JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION
AMERICAN WATER RESOURCES ASSOCIATION
DISCHARGE AND NUTRIENT TRANSPORT BETWEEN LAKES IN A HYDROLOGICALLY
COMPLEX AREA OF VOYAGEURS NATIONAL PARK, MINNESOTA, 2010-2012
Victoria G. Christensen, Eric S. Wakeman, and Ryan P. Maki2
ABSTRACT: An acoustic Doppler velocity meter (ADVM) was deployed in the narrows between Namakan and
Kabetogama Lakes in Voyageurs National Park, Minnesota, from November 3, 2010, through October 3, 2012.
The ADVM can account for wind, seiche, and changing flow direction in hydrologically complex areas. The objectives were to (1) estimate discharge and document the direction of water flow, (2) assess whether specific conductance can be used to determine flow direction, and (3) document nutrient and chlorophyll a concentrations at the
narrows. The discharge direction through the narrows was seasonal. Water generally flowed out of Kabetogama
Lake and into Namakan Lake throughout the ice-covered season. During spring, water flow was generally from
Namakan Lake to Kabetogama Lake. During the summer and fall, the water flowed in both directions, affected
in part by wind. Water flowed into Namakan Lake 70% of water year 2011 and 56% of water year 2012. Nutrient
and chlorophyll a concentrations were highest during the summer months when water-flow direction was unpredictable. The use of an ADVM was effective for assessing flow direction and provided flow direction under ice.
The results indicated the eutrophic Kabetogama Lake may have a negative effect on the more pristine Namakan
Lake. The results also provide data on the effects of the current water-level management plan and may help
determine if adjustments are necessary to help protect the aquatic ecosystem of Voyageurs National Park.
(KEY TERMS: surface water hydrology; nutrients; watershed management; eutrophication; water-level changes;
index velocity method.)
Christensen, Victoria G., Eric S. Wakeman, and Ryan P. Maki, 2016. Discharge and Nutrient Transport between
Lakes in a Hydrologically Complex Area of Voyageurs National Park, Minnesota, 2010-2012. Journal of the
American Water Resources Association (JAWRA) 1-14. DOI: 10.1111/1752-1688.12412
cern, and a study of nutrient cycling (Christensen
et al., 2011) indicated that water flows in an unpredictable pattern in both directions between the
eutrophic Kabetogama Lake and the more pristine
Namakan Lake. Measurements made at Kabetogama
Lake, East End, near Old Dutch Bay (U.S. Geological Survey site no. 482611092483801, referred to as
“the narrows” throughout this article) during the
INTRODUCTION
Artificial water-level management of the large
lakes in Voyageurs National Park, located in Minnesota, along the Canadian border, has led to several
multidisciplinary studies. Yearly cyanobacterial
blooms in Kabetogama Lake are a particular con-
1
Paper No. JAWRA-15-0018-P of the Journal of the American Water Resources Association (JAWRA). Received February 11, 2015;
accepted January 4, 2016. © 2016 American Water Resources Association. Discussions are open until six months from issue publication.
2
Hydrologist (Christensen), Minnesota Water Science Center, U.S. Geological Survey, 2280 Woodale Drive, Mounds View, Minnesota
55112; Supervisory Hydrologic Technician (Wakeman), Minnesota Water Sceince Center, U.S. Geological Survey, Grand Rapids, Minnesota
55744; and Aquatic Ecologist (Maki), Voyageurs National Park, National Park Service, Grand Rapids, Minnesota 55744 (E-Mail/Christensen:
vglenn@usgs.gov).
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oligotrophic. Sources of nutrients to Kabetogama
Lake include recycling of lake bottom sediments
(Christensen et al., 2011) and inflows from areas on
the south shore (Kallemeyn et al., 2003; Christensen
et al., 2011). The IJC will reevaluate the effects of
the changes in operating procedures likely starting in
2016 to determine if the management of water levels
is achieving its objectives. More information on the
change in operating procedures is reported in Kallemeyn et al. (2003) and Christensen and Maki (2015).
The assessment of discharge and water quality can
be difficult in areas where water flows in more than
one direction. In these areas, an acoustic Doppler
velocity meter (ADVM) can be used to monitor both the
velocity and direction of flow. The ADVM method has
been used in other studies where water flows in both
directions, for example, in tidal areas or estuaries (e.g.,
Ruhl and Simpson, 2005; Gotvald and Oberg, 2008;
Chen et al., 2012) and in river systems (e.g., Gotvald
and Oberg, 2008), particularly those in which flow is
stratified (Garcıa et al., 2007). Other applications of
the ADVM include measurement of discharge under
ice (e.g., Morse et al., 2010) and to estimate sediment
in river systems (Wood, 2010). However, the use of an
ADVM in a complex reservoir system, such as that in
Voyageurs National Park, where the direction of flow
is influenced by multiple outlets, appears to be unique
in the literature. The U.S. Geological Survey (USGS),
in cooperation with the National Park Service (NPS),
installed an ADVM to determine the discharge (flow
direction and magnitude) between Namakan Lake and
Kabetogama Lake during 2011 and 2012 water years.
A water year is defined as the 12-month period from
October 1 for any given year through September 30 of
the following year and is designated by the calendar
year in which it ends. The ADVM was expected to provide important information regarding nutrient transport between the two lakes and to increase the
understanding of data from a previous study of nutrient cycling (Christensen et al., 2011). The objectives of
the study described in this article were to (1) estimate
discharge and document the direction of water flow
between Namakan and Kabetogama Lakes, (2) assess
whether specific conductance can be used to determine
flow direction in the narrows, and (3) document nutrient and chlorophyll a (Chla) concentrations at the narrows between Namakan and Kabetogama Lakes.
Loads were not calculated because the discharge
rating from this site was designated as “poor” to “fair.”
The discharge ratings indicate the degree of accuracy
of the discharge record. “Excellent” indicates that
about 95 percent of the daily discharges are within 5
percent of the true value; “good” within 10 percent;
and “fair,” within 15 percent. “Poor” indicates that
daily discharges have less than “fair” accuracy. Different accuracies may be assigned to different parts of the
spring of 2008 indicated that water flowed west from
Namakan Lake to Kabetogama Lake and during the
spring of 2009 water flowed east, from Kabetogama
Lake to Namakan Lake. Another measurement made
in August 2009, showed multidirectional flow
throughout the cross section. The multidirectional
flow complicates the computation of discharge and
nutrient loads. Based on the volume of water flowing
through the narrows during the measurement in
2008, flow from Namakan Lake would be the largest
potential source of nutrients to Kabetogama Lake
other than internal loading (the recycling of bottom
sediments into the water column). However, based
on the volume of water flowing through the narrows
in 2009, the algal blooms and nutrient concentrations in Kabetogama Lake might affect Namakan
Lake (Christensen et al., 2013). This led to concern
over eutrophication and cyanobacteria blooms in
Kabetogama Lake and the potential transport of
nutrients to the more pristine Namakan Lake. In
this article, transport is defined as the conveyance of
solutes and particulates in flow systems, and does
not imply that mass loading or transport was quantified.
In response to documented degradation of the
aquatic ecosystems of Namakan Reservoir (which
includes Kabetogama, Namakan, Sand Point, Little
Vermilion, and Crane Lakes) and of nearby Rainy
Lake (Figure 1), the International Joint Commission (IJC), the international body that sets the
rules governing dam operation on waters shared by
the United States and Canada, changed operating
procedures (rule curves) in January 2000 for dams
that regulate these water bodies (International
Joint Commission, http://www.ijc.org/files/tinymce/
uploaded/2000-01-05_IJC_Order.pdf). The adjacent
dams at Namakan Reservoir’s main outlet, located
at Squirrel and Kettle Falls (Figure 1), control
water flow between the upstream Namakan Reservoir and the downstream Rainy Lake. Squirrel and
Kettle Falls existed as natural outlets between
Namakan and Rainy Lakes prior to European settlement. In addition to this regulated outlet, unregulated flow occurs at Gold Portage (Figure 1) and
Bear Portage (Figure 1).
Rule curves show bands of permitted maximum
and minimum water levels that are allowed throughout the year. These new procedures in 2000 were
expected to restore a more natural water regime and
benefit the aquatic ecosystem by affecting water
levels, water quality, and trophic state. An improvement in trophic state was recently documented for
Kabetogama, the most eutrophic lake in this reservoir system (Christensen and Maki, 2015), however,
Kabetogama Lake remains in the mesotrophic to
eutrophic category, whereas Namakan Lake is
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93º15'
IN A
HYDROLOGICALLY COMPLEX AREA
93º
OF
VOYAGEURS NATIONAL PARK, MINNESOTA, 2010-2012
92º45'
92º30'
48º37'30"
11
Brule
N
ONTARIO
Narrows
CA
ITE NAD
DS
A
TA
TE
T.
71
N.
UN
ot
Gold Portage
Ro
T.
70
N.
S
Riv e
r
Rat
05129290
Squirrel Falls and Kettle Falls
48º30'
Bear Portage
Tom Cod Creek
y
t Ba
Los
Namakan
River
Old Dutch Bay
53
T.
69
N.
482611092483801
122
217
Sullivan
Bay
Ray
Sand
Point
Lake
M
129
oo
se
Daley Brook
48º22'30"
KOOCHICHING CO.
ST. LOUIS CO.
Riv e
r
53
Harrison
Narrows
Johnson
Lake
Ash
Little
Vermilion
Lake
Long
Lake
MINNESOTA
T.
67
N.
Crane
Lake
05129115
R. 23 W.
T.
68
N.
Little
Johnson
Lake
Riv er
R. 22 W.
R. 21 W.
Base from National Park Service
Modified from Christensen and others, 2004
R. 20 W.
R. 19 W.
0
R. 18 W.
rm
Ve
ilio
River
n
Q3
R. 17 W.
R. 16 W.
10 KILOMETERS
0
10 MILES
Lake of
the Woods
96
94
Voyageurs
National Park
92
05133500
Lac la Croix
EXPLANATION
90
48
Voyageurs National Park
Loon River
k
La
up
eS
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05129290
USGS station and number
KNW
KNE
MINNESOTA
KNC
M issi ssi p
46
pi
Riv
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so
ta
Riv
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44
0
0
50
50
100 MILES
Inset map showing sites KNW, KNC (the narrows at USGS
site number 482611092483801) and KNE
100 KILOMETERS
Location Map
FIGURE 1. Location of Voyageurs National Park and Location of the Narrows (inset) between Kabetogama and Namakan Lakes.
discharge record. The “poor” to “fair” rating at the narrows means there is a higher error than most other
gaging sites and calculating loads would compound
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that error. Therefore, the focus of the transport for this
study was in terms of the direction of the flow, which is
important to the resource managers.
3
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CHRISTENSEN, WAKEMAN,
MAKI
the changes in specific conductance in the narrows
might provide an indication of flow direction.
The five natural lakes that make up Namakan
Reservoir (Kabetogama, Namakan, Sand Point, Little
Vermilion, and Crane Lakes; Figure 1) are hydrologically connected. The hydrology of the system is complex, but water generally flows in a northwesterly
direction. Major inputs to the system include the
Namakan River, which flows into Namakan Lake;
the Vermilion River, which flows into Crane Lake;
the Loon River, which flows into Little Vermilion
Lake; and the Ash River, which flows into Kabetogama Lake.
Water flows out of the Namakan Reservoir at three
locations: (1) through the dams at Squirrel Falls and
Kettle Falls at the northwest end of Namakan Lake,
(2) at Bear Portage on the north-central side of
Namakan Lake, and (3) at Gold Portage at the west
end of Kabetogama Lake. The flows are regulated at
Squirrel Falls and Kettle Falls, and unregulated
overflows occur at Bear Portage and Gold Portage
(Figure 1). Gold Portage connects Kabetogama Lake
with Black Bay in Rainy Lake and can be the equivalent of approximately 60% of the flow at Kettle Falls
(International Rainy Lake Board of Control, 1999).
The overflow at Gold Portage starts when the water
level reaches 339.39 m (Kallemeyn et al., 2003). Flow
through Gold Portage occurs most days of the year.
Bear Portage, which is 1 m higher than Gold Portage,
is considered a minor outflow, accounting for about
1% of the outflow from Namakan Reservoir during
1988-99 (Kallemeyn et al., 2003).
Namakan Lake has a surface area of 10,170 ha
and a maximum depth of 46 m (Kallemeyn et al.,
2003). Kabetogama Lake has a surface area of
10,425 ha and a maximum depth of 24 m (Kallemeyn
et al., 2003). Since 1914, lake levels have been controlled by the private sector for multiple uses by
dams at Namakan Reservoir’s main outlets (International Rainy Lake Board of Control, 1999). Prior to
1949, when the first water-level management plan for
this system was established, annual fluctuation was
greater on Namakan Reservoir, where water-level
fluctuations were considered extreme compared to
the more natural conditions on the nearby unregulated Lac la Croix (Meeker and Harris, 2009). The
1949 water-level management plan was updated in
1957 and again in 1970. Each of these plans, including the 1970 plan, allowed larger-than-natural fluctuations on Namakan Reservoir to maintain less-thannatural fluctuations on Rainy Lake (Kallemeyn et al.,
2003). The 1970 water-level management plan was
later determined to be detrimental to the ecosystem
(Kallemeyn et al., 2003).
In an effort to meet the needs of environmental
and economic interests while improving the water
Study Area
Voyageurs National Park (Figure 1) was established in 1975 “to preserve, for the inspiration and
enjoyment of present and future generations, the outstanding scenery, geological conditions, and waterway
system which constituted a part of the historic route
of the voyageurs” (public law 97-405). Most of Voyageurs National Park (referred to as “the Park” in this
article) is water covered and, therefore, recreational
use of the Park is water based (Figure 1). Aquatic
systems support much of the Park’s fauna, including
waterfowl, loons, eagles, beavers, and moose. Water
is an essential element of the Park environment with
respect to both the health of its ecosystem and visitor
enjoyment. Boating and canoeing along scenic waterways, fishing, and swimming are common visitor
activities. Assuring the Park’s waters remain healthy
is fundamental for Voyageurs National Park.
The climate near Voyageurs National Park is continental with moderately warm summers and long
cold winters. The frost-free season ranges from 110 to
130 days (Kallemeyn et al., 2003). Average snowfall
is 172 cm, average temperature is 2.9°C, and average
rainfall is 61 cm (High Plains Regional Climate Center, 2010). Annual evaporation from lake surfaces
averages 63.5 cm (International Rainy Lake Board of
Control and International Lake of the Woods Control
Board, 1984). The lakes are generally ice covered for
5-6 months from mid-November to mid-April or May
(Kallemeyn et al., 2003).
Most of Voyageurs National Park is underlain by
Archean continental crust composed of greenstone,
gneissic, magmatic, granitic, meta-sedimentary, and
schistose bedrock that is resistant to erosion (Ojakangas and Matsch, 1982). Namakan Lake receives most
of its inflow from areas of exposed bedrock (Payne,
1991; Kallemeyn et al., 2003). The Namakan River,
which supplies most of the inflow to Namakan Lake,
drains an area characterized by thin deposits of
Rainy lobe drift (Payne, 1991), which is sandy with
little clay (Hobbs and Goebel, 1982). Kabetogama
Lake receives inflow from an area that is overlain by
calcareous glacial drift from the Des Moines lobe
(Payne, 1991), which is generally clay rich and carbonate rich (Woodruff et al., 2002). These glacial drift
sediments are unusually rich in soluble minerals and
as a result, specific conductance measurements in
Kabetogama Lake (77-107 microSiemens per centimeter at 25 degrees Celsius, ls/cm) are substantially
higher than those in other Park lakes (generally
about 39-78 ls/cm) that drain areas with extensive
granitic bedrock exposures (Kallemeyn et al., 2003).
The difference in specific conductance in Kabetogama
Lake and Namakan Lake (37-55 ls/cm; Christensen
et al., 2004) has led researchers to hypothesize that
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HYDROLOGICALLY COMPLEX AREA
METHODS
Installation of the Acoustic Doppler Velocity Meter
and Discharge Measurement
The ADVM was installed on November 3, 2010,
below the water surface in a representative part of
the cross section in the narrows between Namakan
Lake and Kabetogama Lake (Figure 1). Prior to
installation, several discharge measurements were
made to determine the cross section most suitable for
measuring representative velocities from the ADVM,
and to determine the most suitable type of ADVM to
use. Based on these measurements, an uplooking
ADVM (or vertically oriented ADVM, Figure 2) was
selected. In addition, a separate water-level sensor
was used to accurately monitor stage.
The cross-sectional area was used to develop a
relation between stage and channel area, called a
“stage-area rating.” Discharge measurements of the
cross section were made eight times between May 11,
2011, and October 3, 2012, using an ADCP, while
concurrent measurements of stage and index velocity
were recorded. Stage and index velocities measured
during the discharge measurements were averaged.
Discharge measurements were made over the range
of flows that occurred during the study. Each discharge measurement produced a value of mean channel velocity (V) and index velocity (Vi). After several
measurements were made, a relation between V and
Vi was developed. The stage-area rating was used
(with mean-channel velocity) as a partial solution to
Principles of Operation of the Acoustic Doppler
Velocity Meter
Site characteristics to determine discharge using
common methods require a relatively stable and sensitive relation between stage and discharge (Rantz
et al., 1983). Variable backwater from low-head gradients, wind, seiche, beaver dams, or other factors slow
water velocities and often confound or invalidate this
relation. The ADVMs were developed to address this
deficiency by incorporating the velocity and flow
direction as additional monitored parameters that
can help determine discharge. The ADVMs use transducers that send (pings) and receive (echoes) an
acoustic pulse (Ruhl and Simpson, 2005; Levesque
and Oberg, 2012). A fraction of that acoustic pulse is
reflected by small particles in the water, returning to
the transducer at a frequency that has been shifted
due to the Doppler effect within each acoustic beam.
Water velocities and flow directions of many sections
OF THE
AMERICAN WATER RESOURCES ASSOCIATION
VOYAGEURS NATIONAL PARK, MINNESOTA, 2010-2012
are determined on the basis of the change in the
transmitted acoustic frequency and the geometric
configuration of the transducers (SonTek Corporation,
2000). From these data, fixed subsets of velocity measurements, the index velocity, are monitored.
An ADVM may be anchored either on the side of
the channel (side-looking) or placed at the bottom of
the channel (uplooking, Figure 2). Although an
ADVM continuously measures an index velocity, frequent field measurements of discharge are made to
assess whether the index velocity is representative of
velocities in the entire cross section; to relate discharge to stage, cross-sectional area, and index velocity; and to characterize the high frequency and
seasonal variability of the velocity in the cross section. Discharge measurements made with an acoustic
Doppler current profiler (ADCP) enable hydrographers to evaluate the relation between the uplooking
ADVM velocities, or “index velocity,” and the mean
flow velocity across the channel.
quality and overall health of the ecosystem, the IJC
implemented an order in January 2000 to change the
water-level management plan for the private sector
dams that regulate Rainy Lake and Namakan Reservoir. New water levels were intended to restore a
more natural water regime. These changes were
expected to benefit the aquatic ecosystem by affecting
water levels, water quality, and trophic state and by
improving conditions for aquatic plants, fish, and
wildlife.
The relatively shallow Kabetogama Lake has different water chemistry than Namakan Lake (Kallemeyn et al., 2003; Christensen et al., 2011) and
experiences annual cyanobacterial blooms (Kallemeyn
et al., 2003; Christensen et al., 2013). Kabetogama
Lake has higher specific conductance, nutrient, and
Chla concentrations (Kallemeyn et al., 2003) than
Namakan Lake. In addition to the sources of nutrients on the south side of Kabetogama Lake (cottages
without sewage treatment and some of the streams
flowing into Kabetogama Lake; Payne, 1991), internal
loading is also an important source of nutrients to
Kabetogama Lake (Christensen et al., 2013). These
factors and the observation that yearly cyanobacterial
blooms generally do not occur in other large lakes
within the Park indicate that the response of Kabetogama Lake to the IJC 2000 Rule Curves may differ
from the responses of most or all of the remaining
large lakes in the Park. Therefore, an assessment of
water flow and nutrient transport between Namakan
and Kabetogama Lakes was considered essential to
understanding changes in Kabetogama and Namakan
Lakes that may be due to artificial water-level management.
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A
B
Water surface
Echoes
Pings
Up-looking acoustic
Doppler velocity
meter
FIGURE 2. (A) Photograph of the Uplooking Acoustic-Doppler Velocity Meter (Photo Credit: Eric Wakeman, U.S. Geological Survey), and
(B) Schematic of an Uplooking Acoustic-Doppler Velocity Meter in the Narrows Channel (modified from Ruhl and Simpson, 2005).
compute discharge. This method is explained by the
equation.
Q ¼ VA
Collection and Analysis of Water Samples
Depth profiles of field measurements (temperature,
dissolved oxygen, pH, and specific conductance) were
measured in the narrows every 2 weeks during the
open water season in 2011 and 2012 using techniques
described in Wilde and Radtke (1998). Cross-sectional
profiles of field measurements also were measured
and recorded during cross-sectional sampling. Secchidisk transparency was measured at the narrows to
determine the extent of light limitation to algal
growth. In addition, Secchi-disk transparency was
used to determine the depth at which nutrient samples were collected.
Nutrient samples were collected every 2 weeks
during the open-water seasons in 2011 and 2012. In
general, methods followed standard techniques
ð1Þ
where Q is the computed discharge, V is the mean
velocity of the cross section, and A is the cross-sectional area of the channel (Levesque and Oberg,
2012). For the narrows between Kabetogama and
Namakan Lakes, the regression equation used to estimate discharge was
Q ¼ 0:6337Vi þ 0:0091
ð2Þ
where Q is the estimated discharge and Vi is the
index velocity.
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VOYAGEURS NATIONAL PARK, MINNESOTA, 2010-2012
showed that in general the difference between these
two methods was very small (between 0 and 11%;
Table 1), with eight of nine analyses having 3% difference or less. The highest difference was for Chla
(August 16, 2011), which might be expected due to the
spatial variability in Chla and details the importance
of the decision not to calculate load for Chla. One
sample was collected for comparison of point to composite samples (August 20, 2012). The relative percentage differences (1 and 6%, respectively, Table 1)
for total nitrogen and total phosphorus indicated that
for the narrows, point samples are comparable to composite samples. Two field replicate samples were collected —one in 2011 and one in 2012, in which the
same sampling technique was compared to test for
repeatability. The replicate samples (Table 1) had relative percentage differences between 0 and 1%.
Samples were analyzed by the Natural Resources
Research Institute Laboratory in Duluth, Minnesota.
Total phosphorus (P00665) and total nitrogen (P62855)
were analyzed with the persulfate method for simultaneous determination of nitrogen and phosphorus
(Digestion: SM 4500-PJ; Detection: SM 4500-PE;
American Public Health Association, 1999). Chla
samples were collected from the euphotic zone with a
500-mL to 1-L polyethylene sample container. Chla was
analyzed by spectrophotometry (Ameel et al., 1998).
(U.S. Geological Survey, 2006) for lake water sampling. However, because the narrows was not a typical lake site, having flowing water similar to a river
site during parts of the year, three types of samples
were collected. These were (1) point samples collected
1 m below the water surface at the centroid of the
narrows between the two lakes, (2) composite samples
collected with a Van Dorn sampler and composited
from three subsamples collected at the top, center,
and bottom of the part of the upper water column
equal to twice the Secchi-disk reading (Payne, 1991),
and (3) equal-width increment samples (U.S. Geological Survey, 2006).
The point samples are the environmental samples
used for data analysis in this article. Composite samples and equal-width increment samples were collected during a subset of visits for quality control
purposes. Kabetogama Lake is polymictic, and the site
at the narrows was shown to be well mixed during
sampling conducted in 2008 and 2009 (Christensen
et al., 2011); however, a comparison between point
samples and composite samples was necessary to
determine if composite samples collected routinely
throughout Namakan and Kabetogama Lakes (for
previous and ongoing studies) represent similar concentrations to the point samples collected in this
study, so that sample sets could be combined into a
long-term data record in the future. Equal-width
increment samples were collected once in 2011 and
once in 2012 for comparison to the point samples to
verify that the easier-to-collect point samples were
representative of the cross section. Six samples were
collected during 2011-2012 for quality control
(Table 1). Three replicate samples were collected to
compare equal-width increment samples to point samples. Those three samples were analyzed for three
constituents for nine comparisons. Those comparisons
RESULTS AND DISCUSSION
Discharge Computation and Flow Direction
Field technicians measured discharge eight times
from May 11, 2011, through October 3, 2012 (Table 2)
TABLE 1. Quality-Control Samples Collected at Kabetogama Lake, East End, near Old Dutch Bay, 2011-2012.
Sampling Date
2/10/2011
5/11/2011
8/16/2011
8/20/2012
8/20/2012
8/20/2012
Sample Type1
Point
Point-R
EWI
Point
Point
EWI
Point
EWI
Point
Composite
Composite-R
Composite
Field replicate
Point to EWI comparison
Point to EWI comparison
Point to EWI comparison
Point to composite comparison
Field replicate
TN
RPD
TP
373
354
439
453
535
500
476
475
476
463
458
463
1.0
13
13
19
19
24
23
31
29
31
24
26
24
1.0
0
0.1
1.0
0.3
RPD2
0
0
0
0
0.1
0
Chla
RPD2
—
—
4.4
3.9
3.4
5.4
9.2
9.0
9.2
—
—
—
—
3.0
11
1.0
—
—
Notes: TN, total nitrogen in milligrams per liter; TP, total phosphorus in milligrams per liter; Chla, chlorophyll a in micrograms per liter;
RPD, relative percentage difference; EWI, equal-width increment; R, replicate.
1
A point sample is a grab sample taken at the centroid of the narrows. An EWI is an equal-width increment sample collected at intervals
across the narrows. A composite sample is a composite of three samples collected at three points in the water column.
2
RPD computed as the difference of the two values divided by the mean of the two values 9 100.
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Date and Time
Streamflow1
(m3/s)
Measurement
Rating2
5/11/2011 10:53
7/6/2011 13:30
9/8/2011 12:24
11/14/2011 12:21
4/4/2012 11:31
6/7/2012 9:40
8/20/2012 11:20
10/3/2012 12:39
5.45
5.81
5.55
5.25
4.73
5.92
5.65
5.53
39.9
5.69
6.12
15.1
44.2
0.756
47.0
17.2
Fair
Fair
Poor
Poor
Poor
Poor
Fair
Poor
Notes: m, meters; m3/s, cubic meters per second.
Negative number indicates that water is flowing into Kabetogama
Lake.
2
The measurement rating is an assessment of the physical conditions of the measurement that could affect its accuracy. These
include uniformity of flow distributions in the cross section, crosssectional morphometry, changes in stage or discharge during the
measurement, or other factors (Rantz et al., 1983).
1
with an ADCP. Gage height during ADCP measurements ranged from 4.73-5.92 m (Table 2). The discharge was variable, both in terms of magnitude and
direction. The cross-sectional measurements show a
nonuniform channel shape (Figure 3) with a crosssectional width of 177 m and a maximum depth of
10.4 m. The velocity distribution during the eight
measurements generally appeared well distributed
with very low velocities, as indicated by the blue cells
(Figure 3) in the cross-sectional measurement. The
smallest measured discharge was 0.756 cubic meters
per second (m3/s) occurring on June 7, 2012, and
flowing in the direction of Kabetogama Lake and the
largest measured discharge was 47.0 m3/s occurring
on August 20, 2012, and flowing in the direction of
Namakan Lake (Table 2).
0.00
MAKI
The ADVM recorded gage height and index velocity from November 3, 2010, to October 3, 2012. Daily
gage height data from the ADVM were not available
for 7 days in water year 2011 and for 53 days in
water year 2012 due to frozen equipment. Instantaneous (15-min increment) gage height ranged from
4.41 m (on March 31, 2011 and April 1, 2011) to
5.98 m (on June 11, 2012), which was directly
affected by seiche on windy days. The index velocity
was used to estimate discharge with the methods
described previously (Equation 2).
Estimated discharge from the ADVM (Figure 4)
indicated flow direction changed during the year. The
direction of discharge through the narrows was seasonal, with water generally flowing from Kabetogama
Lake into Namakan Lake throughout the ice-covered
season (5-6 months). The flow reversed direction for
about 1.5 months after ice out, flowing from Namakan Lake to Kabetogama Lake. Throughout the summer and fall (4-5 months), the water flowed variably
in either direction, mainly due to wind action. Overall, during water year 2011, discharge was in the
direction of Namakan Lake for 224 days of the 322day record (70% of the year), and during water year
2012, discharge was in the direction of Namakan
Lake for 174 days of the 313-day record (56% of the
year). Because data were missing for 7 days in water
year 2011 and for 53 days in water year 2012 due to
the frozen equipment, linear interpolation was used
to fill in days of missing record. For water year 2011,
the estimate did not change the results (water flowed
into Namakan Lake 70% of the year). For water year
2012, the interpolated results indicated water flowing
into Namakan Lake 62% of the time. In terms of volume, the results were similar to time. During water
year 2011, 70% of the volume of water was in the
TABLE 2. Discharge Measurements at Kabetogama Lake, East
End, near Old Dutch Bay, Site 482611092483801, 2011-2012.
Gage
Height (m)
AND
Top Q depth
Depth, in meters
3.25
6.50
9.75
Bottom Q depth
River depth
13.00
0.001
0.083
0.166
0.248
0.331
Velocity magnitude, in meters per second
FIGURE 3. Discharge Cross Section Indicating Varying Velocities for an Acoustic Doppler Current Profiler (ADCP) Measurement,
May 11, 2011.
JAWRA
8
JOURNAL
OF THE
AMERICAN WATER RESOURCES ASSOCIATION
DISCHARGE
AND
NUTRIENT TRANSPORT
BETWEEN
LAKES
IN A
HYDROLOGICALLY COMPLEX AREA
OF
VOYAGEURS NATIONAL PARK, MINNESOTA, 2010-2012
Kabetogama Lake, East End, near Old Dutch Bay, station number 482611092483801
Positive discharge indicates water flowing into Namakan Lake, negative discharge indicates water flowing into Kabetogama Lake.
Discharge, in cubic
meters per second
80.00
0.00
9/1/2012
8/1/2012
7/1/2012
6/1/2012
5/1/2012
4/1/2012
3/1/2012
2/1/2012
1/1/2012
12/1/2011
11/1/2011
10/1/2011
9/1/2011
8/1/2011
7/1/2011
6/1/2011
5/1/2011
4/1/2011
3/1/2011
2/1/2011
1/1/2011
12/1/2010
11/1/2010
10/1/2010
-80.00
Date
FIGURE 4. Discharge, Kabetogama Lake East End, near Old Dutch Bay, Site 482611092483801, Water Years 2011 and 2012.
(2003). Minimum values for specific conductance were
similar between 2011 and 2012; however, the maximum specific conductance value was substantially
higher in 2011 (123 ls/cm) than in 2012 (80 ls/cm).
In addition to monitoring the specific conductance
at the narrows, measurements were made 1 km east
of the narrows (referred to as site Kabetogama
Namakan East [KNE]) and 1 km west of the narrows
(referred to as site Kabetogama Namakan West
[KNW]) during routine NPS sampling visits (see inset
map, Figure 1). During each site visit, specific conductance was measured at the surface (TOP), at
about 5 m below the surface (MIDDLE), and at about
10 m below the surface (BOTTOM), resulting in 120
additional specific conductance measurements. Specific conductance for all sites ranged from 49 to 123
(ls/cm). The sites 1 km to the east and west of the
narrows (KNE and KNW) were measured to add a
second line of evidence for water flow direction.
Because the water in Kabetogama Lake is known to
have a higher specific conductance than the water in
Namakan Lake (Payne, 1991), it was hypothesized
that specific conductance could be used to determine
whether one lake was influencing the other by how
close the specific conductance value at the narrows
(site KNC) was to either the KNE value or the KNW
value. Although the KNW site, which was closer to
Kabetogama Lake, had a greater average specific conductance concentration (75 ls/cm) over the 2-year
study period compared to the narrows (69 ls/cm) and
site KNE (68 ls/cm), this average pattern was not
always consistent for individual dates, and the narrows had lower or higher specific conductance values
than either the KNE or the KNW site during many
visits. Looking at the individual measurements in
detail (Supporting Information S1), 13 of 20 visits
were made when the discharge direction was from
Namakan Lake to Kabetogama Lake. For only 5 of
direction of Namakan Lake, whereas in 2012, 55% of
the volume of water flowed in the direction of Namakan Lake. Overall, the ADVM measured positive flow
(defined as flowing from Kabetogama Lake into
Namakan Lake) 62% of the time and negative flow
(defined as flowing from Namakan Lake into Kabetogama Lake) 38% of the time. Although the narrows
has a short-term record, discharge can be compared
with long-term records from Rainy River at Manitou
Rapids, Minnesota (USGS station no. 05133500, with
85 years of record) and Vermilion River near Crane
Lake, Minnesota (USGS station no. 05129115, with
34 years of record) (U.S. Geological Survey, National
Water Information System. Accessed February 9,
2015,
http://waterwatch.usgs.gov/).
Streamflow
records for these two stations indicate that spring
and summer 2011 and 2012 were normal years, with
discharge occurring between the 25th and 75th percentiles, with the exception of April 2011 at both
stations when discharge peaked above normal (95th
percentile) (Figure 5). However, these long-term stations also indicate that winter flows were very low
(around the 10th percentile) during water years 2011
and 2012.
Specific Conductance Concentrations
Specific conductance was measured during 20 visits by NPS personnel over the study period, 11 times
in 2011, and 9 times in 2012 (Supporting
Information S1). The specific conductance values
measured at the narrows (referred to as site Kabetogama Namakan Center [KNC], Figure 1) during
2011-2012 (51-123 ls/cm) were more similar to the
range in specific conductance values from Kabetogama Lake (77-107 ls/cm) than those from Namakan
Lake (39-46 ls/cm) reported by Kallemeyn et al.
JOURNAL
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AMERICAN WATER RESOURCES ASSOCIATION
9
JAWRA
CHRISTENSEN, WAKEMAN,
AND
MAKI
A. USGS 05133500 RAINY RIVER AT MANITOU RAPIDS, MN
(Drainage Area: 19400 square miles, Length of record: 87 years)
Daily average discharge, in cubic meters per second
2,000
1,000
100
NOV
2010
JAN
MAR
MAY
JUL
2011
SEP
NOV
JAN
MAR
MAY
2012
JUL
SEP
MAY
2012
JUL
SEP
B. USGS 05129115 VERMILION RIVER NR CRANE LAKE, MN
(Drainage Area: 905 square miles, Length of record: 35 years)
Daily average discharge, in cubic meters per second
100
10
1
NOV
2010
JAN
MAR
MAY
JUL
2011
SEP
NOV
JAN
MAR
Explanation - Percentile classes
lowest10th percentile
10–24
25–75
75–90
90th percentilehighest
Much below
normal
Below
normal
Normal
Above
normal
Much above
normal
Flow
FIGURE 5. Daily Average Discharge for (A) Rainy River at Manitou Rapids, Minnesota and (B) Vermilion River at Crane Lake, Minnesota.
these 13 visits (38%), the specific conductance value
at KNC was closer to the value at KNE than to the
value at KNW. For the seven visits when discharge
JAWRA
was flowing from Kabetogama Lake to Namakan
Lake, 33% (7 of 21 specific conductance measurements, including TOP, MIDDLE, and BOTTOM mea10
JOURNAL
OF THE
AMERICAN WATER RESOURCES ASSOCIATION
DISCHARGE
AND
NUTRIENT TRANSPORT
BETWEEN
LAKES
IN A
HYDROLOGICALLY COMPLEX AREA
Assessment of Transport
Flow measurements made during a previous nutrient cycling study (Christensen et al., 2011) showed
that water flowed in both directions at the narrows
between Kabetogama and Namakan Lakes. It is not
possible to quantitatively assess the relative importance of nutrient sources to Kabetogama Lake without assessing discharge and nutrient transport at the
narrows between Kabetogama and Namakan Lakes.
It is not known how water-level regulation changes
in 2000 may have affected flow at the narrows. However, Kallemeyn et al. (2003) reported that waterlevel management changes in 2000 would increase
the number of days water flowed through Gold Portage at the west end of Kabetogama Lake from
253 days per year to 325-365 days per year. An analysis of the data at Gold Portage (available at http://
waterdata.usgs.gov) indicates that from 2000 through
2014, water has flowed through Gold Portage an
average of 347 days per year, with the last zero-flow
day occurring on March 30, 2006. It may be that
increased flow from Namakan Lake into Kabetogama
Lake also would occur on more days due to the
changes in water-level management, but with only
2 years of discharge measurement at the narrows
between the lakes, this would be difficult to assess.
This 2-year assessment was meant to provide additional information on the hydrologic variability in the
narrows between Namakan and Kabetogama Lakes.
Research has shown that water-level changes
likely have had water-quality implications in water
bodies throughout the United States (e.g., Hambright
et al., 2004; Hoyer et al., 2005) and in Voyageurs
National Park (Christensen et al., 2004, 2011; Christensen and Maki, 2015). In Kabetogama Lake, blooms
of cyanobacteria occur most years (Kallemeyn et al.,
2003) and have been shown to produce microcystin
(Christensen et al., 2011) to levels beyond the World
Health Organization threshold for safe drinking
water (World Health Organization, 2003). A study of
trophic state (Christensen and Maki, 2015) indicated
that Kabetogama Lake was mesotrophic to eutrophic,
whereas Namakan Lake was oligotrophic. The concern over eutrophication and cyanobacteria blooms in
Kabetogama Lake and the potential transport of
nutrients to the more pristine Namakan Lake were
additional reasons for this study. The greatest con-
Nutrient and Chlorophyll-a Concentrations
Twenty-two water samples were collected at the
narrows during 2011 and 2012 and analyzed for total
nitrogen, total phosphorus, and Chla (Table 3). Total
nitrogen concentrations ranged from 373 (February
10, 2011) to 692 (August 29, 2011) milligrams per liter
(mg/L) with an average concentration of 484 mg/L.
Total phosphorus concentrations ranged from 12 (June
6, 2011) to 41 mg/L (August 29, 2011 and August 8,
2012) with an average concentration of 22 mg/L.
Nutrient concentrations were seasonally variable,
with the largest concentrations in late summer.
Concentrations of Chla ranged from 0.7 (May 31,
2012) to 14.3 (September 14, 2011) micrograms per
TABLE 3. Results of Total Nitrogen, Total Phosphorus, and
Chlorophyll-a Analyses at Kabetogama Lake, East End, near Old
Dutch Bay, 2011-2012.
TN
TP
Chla
2/10/2011
5/11/2011
5/25/2011
6/6/2011
6/20/2011
7/5/2011
7/19/2011
8/1/2011
8/16/2011
8/29/2011
9/14/2011
9/28/2011
5/15/2012
5/31/2012
6/11/2012
6/27/2012
7/10/2012
7/23/2012
8/8/2012
8/20/2012
9/4/2012
9/19/2012
373
453
445
400
439
506
472
534
535
692
604
519
466
410
432
422
462
496
578
476
501
427
13
19
13
12
15
18
15
28
24
41
30
26
18
15
14
16
19
22
41
31
28
23
3.9
3.7
2.8
2.0
3.4
1.9
5.8
3.4
6.4
14.3
7.9
4.3
0.7
3.7
3.0
5.2
8.1
10.2
9.2
5.8
5.3
Note: TN, total nitrogen in milligrams per liter; TP, total phosphorus in milligrams per liter; Chla, chlorophyll a in micrograms per
liter; -, no data.
JOURNAL
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VOYAGEURS NATIONAL PARK, MINNESOTA, 2010-2012
liter (lg/L) with an average concentration of 5.3 lg/L.
Chla concentrations were lower at the narrows
compared to other sites in Kabetogama Lake (Christensen et al., 2011). At the narrows, the greatest concentrations of Chla and nutrients generally occurred
in the summer months.
surements) indicated a KNC value that was closer to
the value at KNW than the value at KNE. An examination of specific conductance differences between the
TOP, MIDDLE, and BOTTOM showed that during
2011, the most variation between KNE and KNW
occurred in the MIDDLE sample for six of seven sampling dates where Namakan Lake was flowing into
Kabetogama Lake; for sampling dates where Kabetogama Lake was flowing into Namakan Lake, and for
2012 sampling dates, no pattern was evident.
Sampling Date
OF
11
JAWRA
CHRISTENSEN, WAKEMAN,
MAKI
under ice). The ADVM results indicate that the
eutrophic Kabetogama Lake receives water from
Namakan Lake only about 30% of the time; thus,
Namakan Lake likely is not a substantial source of
nutrients and Chla to Kabetogama Lake. Loads were
not calculated during this study due to the “fair” to
“poor” rating at the narrows and the lack of samples
collected under ice. However, the transport information is important because resource managers may be
able to narrow their focus for future studies to the
external nutrient sources on the south side of Kabetogama Lake and to the internal sources from loading,
or the recirculation of nutrients from bottom sediments, which were the sources identified in a previous study of nutrient cycling (Christensen et al.,
2013).
centrations of Chla and nutrients generally occurred
in the summer months — those periods when discharge in the narrows was unpredictable, flowing in
both directions. This presents some difficulty in
determining if the historically higher nutrient and
Chla concentrations in Kabetogama Lake are affecting the more pristine Namakan Lake. However,
because the water flowed toward Namakan between
70% (2011) and 56% (2012) of the year, Kabetogama
Lake represents a large potential source of nutrients
to Namakan Lake.
This study provided evidence that water flowed
from Kabetogama Lake into Namakan Lake during
most of the year. Discharge was considered estimated
due to the fair to poor rating, primarily caused by
low and variable velocities and velocity variability in
the cross section. Days of missing record contributed
to a poor rating; however, most missing record
occurred during ice cover, when water was consistently flowing in one direction. The extremely low
winter flows in the area (Figure 5) may have affected
the flow at the narrows, but without a longer period
of record at the narrows, it is difficult to determine if
flow direction was affected. The positive flows at
the narrows (winter months in Figure 4) appear to
correspond with the lower flows at Rainy River at
Manitou Rapids and Vermilion River near Crane
Lake (Figure 5).
Specific conductance values measured at the narrows during 2011-2012 were more similar to the values from Kabetogama Lake than to values from
Namakan Lake, indicating that flow from Kabetogama Lake affects Namakan Lake. However, specific
conductance measurements at sites 1,000 m to either
side of the narrows did not indicate that one lake was
affecting the other. This is possibly a result of the
wind action causing changes in water flow direction
at the surface during the open-water season when all
the specific conductance measurements were made.
In addition, water flow direction may have been
changing frequently during the summer months,
affecting specific conductance measurements at the
top of the water column, especially in 2012. Although
less expensive and easily collected, specific conductance measurements would be a poor substitute for
ADVM measurements to determine flow direction in
these narrows. Continually changing direction of
flow, seiche, and wind affect specific conductance concentrations.
Despite the limitations, the ADVM provided important information regarding transport between Namakan and Kabetogama Lakes and filled some gaps in
the understanding of the hydrology and water quality
of the large lakes in Voyageurs National Park. Specifically, the ADVM captured the seasonal variability
inherent in hydrologic conditions (including those
JAWRA
AND
SUMMARY AND CONCLUSIONS
The USGS and NPS used an ADVM to measure
discharge in a unique setting in Voyageurs National
Park where traditional discharge computation methods were not feasible. The water between Kabetogama Lake and Namakan Lake flows in both
directions, similar to that of an estuary. In addition,
the collection of specific conductance, nutrient, and
Chla samples together with a continuous record of
discharge provided an assessment of transport
between the lakes that was not possible with discrete
measurements.
To address our first objective, to estimate discharge and document direction of flow between Kabetogama and Namakan Lakes, the ADVM recorded
discharge in the narrows between Namakan and
Kabetogama Lakes from November 3, 2010, through
October 3, 2012. The direction of flow through the
narrows was seasonal, with water generally flowing
out of Kabetogama Lake and into Namakan Lake
throughout the ice-covered season (5-6 months). During a few weeks after ice out (about 1.5 months), the
water flow was generally from Namakan to Kabetogama Lake, which might be expected because the
major inflows to the system (Namakan River, Vermilion River, and Loon River) are upstream from
Namakan Lake and these flows would all push
water toward Kabetogama Lake during the spring
runoff period. Throughout the summer and fall
(4-5 months), the water flows in both directions,
affected by wind action. Overall, during water year
2011, discharge was in the direction of Namakan 70%
of the year, and during water year 2012, discharge
was in the direction of Namakan 56% of the year. In
terms of volume, 70% was in the direction of
12
JOURNAL
OF THE
AMERICAN WATER RESOURCES ASSOCIATION
DISCHARGE
AND
NUTRIENT TRANSPORT
BETWEEN
LAKES
IN A
HYDROLOGICALLY COMPLEX AREA
OF THE
AMERICAN WATER RESOURCES ASSOCIATION
VOYAGEURS NATIONAL PARK, MINNESOTA, 2010-2012
The information gained from this study provides
resource managers with a more detailed understanding of the effects of the altered hydrologic regime for
Namakan Reservoir under the most recent set of rules
governing dam operation and the pattern of flow
between Namakan and Kabetogama Lakes. By being
well-informed, resource managers will be able to make
recommendations to the IJC that will best protect the
aquatic resources of Voyageurs National Park.
Namakan Lake during 2011, whereas 55% of the volume of water flowed in the direction of Namakan
Lake in 2012.
To address our second objective, to assess whether
specific conductance can be used to determine flow
direction in the narrows, we measured specific conductance at the narrows and compared the values to
measurements made 1,000 m into Kabetogama Lake
and 1,000 m into Namakan Lake. It appears that
specific conductance is not a good indicator of flow
due to the complexity of the flow pattern and lake
water chemistry in the narrows — in terms of variation in the profile and frequent changes in flow direction.
To address our third objective of documenting
nutrient and Chla data, we reported concentrations
of nutrients and Chla which were highest during the
late summer months when the direction of water flow
was unpredictable. This presents a challenge for lake
managers to determine whether high concentrations
occurring during periods of unpredictable flow are
affecting either lake.
Despite the limitations of the ADVM technology
for nutrient and Chla load calculation, the ADVM
provided estimated daily discharge in an area where
discharge had only been measured a few times. The
ADVM also indicated that water under ice cover
flowed exclusively from Kabetogama Lake to Namakan Lake. These results indicate that eutrophic
Kabetogama Lake may be having a negative effect on
the more pristine Namakan Lake.
This assessment of water flow and nutrient transport was considered essential to understanding
changes in Kabetogama and Namakan Lakes that
may be due to artificial water-level management and
the dams regulating water at Squirrel and Kettle
Falls. Taken in combination with the results of previous Namakan Reservoir water-quality studies, this
study provides an assessment of Kabetogama Lake
nutrient transport to date and indicates that Namakan Lake is not likely a major source of nutrients to
Kabetogama Lake under the current set of rules
governing dam operation on these lakes, which is
information of great importance to the NPS managers as they seek to understand the water quality
of these lakes and the ecological consequences of
artificial water-level management. Other sources of
nutrients to Kabetogama Lake are internal (lake
bottom sediments) and external (inflows from areas
on the south shore). These internal and external
sources of nutrients to Kabetogama Lake likely have
a larger effect on nutrient levels and trophic state
than does input from Namakan Lake and may be
the most appropriate focus for future assessments of
the relative importance of nutrient inputs to Kabetogama Lake.
JOURNAL
OF
SUPPORTING INFORMATION
Additional supporting information may be found in
the online version of this article: specific conductance values recorded at Kabetogama Lake, East End
near Old Dutch Bay and at sites 1,000 m east and
west.
ACKNOWLEDGMENTS
The authors thank the many USGS and NPS technicians who
helped with data collection for this research. These include Russ
Buesing, Josh Larson, John Greene, Jeff Copa, and Ben Otto with
the USGS and Jaime LeDuc, Craig Treat, Jerry Warmbold, Patrick
Ferguson, Sarah Ferguson, James Anderson, and Eric Olson with
the NPS. Any use of trade, firm, or product names is for descriptive
purposes only and does not imply endorsement by the U.S. Government.
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