Patterns of Under Ice Dissolved Oxygen Concentrations Along Transects of Six Clay Influenced Bays
and Three Rivers within the St. Louis River Estuary
Josh Mutchler; University Wisconsin-Superior, McNair Scholar
Dr. Shon Schooler, Research Coordinator, LSNERR
Abstract
Dissolved oxygen is an important component of aquatic ecosystems and affects living organisms from
fish to bacteria and influences ecosystem functions such as carbon and phosphorus cycling and mercury
uptake. Although it is a standard parameter studied in water quality sampling, it is rarely measured in
the winter under the ice. Anecdotal reports indicated anoxic zones in the clay influenced bays within the
St. Louis River Estuary located at the Southwest end of Lake Superior. In February and March 2013 a
study was designed to investigate these reports. We measured under ice dissolved oxygen
concentration, conductivity, salinity, pH, temperature, depth, turbidity, chlorophyll concentration, and
ice thickness along transects from inner bay (or river channel) to mouth in six bays, two of which were
fed by clay influenced rivers (Nemadji and Pokegama). We also recorded these parameters in the St.
Louis River main channel from the base of the first dam to its confluence with Lake Superior. In addition,
we measured photosynthetic active radiation (PAR) through ice and snow and ice alone. Ice thickness
varied from 49 to 81 cm and ice cover was complete throughout the estuary at the time of sampling.
Dissolved oxygen concentration (DO) varied from 2.2% (0.30 mg/L) to 96.1% (14.02 mg/L). Interestingly,
lowest DO was found within the Pokegama River system and increased as the mouth of Pokegama bay
approached the main channel of the St. Louis River. We suspect the increase of DO was due to
interaction between Lake Superior and the St. Louis River driven by the seiche effect from the lake.
However, there was not a detectable pattern for DO between Lake Superior and the Nemadji River.
Introduction
Traditionally estuaries have been defined as semi-enclosed coastal bodies of water which have a
free connection with the open sea and within which sea water is measurably diluted with fresh water
derived from land drainage (Pritchard 1967). Over time the term estuary has been reconstructed to
describe a mixing zone with similar biogeochemical mixing processes but including freshwater, in
addition to saltwater, systems (Herdendorf 1990). In this study we focused on six clay influenced bays,
and two rivers within the St. Louis River Freshwater Estuary, located at the southwest tip of Lake
Superior. The estuary contains close to 2,000 acres of surface water area and 9,412 km 2 of land within
its watershed (Hoffman et al. 2010). The St. Louis River is 288-km in total length and its first obstruction
is the Fond du Lac Dam which is located 38-km upstream from the mouth of the river (Hoffman et al.
2010).
The mixing process that occurs in order to define this as a freshwater estuary is primarily driven
by the seiche effect from Lake Superior. The term seiche refers to the periodic exposure and drying
period of shallow littoral zones within an enclosed body of water due to wind force and atmospheric
pressure (Mackie et al. 2001). Relative to the St. Louis River, the seiche effect from Lake Superior has
been discovered to reverse flow direction of the river, up to the Fond du Lac Dam (Stortz and Sydor
1980). One importance of this phenomenon is that the incoming water from Lake Superior is a source of
oxygen rich water that replenishes the dissolved oxygen within the estuary. Another source of water
input to the system is ground water. During the summer and spring ground water is characterized by
cool, oxygen rich water that is replenished by infiltration of rain water and spring snowmelt. During the
winter months it is usually of lesser quality and can be low in oxygen, high in dissolved mineral salts, and
has relatively higher temperature than surface water (Mackie et al. 2001).
During the 1880’s, the construction of the shipping canal and railroads increased the area’s
economy through distribution of grain, timber and iron ore (Zenith City Press 2011). In 1916 the U.S.
Steel plant began production of coke, iron and steel and continued polluting the surrounding land and
water until the 1980’s when the plant closed (MPCA 2013). Prior to the 1970’s, water quality was poorly
managed in the St. Louis River. In the late 1920’s the Minnesota State Board of Health classified the river
as “pollutional”. The decomposition of organic material in the river caused drastic reductions in
dissolved oxygen concentrations, which resulted in numerous fish-kill events (St. Louis River Alliance
2013). As result of the 1972 amendments to the Federal Water Pollution Control Act, providing the basic
structure for regulating the discharge of pollutants from point sources to waters of the United States,
the quality of the estuary has recovered substantially (EPA). However, according to anecdotal reports,
there are still areas with large masses of subsurface debris, mostly wood waste, within embayments of
the St. Louis River Estuary causing low levels of DO during the winter months.
There are two sources of oxygen in aquatic systems, the atmosphere and photosynthetic
primary production by algae and macrophytes (Mackie et al. 2001). During the winter sources of
dissolved oxygen are assumed to become scarce because ice and snow cover depletes photosynthetic
active radiation (PAR) necessary for photosynthesis to occur. Ice and snow cover also eliminates
interaction between surface water and atmospheric oxygen. During winter months decomposition is a
cause of oxygen depletion because decomposing bacteria utilize oxygen to break down organic material
(Mackie et al 2001). Dissolved oxygen is a necessity for all aquatic life, differing amounts depending on
the organisms requirements for survival. This study focused on dissolved oxygen levels pertaining to
freshwater game fish within the estuary. A few important game fish in the St. Louis River Estuary
include: Black Crappie (Pomoxis nigromaculatus), Northern Pike (Esox lucius), and Walleye (Sander
vitreus). The dissolved oxygen necessary for optimal function varies depending on the species (Table 1)
but generally sub-optimum levels of dissolved oxygen (below 5 mg/l), while not immediately lethal, may
stress fish resulting in delayed mortality (Rottman 1992).
Fish Species
Black Crappie (Pomoxis
nigromaculatus)
Northern Pike (Esox lucius)
Walleye (Sander vitreus)
Tolerance level of DO
 2.6 mg/l
 3.0 mg/l
 5.0 mg/l
Source
Knights et al. 1995
Casselman, J.M. and Lewis,
C.A. 1996
Scherer 1971
Table 1. Tolerance of selected fish species to low dissolved oxygen concentrations
Although bodies of water in temperate regions retain higher levels of oxygen during the winter,
due to the correlation between water temperature and gas solubility properties, sources of dissolved
oxygen in the winter are limited. Cold temperatures result in ice covering most of the estuary through
the months of December to April, eliminating surface water exposure to the atmosphere. Also, ice and
snow limit the penetration of necessary levels of sunlight for photosynthesis to occur. As a result, as
organisms use oxygen during processes such as decomposition, DO is not replenished. In this study we
examined whether this phenomenon occurs for bays and rivers within the St. Louis River Freshwater
Estuary. In order to better understand variation between sites we constructed multiple hypotheses
based on observations of the water quality data. Our first hypothesis suggested that the influence of
snow and ice on the amount of PAR received at surface water is not sufficient for photosynthesis to
occur, eliminating it as a source for dissolved oxygen within the bays during the winter. We believed that
the main source of dissolved oxygen within bays is a result of the sieche effect from Lake Superior or the
influence from rivers running into bays. Our second hypothesis suggested that groundwater upwelling
was causing low levels of dissolved oxygen at bottom levels in which the upper portion of the water
column contained healthy levels of DO. In this study ground water upwelling was characterized by an
increase in conductivity and water temperature near the bottom, along with a decrease in dissolved
oxygen due to poor water quality (Mackie et al. 2001). Our third hypothesis suggested that sites with
higher rates of decomposition near the bottom will result with lower levels of dissolved oxygen due to
bacterial use of oxygen during that process (Mackie et al. 2001). Our fourth hypothesis was formed
based on the extent of the sieche effect reversing river flow up to the Fondu Lac Dam (Stortz and Sydor
1980) suggesting a relationship in which levels of dissolved oxygen within either the St. Louis River or
the Nemadji River were expected to increase as sample points each river system approached Lake
Superior.
Methods
Locations were sampled from February 28, 2013 to March 27, 2013. The entire estuary was
completely frozen over during that time (no open water observed), but Lake Superior was not frozen
beyond 1 km from shore. Sample sites were chosen within six bays (Woodstock, Kilner, Kelly, Kimball,
Pokegama, and Allouez) and three river channels (Nemadji, Pokegama, and St. Louis). Sample sites were
selected to represent the head of each bay, (furthest from the St. Louis River), the midpoint of each bay
and the mouth of each bay (closest to the river). River sites were chosen within the river channel at
varying intervals; in Pokegama from the head of the bay upriver 5.51 km; Nemadji mouth upriver to 7.99
km, and St. Louis from Duluth entry upriver to the Hwy 23 bridge (34.7 km). In the field, a 6-inch electric
ice auger (Ion) was used to access the water under the ice. Snow depth was measured in four different
places, evenly spaced in a circular pattern, within twelve inches of the hole. Photosynthetic Active
Radiation (PAR) was assessed using a LiCor LI-250A light meter paired with a LI-192 underwater PAR
sensor. The sensor was set on a pole with a 13 cm armature to extend under the ice to sides of the ice
hole. Loss of PAR under snow and ice and ice alone was then measured. This was done by first collecting
a measurement in the air, to determine the above-ice ambient level of PAR. With snow still covering the
ice the PAR meter was lowered into the water column just below the ice (13 cm from edge of hole) in
which four measurements were taken, each preceding the previous measurement in a circular pattern
around the hole. Another measurement was then taken in the air to account for the change in light
during time submerged. The ice was then cleared of snow by using a shovel to create a one meter
diameter circular clearing down to the surface of the ice. The PAR measuring process was then repeated
to measure effect of ice alone. Snow depth, PAR, ice depth and water column depth (from the top of the
ice) were measured before water quality parameters were measured. The following water quality
parameters were collected using a YSI 6600 sonde at surface, mid and bottom depths within the water
column; conductivity (mS/cm), pH, salinity (ppt), dissolved oxygen (% and mg/L), temperature (C),
turbidity (NTU), chlorophyll (µg/L) and phycocyanin (cell/mL). During this time, geographic coordinates
were recorded (Garmin 550 GPS, using waypoint averaging to 100% confidence, 3-5 m accuracy).
Area of Study
Dissolved Oxygen (mg/l)
Bottom Levels of DO
0.30 - 5.00
5.01 - 9.00
9.01 - 14.00
Figure A. Google Earth overhead image of the St. Louis River Estuary from the mouth (top right) to the
first dam (bottom left). Colored points represent sample points for this study. Colors correlate to levels
of dissolved oxygen (mg/l) throughout the estuary including Nemadji River (bottom right).
Figure B.) Google Earth close up over head view of Pokegama Bay. We suggest that the land masses
surrounding the mouth of the bay are inhibiting mixing with the main river channel, leading to low levels
of dissolved oxygen and higher levels of suspended solids than the surrounding bays.
Results
PAR Results
At all sites PAR was reduced by over 90% under ice and snow cover between 65 cm and 90 cm.
PAR was reduced by 73 percent to 99 percent under only ice cover, ranging from 49 cm to 78 cm (Table
4).
Water Quality Parameter Results
Results for surface and bottom levels of dissolved oxygen were related to the position of the
sample and the distance to Lake Superior. Linear regression results indicate that there is a correlation
between bottom and surface dissolved oxygen and distance from Lake Superior (Figures 2 and 3).
(All Water quality results can be found in Tables 2 and 3)
Kelly Bay
Throughout Kelly Bay ice depth ranged from 65-75 cm and snow cover ranged from 10-28cm.
Total water depth ranged from 1.44-3.40 meters and water temperature varied between (0.07 ̊C 1.86 ̊C). At the head of the bay ambient light PAR was 284.8 µmol photons/m2/second PAR decreased
to an average value of 0.8 µmol photons/m2/second under 85 cm of ice and snow. The second ambient
light PAR reading was 266 µmol photons/m2/second. PAR was reduced to an average value of 8.5 µmol
photons/m2/second under 70 cm of ice. Total water depth was 1.44 meters. At the surface sample point
within the water column water temperature was 0.07 ̊C with a pH of 7.54 and conductivity was 0.33
Dissolved oxygen at the surface of the bay was 9.8 mg/l. At the bottom sample point water temperature
was 0.14 C
̊ with a pH of 7.45 and conductivity was 0.331 µS/cm. Dissolved oxygen at the bottom of the
bay was 9.08 mg/l.
At the midpoint of the bay ambient light PAR was 596.8 µmol photons/m2/second PAR
decreased to an average value of 0.6 µmol photons/m2/second under 90cm of ice and snow. The
second ambient light PAR reading was 558.5 µmol photons/m2/second. PAR reduced to an average
value of 16.5 µmol photons/m2/second under 65 cm of ice. Total water depth was 3.40 meters. At the
surface sample point within the water column water temperature was 0.11 ̊C with a pH of 7.45 and
conductivity was 0.325 µS/cm Dissolved oxygen at the surface was 9.23 mg/l. At the midway sample
point water temperature was 0.20 ̊C with a pH of 7.39 and conductivity was 0.324 µS/cm Dissolved
oxygen at the midway sample point was 8.70 mg/l. At the bottom sample point water temperature was
1.86 ̊C with a pH of 7.24 and conductivity was 0.392 µS/cm. Dissolved oxygen at the bottom of the bay
was 4.52 mg/l (Figure 1.)
At the mouth of Kelly bay ambient light PAR was 548 µmol photons/m2/second PAR decreased
to an average value of 1.0 µmol photons/m2/second under 86 cm of ice and snow. The second ambient
light PAR reading was 572.8 µmol photons/m2/second. PAR reduced to an average value of 7.8 µmol
photons/m2/second under 75 cm of ice. Total water depth was 2.7m. At the surface sample point within
the water column water temperature was 0.32 ̊C, pH 7.48 and conductivity was 0.321 µS/cm. Dissolved
oxygen at the surface of the bay was 9.03 mg/l. At the midway sample point water temperature was
0.22 ̊C , pH 7.43 and conductivity was 0.32 µS/cm. Dissolved oxygen at the midway point was8.86 mg/l.
At the bottom sample point water temperature was 0.48 ̊C, pH 7.38 and conductivity was 0.33 µS/cm.
Dissolved oxygen at the bottom of the bay was 8.44 mg/l.
Kimball Bay
Throughout Kimball Bay ice thickness ranged from 59-63 cm and snow cover ranged from 19-27
cm Total water depth ranged from 2.62 – 4.61 meters and water temperature varied between 0.23 ̊C –
1.36 ̊C. At the head of Kimball bay ambient light PAR was 1265 µmol photons/m2/second PAR
decreased to an average value of 3.1 µmol photons/m2/second under 86 cm of ice and snow. The
second ambient light PAR reading was 1324.6 µmol photons/m2/second. PAR reduced to an average
value of 124 µmol photons/m2/second under 59 cm of ice. Total water depth was 2.62 meters. At the
surface sample point within the water column water temperature was 0.36 ̊C, pH 7.71 and conductivity
was 0.344 µS/cm. Dissolved oxygen at the surface of the bay was 9.2 mg/l. At the midway sample point
water temperature was 0.24 ̊C, pH 7.38 and conductivity was 0.350 µS/cm. Dissolved oxygen was 8.38
mg/l. At the bottom sample point water temperature was 0.56 ̊C, pH of 7.27 and conductivity was
0.358 µS/cm. Dissolved oxygen at the bottom of the bay was 7.58 mg/l.
At the middle of the Kimball Bay ambient light PAR was 893 µmol photons/m2/second PAR
decreased to an average value of 2.1 µmol photons/m2/second under 85 cm of ice and snow. The
second ambient light PAR reading was 664.8 µmol photons/m2/second. PAR reduced to an average
value of 22 µmol photons/m2/second under 63 cm of ice. Total water depth was 3.63 meters. At the
surface sample point within the water column water temperature was 0.84 ̊C, pH 7.30 and conductivity
was 0.36 µS/cm. Dissolved oxygen at the surface of the bay was 7.52 mg/l. At the middle sample point
water temperature was 0.50 ̊C with a pH of 7.41 and conductivity was 0.348 µS/cm Dissolved oxygen
was 8.42 mg/l. At the bottom sample point water temperature was 0.56 C
̊ with a pH of 7.6 and
conductivity was 0.356 µS/cm Dissolved oxygen at the bottom of the bay was 11.49 mg/l.
At the mouth of the bay ambient light PAR was 1082 µmol photons/m2/second PAR decreased
to an average value of 4.8 µmol photons/m2/second under 85 cm of ice and snow. The second ambient
light PAR reading was 929.7 µmol photons/m2/second. PAR reduced to an average value of 22 µmol
photons/m2/second under 63 cm of ice. Total water depth was 4.61 meters. At the surface sample
point within the water column water temperature was 0.23 ̊C with a pH of 7.44 and conductivity was
0.34 µS/cm. Dissolved oxygen at the surface of the bay was 8.19 mg/l. At the middle sample point water
temperature was 0.42 ̊C with a pH of 7.37 and conductivity was 0.340 µS/cm. Dissolved oxygen was
7.86 mg/l. At the bottom sample point water temperature was 1.36 ̊C with a pH of 7.33 and
conductivity was 0.348 µS/cm. Dissolved oxygen at the bottom of the bay was 7.31mg/l.
Kilner Bay
Throughout Kilner Bay ice depth ranged from 59-60cm and snow cover ranged from 21-25 cm.
Total water depth ranged from1.25-3.77 m and water temperature varied between 0.08 ̊C -1.33 C
̊ . At
the head of the bay ambient light PAR was 253 µmol photons/m2/second PAR decreased to an average
value of 0.6 µmol photons/m2/second under 81 cm of ice and snow. The second ambient light PAR
reading was 207.6 µmol photons/m2/second. PAR reduced to an average value of 15 µmol
photons/m2/second under 60 cm of ice. Total water depth was 1.25 m. At the surface sample point
water temperature was 0.08 ̊C with a pH of 7.49 and conductivity was 0.350 µS/cm. Dissolved oxygen
was 9.29 mg/l. At the middle sample point water temperature was 0.21 C
̊ with a pH of 7.45 and
conductivity was 0.35 µS/cm. Dissolved oxygen was 8.93 mg/l. At the bottom sample point water
temperature was 0.25 ̊C with a pH of 7.42 and conductivity was 0.35 µS/cm. Dissolved oxygen at the
bottom of the bay was 8.73 mg/l.
At the middle of the bay ambient light PAR was 705 µmol photons/m2/second PAR decreased
to an average value of 1.5 µmol photons/m2/second under 82.5 cm of ice and snow. The second
ambient light PAR reading was 642.6 µmol photons/m2/second. PAR reduced to an average value of
36.9 µmol photons/m2/second under 59cm of ice. Total water depth was 3.49 m. At the surface sample
point within the water column water temperature was 0.08 ̊C with a pH of 7.51 and conductivity was
0.35 µS/cm. Dissolved oxygen at was 9.33 mg/l. At the middle sample point water temperature was
0.49 ̊C with a pH of 7.44 and conductivity was 0.35 µS/cm. Dissolved oxygen was 8.97 mg/l. At the
bottom sample point water temperature was 1.33 ̊C with a pH of 7.30and conductivity was 0.362
µS/cm. Dissolved oxygen at the bottom of the bay was 6.45 mg/l.
At the mouth of the bay ambient light PAR was 785.3 µmol photons/m2/second PAR decreased
to an average value of 6.5 µmol photons/m2/second under 83.5 cm of ice and snow. The second
ambient light PAR reading was 645µmol photons/m2/second. PAR reduced to an average value of 55.1
µmol photons/m2/second under 59cm of ice. Total water depth was 3.77m. At the surface sample point
water temperature was 0.20 ̊C with a pH of 7.56 and conductivity was 0.33 µS/cm. Dissolved oxygen
was 9.00 mg/l. At the middle sample point water temperature was 0.54 C
̊ with a pH of 7.42 and
conductivity was 0.33 µS/cm. Dissolved oxygen was 8.28 mg/l. At the bottom sample point water
temperature was 1.33 ̊C with a pH of 7.32 and conductivity was 0.36 µS/cm. Dissolved oxygen at the
bottom of the bay was 6.44 mg/l.
Pokegama Tributary
Throughout the Pokegama Bay Tributary ice depth ranged from 60-62cm, snow cover ranged
from 25-30cm and total water depth ranged from 1.49-2.2 m. water temperature varied between
0.24 ̊C – 1.93 ̊C. At the head of the bay ambient light PAR was 1853 µmol photons/m2/second PAR
decreased to an average value of 3.88 µmol photons/m2/second under 87.25 cm of ice and snow. The
second ambient light PAR reading was 1645 µmol photons/m2/second. PAR reduced to an average value
of 52.8 µmol photons/m2/second under 61 cm of ice. Total water depth was 1.49m. At the surface
sample point within the water column water temperature was 0.24 ̊C with a pH of 7.18 and
conductivity was 0.34 µS/cm. Dissolved oxygen was 6.67 mg/l. At the middle sample point water
temperature was 0.80 ̊C with a pH of 7.11 and conductivity was 0.349 µS/cm Dissolved oxygen was 5.01
mg/l. At the bottom sample point water temperature was 0.91 ̊C with a pH of 7.08 and conductivity
was 0.35 µS/cm. Dissolved oxygen at the bottom of the bay was 3.40 mg/l (Figure 1). At the midway
point of the bay ambient light PAR was 1931 µmol photons/m2/second PAR decreased to an average
value of 3.56 µmol photons/m2/second under 89.7 cm of ice and snow. The second ambient light PAR
reading was 1891.8 µmol photons/m2/second. PAR reduced to an average value of 96.84 µmol
photons/m2/second under 60 cm of ice. Total water depth was 2.2m. At the surface sample point water
temperature was 0.79 ̊C with a pH of 7.14 and conductivity was 0.34 µS/cm. Dissolved oxygen was 6.44
mg/l. At the middle sample point water temperature was 1.37 ̊C with a pH of 6.63 and conductivity was
0.355 µS/cm. Dissolved oxygen was 3.08 mg/l (Figure 1.) At the bottom sample point water temperature
was 1.93 ̊C with a pH of 6.94 and conductivity was 0.358 µS/cm Dissolved oxygen at the bottom of the
bay was 1.39 mg/l (Figure 1.). At the mouth of the bay ambient light PAR was 1648.8 µmol
photons/m2/second PAR decreased to an average value of 2.71 µmol photons/m2/second under 86.5
cm of ice and snow. The second ambient light PAR reading was 1619.7 µmol photons/m2/second. PAR
reduced to an average value of 98.93 µmol photons/m2/second under 62 cm of ice. Total water depth
was 1.96 m. At the surface sample point within the water column water temperature was 0.27 ̊C with a
pH of 7.02 and conductivity 0.33 µS/cm. Dissolved oxygen was 7.93mg/l. At the middle sample point
water temperature was 0.76 ̊C with a pH of 6.80 and conductivity was 0.34 µS/cm Dissolved oxygen
was 6.17 mg/l. At the bottom sample point water temperature was 1.11 C
̊ with a pH of 6.59 and
conductivity was 0.35 µS/cm. Dissolved oxygen at the bottom of the bay was 4.28 mg/l (Figure 1).
Pokegama Bay
Throughout Pokegama Bay ice thickness ranged from 49 cm - 52 cm. Total water depth ranged
from 80 cm - 170 cm and water temperature varied between 0.04 ̊C- 0.79 ̊C. At the midpoint of the bay
ambient light PAR was 1567.1 µmol photons/m2/second PAR decreased to an average value of 2.33
µmol photons/m2/second under 78.75 cm of ice and snow. The second ambient light PAR reading was
1412.9 µmol photons/m2/second. PAR reduced to an average value of 112.5 µmol photons/m2/second
under 52 cm of ice. Total water depth was 0.8m. At the surface sample point within the water column
water temperature was 0.05 ̊C with a pH of 7.01 and conductivity was 0.41 µS/cm. Dissolved oxygen
was 0.52 mg/l (Figure 1.). At the mouth of the bay ambient light PAR was 1286 µmol
photons/m2/second PAR decreased to an average value of 3.4 µmol photons/m2/second under 78.5 cm
of ice and snow. The second ambient light PAR reading was 1249 µmol photons/m2/second. PAR
reduced to an average value of 337 µmol photons/m2/second under 49 cm of ice. Total water depth
was 1.7m. At the surface sample point within the water column water temperature was 0.04 ̊C with a
pH of 7.04 and conductivity was 0.32 µS/cm. Dissolved oxygen was 8.49 mg/l. At the middle sample
point water temperature was 0.3 ̊C with a pH of 6.86 and conductivity was 0.33 µS/cm. Dissolved
oxygen was 7.10 mg/l. At the bottom sample point water temperature was 0.8 C
̊ with a pH of 6.45 and
conductivity was 0.34 µS/cm. Dissolved oxygen at the bottom of the bay was 5.93 mg/l.
Woodstock Bay
Throughout Woodstock Bay ice depth ranged from 58 cm -66 cm and snow cover ranged from
19 cm - 31 cm Total water depth ranged from 1.80-2.41m and water temperature varied between
0.05 ̊C -1.02 ̊C. At the head of the bay ambient light PAR was 733.1 µmol photons/m2/second PAR
decreased to an average value of 7.92 µmol photons/m2/second under 85 cm of ice and snow. The
second ambient light PAR reading was 691 µmol photons/m2/second. PAR reduced to an average value
of 64.47 µmol photons/m2/second under 60 cm of ice. Total water depth was 1.80 m At the surface
sample point within the water column water temperature was 0.08 ̊C with a pH of 7.56 and
conductivity was 0.32 µS/cm. Dissolved oxygen was 11.01 mg/l. At the middle sample point water
temperature was 0.31 ̊C with a pH of 7.41 and conductivity was 0.33 µS/cm. Dissolved oxygen was 9.98
mg/l. At the bottom sample point water temperature was 0.58 ̊C with a pH of 7.42 and conductivity
was 0.324 µS/cm. Dissolved oxygen at the bottom of the bay was 9.58 mg/l.At the midway point of the
bay ambient light PAR was 721.6 µmol photons/m2/second PAR decreased to an average value of 1.28
µmol photons/m2/second under 88.75 cm of ice and snow. The second ambient light PAR reading was
680.8 µmol photons/m2/second. PAR reduced to an average value of 49.77 µmol photons/m2/second
under 68 cm of ice. Total water depth was 2.41m. At the surface sample point within the water column
water temperature was 0.05 ̊C with a pH of 7.47 and conductivity was 0.32 µS/cm. Dissolved oxygen
was 10.47 mg/l. At the middle sample point water temperature was 0.28 ̊C with a pH of 7.43 and
conductivity was 0.32 µS/cm. Dissolved oxygen was 10.3 mg/l. At the bottom sample point water
temperature was 1.02 ̊C with a pH of 7.26 and conductivity was 0.40 µS/cm. Dissolved oxygen at the
bottom of the bay was 8.12 mg/l.At the mouth of the bay ambient light PAR was 605.5 µmol
photons/m2/second PAR decreased to an average value of 1.29 µmol photons/m2/second under 85.25
cm of ice and snow. The second ambient light PAR reading was 578.4 µmol photons/m2/second. PAR
reduced to an average value of 28.3 µmol photons/m2/second under 66 cm of ice. Total water depth
was 2.38m. At the surface sample point within the water column water temperature was 0.06 ̊C with a
pH of 7.54 and conductivity was 0.31 µS/cm. Dissolved oxygen was 10.23 mg/l. At the middle sample
point water temperature was 0.26 ̊C with a pH of 7.46 and conductivity was 0.32 µS/cm. Dissolved
oxygen was 9.77 mg/l. At the bottom sample point water temperature was 0.83 ̊C with a pH of 7.37
and conductivity was 0.35 µS/cm. Dissolved oxygen at the bottom of the bay was 8.97 mg/l. Within
Allouez bay one sample point was selected to represent the bay in this study. Ice thickness was 54 cm
and water depth was 1.55 meters to the top of the ice. Water temperature at the surface was 0.06 ̊C
and conductivity was 0.28 µS/cm. Dissolved oxygen was 7.7 mg/l and pH was 6.95. Water temperature
at the bottom was 0.10 ̊C and conductivity was 0.28 µS/cm. dissolved oxygen was 7.9 and pH was 6.97.
Pokegama River
In the Pokegama River ice thickness ranged from 63 cm - 78cm. Total water depth ranged from
1.04 - 2.36 meters and water temperature varied from 0.02 ̊C - 1.82 ̊C. At the Pokegama River
headwaters site (upstream from the highway 105 bridge) ambient light PAR was 559.1 µmol
photons/m2/second PAR decreased to an average value of 0.50 µmol photons/m2/second under 88 cm
of ice and snow. The second ambient light PAR reading was 745.2 µmol photons/m2/second. PAR
reduced to an average value of 2.36 µmol photons/m2/second under 78 cm of ice. Total water depth
was 1.04m .At the surface sample point within the water column water temperature was 0.8 ̊C with a
pH of 7.23 and conductivity was 1.1 µS/cm. Dissolved oxygen was 1.17 mg/l. Downstream from highway
105 bridge, total water depth was 1.15m At the surface sample point within the water column water
temperature was 0.33 ̊C with a pH of 6.96 and conductivity was 0.83 µS/cm Dissolved oxygen was 0.27
mg/l. At the bottom sample point water temperature was 0.34 ̊C with a pH of 6.54 and conductivity was
0.83 µS/cm. Dissolved oxygen at the bottom of the bay was 0.35 mg/l. At the sample site near the
weather station total water depth was 2.36m. At the surface sample point water temperature was
0.02 ̊C, pH was 7.09 and conductivity was 0.75 µS/cm. Dissolved oxygen under the ice was 1.34 mg/l. At
the midway sample point water temperature was 1.08 ̊C, pH was 7.03 and conductivity was 0.77
µS/cm. dissolved oxygen in the middle of the water column was 0.55 mg/l. At the bottom sample point
water temperature was 1.82 ̊C, pH 7.02 and conductivity was 0.77 µS/cm. Dissolved oxygen at the
bottom of the water column was 0.30 mg/l. At the sample site upstream from the MET station total
water depth was 1.57m. The surface water temperature was 0.19 ̊C, pH 7.15 and conductivity was 0.81
µS/cm. Dissolved oxygen just below the ice was 0.90 mg/l. The bottom water temperature was 0.41 ̊C,
pH 7.12 and conductivity was 0.81 µS/cm. Dissolved oxygen at the bottom was 0.50mg/l
Nemadji River
On the Nemadji River ice thickness ranged from 68-81cm. Water depth ranged from 2.60-3.10 m
and water temperature ranged from 0.02 - 0.70 ̊C. For the furthest upstream site water depth was 2.60
m. Water temperature at the surface was 0.13 ̊C, pH 7.70 and conductivity was 0.30 µS/cm. Dissolved
oxygen at the surface was 11.69 mg/l. At mid depth water temperature was 0.09 ̊C, pH 7.59 and
conductivity was 0.28 µS/cm. Dissolved oxygen at mid depth was 11.50 mg/l. At the bottom the water
temperature was 0.02 ̊C, pH 7.53 and conductivity was 0.29 µS/cm. Dissolved oxygen at the bottom
was 11.44 mg/l. At the midway sample site water depth was 2.69m. Water temperature at the surface
was 0.70 ̊C, pH 7.50 and conductivity was 0.291 µS/cm. Dissolved oxygen at the surface was 11.20 mg/l.
At the midway sample water temperature was 0.24 C
̊ , pH 7.41 and conductivity was 0.291 µS/cm.
Dissolved oxygen was 10.99 mg/l. At the bottom the water temperature was 0.62 ̊C, pH 7.36 and
conductivity 0.289 µS/cm. Dissolved oxygen was 10.83 mg/l. At the site closest to the mouth of the river
upstream from highway 53, water depth was 3.1 m. Water temperature at the surface was 0.31 ̊C, pH
7.61 and conductivity was 0.30 µS/cm. Dissolved oxygen was 11.08 mg/l. At the midway sample point
water temperature was 0.14 ̊C, pH 7.53 and conductivity was 0.30 µS/cm. Dissolved oxygen was 10.95
mg/l. At the bottom water temperature was 0.16 ̊C, pH 7.48 and conductivity was 0.30 µS/cm.
Dissolved oxygen was 10.86 mg/l.
St. Louis River
Throughout the St. Louis River ice thickness ranged from 49 cm to 61 cm. Water depth ranged
from 0.96 meters to 5.22 meters. At the Highway 23 Bridge sample point, representing the upper St.
Louis River ice thickness was 61 cm and water depth was 2.68 meters from the top of the ice. At the
surface water temperature was 0.09 and conductivity was 0.251 µS/cm. Dissolved oxygen was 12.9 mg/l
and pH was 7.78. At the midway sample point water temperature was 0.27 ̊C and conductivity was
0.257 µS/cm. Dissolved oxygen was 10.8 mg/l and pH was 7.64. Near the bottom water temperature
measured 4.74 ̊C and conductivity was 0.908 µS/cm. Dissolved oxygen was 4.0 mg/l and pH was
6.84.Near the boat launch in Oliver, Wisconsin ice thickness was 56 cm and water depth was 5.22
meters to the top of the ice. At the surface water temperature was 0.03 ̊C and conductivity was 0.254
µS/cm. Dissolved oxygen was 14.0 mg/l and pH was 7.86. At the Spirit Lake Marina in Duluth,
Minnesota, representing the midway sample site for the St. Louis River, ice thickness was 49 cm and
water depth was 0.96 meters to the top of the ice. At the surface water temperature was 0.02 and
conductivity was 0.275 µS/cm. Dissolved oxygen was 12.5 mg/l and pH was 7.65. Near the bottom water
temperature measured 0.03 ̊C and conductivity was 0.264 µS/cm. Dissolved oxygen was 12.5 mg/l and
pH was 7.68.Near the Arrowhead Pier ice thickness was 54 cm and water depth was 1.21 meters to the
top of the ice. At the surface water temperature was 0.08and conductivity was 0.275 µS/cm. Dissolved
oxygen was 12.3 mg/l and pH was 7.61. Near the bottom water temperature measured 0.07 ̊C and
conductivity was 0.274 µS/cm. Dissolved oxygen was 12.3 mg/l and pH was 7.59.Within the Superior
Bay, representing the mouth of the St. Louis River, ice thickness was 49 cm and water depth was 3.67
meters to the top of the ice. At the surface water temperature was 0.09 and conductivity was 0.21
µS/cm. Dissolved oxygen was 11.8 mg/l and pH was 7.39. At the midway sample point water
temperature was 0.23 ̊C and conductivity was 0.227 µS/cm. Dissolved oxygen was 11.8 mg/l and pH
was 7.46. Near the bottom water temperature measured 0.17 ̊C and conductivity was 0.228 µS/cm.
Dissolved oxygen was 11.8 mg/l and pH was 7.40.
Barkers Island
At Barker’s Beach on Barker’s Island between the dock at LSNERR and the north end of the
"pickle pond" ambient light PAR was 1459 µmol photons/m2/second PAR decreased to an average value
of 4.98 µmol photons/m2/second under 65.25 cm of ice and snow. The second ambient light PAR
reading was 464 µmol photons/m2/second. PAR reduced to an average value of 49.05 µmol
photons/m2/second under 49 cm of ice. Ice thickness was 49 cm and water depth was 1.25 meters from
the top of the ice. At the surface water temperature was 0.08 ̊C and conductivity was 0.359. Dissolved
oxygen was 11.17 mg/l and pH was 7.58. At the midway sample point water temperature was 0.06 ̊C
and conductivity was 0.359 µS/cm. Dissolved oxygen was 10.89 mg/l and pH was 7.41. Near the bottom
water temperature measured 0.23 ̊C and conductivity was 0.375 µS/cm. Dissolved oxygen was 10.72
mg/l and pH was 7.44.At Barker’s Island between the marina and the south east end of the “pickle
pond” ambient light PAR was 1244 µmol photons/m2/second PAR decreased to an average value of 7.78
µmol photons/m2/second under 72 cm of ice and snow. The second ambient light PAR reading was not
recorded. Ice thickness was 61 cm and water depth was 2.42 meters from the top of the ice. At the
surface water temperature was 0.14 ̊C and conductivity was 0.231 µS/cm. Dissolved oxygen was 11.26
mg/l and pH was 7.66. At the midway sample point water temperature was 0.19 ̊C and conductivity
was 0.237 µS/cm. Dissolved oxygen was 11.05 mg/l and pH was 7.40. Near the bottom water
temperature was 0.36 ̊C and conductivity was 0.257 µS/cm. Dissolved was 10.45 mg/l and pH 7.2.
Table 2. All water quality parameter and physical characteristics for half of the sites within the SLRE.
Table 3. All water quality parameters and physical characteristics for the remaining sample sites with the SLRE.
Table 4. Photosynthetic Active Radiation (PAR) data indicated that 99 % of ambient light was depleted when measured under snow and ice.
Minimizing photosynthesis as a source for dissolved oxygen during the winter.
Figure 1. Levels of dissolved oxygen throughout the water column for all sample positions within clay
influence bays. The red line indicates threshold for dissolved oxygen which is 5 mg/l. Concentrations
below the threshold will be stressful to fish and an absence from the sampled location is expected
(Rottman 1992).
Correlation Between Bottom Dissolved Oxygen
and the Distance From Lake Superior
Dissolved Oxygen (mg/l)
14.00
12.00
R² = 0.3431
10.00
8.00
6.00
4.00
2.00
0.00
0
5
10
15
20
25
30
Distance from Lake Superior (km)
Figure 2. Evidence suggesting that the seiche effect from Lake Superior potentially replenishes bays and
rivers with oxygenated water. R-squared values reflect the correlation between levels of dissolved
oxygen at the bottom depths, relative to the distance from Lake Superior (Duluth Entry).
Correlation between Surface Dissolved Oxygen
and the Distance From Lake Superior
14.00
Dissolved Oxygen (mg/l)
12.00
10.00
R² = 0.1464
8.00
6.00
4.00
2.00
0.00
0
5
10
15
20
25
30
Distance from Lake Superior (km)
Figure 3. Evidence suggesting that the seiche effect from Lake Superior potentially replenishes bays and
rivers with oxygenated water. R-squared values reflect the correlation between levels of dissolved
oxygen at the surface (under ice), relative to the distance from Lake Superior (Duluth Entry).
Discussion
Throughout the St. Louis River itself, ice and snow cover reduced the amount of photosynthetic
active radiation (PAR) over ninety percent at all sites. The effect of ice cover alone was enough to reduce
PAR to levels between 70 -90 percent which are not expected to maintain photosynthesis. We believe
that early ice cover, during late October and November would not degrade PAR levels as much, allowing
photosynthesis to be a source of dissolved oxygen within the bays.
Levels of dissolved oxygen were suitable for the presence of fish except for the sample site at the
Highway 23 Bridge. At this site, the bottom water temperature increased from 0.27 ̊C to 4.74 ̊C and
conductivity increased from 0.257 µS/cm to 0.908 µS/cm. Dissolved oxygen decreased from 10.8 mg/l to
4.0 mg/l (below the threshold) and pH dropped from 7.64 to 6.84. This variation in the water quality
parameters strongly suggests and influence from ground water upwelling. Our findings also suggest that
there is a slight correlation expressing an increase in levels of dissolved oxygen as sample sites of the St.
Louis River approach Lake Superior (at harbor entries). There is a stronger relationship between bottom
DO levels and distance from Lake Superior (R^2= 0.3431) than surface levels of dissolved oxygen
(R^2=0.1464).
Within the Pokegama Bay system, including the tributary bay and the Pokegama River, water
quality parameters indicated multiple areas in which water quality was not suitable for the presence of
fish based on dissolved oxygen concentrations. At the head of the Pokegama tributary, dissolved oxygen
dropped below the 5 mg/l threshold near the bottom. No other parameters showed signs of
groundwater upwelling. At the mid bay site in the Pokegama tributary water temperature at the midcolumn sample point was 1.37 ̊C and 1.93 ̊C at the bottom sample point which is relatively high
compared to the rest of the tributary. Midway and bottom levels also indicated levels of DO below the 5
mg/l threshold. At the midway sample point, dissolved oxygen was 3.08 mg/l and 1.39 mg/l at the
bottom. Because there is no sign of an increase in conductivity it is not clear whether or not there was
ground water influence at this site. At the mouth of the Pokegama Tributary water temperature near
the bottom increased from 0.76 ̊C -1.11 ̊C and dissolved oxygen levels decreased from 6.17 mg/l to
4.28 mg/l. Based on a small change in temperature and consistent levels for conductivity we do not
believe there is ground water upwelling occurring at this site and more strongly suggest that
decomposition is the cause for dissolved oxygen levels below the threshold. At the mid bay sample point
of Pokegama Bay, the surface water temperature was 0.05 and the reading for dissolved oxygen was
0.52 mg/l. This is the lowest value for dissolved oxygen found throughout this study and could be the
results of multiple influences. We suggest that low levels of dissolved oxygen are a result of the water
depth only being 28 cm. Also, this site is located close to the mouth of the Pokegama River, which has
been found to have low levels of dissolved oxygen in the winter. At the mouth of Pokegama Bay
dissolved oxygen levels were suitable for the presence of fish.
Throughout Kelly Bay levels of dissolved oxygen and water temperatures were ordinary except
for the mid bay sample point .Water temperature increased from 0.020 ̊C to 1.66 ̊C and dissolved
oxygen dropped from 8.70 mg/l to 4.52 mg/l. Although conductivity did not increase as expected for
upwelling there is reason to suspect ground water upwelling at this site based on water temperature
and dissolved oxygen. Throughout Kimball bay, levels of dissolved oxygen were suitable for the presence
of fish. At the mid bay sample point the first occasion where dissolved oxygen is higher near the bottom
than the surface was recorded. The surface reading was 7.52 mg/l and bottom reading was 11.49 mg/l.
Also temperature dropped from 0.84 ̊C at surface to 0.56 ̊C at the bottom. Reasoning for this occurrence
is not understood and further investigation is needed.
Throughout Kilner Bay, all levels of dissolved oxygen were suitable for the presence of fish. At
the mid bay sample site levels of dissolved oxygen were above the threshold but there was an increase
in water temperature at the bottom, increasing from 0.49 ̊C to 1.33 ̊C without an increase in
conductivity. Dissolved oxygen did decrease from 8.97 mg/l to 6.45 mg/l but stayed above the
threshold. This also occurred at the mouth of the bay. Water temperature increased from 0.54 ̊C to
1.33 ̊C, without an increase in conductivity. Levels of dissolved oxygen did decrease from 8.28 mg/l to
6.44 mg/l but stayed above the threshold.
Conclusion
We conclude there were multiple areas within the Pokegama Bay and river system that
expressed zones of stressful levels of DO (< 5mg/l). These areas included the main bay, tributary bay and
the Pokegama River channel. Although the presence of certain fish species (Table 1.) is not expected in
these stressful zones, we cannot confirm certainty of absence due to a variation in tolerance levels, also
because fish surveys were not conducted. We suspect that the Pokegama River contributes to the low
levels of dissolved oxygen within Pokegama Bay. Also, the land mass located at the mouth of Pokegama
bay was assumed to be a major factor contributing to DO deficiency. By restricting influential mixing
with the St. Louis River, this land mass could be the cause of higher turbidity and lower levels of
dissolved oxygen within the bay (Figure B). We did discover a correlation between bottom and surface
levels of dissolved oxygen within the St. Louis River and the distance from Lake Superior. Data pertaining
to this same correlation between the Nemadji River and Lake Superior were not provided due to
insufficient data collection. The extent of the seiche effect from Lake Superior during the winter has not
yet been understood but future studies on this issue are important in order to determine the source and
the distribution patterns of dissolved oxygen within the St. Louis River Estuary during the winter
months.
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