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Water Quality and Robots: Educating Minnesota Youth�

Depts. Of Computer Science and Engineering; Soil, Water and Climate, and Extension's Center for Youth Development at the University of Minnesota;

and High Tech Kids

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This material is supported by the Environmental and Natural Resources Trust Fund (ENRTF) of the State of Minnesota.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the ENRTF.

Acknowledgement

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Minnesota Lake Environmental Themes�

Module 2.2: Lake Monitoring, Lake Eutrophication and Trophic State, and Lake Water Quality Standards

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Lake Environmental Monitoring Theme

Minnesota Lake Environmental Monitoring Module LET2.2 Objectives:

1) Explain key lake water quality monitoring indicators and standards

2) Learn how to monitor water quality and assess eutrophication and impaired water

3) Introduce LakeFinder web browser for assessing lake water quality

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Minnesota Lake Water Quality Monitoring

Water quality is monitored by MPCA in order to protect and restore lake health for beneficial uses such as drinking water, aquatic habitat and life, swimming, fishing and boating

Water quality is monitored by measuring:

Total phosphorus concentration
Chlorophyll a concentration
Lake clarity and turbidity
Lake temperature
pH
Oxygen

Poor water quality often results in:

Algal blooms and fish kills
Cloudy water
Drinking water advisories

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Lake Phosphorus Concentration

Phosphorus is a key nutrient (think fertilizer) for growth of microscopic plants (algae) in a lake

Large increases in P concentration can cause algae blooms

Phosphorus in a lake can be caused by natural and human sources

Natural sources of P include release of P adsorbed to sediments at bottom of lake, and decomposition of organic matter and plants growing in lake
Human sources of P include agricultural or urban runoff and erosion or treated municipal wastewater

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Turbidity

Water clarity in many Minnesota lakes is assessed using measurements of turbidity (the Secchi disk depth also assesses water clarity using a different method)

Turbidity measures the amount of light scattered by suspended particles as light passes through water

Turbidity in a lake is excessive when:

Water has a turbidity exceeding 25 nephelometric turbidity units (NTU), meaning the water looks cloudy

Light penetration in lakes is decreased at high turbidity levels, causing:

Decreased photosynthesis and growth by submerged aquatic vegetation
Increased difficulty for aquatic organisms to breathe

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Lake Chlorophyll a Concentration

Chlorophyll a (Chl a) is a plant pigment in algae and plants that absorbs light as the first step in photosynthesis

Chlorophyll a (Chl a) concentration of lakes is measured by collecting water samples, filtering out the algae, extracting the Chl a and measuring its concentration in a laboratory

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Lake Chlorophyll a Concentration

Chlorophyll a concentration increases as the number and biomass of phytoplankton (algae) in a lake increase

Chl a levels become unsafe during algae blooms
Some algae are toxic (blue-green algae)
When algae die and decompose at the bottom of lake, oxygen levels in lake decrease, often leading to fish kills

Chl a concentrations are measured in micrograms per liter of water (µg/L which is the same as a ppb)

One microgram is one millionth of a gram
One liter of water contains 1000 grams of water
Therefore, one µg/L is a billionth of a liter – same as the units used to measure total phosphorus (parts per billion or ppb)

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Lake Water Clarity

Lake water clarity is reduced when lakes have high concentrations of total phosphorus (TP), chlorophyll a, and suspended soil particles

Lake water clarity is measured by lowering a Secchi disk (with alternating black and white quadrants) on a rope into the lake and measuring the depth to which you can still see the disk

The deeper you can see the disk, the greater the Secchi disk depth and the better the lake water clarity

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Lake Phosphorus Concentration

Phosphorus is a key nutrient (think fertilizer) for growth of microscopic plants (algae) in a lake

Large increases in P concentration can cause algae blooms

Phosphorus concentrations are assessed by analyzing water samples collected in a lake

Units of measurement are in micrograms per liter of water (µg/L which is the same as a ppb)
One liter of water contains 1000 grams of water
Therefore, one µg/L is a billionth of a liter – same as the units used to measure total phosphorus (parts per billion or ppb)

Optional Activity #8a (what is a ppb?)

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Activity #8b: pH

pH is a measure of hydrogen ion concentration in water

Neutral values occur when pH is 7.0
Water is increasingly acidic as pH levels drop below 7.0
Water is increasingly alkaline (basic) as pH levels increase above 7.0

Stratified eutrophic lakes are characterized by :

Surface water with pH levels between 7.5 and 8.5
Deep water with pH levels between 6.5 and 7.5 because of higher concentrations of carbon dioxide produced by decomposing algae

Generally, desirable pH levels in a lake are between 6.5 and 8.5

Use pH test strips at home on test liquids

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Temperature

Temperature is considered a “pollutant” in Minnesota lakes

Temperature of Minnesota lakes has increased by 3 to 4 degrees Fahrenheit during summer over the last 50 years during
The length of winter ice cover has also decreased by nearly two weeks

Fish can be distinguished based on the temperatures they can tolerate

Trout thrive in cold, deep northern Minnesota lakes that average 50 degrees F, and cannot tolerate temperatures higher than 68 degrees F
Bass, walleye and perch can tolerate higher temperatures ranging from 60-80 degrees F, and prefer southern lakes

Lake temperature affects water density and stratification, cool water is denser than warm water and settles to lake bottom.

What temperatures can trout and bass tolerate in degrees Celsius?

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Activity #9: Temperature

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Oxygen

Aquatic organisms need oxygen to breathe

Temperature affects water density in Minnesota lakes

Water has a maximum density at 39 degrees Fahrenheit
During winter, ice forms at the lake surface, but denser water below the ice has a lower freezing point and remains unfrozen, allowing fish to survive

Lakes become stratified by temperature in summer

Epilimnion (in surface water)

During summer, lakes warm up and water at the surface becomes less dense (epilimnion). This water is high in oxygen because of plants and algae.

Hypolimnion (in deep water)

The deeper water is cooler and denser and sinks (hypolimnion). Because there are few plants or algae in this deeper cooler water, it has low oxygen

Stratification is harmful to fish

With severe stratification, oxygen concentrations in deep water can become so low that fish cannot survive
Yet, if they try to move upward to the lake surface to get more oxygen, they face higher temperatures that may not allow them to survive

Temperature Stratification

epilimnion

hypolimnion

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How Does a Fish Breathe Under Water?

Fish need oxygen to breathe

Fish suck in water with their mouth

Water is forced back out to the lake through the fish gills
As water passes over the gills, the gills extract oxygen from the water
Oxygen then is transferred from the gills to blood that circulates through the gills
In turn, the blood passes carbon dioxide waste from the fish back into the water that is expelled from the gills

Gills are like our lungs, except that they only work when submerged in water

Blood passing through the gills then circulates throughout the body of the fish

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Other Lake Pollutants: Mercury

Mercury is a major pollutant in many Minnesota lakes

The source of mercury is burning of coal for energy, which creates mercury gas that can be transported to a lake through air by wind
Once in sediments or lake water, microorganisms can turn mercury into a more toxic form known as methyl mercury that is easily taken up by fish

Mercury pollution in a lake occurs when:

More than 10% of the fish have a mercury concentration greater than 0.2 parts per million (ppm), or
Lake water has a mercury concentration greater than 1.3 nanograms per liter (ng/L)

Fish in northeastern Minnesota lakes have higher mercury concentrations than fish from other lake regions

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Other Lake Pollutants: Chloride

Chloride is a major pollutant in many Minnesota lakes

The main source of chloride is road salt used to prevent icy roads
Agricultural fertilizers are a smaller source of chloride

Chloride pollution in a lake occurs if:

Lake water has a chloride concentration greater than 230 milligrams per liter (mg/L)
One mg/L is the same as a part per million (ppm)

One teaspoon of salt (2,300 mg) added to a gallon of water causes severe pollution

Salt is spread on roads, parking lots and sidewalks to melt ice in winter

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Lake Eutrophication

Eutrophication is a serious problem in many Minnesota lakes

Eutrophication often occurs when lakes have excessive concentrations of nutrients such as phosphorus
Nutrients cause algal growth

Eutrophication often leads to oxygen depletion and fish kills

When algae bloom, die and then settle to the lake bottom they begin to decompose
Decomposition reduces oxygen concentrations near the lake bottom, causing fish to die

Eutrophication is assessed by measuring total phosphorus, chlorophyll a pigments, and water clarity

If these measurements violate water quality standards, the lake is said to be impaired by eutrophication

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Trophic State Index (TSI) Levels

The Trophic State Index (TSI) measures lake algal biomass and nutrient enrichment on a scale of 0 to 100, with lower numbers indicating better health and water clarity due to lower algal biomass and nutrient enrichment

Trophic State Index is used to define four classes of trophic status:

Oligotrophic (TSI <35) – Few nutrients (phosphorus), high levels of dissolved oxygen, low algal concentrations, deep, clear water that supports trout
Mesotrophic (TSI of 35 to 50) – Medium amount of nutrients, moderately clear water that supports bass and walleye, some algal blooms in late summer, oxygen depletion at bottom of lake as algae die and decompose
Eutrophic (TSI of 50 to 70) – Nutrient rich, highly productive algae growth, shallow lakes, seasonally deficient in oxygen, may lead to fish kills, carp dominate
Hypereutrophic (TSI >70) – Extremely rich in nutrients, highest amount of algae growth, lowest oxygen, many fish kills

Impaired lakes have Trophic State Index (TSI) values greater than about 30 – 65, depending on the Ecoregion

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Trophic Classes for Total Phosphorus

For Total Phosphorus (TP) measurements, lower values mean better water clarity and lower nutrient enrichment, while higher values of TP indicate poorer water clarity and higher nutrient enrichment

US EPA defines four classes of Trophic State for TP measurements (in ppb):

Oligotrophic: <12 µg/L
Mesotrophic: 12 to 30 µg/L
Eutrophic: 30 to 100 µg/L
Hypereutrophic: >100 µg/L

US EPA Nat’l Lakes Assessment

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Trophic Classes for Chlorophyll a

For Chlorophyll a (Chl a) measurements, lower values mean better water clarity and lower nutrient enrichment, while higher values of Chl a indicate poorer water clarity and higher nutrient enrichment

US EPA defines four classes of Trophic State for Chl a measurements (in ppb):

Oligotrophic: <10 µg/L
Mesotrophic: 10 to 20 µg/L
Eutrophic: 20 to 60 µg/L
Hypereutrophic: >60 µg/L

US EPA Nat’l Lakes Assessment

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Trophic Classes for Water Clarity

For Secchi disk depth measurements, lower values mean poor water clarity and high nutrient enrichment, while higher values of Secchi disk depth indicate better water clarity and lower nutrient enrichment

US EPA defines four classes of Trophic State for Secchi disk depth measurements (in m):

Oligotrophic: >3.5 m
Mesotrophic: 2 to 3.5 m
Eutrophic: 0.7 to 2 m
Hypereutrophic: <0.7 m

US EPA Nat’l Lakes Assessment

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Lake Ecoregion Water Quality Standards

Minnesota established its own Numerical lake water quality standards for each Ecoregion to account for differences in lake depth and tolerance of fish in northern versus southern Minnesota

When these standards are violated, the lake is listed as being impaired, there are currently 2,222 lakes on the impaired list

For impaired lakes, goals and strategies are developed to clean up the lake

Water quality standards are set for:

Total phosphorus concentration
Chlorophyll a concentration
Lake clarity
Mercury and chloride are other common lake pollutants

Water quality standards are more strict for the:

N. Lakes and Forests Ecoregion than for
N. Central Hardwood Forest Ecoregion, which is more strict than for the
N. Glaciated Plains and W. Corn Belt Plains Ecoregions

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Activity #10: Impaired Lake 1

Fleming Lake near Palisade in Aitken Co. is impaired for nutrients

Use LakeFinder for this lake

https://www.dnr.state.mn.us/lakefind/index.html

Scroll down to Lake reports and use the Water Quality/ Water Quality Summary to determine Trophic State Index (TSI) and the 10-yr summer averages for:

Lake transparency (m)
Chlorophyll a concentration (ppb)
Total phosphorus concentration (ppb)

How do these water quality averages compare with Minnesota water quality standards for the N. Lakes and Forests Ecoregion?

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Answers: Impaired Lake 1

Fleming Lake near Palisade in Aitken Co. is impaired for nutrients

Use Water Quality option in LakeFinder to find the trophic state index (TSI) for this lake

Water Quality Summary for 10-yr summer averages:

Lake transparency (1 m)
Chlorophyll a concentration (42 ppb)
Total phosphorus concentration (63 ppb)

How do these water quality averages compare with Minnesota water quality standards for the N. Lakes and Forests Ecoregion?

Lake transparency (2 m)
Chlorophyll a concentration (9 ppb)
Total phosphorus concentration (30 ppb)

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Activity #10: Impaired Lake 2

Cokato Lake in Wright Co. is impaired for nutrients

Use LakeFinder for this lake

https://www.dnr.state.mn.us/lakefind/index.html

Scroll down to Lake reports and use the Water Quality/Water Quality Summary to find the trophic state index (TSI) and determine 10-yr summer averages for:

Lake transparency (m)
Chlorophyll a concentration (ppb)
Total phosphorus concentration (ppb)

How do these water quality averages compare with Minnesota water quality standards for the N. Central Hardwood Forest Ecoregion?

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Answers: Impaired Lake 2

Cokato Lake in Wright Co. is impaired for nutrients

Use Water Quality option in LakeFinder to find the trophic state index (TSI) for this lake

Water Quality Summary for 10-yr summer averages:

Lake transparency (2 m)
Chlorophyll a concentration (32 ppb)
Total phosphorus concentration (53 ppb)

How do these water quality averages compare with Minnesota water quality standards for the N. Central Hardwood Forest Ecoregion?

Lake transparency (1.4 m)
Chlorophyll a concentration (14 ppb)
Total phosphorus concentration (40 ppb)

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Activity #10: Impaired Lake 3

Long Tom Lake near Ortonville in Big Stone Co. is impaired for nutrients

Use Water Quality option in LakeFinder for this lake

https://www.dnr.state.mn.us/lakefind/index.html

Scroll down to Lake reports and use the Water Quality/Water Quality Summary to find the trophic state index (TSI) and determine 10-yr summer averages for:

Lake transparency (m)
Chlorophyll a concentration (ppb)
Total phosphorus concentration (ppb)

How do these water quality averages compare with Minnesota water quality standards for the N. Glaciated Plains Ecoregion?

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Answers: Impaired Lake 3

Long Tom Lake near Ortonville in Big Stone Co. is impaired for nutrients

Use Water Quality option in LakeFinder to find the trophic state index (TSI) for this lake

Water Quality Summary for 10-yr summer averages:

Lake transparency (2 m)
Chlorophyll a concentration (50 ppb)
Total phosphorus concentration (598 ppb)

How do these water quality averages compare with Minnesota water quality standards for the N. Glaciated Plains Ecoregion?

Lake transparency (0.9 m)
Chlorophyll a concentration (22 ppb)
Total phosphorus concentration (65 ppb)

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Activity #10: Impaired Lake 4

Eagle Lake near Mountain Lake in Cottonwood Co. is impaired for nutrients

Use Water Quality option in LakeFinder for this lake

https://www.dnr.state.mn.us/lakefind/index.html

Scroll down to Lake Reports and use the Water Quality/Water Quality Summary to to find the trophic state index (TSI) and determine 10-yr summer averages for:

Lake transparency (m)
Chlorophyll a concentration (ppb)
Total phosphorus concentration (ppb)

How do these water quality averages compare with Minnesota water quality standards for the W. Corn Belt Plains Ecoregion?

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Answers: Impaired Lake 4

Eagle Lake near Mountain Lake in Cottonwood Co. is impaired for nutrients

Use Water Quality option in LakeFinder to find the trophic state index (TSI) for this lake

Water Quality Summary for 10-yr summer averages:

Lake transparency (N/A)
Chlorophyll a concentration (52 ppb)
Total phosphorus concentration (116 ppb)

How do these water quality averages compare with Minnesota water quality standards for the W. Corn Belt Plains Ecoregion?

Lake transparency (0.9m)
Chlorophyll a concentration (22 ppb)
Total phosphorus concentration (65 ppb)

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