2 of 2
samples)

Due to a thin hypolimnion.
thermocline or epilimnion water may
have been present in the Winkler
sample.

The accuracy RPD for both
surface samples passed the QC
criterion. CTD DO values are
considered valid.

Not Applicable

Sept 11-12

Temperature accuracy
check exceeded QC
criterion (4 of 10 samples)

Temperature of the hull may be
affecting the measurements from the
hull-mounted transducer.

Suspected issue with QC sample
methodology and does not affect
quality of CTD data. CTD
temperature values are
considered valid.

Independent temperature sensor will
be used for 2018 surveys.

Winkler precision check
exceeded the QC criterion
(4 of 15 samples)

Analyst error

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Additional training and/or
observational period will be required
for inexperienced analysts. Run
additional replicate analyses until
consistency is achieved.

CTD DO accuracy check
exceeded the QC criterion
(1 of 8)

Undetermined. Probe values were
slightly higher than neighboring
stations.

CTD DO values for ER31 are not
considered valid.

Recast CTD and/or re-sample for
Winkler Titration while on station, if
possible.

DECEMBER 2022

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Survey

Issue

Cause

Decision

Corrective Actions

SeaBird vs. Winkler for
<5.00 mg/L Accuracy
differences exceeded the
QC criterion (5 of 7
samples)

Due to a thin hypolimnion.
thermocline or epilimnion water may
have been present in the Winkler
sample.

8 of 9 samples where DO >5.00
mg/L were within QC criteria.
CTD DO values are considered
valid.

Not Applicable

Oct 2-3

Winkler precision check
exceeded the QC criterion
(4 of 12 samples)

Analyst error

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Additional training and/or
observational period will be required
for inexperienced analysts. Run
additional replicate analyses until
consistency is achieved.

DECEMBER 2022

PAGE | A-3

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

A summary of 2018 results not meeting acceptance criteria is provided in the table below.

Table A-2. Quality control (QC) scorecard of 2018 CTD-collected temperature and dissolved oxygen (DO) data not meeting acceptance criteria.

Survey

Issue

Cause

Decision

Corrective Actions

June 7-8

Temperature accuracy
check exceeded QC
criterion (1 of 2 samples)

Surface Temp and Probe Temp may
not have been taken at same depth.

Suspected issue with QC sample
methodology and does not affect
quality of CTD data. CTD
temperature values are
considered valid.

Ensure routine and QC measurements
are taken at the same depth.

June 26-27

Winkler precision check
exceeded the QC criterion
(3 of 4 samples)

Analyst error.

Replicate CTD casts are within
QC criteria. CTD DO values are
considered valid.

Run additional replicate analyses
until consistency is achieved.

July 19-20

Winkler precision check
exceeded the QC criterion
(1 of 4 samples)

Titrant ran out on station. Titrant may
have been too concentrated.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Ensure there is enough titrant for
entire station before beginning
analysis.

Aug 13-14

Winkler precision check
exceeded the QC criterion
(2 of 4 samples)

Cause cannot be determined.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Run additional replicate analyses
until consistency is achieved.

Aug 21-22

Winkler precision check
exceeded the QC criterion
(2 of 4 samples)

Cause cannot be determined.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Run additional replicate analyses
until consistency is achieved.

Sept 5-6

SeaBird vs. Winkler for
<5.00 mg/L Accuracy
differences exceeded the
QC criterion (1 of 2
samples)

Oxygen may have been introduced to
sample via bubbles. CTD DO value is
0.06 mg/L.

Surface sample for this station
(DO >5.00 mg/L) met QC
criterion. CTD DO values are
considered valid.

Care should be used when filling
collection bottle to reduce the risk of
introducing air bubbles to the sample.
Run additional replicate analyses
until consistency is achieved.

DECEMBER 2022

PAGE | A-4

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Survey

Issue

Cause

Decision

Corrective Actions

Winkler precision check
exceeded the QC criterion
(1 of 4 samples)

Cause cannot be determined.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Run additional replicate analyses
until consistency is achieved.

Sept 24-26

Temperature accuracy
check exceeded QC
criterion (2 of 2 samples)

Surface Temp and Probe Temp may
not have been taken at same depth.

Suspected issue with QC sample
methodology and does not affect
quality of CTD data. CTD
temperature values are
considered valid.

Ensure routine and QC measurements
are taken at the same depth.

Oct 3-4

Temperature accuracy
check exceeded QC
criterion (1 of 2 samples)

Surface Temp and Probe Temp may
not have been taken at same depth.

Suspected issue with QC sample
methodology and does not affect
quality of CTD data. CTD
temperature values are
considered valid.

Ensure routine and QC measurements
are taken at the same depth.

DECEMBER 2022

PAGE | A-5

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

A summary of 2019 results not meeting acceptance criteria is provided in the table below.

Table A-3. Quality control (QC) scorecard of 2019 CTD-collected temperature and dissolved oxygen (DO) data not meeting acceptance criteria.

Survey

Issue

Cause

Decision

Corrective Actions

Winkler precision check
exceeded the QC criterion
(1 of 5 samples)

Cause cannot be determined. Sample
was 0.02 mg/L above limit.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Run additional replicate analyses
until consistency is achieved.

June 5

Temperature accuracy
check exceeded QC
criterion (1 of 3 samples)

Surface Temp and Probe Temp may
not have been taken at same depth.

Suspected issue with QC sample
methodology and does not affect
quality of CTD data. CTD
temperature values are
considered valid.

Ensure routine and QC measurements
are taken at the same depth.

June 27

Winkler precision check
exceeded the QC criterion
(1 of 4 samples)

Cause cannot be determined. Sample
was 0.02 mg/L above limit.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Run additional replicate analyses
until consistency is achieved.

Winkler precision check
exceeded the QC criterion
(1 of 4 samples)

Oxygen may have been introduced to
sample via bubbles.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Run additional replicate analyses
until consistency is achieved.

July 17

Temperature accuracy
check exceeded QC
criterion (2 of 2 samples)

Surface temperatures were not taken
during survey. Surface temperature
values nearest NOAA surface buoy
were used.

CTD Temperature values cannot
be varied. Descension should be
used for this dataset.

Ensure surface temperature
measurements are made during the
survey.

July 31

Winkler precision check
exceeded the QC criterion
(1 of 4 samples)

Cause cannot be determined. Sample
was 0.01 mg/L above limit.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Run additional replicate analyses
until consistency is achieved.

Temperature accuracy
check exceeded QC
criterion (2 of 2 samples)

Surface Temp and Probe Temp may
not have been taken at same depth.

CTD Temperature values cannot
be varied. Descension should be
used for this dataset.

Ensure routine and QC measurements
are taken at the same depth.

Aug 26

Temperature accuracy
check exceeded QC
criterion (1 of 1 samples)

Surface Temp and Probe Temp may
not have been taken at same depth.

CTD Temperature values cannot
be varied. Descension should be
used for this dataset.

Ensure routine and QC measurements
are taken at the same depth.

DECEMBER 2022

PAGE | A-6

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LAKE ERIE DISSOLVED OXYGEN MONITORING PROGRAM TECHNICAL REPORT

Survey

Issue

Cause

Decision

Corrective Actions

Sept 5

Winkler precision check
exceeded the QC criterion
(1 of 4 samples)

One sample was much lower (0.61
mg/L) than the others. Titration might
not have been completed to
appropriate end point.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Run additional replicate analyses
until consistency is achieved.

Sept 26

Winkler precision check
exceeded the QC criterion
(2 of 4 samples)

Cause cannot be determined.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Run additional replicate analyses
until consistency is achieved.

Temperature accuracy
check exceeded QC
criterion (2 of 2 samples)

Surface Temp and Probe Temp may
not have been taken at same depth.

CTD Temperature values cannot
be varied. Descension should be
used for this dataset.

Ensure routine and QC measurements
are taken at the same depth.

Oct 9

Winkler precision check
exceeded the QC criterion
(1 of 4 samples)

Oxygen may have been introduced to
sample via bubbles. CTD DO value is
0.25 mg/L.

QC sample exceedance does not
affect quality of CTD data. CTD
DO values are considered valid.

Care should be used when filling
collection bottle to reduce the risk of
introducing air bubbles to the sample.
Run additional replicate analyses
until consistency is achieved.

Temperature accuracy
check exceeded QC
criterion (2 of 2 samples)

Surface Temp and Probe Temp may
not have been taken at same depth.

CTD Temperature values cannot
be varied. Descension should be
used for this dataset.

Ensure routine and QC measurements
are taken at the same depth.

DECEMBER 2022

PAGE | A-7

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