Report on the Transparency of Minnesota Lakes - Minnesota Pollution

Report on the Transparency of Minnesota Lakes - Minnesota Pollution

Minnesota Pollution Control Agency 520 Lafayette Road North Saint Paul, MN 55155-4194 http://www.pca.state.mn.us 651-296-6300 or 800-657-3864 toll fr...

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Minnesota Pollution Control Agency 520 Lafayette Road North Saint Paul, MN 55155-4194 http://www.pca.state.mn.us 651-296-6300 or 800-657-3864 toll free TTY 651-282-5332 or 800-657-3864 toll free Available in alternative formats

Volunteer lake monitors are one of Minnesota’s most important lake water quality tracking systems. The Minnesota Pollution Control Agency thanks the Citizen Lake-Monitoring Program volunteers for their efforts in collecting water quality data. Their efforts toward protecting the surface waters of Minnesota are greatly appreciated.

Authors and Contributors Johanna Schussler Jennifer L.K. Klang Kacy Bobzien Sandy Simbeck Shane Hanley Andrea Ebner

Editing and Graphics Peggy Hicks Mike Nelson Beth Tegdesch

wq-lar2-07

The MPCA is reducing printing and mailing costs by using the Internet to distribute reports and information to a wider audience. For additional information, see the Web site: http:// www.pca.state.mn.us/water/clmppublications.html#annualreports

Table of Contents Page List of Figures............................................................................................................................................... i List of Tables ................................................................................................................................................ i Introduction...................................................................................................................................................1 Secchi Transparency .....................................................................................................................................2 Ecoregions and Lake Water Quality .............................................................................................................2 Trophic State Index.......................................................................................................................................4 2007 CLMP Secchi Season Summary ..........................................................................................................6 CLMP+ Program: Updates for 2007.............................................................................................................9 Hammal Lake Trophic Status Example ......................................................................................................10 Glossary ......................................................................................................................................................14 Bibliography ...............................................................................................................................................15 Appendix I. 2007 CLMP Data and Participants .........................................................................................16 Appendix II. Carlson’s Trophic State Index ...............................................................................................71

List of Figures Page

1. Water Year Precipitation and Departure from Normal Maps ................................................................3 2. Typical Summer-Mean Secchi Transparency ........................................................................................5 3. 2007 CLMP Lakes Monitored by County..............................................................................................7 4. 2007 CLMP Lakes Summer-Mean Secchi Transparency ......................................................................8 5. Hammal Lake Bathymetric Map and Monitoring Location.................................................................10 6. Hammal Lake Total Phosphorus and Chlorophyll-a Results for 2007 ................................................11 7. Hammal Lake Secchi Transparency for 2007 ......................................................................................12 8. Carlson’s Trophic State Index..............................................................................................................13

List of Tables Page 1. Summer-Mean Secchi Transparency Measures by Ecoregion...............................................................4 2. Summer-Mean Water Quality Parameters for Hammal Lake ..............................................................11 3. Trophic Status Indicators for Hammal Lake ........................................................................................12

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 i

Introduction The Citizen Lake-Monitoring Program (CLMP) began in 1973 at the University of Minnesota, and was developed by Dr. Joe Shapiro. During that first year, volunteers monitored 74 lakes. Administration of the CLMP was transferred to the Minnesota Pollution Control Agency (MPCA) in 1978. The CLMP continues to be a cost-effective mechanism for obtaining good, basic water quality data on many of Minnesota’s lakes. Information about lake water quality is vital for assessing a lake’s physical condition and recreational suitability. Minnesota has more than 12,000 lakes and a limited number of state staff to monitor them. The participation of citizen volunteer monitors in the CLMP effectively increases the monitoring capabilities of the state. Volunteers provide the state and others with valuable information on the water quality of Minnesota’s lakes. The CLMP involves the voluntary participation of citizens residing on or near lakes or those who are frequent lake users. These participants are asked to take weekly transparency measurements on their lake during the summer using a Secchi disk. At least eight to ten readings per season are needed to adequately define each summer’s water quality. Through this process, the volunteers can learn about the water quality of lakes in their area and gain a greater awareness of the causes and effects of lake degradation. Data from the CLMP are entered into the U.S. Environmental Protection Agency’s water quality database (called STORET) along with all other water quality data collected by the MPCA. For many lakes, CLMP data is the only water quality information available. These data are used to analyze water quality trends, characterize trophic status (biological productivity), provide ground-truthing for remote satellite water quality imagery, and provide a basis for water quality goal setting. Several topics will be covered in this report. First, a discussion of how Secchi depth transparency means is related to water quality. Following that will be two sections on how, using Secchi transparency data, lakes can be compared and lake trophic status can be determined. Next, there is a brief summary of the 2007 water monitoring season, followed by an update on the advanced Citizen Lake-Monitoring Program (CLMP+). The final section will wrap up with an example showing the determination of a trophic state index for a lake. Appendix I contain seasonal averages, sorted by county, for all lakes, sites and volunteers participating in the CLMP during the 2007 season.

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 1

Secchi Transparency – What does it measure, and what can influence it? Secchi transparency is a measure of the depth of light penetration in the water column. The term “clarity” is often used interchangeable with “transparency.” These measurements provide a basis for assessing water quality, estimations of trophic status and documentation of trends in water quality over time. Secchi transparency can vary greatly among Minnesota’s lakes. In many Minnesota lakes, Secchi transparency provides an indirect measure of the amount of algae in the water (see Trophic State Index). In some lakes, suspended sediments or color caused by dissolved organic material may limit transparency. Precipitation is another factor that can affect the water quality of Minnesota’s lakes. In “wet years,” excessive precipitation in a lake’s watershed often leads to high amounts of runoff and high nutrient loading. This may result in increased algae, and possibly increased suspended sediments in the lake, leading to reduced transparency; however, these impacts may be moderated by increased “flushing” of the lake. In “dry years,” the inverse may be true and some lakes may experience increased transparency during periods of low runoff and decreased nutrient loading. It is important to note that no two lakes respond in exactly the same fashion to “wet” or “dry” years. Several consecutive years of monitoring are often needed to understand how your lake responds to climatic changes. Figure 1 shows precipitation in Minnesota from October 2006 to September 2007 (Water Year 2007). Figure 1 also shows the precipitation “departure from normal” or how far from average precipitation in 2007 was across the state. This figure shows that precipitation in much of the central region of Minnesota was near or up to six inches below normal, while southeast and extreme western portions of Minnesota experienced above normal precipitation. As discussed above, these variations can have impacts on water quality in area lakes.

Ecoregions and Lake Water Quality Ecoregions are areas of similar soil, geomorphology, land use, and potential natural vegetation. These factors provide a good basis for comparing differences and similarities in Minnesota’s lakes by grouping lakes according to their physical characteristics (i.e. grouping lakes with forested shores and rocky substrates together). The U.S. Environmental Protection Agency divided Minnesota into seven fairly distinct ecoregions (Figure 2). Reference lakes, which represent lakes minimally impacted by surrounding land-uses, were sampled by the MPCA to characterize trophic status conditions for each ecoregion (Heiskary and Wilson, 1989). This yields a baseline for comparison to other lakes. In other words, the reference lakes are the yardsticks by which we measure other lakes. Below is a description of the four ecoregions that contain 98 percent of Minnesota’s lakes. Table 1 (and Figure 2) lists typical Secchi readings for reference lakes in each ecoregion. The Northern Lakes and Forests ecoregion (NLF) is predominately forested with numerous lakes and is located in the northeastern part of Minnesota (Figure 2). These lakes tend to be relatively small and deep, and they stratify (form layers) during the summer. The North Central Hardwood Forests ecoregion (NCHF) is a transitional region that stretches from the northwestern part of Minnesota to east central Minnesota and includes the Twin Cities area. It has numerous lakes in rolling terrain with various land uses and a high population density. Lakes in this ecoregion also tend to be deep and have relatively small surface areas. The Western Corn Belt Plains ecoregion (WCBP) is located in the southern one-third of Minnesota. It has rolling terrain and is extensively cultivated with row crops. WCBP lakes tend to be shallow, well mixed, and have relatively large surface areas. The Northern Glaciated Plains ecoregion (NGP) is located along the southwestern half of the state. It is similar to the WCBP ecoregion in many ways, also having rolling terrain and extensive cultivation of row crops. It typically has a lower precipitation rate and higher evaporation rate than the WCBP ecoregion. The lakes in the NGP ecoregion are typically shallow and do not stratify during the summer.

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 2

Figure 1. Water Year Precipitation & Departure from Normal Maps

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 3

Lakes of similar make up (soils, depth, land use, etc.) can be compared against the ranges of values expected in a specific ecoregion. To do this, determine the ecoregion in which the lake of interest is located. Next, compare the summer mean Secchi depth (June to September) to the ranges below (Table 1). If the Secchi depth is shallower than the range listed, the lake is in the lower 25 percent of lakes for clarity – poorer clarity than the expected range for lakes of that ecoregion. If the Secchi transparency is deeper than the range listed, the lake is in the upper 25 percent of lakes for the ecoregion – better clarity than the expected range. If a lake is on the border of two ecoregions, the clarity will often overlap the ranges of the ecoregions it spans. These lakes would be in a transition zone between ecoregions, and a closer look at land use, soil type, and vegetation may be required to determine which ecoregion is the best fit. Table 1. Summer-Mean Secchi Transparency Measures by Ecoregion Based on interquartile ranges for reference lakes1

Parameter

Northern Lakes And Forests

North Central Hardwood Forests

Western Corn Belt Plains

Northern Glaciated Plains

Secchi (feet)

8 -15

4.9 - 10.5

1.6 - 3.3

1.0 - 3.3

Secchi (meters)

2.4 - 4.6

1.5 - 3.2

0.5 - 1.0

0.3 - 1.0

1

Interquartile range is determined by sorting measures from lowest to highest and represents those measures between the 25th and 75th percentile.

Trophic State Index While the ecoregion classification allows for comparison between lakes of similar origin, land use, etc., Carlson’s Trophic State Index allows for comparison of any lakes, independent of their location or land use. Secchi transparency data can be used to convey information on the quality of lakes and allow for estimation of the amount of algae (chlorophyll-a) and nutrients (phosphorus) in a lake. Carlson’s Trophic State Index (TSI) is a common means for characterizing a lake’s trophic state. The term “trophic state” refers to the level of biological productivity in a lake as measured by phosphorous content, algae abundance, and depth of light penetration. Carlson’s TSI (Carlson 1977) is one means available to examine the relationship between total phosphorus, chlorophyll-a, and Secchi disk readings in a lake and its overall productivity. Individual TSI values can be calculated from the following equations: Total phosphorus TSI (TSIP) = 14.42*[ln(TP average)] + 4.15 Chlorophyll-a TSI (TSIC) = 9.81*[ln(Chlorophyll-a average)] + 30.6 Secchi disk TSI (TSIS) = 60 - (14.41*[ln(Secchi average)]) Total phosphorus and chlorophyll-a are measured in micrograms per liter (μg/L) and Secchi transparency is measured in meters (3.281 feet per meter). The ln function in these equations is the “natural log” which is different than the “log” function. [The ln key is generally found next to the log key on most calculators.] The TSI scale ranges from 0 (ultra-oligotrophic – very nutrient poor, low vegetation or algae) to 100 (hypereutrophic – very nutrient rich, high amounts of vegetation or algae). Increasing trophic status values indicate more eutrophic conditions (higher productivity). Although total phosphorus and chlorophyll-a concentrations are not measured in the basic CLMP program, the summer-mean Secchi transparency generally provides a good indication of trophic status and can be used to estimate likely ranges of total phosphorus and chlorophyll-a for most Minnesota lakes.

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 4

Figure 2. Typical Summer-Mean Secchi Transparency Based on Interquartile Ranges for Reference Lakes

Northern Minnesota Wetlands

Northern Lakes and Forests 8 - 15 Ft 2.4 - 4.6 M

Red River Valley

North Central Hardwood Forest 4.9 - 10.5 Ft 1.5 - 3.2 M

Northern Glaciated Plains 1.0 - 3.3 Ft 0.3 - 1.0 M

Driftless Area

Western Corn Belt Plains 1.6 - 3.3 Ft 0.5 - 1.0 M

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 5

2007 CLMP Secchi Season Summary During the 2007 monitoring season, 1,187 CLMP volunteers monitored 2,110 sites on 1,263 lakes (Figure 3) taking 16,469 individual Secchi readings. The statewide seasonal mean transparency for the 2007 season was 9.9 feet. Knife Lake in Lake County, monitored by the Northern Tier High Adventure Boy Scout Camp, had the deepest individual Secchi transparency reading (60 feet on 08/15/2007); followed closely by Sabin Lake (Embarrass Pit) in St. Louis County monitored by Ed and Lee Steblay with Secchi transparency readings of 57 and 54 feet on 8/12/2007 and 08/28/2007, respectively). Three lakes – Clearwater (Cook County), Caribou (Itasca County) and Sabin Lake (St. Louis County), had summer average Secchi transparency readings (based on at least three readings) of 30 feet or more in 2007. Three lakes had summer average Secchi transparency readings of less than one foot in 2007. These lakes were Curtis Lake in Yellow Medicine County (0.5 feet), Fountain Lake in Wright County (0.5 feet) and Wakanda (main basin) Lake in Kandiyohi County (0.4 feet). These same three lakes had maximum individual Secchi transparency readings of one foot or less - Curtis Lake (0.5 feet), Fountain Lake (0.5 feet) and Wakanda (main basin) Lake (0.5 feet). Two lakes also recorded individual transparency values of zero feet (0.0) – Diamond Lake (Kandiyohi County) and Zumbro Lake (Olmsted County). Citizens monitored 121 lakes in Lake County, making it the county with the highest participation. The counties with the next highest number of lakes monitored in 2007 were Saint Louis County with 102 lakes, Cook County with 95 lakes, Crow Wing County with 92 lakes, and Itasca County with 91 lakes. Twelve counties only had one lake monitored by CLMP volunteers. Twenty-three counties had no citizen lake monitoring activities in 2007. Summer-mean, minimum and maximum Secchi values were calculated for each CLMP site. Participant names and individual 2007 summer-mean (June through September) Secchi data for each site are listed in Appendix I. It is important to note that only data collected for the Citizen Lake-Monitoring Program was used to calculate the values found in this appendix.

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 6

KITTSON

LAKE OF THE WOODS

Figure 3. 2007 CLMP Lakes Monitored by County

ROSEAU

MARSHALL KOOCHICHING PENNINGTON COOK

BELTRAMI RED LAKE CLEARWATER

POLK

3

LAKE

28 ST. LOUIS ITASCA

4

5

CASS

HUBBARD

47

BECKER

CLAY

121

102

91

MAHNOMEN

NORMAN

95

77

55 CROW WING

WADENA

WILKIN OTTER TAIL

CARLTON

AITKIN

92

4

13

30

50

PINE MILLE LACS

20

32

1

12 BENTON

TRAVERSE

POPE

STEVENS

BIG STONE

1

1

STEARNS

13

ISANTI

SHERBURNE

31

2

22

CHIPPEWA

YELLOW MEDICINE

LYON

PIPESTONE

2

ROCK

MURRAY

5 NOBLES

BROWN

2

COTTONWOOD WATONWAN

2

LE SUEUR

12

1 BLUE EARTH

1

DAKOTA

4

NICOLLET

1

2

20

SCOTT

1

REDWOOD

21

30

21

SIBLEY LINCOLN

RAMSEY

HENNEPIN

CARVER

3

RENVILLE

1

11

34 MCLEOD

13

ANOKA

WRIGHT

MEEKER

15

LAC QUI PARLE

4

15

SWIFT KANDIYOHI

7

CHISAGO

4

17

4

WASHINGTON

1

MORRISON

DOUGLAS

KANABEC

TODD GRANT

23 GOODHUE RICE WABASHA

12

WASECA STEELE

DODGE

1

5

JACKSON

MARTIN

FARIBAULT

FREEBORN

4

5

1

2

2007 Report on the Transparency of Minnesota Lakes

OLMSTED

WINONA

3 MOWER

FILLMORE

HOUSTON

Minnesota Pollution Control Agency May 2008 7

Figure 4. 2007 CLMP Lakes Summer-Mean Secchi Transparency

Average Transparency (ft) Less than 2.0 2.0 - 4.9 5.0 - 7.9 8.0 - 14.9 15.0 or Great

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 8

CLMP+ Program: Updates for 2007 The advanced Citizen Lake Monitoring Program (CLMP+) takes volunteer monitoring beyond the Secchi disk. In CLMP+, volunteers also collect water chemistry and temperature data in addition to transparency data. During the summer of 2007, eleven lakes in Aitkin County were sampled as a part of the CLMP+ program. These lakes were selected because they were a priority within Aitkin County or they lacked water quality data beyond Secchi transparency data. The combination of water chemistry and Secchi data provides a good baseline for assessing water quality in these lakes. Lakes included in the study were: Blind (01-0188), Elm Island (01-0123), Esquagamah (01-0147), Fleming (010105), Hammal (01-0161), Horseshoe (01-0034), Nord (01-0117), Rat (01-0077), Ripple (01-0146), Spirit (010178), and Waukenabo (01-0136). All equipment and analytical costs for the samples were provided and paid for by the Minnesota Pollution Control Agency (MPCA). Volunteers on these lakes collected water chemistry samples and temperature profiles one to two times per month. Janet Smude with the Aitkin County Soil and Water Conservation District (SWCD) helped plan and coordinate the sample shipping. Johanna Schussler, Jennifer Klang and Pam Anderson, MPCASt. Paul office, helped plan, train volunteers, and monitor lakes participating in the 2007 program. Special thanks to the volunteers who helped make this project a success: Kevin Pullis (Blind Lake), Rick Gerber (Elm Island Lake), Kathryn & John Miller (Esquagamah Lake), Lawrence & Joyce Fulton (Fleming Lake), Dave Graf (Hammal Lake), Greg Meredyk (Horseshoe Lake), Gordon Prickett (Nord Lake), Carole Holten (Rat Lake), Evan, Mary, Isaiah, Naomi & Hannah Green and Bob Gangl (Ripple Lake), Ken Hakes (Spirit Lake), and Kenneth Lebens (Waukenabo Lake). Thanks also to the Horseshoe Lake Inn who provided access to Horseshoe Lake. MPCA staff and volunteer monitors collected quality assurance and quality control samples for this project. A report providing full results of the CLMP+ monitoring in Aitkin County is available on the MPCA web site: http://www.pca.state.mn.us/water/clmp-publications.html#reports.

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 9

Hammal Lake Trophic Status Example The following is an excerpt from the 2007 CLMP+ report for Aitkin County (Anderson, 2008). This example, using water quality data from Hammal Lake, shows how Secchi depth compares to chlorophyll-a and total phosphorus in terms of the Trophic State Index. By verifying this relationship, we can continue to use Secchi depth as a reliable indicator of the nutrients and algal productivity in the lake. Equations used in these calculations can be found on page 6.

Hammal (01-0161) Hammal Lake is a fairly large, shallow lake located four miles southwest of Aitkin, Minnesota. It is in the upper ten percent of the lake in terms of its size; covering 374 acres. Hammal Lake has a maximum depth of 44 feet and there is one public access for the lake. Its immediate and total watersheds are nearly identical, covering only 2.2 mi2 and consists primarily of forested and water/marsh uses. The watershed–to-lake ratio is 4:1. Based on the total watershed area, its water residence time is estimated to be about three years. Water quality data was collected in June, July, August, and September, 2007 by volunteer lake monitor Dave Graf. (Data was also collected in late May, mid July and mid September by MPCA staff.) One site, site 201, was used for monitoring (Figure 5). Figure 5. Hammal Lake Bathymetric Map and Monitoring Location

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 10

Table 2. Summer-Mean Water Quality Parameters for Hammal Lake (Based on 2007 Epilimnetic Data Collected by Volunteers and MPCA Staff)

Parameter

Hammal Lake

Typical Range for NLF1 Ecoregion

TP (µg/L)

18

14 – 27

Chl-a (µg/L)

6

< 10

Secchi (m)

3.3

2.4 – 4.6

10.7

8 – 15

Secchi (ft) 1

th

th

Typical range is the 25 – 75 percentile of summer means from reference lakes specific to an ecoregion.

Total phosphorus (TP) concentrations averaged 18 µg/L in Hammal Lake during the summer of 2007. This value is within the range of concentrations for reference lakes in this ecoregion (Table 2). TP concentrations ranged from 10 – 35 μg/L (Figure 6) and peaked in late August. Chlorophyll-a concentrations for Hammal Lake averaged 6 μg/L; which is within the ecoregion reference range (Table 2). Concentrations on ranged from 1.7 – 12.4 µg/L and generally increased over the summer, peaking in late September (Figure 6). Based on the data, Hammal Lake would not have experienced nuisance or severe nuisance algae blooms in 2007. Figure 6. Hammal Lake Total Phosphorus and Chlorophyll-a Results for 2007

Hammal Lake 2007 Total Phosphorus & Chlorophyll-a 40 TP Chl-a

PPB

30

20

10

0 *5/23

6/10

6/25

7/9

*7/18

8/13

8/27

9/10

*9/19

Date * Data on these dates were collected by MPCA staff

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 11

Secchi disk transparency on Hammal Lake ranged from 8.5 feet (2.6 meters) in mid-August to 14.8 feet (4.5 meters) in late May (Figure 7) and averaged 10.7 feet (3.3 meters). These transparency measures are within the typical range for ecoregion reference lakes (Tables 1 and 2). Characterization of Hammal Lake’s physical condition ranged from “crystal clear” to “not quite crystal clear” (Classes 1 and 2). Recreational suitability ratings ranged from “beautiful” to “minor aesthetic problems” (Classes 1 and 2). The change in transparency of Hammal Lake over the course of the summer is fairly typical for mesotrophic lakes in Minnesota. Transparency is highest in the spring when the water is cool and algae populations are low. Frequently, zooplankton (small crustaceans that feed on algae) populations are also high at this time of year but decline later in the summer due to predation by young fish. As the waters warm throughout the summer, the algae (represented in Figure 6 by chlorophyll-a) become more abundant and the transparency declines (Figure 7). Figure 7. Hammal Lake Secchi Transparency for 2007

Hammal Lake 2007 Secchi Transparency 0 -2

Transparency (ft)

-4 -6 -8 -10 -12 -14 -16 -18 -20 *5/23

6/10

6/25

7/9

*7/18

8/13

8/27

9/10

*9/19

Date

*Data on these dates were collected by MPCA staff Trophic State Index (TSI) values for TP and chlorophyll-a for Hammal Lake compare very favorably to each other, while the TSI value for Secchi transparency is slightly, but not significantly lower (Table 3). As such, Secchi transparency should be a good estimator for overall water quality within Hammal Lake as well as a good tool for examining water quality trends for the lake. The overall TSI value of 46 indicates mesotrophic conditions for Hammal Lake. Table 3. Trophic Status Indicators for Hammal Lake

TSI Parameter

Hammal Lake TSI Value

Phosphorus

46

Chl-a

48

Secchi

43

Overall TSI

46

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 12

Figure 8. Carlson’s Trophic State Index, based on a scale of 0 – 100. (Carlson 1977)

TSI < 30

Classical Oligotrophy: Clear water, oxygen throughout the year in the hypolimnion, salmonid fisheries in deep lakes.

TSI 30 - 40

Deeper lakes still exhibit classical oligotrophy, but some shallower lakes will become anoxic in the hypolimnion during the summer.

TSI 40 - 50

Water moderately clear, but increasing probability of anoxia in hypolimnion during summer.

TSI 50 - 60

Lower boundary of classical eutrophy: Decreased transparency, anoxic hypolimnia during the summer, macrophyte problems evident, warm-water fisheries only.

TSI 60 - 70

Dominance of blue-green algae, algal scums probable, extensive macrophyte problems.

TSI 70 - 80

Heavy algal blooms possible throughout the summer, dense macrophyte beds, but extent limited by light penetration. Often would be classified as hypereutrophic.

TSI > 80

Algal scums, summer fish kills, few macrophytes, dominance of rough fish. OLIGOTROPHIC 20

25

MESOTROPHIC

30

35

40

EUTROPHIC

45

50

55

HYPEREUTROPHIC 60

65

70

75

80

X

TROPHIC STATE INDEX 15

10 8

7

6

5

4

SECCHI DEPTH (meters)

3

2

1.5

1

0.5

0.3

X 0.5

1

2

3

4

5

7

CHLOROPHYLL-A (μg/l)

10

15 20

30

40

60 80 100

150

X 3

5

7

10

TOTAL PHOSPHORUS (μg/l)

15

20 25 30

40

50 60

80 100

150

X

Key: NCHF Ecoregion Range, 25th – 75th percentile: Hammal Lake:

X

After Moore, L. and K. Thornton, [Ed.]1988. Lake and Reservoir Restoration Guidance Manual. USEPA. EPA 440/5-88-002. Note: A blank copy of this TSI form is in Appendix II for you to use with calculations from your own lake.

2007 Report on the Transparency of Minnesota Lakes

Minnesota Pollution Control Agency May 2008 13

Glossary Alkalinity: Capacity of a lake to neutralize acid. Chloride: Common anionic form of chlorine which carries one net negative charge. A common anion in many waters. Chlorophyll-a: The main pigment in algae. It is used to measure aquatic productivity. Ecoregion: Areas of relative homogeneity based on land use, soils, topography and potential natural vegetation. Epilimnion: Most lakes form three distinct layers of water during summertime weather. The epilimnion is the upper layer and is characterized by warmer and lighter water. Eutrophic: Describes a lake of high photosynthetic productivity. Nutrient rich. Hypolimnion: The bottom layer of lake water during the summer months. The water in the hypolimnion is denser and much colder than the water in the upper two layers. Littoral Area: The shallow areas around a lake's shoreline, dominated by aquatic plants. Mesotrophic: Describes a lake of moderate photosynthetic productivity. Metalimnion: The middle layer of lake water during the summer months. Nitrite/Nitrate Nitrogen: The weight of concentration of the nitrogen in the nitrate ion. Oligotrophic: Describes a lake of low photosynthetic productivity. Phosphate: An essential nutrient containing phosphorus and oxygen. Phosphate is often a critical nutrient in lake eutrophication management. Phosphorus: Phosphorus is an element that can be found in commercial products such as foods, detergents, and fertilizers as well as in larger amounts naturally in organic materials, soils, and rocks. Phosphorus is one of many essential plant nutrients. Phosphorus form