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 iii

2. Specific conductance and alkalinity for selected sites in Voyageur

3 Vertical profiles for Namakan Lake and Sand Point Lake, July 199

4. Nutrient concentrations for selected sites in Voyageurs National P

5 Trophic-state indices for selected sites in Voyageurs National Park 

7DEOHV

1. Sampling sites in Voyageurs National Park, July 1999 .......................................

2. Physical properties and chemical constituents determined for water samples col

3. Results of analyses for quality-assurance replicate samples collected in Rainy L

Minnesota, site 16, in Voyageurs National Park, Northern Minnesota ..............

&RQYHUVLRQ)DFWRUV

Multiply inch-pound unit By 

foot (ft) 0.3048 

acre-foot (acre-ft) 0.001 
 iv
1

Voyageurs National Park in northern Minnesota (fig. 1) was established 

in 1975 to preserve, and provide for 

the public’s enjoyment, scenic and 

natural resources along a historic 

waterway. Lakes and waterways, 

which compose a major portion of the 

Park, provide recreational use, and 

aquatic systems provide support for 

much of the Park’s fauna. Water quality is an essential element of the Park 

environment because of its importance to ecosystems and visitor enjoyment.

 A water-quality study was undertaken by the U.S. Geological Survey 

in cooperation with the National Park 

Service. A study, conducted from 

1977 through 1984, collected waterquality data in the newly established 

Park and provided a basis for evaluating changes in water quality that may 

occur with time (Payne, 1991). Water 

quality can change over time; thus, 

periodic determinations of water quality are needed to assess current conditions and to detect temporal changes. 

During 1999, a subset of sampling 

sites used during the 1977–84 study 

ity in the Park.

3XUSRVHDQG6FRSH

The purpose of this report is 

present the results of water-qual

sampling and analyses done dur

1999 and compare those results 

data collected from the 1977–84 

study. The 1999 data collection 

included physical properties, sel

trace elements, bacteria, and trop

state indicators at seven samplin

sites located in five selected lake

bays, and at the mouths of two r

that flow into the Park.

$SSURDFKDQG0HWKRG

The 1977–84 study characte

water quality on the basis of sam

collected at 41 sites located in th

Park’s lakes, bays, and streams. 

pling in the Park’s large lakes an

bays was done during 1977–83, 

whereas sampling during 1984 

focussed only on smaller lakes i

Park’s interior. A subset of seven 

was selected from the original 41 

for sampling during the 1999 stu

(table 1). Five of the selected sit

were chosen to represent water q
2

R 23 W R 22 W R 21 W R 20 W R 19 W 

MINNESOTA

KOOCHICHI

ST. LOUIS 

Ash 

0 

0 10 KILOMETERS

EXPLANATION

Voyageurs National Par

Sampling site and numb

Streamflow-gaging stat

12

Figure 1. Location of Voyageurs National Park and wa

River

Minnesota River

Lake Superior

94°

92°

90°

96°

48°

46°

44°

0 50 100 MILES

0 50 100 KILOMETERS

Location Map

Study Area

Mississippi

Voyageurs

National Park Lac la

Croix

Site

MINNESOTA
3

Air pressure mm Hg 

Water temperature °C 

Transparency, Secchi disk feet 

Specific conductance, field uS/cm @ 25 

Specific conductance, laboratory uS/cm @ 25 

Field pH standard uni

Laboratory pH standard uni

Dissolved oxygen mg/L 

Fecal coliform bacteria, membrane filter col/100 mL 

Total alkalinity, as CaCO3 mg/L 

Dissolved nitrite nitrogen mg/L 

Dissolved nitrite plus nitrate nitrogen mg/L 

Dissolved ammonia nitrogen mg/L 

Dissolved ammonia plus organic nitrogen mg/L 

Total ammonia plus organic nitrogen mg/L 

Total phosphorus mg/L 

Dissolved phosphorus mg/L 

Dissolved orthophosphorus mg/L 

Total arsenic μg/L 

Total barium ug/l 

Total cadmium μg/L 

Total chromium μg/L 

Total copper μg/L 

Total lead μg/L 

Total nickel μg/L 

Total selenium μg/L 

Total silver μg/L 

Total zinc μg/L 

Chlorophyll a μg/L 

Chlorophyll b μg/L 
4

evidence of sample contamination. 

All trace-metal concentrations were 

less than the method reporting limit 

(MRL) for each constituent. Nutrient 

concentrations were greater than or 

during 1999 was compared with 

that were collected during 1977–

(Payne, 1991). Most of the samp

during the previous study were c

lected during May and August, b

Table 3. Results of analyses for quality-assurance replicate samples collected in 

Minnesota, site 16, in Voyageurs National P

 [mg/L, milligrams per liter; μg/L, micrograms/L; μS/cm, micr

Dissolved nitrite 

nitrogen

 (mg/L)

Dissolved 

nitrite plus 

nitrate 

nitrogen 

(mg/L)

Dissolved 

ammonia 

nitrogen 

(mg/L)

Dissolved 

ammonia plus 

organic 

nitrogen

 (mg/L)

To

p

Sample 1 0.001 <0.005 0.003 0.308 0.4

Sample 2 0.001 <0.005 0.005 0.398 0.4

Dissolved 

orthophosphorus

(mg/L)

Total arsenic 

(μg/L)

Total barium 

(μg/L)

Total 

cadmium

 (μg/L)

Sample 1 0.003 <1 11.898 <1 <1 

Sample 2 0.003 <1 12.111 <1 <1 

Total nickel

(mg/L)

Total 

selenium 

(mg/L)

Total silver

(mg/L)

Total zinc

(mg/L)

C

Sample 1 <1 <1 <1 <40 1.

Sample 2 <1 <1 <1 <40 2.4 
5

0

10

20

30

40

50

60

80

90

70

ALKALINITY, TOTAL AS CALCIUM CARBO

IN MILLIGRAMS PER LITER

SPECIFIC CONDUCTANCE, IN MICROSEIM

CENTIMETERS AT 25 DEGREES CELS

175

150

125

100

75

50

25

0

BLACK

BAY

KABETOGAMA

LAKE

NAMAKAN

LAKE

RAINY

LAKE

SAND POINT

LAKE

SULLIVAN

BAY

Figure 2. Specific conductance and alkalinity for selected sites in Voyag

Outlier

Nearest value within

1.5 interquartile range

Interqu

75th Percentile

Median

25th Percentile

1999 Value

EXPLANATION
6

DEPTH, 

90

80

70

60

50

50

60

70

80

90

DEPTH, 

DEPTH, IN FEET

DEPTH, IN FEET

0 0

10 10

20 20

30 30

40 40

50 50

60 60

70 70

80 80

90 90

Figure 3. Vertical profiles for Namakan Lake (Site 14) and Sand 

5 10 15 20 25 30

Sand Point Lake Sand Point Lake

Namakan Namakan Lake

Namakan Lake Namakan Lake

40 

5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.2 

WATER TEMPERATURE, IN DEGREES CELSIUS 

DISSOLVED-OXYGEN, IN MILLIGRAMS PER LITER 
7

gg y 

1999 were less than the method 

reporting limit (0.005 mg/L) in samples from Black Bay, Kabetogama 

Lake, Sand Point Lake, and Sullivan 

Bay (fig. 4). Nitrite plus nitrate concentrations also were low in samples 

from Rainy Lake (0.017 mg/L) and 

Namakan Lake (0.012 mg/L). Nitrite 

plus nitrate nitrogen concentrations 

were less than the 25th percentile for 

1977–83 data for all sites except Sullivan Bay (fig. 4). In hypolimnetic 

waters (Namakan Lake and Sand 

Point Lake, nitrite plus nitrate nitrogen concentrations were greater relative to epilimnetic waters. The nitrite 

plus nitrate nitrogen concentration 

(0.021mg/L) in the July 1999 sample 

from Namakan Lake at mouth of 

Namakan River was greater than concentrations at the other sites, but was 

less than concentrations measured at 

the same site during May 1982 (0.05 

mg/L) and August 1982 (0.13 mg/L). 

The low nitrite plus nitrate concentrations in epilimnetic water relative to 

hypolimnetic water and inflowing 

water from the Namakan River probably reflect phytoplankton utilization 

of nitrate. Nitrite concentrations in all 

pq

range of 1977–83 concentrations 

sites except Black Bay where the 

1999 concentration was less than 

25th percentile (fig. 4).Total nitr

concentrations are summations o

concentrations of dissolved nitri

plus nitrate nitrogen and total am

nia plus organic nitrogen. These 

culated total nitrogen concentrat

for both the 1977–83 and 1999 d

sets are shown in figure 4. Total 

gen concentrations in 1999 were 

than median values for 1977–83 

the major water bodies except S

van Bay. The most substantial d

ence between the 1977–83 value

1999 values occurred in Black B

Total-phosphorus concentra

in Kabetogama Lake, Sullivan B

and Black Bay during 1977–83 

greater in May than in August 

(Payne,1991). Because of this se

sonal variability, it was deemed 

appropriate to compare the July 

results with results from August 

1977–83 (fig. 4). The largest dif

ences are seen in Black Bay and 

Kabetogama Lake where 1999 c

centrations are substantially low

than median values for 1977–83
8

BLACK

BAY

KABETOGAMA

LAKE

NAMAKAN

LAKE

RAINY

LAKE

SAND POINT

LAKE

SULLIVAN

BAY

Figure 4. Nutrient concentrations for selected sites in Voyageurs N

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

TOTAL PHOSPHORUS, IN MILLIGRAM

2.0

1.5

1.0

0.5

0

TOTAL NITROGEN, IN MILLIGRAMS 

Outlier

Nearest value within

1.5 interquartile range

Interqu

75th Percentile

Median

25th Percentile

1999 Value

EXPLANATION
9

Black Bay (U.S. Geological Survey, 

1981).

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6WUDWLILFDWLRQ

Well developed thermal stratification, as evidenced by a thermocline, 

was present in Namakan Lake and 

Sand Point Lake. The temperature 

profiles for these sites (fig. 3) show 

distinct thermal zones. While both 

sites have similar thermal stratification, only Sand Point Lake shows 

warmer, higher-conductance water 

overlying cooler, lower-conductance 

water (fig. 3). The dissolved-oxygen 

profiles (fig. 3) for these sites show a 

distinct pattern, common to both sites, 

whereby dissolved-oxygen concentrations decrease to a minimum near the 

upper boundary of the thermocline 

and then increase with depth near the 

lower boundary of the thermocline. 

The vertical distribution of pH values, 

in contrast, shows a gradual decline 

with depth that steepens slightly at the 

top of the thermocline (fig. 3). 

Thermal profiles determined during July 1999 in Namakan Lake and 

Sand Point Lake were similar to pro

pp

concentrations may be preferabl

TSI values computed from total 

phorus concentrations (TSI TP) 

because data from lakes in Voya

National Park at times exhibit a 

fit to Carlson’s regression that re

chlorophyll a to total phosphoru

Indices computed from Secchi-d

transparency (TSI SD), while re

sive to algal biomass, also are aff

by soluble organic substances th

color some of the Park’s water b

TSI were computed from ch

phyll a data collected during Jul

1999 and compared to indices co

puted from summer (August) da

lected during 1977–83. Results a

shown in figure 5. Examining T

values based on chlorophyll a (T

CHL), the greatest differences 

between 1977–83 and 1999 are 

Sullivan Bay, Kabetogama Lake

Black Bay. The 1999 TSI CHL v

for these water bodies, which ar

more than 20 scale units less tha

median values for 1977–83, indi

decreased biomass. Chlorophyll 

concentrations in these water bo

during 1999 were 10–13 percent 

median values for the 1977–83 s
10

SECCHI-DISK TRANSPARE

16

14

12

10

8

6

35

40

45

50

55

60

TROPHIC-STATE INDEX, BASED 

TRANSPARENC

TROPHIC-STATE INDEX, BASED ON TOTAL PHOSPHORUS

75

70

65

60

55

50

45

40

35

30

BLACK

BAY

KABETOGAMA

LAKE

NAMAKAN

LAKE

RAINY

LAKE

SAND POINT

LAKE

SULLIVAN

BAY

Figure 5. Trophic-state indices for selected sites in Voyageurs National Park f

Outlier

Nearest value within

1.5 interquartile range

Interquartile range

75th Percentile

Median

25th Percentile

1999 Value

EXPLANATION
11

cific conductance, an increase, was seen in the epilimnetic 

waters in Sand Point Lake, which may have been influenced by above normal inflow from the Vermilion River 

during the summer of 1999. The most change in alkalinity, 

a decrease, was seen in Black Bay and Kabetogama Lake. 

Lower alkalinity in Black Bay may reflect above normal 

inflow from Kabetogama Lake. Alkalinity in Kabetogama 

Lake may reflect inflow of relatively low alkalinity water 

from Namakan Lake.

Nutrient concentrations showed a decrease in nitrite 

plus nitrate nitrogen concentrations at all sampling sites 

and a decrease in total phosphorus concentrations in Black 

Bay and Kabetogama Lake relative to the 1977–83 period.

Trace metals were detected less frequently in samples 

collected during 1999 compared to the 1977–83 period. 

Chromium, lead, selenium, and zinc, which were detected 

in some samples during 1977–83, were all reported at less 

than the method reporting limit in samples collected during 

1999. Arsenic was detected at three sites. Barium and copper were detected in all samples collected during 1999. 

position and 

lakes were s

the presence 

of Sand Poi

hypolimnio

Trophic 

rophyll a m

median 197

largest chan

Kabetogam

concentratio

mined durin

phosphorus 

indicated a 

Kabetogam

than the cha

concentratio

phosphorus 

of algal pro

limiting trop
12