9S

6507

600-4

y oe S a
° gs ° °
° 3° °
I rt nt

GROSS PRIMARY PRODUCTIVITY (mg CARBON FIXED/m3/hr)
3
.

FIGURE 21, AVERAGE GROSS PRIMARY PRODUCTION IN THE LIMNETIC PHOTIC ZONE (STATION 4)



Coleosphaerium, still another blue-green, at 8m, Generic variation
within a major group also occurred in different littoral and limnetic
regions,

Quantitative Features

Concentration in samples from the limnetic zome varied from more
than 55,000,000 to 12,000 units per 1. Seasonal influences, insofar as
these may be determined from only 3 years records, appear to result in
spring, summer, and autumn maxima, with winter, late spring, and late
summer minima. Diatoms have been largely responsible for the spring
and fall elevations and blue-greens for the major summer growth, but
diatoms replaced blue-greens in summer of 1969 following an application
of algicide. Green algae exhibited about 5 peaks per year, three in
summer and one each in spring and winter, They achieved dominance only
in winter, but they were more numerous than diatoms during summer, except
in 1969, The greatest concentration observed, 55,114,200 units per
liter occurred at 6 m in the limnetic zone during a spring diatom
maximum, and diatoms comprised 99.7% of the total population. Diatms
were also dominant in surface and near surface waters, but their con-
céntrations were somewhat less, being 50,657,500 per 1 at the surface
and 42,802,600 at 2m. Greater concentration at 6 m may have been due
to settling. The highest observed summer concentration when blue-
greens were dominant was slightly more than 6,000,000 per 1. Phyto-
plankters were several times as concentrated in spring of 1971 than
during either preceeding year, but summer densities were comparable
to those of 1969 and 1970 (Figures 16, 17, and 18).

Lake Sallie, although with a long history of cultural eutro-
phication, was not dominated by blue-green phytoplankton except on a
seasonal basis, and this seasonal dominance did not appear very firm,
but rather finely balanced against incursion by diatoms. Green aglae,
even when dominant, never attained numbers near those reached by
diatoms and blue-greens at their peaks.

Attached Vegetation

Chara sp. grew on the bottom and Cladophora sp. and Gleotrichia
natans (Hed.) Rab, were attached to aquatic flowering plants, Star
duckweed (Lemna Trisulca L.) grew both free floating and attached to
other vegetation, but other duckweeds (Lemna minor L., Spirodela
Polyrhiza (L.) Schleid., and Wolffia columbiana Karst.) were all surface
floaters, Macrophytes observed were;

Najas flexilis (Willd.) Rostk. & Schmidt
Potamogeton amplifolius Tuckerm,

P. crispus L.

P. filiformis var. Macounii Marong.
pectinatus L.

P. praelongus Wulf.

20


RESEARCH REPORTING SERIES

Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:

1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research

4. Environmental Monitoring

5. Socioeconomic Environmental Studies

This report has been assigned to the ECOLOGICAL
RESEARCH series. This series describes research
on the effects of pollution on humans, plant and
animal species, and materials. Problems are
assessed for their long- and short-term
influences. Investigations include formaticn,
transport, and pathway studies to determine the
fate of pollutants and their effects. This work
provides the technical basis for setting standards
to minimize undesirable changes in living
organisms in the aquatic, terrestrial and
atmospheric environments.

For sale by the Superintendent of Documents, U.S, Government Printing Office, Washington, D.C. 20402 - Price $1.25


TABLE 2--Continued

Ortho Total Temp.
Mg++ O% POg PO4 NH3-N NO2-N NO3-N °c
107.8 8.62 0.18 0.76 0.09 0.006 0.020 9.0
107.8 8.62 0.25 1.28 0.10 0.004 0.008 9.0
107.8 8.53 0.25 0.76 0.10 0.006 0,009 9.0
107.8 8.53 0.12 1.00 0.40 0.004 0.013 9.0
117.6 8.82 0.25 1.00 0.11 0.006 0.011 9.0
117.6 10.00 0.12 0.62 0.15 0.008 0.007 9.0
127.4 9.90 0.18 1.14 0.15 0.008 0.009 9.0
127.4 9.90 0.12 0.76 0.12 0.006 0.009 9.0
127.4 9.11 0.12 0.76 0.10 0,006 0.011 9.0
127.4 12.40 0.12 0.76 0.92 0.010 0.007 5.5
117.6 12.40 0.25 0.76 0.97 0.008 0.009 5.5
117.6 12.30 0.12 0.50 0.92 0.008 0.004 5.5
117.6 12.20 0.12 0.50 0.79 0.010 0.005 5.5
127.4 13,20 0) 0.50 0.48 0.012 to) 3.5
127.4 13.20 0.11 0.36 0.38 0.010 0.007 3.5
127.4 13.20 0.1L 0.36 0.37 0.008 0.004 3.5
137.2 16.07 ie) 0.24 0.25 0.008 0.010 io)
127.4 14.31 0 0.12 0.49 0.006 0.006 1.0
127.4 14,31 0) 0.12 0.12 0.008 0.010 1.0
127.4 13.56 0) 0.24 0.20 0.006 0.009 1.0
127.4 9.99 ) 0.24 0.49 0.006 0.011 2.0
147.0 6.47 0.06 0.50 0.38 0.015 0.020 2.5
137.2 15.48 0.05 0.10 0.27 0.008 0.004 1.0
137.2 14,99 ) 0.24 0.25 0.004 0.004 2.0
127.4 6.66 ) 0.24 0.32 0.006 0.009 3.0
127.4 15.20 0.18 0.24 0.23 0.006 0.011 1.0
127.4 15.10 0.05 0.24 0.18 0.008 0.009 2.0
127.4 13.10 0 0.24 0.20 0.008 0.009 2.0

63


9L

TABLE 4

ACID-SOLUBLE PHOSPHORUS (AS PO,-P) OF AIR DRIED SEDIMENTS
FROM LAKE SALLIE, MINNESOTA, EXPRESSED AS
GRAMS PER KILOGRAM OF SEDIMENTS

Station
1 3 4 6 7 8 9 12 21
Depth (m)

0.5 9.0 16.5 7.5 1.0 0.5 0.5 0.3 0.3
7 November 1970 0.37 1.30 1.24 - 0.51 0.29 0.28 0.31 0.33
19 December 1970 - - 1,22 - - 0.24 0.23 0.42 0.41
18 March 1971 0.50 - - - - 0.34 - 0.27 0.39
8 May 1971 0.14 - 1.63 1.57 - 0.15 0.30 0.38 0.31
25 June 1971 0.45 1.47 - 1.23 0.30 0.16 0.29 0.26 0.16
21 July 1971 1.33 1.28 1.75 1.16 0.35 1.57 0.42 0.29 0.21
30 October 1971 0.19 - 0.83 - - 0.24 0.30 0.18 0.33
10 December 1971 - - - - - 0.19 0.26 0.30 0.52
31 December 1971 - ~ 1.18 - - - - -



DISCUSSION
Climatological Features

Climate during the period of this study differed somewhat from
norms established over 1946-60. Average January and July temperatures
were slightly lower than these norms, Total annual precipitation was
below normal in 1969 and '70 but above it in 1971. Months with great-
est precipitation were July 1969, June 1970, and September 1971 (Table
1).

Physical Features
ice Cover

Ice cover endured from around mid November until Mid April each
winter. Ice became covered with snow that varied from 40 (1968-69)
to 12 (1969-70) to 5 inches (1970-71). There was some drifting during
the last winter giving 24.5 cm (10 inches) of snow in some areas.
Heavy snowfall occuring during early freezing in 1968 reduced ice thick-
ness to as little as 15,24 cm (6 inches) on central lake areas, and
produced an opaque spongy ice except near shore, Ice formed during
subsequent winters was clear and firm and varied from 61-91 cm (24 to
36 inches) in thickness, Noticeable surface flooding of ice occured
in March 1971,

Temperature

Water temperature responded rather quickly to seasonal air temp-
erature change, and there were generally distinct differences between
temperatures of surface and deeper waters in summer and winter (Figures
7 and 8). Thermal stratification (summer stagnation) endured continually
from mid July until September 1969, when the thermocline varied from 5
to 8m in depth. In 1970 a thermocline that became established June 6
disappeared 20 days later and did not recur, In 1971 a thermocline was
present in early May, again on June 3, to June 10, then again from June
15 until July 21, and finally from August 12 to August 20. Its position
and thickness during these periods appear in Figure 9, Winter stagna-
tion was well developed each year (Figures 7 and 8).

Light and Light Transmission

Solar energy was recorded, with a few interruptions, from June 8

to December 23, 1971. Mean daily values in langleys were: June, 477;
July, 559; August, 502; September, 348; October 187; November 132; and
December, 103. The maximum daily value, 708 langleys, occurred July 5,
and the minimum, 42 langleys, December 1, Surface light intensity
(total) varied from 402 to 7,153 foot candles at times of light penetra-
tion measurements. Total light intensities (as % of surface irradiation)
at depths of 1 and 3 m varied during open water seasons over the 3 year

10


TABLE 2--Continued

Ortho Total Temp.
Mg++ Oo PO4 PO4 NH3-N NO-N NO3-N °c
112.7 0.20 o.1l 0.50 1.00 0.006 ie} 20.0
107.8 7.33 ie} 0.36 0.31 ie} 0.007 18.0
107.8 7.33 0 0.50 0.33 0.001 0.003 18.0
107.8 7.23 ie) 0.50 0.33 ie} 0.004 18.0
107.8 7.13 ie} 0.50 0.31 0.001 0.005 18.0
112.7 7.13 ie} 0.50 0.31 0.001 0.005 18.0
107.8 8.90 ie} 0.50 0.15 ie) 0.012 20.5
107.8 8.80 ie} 0.36 0.25 ie} 0.21 20.5
107.8 8.80 i} 0.50 0.22 ie} 0.017 20.5
117.6 3.30 0.05 0.50 0.56 0.004 0.024 19.0
117.6 0.20 0.52 0.64 0.95 0.004 0.015 18.0
112.7 6.60 0.11 0.50 0.54 0.004 0.017 20.0
117.6 6.40 0.11 0.50 0.54 0.002 0.015 20.0
112.6 ie} 0.60 0.92 1.69 ie) 0.012 19.0
112.7 8.12 0.25 0.92 0.32 0.002 0.019 21.0
117.6 7.92 0.05 0.64 0.33 0.004 0.017 21.0
117.6 7.72 0.25 0.92 0.38 ie} 0.021 21.0
117.6 6.14 0.14 0.64 0.45 0.003 0.025 20.0
122.5 2.48 0.32 0.64 0.94 0,003 0.018 20.0
117.6 6.70 ie} 0.59 0.42 0.005 0.005 19.0
117.6 6.60 0.19 0.64 0.43 0.004 0.006 19.0
112.7 3.70 0.26 0.52 0.67 0.006 0.011 19.0
127.4 7.80 0.12 0.64 0.26 0.004 0.011 17.0
117.6 7.70 0.12 0.78 0.39 0.004 0.008 17.0
117.6 6.00 0.25 0.92 0.50 0.004 0.008 17.0
112.7 10.60 0.09 0.64 0.01 0.002 0.017 15.0
112.7 10.00 0.09 0.64 0.01 0.002 0.013 14.5
112.7 6.80 0.09 0.64 0.01 0.002 0.019 14.0
117.6 7.10 0.12 0.92 0.01 0.004 0.020 14.0
107.8 9.50 0.05 0.64 0.18 0.005 0.020 17.0
107.8 5.60 0.05 0.78 0.35 0.004 0.026 15.0
107.8 2.70 0.36 0.64 0.47 0.004 0.033 14.0
112.7 9.29 0.12 0.64 0.23 0.005 0.012 12.0
112.7 9.29 0.12 0.64 0.25 0.004 0.013 12.0
112.7 9.09 0.12 0.64 0.25 0.004 0.013 12.0
107.8 8.99 19) 0.52 0.19 0.004 0.013 12.0
117.6 11.40 0.12 0.28 0.13 0.004 0.013 10.0
117.6 10.30 0.05 0.50 0.13 0.002 0.015 10.0

69


ACKNOWLEDGEMENTS

Several persons and agencies gave invaluable assistance and
encouragement to this project. The Minnesota Department of Conser-
vation provided laboratory and dock facilities and winter transpor-
tation at the Lake Sallie Fishery Station, and gave advice on many
matters from overall planning to equipment problems. Indebtedness
is expressed to Dr. John B. Moyle, Director of Research, St. Paul,
and to the following Lake Sallie personnel: William Joy, Manfred

Branby, Donald Olson, Walter Wiese, Coleman Nordhausen, and James
Hunnel.

The Pelican River Watershed District and the City of Detroit
Lakes were very helpful in furnishing background information and the
assistance of some key personnel. Special recognition is due
Winston C. Larson, of Winston C. Larson and Associates, Consulting
Municipal Engineers, and Dr. T. A, Rogstad, Chairman, Pelican River
Watershed District, who have for years endeavored to resolve the
Lake Sallie problem and are still attacking it with undiminished
enthusiasm, for encouragement and much timely assistance.

Discharges were provided by the U.S. Geological Survev, St. Paul,
Minnesota. Charles R. Collier, District Chief, William B. Mann IV,
and Thomas Winter of that office also furnished information on ground
water and water budgets.

Donald W. Shultz, Chemist, Pacific Northwest Water Laboratory,
EPA, supervised chemical analyses of weed, fish, and sediment
samples.

Close estimates of weeds were greatly aided by the excellent
cooperation of Carl Aarness, harvester operator.

The project was supported by a grant (16010 DFI) from the Environ-
mental Protection Agency and very fine assistance was furnished by

Drs. Kenneth Malueg and Charles F., Powers, Project Officers.

The deepest appreciation is expressed to all the above individuals
and organizations, none of whom gave sparingly.

27


FROM FOX
AKE

FIGURE 4, LAKE SALLIE SAMPLING STATIONS

34


mg CARBON FIXED /m3/hr/ly

50,00

BASED UPON MEAN VALUE WITHIN PHOTIC ZONE
———-— BASED UPON SURFACE VALUE

apni. ' may | JUNE | gulyY | aucust | sePTEMBER OCTOBER

FIGURE 26, PHOTOSYNTHETIC EFFICIENCY AT STATION 4 puRING 1971


FIGURES

30


TABLE 2

VERTICAL VARIATION IN WATER CHEMISTRY AT STATION 4, LAKE
SALLIE, MINNESOTA (Concentrations, except pH, in ppm)

Depth CO3 HCO 3 Total
Date (m) pH Alk. Alk. Hardness Cat+

1970

10 October ie} 8.85 40 126 166.6 58.8
2 8.80 40 136 166.6 58.8

5 8.80 40 136 166.6 58.8

8 8.90 36 140 186.2 58.8

121 8.90 40 138 176.4 58.8

23 October ie} 8.75 32 142 186.2 68.6
4 8.75 32 142 186.2 58.8

8 8.75 32 142 186.2 58.8

12 8.75 32 142 186.2 58.8

6 November 0 8.80 36 137 186.2 58.8
3 8.80 34 140 176.4 58.8

6 8.80 34 140 176.4 58.8

9 8.80 34 138 176.4 58.8

13 November lo) 8.85 40 134 186.2 58.8
4 8.85 40 134 186.2 58.8

8 8.85 40 134 186.2 58.8

19 December ie} 9.00 44 142 196.0 58.8
2 8.90 48 140 186.2 58.8

4 8.90 48 140 186.2 58.8

6 8.90 44 146 186.2 58.8

8 8.60 24 178 196.0 68.6

12 8.25 8 227 225.4 78.4

29 December ie) 8.90 44 150 196.0 58.8
4 8.90 44 146 196.0 58.8

8 8.30 12 193 196.0 68.6

1971

7 January ie) 9.00 44 160 196.0 68.6
2 8.90 40 154 186.2 58.8

4 8.85 40 155 186.2 58.8

62


Ov

PERCENTAGE SURFACE LIGHT INTENSITY

------ | METER DEPTH
3 METER DEPTH

405
35:
30:
25
20:
15:
10:

54

45:
35: oN A

304

15:
10:

354
304

20-
154
lo-

54 ~~

-
1971

IT T y La >
25305 10 20 3! 10 20 30 10 20 31 10 20 31 10 20 30 10 20 31
APRIL MAY JUNE JULY AUGUST SEPTEMBER OCTOBER

FIGURE 10, ANNUAL VARIATION IN LIGHT INTENSITY AT 1 AND 3 M,

10 20 30
NOVEMBER


APPENDIX

82


INTRODUCTION

Eutrophication is a term somewhat loosely applied today to both
natural aging of lakes and nutrient and organic matter enrichment of
all water bodies, Enrichment is frequently augmented by man, which
has led to coinage of the term, "cultural eutrophication", and
evidence has been presented that suggests it began in the Bronze Age
in Europe (Hasler, 1947). ZUrichsee in Switzerland exhibited gradual
increases in phosphorus, nitrogen, and chloride from 1888 to 1916,
during which time cyprinids replaced coregonid fishes, blue-green
algae succeeded diatoms as dominant phytoplankters, and oxygen was
reduced in deep water (Minder, 1926, '38, '43). Some other European
lakes have had similar histories (Hasler, 1947). Cultural enrich-
ment has also affected a number of North American lakes, but few of
them were studied before they posed problems. The Yahara River lakes
near Madison, Wisconsin; Lake Sebasticook, Maine; and Lake Washington
near Seattle have probably received as much attention as any (U.S.
DHEW, 1969; Hasler, 1947, Sawyer, 1947; Edmondson 1961, ‘oo, '68).

It has been proposed (Livermore, 1954) that nutrient content of
lakes may be reduced by removing large quantities of aquatic plants.
Weed harvest has generally been concerned with clearing lakes and
canals for recreation and navigation (e.g. Blanchard, 1965), but some
attention has been given to water weeds as livestock feed (Bailey,
1965; Lange, 1965). Yount (1964) and Yount and Crossman (1970)
suggested that aquatic plant harvest was one of the more promising
solutions for reducing lake productivity.

In 1968 the National Eutrophication Research Program, Federal
Water Quality Administration, funded a study on Lake Sallie, Minnesota
of the effects of large scale weed harvest on lake nutrient content.
A research grant was awarded to the University of North Dakota to de-
termine the basic limnological nature of this lake and varied effects
of weed removal, This article, largely based on data appearing in
Peterson (1971) and Smith (1972), comprises the final report on this
project.

Present addresses:

Spencer A, Peterson

U.S. Environmental Protection Agency

Pacific Northwest Environmental Research Laboratory
Corvallis, Oregon 97330

Wintfred L, Smith

Department of Biology

University of Tennessee at Martin
Martin, Tennessee 38237


ABSTRACT

After more than 60 years of cultural eutrophication Lake Sallie
supports dense growths of phytoplankton and rooted vegetation. Its
major water mass has the chemical character imparted by photosynthesis
at all seasons, and chemical effects of decomposition are rather
localized. Phytoplankton dominance alternates among diatoms, blue-
green, and green algae, in that order of abundance, Prior to operation
of a weed harvester, attached plants grew densely over 34% of the
bottom area. The bulk of nitrogen and phosphorus is usually contained
in the water mass, with noticeably smaller amounts in upper bottom
sediments and biota. The fish population, less than one half the mass
of weeds, contained considerable more N and P than weeds in 1971.
Harvest in 1970 evidently reduced weed density in 1971, and increased
the cost per unit of nutrients removed. Nitrogen and phosphorus
removed in weeds were insignificant when compared with annual waste-
water effluent contributions to the lake. Cost of phosphorus removal
by weed harvest was $61 and $199 per pound in 1970 and '71, respect-
ively; nitrogen cost $8 and $21 and carbon $0.64 and $1.62 per pound
for the same two years.

This report was submitted in fulfillment of Project Number

16010 DFI under the sponsorship of the Water Quality Office, Environ-
mental Protection Agency.

iii


Le

~ 4 Mm AIC

O J

” 20} SURFACE

a GY
2

ce 10}

Wo | 10 METERS

> 4

Ld 4

- Of

T T v T T T T T T T
SEP OCT NOV pec | JAN FEB MAR APR MAY JUN JUL AUG SEP

1969 1970

FIGURE 7. TEMPERATURE VARIATION AT SURFACE AND 10 METERS


TABLE 2--Continued

Depth C03 HCO3 Total
Date (m) ph Alk. Alk. Hardness Cat+
14 8.10 4 166 181.3 68.6
29 July 0 8.70 20 142 176.4 68.6
2 8.65 20 142 176.4 68.6
4 8.65 20 141 176.4 68.6
8 8.65 20 143 176.4 68.6
14 8.65 20 144 176.4 63.7
12 August ie} 8.90 36 124 166.6 58.8
2 8.90 34 127 166.6 58.8
4 8.90 32 127 166.6 58.8
8 8.60 18 147 176.4 58.8
14 8.25 6 165 186.2 68.6
25 August ie) 8.70 26 135 176.4 63.7
6 8.70 26 133 176.4 58.8
14 8.05 2 167 181.2 68.6
4 September ie} 8.85 30 129 176.4 63.7
2 8.85 30 129 176.4 58.8
4 8.80 28 130 176.4 58.8
8 8.70 24 136 176.4 58.8
14 8.55 16 150 181.3 58.8
12 September ie} 8.70 24 137 176.4 58.8
8 8.70 24 138 176.4 58.8
14 8.50 16 148 176.4 63.7
17 September ie} 8.70 28 133 181.3 53.9
8 8.70 28 132 176.4 58.8
14 8.70 26 139 176.4 58.8
24 September ie} 8.90 36 129 181.3 68.6
2 8.85 34 131 181.3 68.6
8 8.70 26 139 181.3 68.6
14 8.70 26 141 186.2 68.6
1 October ie) 8.70 28 137 181.3 73.5
8 8.50 14 isl 181.3 73.5
14 8.30 4 156 181.3 73.5
8 October ie} 8.55 16 146 186.2 73.5
4 8.55 16 146 181.3 68.6
8 8.55 16 147 181.3 68.6
14 8.50 14 149 176.4 68.6
15 October ie} 8.80 34 131 186.2 68.6
8 8.80 34 131 186.2 68.6

68


LL

TABLE 6 ~-Continued
Plant
Part Concentration
1/3
° % mg/g
weodoy
ae 2 c , © “~ 1
Plant Description paea Pp N Cc Hq Ca Mg Na Co Cu Fe Mn Mo an
Potamogeton richardsonii x 0,33 2.8 27.9 3.7 45.0 3.20.70 5. 0.100 0.015 0.870 0.441<0.065 0.026
x 0.31 2.8 27.3 3.7 44.0 3.20.80 5. 0.009 0.024 0.940 0.451 <0.065 0.026
x 0.34 2.5 25.7 3.2 44.0 2.7 1.10 9. 0.009 0.020 1.040 0.270 $0.065 0.034
Microcystis scum N.A.? 0.72 8.1 43.0 6.2 3.9 2.00.60 3. 0.018 0.023 0.780 0.223 <0.065 0.007
Periphyton removed
from Vallisneria N.A. 0.46 2.7 22.9 3.8 46.0 3.7 0.36 1. 0.022 0.023 1.06 0.510 40.065 0.090

aNot Applicable


EPA-660/3-73-001
July 1973 Ecological Research Series

WEED HARVEST AND LAKE
NUTRIENT DYNAMICS

Office of Research and Development

U.S. Environmental Protection Agency
Washington, D.C. 20460


EPA Review Notice

This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents necessarily
reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or

commercial products constitute endorsement or recommenda-
tion for use.


costs include operation, maintenance, trucking of weeds to points
outside the drainage basin, and harvester depreciation. Increased per
unit costs in 1971 reflect lower weed density.

Water and Nutrient Budgets

Surface water enters Lake Sallie via the Pelican River (major
source) and outlets from Fox and Monson Lakes, and exits only via
the Pelican River. Ground water inflow apparently exceeds seepage
from the lake, as surface outlow always exceeded inflow from the river

and lakes. Quantities of water and nutrients entering and leaving in
surface flow appear below.

Water Years

1968-69 1969-70 1970-71
Water Inflow m> 20,197,256 17,858,188 17, 849, 207
Outflow nm 22,716,382 19,087,138 20,807,164
Phosphorus | Inflow kg 10,140* 7,470%* 15,643%**
Outflow kg 5, 810% 2, 510% 1, 758%%
Nitrogen? Inflow kg_ 11,650 5,594 10,567
Outflow kg 9,720 2,640 7,217

* Soluble P
** Total P
1 NH3 - N+ N09 - N+NO3-N

Soluble P only was measured in 1968-69. In subsequent years the
mean ratio of soluble P to total P was 1:1.7, and, if this may be applied
to the 1968-69 water year, total P entering then would exceed 17,000
kg and that leaving around 9,900 kg. Both P and N declined noticeably in
1969-70, but recovered substantially in 1970-71. P and N content of Lake
Sallie water was, in kilograms:

1968-69 1969-70
P 2,270% 9, 690%
N 24,740 5,070
* Soluble P
**x Total P

25


Order

Order

Chlorococcales

Actinastrum gracillimum Lag.

Ankistrodesmus falcatus (Corda) Ralfs

Characium gracilipes Lamb.

Characium limneticus Lem.

Chlorella ellipsoidea Gern.

Chlorella vulgaris Beyern.

Closteriopsis longissima Lemm.

Coelastrum microporum Naeg.

Crucigenia fenestrata Sch.

Crucigenia irregularis Wille

Crucigenia Lauterbornii Sch.

Crucigenia quadrata Mor.

Crucigenia rectangularis (A. Braun) Gay

Dictyosphaerium Ehrenbergianum Naeg.

Dictyosphaerium pulchellum Wood

Kirchneriella obesa (W. West) Schmid.

Lagerheimia ciliata G. M. Sm.

Lagerheimia citriformis (Snow) G. M. Sm.

Micractinium pusillum Fres.

Nephrocytium sp. Naeg.

Oocystis sp. Naeg.

Oocystis parva W. and W.

Pediastrum Boryanum (Turp.) Meneg.

Pediastrum duplex Meyen

Pediastrum simplex (Meyen) Lem.

Planktosphaeria gelatinosa G. M. Sm.

Quadrigula lacustris (Chod.) G. M. Sm.

Scenedesmus arcuatus Lem.

Scenedesmus bijuga (Turp.) Lag.

Scenedesmus dimorphus (Turp.) Kutz.

Scenedesmus guadricauda Chod.

Scenedesmus guadricauda var. longispina (Chod.)
G. M. Sm.

Scenedesmus guadricauda var. maxima W. and W.

Schroderia Judayi G. M. Sm.

Selenastrum gracile Reinsch.

Tetradesmus wisconsinense G. M. Sm.

Tetraedron regulare Kutz.

Tetraedron arthrodesmiforme (G. S. West) Wolo.

Tetraedron pentaedricum W. and W.

Tetraedron sp. Kutz.

Tetrallantos Lagerheimii Teil.

Zygnematales

Closterium moniliforme (Bory) Ehr.

84


62

TABLE 8

PRIMARY PRODUCTIVITY OF SUBMERGED VASCULAR PLANTS AND
ASSOCIATED PLANKTON, LAKE SALLIE, MINNESOTA

Net Production

Rooted Plank- Rooted

Date Location Time Total? Plants? __ton@ Plants Plankton?
12 August 1970 ac 1100-1145 1187 780 407 - -
1145-1600 587 84 503 - -
19 August 1971 pd 2230-0800 - 375 -375 ie} -6.0 oO
20 August 1971 Bd 1100-1500 713 475 238 7.6 68.0
1500-2030 250 216 43 3.5 12.3
2030-1130 - 411 -388 - 24 -6.2 - 6.9
5 September 1971 ce 0715-0915 238 119 119 3.7 92.2
0915-1215 475 158 317 5.0 245.7
1215-1415 119 -119 238 3.7 184.5
1415-1615 475 237 238 7.4 184.5
1615-1815 0 ie} Oo Oo ie}

10 September 1971 pf 1700-1900 - 119 ie) -119 0 - 41.9


MATERIALS AND METHODS

The basic plan was to determine major limnological characteristics
of the lake, then harvest weeds and ascertain what changes were brought
about. Amounts of nutrients removed in weeds would also be ascertained.
Details follow:

Sampling

Sampling was carried out at the 21 sites shown in Figure 4, with
frequency varying from daily to semi-weekly to weekly in summer and
from weekly to biweekly in winter. Postponements were caused by unsafe
ice in early and late winter, and occasionally by adverse winter weather.
The surface was included at all sites and varied depths down to 16 m at
selected sites in the limnetic zone, in order to monitor depth and
duration of thermal stratification and its chemical and biological effects.

Physical Features

Temperature and light penetration were routinely measured, the
former with a thermistor thermometer and the latter with a submarine
relative irradiance meter with green, red, and blue filters. Measure-
ments were made during open water seasons and under ice. Discharge in
and out of the lake was recorded by the U.S. Geological Survey, St.
Paul, Minnesota, and weather data were obtained from Radio Station KDLM,
4.5 kilometers (2.8 miles) NE of Lake Sallie. Solar radiation was
monitored in 1971 with a pyranograph.

Chemical Features

Samples were taken with a Kemmerer Sampler (plastic) and transferred
to iced chests in summer and heated ones in winter for transport to a
lakeside laboratory for immediate performance of the following analyses:
carbonate and bicarbonate alkalinity, total, calcium and magnesium
hardness, ammonia, nitrite, and nitrate nitrogen, total phosphorus,
orthophosphate, and oxygen. Oxygen was also measured in the field by
dragging a galvanic cell probe along a series of transects extending
across and up and down the lake, AIl analyses except total P and NO3
were according to Standard Methods, 12th edition (A.P.H.A., 1965).
Total phosphorus was according to Krawczyk (1969), and NO3 to Strickland
and Parsons (1965).

Aquatic macrophytes were prepared for analysis by drying and mill-
ing to pass a 60 mesh screen. Nitrogen and carbon were determined with
a hydrogen-nitrogen-carbon gas analyzer and total phosphorus with the
one solution ascorbic acid technique (Strickland and Parsons, 1965),
with persulfate digestion. Sediment samples were air dried and anlyses
were performed on the materials fine enough to pass through a 60 mesh
screen, Total nitrogen was determined by the modified micro-Kjeldahl
method of Koch and McMeekin (1924) for some sediment samples. Phosphorus


ICE COV.

ICE COVER

—— SURFACE
—— 4 METERS
---- 8 METERS

YaLIT / GNVSNOHL

100,0005

10,000
1,0004
100+

1971

CONTINUED

49

M

FIGURE 16,

Tho’ FIM A

1970



Division Eumycophyta

Fungal spores

Division Tracheophyta

Pollen grains

Phylum Rotifera

Rotifer eggs

Phylum Annelida

Class Oligochaeta

Aeolosoma sp. (eggs)

Phylum Arthropoda

Class Crustacea

Order Cladocera

Ephippia

#U,S, GOVERNMENT PRINTING OFFICE: 1973-846-309/44 1-3. 91.


TABLE 2--Continued

Depth C03 HCO3 Total
Date (m) pH Alk. Alk. Hardness Cat+
14 8.75 32 132 186.2 68.6
22 October ie} 8.80 34 129 176.4 58.8
5 8.80 34 129 176.4 58.8
1o 8.55 20 144 176.4 68.6
29 October 0 8.60 20 146 186.2 68.6
6 8.60 24 140 186.2 68.6
13 8.60 24 140 186.2 6f.6
12 November te) 8.15 6 162 196.0 68.6
4 8.55 20 149 196.0 68.6
8 8.25 8 156 186.2 78.4
12 7.20 te) 158 205.8 68.6
11 December ie} 8.65 28 156 215.6 78.4
5 8.50 20 164 215.6 78.4
10 7.55 ie) 192 215.6 78.4
22 December ie) 8.40 16 177 225.4 88.2
5 8.30 16 182 207.7 88.2
10 7.60 ie} 196 205.8 78.4
14 7.50 ie} 205 215.6 88.2
31 December ie} 8.40 18 187 225.4 88.2
5 8.20 12 192 215.6 88.2
10 7.50 i) 202 205.8 88.2
14 7.50 ie} 202 225.4 88.2

70


FIGURE 1.

4
N

BATHYMETRIC MAP
MINNESOTA.

31

° 6601320
SCALE IN FEET
° 250 500

SCALE IN METERS

OF LAKE SALLIE,


Om

§ § §), § g £8
o
x i
2 3,
2 38
a a
2°
t
i i ps 1 ul q Li 3} if Ul
8 g 2 ° 8 B 8 g 2
NOISSIWSNVUL SOVLN3IONSd NOISSINSNVYL 39VLNS0YNAd
€ &
aa ai S
©
x oO
a
3 "&
oO
°
NOISSINSNVYL AOVLNADY3ad z
if
8 ¢ 8 & 8 ©

627

525
am

400

CONTINUED

FIGURE 11,

43


THOUSAND / LITER

5,000] 1969

TTT re

ao--- | METER
—— 2 METERS
oe» 3 METERS

t
50+ | —— suRF
t
t

TTT

AUG SEP OCT

FIGURE 16, VARIATION IN LIMNETIC PHYTOPLANKTON
CONCENTRATION AT DIFFERENT DEPTHS

48



\ JUSKRAT
LAKE

>75% SAND

<25% SAND

FIGURE 12, DISTRIBUTION OF SAND IN LAKE SALLIE SEDIMENTS

44


TABLE 3~~Continued

Component

H,0 Sol. P Total P Ca-P Al-P Fe-P Total N Carbon

Date Stations mg/kg g/kg mg/kg % &
September 28 1, 2, 8, 9 6.89 0.23 102.18 a 0.86 0.40 2.19
4, 5, 6 49.90 1.35 407.33 oe 8.94 1.42 15.16
November 15 1, 2, 12 12.00 0.25 124.33 a 2.23 0.27 2.47
3, 4 26.35 0.90 290.00 aoe 5.94 0.86 8.90

1970

January 25 1, 8, 9, 12 9.70 0.23 144.75 oe 1.29 0.20 2.91
4 16.70 0.70 200.00 oo 6.38 0.80 9.88
May 22 1, 9, 12 7.32 0.25 175.33 oe 2.75 0.20 1.77
4 52.40 1.46 492.00 oe oe 1.40 15.30

July 10 1, 8, 9, 12 11.91 0.31 128.15 oe 2.64 0.25 2.69

4upper row of values per each date.

Duower row of values per each date.


LIST OF PLANKTERS OBSERVED 1968-71
Bacteria
Division Schizophyta
Class Schizomycetes

Sphaerotilus natans Kutz.

Algae

Division Chlorophyta
Class Chlorophyceae

Order Volvocales

Chlamydomonas sp. Ehr.
Eudorina elegans Ehr.

Gonium formosum Pasch
Pandorina morum (Mull.) Bory
Pleodorina californica Shaw

Volvox globator L.

Order Tetrasporales

Elakatothrix gelatinosa Wille
Ererella bornhomensis Conrad.

Gloeocystis gigas (Kutz.) Lag.
Gloeocystis major Ger. ex Lem.

Gloeocystis planctonica (W. and W.) Lem.
Sphaerocystis Schroeteri Chod.

Order Ulotrichales

Stichococcus bacillaris Naeg.

83


se

TEMPERATURE (°C)

SURFACE ——
6m----
t@m——-

254

nN
fo}
i

ICE COVER

ICE COVER

a
r

Ss
r

J F M A M J J A s 0 N D

FIGURE 8, TEMPERATURE VARIATION WITH DEPTH, 1971


EPA~-660/3-73-001
July 1973

WEED HARVEST AND LAKE NUTRIENT DYNAMICS

by
Joe K. Neel

Spencer A. Peterson
Wintfred L. Smith

Department of Biology
University of North Dakota
Grand Forks, North Dakota 58201

Project No. 16010 DFI

Project Officer
Dr. Charles F. Powers
Pacific Northwest Environmental Research Laboratory
Corvallis, Oregon 97330

Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460


19

TABLE 1

MEAN TEMPERATURE AND PRECIPITATION RECORDED
AT DETROIT LAKES, MINNESOTA

1946-19607 1969? 1970? 1971» 1969-1971
Mean Mean Mean Mean Mean Mean
Temp. Precip. Temp. Precip. Temp. Precip. Temp. Precip. Temp. Precip.
Month (°c) (om) (2c) (cm) (2c) (om) (°c) (om) (°c) (cm)
January -15.1 1.80 -18.3 4.17 -16.5 0.41 -18.7 1.88 -17.8 2.15
February -12.9 1.73 -10.5 2.01  -13.7 0.66 -11.9 2.34 -12.0 1.67
March ~ 5.5 2.51 - 8.8 0.30 - 8.7 2.34 - 6.3 1.83 - 7.9 1.49
April 4.5 5.13 8.1 2.74 3.8 7.29 6.9 2.13 6.3 4.05
May 12.2 7.59 12.4 5.61 11.2 4.63 10.8 4.01 11.5 4.75
June 17.7 9.63 13.6 - 18.6 13.72 18.5 13,44 16.9 13.58
July 21.2 9.09 19.1 11.10 20.8 3.94 17.5 11.48 19,1 8.84
August 19.7 9.53 21.1 2.11 19.2 0.69 18.1 6.96 19.5 3.25
September 13.9 4,98 14,1 5.97 14.3 6.88 14.2 17.07 14.2 9.97
October 7.4 3.48 9.5 7.42 6.6 5.92 8.6 11.43 8.2 8.26
November 3.1 2.49 - 1.7 4.53 3.7 1.07 - 2.2 3.05 - 0.1 2.27
December ~11.2 - 8.9 2.69 -12.4 -11.1 0.64 -10.8
Total 51,34 66.22

AaModified from D. C. Reedstrom and R. A. Carlson, 1969, A biological survey of the Pelican
River watershed, Becker, Clay, and Ottertail Counties, Minn. Dept. Conserv. Special Publ. No. 65.

by.s. Dept. of Commerce, Climatological data.


LY

PERCENTAGE OF TOTAL PLANKTON

1005

904

70-

605

507

40+

307

204

a

BLUE—-GREENS —~—-——
DIATOMS
GREENS

_—

NoDtTuTFIMA Mut ylaAtTs to!
1970 1971

FIGURE 15, MEAN MONTHLY PERCENTAGES MAJOR PHYTOPLANKTON GROUPS

IN SURFACE WATER, STATION


P. Richardsonii (Benn.) Rydb.

Ruppia mar aL.

Alisma gramineum var. Geyeri (Torr.) Sam.
Scirpus actus Muhl.

Heteranthera dubia (Jacq.) MacM.

Elodea canadensis Michx.

Vallisneria americana Michx.
Ceratophyllum demersum L.

Myriophyllum exalbescens Fern.

Nuphar variegatum Engelm.
Nymphaea tuberosa Paine

These macrophytes covered about 34% of the total lake area, all
above the 3 m contour except Potamogeton praelongus which grew down
to 6 m (Figure 19). In 1969 and '70 Myriophyllum and Potamogeton
pectinatus tended to predominate, especially the former, in the
northern half of the lake and along the south shore. Scirpus beds have
been prominent along the eastern and northern shores and in a smaller
area on the west just north of the hilus, Littoral areas in other lake
regions were largely covered by a mixture of Ruppia, Potamogeton Richard-
sonii, Vallisneria, and Ceratophyllum, in which other species were
widely scattered. Duckweeds were most conspicuous in shallow areas,
especially near Scirpus beds. Gleotrichia first appeared epiphytic
on macrophytes and later became free floating. It and Nostoc became
very abundant on the bottom in late fall.

Weed distribution in 1971 was quite similar to that noted in '69
and '70, but all species, except Scirpus, which was not harvested,
were noticeably less abundant. Potamogeton pectinatus was more
prominent in weed harvester hauls and growth was most luxuriant in
Areas 3, 5, and 5, whereas in 1970 it had been greatest in Area 2
followed closely in Area 3.

Standing Crop

Standing Crop of aquatic flowering plants and their epiphytes,
based on weed harvester hauls from known areas in July and August 1971,
was estimated at 119,599 kilograms dry weight for all weed bearing
areas (34% of the total lake area). This figure includes roots which
had harvesting tests indicated were 13% dry weight of the portion usually
taken by the harvester. Average dry weight of harvester hauls was 58.8
g/sq. m. The 1970 harvest was 2.9 times as great as that of 1971 for
comparable harvester effort.

Primary Production
By Phytoplankton

Two hour exposure periods were adopted as standard for light and
dark bottle tests, and duplicate sets indicated this gave a precision


concentrated under 5.5 m than under 1 m or less of water, although
C:N ratios were little changed. Total P was about 3.5 times more
concentrated under deeper water, largely in calcium and iron combin-
ations, with the latter more prevalent. Aluminum P was significantly
less common, but was also greater under deeper water. Calcium
phosphorus was 12 times as great as the water soluble fraction. In
1970-71 sediment analysis was restricted to total N and total P, but
increases with water depth were still apparent (Tables 3, 4, and 5).

Aquatic Macrophytes

Analyses of upper, middle, and lower one thirds (including roots)
of 8 species of rooted plants collected in September 1968 showed
rather uniform concentrations of most elements measured (P, N, C, H,
Ca, Mg, Na, K, Co, Cu, Fe, Mn, Mo, and Zn) throughout the plant,
although they varied in different species, P was greater in upper
sections of Myriophyllum exalbescens .and Vallisneria americana; calcium
was most concentrated in Potamogeton Richardsonii and Elodea canadensis,
and the upper two thirds of Vallisneria; and sodium was highest in the
root sections of the four species whose lower 1/3 was analyzed (Scirpus
validus, Myriophyllum, Potamogeton pectinatus, and P. Richardsonii)
(Tables 6 and 7).

Weed Harvester Catches

Organisms gathered by the weed harvester included aquatic macro-
phytes plus periphyton and any animals living in the vegetation.
Carbon content of this assemblage was rather uniform throughout the
lake weed beds in 1970 and 1971, as were nitrogen and phosphorous in
1971. However, in 1970 P was 2,4 times as concentrated in Area 1 than
in areas 8 and 9 and exhibited a gradual decrease around the lake
counterclockwise from Station 1, Nitrogen was more concentrated in
Areas 1 and 2 in 1970, Ranges in ppm per dry weight of weeds were as
follows: 1970. p, 1,900 - 4,500; N, 21,000 ~ 29,900; C, 277,000 -
370,000, 1971. P, 2,200 - 3,450; N, 18,300 - 32,000; C, 294,000 -
336,000 (Table 7).

Fish

Ten species of fish were analyzed in toto for P, N, and C, Sun-
fishes (3 species) had higher levels of P than perch, walleye, pike,
white sucker, or bullheads (3 species). Range among these species
was 0.49 - 0.85% wet weight. Nitrogen (range 1,83 - 2.61% wet wt.)
and carbon (range 7.91 - 9.97% wet wt.) showed no marked relationship
to fish species.

Plankton
Plankton, including detritus, was analyzed only for phosphorus.

P tended to be more concentrated in plankton from the upper 2 m of the
limnetic zone, but at times was about as concentrated in spspended

17


15.

16,

7.

18.

19,

20.

21.

22.

23,

24,

25.

26.

27.

28.

29,

30.

Minder, L., "Biologisch - chemische untersuchungen in Zur ichsee ,""
Rev. d'Hydrologie 3:1-69 (1926)

Minder, L., "Der Zurichsee als eutrophierungsphanomen, Summarische
ergebnisse aus funfzig jahren 2urichseeforschung," Geol, Meere
Binnegewdsser 2(2):28-299 (1938)

Minder, L., "Neuere untersuchungen uber den sauerstoffgehalt und die
eutrophie des Zurichsees," Arch. f, Hydrobiol. 40(1):279-301 (1943)

Moyle, J. B., "Classification of lake waters upon the basis of hardness,"
Proc. Minn. Acad. Sci. 13:8-12 (1945a)

Moyle, J. B., "Some chemical factors influencing the distribution of
aquatic plants in Minnesota," Amer. Midl, Nat. 34:402-420 (1945b)

Moyle, J. B., "Relationships between chemistry of Minnesota surface
waters and wildlife management," J. Wildl. Mgmt, 20:303-320 (1956)

Olson, Donald, Personal communication (1971, '72)

Peterson, S. A., "Nutrient dynamics, nutrient budgets, and weed harvest
as related to the limnology of an artifically enriched lake," Unpub.
doctoral dissertation, Univ. of North Dakota xvii + 210 pp. (1971)

Reedstrom, D. C, and R. A. Carlson, "A biological survey of the Pelican
River watershed, Becker, Clay, and Ottertail Counties," Minnesota
Dept. Conserv. Spec. Pub. No. 65, 117 pp. (1969)

Sawyer, C. N., "Fertilization of lakes by agricultural and urban
drainage," Jour. N.E. Water Works Ass'n, 61:109-127 (1947)

Smith, W. L., "Plankton, weed growth, primary productivity, and their
relation to weed harvest in an artificially enriched lake," Unpub.
doctoral dissertation, Univ. of North Dakota xv + 222pp. (1972)

Strickland, J. D. H. and T. R. Parsons, "A manual of sea water analysis,"
Fish. Research Board of Canada, viii + 203 pp. (1965)

U. S. Department of Health, Education, and Welfare, "Fertilization and
algae in Lake Sebasticook, Maine," Fed. W.P.C.A., Tech. Ser. Program,
R. A. Taft San Engr. Center, Cincinnati, Ohio, 124 pp. (1966)

Wright, H. E., Jr., "Role of the Wadena Lobe in Wisconsin glaciation
of Minnesota," Geol. Soc. Amer, Bull. 73:73-100 (1962)

Yount, J. L., "Aquatic nutrient reduction-potential and possible methods,"
Rep. of Florida Anti-Mosquito Ass'n., (35th Annual Meeting) St, Augustine,
Florida (1964)

Yount, J. L. and R. A. Crossman, Jr., "Eutrophication control by plant
harvesting," Jour. Water Poll. Cont. Fed., Res. Suppl. 42:R173-R183
(1970)

29


€s

GROSS PRIMARY PRODUCTIVITY (mg CARBON FIXED/m3/hr)

6505

600-4

500+

4004

3004

20044

1004

4

T

L
Miuvlt ul ATS' OTN ATM Ty Ty Tat

1969 1970 1971

FIGURE 20, GROSS PRIMARY PRODUCTION IN LIMNETIC SURFACE WATER (STATION 4)

so NN?


TABLE 2--Continued

Ortho

Total

Temp
Mgt+ 0 POg PO4 NH3-N NO2-N NO3-N ec
117.6 10.20 co) 0.50 0.13 0.002 0.013 10.0
117.6 12.90 0.05 0.24 0.11 0.004 0.014 12.0
117.6 12.40 0 0.24 0.12 0.004 0.011 11.0
117.6 6.80 ) 0.50 0.12 0.004 0.014 10.5
117.6 9.40 0) 0.38 0.12 ) 0.013 9.0
117.6 9.40 0.05 0.50 0.16 0.006 0.007 9.0
117.6 9.30 fo) 0.38 0.21 0.004 0.009 9.0
127.4 13.80 0) 0.38 0.15 0.004 0.011 2.0
127.4 13.30 0.12 0.66 0.13 0.004 0.011 2.0
107.8 11.80 0.09 0.56 0.15 0.004 0.011 2.0
137.2 5,20 0.12 0.50 0.15 0.004 0.011 3.0
137.2 14.80 0.19 0.38 0.06 0.004 0.013 2.0
137.2 13.20 0.19 0.38 0.09 0.004 0.030 2.5
137.2 1.80 0.12 0.24 0.15 0.006 0.018 3.5
137.2 14.40 0.01 0.02 0.09 0.010 0.025 1.5
119.5 12.80 0.01 0.01 0.15 0.006 0.051 2.0
127.4 1.00 0 0.01 0.30 0.012 0.018 3.5
127.4 0.60 ) 0.01 0.38 0.006 0.011 4.0
137.2 13.00 0.25 0.24 0.22 0.008 0.039 1.5
127.4 11.80 0.25 0.50 0.24 0.006 0.050 2.0
117.6 0.80 0.12 0.38 0.32 0 0.021 3.5
137.2 0.40 0.12 0.38 0.46 0 0.015 4.0

71


Nutrient Removal

By Weed Harvester

As mentioned previously, the weed harvester removed algae, in-
vertebrates, and fishes with aquatic flowering plants. Total wet
weight of these organisms removed was greater for each area except
No. 5 in 1970 and 3,8 times greater for the entire lake as shown in
the following table:

Kg (wet weight) of Weeds Removed

Area 1970 1971

1 97,853 6,578
2 138,119 1,928
3 105,351 31,477
4 5,770 1,850
5 19,856 54,711
6 47,430 14,520
7 673 0
8 3,336 0
9 9,616 0
Total 428,034 111,064

Dry weight of weeds removed amounted to 30,371 kg (66,816 lbs.)
in 1970 and 10,366 kg (22,805 lbs.) in 1971. Kilograms of nutrients
taken out with weeds were as follows:

1970 1971
Phosphorus 100 26
Nitrogen 721 248
Carbon 10,699 3,219

23


Phylum Gastrotricha
Class Chaetonotoidea
Chaetonotus sp. Ehr.
Phylum Rotifera
Class Bdelloidea

Order Bdelloida

Philodina sp. Ehr.
Class Monogononta

Order Ploima

Anuraeopsis sp. Laut.

Asplanchna priodonta Gosse
Brachionus sp. Pallas

Brachionus calyciflorus Ahl.
Cephalodella auriculata Bory de St. Vincent
Colurella sp. Bory do St. Vincent
Euchlanis sp. Ehr.

Keratella cochlearis (Gosse)
Keratella quadrata (Mull.)

Lecane sp. Nitz.

Monostyla sp. Ehr.

Polyarthra euryptera (Wierz.)
Polyarthra vulgaris Carl.
Synchaeta pectinata Ehr.
Trichocerca multicrinis Kell.
Trichocerca similis Ehr.

Order Flosculariaceae
Conochilus sp. Hlava

Filinia longiseta (Ehr.)
Sinantherina socialis (L.)

89


STUDY AREA

Lake Sallie (Fig. 1) has received nutrients supplied by waste-
waters from the city of Detroit Lakes, Minnesota (1970 population
nearly 7,000) for more than 60 years (Larson,--1961). Waters enriched
by these wastes, which are now treated by, settling, biofiltration,
aeration, a stabilization pond, and flow through a peat bed, in that
order, follow a somewhat circuitous route into Lake Sallie, that
requires passage through 2 other lakes (Fig..2). This city also exper-
imented with lime precipitation and spray irrigation as means of nutrient
removal, but abandoned the first after facilities proved inadequate and
the second when data collection arrangements failed. Civil suit brought
against the city in 1951 by lake property owners was dismissed for lack
of evidence, but the city is now under orders from the Minnesota Pol-
lution Control Agency to reduce nutrients, especially phosphorus, to
noncritical levels. One hundred and sixty eight cottages along the
shores of Lake Sallie, occupied for varying periods during the year,
discharge wastes to individual septic tanks usually situated in ground
areas draining to the lake.

Lake Sallie is part of the Pelican River lake chain in north-
western Minnesota, which is contributory to the Ottertail River and
the Red River of the North. The topography of the Pelican River water-
shed was primarily determined by Wisconsin glaciation during the Pleis-
tocene Epoch, which sent at least 4 lobes of its ice sheet into Minn-
esota. The Wadena lobe, which moved into the area from the Northwest,
and the Des Moines lobe, advancing along the Red River Valley, were
chiefly involved in formation of this watershed, The Wadena lobe formed
the hilly region (Fergus Falls Moraine) to the east, and as it retreated,
the Des Moines lobe, moving east from the Red River Valley, overrode this
moraine and carried till with it. Withdrawal of the latter lobe added
to deposits on the Fergus Falls Moraine and formed outwash areas to
either side of it (Fig. 3). This hilly, glacial overlap region is know
as the Alexandria Morainic Complex (Wright, 1962). Melting of buried
blocks of ice formed the lakes (kettle basins) as the glaciers retreated,

A thick layer of glacial drift now lies within the Pelican River
watershed (Fig. 3). Outwash gravel forms the central area, with till
on either side. Glacial drift exceeds 91 m in thickness in the general
area, and outwash deposits vary from 1 to 24 m or more in thickness
(Allison, 1932). Watershed soils range from well drained, medium
textured sandy loam developed from calcareous, buff colored glacial till
on the east to dark-colored coarse to medium textured material, formed
from outwash near the center, to well drained dark soil produced from
calcareous galcial till on the west (Reedstrom and Carlson, 1969).

About 45% of the Pelican River Watershed is used for agriculture
(small grains, hay, and pasture), water and marsh areas comprise 29%,
forests 23%, and urban and residential areas 3%,


cL

TABLE 3

NITROGEN, CARBON, AND PHOSPHORUS CONCENTRATION IN SEDIMENTS COLLECTED FROM

SHALLOW® AND DEEP WATER AREAS OF LAKE SALLIE, MINNESOTA

Component
H20 Sol. P Total P Ca-P Al-P Fe-P Total N Carbon
Date Stations mg/kg g/kg mg/kg % %
1968
September 28 1, 2, 12 0.72 125.90 0.09 6.93 0.64 5.16
3, 4 1.17 22.80 0.14 14.30 2.40 13.65
October 19 1, 2, 8, 9, 12 0.43 . : 0.37 4.54
3, 5, 6, 10, 11 . 1.41 . 1.40 14.86
November 2 i, 8, 9, 12 10.20 0.37 175.60 0.08 1.96 0.37 3.85
3, 4, 5, 6, 10, 11 . 1.49 . . 1.43 15.01
November 16 1, 2, 7 0.80 . 0.85 9.33
4, 5, 6 1.42 . . 1.40 14.73
1969
February 7 1, 2, 8, 9 10.40 0.27 136.00 0.19 0.51 0.08 4.29
3 30.40 1.43 407.00 0.20 9.51 .
April 26 1, 2, 8, 9, 12 20.54 0.30 150.00 0.03 3.66 0.18 4.49
3, 4, 5, 6, 10, ll 45.82 1.25 349.20 0.07 6.17 1.25 16.97
June 6 1, 2, 8, 9, 12 13.52 0.32 206.50 0.04 3.56 0.47 5.21
4, 5, 6, 10, 11 34.66 1.35 391.30 0.10 9.04 1.51 15.01
August 17 1, 2, 8, 12 13.17 0.27 125.67 oe 3.14 0.22 2.20
3, 4 27.58 0.77 295.00 6.19 0.85 9.88


BL

TABLE 7

CHEMICAL ANALYSIS OF AQUATIC MACROPHYTES FROM
SELECTED AREAS IN LAKE SALLIE, MINNESOTA

Total Total Total
Cc N P
Date Sample Remarks g/ke g/kg g/ke
12 Jaly 19721 Transect 3-1 Almost entirely Potamogeton pectinatus 336 18.3 2.25
20 July 1971 Transect 5-2 Mixture of Ruppia maritima and
P. pectinatus 311 23.7 2.60
27 July 1971 Area 3 From 0.283 m° sample 294 21.0 2.135
30 July 1971 Transect 1-1 Mixture of Myriophyllum exalbescens
and P. pectinatus 286 28.7 2.74
5 August 1971 Area 6 From 0.283 m° sample 250 ek. 2.54
10 August 1971 Transect 4-1 Mixture of M. exalbescens and
P. pectinatus 305 23.7 2.295
10 August 1971 Transect 5-3 Mixture of M. exalbescens and
P. pectinatus 315 21.3 2.165
16 August 1971 Transect 6-1 0-15 m from Pelican R., mostly
M. exalbescens 307 25.3 2.515
16 August 1971 Transect 6-1 30-45 m from Pelican R., mostly
M. exalbescens 305 25.0 3.02
16 August 1971 Transect 6-1 75-90 m from Pelican R.,
M. exalbescens and P. pectinatus 328 28.3 2.50
16 August 1971 Transect 6-1 90-105 m from Pelican R., mostly
PB. pectinatus 312 25.3 2.683


TABLES

Mean Temperature and Precipitation Recorded at
Detroit Lakes, Minnesota

Vertical Variation in Water Chemistry at Station 4,

Lake Sallie, Minnesota 64,
67,
70,

Nitrogen, carbon, and phosphorus concentration in
sediments collected from shallow and deep water
areas of Lake Sallie, Minnesota

Acid-Soluble phosphorus of air dried sediments
from Lake Sallie

Total Kjeldahl nitrogen of sediments, Lake Sallie,
Minnesota

Concentration of certain elements in various aquatic
plants, Lake Sallie, Minnesota, September 16, 1968

Chemical analyses of aquatic macrophytes from certain
areas in Lake Sallie

Primary productivity of submerged vascular plants and
associated plankton

Water and nitrogen and phosphorus budgets in Lake
Sallie 1968-69 to 1970-71

viii

62,
65,
68,
71

72,

76,

79,

63
66
69

74

75

77

78

80

81


TABLE 6

CONCENTRATION OF CERTAIN ELEMENTS IN VARIOUS AQUATIC PLANTS
FROM LAKE SALLIE, MINNESOTA, SEPTEMBER 16, 1968

Plant
Part
1/3 Concentration
0 % ng/g
wed ow
Aso ——*~— “~ 1
Plant Description pay ip N CoH Ca Mg Na K Co Cu Fe Mn Mo Zn
Scirpus validus x 0.19 2.6 39.8 5.8 2.0 1.6 0.46 6.0 0.008 0.019 0.142 0.350 0.105 0.046
x 0.20 2.6 42.6 5.3 2.0 1.3 0.50 7.0 0.008 0.018 0.142 0.178 0.095 0.380
x 0.20 2.1 44.1 6.0 1.6 2.21.00 7.0 0.006 0.022 0.094 0.051 0.065 0.440
Myriophyllum exalbescens x 0.34 3.6 34.9 4.8 11.0 2.6 2.80 6.0 0.015 0.025 0.456 0.158 €0.065 0.105
x 0.31 3.4 37.0 5.4 12.0 2.3 5.50 8.5 0-006 0.022 0.260 0.120 ¢€0.065 0.048
x 0.29 2.8 31.9 4.4 30.0 2.8 3.60 6.5 0.008 0.027 0.420 0.156 $0.065 0.030
Lemna trisulca x x x 0.64 4.2 38.5 6.2 10.0 2.81.20 16.0 0.032 0.020 0.379 0.850 €0.065 0.070

Ceratophyllum demersum x xX x 0.48 3.4 37.4 6.0 3.2 5.11.40 12.0 0.036 0.042 0.427 0.860 ¢0.200 0.087

Nymphaea tuberosa x 0.23 1.6 38.7 5.8 2.0 2.7 9.80 12.0 0.023 0.023 0.171 0.227 €0.065 0.029
x 0.32 4.6 43.9 5.9 2.7 1.8 6.00 7.0 0.016 0.016 0.124 0.162 <0.065 0.065

Vallisneria americana x x 0.43 3.6 31.3 4.9 32.0 2.8 1.80 22.0 0.012 0.023 0.640 0.580 <0.065 0.029
x 0.28 3.2 29.1 4.4 3.5 2.5 5.60 34.0 0.017 0.017 1.330 0.830 <0.065 0.028

Elodia canadensis x x x 0.37 3.2 27.1 4.0 36.0 3.41.90 6.0 0.008 0.026 0.540 0.293 <0.065 0.055
Potamogeton pectinatus x 0.30 2.5 35.7 5.7 12.0 2.8 3.80 10.0 0.008 0.015 0.172 0.118 <0.065 0.026
x 0.27 2.3 39.5 5.5 4.2 2.4 4.20 10.0 0.014 0.012 0.180 0.094 <0.065 0.023

x 0-25 2.3 38.9 5.2 2.8 1.7 5.20 12.0 0.026 0.021 1.660 0.105 <0.110 0.038


Division Cyanophyta
Class Myxophyceae

Order Chroococcales

Aphanocapsa sp. Naeg.

Aphanothece nidulans Naeg.
Chroococcus Spersus (Keissl.) Lem.
Chroococcus limneticus Lem.
Coelosphaerium dubium Grun.
Coelosphaerium Ktitzingianum Naeg.
Coelosphaerium Naegelianum Ung.
Dactylococcopsis Smithii Chod. and Chod
Gomphosphaeria aponina Kutz.
Marssoniella elegans Lem.
Merismopedia punctata Meyen
Microcystis aeruginosa Kutz.
Microcystis flos-aguae (Wittr.) Kirch.

Order Hormogonales

Anabaena sp. Bory

Anabaena circinalis (Har.) Rab.
Anabaena spiroides Kleb.
Aphanizomenon flos-aquae (L.) Ralfs
Gleotrichia natans (Hed.) Rab.
Lyngbya sp. C. A. Ag.

Oscillatoria sp. Vauch.
Oscillatoria curviceps C. A. Ag.
Oscillatoria limosa (Roth) C. A. Ag.
Oscillatoria princeps Vauch.

um sp. Kutz.

Spirulina major Kutz.

Animals
Phylum Protozoa
Class Sarcodina
Order Testacea
Centropyxis aculeata (Ehr.) Stein

Difflugia sp. Lecl.
ifflugia lebes Pen.

87


= °

o

aq

- x

—_ =§

= 5

4 =

—_ 7

<q

= =

i 2

—L fo}

on

Be

= <§

TT 73>

5

=

7

°

lo S

wn

2

<q

5
re ras
$2328 8 ° 8 8 8 8

(44 /Qui/o6us) NOILONGONd AYVWIUd L3N (24/ g¥/o5w) NOILVaIdS ay

55

NET PRIMARY PRODUCTION AND RESPIRATION RATES IN SURFACE WATER AT STATION 4

FIGURE 22,


100,0005 ICE COVER ICE_COV.

~-77 BLUE-GREEN ALGAE
—— GREEN ALGAE
—— DIATOMS

THOUSAND/LITER

10,000-+

1000-4

100-4

1970 t97!

FIGURE 18, SEASONAL SUCCESSION IN CONCENTRATION OF
MAJOR PHYTOPLANKTON GROUPS IN SURFACE WATER
AT STATION 4,

51


then alkalinity by as much as 25 mg/l.

Hardness and alkalinity were rather uniform from surface to
bottom during periods of complete circulation, but both changed with
depth during times of stagnation. The usual tendency then was to
increase with depth, and this appeared generally true when upper- and
lowermost waters were compared, but there were several occasions when
intermediate waters were lower than those above and below; and there
were 2 periods during the 1969-70 winter when lenses of harder water
appeared to flow through the limnetic zone at a depth of 2 meters.
When they disappeared no hardness increase was noted at 4 or 6 meters,
and it is assumed that they moved out of the sampled area (Station 4)
laterally. Inflow of the Pelican River has at times exhibited hard-
ness concentrations very near those of these lenses, and it seems
reasonable that its discharge may pass through the lake as an inter-
flow when ice cover stills wind driven circulation. With one excep-
tion, which may have resulted from an analytical error, hardness and
alkalinity augmentation occurred in surface water under ice cover and
likely represented retention of freeze-out in the upper, lighter
water,

Both hardness and alkalinity varied in different regions of the
littoral zone, especially when mixing into lake water was slowed by
ice cover, Ranges on three occasions in late winter at 12 alongshore
stations in mg/l were:

Date Total Alkalinity Total Hardness
3/15/69 198 - 242 210 - 250
2/06/70 196 - 326 215 - 323
3/07/70 182 - 408 196 - 372

Highest values occurred at Station 9, where concentration
diminished rapidly with distance from shore. Maximum concentrations
recorded there were 428 mg/1 alkalinity and 431 mg/l hardness in
January 1971. Concentration at most shoreline stations decreased
abruptly when wind driven circulation returned with ice melt. Areas
most dominated by inflowing water (e.g. Station 1 at the Pelican River
inlet) tended to remain more mineralized than the lake, but they were
reduced to the general limnetic level by strong winds. Hardness and
alkalinity were generally most concentrated during the winter and most
dilute during open water seasons in surface and deeper waters (Table
2).

Calcium and Magnesium

In limnetic water calcium (as Caco) varied from slightly less
than 60 to almost 100 mg/l (Table 2). Greatest concentrations noted
were in deep water during times of stagnation. Magnesium exhibited a

13


60-4

40+

305

20-

22 JUN 71!

\

PERCENTAGE TRANSMISSION

ey

0.5m
Zz
2
an
g

Lom z
z
4
a
E
WwW
a
=
2

1.5m y
4
w
a.

2.0m

2.5m

FIGURE 11, CONTINUED

42

60>

b
fo}
1

gi
fo}
L

8
1

24 JUN 71

0.5m

1.0m

L5m



ICE COVER

STATION 4
STATION 8 — —

ICE COVER
STATION | ---—

Ss'O'N DU FM AM Jd J A'S O'N Du FM AM ag J aA’S'O'N D

1971
BOD VARIATION AT 3 LAKE SALLIE STATIONS

1970

FIcuRE 14,

1969

i

(70 Wdd) %a0a

46


TABLE 5

TOTAL KJELDAHL NITROGEN, AS PERCENTAGE OF DRY WEIGHT
OF SEDIMENTS, LAKE SALLIE, MINNESOTA

cL

Station

1 3 4 6 7 12 21
Depth (m)

Date 0.5 9.0 16.5 7.5 1.0 0.5 0.5 0.3 0.3
7 November 1970 0.29 1.15 1.98 - 0.13 0.33 0.09 0.13 o.1l
19 December 1970 - - 1.23 - - 0.18 0.07 0.21 0.17
18 March 1971 0.13 - - - - 0.17 - 0.11 0.26
8 May 1971 0.06 - 1.30 1.28 - 0.10 0.08 o.1l 0.12
25 June 1971 0.36 0.85 - 1.38 0.15 0.13 0.08 0.08 o.1l
21 July 1971 0.88 1.13 0.80 2.00 0.17 0.55 0.12 0.08 0.10
30 October 1971 0.09 - 0.48 ~ - 0.50 0.10 0.08 0.11
10 December 1971 - - - - - O.11 0.11 0.09 o.1l
- - 1.07 - - - - - -

31

December 1971



was extracted wich 0.6NHcl, and, after filtering’and dilution, tested
with standard reagents. Twenty eight samples of.11 species of: macro-
phytes had Ca, Mg, Na, K, Co, Cu, Fe, Mn, No, and Zn measured. Peri-
phyton was normally included with macrophytes.‘ Ca, Al, and Fe of some
sediment samples were determined by the method ‘of Chang and Jackson
(1957). Nutrient analyses of fish flesh were'performed on dried*samples
of ground whole fishes, using the same methods described for plants.

Sediment samples to a depth of 15 cm (6") were taken with an
Ekman dredge and air dried and graded with sieves prior to analysis.
Aquatic macrophytes were collected by hand prior:to weed harvest, but
after this process was underway 0.024 cubic meter (1 cu. ft.) samples
were picked off the harvester apron, dried, grated. through 6.35 mm
(1/4") hardware cloth, and portions of them analyzed. These samples
contained periphyton, snails, insects, crustaceans, and small fishe
in addition to weeds, and represented all materials removed by the
harvestor,

Biological Features

Weed areas were mapped prior to harvest by collecting along a
large number of transects extending across weed beds perpendicular to
shore. Dominant species were noted for each area, Plankton was
collected in several regions, but most sampling was confined to the
deepest lake area where samples were vertically spaced at 2 m intervals
in the euphotic zone and at varying depths in the aphotic. Samples of
4 1 were concentrated to 200 ml by settling. Counts were made in
Sedgewick - Rafter cells, using the strip method for common forms and
counting the whole cell for rare organisms, Plankton units were 1
ocular grid (.49 sq. mm) for large irregular colonies, 100 micron
lengths for filamentous algae, individual colonies for such organisms
as Pediastrum and Crucigenia, and individuals for single celled algae
and zooplankters.

Primary production by plankton, net and gross, was measured by
oxygen change in light and dark bottles filled with water from varied
depths in the euphotic and aphotic zones and returned to these depths
for incubation, which was for 2 hour periods, except during colder
seasons with low plankton densities, when it was 6 hours. Results were
converted to mg C fixed/cu.m/hr. Primary production by macrophytes and
their investing periphyton was arrived at by isolating an area of lake
bottom and its vegetation in a large cylinder of clear vinyl film and
noting changes in pH, free COj, and alkalinity at frequent intervals
(usually 2 hours) in the enclosed water.

Light and dark bottles were filled and suspended inside the
cylinder to estimate changes attributable to phytoplankton. Calcula-
tion was as follows:


os

1,001

fevetia

THOUSAND / LITER
roy
£

San wenntt

Ss

po iil

BLUE-GREEN ALGAE
GREEN ALGAE 2 =-~-=—
DIATOMS -__
ANIMALS -—-

3°

vuc ‘auc ' sep * OCT “yoveewar

“gun “yur ‘aus sep ‘ oct *

1969 1970

FIGURE 17, VARIATION IN CONCENTRATION OF MAJOR PLANKTON

GROUPS IN SURFACE WATER


SECTION
I
IL
IIL
Iv
Vv

VI

VIL
VIIL

IX

XL

CONTENTS

Conclusions

Recommendations

Introduction

Study Area

Materials and Methods

Discussion
Climatological Features
Physical Features
Chemical Features
Biological Features
Water and Nutrient Budgets
Effects of Weed Harvest

Acknowledgments

References

Figures

Tables

Appendices

PAGE

10
10
10
11
18
25
26
27
28
30
60

82


TABLE 2--Continued

Ortho Total Temp.
Mg++ 05 PO, PO, NH3-N NO,-N NO3-N oc
156.8 2.20 0 0.24 0.27 0.004 0.004 10.0
147.0 7.20 0.05 0.64 0.27 0.004 0.006 10.0
127.4 11.10 0 0.24 0.38 0.004 0.004 18.0
132.3 11.70 f°) 0.10 0.27 0.004 0.004 15.0
122.5 8.80 to) 0.24 0.25 0.001 0.007 13.0
127.4 4.80 0 0.50 0.33 0.004 0.004 13.0
107.8 10.00 to) 0.24 0.32 0.001 0.005 17.0
122.5 10.20 ) 0.36 0.33 ) 0.006 17.0
117.6 6.20 0 0.24 0.40 0.001 0.005 14.0
127.4 3.40 0 0.24 0.40 0.004 0) 14.0
107.8 8.90 ) 0.36 0.36 0.004 0.004 22.5
107.8 8.60 0.12 0.24 0.36 ) 0.008 22.5
107.8 8.00 0.05 0.50 0.31 i) 0.008 22.0
117.6 1.40 0 0.24 0.48 0 0.012 16.0
112.7 0.10 6.12 0.24 1.18 0) 0.012 15.5
107.8 9.70 0.05 0.24 0.28 0.004 0.002 22.0
117.6 9.60 0 0.24 0.28 0.004 0.002 22.0
117.6 9.60 0.12 0.12 0.32 0.004 0.002 22.0
117.6 5.90 0.05 0.24 0.33 0.001 0.007 20.0
127.4 0.20 0.19 0.24 0.74 0.004 0.002 16.0
122.5 0.10 0.12 0.50 0.82 0.001 0.005 16.0
112.7 8.10 0.12 0.24 0.36 0.001 0.007 23.0
117.6 8.20 0 0.50 0.37 0.001 0.009 23.0
117.6 7.70 0.12 0.36 0.39 0.001 0.007 22.5
117.6 1.40 0.18 0.36 0.77 0.001 0.007 19.0
127.4 0.20 0.32 0.50 1.08 0.017 0.008 18.0+
127.4 to) 0.32 0.50 1.33 0.004 0.004 17.0
117.6 7.52 0.12 0.50 0.33 0.004 0.004 21.0
112.7 7.52 0.12 0.64 0.37 0.001 0.005 21.0
112.7 6.53 0.12 0.50 0.46 0) 0.006 21.0
117.6 0.40 0.25 0.50 1.11 0.001 0.003 18.5
126.5 ) 0.51 1.02 2.07 ) 0.004 17.0
122.5 O) 0.77 1.16 2.60 ) 0.004 17.0
112.7 8.89 ) 4.86 0.32 0.001 0.005 21.0
112.7 8.48 ) 0.36 0.32 0.004 0.004 21.0
112.7 7.88 () 0.36 0.36 0.001 0.005 21.0
112.7 3.23 0.11 0.50 0.74 0.004 0,002 20.0
112.7 1.21 0.11 0.50 0.81 0.006 0.002 20.0

67


of +10 mg C fixed/m3/hr.

Nutrient concentrations declined along the course of the Pelican
River inflow into Lake Sallie, and this was also true of the rate of
primary production upon some, but not.all occasions, It was often
greater at Station 4 in the limmetic zone than at Station 1 or in
Muskrat Lake. Variation among stations in the limmetic zone appeared
to be normal. :

Most measurements were made at Station 4 near the heart of the
limnetic zone. Surface water there showed maxima in late summer or
early fall each year, but summer and fall activity varied noticeably
over 1969-'71, Average values for the euphotic zone gave a three-year
pattern that resembled that for surface water, but generally had
sharper and fewer peaks. In 1969 and '71, means for the euphotic zone
maxima were comparable with highest rates developed in surface water,
but the average value was much below that of the surface in 1970
(Figures 20 and 21). Surface productivity showed a progressive increase
from 1969 through 1971 with respect to total amount of carbon fixed
per growing season. These upper waters accounted for 68% of pro-
duction at Station 4 over the three-year period. Net production was
greater and respiration less in 1971 than in '69 or '70 in both
surface water and throughout the euphotic zone (Figures 22 and 23).

Productivity varied with depth in the euphotic zone (Figure 24)
and with time of the day (Figure 25) for which no pattern appeared
consistent. There was also no definite relationship with intenstiy
or amount of light on either a daily or a seasonal basis, but photo-
synthetic efficienty (mg C fixed per solar radiation unit) was great-
est in late afternoon and in early September and during most of
October when solar energy was noticeably below values occurring in
July and August (Figure 26). : :

By Attached Vegetation

Measurements within the plastic cylinder chiefly if not exclusively
represent the activity of flowering plants, largely Myriophyllum, and
phytoplankton, as very few attached algae were ever enclosed. Depth of
sampling and bottle suspension inside the cylinder was 10 cm. Net
productivity attributable to the rooted plants (total for the cylinder
minus that for the light bottle suspended inside) ranged from -338 to
780mg C/m3/hr and that attributable to plankton from -119 to 503 mg
C/m3/hr. On a net productivity per gram of dry weight basis phytoplank-
ton greatly outstripped the rooted vegetation, but dry weight of the
rooted vegetation included many more parts, roots, fibers, etc., that
are not photosynthetic. It is likely that rates for attached vegetation
would have been higher had attached algae been enclosed with other plants.
Thermal and oxygen stratification usually developed within the cylinder.
Light intensity declined markedly with depth inside the cylinder, usually
being less than 5% of surface values at 1 m (Table 8).

22


TABLE 2--Continued

Ortho Total Temp.
Mg++ 05 POg PO, NH3-N NO2-N NO3-N °c
127.4 12.00 ce) 0.22 0.20 0.006 0.006 2.5
137.2 5.70 0.32 0.24 0.28 0.012 0.014 2.5
147.0 4.20 0.12 0.50 0.30 0.008 0.014 3.0
142.1 2.60 0.25 0.76 0.37 0.008 0.014 3.0
127.4 14.90 0.25 0.38 - 0.008 - 1.0
127.4 15.10 0.18 0.24 - 0.012 ie} 2.0
127.4 13.60 9.63 0.24 - 0.017 - 2.0
137.2 11.80 0.25 0.38 - 0.012 - 3.0
147.0 5.90 0.18 1.02 - 0.030 - 3.0
156.8 2.00 0.18 0.62 - 0.35 - 3.5
147.0 13.33 0.12 0.38 0.16 0.023 0.011 0.0
147.0 12.84 (e) 0.24 0.16 0.026 0.008 2.0
156.8 11.47 (e) 0.24 0.23 0.030 0.011 1.5
156.8 6.27 0.38 0.64 0.55 0.026 0.015 2.0
156.8 8.82 0.25 0.50 0.40 0.028 0.011 3.0
156.8 3.43 0.25 0.64 0.46 0.026 0.035 3.0
137.2 14.00 0.12 0.10 0.20 0.019 0.009 1.0
137.2 12.50 0.19 0.28 0.22 0.024 0.004 2.0
147.0 11.20 0.25 0.28 0.26 0.024 0.01] 2.5
156.8 6.60 0.38 0.76 0.28 0.024 0.050 3.0
166.6 5.00 0.38 0.76 0.32 0.028 0.058 4.0
156.8 ie} 0.25 1.02 0.20 0.021 0.109 4.0
137.2 13.90 0.06 0.30 0.40 0.004 0.004 7.5
137.2 13.90 0.06 0.30 0.31 0.008 ie} 7.0
137.2 13.90 0.12 0.50 0.36 0.006 0.002 7.0
137.2 13.90 0.06 0.30 0.44 0.004 0.007 7.0
137.2 13.72 0.06 0.30 0.28 0.004 0.007 7.0
137.2 13.72 0.12 0.50 - 0.006 0.005 7.0
127.4 12.25 ie} 0.24 1.15 0.004 0.004 7.0
127.4 12.54 ie) 0.24 1.28 0.004 0.004 7.5
127.4 12,44 ie} 0.24 1.28 0.004 0.004 7.5
127.4 12.44 0.06 0.36 1.41 0.004 0.004 7.5
142.1 12.00 0.05 0.24 0.48 0.001 0.007 12.0
142.1 12.00 0.05 0.10 0.59 0.004 0.004 12.0
142.1 12.00 ie) 0.10 0.43 0.004 0.004 11.5
142.1 12.00 0.05 0.24 0.39 0.004 0.004 9.5
137.2 11.60 ie} 0.24 0.15 0.001 0.007 11.5
137.2 11.80 ie) 0.10 0.19 0.004 0.004 10.5

65


Bs

tiny
100- ih Hi4
t \GRoss PRIMARY PRODUCTION
H \ t /he—LANGLEYS Hi2
i. Ne
3,805 ! i laah F10
Ss Hl ho PNA w
ue) { VV \ rN h 1 v I t a
£ t wr oNA CN a ! vi r8 oO
3 N NAG ' 1 z
Es H V 1 N | s
2604 i Vu 7 ré —
3 i nis
' “4 1 .
& i Vt} 4
I al \
\
ao, |i ‘ Le
No? patetetn
V4
T T T T T T
0800 1000 1200 1400 1600 1800 2000 2200
FIGURE 25, VARIATION IN INCIDENT SOLAR RADIATION (LANGLEYS) AND

JUNE

HOURLY CHANGE IN PRIMARY PRODUCTION RATE AT STATION 4,


2.6 mg/1 in summer and to 1,5 mg/l in winter). Greater concentration
in upper waters (1.25 mg/1) occurred during periods of full circula-
tion when maxima attained in bottom waters during stratification were
reduced. Surface concentration varied in different lake regions.
Highest values (slightly above 4.0 mg/1) were observed at Station 9
under ice cover, which suggests that inflow there was contaminated,
but concentrations above the general lake level were also noted at
Stations 1, 12, 19, and 21. These ammonia values were induced by in-
flowing surface and ground water. That entering at Station 1 represent-
ed by far the greatest volume, and was considered most influential on
the character of the lake, Concentration in the limnetic zone was
eed always greater than 0.1 and usually-more than 0.2 mg/l (Table

Nitrite

Nitrite was usually, but not invariably, found in samples from
all areas, depths, and dates. It disappeared in August 1969 from all
sampled areas, and was missing at times in summer from some stations.
Its concentration was generally well below 0.01 mg/l at all depths
during open water seasons, but it increased to 0.1 at Stations 1 and
4 for a short period in September, 1970. With stratification maximums
(up to 0.1 mg/1 in March 1970) occurred at intermediate depths (6 to
8 m) under ice and at intermediate or maximum depth with open water,
when increases rarely occurred below stable thermoclines (Table 2).

Nitrate

Nitrate was most concentrated at all depths under ice cover,
when the maximum observed concentration (0.34 mg/l) occurred in surface
water at 3 stations, Vertically in the limmetic zone, it attained
peak values at 6 and 8 m during winter of 1969-70, but during the 1970-
71 winter its maximum was at 14 m. Inflow via the Pelican River
generally had higher nitrate concentration than that leaving the lake.
Nitrate was rarely absent from surface water, but zero values there
were noted during all seasons except under ice cover (Table 2).

Phosphorus

Available phosphorus (P04) generally was most concentrated in
deeper waters of the limnetic zone, especially during periods of strat-
ification (the 9.2 mg/l maximum was in the hypolimnion in 1969), but
it tended to disappear from surface waters during the growing season,
although this occurred infrequently in 1969, It varied markedly in
surface water at Station 1, where maximum values (4.8 mg/1) occurred,
but it reached comparable levels in other littoral areas (Stations 9,
10, and 12) under ice cover, Its maximum for the limmetic zone surface
(1.4 mg/1) occurred in September 1969, Surface values there were
usually less than 0.20 mg/l. Orothophosphate was consistently higher
in inflowing than in outflowing water, declining to zero in the latter
for about 30 consecutive days im July and August 1971. Surface water

15


STABILIZATION
LAGOON

Cy

AERATED
POND

WASTE
TREATMENT
PLANT

0 500 1000
SCALE IN METERS

DETROIT
LAKE

REARING

LAKE SALLIE

FIGURE 2.
FLOW ROUTE OF WASTEWATER EFFLUENT FROM
DETROIT LAKES TO LAKE SALLIE.

32


\

\ Le MUSKRAT
LAKE
— EXTENT OF \
Ri] ROOTED
VEGETATION
9] scirpus

POTAMOGETON
& RUPPIA

MYRIOPHYLLUM

FIGURE 19, AREAS WITH ROOTED VEGETATION


matter from deepest water. It varied from place to place in samples
from surface water, once achieving 47,000 ppm per dry weight at
Station 12, Plankton from the limnetic zone had markedly lower P
concentrations in fall than in summer, but seasonal trends were much
less marked in the littoral zone.

Biological Features
Plankton
Qualitative Features

Collections made over the three year period yielded 188 plankton
organisms that are listed in the appendix. Green algae, largely
chlorococcales, accounted for the largest number of species (59);
diatoms had 38, blue-green algae 25, ciliate protozoans 21, and
rotifers 19 species, Less numerous groups, copepods (3), cladocerans
(7), suctorians (2), amoeboid protozoans (4), dinoflagellates (3),
eryptophyceans (1), euglenophytes (3), chrysophytes (1), xanthophytes
(1), and identifiable bacteria (1), gave 26 species.

Seasonal Occurrence

Seasonal patterns were usually considerably modified by location
in the lake, and sometimes were unstable during periods with chang-
ing dominant groups. In the limnetic zone, as exemplified by Station
4, the general tendency appeared to be dominance by diatoms in spring
giving way to blue-greens in summer to diatoms again in autumn and
early winter and to green algae (Chlamydomonas) and/or pyrrophytes
(Cryptomonas) in winter. However, this was by no means a fixed order
of succession. For example, Microcystis (a blue-green) replaced
Chlamydomonas as the dominant plankter in surface water in February
1971,. but was replaced by the latter in March. Chlamydomonas did not
loose dominance in deeper water, In June 1971, dominance changed from
Stephanodiscus (a diatom) to Microcystis, back to Stephanodiscus, and
then to the blue-greens Anabaena and Aphanizomenon. Blue-greens, with
Gomphosphaeria and Oscillatoria entering dominant ranks in August and
September, were thereafter most prevalent until late September when
they were replaced for about 10 days by the diatoms Melosira and
Stephanodiscus. Aphanizomenon regained dominance in surface water on
October 1, and was only slightly less numerous than Stephanodiscus at
2m, but it was "ousted" for good by the latter on October 9, This
diatom gave way to Chlamydomonas on December 11, and eleven days later
this green alga was joined by Cryptomonas, which had also appeared in
dominant ranks with Aphanizomenon in surface water on October'1l.
Vacillating dominance between blue-greens and diatoms in late spring
and early fall suggests that competition between them is rather finely
balanced and that swings to either side may be occasioned by minor
environmental changes, In August 1969 a dense Aphanizomenon popula-
tion was severely reduced by applications of copper sulfate along the

18


Cosmarium sp. Breb.
Staurastrum paradoxum Meyen
Mougeotia sp. (C. A. Ag.) Wittr.

Division Chrysophyta
Class Xanthophyceae

Order Heterococcales

Ophiocytium capitatum Woll.

Class Chrysophyceae

Order Chrysomonadales

Dinobryon divergens Imh.
Class Bacillariophyceae

Order Centrales

Melosira granulata (Ehr.) Ralfs
Stephano: cus astraea (Ehr.) Grun.
Stephanodiscus astraea var. minutula (Kutz.) Grun

Order Pennales

Amphiprora sp. Ehr.

Aste. nella formosa Hass.
Cocconeis pediculus Ehr.
Cocconeis scutellum Ehr.
Cymatopleura solea (Breb.) W. Sm.
Cymbella cistula (Hemp.) Grun.
Cymbella lanceolata (Ehr.) v. Heur.
Cymbella prostata (Berk.) Cl.
Cymbella tumida (Breb.) v. Heur.
Cymbella sp. Ag.

Diatoma sp. DeCand.

Epithemia sorex Kutz.

Epithemia sp. Breb.

Epithemia turgida (Ehr.) Kutz.

85


ee an

: | | |

DEPTH (m)

v qT q qT qT q u qT
APRIL 30 MAY 3! JUNE 30 JULY 31 AUGUST

FIGURE 9, POSITION AND THICKNESS OF THERMOCLINE DURING
OPEN WATER SEASON, 19/1, IN LAKE SALLIE

39

—
3!


08

TABLE 8--Continued

Net Production

Rooted Plank- Rooted

Date Location Time Total? Plants? _ ton@ Plants? Plankton

11 September 1971 pf 0700-0900 178 0 178 0 62.7
0900-1200 911 594 317 15.2 111.6

1200-1530 950 679 271 17.4 95.4

amg C/m3/nr.
bmg C/g dry weight/hr.
©250 m NW of Station 1. Enclosed M. exalbescens. Depth 1 m.

don weed harvest transect 5-3. Enclosed M. exalbescens (19.0 g dry wt) and mixture of

Pp. pectinatus and R. maritima (43.5 g combined dry wt). Dominant algae were M. aeruginosa,
A. spiroides and Lyngbya sp. (17.5 mg/l dry wt). Depth 1m.

€25 m NW of Station 1. Enclosed M. exalbescens (31.9 g dry wt). Dominant alga was
O. curviceps (12.9 mg/l dry wt). Depth 0.5 m.

fon weed harvest transect 3-1. Enclosed M. exalbescens (22.7 g dry wt), R. maritima

(9.0 g dry wt), and P. pectinatus (7.3 g dry wt). Dominant alga was A. spiroides (14.2 mg/l
dry wt). Depth 1.1m.


mg C fixed/m3/hr
190 200 400 600 800
1 | 4. L 3

<<
Te
—_

_

/
/

/

---- 13 JUL 69
— 15 AuG 69

—— 25 AUG 69

mg C fixed/m3/hr
190 200 400 600 800
4

ee

—--- 2 JUN 70
—— 16 JUL 70
—— 24 AUG 70

mg C fixed/m3/hr
200 400 690

---- 30 JUN 7!
—— 20 AUG 7!
—— Il SEP 71

FIGURE 24, VERTICAL VARIATION IN GROSS PRIMARY PRODUCTION

ON SELECTED DATES AT STATION

57


18

TABLE 9

WATER AND NITROGEN AND PHOSPHORUS BUDGETS IN LAKE SALLIE 1968-69 TO 1970-71

WATER YEAR
1968-69 1969-70 1970-71
Total Total Water Total Total Water Total Total Water
N P Flow N P Flow N P Flow
kg kg m?x106 kg kg m2x106 kg kg m3x106
A. In Lake Sallie
Water 24,740 2,270* - 5,070 9,690 - 21,231 16,513 -
Weeds ~ - - 8,149** 1,038** - 2,810 358 ~
Fish 7,210 1,980 - 4,270 1,220 - 11,594 3,152 -
Sediment 1,014 95 - 748 73 - 738 89 -
Total 32,494 4,345 - 21,412 12,415 - 36,729 20,112 -
B. Input
Pelican R. 11,360 10,020 18.96 5,590 7,060 16.77 10,568 15,169 16.88
Fox Lake 200 80 0.78 180 310 0.66 393 305 0.62
Monson L. 90 20 0.48 80 100 0.41 217 169 0.35
Total 11,650 10,140 20.22 5,850 7,470 17.84 11,178 15,643 17.85
C. Outflow 9,720 5,810 22.71 2,640 2,510 19.08 7,217 7,758 20.81
D. Net Gain 1,930 4,330 -2.49 3,210 4,960 ~1.24 3,961 7,885 -2.96
or Loss
(B-C) to
Lake
E. Removed by
Harvest
Fish - - - 1,590 406 - 786 207 -
Weeds - - - 721 100 - 248 26 -
Total - - - 2,311 506 - 1,034 233 -

* Soluble P
**Approximation from 1971 standing crop data and 1970 harvest.


Mean quantities contained in the upper 15 cm (6"). of sediments
in 1968, '69, and '70, in kilograms, were 73 P and 748 N, whereas in
1971 they were 89 and 738 kilograms, respectively. Total volume of
sediments to this depth is about 795,000 m?. Estimates of total wet
weight of fishes (Olson, 1971, '72) and quantities of P, N, and C
tied up in them, all in kg, follow:

1969 1970 1971

Fish 347, 545 212,090 594,740
Pp 1,980 1,220 3,152
N 7,210 4,270 11,594
c 30,340 18, 006 55,013

The 1971 standing crop of aquatic flowering plants and organisms
gathered with them by the harvester, plus roots and lower stems not
taken by the harvester, has been estimated as 119,520 kilograms, dry
weight. This figure is based on a mean standing crop of 66.4 g/sq. m.,
dry weight, over an area of 1,800,000 sq. m. (34% of the total lake
area). Since percentages of P, N, and C in dried weeds were .30, 2.35,
and 30.87, respectively, total nutreint content of weeds and associated
organisms in 1971 was 358 kg P, 3810 kg N, and 36,920 kg Cc.

Nitrogen and phosphorus budgets (Table 9) indicate that harvest of
fish and weeds to the extent possible with present equipment and practices
did not offset yearly gains via surface inflow. Removal of all fish and
weeds would make an inroad on previously accumulated N, but would not
equal any annual P increment recorded to date, With the exception of
1969-70 much more N and P were contained in the water mass than in bodies
of organisms and sediments combined, and concentration of these two
elements would be subject to rather rapid reduction if their discharge
in wastewater to the Pelican River was curtailed.

Effects of Weed Harvest

Two years of weed harvest did not alter the basic chemical nature
of the water mass nor the general pattern of nutrient dynamics in the
water, One year's harvest greatly reduced weed concentration in affected
areas and occasioned some change in dominant forms. Denser plankton con-
centration occurred the first year following harvest, the amount of
carbon fixed by phytoplankton increased, and the ratio of planktonic
respiration to photosynthesis decreased. These latter developments suggest
that weeds compete with phytoplankton, and, that weed removal should not
be expected to aid phytoplankton control unless it depletes nutrient
supplies beyond annual increments.

26


RECOMMENDATIONS

1. In view of its cost and inefficiency, weed harvest is not recom-
mended as a method for lowering nutrient supplies in a lake receiving
cultural enrichment. Unless it can remove more than a year's incre-
ment of nutrients from outside sources, it will be inconsequential or
even detrimental to alleviation of undesirable phytoplankton growth,
It could be applied to hasten recovery of an eutrophied lake whose
nutrient source has been significantly curtailed, but annual outside
contributions would have to be low and many weeds in harvestable
situations,

2, Harvesting evidently interferes with weed growth and renewal, and
operation during a second year may be expected to remove much fewer
weeds; thus a few years may need:elapse before the method may be
economically reapplied to an originally justifiable situation, i.e.,
where it could remove more than 1 year's nutrient increment. Justi-
fication may be determined from annual nutrient load entering the
lake, standing harvestable weed crop, and weed nutrient concentration.

3. In order to reach most weeds it would be desirable to have harvest~
ers capable of operating in 2 feet of water,

4. Removal of weeds and fish may hasten "de-eutrophication" after
elimination of nutrient inflow, but the latter appears to be a
mandatory first step for any real success.

5. Where the presence of weeds poses problems, cutting and removal
can apparently bring about improvement for at least one growing season
following the harvest year.


24 AUG 70

2 JUN 70

1.0m
15m

i
oO
gE
o
3
+
3 5 a 2 6 5
NOISSINSNVYUL FOVLNR0Y3d
§ 58
—
Wee =« & é EC dare
&
ge <
® 8
o
° 3
t i Ll f i tT ul
e @e8 ¢s8 @ 2 © & 2 3 E °
NOISSINSNVYL SOVLNS08Sd NOISSINSNYYL FOVLNS0Uad

nm

SEASONAL CHANGES IN WAVE LENGTH PENETRATION

FIGURE 11,


FINDINGS AND CONCLUSIONS

1. Cultural enrichment of Lake Sallie has produced a highly photo-
synthetic lake rich in phytoplankton and attached vegetation.

2. The chemical character of the major water mass is normally that
imparted by photosynthesis, since the rate of decomposition has been
too low to alter upper waters greatly even under ice and snow.

3. Phytoplankton is not dominated by any major group, but its com-
position usually varies with season with one of four groups predomin-
ating. Greatest densities (55,000,000+ per 1) have been achieved by
diatoms; blue-green algae have attained more than 6,000,000 units per
1. Other ranking groups (green algae and Cryptophyceae) have been
much less numerous.

4, The major nutrient source is the Pelican River which receives the
waste water effluents from Detroit Lakes. A progressive downlake
decrease in nutrients is usually evident between the inlet and outlet
of this river, but some variation has occurred.

5. The bulk of nitrogen and phosphorus is usually contained in the
water mass (quantities for weeds the exceptional year are based on
approximations) with considerably lesser amounts in upper sediment
layers and bodies of organisms. The fish population, although less
in mass, has had more contained nutrients than the rooted plant
assemblage,

6. After one year's harvest, density of weeds was about 1/4 as great
the following year and phytoplankton density and photosynthesis
increased.

7. Weed removal plus the annual controlled fish harvest took out insig-
nificant amounts of nitrogen and phosphorus with respect to amounts
brought in annually by the Pelican River.

8. Cost of nutrient removal by weed harvest increased with declining
weed density, e.g., phosphorus from $16 and $199 per pound from 1970
to 1971.

9, Weed harvest can exert little control on phytoplankton unless it
removes more nutrients than are annually contributed from outside
sources, and may actually expedite phytoplankton development if this
condition is not met.

10. Since most nitrogen and phosphorus usually occur in the water mass
they could be expected to decline soon following significant reduction
of nutrients in wastewater entering the Pelican River.


FIGURE 5. TRANSECTS FOR TOWING OXYGEN PROBE

35


similar pattern of variation, but its range was noticeably higher, from
108 to 147 mg/1 in 1970-71. Littoral stations attained greater concen-
trations of both ions under ice cover, and at times in some of those
areas calcium attained greater concentrations than magnesium, These
occurrences suggest that ground water entering this lake system is
normal for this general area in having more calcium than magnesium, and
this has been confirmed by analyses of well water in 1972. Preponder-
ance of magnesium in a lake fed by such ground water indicated photo-
synthesis overshadowing decomposition in magnitude and placing the

more soluble MgCO3, in a more favorable position than CaCO3 to recombine
with CO. This condition has been noted in other eutrophic lakes in
this general area, Both ions increased when CO) appeared in bottom
water at Station 4, but magnesium to a greater extent.

Oxygen

Level of oxygen in Lake Sallie was frequently determined by
photosynthesis and respiration. During open water seasons the entire
lake surface commonly exhibited oxygen pulses with concentration
declining to near zero in the early morning hours and building up to
supersaturated values by early afternoon. Greatest concentration (as
% saturation) was usually produced by macrophytes and attached algae
in the littoral zone (out to 3 m depth), and, as would be expected,
lowest concentrations also frequently occurred in this area, Strati-
fication in summer and winter frequently occasioned oxygen depletion
in deeper waters, but oxygen was always found in surface water, even
under heaviest ice and snow cover, In fact, photosynthetic production
of oxygen occurred at intervals under ice cover, at one time giving an
increase of about 3 mg/1 between sampling dates, although light
measurement consistently indicated no penetration through the ice.
Carbonate alkalinity and pH increase accompanied oxygen elevations, and
there seems no doubt that photosynthesis was operative at those times.
Since photosynthesis occurred between visits it is assumed that light
penetrated ice at times that were missed by the sampling schedule
(Table 2).

Biochemical Oxygen Demand

Maxima of this parameter appeared to normally characterize early
spring, late summer, and autumn in the limmetic zone, but peaks
occurred at other times in Pelican River inflow (Figure 14). Increases
and decreases in BOD were rather closely associated with those of plank-
ton, and it would appear that suspended organisms and their detritus
were major contributors to BOD in the largest lake area.

Nitrogen
Ammonia
This form of nitrogen was consistently present in all areas and

depths sampled in Lake Sallie. In the limmetic zone it was most con-
centrated in deeper waters during summer and winter stagnation (up to

14


CvP = A or B x 0.27 - CP

where
CVP = Carbon fixed by vascular plants and their periphyton (mg/m?)
A= free COj used (mg/m)
B = Carbonate increase + total alkalinity decrease (mg/m) x 0.44
CP = Carbon fixed by plankton (mg/m3)

At the end of incubation a volume of water was taken from the
cylinder for membrane filtration and determination of plankton dry
weight, and all attached vegetation was removed from the cylinder to
ascertain its dry weight.

Weed Harvesting

Weeds were removed with a mechanical cutting, loading and unload-
ing maching (Marine Scavenger Model 258-II) manufactured by Aquatic
Controls Co. This unit has a capacity of 11.363 kg (25,000 lbs.) per
hour, a pay load of 3,636 Kg (8,000 1bs.), a draft of 41-61 cm (16-24
inches), and can cut to a depth of 1.52 m (5 feet). Minimum practical
working depth is about a meter (3.28 ft.). The lake was divided into
9 harvest areas (Fig. 6), and loads removed from each were recorded.
Twenty nine harvester loads were weighted wet, and 0.024 m3 (one cubic
foot) samples removed from them were weighed wet, dried, and reweighed.
Wet harvester load weights divided by wet weights of 0.024 m3 samples
allowed computation of number of cubic units per load (m3 or £t3), Wet
and dry weights of 0.024 m3 samples were then applied to harvester
loads to determine total wet and dry weights removed from each area
and the lake. This size samples were taken from many harvester loads
that were not weighed. Nutrient loads per harvest area and lake were
computed from their concentration in dried samples.

The weed harvester was also used in mapping macrophyte distribution
and determination of standing crop. A standard length of line, floated
and marked at set intervals was used to guide the harvester over a
known area 2.4 x 91 meters (8 x 300'); and any species changes with
distance along each cutting transect could be referred to the nearest
line marker, Chemical sampling sites are shown in Figure 4, locations
of oxygen transects in Figure 5, and weed harvest areas in Figure 6.


10
11
12
13
14

15

16

17

18

19

20

FIGURES

Bathymetric map of Lake Sallie Minnesota

Flow Route of Wastewater Effluent from Detroit
Lakes to Lake Sallie

Glacial Deposits in the Pelican River Watershed
Lake Sallie Sampling Stations

Transects for Towing Oxygen Probe

Weed Harvest Areas in Lake Sallie

Temperature Variation at Surface and 10 Meters
Temperature Variation with Depth, 1971

Position and Thickness of Thermocline 1971, in
Lake Sallie

Annual Variation in Light Intensity at 1 and 3m
Seasonal Changes in Wave Length Penetration 41,
Distribution of Sand in Lake Sallie Sediments
Variation in Surface Water pH at 3 Lake Sallie Sites
BOD Variation at 3 Lake Sallie Stations

Mean Monthly Percentages of Major Phytoplankton
Groups in Surface Water, Station 4

Variation in Limnetic Phytoplankton Concentration
with Depth

Variation in Concentration of Major Plankton Groups
in Surface Water

Seasonal Succession in Concentration of Major Phyto-
plankton Groups in Surface Water at Station 41

Areas with Rooted Vegetation

Gross Primary Production in Limnetic Surface Water
(Station 4)

42,

48,

33
34
35
36
37
38

39

40
43
44
45
46

47

49

50

51

52

53


TABLE 2-~Continued

Depth CO3 HCO3 Total
Date (m) pH Alk. Alk. Hardness Cat+
6 8.80 36 164 186.2 58.8
8 8.05 ie) 220 215.6 78.4
10 7.90 io) 230 225.4 78.4
12 7,60 ie} 228 230.3 88.2
22 January 0 8.80 40 156 196.0 68.6
2 8.80 44 153 196.0 68.6
4 8.80 40 156 196.0 68.6
6 8.70 32 168 205.8 68.6
8 8.10 4 218 235.2 88.2
10 7.80 te) 230 254.8 98.0
6 February le) 8.70 36 170 215.6 68.6
2 8.80 40 168 215.6 68.6
4 8.55 28 185 225.4 68.6
6 8,10 6 225 235.2 78.4
8 8.40 18 199 225.4 68.6
10 7.80 ie) 237 245.0 88.2
il February io) 8.80 48 156 205.8 68.6
2 8.75 36 164 205.8 68.6
6 8.70 32 172 215.6 68.6
8 7.80 8 200 235.2 78.4
12 8.20 ie} 232 254.8 88.2
14 7.50 ie) 254 254.8 98.0
23 April ie) 8.70 34 157 205.8 68.6
2 8.70 32 150 205.8 68.6
4 8.65 34 157 205.8 68.6
8 8.65 34 157 205.8 68.6
10 8.60 32 160 205.8 68.6
14 8.60 32 160 205.8 68.6
30 April 0) 8.70 38 152 215.6 88.2
2 8.65 34 153 215.6 88.2
4 8.65 34 157 215.6 88.2
8 8.65 34 157 215.6 88.2
7 May ie) 8.70 34 155 210.7 68.6
2 8.70 34 155 210.7 68.6
4 8.70 34 155 210.7 68.6
8 8.70 34 155 210.7 68.6
28 May 0 8.70 32 155 205.8 68.6
4 8.70 32 155 205.8 68.6

64


southeast shore, and, when effects of this algicide wore off,
Aphanizomenon was replaced in dominance by Melosira, which achieved
even greater concentrations. Melosira was gradually replaced by
Stephanodiscus, which became dominant in mid-October. This applica-
tion of algicide resulted in diatoms assuming dominance about 2
months earlier than they did in succeeding years (Figure 15).

Variation in Surface Water

Plankton composition, even with regard only to major groups,
exhibited considerable variation at any time in both littoral and
limnetic zones. In August 1969 blue-greens comprised 90% of the
population at Station 1, 10% at Station 2, 5% at Station 4, 2% at
Station 8, and 20% at Station 11. For the same period diatoms were
2% at Station 1, 40% at Station 2, 85% at Station 4, 38% at Station
8, and 40% at Station 11. Greens ranged from 1 - 30% of the popula-
tions at these stations, and other groups from 4 to 30%, In June
1970 (1 series of samples) composition was as follows: Station 1,
42% blue-greens, 58% diatoms; Station 2, 35% blue-greens, 63% diatoms,
others 2%; Station 4, 72% blue-greens, 23% diatoms, 2% greens, 2%
dinoflagellates, and 1% others; Station 8, 25% blue-greens, 65% diatoms,
3% greens, 5% dinoflagellates, and 2% others; and Station 11, 80%
blue-greens, 18% diatoms, and 2% others, Hence, seasonal dominance
varied with location, and neither littoral nor limnetic zone exhibited
any general uniformity.

Variation with Depth

Frequently the group dominant at the surface was also prevalent
all the way down to 10 m, although with as much as 30% variation in
degree of dominance. On other occasions dominance changed to another
group at an intermediate depth and back to the surface dominant in
deepest water, In August 1969 diatoms formed from 90 - 98% of the
population down to 3m, 2% at 5 m (where blue-greens amounted to 98%),
98% at 7 m, and 95% at 5m. Zooplankters were concentrated in deeper
water at times, and Coleps was often conspicuous in these build-ups.
In September 1969 diatoms were dominant and varied from 52% of the
population at 2m to 80% at 8m. Blue-greens, second in abundnace,
varied from 10 to 25% of the populations having both minimum and
maximum values at intermediate depths. Greens had 2% of the population
in deepest water and 15% at 2 m; dinoflagellates ranged from 0 - 15%
of the populations at varied depths, being most numerous at 4 m; and
zooplankters varied from 1 - 18% with most numbers in deepest water,
In summer of 1970 blue-greens were dominant at all depths, but they
were replaced at all levels except 1 m by diatoms in October.

At the generic level variation was often rather marked during
periods of dominance by one of the larger groups. For example, on
July 5, 1971, Aphanizomenon, dominant in upper water, was replaced by
another blue-green, Gomphosphaeria, at 6 m, and by Gomphosphaeria and

19


Lake Sallie is kidney-shaped with its long axis lying north-
east to southwest (Fig. 1), The area lying north of its indentation
(hilus) has a somewhat irregular bottom formed by depressions and
elevations, while that south of the hilus is practically flat below
the shoreline slopes. The deepest area in the lake lies between
these two distinctive areas, east of the indentation. The Pelican
River enters through Muskrat Lake, which was formed by a dam, with
weirs for water level control, across the river inlet. Lake Sallie
has the following dimensions:

Area - 5,30 km? (1309.6 acres)
Length, total - 3,32 km (2.06 mi.)

Width, Maximum - 2.01 km (1.25 mi.)

Depth, Maximum - 16.5 m (55 ft.)
Depth, mean ~ 6.35 m (20,86 ft.)
Volume - 33.7 x 106m3 (1.18 x 109 ft.3)
Shoreline, length - 9.5 km (5.9 mi.)

Shore development - 0.65

Area and volume have the following magnitudes at the listed

depths:
Depth rea Votune

% of
m £t m2 fr2 m3 £3 total
oO - 1.52] 0- 5 | 5,300,000| 57,145,472| 8,069,397 | 284,930,408 | 23.94
1.52 - 3.05 | 5-10 | 4,460,000] 47,998,712] 6,776,281 | 239,270,482 | 20.11
3.05 - 4.57 | 10-15 | 3,410,000] 36,708,996| 5,183,360 | 183,024,441 | 15.37
4.57 - 6.09 15-20 | 3,020,000] 32,545,043] 4,595,619 | 162,271,306 | 13,64
6.09 - 9.14 | 20-30 | 2,660,000] 28,659,848] 8,093,996 | 285,798,998 | 24.04
9.14 - 12.19 | 30-40 290,000| 3,101,187] 875,824 | 30,925,345 2.6d
12.19 - 15.24 | 40-50 30,000] 331,026 93,486 | 3,300,990 0.24
15.24 - 16.50 | 5u-55 10,000 87,112 12,299 434,277 0.04
Totals: | 33,700,262 | 1,189,956,247 100

At the .yinning of this investigation Lake Sallie had luxuriant

summer growths of rooted aquatic plants extending out to the 3 m (10

ft.) contour and some patches of Potamogeton praelongus extending out
to 6m (18 ft.). Weeds covered about 34% of the total bottom area,


Mean percentages of nutrients in dried weeds were:

1970 1971.
P 0.27 0.265
N 2.34 2.46
c 32.25 30.73

In 1970 weeds from Areas 1 and 2 (near the Pelican River inlet)
had noticeably higher percentages of phosphorus and nitrogen than
those from areas farther down lake. This was not true for P in 1971
when quantities available to the harvester in Areas 1 and 2 amounted
to but a small fraction of the mass removed in 1970, but weeds from
Area 1 still had the maximum nitrogen concentration. In the 6 most
productive areas (1970) nitrogen ranged from 3 to 10 times the con-
centration of P, and C varied from 64 - 155 times as great as P; in
1971 N was 4.5 to 10 times as great as P and C from 72 - 132 times.

Removed in Fish

Commercial and sport fishermen took out 76,530 kg of fish (mostly
bullheads) in 1969-70, and 39,129 kg in 1970-71. Mean concentrations
of P, N, and C in tested specimens were 0.53, 2.01, and 9.25%,
respectively, which would indicate that quantities removed were:

1969-70 1970-71
P 406 kg 207 kg
N ‘1,591 kg 786 kg
c 7,109 kg 3,619 kg

Thus, 76,530 kg wet weight of fush contained slightly more than
4 times as much P, more than twice as much N, and slightly more than
2/3 as much C as 428,034 kg, wet weight, of weeds in 1970. In 1971,
39,120 kg wet weight of fish gave almost 10 times the amount of P,
3.15 times the quantity of N, and slightly more C than 111,064 kg,
wet weight, of weeds.

Costs per pound of nutrient removal by weed harvester were:

1970 1971
P 61.19 $198.92
N $ 8,24 21.04
c $ 0.64 $1.62

24


Epithemia zebra (Ehr.) Kutz.
Eunotia sp. Ehr.

Fragillaria capucina Desm.
Fragillaria crotonensis Kitt.
Gomphonema acuminatum Ehr.
Gomphonema sp. Hust.

Gomphonema lanceolatum Ehr.
Gomphonema olivaceum (Lyng.) Kutz.
Gomphonema parvulum (Kutz.)
Navicula cuspidata Kutz.

Navicula sp. Bory

Nitzschia amphibia Grun.
Nitzschia sigmoidea (Ehr.) W. Sm.
Nitzschia sp. Hass.

Rhopalodia sp. O. Mull.
Stauroneis sp. Ehr.

Surirella sp. Turp.

Synedra rumpens Kutz.
Synedra ulna (Nitzsch.) Ehr.

Synedra sp. Ehr.

Division Euglenophyta
Order Euglenales
Euglena sp. Ehr.

Phacus sp. Duj.
Trachelomonas sp. Ehr.

Division Pyrrophyta
Class Dinophyceae
Order Peridiniales
Ceratium hirudinella (O. F. Mull.) Duj

Glenodinium berolinense (Lem.) Lindem.
Peridinium sp. Ehr.

Class Cryptophyceae

Cryptomonas sp. Ehr.

86


The lake is situated in a transition zone between boreal forest
and western prairie, and water quality is somewhat intermediate between
that of the forest and prairie, leaning more toward that of the former,
which is considered hard, whereas that of the prairie region is classed
as alkaline (Moyle, 1945, '56; Allison, 1932). This region has rather
warm summers and cold winters, Over the period 1946-60 mean daily
minimum temperatures occuring in January averaged -15.1°C (4.9°F) and
mean daily maximums recorded in July averaged 21.2°C (70.1°F). During
this time average annual precipitation was 49.86 cm (23.57 in.).
Evaporation exceeds precipitation by about 25.4 cm(10") per year. About
68% of the annual precipitation occurs from May through September. Depth
‘of winter snowfall varies, as does thickness of ice on the lake, depend-
ing upon precipitation, wind, and temperature patterns. In 1968-69 ice
was unsafe for walking on a large central area, but in subsequent winters
it has become thick enough to permit foot and vehicle travel to all parts.

It was assumed that knowledge of major limnological characteristics
prior to and following weed harvest in this lake with a long history of
enrichment would indicate environmental consequences of weed removal as
well as its efficiency in reducing nutrients,


SELECTED WATER 1, Report No. | 2. 3. Accession No.

RESOURCES ABSTRACTS W
INPUT TRANSACTION FORM
4. Title 5. Report Date

WEED HARVEST AND LAKE NUTRIENT DYNAMICS

8 Performing Organization
7. Author(s) Report No.

Neel, Joe K., Peterson, Spencer A., and Smith, Wintfred L. |/% Project No.

). Organization

©

JI, Contract/Grant No.
16010 DFI

13. Type of Report and
Period Covered

Department of Biology
University of North Dakota

12, Sponsoring Organization Environmental Protection Agency

15, Supplementary Notes Environmental Protection Agency report
number EPA-660/3-73-001, July 1973.

16. Abstract After more than sixty years of cultural eutrophication Lake Sallie, Minnesota,
supports dense growths of phytoplankton and rooted vegetation. Its major water mass
has the chemical character imparted by photosynthesis at all seasons, and chemical
effects of decomposition are rather localized. Phytoplankton dominance alternates
among diatoms, blue-green, and green algae in that order of abundance. Prior to
operation of a weed harvester, attached plants grew densely over 34% of the bottom
area. The bulk of nitrogen and phosphorus is usually contained in the water mass,
with noticeably smaller amounts in upper bottom sediments and biota. The fish
population, less than one half the mass of weeds, contained considerable more N
and P than weeds in 1971. Harvest in 1970 evidently reduced weed density in 1971,
and increased the cost per unit of nutrients removed. Nitrogen and phosphorus
removed in weeds were insignificant when compared with annual water borne waste
effluent contributions to the lake. Cost of phosphorus removal by weed harvest
was §61 and $199 per pound in 1970 and 1971, respectively; nitrogen cost $8 and
$21 and carbon $0.6) and $1.62 per pound for the same two years.

17a. Descriptors

* Eutrophication, “Nutrients, Nutrient budgets, Water pollution,
Nutrient distribution in lake water, sediments, biota
Watershed pollution, *Weed harvest and Nutrient Removal

17b.Identifers Eutrophication, Pelican River, Minnesota, “Weed harvest and nutrient
removal

17e. COVSRR Field & Group 05 C

18. Availabilit; 19. Security Class. 21. No. of Send To:
” (Report) Pages
: . j ATER RESOURCES SCIENTIFIC INFORMATION CENTER
20. Security Class. | 22. Price US. DEPARTMENT OF THE INTERIOR
(Page) WASHINGTON, D.C. 20200

a an
Abstractor Joe K, Neel Institution University of North Dakota

WRSIC 102 (REV JUNE 1971) GPO 913.261



TABLES

60


TABLE 2--Continued

Depth C03 HCO3 Total
Date (m) pH Alk. Alk. Hardness Cat+
8 8.50 24 165 225.4 68.6
12 8.40 16 177 225.4 78.4
4 June ie) 8.80 40 152 210.7 83.3
2 8.80 40 152 205.8 73.5
6 8.60 28 164 196.0 73.5
10 8.40 16 179 196.0 68.6
9 June ie} 8.85 36 154 186.2 78.4
2 8.85 38 i55 196.0 73.5
6 8.65 28 167 196.0 78.4
8 8.35 12 184 196.0 68.6
21 June ie} 8.75 32 150 176.4 68.6
2 8.70 28 154 176.4 68.6
4 8.70 28 157 176.4 68.6
8 8.20 4 192 196.0 78.4
12 7.90 0 202 196.0 83.3
29 June ie} 8.80 32 148 186.2 78.4
2 8.80 36 144 181.3 63.7
4 8.80 36 144 186.2 68.6
6 8.70 28 157 186.2 68.6
8 7.80 ie} 202 205.8 78.4
10 7.75 ie} 206 200.9 78.4
7 July 0 8.80 32 145 176.4 63.7
2 8.80 32 145 176.4 58.8
4 8.80 32 144 176.4 58.8
8 8.05 2 187 186.2 68.6
10 7.80 io) 200 200.9 73.5
14 7.70 0 205 200.9 73.5
14 July 10) 8.70 28 136 176.4 58.8
2 8.70 28 135 176.4 63.7
6 8.70 28 138 176.4 63.7
8 7.90 ie) 176 186.2 68.6
10 7.50 ie} 195 200.9 74.4
14 7.40 0 200 205.8 83.3
22 July ie) 8.80 30 135 176.4 63.7
2 8.75 28 136 176.4 63.7
4 8.75 26 137 176.4 68.6
8 8.50 16 152 176.4 68.6
12 8.30 10 160 181.3 68.6

66


period (Figure 10), and no light was observed to penetrate ice cover,
even the minimum (around 24.5 cm or 10 in.) considered safe for
observers. Light penetration during open water seasons was commonly
restricted by trubidity due to plankton growth, especially blue-green
algae near the surface, The 1% level of incident radiation usually
occurred at 3 to 3.5 m, but in autumn sometimes reached 8.5 m. Very
faint light was sometimes detected at 10 m. Penetration of green, blue,
and red wave lengths varied over the seasons, with green and red usually
with greater intensity and range (Figure 11). Red was sometimes notice-
ably stronger than green near the surface, but green usually accounted
for most light intensity at depths of 2 m and greater.

Sediment

Shoal areas, which comprise about 45% of the bottom area, are
largely sand, and deeper areas are largely covered with silt and
clay, having a gyttja consistency when wet (Figure 12). Bars of cobble
sized rocks and sand extend out from shore in some areas,

Chemical Features
Lake Water
Hydrogen Ion Concentration

Surface waters of the limnetic area of Lake Sallie had pH values
well above 8.0 at all seasons during open water and under ice and snow
cover (Figure 13). Deeper water pH fell below 8.0 during summer and
winter stagnation but rose above 8.0 during periods of full circulation.
Littoral areas, especially those affected by ground and surface inflow,
e.g. the Pelican River, Fox and Monson Lake discharges, and Station 9
often had pH below 8.0; but at times had the highest pH recorded (up to
9.7). Low values occurred in winter when anaerobic or nearly anaerobic
waters built up in these areas, and high values in summer with acceler-
ated photosynthesis responding to inflow nutrients, Surface pH in the
limnetic zone rarely exceeded 9.0, reaching 9.2 on a few occasions in
1969.

These pH data indicate a virtual isolation of most upper waters
from areas with greatest decomposition over most of the year, wide-
spread effects of photosynthesis in upper waters, and relatively minor
water volume (in littoral areas and in a few deep pockets) undergoing
pronounced changes due to decomposition. Persistence of high pH in the
absence or near absence of photosynthesis under ice and snow further
attests to the general low level of decomposition. Upon a few occasions
a minor pH increase (0.1 pH) occurred in water in contact with the ice
cover, and it is assumed that these elevations were due to photosynthesis
since they were usually accompanied by slight increases in carbonate and
oxygen. Winter sampling occurred at weekly and biweekly intervals, and
although no light penetration through ice was recorded, it could have

il


concentrations were higher in 1969 than in 1970-and 1971;

Total phosphorus occurrence and variation generally paralleled
those of PO,, but its. concentration was substantially higher. It
increased with depth, declined from winter maxima during the growing
season, and was almost always more concentrated in inflowing-than in
outflowing water. Its level was also greater in 1969 than in 1970
and 1971.

Miscellaneous Water Chemical Features

Sulfate, analyzed infrequently, had generally low levels (6.0 -
7.5 mg/1), but was about 3 times as concentrated (20.5, - 27.5 mg/1)
in inlet and outlet. Reasons for increase at the outlet are unkuown.
Conductivity, measured only once during summer stagnation, showed an
increase with depth, (320 umhos at. 9-.m):and was. greatest in surface
water in Stations 1.and 9, which was not amazing considering greater
mineral content at those stations. Hydrogen sulfide measured at-1 m
intervals down to 15’m at Station 4 on July 8, 1971, occurred only at
8 m and below, increasing from 0.1 at 8 m to 5 mg/1 at 15 m.

The Pelican River above Muskrat Lake usually had more ortho-
phosphate, ammonia, and nitrate nitrogen than this lake's discharge,
but total P was more frequently greater in the discharge. Evidently
a significant share of the PO, entering Muskrat Lake was incorporated
into organic matter before reaching Lake Sallie. , Analyses of the
Pelican River above and below where it receives, the ditch from St.
Clair (see Figure 2) confirmed high nutrient content of- drainage
receiving Detroit Lakes waste water effluent,

Rainwater collected near Station 1. in September and: October 1971
was acidic (pH 3.8-4,2), at times contained PO, (0.25 mg/1). and always
bore nitrogen (NH3-N, .05-.75; NO2-N, .004-.006; NO3-N, .054-.426
mg/1). Ice and snow from atop the lake in November and December 1971
had \.38-.52 mg/1 POg and .053-.414 mg/l NO3-N. Concentrations in the
ice were considerably greater than those in surface water on dates of
collection. Reasons for this increase are only speculative at this
time.

. Samples taken: through ice in the littoral zone in the winters of
1968-1969 and 1969-1970 disclosed a lack of oxygen at Station 9, A
transect run perpendicular to shore. there in March 1970 showed an oxy-
genless condition out to about 90 m from shore, but a rapid increase
to 6.28 mg/l at 105 m,. The anaerobic, zone. also extended. alongshore
for about 100 m on either side of Station 9.

Sediments

Nitrogen and phosphorus were considerably lower in sediments in
shallow than in deeper lake areas, Nitrogen was about 4 times as

16


ICE COVER

ICE COVER

STATION 4 STATION 8 ——

STATION 1—-——

9.57

754

45

1971

1970

FIGURE 13, VARIATION IN SURFACE WATER pH AT 3 LAKE SALLIE SITES


Phylum Tardigrada

Order Eutardigrada

Macrobiotus sp. Schultze
Phylum Arthropoda
Class Arachnida

Order Hydracarina

Larval mites
Class Crustacea

Order Cladocera
Alona affinis (Ley.)
Alona monocantha Sars
Bosmina longirostris (O. F. Mull.)
Ceriodaphnia sphaericus (0. F. Mull.)
Daphnia longiremis Sars
Simocephalus sp. Schgd.

Order Podocopa
Ostracod sp.
Order Eucopepoda
Cyclops sp. O. F. Mull.

Diaptomus sp. Westw.
Nauplii

Miscellaneous
Division Chlorophyta

Volvocalean spores

90


10.

1l.

12,

13.

14,

REFERENCES

Allison, I. S., "The geology and water resources of northwestern
Minnesota," Minn. Geol, Sur. Bull. No. 22, 245 pp. (1932)

American Public Health Association, "Standard methods for the examin-
ation of water and wastewater," 12th ed., New York, 769 pp. (1965)

Bailey, T. A., “Commercial possibilities of dehydrated aquatic plants,"
Proc. So. Weed Conf. 18:543-551 (1965)

Blanchard, J. L., "Aquatic weed harvester operational report," Proc.
So. Weed Conf, 18:477-479 (1965)

Chang, S. C., and M. L. Jackson, "Soil phosphorus fractions in some
representative soils," Jour. Soil Sci. 9:109-119 (1957)

Edmondson, W. T., "Changes in Lake Washington following an increase in
the nutrient income," Verh. Internat. Verein. Limnol. 14:167-175 (1961)

Edmondson, W. T., "Changes in the oxygen deficit of Lake Washington,"
Verh, Internat, Verein, Limnol. 16:153-158 (1966)

Edmondson, W. T., "Lake eutrophication and water quality management:
The Lake Washington Case," In Water Quality Control, Univ. of Washington
Press, Seattle, pp. 139-178 (1968)

Hasler, A. D., "Eutrophication of lakes by domestic drainage," Ecology
28:383-395 (1947)

Koch, F. C., and T. L. McMeekin, "A new direct Nesslerization Micro-
Kjeldahl method and a modification of the Nessler-Fohn reagent for
ammonia," J. Amer, Chem, Soc. 46:2066-2069 (1924)

Krawezyk, D. F., "Analytical techniques for the national eutrophication
research program," Fed. Wat, Poll. Cont. Admn., Pacific Northwest Water
Lab, 141 pp. (1969)

Lange, S. R., "The control of aquatic plants by commercial harvesting,
processing, and marketing," Proc. So, Weed Conf. 18:536-542 (1965)

Larson, W. C., "Spray irrigation for the removal of nutrients in sewage
treatment plant effluent as practiced at Detroit Lakes, Minnesota,"
Trans, 1960 Seminar: Algae and Metropolitan Wastes, U. S. DHEW,
Cincinnati, Ohio, pp. 125-129 (1961)

Livermore, D. F., "Harvesting underwater weeds," Waterworks Eng.
107:118-121 (1954)

28


occurred between sampling dates. There was usually a slight pro-
gressive decline in surface water pH with time under ice cover in the
limnetic zone, with a few interruptions occasioned by rare. periods of
photosynthesis.

Alkalinity
Carbonate

As may be inferred from the above account of pH, carbonate occurred
in surface waters of the limmetic zone at all seasons, was absent from
deeper waters during summer and winter stagnation, and from some littoral
areas at intervals, Its concentration reached 100 mg/1 (as caco3) in
Muskrat Lake discharges and attained 48 mg/l in the limnetic zone. It
increased slightly under ice cover when pH and oxygen changes indicated
photosynthesis, as would be expected.

Bicarbonate

This ion had its minimum recorded concentration in surface waters
of the limnetic zone when photosynthesis was most pronounced and achieved
its maxima for this zone in deeper waters during winter stagnation. The
most recorded in the limnetic zone was 230 mg/1 during winter, but Stations
9 and 21 in the littoral zone and Station 1 in Muskrat Lake discharge
often exhibited higher values under ice. The highest recorded value was
428 mg/1 at Station 9 in January 1971. That area appeared to receive
considerable ground water during winter, or this water was more isolated
there under ice. During open water seasons photosynthesis was noted to
reduce bicarbonate to 124 mg/l in surface water of the limnetic zone.
In most waters this much bicarbonate would provide sufficient CO, for
photosynthesis and there seems no reason to suspect that it would be
limiting in Lake Sallie,

Hardness

Total hardness varied above and below total alkalinity in concen-
tration suggesting that at times cations other than those contributing
hardness were combined with carbonate and bicarbonate. From October
1968 until June 1969 hardness continually exceeded alkalinity in surface
water of the limnetic zone, but this was not true for the remainder of
that growing season, nor for the 1969-70 winter, nor for the 1970 open
water period. In autumn of 1970 and early in the 1970-71 winter hard-
ness overshadowed alkalinity in upper limnetic water, but alkalinity
pulled even in late December and went ahead in early January. , Hardness
came to the fore again in early February and was thereafter greater
than alkalinity until early June 1971, when it fell slightly below. It
became dominant again in late June and remained so through December 31,
1971, The hardness maximum recorded in surface limnetic water during
1970-71 was 225 mg/l, whereas that of alkalinity was 206 mg/1. Minimums
during the same period were 167 hardness and 149 for alkalinity. Alka-~
linity exceeded hardness by as much as 8 mg/1, but hardness was greater

12


Il

rly

TTA TS TON MT oD AS TOT NAT Mg Ty TAS TOT

rr ar ae
°o
$8 3 3

e ¢ ¢ & g@ g ¢
3 °° °
© o vv mM & 2

(4U/g41/98W) NOILONGOYd AMWWIYd L3N (44/g4/96w) NOILVIdS3y

1971

1970

1969

NET PRIMARY PRODUCTION AND RESPIRATION RATES WITHIN THE PHOTIC ZONE AT STATION 4

FIGURE 23,


21

22

23

24

25

26

Average Gross Primary Production in the Limnetic
Photic Zone

Net Primary Production and Respiration Rates in
Surface Water at Station 4

Net Primary Production and Respiration Rates within
the Photic Zone at Station 4

Vertical Variation in Gross Primary Production on
Selected Dates at Station 4

Variation in Incident Solar Radiation (Langleys)
and Hourly Change in Primary Production Rate at
Station 4, June 24, 1971

Photosynthetic Efficiency at Station 4 During 1971

54

55

56

57

58

59


Order Heliozoa

Actinosphaerium sp. Stein

Class Ciliata

Order Holotricha

Coleps sp. Nitz.
Cyclidium sp.
Didinium sp. Stein
Enchelys sp.
Frontonia sp. Ehr.

Lacrymaria sp. Ehr.

Prorodon sp. Ehr.
Saprophilus sp. Stokes
Trachelophullum sp. Clap. and Lach

Order Spirotricha

Caenomorpha sp.
Codonella sp. Haeck.

Euplotes sp. Ehr.

Halteria sp. Duj.

Oxytricha sp. Ehr.

Strombidium sp. Clap. and Lach.
Strombilidium sp. Schew.
Stylonchia sp. Ehr.

Order Peritricha

Epistylis sp. Ehr.
Thuricola sp.

Vaginicola sp. Lam.
Vorticella sp. L.

Order Suctoria

Acineta sp. Ehr.
Tokophyra sp. Buts.

Phylum Nematoda

Nematode sp.

88


SON

LAKE ENE

Sod

PARK

e
g N AUDUBON® S4DETROIT
? e S J TES LAKES
LAKE
= A\IW 3Y SALLIE
s

CLAYEY MORAINE .f

q

Lf
\

UTWASH GRAVEL

KE) SANDY MORAINE

DS

Lage _
CBZ

PELICAN RIVER

OES MOINES
TILL WATERSHED

FIGURE 3. GLACIAL DEPOSITS IN THE PELICAN RIVER
WATERSHED (A) TOPOGRAPHIC (B) CROSS-
SECTIONAL. (REDRAWN FROM ALLISON, 1932)

33


Loapine site=/\

FROM FOX
LAKE

FIGURE 6, WEED HARVEST AREAS IN LAKE SALLIE

36