Birch Lake
11-0412-00 CASS COUNTY
Summary
Birch Lake is located near Hackensack, MN in Cass County. It covers 1,267
acres, which places it in the upper 10% of lakes in Minnesota in terms of
size.
Birch Lake has one inlet and one outlet, which classify it as a drainage lake.
It consists of two basins. The east basin (Lower Birch) is shallow with a
maximum depth of 25 feet and a mean depth of approximately seven feet.
The west basin (Upper Birch) has a maximum depth of 45 feet and a mean depth of about 20 feet.
Birch Lake is in the Boy River Watershed. The Boy River flows into Birch Lake from Ten Mile Lake
and outlets to Paquet Lake. From there, the Boy River flows through numerous lakes and
eventually empties into Leech Lake. The Leech Lake River exits Leech Lake and flows east into
the Mississippi River.
Water quality data have been collected on Birch Lake on and off since 1989. These data show
that the lake is mesotrophic (page 9). Mesotrophic lakes are commonly found in north central
Minnesota and have clear water with occasional algal blooms in late summer.
The Birch Lake Association has been involved in numerous activities including water quality
monitoring, education, lake-wide septic surveys, Healthy Lakes Initiative, and is a member of the
Association of Cass County Lakes.
Vitals
MN Lake ID:
County:
Ecoregion:
Major Drainage
Basin:
Latitude/Longitude:
Water Body Type:
Monitored Sites
(Primary):
Monitored Sites
(Secondary):
Physical Characteristics
11-0412-00
Cass
Northern Lakes and Forest
Upper Mississippi River
46.94166667/-94.54472222
Public
201, 204
202, 203, 205, 206
Surface area (acres):
Littoral area (acres):
% Littoral area:
Max depth (ft):
Mean depth (ft):
Lakeshed size (acres):
Lakeshed : lake area ratio
Inlets
Outlets
Accesses
1,267
755
59%
45
(m): 13.7
15.8
(m): 4.8
4,992
3.9:1
1
1
1 public
Invasive species present: none documented
Data Availability
Transparency data
Numerous yearly secchi readings from 1989-2008
through the MPCA CLMP program.
Chemical data
Total Phosphorus and Chlorophyll a data have been
collected in 1989, 2004, 2005, 2006, and 2008.
Inlet/Outlet data
No inlet or outlet monitoring has been conducted.
Recommendations
For recommendations refer to page 12.
Birch Lake
Report generation: RMB Environmental Laboratories
1 of 12
Figure 1. Map of Birch Lake illustrating bathymetry, lake sample site locations, stream inlets and outlets and
aerial land use. The pink shaded areas in the lake illustrate the littoral zone, where the sunlight can usually
reach the lake bottom allowing aquatic plants to grow.
Lake Site
Depth (ft)
Monitoring Programs
201 (103) *Primary Site
45
202
203 (102)
204 (101)
205
206
30
30
20
30
30
CLMP: 1984-1985, 1989-1990, 2002-2006, 2008;
MPCA: 1989, 2004; RMB Lab: 2008
CLMP: 1986, 1988
CLMP: 1989-1990, 1995-1997, 2004; MPCA: 1989, 2004
CLMP: 1989-1993, 1995-1997, 2002-2006; MPCA: 1989, 2004
CLMP: 1991-1993
CLMP: 2002-2007; Outdoor Corps: 2004-2006
Birch Lake
Report generation: RMB Environmental Laboratories
2 of 12
The information below describes available chemical data for the primary sites (201, 203, 204) of
Birch Lake through 2008. The data set is limited, and all parameters with the exception of total
phosphorus, chlorophyll a and secchi depth, are means for just 1989 and 2004 data.
Minnesota is divided into seven ecoregions based on land use, vegetation, precipitation and
geology. The MPCA has developed a way to determine the "average range" of water quality
expected for lakes in each ecoregion. For more information on ecoregions and expected water
quality ranges, see page 11.
Impaired
Waters
Standard2
Parameter
Mean
Ecoregion
Range1
Total phosphorus (ug/L)
18
14 - 27
> 35
Chlorophyll a (ug/L) 3
4.4
4 - 10
> 12
Chlorophyll a max (ug/L)
9
<15
Secchi depth (ft)
13
7.5 - 15
Dissolved oxygen
see page 8
Total Kieldahl Nitrogen
0.73
0.4 - 0.75
Indicates insufficient nitrogen to
support summer nitrogeninduced algae blooms.
Alkalinity (mg/L)
106
40 - 140
Indicates a low sensitivity to
acid rain and a good buffering
capacity.
Color (Pt-Co Units)
9.5
10 - 35
Indicates clear water with little
to no tannins (brown stain).
pH
8.6
7.2 - 8.3
Characteristic of a hard water
lake. Lake water with pH less
than 6.5 can affect fish
spawning and the solubility of
metals in the water.
Chloride (mg/L)
1.3
0.6 - 1.2
Slightly above the expected
range for the Ecoregion, but still
considered low level.
Total Suspended Solids
2.1
<1 - 2
Indicates low suspended solids
and clear water.
Conductivity (umhos/cm)
186
50 - 250
Within the expected range for
the ecoregion.
Total Nitrogen :Total
Phosphorus
45:1
25:1 – 35:1
Indicates the lake is
phosphorus limited, which
means that algae growth is
limited by the amount of
phosphorus in the lake.
Interpretation
Results are within the expected
range for the ecoregion. For
more information about
Impaired Waters Assessment,
see page 12.
< 4.5
Dissolved oxygen depth profiles
show that the deep areas of the
lake are anoxic in late summer.
(mg/L)
(mg/L)
Data Source: 1989 & 2004 Minnesota Pollution Control Agency LAP Assessments
1
th
th
The ecoregion range is the 25 -75 percentile of summer means from ecoregion reference lakes
For further information regarding the Impaired Waters Assessment program, refer to http://www.pca.state.mn.us/water/tmdl/index.html
3
Chlorophyll a measurements have been corrected for pheophytin
Units: 1 mg/L (ppm) = 1,000 ug/L (ppb)
2
Birch Lake
Report generation: RMB Environmental Laboratories
3 of 12
Water Quality Characteristics - Historical Means
Years monitored: 1984-1986, 1988-1993, 1995-1997, 2001-2008
Parameters
Total Phosphorus Mean (ug/L):
Total Phosphorus Min:
Total Phosphorus Max:
Number of Observations:
Chlorophyll a Mean (ug/L):
Chlorophyll-a Min:
Chlorophyll-a Max:
Number of Observations:
Secchi Depth Mean (ft):
Secchi Depth Min:
Secchi Depth Max:
Number of Observations:
Primary
Site
201
Site
203
Site
204
16.3
8.0
39.0
16
17.2
12.0
23.0
9
18.4
10.0
37.0
11
20.4
5.0
42.0
14
4.0
1.0
7.0
13
5.2
2.7
8.3
8
3.8
2.4
7.6
10
4.7
1.0
9.0
14
11.8
7.5
20.5
85
13.5
6.9
19.5
143
12.7
7.0
21.5
118
Site
202
12.1
6.5
20.0
21
Site
205
14.1
9.0
29.0
55
Site
206
13.0
8.3
22.0
65
Figure 2. Birch Lake total phosphorus, chlorophyll a and transparency historical ranges. The arrow
represents the range and the black dot represents the historical mean (Primary Site 201). Figure adapted
after Moore and Thornton, [Ed.]. 1988. Lake and Reservoir Restoration Guidance Manual. (Doc. No. EPA 440/5-88-002)
Birch Lake
Report generation: RMB Environmental Laboratories
4 of 12
Transparency (Secchi Depth)
Transparency is how easily light can pass through a substance. In lakes it is how deep sunlight
penetrates through the water. Plants and algae need sunlight to grow, so they are only able to
grow in areas of lakes where the sun penetrates. Water transparency depends on the amount of
particles in the water. An increase in particulates results in a decrease in transparency. The
transparency varies year to year due to changes in weather, precipitation, lake use, flooding,
temperature, lake levels, etc.
For all the sites that had more than two years of data, the mean transparency ranges from 11.8 to
13.5 feet. The transparency throughout the lake appears to be relatively uniform.
Figure 3 shows the disjointed nature of the transparency data set. Since 2002, sites 201 and 206
in the large basin show the best transparency, and site 204 in the small basin has slightly lower
transparency.
Transparency monitoring should be continued annually at sites 201, 203 and 204 in order to track
water quality changes.
18
16
14
12
10
8
6
4
2
0
Site 201
Site 203
Site 204
Site 206
19
8
19 4
8
19 5
8
19 6
8
19 7
8
19 8
8
19 9
9
19 0
9
19 1
9
19 2
9
19 3
9
19 4
9
19 5
9
19 6
9
19 7
9
19 8
9
20 9
0
20 0
0
20 1
0
20 2
0
20 3
0
20 4
0
20 5
0
20 6
0
20 7
08
Secchi Depth (ft)
Transparency: Annual Means
Figure 3. Annual mean transparency for sites 201, 203, 204 and 206.
Birch Lake transparency ranges from 7 to 21.5 ft at the primary site (201). Figure 4 shows the
seasonal transparency dynamics. Birch Lake transparency is highest in May and then decreases
steadily throughout the summer. The transparency in deep lakes usually recovers in late
September-October, but Birch Lake is most likely not deep enough to recover to spring
transparency in the fall. Transparency dynamics are related to algae population dynamics and
lake turnover.
Birch Lake
Report generation: RMB Environmental Laboratories
5 of 12
Figure 4. Seasonal transparency dynamics and year-to-year comparison (Primary Site 201). The shaded
yellow line represents the average from 2002-2008.
User Perceptions
When volunteers collect secchi depth readings, they record their perceptions of the water based on
the physical appearance and the recreational suitability. These perceptions can be compared to
water quality parameters to see how the lake "user" would experience the lake at that time.
Looking at transparency data, as the secchi depth decreases the perception of the lake's physical
appearance rating decreases. Birch Lake was rated as being "not quite crystal clear " 67% of the
time between 1989-2008 (Figure 5).
4%
Physical Appearance Rating
0%
29%
Crystal clear water
67%
Not quite crystal clear – a little algae visible
4%
Definite algae – green, yellow, or brown color
apparent
0%
High algae levels with limited clarity and/or mild
odor apparent
0%
Severely high algae levels
29%
67%
Figure 5. Physical appearance rating, as rated by the volunteer monitor (1989-2008).
Birch Lake
Report generation: RMB Environmental Laboratories
6 of 12
As the secchi depth decreases, the perception of recreational suitability of the lake decreases.
Birch Lake was rated as being "beautiful" 57% of the time from 1989-2008 (Figure 6).
1%
0%
Recreational Suitability Rating
57%
Beautiful, could not be better
42%
Very minor aesthetic problems; excellent for
swimming, boating
1%
Swimming and aesthetic enjoyment of the lake
slightly impaired because of algae levels
0%
Desire to swim and level of enjoyment of the lake
substantially reduced because of algae levels
0%
Swimming and aesthetic enjoyment of the lake
nearly impossible because of algae levels
42%
57%
Figure 6. Recreational suitability rating, as rated by the volunteer monitor (1989-2008).
Total Phosphorus
Total Phosphorus
45
Total Phosphorus (ug/L)
Birch Lake is phosphorus
limited, which means that
algae and aquatic plant
growth is dependent upon
available phosphorus.
40
35
ug
12
-S
ep
29
-A
l
18
-J
ul
1Au
g
15
-A
ug
Ju
4-
6Ju
n
20
-J
un
23
-M
ay
Total phosphorus was
30
Site 201, 1989
evaluated in Birch Lake in
Site 201, 2004
25
1989, 2004, 2005, 2006,
Site 201, 2008
20
and 2008 (Figure 7). The
Site 203, 2004
15
data indicate a slight
Site 204, 1989
10
increase in phosphorus
Site 204, 2004
5
from the beginning of the
Site 206, 2004
summer to the end. This
0
pattern is typical for
Site 206, 2005
Minnesota lakes. All sites
Site 206, 2006
were relatively similar
across sampling years and
Figure 7. Historical total phosphorus concentrations (ug/L) for Birch Lake
varied year-to-year.
(data sets from 1989, 2004-2006, 2008).
Phosphorus levels can vary
year-to-year due to natural
variations including precipitation, lake use, and weather.
Phosphorus should continue to be monitored to track any future changes in water quality.
Birch Lake
Report generation: RMB Environmental Laboratories
7 of 12
Chlorophyll a
14
Site 201, 1989
12
Site 201, 2004
10
Site 201, 2008
8
Site 203, 2004
Site 204, 1989
6
Site 204, 2004
4
Site 206, 2004
2
Site 206, 2005
Site 206, 2006
4Ju
l
18
-J
ul
1Au
g
15
-A
ug
29
-A
ug
12
-S
ep
0
23
-M
ay
6Ju
n
20
-J
un
Chlorophyll a
concentrations greater
than 10 ug/L are
perceived as a mild algae
bloom, while
concentrations greater
than 20 ug/L are
perceived as a nuisance.
Chlorophyll a
Chlorophyll a (ug/L)
Chlorophyll a is the
pigment that makes
plants and algae green.
Chlorophyll a is tested in
lakes to determine the
algae concentration or
how "green" the water is.
Chlorophyll a was
evaluated in Birch Lake in
1989, 2004, 2005,
Figure 8. Chlorophyll a concentrations (ug/L) for Birch Lake (data sets from 1989,
2006, and 2008 (Figure
2004-2006, 2008).
8). Chlorophyll a
concentrations for all
dates at all sites remained below 10 ug/L, indicating clear water most of the summer. There was
not much variation between sites over the years monitored, and chlorophyll a concentrations
increased steadily toward the end of the summer. This pattern is typical for Minnesota lakes.
Dissolved Oxygen
D issolved Oxygen
(mg/L)
0
0
2
4
6
8 10
Dissolved Oxygen (DO) is the amount of oxygen dissolved in lake water.
Oxygen is necessary for all living organisms to survive, except for some
bacteria. Living organisms breathe in oxygen that is dissolved in the
water. Dissolved oxygen levels of <5 mg/L are typically avoided by
game fish.
1
2
3
4
Depth
(m )
5
6
7
8
9
10
Dissolved oxygen profiles from 1999-2004 indicate that Lower Birch (site
204), which has a maximum depth of 20 ft mixes throughout the
summer. Due to the shallow nature of Lower Birch, a few windy days
can cause the lake to mix.
Upper Birch Lake has a maximum depth of 45 ft, and stratifies
throughout the summer. Benthic phosphorus samples taken in 2004
indicate internal loading occurs in Upper Birch when the hypolimnion is
anoxic (31-184 ug/L). Figure 9 illustrates stratification in July of 2004.
Figure 9. Dissolved oxygen and temperature profile for Birch Lake on July 14,
2004 at sites 201, 203, 204.
11
Birch Lake
Report generation: RMB Environmental Laboratories
8 of 12
Trophic State Index
Phosphorus (nutrients),
chlorophyll a (algae
concentration) and Secchi depth
(transparency) are related. As
phosphorus increases, there is
more food available for algae,
resulting in increased algal
concentrations. When algal
concentrations increase, the
water becomes less transparent
and the Secchi depth decreases.
Upper Birch
Site 201
43
43
41
42
Trophic State Index
Site 203
TSI Total Phosphorus
45
TSI Chlorophyll-a
46
TSI Secchi
42
TSI Mean
44
Mesotrophic
Mesotrophic
Trophic State:
Numbers represent the mean TSI for each parameter.
Hypereutrophic
70
Eutrophic
The mean TSI for Birch Lake indicates that it
is mesotrophic (Figure 10). There is good
Birch Lake
agreement between the TSI for phosphorus,
chlorophyll a and transparency, indicating
that these variables are strongly related. In addition, all
sites are relatively similar in TSI.
Mesotrophic lakes (TSI 40-50) are characterized by
moderately clear water most of the summer. "Meso"
means middle or mid; therefore, mesotrophic means a
medium amount of productivity. Mesotrophic lakes are
commonly found in central Minnesota and have clear
water with some algal blooms in late summer.
30-40
40-50
50-60
60-70
70-80
>80
Attributes
Oligotrophy: Clear water, oxygen throughout
the year at the bottom of the lake, very deep
cold water.
Bottom of shallower lakes may become anoxic
(no oxygen).
Mesotrophy: Water moderately clear most of
the summer. May be "greener" in late summer.
Eutrophy: Algae and aquatic plant problems
possible. "Green" water most of the year.
Blue-green algae dominate, algal scums and
aquatic plant problems.
Hypereutrophy: Dense algae and aquatic
plants.
Algal scums, few aquatic plants.
Mesotrophic
100
The results from these three measurements cover
different units and ranges and thus cannot be directly
compared to each other or averaged. In order to
standardize these three measurements to make them
directly comparable, we convert them to a trophic state
index (TSI).
TSI
<30
Lower Birch
Site 204
45
43
40
43
50
Mesotrophic
40
Oligotrophic
0
Figure 10. Trophic state index chart with
corresponding trophic status.
Fisheries & Recreation
Trout fisheries dominate.
Trout fisheries in deep lakes only. Walleye,
Tullibee present.
No oxygen at the bottom of the lake results in
loss of trout. Walleye may predominate.
Warm-water fisheries only. Bass may
dominate.
Dense algae and aquatic plants. Low water
clarity may discourage swimming and boating.
Water is not suitable for recreation.
Rough fish (carp) dominate; summer fish kills
possible.
Source: Carlson, R.E. 1997. A trophic state index for lakes. Limnology and Oceanography. 22:361-369.
Birch Lake
Report generation: RMB Environmental Laboratories
9 of 12
Trend Analysis
For detecting trends, a minimum of 8-10 years of data with 4 or more readings per season are
recommended. Minimum confidence accepted by the MPCA is 90%. This means that there is a
90% chance that the data are showing a true trend and a 10% chance that the trend is a random
result of the data. Only short-term trends can be determined with just a few years of data, because
there can be different wet years and dry years, water levels, weather, etc, that affect the water
quality naturally.
There is not enough historical data to perform trend analysis for total phosphorus or chlorophyll a
on Birch Lake. Sites 201 and 204 had at least 8 years of transparency data, which was enough
data to perform a long-term trend analysis. The data was analyzed using the Mann Kendall Trend
Analysis.
Lake Site
Parameter
Date Range
Trend
Probability
201 (Upper Birch)
Transparency
1989-1990, 2002-2006, 2008
No Trend
--
204 (Lower Birch)
Transparency
1989-1993, 1995-1997, 2002-2006
Declining
99.9%
Figure 11. Transparency trend for site 204 from 1989-1993, 1995-1997, 2002-2006.
Site 201 in Upper Birch had no trend occurring, which means that the transparency has remained
constant over 1989-1990, 2002-2006, 2008. At site 204 in Lower Birch, the transparency has
declined an average of approximately 2 feet over 1989-1993, 1995-1997, 2002-2006 (Figure 11).
Lower Birch is smaller and shallower than Upper Birch, and it has the city of Hackensack on its
eastern shore. Land use practices around Lower Birch should be investigated for improvement
opportunities. Transparency monitoring should continue at both sites so that this trend can be
tracked in future years.
Birch Lake
Report generation: RMB Environmental Laboratories
10 of 12
Ecoregion Comparisons
Minnesota is divided into seven ecoregions based on
land use, vegetation, precipitation and geology. The
MPCA has developed a way to determine the
"average range" of water quality expected for lakes in
each ecoregion. From 1985-1988, the MPCA
evaluated the lake water quality for reference lakes.
These reference lakes are not considered pristine, but
are considered to have little human impact and
therefore are representative of the typical lakes within
the ecoregion. The "average range" refers to the 25th
- 75th percentile range for data within each ecoregion.
For the purpose of this graphical representation, the
means of the reference lake data sets were used.
60
30
50
25
0
5
40
30
20
10
NLF
Ecoregion
Birch
b
10
15
20
crystal
clear
0
0
a
15
5
10
increased
algae
20
Secchi depth (ft)
Chlorophyll-a (ug/L, ppb)
Total Phosphorus (ug/L, ppb)
Birch Lake is in the Northern
Lakes and Forests
Ecoregion. The mean total
phosphorus, chlorophyll a
and transparency (secchi
depth) for Birch are all within
the expected ecoregion
ranges (Figures 12a-c).
25
NLF
Ecoregion
Birch
c
NLF
Ecoregion
Birch
Figures 12a-c. Birch Lake ranges compared to Northern Lakes and Forest Ecoregion ranges. The Birch
Lake total phosphorus and chlorophyll a ranges are from 16 data points collected in May-September of 1989,
2004, and 2008. The Birch Lake secchi depth range is from 118 data points collected in May-September
from 1984-2008.
Birch Lake
Report generation: RMB Environmental Laboratories
11 of 12
Inlet/Outlet Data Assessment
No inlet or outlet data have been collected for Birch Lake. The inlet to Birch Lake drains from Ten
Mile Lake, which has very low in-lake phosphorus concentrations.
Assessment/Findings Recommendations
Transparency
Transparency monitoring at sites 201 and 204 should be continued annually. It is important to
continue transparency monitoring weekly or at least bimonthly every year to enable year-to-year
comparisons and trend analyses.
Impaired Waters Assessment 303(d) List
There are two main types of Impaired Waters Assessment for lakes: eutrophication (excess
phosphorus) for aquatic recreation and mercury in fish tissue for aquatic consumption. Birch Lake
is not listed as impaired for eutrophication or mercury in fish tissue.
Aquatic Recreational Use Assessment 305(b)
In the 2008 MPCA Aquatic Use Assessment (305(b)), Birch Lake was classified being fully
supporting for Aquatic Recreational Use.
Inlet/Outlet Assessment
Because of the lack of inlet/outlet data, a mass balance project should be considered. This study
answers questions about nutrient loading into the lake and nutrient budget within the lake.
Organizational contacts and reference sites
Birch Lake Association
Cass County Environmental
Services Department
303 Minnesota Avenue W, P.O. Box 3000, Walker, MN 56484-3000
(218) 547-7241
http://www.co.cass.mn.us/esd/home_esd.html
DNR Fisheries Office
7316 State Hwy 371 NW, Walker, MN 56484
(218) 547-1683
http://www.dnr.state.mn.us/lakefind/index.html
Regional Minnesota Pollution
Control Agency Office
7678 College Road, Suite 105, Baxter, MN 56425
(218) 828-2492
http://www.pca.state.mn.us
Regional Board of Soil and Water
Resources Office
1601 Minnesota Drive, Brainerd, MN 56401
(218) 828-2383
http://www.bwsr.state.mn.us
Birch Lake
Report generation: RMB Environmental Laboratories
12 of 12