Survey of Reservoir Greenhouse Gas Emissions Monroe Lake Water Quality Survey

Survey of Reservoir Greenhouse gas Emissions

file:///P:/PDF_Harvest/ScienceInventory/ScienceInventoiyHarvest/600.

Survey of Reservoir Greenhouse gas
Emissions

Monroe Lake Water Quality Survey

Jake Beaulieu
25 July, 2022

1. Background

Between 2020 and 2023 the US Environmental Protection Agency (USEPA) will survey water quality and
greenhouse gas (GHG) emissions from 108 reservoirs distributed across the United States (Figure 1). The
objective of the research is to estimate the magnitude of GHG emissions from US reservoirs.

All reservoirs included in this study were previously sampled by the USEPA during the 2017 National Lakes
Assessment (2017 NLA). Data from the 2017 NLA can be found at the EPA website (https://www.epa.gov/national-
aquatic-resource-surveys/data-national-aquatic-resource-surveys). Data for Monroe Lake can be found under
SITE J D NLA17JN-10009.

Afield sensor is used to measure chlorophyll a, dissolved oxygen, pH, specific conductivity, water temperature,
and turbidity near the water surface at a minimum of 15 locations within each reservoir. Water samples are
collected from the deepest site for analysis of nutrients and chlorophyll a.

This preliminary report presents water quality results for Monroe Lake. These data will be included in a formal
peer-reviewed publication to be submitted for publication in 2024.

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mm

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Coastal Plains
Northern Appalachians
Northern Plains
Southern Appalachians
Southern Plains
Temperate Plains
Upper Midwest
Western Mountains

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UPR-EGP, arid the GIS User Community

Figure 1. Location of the 108 Reservoirs Included in Study.

2. Monroe Lake Survey Design

The Monroe Lake survey design included 20 sampling sites that were sampled on 2020-08-10. Water chemistry
samples were collected from a 9.8m deep site nearby the dam (Figure 2). Click on any of the sites to see the site
id, water temperature, pH, turbidity, and dissolved oxygen at the water surface.

+ Sample sites

I—I .-O sensor sites

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35a

Figure 2. Location of the 15 sampling sites in Monroe Lake.

3. Lake Disturbance and Trophic Status

Lakes are often classified according to their trophic state. There are four trophic state categories that reflect
nutrient availability and plant growth within a lake. A eutrophic lake has high nutrients and high algal and/or
macrophyte plant growth. An oligotrophic lake has low nutrient concentrations and low plant growth. Mesotrophic
lakes fall somewhere in between eutrophic and oligotrophic lakes and hypereutrophic lakes have very high
nutrients and plant growth. Lake trophic state is typically determined by a wide variety of natural factors that
control nutrient supply climate, and basin morphometry. A metric commonly used for defining trophic state is the
concentration of chlorophyll a, an indicator of algae abundance, in the water column. Chlorophyll a concentration
was 4 ug/L during the sampling, indicating the lake was mesotrophic.

Trophic State Classification

Analyte

Oligotrophic

Mesotrophic

Eutrophic

Hypereutrophic

chlorophyll a (ug/L)

<=2

>2 and <=7

>7 and <=30

>30

In addition to classifying lakes by trophic status, lakes can be classified by degree of disturbance relative to
undisturbed lakes (i.e. reference lakes) within the ecoregion. Degree of disturbance can be based on a wide
variety of metrics, but here we use nutrients (total phosphorus (tp), total nitrogen (tn)), suspended sediment
(turbidity), chlorophyll a, and dissolved oxygen (do). Lake disturbance values range from least to moderately
disturbed.

Chemical Condition Indicators Measured at Water Chemistry Site

Threshold Values	Observed Values

parameter

units

least disturbed

moderately disturbed

most disturbed

concentration

status

do

mg/l

>5

>3 f

i<5

<3

8

least disturbed

turbidity

NTU

<3.32

>3.32 (

x <4.67

>4.67

3.60

moderately disturbed

tp

ug/i

<34

>34 i

CO
LO

V

>56

24

least disturbed

tn

ug/l

<657

>657 I

A
CO
CO
CD

>830

200

least disturbed

chlorophyll a

ug/l

<6.85

>6.85 f

A
CO
oo

>13.8

4.1

least disturbed

4. Within-lake Spatial Patterns

A field sensor was used to measure water temperature, pH, dissolved oxygen, and turbidity near the water surface

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at all sampling sites. Data are reported in figures and tables below. Hover the curser over any point in the figures
to reveal the sitelD corresponding to the adjacent data table. Alternatively, click on any row in the data table to
reveal the location of the sampling site on the map.

Dissolved oxygen and pH, indicators of algal activity, were highest in the upper reaches of the reservoir. This
pattern often occurs when tributaries are the primary nutrient source to reservoir surface waters. Algal activity is
highest in the high nutrient waters, causing dissolved oxygen and pH to be elevated (e.g. photosynthesis produces
oxygen and consumes dissolved inorganic carbon, causing pH to increase). High turbidity was associated with
high DO and pH, potentially reflecting high algal biomass. Closer to the dam, surface water was clearer and had
lower dissolved oxygen, possibly because algal activity was limited by relatively lower nutrient availability.



water

sitelD

temp

1

27.82

2

26.99

3

27.07

4

27.36

5

29.77

6

27.78

7

27.92

8

26.78

9

26.87

10

27.36

11

27.02

12

29.06

13

29.48

14

28.68

15

27.33

16

30.26

17

29.99

18

27.79

19

29.6

20

30.17

sitelD

pH

1

8.34

2

8.3

3

8.12

4

8.69

5

9.01

6

8.3

7

8.63

8

8.43

9

8.5

10

8.35

11

8.49

Water
Temp.

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sitelD

pH

12

9.27

13

8.78

14

8.31

15

8.5

16

9.69

17

9.44

18

8.28

19

9.59

20

9.15



Turbidity

sitelD

(NTU)

1

2.8

2

2.3

3

4.4

4

4.4

5

21.3

6

1.8

7

4.3

8

3.3

9

4.4

10

1.7

11

3.2

12

13

13

16

14

1.8

15

3.6

16

17

17

16.8

18

1.5

19

17.7

20

25.3



DO

sitelD

(mg/L)

1

8.36

2

7.5

3

7.46

4

7.63

5

10.67

6

7.37

7

7.21

8

8.69

9

8.76

10

7.54

11

7.46

Turbidit
{NTU)

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Dissolved

Oxygen

(mg/L)

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Getmapping, Aerogrid, IGN, IGP, UPR-EGP, and the GIS User Community	_

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sitelD (mg/L)

12 6.91

13 10.86

14 7.32

15 8.83

16 10.64

17 10.02

18 8.36

19 10.78

5. Depth Profiles To W

Dissolved oxygen is one of the most important environmental factors affecting aquatic life. The biological demand
for oxygen is often greatest near the sediment where the decomposition of organic matter consumes oxygen
through aerobic respiration. Near the surface of lakes, photosynthesis by phytoplankton produces oxygen, often
leading to a general pattern of decreasing oxygen availability with increasing depth. This pattern can be
exacerbated by thermal stratification. Thermal stratification occurs when lake surface waters are warmed by the
sun, causing the water to become less dense and float on top of the deeper, cooler lake water. Since the deeper
layer of water cannot exchange gases with the atmosphere, the dissolved oxygen content of the deep water
cannot be replenished from the atmosphere. As a result, the deep water can become progressively depleted of
oxygen as it is consumed by biological activity, sometimes causing dissolved oxygen to become sufficiently scarce
to stress oxygen sensitive organisms including some fish and insects.

The deepest sampling location in Monroe Lake was 9.8 m deep. The water was strongly stratified at the sampling
site, yet dissolved oxygen exceeded 4 mg/L at the lake bottom.

Monroe Lake Depth Profiles

Temperature (°C)

10 15 20 25 30

Dissolved Oxygen (mg L 1)

1. Jake Beaulieu, United States Environmental Protection Agency, Office of Research and Development,
Beaulieu.Jake@epa.gov (mailto:Beaulieu.Jake@epa.gov)«J

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