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
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EPA-660/3-73-001
July 1973
WEED HARVEST AND LAKE JJUTRIENT 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
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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.
11
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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.
111
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CONTENTS
SECTION
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
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
Acknowle dgmen t s
References
Figures
Tables
Appendices
PAGE
1
2
3
4
7
10
10
10
11
18
25
26
27
28
30
60
82
v
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FIGURES
No. Pag6
1 Bathymetric map of Lake Sallie Minnesota 31
2 Flow Route of Wastewater Effluent from Detroit 32
Lakes to Lake Sallie
3 Glacial Deposits in the Pelican River Watershed 33
4 Lake Sallie Sampling Stations 34
5 Transects for Towing Oxygen Probe 35
6 Weed Harvest Areas in Lake Sallie 36
7 Temperature Variation at Surface and 10 Meters 37
8 Temperature Variation with Depth, 1971 38
9 Position and Thickness of Thermocline 1971, in 39
Lake Sallie
10 Annual Variation in Light Intensity at 1 and 3m 40
11 Seasonal Changes in Wave Length Penetration 41, 42, 43
12 Distribution of Sand in Lake Sallie Sediments 44
13 Variation in Surface Water pH at 3 Lake Sallie Sites 45
14 BOD Variation at 3 Lake Sallie Stations 46
15 Mean Monthly Percentages of Major Phytoplankton 47
Groups in Surface Water, Station 4
16 Variation in Limnetic Phytoplankton Concentration 48, 49
with Depth
17 Variation in Concentration of Major Plankton Groups 50
in Surface Water
18 Seasonal Succession in Concentration of Major Phyto- 51
plankton Groups in Surface Water at Station 41
19 Areas with Rooted Vegetation 52
20 Gross Primary Production in Limnetic Surface Water 53
(Station 4)
vi
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21 Average Gross Primary Production in the Limnetic 54
Photic Zone
22 Net Primary Production and Respiration Rates in 55
Surface Water at Station 4
23 Net Primary Production and Respiration Rates within 56
the Photic Zone at Station 4
24 Vertical Variation in Gross Primary Production on 57
Selected Dates at Station 4
25 Variation in Incident Solar Radiation (Langleys) 58
and Hourly Change in Primary Production Rate at
Station 4, June 24, 1971
26 Photosynthetic Efficiency at Station 4 During 1971 59
vn
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TABLES
No. Page
1 Mean Temperature and Precipitation Recorded at 61
Detroit Lakes, Minnesota
2 Vertical Variation in Water Chemistry at Station 4, 62, 63
Lake Sallie, Minnesota 64, 65, 66
67, 68, 69
70, 71
3 Nitrogen, carbon, and phosphorus concentration in 72, 73
sediments collected from shallow and deep water
areas of Lake Sallie, Minnesota
4 Acid-Soluble phosphorus of air dried sediments 74
from Lake Sallie
5 Total Kjeldahl nitrogen of sediments, Lake Sallie, 75
Minnesota
6 Concentration of certain elements in various aquatic 76, 77
plants, Lake Sallie, Minnesota, September 16., 1968
7 Chemical analyses of aquatic macrophytes from certain 78
areas in Lake Sallie
8 Primary productivity of submerged vascular plants and 79. 80
associated plankton
9 Water and nitrogen and phosphorus budgets in Lake 81
Sallie 1968-69 to 1970-71
Vlll
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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.
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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.
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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 (Easier, 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, 'bo, '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 Grossman (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
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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 known
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 297o,
forests 2370, and urban and residential areas 37o.
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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 km2 (1309.6 acres)
Length, total - 3.32 1cm (2.06 mi.)
Width, Maximum - 2.01 Ion (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
m ft
0 - 1.52
1.52 - 3.05
3.05 - 4.57
4.57 - 6.09*"
6.09 - 9.14
9.14 - 12.19
12.19 - 15.24
15.24 - 16.50
0- 5
5-10
10-15
^.5-20
20-30
30-40
40-50
5U-55
Area
m2 ft2
5,300,000
4,460,000
3,410,000
3,020,000
2,660,000
290,000
30,000
10,000
57,145,472
47,998,712
36,708,996
32,545,043
28,659,848
3,101,187
331,026
87,112
Totals :
Volume
m3 ft3
8,069,397
6,776,281
5,183,360
4,595,619
8,093,996
875,824
93,486
12,299
33,700,262
284,930,408
239,270,482
183,024,441
162,271,306
285,798,998
30,925,345
3,300,990
434,277
1,189,956,247
% of
total
23.94
20.11
15.37
13.64
24.02
2.6C
0.28
0.04
100
At the ^ginning 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 6 m (18 ft.). Weeds covered about 34% of the total bottom area.
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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.
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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. All analyses except total P and N03
were according to Standard Methods, 12th edition (A.P.H.A., 1965).
Total phosphorus was according to Krawczyk (1969) , and NO^ 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
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was extracted w'.uh G.GNHcl, and, after filtering 'and dilution, tested
with standard reagents. Twenty eight samples of 11 species of macro-
phytes had Ca, Mg, Na, K, Co, Gu, 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 metho'd '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
harvester.
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 CC^j 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:
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CVP = A or B x 0.27 - CP
where
CVP = Carbon fixed by vascular plants and their periphyton (mg/m3)
A = free CC^ used (mg/m3)
B = Carbonate increase + total alkalinity decrease (mg/m3) 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 258-11) manufactured by Aquatic
Controls Co. This unit has a capacity of 11.363 kg (25,000 Ibs.) per
hour, a pay load of 3.636 Kg (8,000 Ibs.), 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 ft3). 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.
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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 8 m 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 7o of surface irradiation)
at depths of 1 and 3 m varied during open water seasons over the 3 year
10
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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
11
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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 limnetic 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 CaCO^) in
Muskrat Lake discharges and attained 48 mg/1 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/1 in surface water of the limnetic zone.
In most waters this much bicarbonate would provide sufficient C02 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. t 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,
19.71. The hardness maximum recorded in surface limnetic water during
1970-71 was 225 mg/,1, 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
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then alkalinity by as much as 25 mg/1.
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/1 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/1 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/1 (Table 2). Greatest concentrations noted
were in deep water during times of stagnation. Magnesium exhibited a
13
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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 MgCO^ in a more favorable position than CaCC^ to recombine
with CC>2. This condition has been noted in other eutrophic lakes in
this general area. Both ions increased when C02 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
7o 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 limnetic 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 limnetic zone it was most con-
centrated in deeper waters during summer and winter stagnation (up to
14
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2.6 mg/1 in summer and to 1.5 mg/1 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
nearly always greater than 0.1 and usually more than 0.2 mg/1 (Table
2).
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/1 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 thermodines (Table 2).
Nitrate
Nitrate was most concentrated at all depths under ice cover,
when the maximum observed concentration (0.34 mg/1) occurred in surface
water at 3 stations. Vertically in the limnetic 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/1 maximum was in the hypolimnlon 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 limnetic zone surface
(1.4 mg/1) occurred in September 1969. Surface values there were
usually less than 0.20 mg/1. Orothophosphate was consistently higher
in inflowing than in outflowing water^ declining to zero in the latter
for about 30 consecutive davs in Julv and August 1971. Surface water
15
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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 unknown.
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.
Glair (see Figure 2) confirmed high nutrient content of- drainage
receiving Detroit Lakes waste water effluent.
Rainwater collected near Stat,ion 1 in September and- October 1971
was acidic (pH 3.8-4.2), at times contained PO^ (0.25 mg/l)-and always
bore nitrogen (NH3-N, .05-.75; N02-N, .004-.006; N03-N, .054-.426
mg/1). Ice and snow from atop the lake in November and December 1971
had .38-.52 mg/1 P04 and .053-.414 mg/1 N03-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/1 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
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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
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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),
cryptophyceans (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
2 m, 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-'1.
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
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southeast shore, and, when effects of this algicide wore off,
Aphanizomenon was replaced in dominance by Melosira, which achieved
even greater concentrations, frlelosira 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 3 m, 2% at 5 m (where blue-greens amounted to 98%),
98% at 7 m, and 95% at 5 m. 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 2 m to 80% at 8 m. 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
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Coleosphaerium, still another blue-green, at 8 m. 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 99.770 of the total population. Diatoms
were also dominant in surface and near surface waters, but their con-
centrations were somewhat less, being 50,657,500 per 1 at the surface
and 42,802,600 at 2 m. 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.
£. crispus L.
P_. filiformis var. Macounii Marong.
P_. pectinatus L.
£. praelongus Wulf.
20
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_P. Richardsonii (Benn.) Rydb.
Ruppia maritima L.
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 (3470 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
21
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of +10 rag 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 limnetic zone than at Station 1 or in
Muskrat Lake. Variation among stations in the limnetic 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
780 mg C/m3/hr and that attributable to plankton from -119 to 503 mg
C/m /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
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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
1
2
3
4
5
6
7
8
9
Total
1970
97,853
138,119
105,351
5,770
19,856
47,430
673
3,336
9,616
428,034
1971
6,578
1,928
31,477
1,850
54,711
14,520
0
0
0
111,064
Dry weight of weeds removed amounted to 30,371 kg (66,816 Ibs.)
in 1970 and 10,366 kg (22,805 Ibs.) in 1971. Kilograms of nutrients
taken out with weeds were as follows:
1970
1971
Phosphorus
Nitrogen
Carbon
100
721
10,699
26
248
3,219
23
-------
Mean percentages of nutrients in dried weeds were:
1970 1971
p
N
c
0.27
2.34
32.25
0.265
2.46
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:
P
N
C
1969-70
406 kg
1,591 kg
7,109 kg
1970-71
207 kg
786 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:
P
N
C
1970
$61.19
$ 8.24
$ 0.64
1971
$198.92
$ 21.04
$ 1.62
24
-------
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
Water
Phosphorus
Nitrogen
Inflow m^
3
Outflow m
Inflow kg
Outflow kg
Inflow kg
Outflow kg
1968-69
20,197,256
22,716,382
10,140*
5,810*
11,650
9,720
1969-70
17,858,188
19,087,138
7,470**
2,510**
5,594
2,640
1970-71
17,849,207
20,807,164
15,643**
7,758**
10,567
7,217
* Soluble P
** Total P
1 NH3 - N + N02 - N + N03 - 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:
P
N
1968-69
2,270*
24,740
1969-70
9,690**
5,070
1970-71
16,513**
21,231
* Soluble P
** Total P
25
-------
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 c 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
P
N
C
347,545
1,980
7,210
30,340
212,090
1,220
4,270
18,006
594,740
3,152
11,594
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 C.
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
-------
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 Survey, 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
s amp1e s.
Close estimates of weeds were greatly aided by the excellent
cooperation of Carl Aarness, harvester operator.
The project was supported by a grant (16010 DPI) 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
-------
REFERENCES
1. Allison, I. S., "The geology and water resources of northwestern
Minnesota," Minn. Geol. Sur. Bull. No. 22, 245 pp. (1932)
2. American Public Health Association, "Standard methods for the examin-
ation of water and wastewater," 12th ed., New York, 769 pp. (1965)
3. Bailey, T. A., "Commercial possibilities of dehydrated aquatic plants,"
Proc. So. Weed Conf. 18:543-551 (1965)
4. Blanchard, J. L., "Aquatic weed harvester operational report," Proc.
So. Weed Conf. 18:477-479 (1965)
5. Chang, S. C., and M. L. Jackson, "Soil phosphorus fractions in some
representative soils," Jour. Soil Sci. 9:109-119 (1957)
6. Edmondson, W. T. , "Changes in Lake Washington following an increase in
the nutrient income," Verh. Internat. Verein. Limnol. 14:167-175 (1961)
7. Edmondson, W. T., "Changes in the oxygen deficit of Lake Washington,"
Verh. Internat. Verein. Limnol. 16:153-158 (1966)
8. 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)
9. Hasler, A. D. , "Eutrophication of lakes by domestic drainage," Ecology
28:383-395 (1947)
10. 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)
11. Krawczyk, D. F. , "Analytical techniques for the national eutrophication
research program," Fed. Wat. Poll. Cont. Admn., Pacific Northwest Water
Lab, 141 pp. (1969)
12. Lange, S. R., "The control of aquatic plants by commercial harvesting,
processing, and marketing," Proc. So. Weed Conf. 18:536-542 (1965)
13. 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)
14. Livermore, D. F., "Harvesting underwater weeds," Waterworks Eng.
107:118-121 (1954)
28
-------
15. Minder, L., "Biologisch - chemische untersuchungen in Zurichsee,"
Rev. d'Hydrologie 3:1-69 (1926)
16. Minder, L., "Der Zurichsee als eutrophierungsphanomen. Summarische
ergebnisse aus funfzig jahren Zurichseeforschung," Geol. Meere
Binnegewasser 2(2):28-299 (1938)
17. Minder, L. , "Neuere untersuchungen uber den sauerstoffgehalt und die
eutrophie des Zurichsees," Arch. f. Hydrobiol. 40(1):279-301 (1943)
18. Moyle, J. B. , "Classification of lake waters upon the basis of hardness,"
Proc. Minn. Acad. Sci. 13:8-12 (1945a)
19. Moyle, J. B. , "Some chemical factors influencing the distribution of
aquatic plants in Minnesota," Amer. Midi. Nat. 34:402-420 (1945b)
20. Moyle, J. B., "Relationships between chemistry of Minnesota surface
waters and wildlife management," J. Wildl. Mgmt. 20:303-320 (1956)
21. Olson, Donald, Personal communication (1971, '72)
22. 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)
23. 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)
24. Sawyer, Co N., "Fertilization of lakes by agricultural and urban
drainage," Jour. N.E. Water Works Ass'n. 61:109-127 (1947)
25. 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)
26. Strickland, J. D. H. and T. R. Parsons, "A manual of sea water analysis,"
Fish. Research Board of Canada, viii + 203 pp. (1965)
27. 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)
28. Wright, H. E., Jr., "Role of the Wadena Lobe in Wisconsin glaciation
of Minnesota," Geol. Soc. Amer. Bull. 73:73-100 (1962)
29. Yount, J. L. , "Aquatic nutrient reduction-potential and possible methods,"
Rep. of Florida Anti-Mosquito Ass'n., (35th Annual Meeting) St. Augustine,
Florida (1964)
30. Yount, J. L. and R. A. Grossman, Jr., "Eutrophication control by plant
harvesting," Jour. Water Poll. Cont. Fed., Res. Suppl. 42:R173-R183
(1970)
29
-------
FIGURES
30
-------
FROM FOX
LAKE
VSKRAT
LAKE
0 660 ISZO
SCALE IN FEET
0 250 500
SCALE IN METERS
FIGURE 1. BATHYMETRIC MAP OF LAKE SALLIE,
MINNESOTA.
31
-------
STABILIZATION
LAGOON
CITY OF
DETROIT
LAKES
WASTE
TREATMENT
PLANT
SCALE IN METERS
FIGURE 2.
FLOW ROUTE OF WASTEWATER EFFLUENT FROM
DETROIT LAKES TO LAKE SALLIE.
32
-------
LAKE
PARK
UDUBON*
CLAYEY MORAINE
OUTWASH GRAVEL
ETROIT
LAKES
LAKE
SALLIE
VERGAS
(a)
km
FERGUS FALLS
(b)
-ALEXANDRIA MORAINIC COMPLEX
DES MOINES
TILL
PELICAN RIVER
WATERSHED
FERGUS FALLS
"•—MORAINE
FIGURES. GLACIAL DEPOSITS IN THE PELICAN RIVER
WATERSHED (A)TOPOGRAPHIC (B) CROSS-
SECTIONAL. (REDRAWN FROM ALLISON, 1932)
33
-------
FROM FOX
PELICAN
IVER
FIGURE 4, LAKE SALLIE SAMPLING STATIONS
34
-------
FIGURE 5, TRANSECTS FOR TOWING OXYGEN PROBE
-------
LOADING SITE
FROM FOX
LAKE
PELICAN
RIVER
FIGURE 6. WEED HARVEST AREAS IN LAKE SALLIE
36
-------
r ^
u
LU
20-
LU
Q_
LJ
o-
i ri^
SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
1969
1970
FIGURE 7, TEMPERATURE VARIATION AT SURFACE AND ID METERS
-------
SURFACE
6m
12m
00
I ICE COVEfT
FIGURE 8, TEMPERATURE VARIATION WITH DEPTH, 1971
-------
2-
3-
4-
5-
6-
18-
j
9-
10-
12-
13-
14-
i r
APRIL 30 MAY 31 JUNE 30 JULY 31 AUGUST 31
FIGURE 9, POSITION AND THICKNESS OF THERMXLINE DURING
OPEN WATER SEASON, 197L IN LAKE SALLIE
39
-------
I METER DEPTH
3 METER DEPTH
35
30H
25
20
15
10-1
\/
««
o
H 45
o 40-
j 35
uj 30-
<£ 25-
fe 20
= IS
- '?
CD 5
£ 0J
UJ
o
u 35-i
°- 30-
25-
20-
15-
10-
5-
0
/N
25305 10 20 31 10 20 30 10 20 31 10 20 31 10 20 30 10 20 31 10 20 30
APRIL MAY JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER
FIGURE ID, ANNUAL VARIATION IN LIGHT INTENSITY AT 1 AND 3 M,
-------
2 JUN 70
24 AU6 70
CO
CO
CO
&
£
at
ui
70-
60-
50-
40-
30-
20-
10-
0
40-i
0,5m
LOm
1,5m
486
538
nm
617
24 APR 71
0.5m
400
40-1
§30-1
CO
CO
s
CO
2
<
a:
f- 20-
UJ
UJ
u
a:
ff ioH
627
0.5m
486 538 617
nm
FIGURE 11, SEASONAL CHANGES IN WAVE LENGTH PENETRATION
41
-------
60-i
24 JUN 71
50-
40-
30-
20-
400
0.5m
627
FIGURE 11, CONTINUED
42
-------
50-
20 AUQ 71
0.5m
.Om
400
627
FIGURE II, CONTINUED
43
-------
USKRAT
LAKE
>75% SAND
SAND
FIGURE 12, DISTRIBUTION OF SAND IN LAKE SALLIE SEDIMENTS
44
-------
9.5-1
ICE COVER
[ICE COVER"
STATION I STATION 4
STATSON 8
9.0-
X
Q.
8.5^
8.0
7.5-
7.0-
N D J F
1970
M
N
1971
FIGURE 13, VARIATION IN SURFACE WATER pH AT 3 LAKE SALLIE SITES
-------
10-
9-
8-
7-
-------
ICE COVER
ICE COVER
BLUE-GREENS
DIATOMS
GREENS
0 ' H ' D
1971
FIGURE 15, MEAN MONTHLY PERCENTAGES OF MAJOR PHYTOPLANKTON GROUPS
IN SURFACE WATER/ STATION 4
-------
cr
UJ
z
<
co
10,000;
5,000-
500-
100
10,000;
5,000:
l,000r
500-
CO
ZD
o
I-
100:
50-
1969
1970
SURF
METER
— 2 METERS
—• 3 METERS
APR ' MAY ' JUN ' JUL ' AU6 ' SEP ' OCT '
FIGURE 16, VARIATION IN LIMNETIC PHYTOPLANKTON
CONCENTRATION AT DIFFERENT DEPTHS
48
-------
IOO,OOO-i
ICE COVER
HCE COV.
10,000-
1,000-
100-
— SURFACE
— 4 METERS
— 8 METERS
N" D
1970
J'F'M'A'M'J'J
A ' S 0 N D
1971
FIGURE 16, CONTINUED
49
-------
lO.OOOg
o:
LU
1,000:
100:
CO
Z)
o
X
10=
BLUE-GREEN ALGAE
GREEN ALGAE
DIATOMS
ANIMALS
JUL rAUG ' SEP ' OCT NOV**MAY JUN JUL
V
SEP OCT
1969
1970
FIGURE 17, VARIATION IN CONCENTRATION OF MAJOR PLANKTON
GROUPS IN SURFACE WATER
-------
100,000-1
10,000-
tr
LU
1,000-
en
;}
o
I
100-
IICE cov. I
BLUE-GREEN ALGAE
GREEN ALGAE
DIATOMS
s
N
1970
1971
FIGURE 18. SEASONAL SUCCESSION IN CONCENTRATION OF
MAJOR PHYTOPLANKTON GROUPS IN SURFACE WATER
AT STATION 4,
51
-------
\
V
EXTENT OF
ROOTED
VEGETATION
SCIRPUS
POTAMOGETON
8 RUPPIA
MYRIOPHYLLUM
U^MUSKRAT
LAKE
FIGURE 19, AREAS WITH ROOTED VEGETATION
52
-------
Ul
OJ
650-1
600-
10
Q
uj 500-
X
o
CD
QC.
S 400-
9
J
>-
H
E 300-
o
cc
a,
E 200-
a
a.
co
co
g 100-
&
1 S ' 0
1969
N
J ' A ' S
1970
N
M
J ' A
1971
FIGURE 20, GROSS PRIMARY PRODUCTION IN LIMNETIC SURFACE WATER (STATION
-------
650-,
Ul
-P-
AIS'OIN"MIJIJIAIS'OIN"AIMIJIJIAISIOIN
FIGURE 21, AVERAGE GROSS PRIMARY PRODUCTION IN THE LIMNETIC PHOTIC ZONE (STATION
-------
600-1
o
500-
f
1 400-
o
1 300-
200-
g- 100-
100-
PO
6.
200-
2 300-
©
<
a,
yj
400-
0
N
A
M
1970
J A
1971
FIGURE 22, NET PRIMARY PRODUCTION AND RESPIRATION RATES IN SURFACE WATER AT STATION 4
-------
*E 600-j
o
a>
•i. 500
z
o
1- 400-
o
o
g SCO-
IS 200-
cc
Q- 100-
t-
U-H-lh
10 100-
o
I 200-J
300-
IT
a. 400H
co
o:
AISIOIN"MIJIJIAISIOIN"A'MIJIJ ' A ' s ' o '
1969 1970 1971
FIGURE 23. NET PRIMARY PRODUCTION AND RESPIRATION RATES WITHIN THE PHOTIC ZONE AT STATION
-------
mg C fixed/mVhr
-100
0
m
o
100
200
400
600
800
2-
4-
6J
13 JUL 69
15 AUG 69
25 AUG 69
-100 0 100 200
I I i
mg C fixed/m3/hr
400
600
i
800
m
2-
4-
6-
8-
10-
2 JUN 70
16 JUL 70
24 AUG 70
mg C fixed/mVhr
0-
m
2-
4-
6J
200
i
400
600
I
30 JUN 71
20 AUG 7!
SEP 71
FIGURE 24, VERTICAL VARIATION IN GROSS PRIMARY PRODUCTION
ON SELECTED DATES AT STATION 4
57
-------
00
100-
w80-
jc
\
ro
E
*^X,
T3
E
40-
i-\
! \
! %
I \GROSS.PRIMARY PRODUCTION
I l >*•
' \
1 »
1 '
N-_.
1
I
1
I
H
i
i
i
i
i
i
i
i
tS
w
* '~\
\'
' fa« LAN6LEYS
I t
1 I .
1 I h
, * ! VM/
\ |5 V
\ |t ' f i
\' ' \'
V i /SJ
t 1 /
k
-------
50.00
2O-
JC -
"-S
ro
E
O
UJ
X
g "0-
cc
O
o>
E
BASED UPON MEAN VALUE WITHIN PHOTIC ZONE
BASED UPON SURFACE VALUE
APRIL
MAY
JUNE
JULY
AUGUST
SEPTEMBER
OCTOBER
FIGURE 26, PHOTOSYrrmETIC EFFICIENCY AT STATION 4 DURING 1971
-------
TABLES
60
-------
TABLE 1
MEAN TEMPERATURE AND PRECIPITATION RECORDED
AT DETROIT LAKES, MINNESOTA
1946-1960a
Month
January
February
March
April
May
June
July
August
September
October
November
December
Total
Mean
Temp.
(°0
-15.1
-12.9
- 5.5
4.5
12.2
17.7
21.2
19.7
13.9
7.4
3.1
-11.2
Mean
Precip.
(cm)
1.80
1.73
2.51
5.13
7.59
9.63
9.09
9.53
4.98
3.48
2.49
1.80
59.76
1969b
Mean
Temp.
(°0
-18.3
-10.5
- 8.8
8.1
12.4
13.6
19.1
21,1
14.1
9.5
- 1.7
- 8.9
Precip.
(cm)
4.17
2.01
0.30
2.74
5.61
11.10
2.11
5.97
7.42
4.53
2.69
51.34
1970b
Mean
Temp.
(°C)
-16.5
-13.7
- 8.7
3.8
11.2
18.6
20.8
19.2
14.3
6.6
3,7
-12.4
Precip.
(cm)
0.41
0.66
2.34
7.29
4.63
13.72
3.94
0.69
6.88
5.92
1.07
1.98
49.53
1971b
Mean
Temp.
(°0
-18.7
-11.9
- 6.3
6.9
10.8
18.5
17.5
18.1
14.2
8.6
- 2.2
-11.1
Precip.
(cm)
1.88
2.34
1.83
2.13
4.01
13.44
11.48
6.96
17.07
11.43
3.05
0.64
66.22
1969-1971
Mean
Temp.
<°0
-17.8
-12.0
- 7.9
6.3
11.5
16.9
19,1
19.5
14.2
8.2
- 0.1
-10.8
Precip.
(cm)
2.15
1.67
1.49
4.05
4.75
13.58
8.84
3.25
9.97
8.26
2.27
1.77
62.05
aModified 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,
bU.S. Dept. of Commerce, Climatological data.
-------
TABLE 2
VERTICAL VARIATION IN WATER CHEMISTRY AT STATION 4, LAKE
SALLIE, MINNESOTA (Concentrations, except pH, in ppm)
r
Depth
Date (m)
3,970
10 October 0
2
5
8
11
23 October 0
4
8
12
6 November 0
3
6
9
13 November 0
4
8
19 December 0
2
4
6
8
12
29 December 0
4
8
1971
7 January 0
2
4
pH
8.85
8.80
8.80
8.90
8.90
8.75
8.75
8.75
8.75
8.80
8.80
8.80
8.80
8.85
8.85
8.85
9.00
8.90
8.90
8.90
8.60
8.25
8.90
8.90
8.30
9.00
8.90
8.85
co3
Alk.
40
40
40
36
40
32
32
32
32
36
34
34
34
40
40
40
44
48
48
44
24
8
44
44
12
44
40
40
HC03
Alk.
126
136
136
140
138
142
142
142
142
137
140
140
138
134
134
134
142
140
140
146
178
227
150
146
193
160
154
155
Total
Hardness
166.6
166.6
166.6
186.2
176.4
186.2
186.2
186.2
186.2
186.2
176.4
176.4
176.4
186.2
186.2
186.2
196.0
186.2
186.2
186.2
196.0
225.4
196.0
196.0
196.0
196.0
186.2
186.2
Ca++
58.8
58.8
58.8
58.8
58.8
68.6
58.8
58.8
58.8
58.8
58.8
58.8
58.8
58.8
58.8
58.8
58.8
58.8
58.8
58.8
68.6
78.4
58.8
58.8
68.6
68.6
58.8
58.8
62
-------
TABLE 2—Continued
Mq++
107.8
107.8
107.8
107.8
117.6
117.6
127.4
127.4
127.4
127.4
117.6
117.6
117.6
127.4
127.4
127.4
137.2
127.4
127.4
127.4
127.4
147.0
137.2
137.2
127.4
127.4
127.4
127.4
°2
8.62
8.62
8.53
8.53
8.82
10.00
9.90
9.90
9.11
12.40
12.40
12.30
12.20
13.20
13.20
13.20
16.07
14.31
14.31
13.56
9.99
6.47
15.48
14.99
6.66
15.20
15.10
13.10
Ortho
P04
0.18
0.25
0.25
0.12
0.25
0.12
0.18
0.12
0.12
0.12
0.25
0.12
0.12
0
0.11
0.11
0
0
0
0
0
0.06
0.05
0
0
0.18
0.05
0
Total
P04
0.76
1.28
0.76
1.00
1.00
0.62
1.14
0.76
0.76
0.76
0.76
0.50
0.50
0.50
0.36
0.36
0.24
0.12
0.12
0.24
0.24
0.50
0.10
0.24
0.24
0.24
0.24
0.24
NH3-N
0.09
0.10
0.10
0.40
0.11
0.15
0.15
0.12
0.10
0.92
0.97
0.92
0.79
0.48
0.38
0.37
0.25
0.49
0.12
0.20
0.49
0.38
0.27
0.25
0.32
0.23
0.18
0.20
N02-N
0.006
0.004
0.006
0.004
0.006
0.008
0.008
0.006
0,006
0.010
0.008
0.008
0.010
0.012
0.010
0.008
0.008
0.006
0.008
0.006
0.006
0.015
0.008
0.004
0.006
0.006
0.008
0.008
N03-N
0.020
0.008
0,009
0.013
0.011
0.007
0.009
0.009
0.011
0.007
0.009
0.004
0.005
0
0.007
0.004
0.010
0.006
0.010
0.009
0.011
0.020
0.004
0.004
0.009
0.011
0.009
0.009
Temp.
°c
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
5.5
5.5
5.5
5.5
3.5
3.5
3.5
0
1.0
1.0
1.0
2.0
2.5
1.0
2.0
3.0
1.0
2.0
2.0
63
-------
TABLE 2—Continued
Depth
Date (m)
6
8
10
12
22 January 0
2
4
6
8
10
6 February 0
2
4
6
8
10
11 February 0
2
6
8
12
14
23 April 0
2
4
8
10
14
30 April 0
2
4
8
7 May 0
2
4
8
28 May 0
4
pH
8.80
8.05
7.90
7,60
8.80
8.80
8.80
8.70
8.10
7.80
8.70
8.80
8.55
8.10
8.40
7.80
8.80
8.75
8.70
7.80
8.20
7.50
8.70
8.70
8.65
8.65
8.60
8.60
8.70
8.65
8.65
8.65
8.70
8.70
8.70
8.70
8.70
8.70
co3
Alk.
36
0
0
0
40
44
40
32
4
0
36
40
28
6
18
0
48
36
32
8
0
0
34
32
34
34
32
32
38
34
34
34
34
34
34
34
32
32
HC03
Alk.
164
220
230
228
156
153
156
168
218
230
170
168
185
225
199
237
156
164
172
200
232
254
157
150
157
157
160
160
152
153
157
157
155
155
155
155
155
155
Total
Hardness
186.2
215.6
225.4
230.3
196.0
196.0
196.0
205.8
235.2
254.8
215.6
215.6
225.4
235.2
225.4
245.0
205.8
205.8
215.6
235.2
254.8
254.8
205.8
205.8
205.8
205.8
205.8
205.8
215.6
215.6
215.6
215.6
210.7
210.7
210.7
210.7
205.8
205.8
Ca++
58.8
78.4
78.4
88.2
68.6
68.6
68.6
68.6
88.2
98.0
68.6
68.6
68.6
78.4
68.6
88.2
68.6
68.6
68.6
78.4
88.2
98.0
68.6
68.6
68.6
68.6
68.6
68.6
88.2
88.2
88.2
88.2
68.6
68.6
68.6
68.6
68.6
68.6
64
-------
TABLE 2—Continued
.
Mg++
127.4
137.2
147.0
142.1
127.4
127.4
127.4
137.2
147.0
156.8
147.0
147.0
156.8
156.8
156.8
156.8
137.2
137.2
147.0
156.8
166.6
156.8
137.2
137.2
137.2
137.2
137.2
137.2
127.4
127.4
127.4
127.4
142.1
142.1
142.1
142.1
137.2
137.2
°2
12.00
5.70
4.20
2.60
14.90
15.10
13.60
11.80
5.90
2.00
13.33
12.84
11.47
6.27
8.82
3.43
14.00
12.50
11.20
6.60
5.00
0
13.90
13.90
13.90
13.90
13.72
13.72
12.25
12.54
12.44
12.44
12.00
12.00
12.00
12.00
11.60
11.80
Ortho
P04
0
0.32
0.12
0.25
0.25
0.18
9.63
0.25
0.18
0.18
0.12
0
0
0.38
0.25
0.25
0.12
0.19
0.25
0.38
0.38
0.25
0.06
0.06
0.12
0.06
0.06
0.12
0
0
0
0.06
0.05
0.05
0
0.05
0
0
Total
P04
0.22
0.24
0.50
0.76
0.38
0.24
0.24
0.38
1.02
0.62
0.38
0.24
0.24
0.64
0.50
0.64
0.10
0.28
0.28
0.76
0.76
1.02
0.30
0.30
0.50
0.30
0.30
0.50
0.24
0.24
0.24
0.36
0.24
0.10
0.10
0.24
0.24
0.10
NH3-N
0.20
0.28
0.30
0.37
-
-
-
-
-
-
0.16
0.16
0.23
0.55
0.40
0.46
0.20
0.22
0.26
0.28
0.32
0.20
0.40
0.31
0.36
0.44
0.28
-
1.15
1.28
1.28
1.41
0.48
0.59
0.43
0.39
0.15
0.19
NO2-N
0.006
0.012
0.008
0.008
0.008
0.012
0.017
0.012
0.030
0.35
0.023
0.026
0.030
0.026
0.028
0.026
0.019
0.024
0.024
0.024
0.028
0.021
0.004
0.008
0.006
0.004
0.004
0.006
0.004
Oc004
0.004
0.004
0.001
0.004
0.004
0.004
0.001
0.004
NO3-N
0.006
0.014
0.014
0.014
-
0
-
-
-
-
0.011
0.008
0.011
0.015
0.011
0.035
0.009
0.004
0.01]
0.050
0.058
0.109
0.004
0
0.002
0.007
0.007
0.005
0.004
0.004
0.004
0.004
0.007
0.004
0.004
0.004
0.007
0.004
Temp.
°C
2.5
2.5
3.0
3.0
1.0
2.0
2.0
3.0
3.0
3.5
0.0
2.0
1.5
2.0
3.0
3.0
1.0
2.0
2.5
3.0
4.0
4.0
7.5
7.0
7.0
7.0
7.0
7.0
7.0
7.5
7.5
7.5
12.0
12.0
11.5
9.5
11.5
10.5
65
-------
TABLE 2—Continued
Depth
Date (m)
8
12
4 June 0
2
6
10
9 June 0
2
6
8
21 June 0
2
4
8
12
29 June 0
2
4
6
8
10
7 July 0
2
4
8
10
14
14 July 0
2
6
8
10
14
22 July 0
2
4
8
12
PH
8.50
8.40
8.80
8.80
8.60
8.40
8.85
8.85
8.65
8.35
8.75
8.70
8.70
8.20
7.90
8.80
8.80
8.80
8.70
7.80
7.75
8.80
8.80
8.80
8.05
7.80
7.70
8.70
8.70
8.70
7.90
7.50
7.40
8.80
8.75
8.75
8.50
8.30
C03
Alk.
24
16
40
40
28
16
36
38
28
12
32
28
28
4
0
32
36
36
28
0
0
32
32
32
2
0
0
28
28
28
0
0
0
30
28
26
16
10
HCO3
Alk.
165
177
152
152
164
179
154
155
167
184
150
154
157
192
202
148
144
144
157
202
206
145
145
144
187
200
205
136
135
138
176
195
200
135
136
137
152
160
Total
Hardness
225.4
225.4
210.7
205.8
196.0
196.0
186.2
196.0
196.0
196.0
176.4
176.4
176.4
196.0
196.0
186.2
181.3
186.2
186.2
205.8
200.9
176.4
176.4
176.4
186.2
200.9
200.9
176.4
176.4
176.4
186.2
200.9
205.8
176.4
176.4
176.4
176.4
181.3
Ca++
68.6
78.4
83.3
73.5
73.5
68.6
78.4
73.5
78.4
68.6
68.6
68.6
68.6
78.4
83.3
78.4
63.7
68.6
68.6
78.4
78.4
63.7
58.8
58.8
68.6
73.5
73.5
58.8
63.7
63.7
68.6
74.4
83.3
63.7
63.7
68.6
68.6
68.6
66
-------
TABLE 2—Continued
Mg++
156.8
147.0
127.4
132.3
122.5
127.4
107.8
122.5
117.6
127.4
107.8
107.8
107.8
117.6
112.7
107.8
117.6
117.6
117.6
127.4
122.5
112.7
117.6
117.6
117.6
127.4
127.4
117.6
112.7
112.7
117.6
126.5
122.5
112.7
112.7
112.7
112.7
112.7
°2
9.20
7.20
11.10
11.70
8.80
4.80
10.00
10.20
6.20
3.40
8.90
8.60
8.00
1.40
0.10
9.70
9.60
9.60
5.90
0.20
0.10
8.10
8.20
7-70
1.40
0.20
0
7.52
7.52
6.53
0.40
0
0
8.89
8.48
7.88
3.23
1.21
Ortho
P04
0
0.05
0
0
0
0
0
0
0
0
0
0.12
0.05
0
0.12
0.05
0
0.12
0.05
0.19
0.12
0.12
0
0.12
0.18
0.32
0.32
0.12
0.12
0.12
0.25
0.51
0.77
0
0
0
0.11
0.11
Total
P04
0.24
0.64
0.24
0.10
0.24
0.50
0.24
0.36
0.24
0.24
0.36
0.24
0.50
0.24
0.24
0.24
0.24
0.12
0.24
0.24
0.50
0.24
0.50
0.36
0.36
0.50
0.50
0.50
0.64
0.50
0.50
1.02
1.16
4.86
0.36
0.36
0.50
0.50
NH3-N
0.27
0.27
0.38
0.27
0.25
0.33
0.32
0.33
0.40
0.40
0.36
0.36
0.31
0.48
1.18
0.28
0.28
0.31
0.33
0.74
0.82
0.36
0.37
0.39
0.77
1.08
1.33
0.33
0.37
0.46
1.11
2.07
2.60
0.32
0.32
0.36
0.74
0.81
NO2-N
0.004
0.004
0.004
0.004
0.001
0.004
0.001
0
0.001
0.004
0.004
0
0
0
0
0.004
0.004
0.004
0.001
0.004
0.001
0.001
0.001
0.001
0.001
0.017
0.004
0.004
0.001
0
0.001
0
0
0.001
0.004
0.001
0.004
0.006
NO3-N
0.004
0.006
0.004
0.004
0.007
0.004
0.005
0.006
0.005
0
0.004
0.008
0.008
0.012
0.012
0.002
0.002
0.002
0.007
0.002
0.005
0.007
0.009
0.007
0.007
0.008
0.004
0.004
0.005
0.006
0.003
0.004
0.004
0.005
0.004
0.005
0,002
0.002
Temp.
°C
10.0
10.0
18.0
15.0
13.0
13.0
17.0
17.0
14.0
14.0
22.5
22.5
22.0
16.0
15.5
22.0
22.0
22.0
20.0
16.0
16.0
23.0
23.0
22.5
19.0
18.0+
17.0
21.0
21.0
21.0
18.5
17.0
17.0
21.0
21.0
21.0
20.0
20.0
67
-------
TABLE 2—Continued
Depth
Date (m)
14
29 July 0
2
4
8
14
12 August 0
2
4
8
14
25 August 0
6
14
4 September 0
2
4
8
14
12 September 0
8
14
17 September 0
8
14
24 September 0
2
8
14
1 October 0
8
14
8 October 0
4
8
14
15 October 0
8
ph
8.10
8.70
8.65
8.65
8.65
8.65
8.90
8.90
8.90
8.60
8.25
8.70
8.70
8.05
8.85
8.85
8.80
8.70
8.55
8.70
8.70
8.50
8.70
8.70
8.70
8.90
8.85
8.70
8.70
8.70
8.50
8.30
8.55
8.55
8.55
8.50
8.80
8.80
C03
Alk.
4
20
20
20
20
20
36
34
32
18
6
26
26
2
30
30
28
24
16
24
24
16
28
28
26
36
34
26
26
28
14
4
16
16
16
14
34
34
HCO3
Alk.
166
142
142
141
143
144
124
127
127
147
165
135
133
167
129
129
130
136
150
137
138
148
133
132
139
129
131
139
141
137
151
156
146
146
147
149
131
131
Total
Hardness
181.3
176.4
176.4
176.4
176.4
176.4
166.6
166.6
166.6
176.4
186.2
176.4
176.4
181.2
176.4
176.4
176.4
176.4
181.3
176.4
176.4
176.4
181.3
176.4
176.4
181.3
181.3
181.3
186.2
181.3
181.3
181.3
186.2
181.3
181.3
176.4
186.2
186.2
Ca++
68.6
68.6
68.6
68.6
68.6
63.7
58.8
58.8
58.8
58.8
68.6
63.7
58.8
68.6
63.7
58.8
58.8
58.8
58.8
58.8
58.8
63.7
53.9
58.8
58.8
68.6
68.6
68.6
68.6
73.5
73.5
73.5
73.5
68.6
68.6
68.6
68.6
68.6
68
-------
TABLE 2—Continued
Mg++
112.7
107.8
107.8
107.8
107.8
112.7
107.8
107.8
107.8
117.6
117.6
112.7
117.6
112.6
112.7
117.6
117.6
117.6
122.5
117.6
117.6
112.7
127.4
117.6
117.6
112.7
112.7
112.7
117.6
107.8
107.8
107.8
112.7
112.7
112.7
107.8
117 .6
117.6
°2
0.20
7.33
7.33
7.23
7.13
7.13
8.90
8.80
8.80
3.30
0.20
6.60
6.40
0
8.12
7.92
7.72
6.14
2.48
6.70
6.60
3.70
7.80
7.70
6.00
10.60
10.00
6.80
7.10
9.50
5.60
2.70
9.29
9.29
9.09
8.99
11.40
10.30
Ortho
P04
0.11
0
0
0
0
0
0
0
0
0.05
0.52
0.11
0.11
0.60
0.25
0.05
0.25
0.14
0.32
0
0.19
0.26
0.12
0.12
0.25
0.09
0.09
0.09
0.12
0.05
0.05
0.36
0.12
0.12
0.12
0
0.12
0.05
Total
P04
0.50
0.36
0.50
0.50
0.50
0.50
0.50
0.36
0.50
0.50
0.64
0.50
0.50
0.92
0.92
0.64
0.92
0.64
0.64
0.59
0.64
0.52
0.64
0.78
0.92
0.64
0.64
0.64
0.92
0.64
0.78
0.64
0.64
0.64
0.64
0.52
0.28
0.50
NH3-N
1.00
0.31
0.33
0.33
0.31
0.31
0.15
0.25
0.22
0.56
0.95
0.54
0.54
1.69
0.32
0.33
0.38
0.45
0.94
0.42
0.43
0.67
0.26
0.39
0.50
0.01
0.01
0.01
0.01
0.18
0.35
0.47-
0.23
0.25
0.25
0.19
0.13
0.13
N02-N
0.006
0
0.001
0
0.001
0.001
0
0
0
0.004
0.004
0.004
0.002
0
0.002
0.004
0
0.003
0.003
0.005
0.004
0.006
0.004
0.004
0.004
0.002
0.002
0.002
0.004
0.005
0.004
0.004
0.005
0.004
0.004
0.004
0.004
0.002
NO3-N
0
0.007
0.003
0.004
0.005
0.005
0.012
0.21
0.017
0.024
0.015
0.017
0.015
0.012
0.019
0.017
0.021
0.025
0.018
0.005
0.006
0.011
0.011
0.008
0.008
0.017
0.013
0.019
0.020
0.020
0.026
0.033
0.012
0.013
0.013
0.013
0.013
0.015
Temp.
°C
20.0
18.0
18.0
18.0
18.0
18.0
20.5
20.5
20.5
19.0
18.0
20.0
20.0
19.0
21.0
21.0
21.0
20.0
20.0
19.0
19.0
19.0
17.0
17.0
17.0
15.0
14.5
14.0
14.0
17.0
15.0
14.0
12.0
12.0
12.0
12.0
10.0
10.0
69
-------
TABLE 2—Continued
Depth
Date (m)
14
22 October 0
5
10
29 October 0
6
13
12 November 0
4
8
12
11 December 0
5
10
22 December 0
5
10
14
31 December 0
5
10
14
PH
8.75
8.80
8.80
8.55
8.60
8.60
8.60
8.15
8.55
8.25
7.20
8.65
8.50
7.55
8.40
8.30
7.60
7.50
8.40
8.20
7.50
7.50
C03
Alk.
32
34
34
20
20
24
24
6
20
8
0
28
20
0
16
16
0
0
18
12
0
0
HCO3
Alk.
132
129
129
144
146
140
140
162
149
156
158
156
164
192
177
182
196
205
187
192
202
202
Total
Hardness
186.2
176.4
176.4
176.4
186.2
186.2
186.2
196.0
196.0
186.2
205.8
215.6
215.6
215.6
225.4
207.7
205.8
215.6
225.4
215.6
205.8
225.4
Ca++
68.6
58.8
58.8
68.6
68.6
68.6
er ,6
68.6
68.6
78.4
68.6
78.4
78.4
78.4
88.2
88.2
78.4
88.2
88.2
88.2
88.2
88.2
70
-------
TABLE 2—Continued
Mg++
117.6
117.6
117.6
117.6
117.6
117.6
117.6
127.4
127.4
107.8
137.2
137.2
137.2
137.2
137.2
119.5
127.4
127.4
137.2
127.4
117.6
137.2
°2
10.20
12.90'
12.40
6.80
9.40
9.40
9.30
13.80
13.30
11.80
5.20
14,80
13.20
1.80
14.40
12.80
1.00
0.60
13.00
11.80
0.80
0.40
Ortho
P04
0
0.05
0
0
0
0.05
0
0
0.12
0.09
0.12
0.19
0.19
0.12
0.01
0.01
0
0
0.25
0.25
0.12
0.12
Total
P04
0.50
0.24
0.24
0.50
0.38
0.50
0.38
0.38
0.66
0.56
0.50
0.38
0.38
0.24
0.02
0.01
0.01
0.01
0.24
0.50
0.38
0.38
NH3-N
0.13
0.11
0.12
0.12
0.12
0.16
0.21
0.15
0.13
0.15
0.15
0.06
0.09
0.15
0.09
0.15
0.30
0.38
0.22
0.24
0.32
0.46
N02-N
0.002
0.004
0.004
0.004
0
0.006
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.006
0.010
0.006
0.012
0.006
0.008
0.006
0
0
N03-N
0.013
0.014
0.011
0.014
0.013
0.007
0.009
0.011
0.011
0.011
0.011
0.013
0.030
0.018
0.025
0.051
0.018
0.011
0.039
0.050
0.021
0.015
Temp
°C
10.0
12.0
11.0
10.5
9.0
9.0
9.0
2.0
2.0
2.0
3.0
2.0
2.5
3.5
1.5
2.0
3.5
4.0
1.5
2.0
3.5
4.0
71
-------
TABLE 3
NITROGEN, CARBON, AND PHOSPHORUS CONCENTRATION IN SEDIMENTS COLLECTED FROM
SHALLOW3 AND DEEPb WATER AREAS OF LAKE SALLIE, MINNESOTA
Date
1968
September 28
October 19
November 2
November 16
1969
February 7
April 26
June 6
August 17
Stations
1,
3,
1,
3,
1,
3,
1,
4,
1,
3
1,
3,
1,
4,
1,
3,
2, 12
4
2, 8,
5, 6,
8, 9,
4, 5,
2, 7
5, 6
2, 8,
2, 8,
4, 5,
2, 8,
5, 6,
2, 8,
4
9, 12
10, 11
12
6, 10, 11
9
9, 12
6, 10, 11
9, 12
10, 11
12
H2O Sol. P
mg/kg
10
10
30
20
45
13
34
13
27
• •
• •
.20
• •
.
• •
.40
.40
.54
.82
.52
.66
.17
.58
Total P
g/kg
0.72
1.17
0.43
1.41
0.37
1.49
0.80
1.42
0.27
1.43
0.30
1.25
0.32
1.35
0.27
0.77
Component
Ca-P Al-P
mg/kg
125.
22.
•
175.
•
f
•
136.
407.
150.
349.
206.
391.
125.
295.
90 0.09
80 0.14
. .
60 0.08
. .
• • •
. .
00 0.19
00 0.20
00 0.03
20 0.07
50 0.04
30 0.10
67 . .
00 . .
Fe-P
6.93
14.30
• •
1.96
• •
. .
• •
0.51
9.51
3.66
6.17
3.56
9.04
3,14
6.19
Total N
0.64
2.40
0.37
1.40
0.37
1.43
0.85
1.40
0.08
• •
0.18
1.25
0.47
1.51
0.22
0.85
Carbon
5.16
13.65
4.54
14.86
3.85
15.01
9.33
14.73
4.29
• •
4.49
16.97
5.21
15.01
2.20
9.88
-------
TABLE 3—Continued
UJ
Date
September 28
November 15
1970
January 25
May 22
July 10
Stations
1,
4,
1,
3,
1,
4
1,
4
1,
2, 8, 9
5, 6
2, 12
4
8, 9, 12
9, 12
8, 9, 12
H20 Sol. P
mg/kg
6.
49.
12.
26.
9.
16.
7.
52.
11.
89
90
00
35
70
70
32
40
91
Total P
g/kg
0.
1.
0.
0.
0.
0.
0.
1.
0.
23
35
25
90
23
70
25
46
31
Component
Ca-P Al-P
mg/kg
102.
407.
124.
290.
144.
200.
175.
492.
128.
18 . .
33 . .
33 . .
00 . .
75 . .
00 . .
33 . .
00 . .
15 . .
• • •
Fe-P
0.86
8.94
2.23
5.94
1.29
6.38
2.75
• •
2.64
Total N
%
0.40
1.42
0.27
0.86
0.20
0.80
0.20
1.40
0.25
Carbon
%
2,19
15.16
2.47
8.90
2.91
9.88
1.77
15.30
2.69
aUpper row of values per each date.
Lover row of values per each date.
-------
TABLE 4
ACID-SOLUBLE PHOSPHORUS (AS PO4~P) OF AIR DRIED SEDIMENTS
FROM LAKE SALLIE, MINNESOTA, EXPRESSED AS
GRAMS PER KILOGRAM OF SEDIMENTS
—i
-O
7 November 1970
19 December 1970
18 March 1971
8 May 1971
25 June 1971
21 July 1971
30 October 1971
10 December 1971
31 December 1971
1
0.5
0.37
-
0.50
0.14
0.45
1.33
0.19
-
-
3 4
9.0 16.5
1.30 1.24
1.22
-
1.63
1.47
1.28 1.75
0.83
-
1.18
Station
678
Depth (m)
7.5 1.0 0.5
0.51 0.29
0.24
0.34
1.57 - 0.15
1.23 0.30 0.16
1.16 0.35 1.57
0.24
0.19
_ _ _
9
0.5
0.28
0.23
-
0.30
0.29
0.42
0.30
0.26
-
12
0.3
0.31
0.42
0.27
0.38
0.26
0.29
0.18
0.30
-
21
0.3
0.33
0.41
0.39
0.31
0.16
0.21
0.33
0.52
-
-------
TABLE 5
TOTAL KJELDAHL NITROGEN, AS PERCENTAGE OF DRY WEIGHT
OF SEDIMENTS, LAKE SALLIE, MINNESOTA
Date
7 November 1970
19 December 1970
18 March 1971
8 May 1971
25 June 1971
21 July 1971
30 October 1971
10 December 1971
31 December 1971
1
0.5
0.29
-
0.13
0.06
0.36
0.88
0.09
-
-
3 4
9.0 16.5
1.15 1.98
1.23
-
1.30
0.85
1.13 0.80
0.48
-
1.07
Station
678
Depth (m)
7.5 1.0 0.5
0.13 0.33
0.18
0.17
1.28 - 0.10
1.38 0.15 0.13
2.00 0.17 0.55
0.50
0.11
- - -
9
0.5
0.09
0.07
-
0.08
0.08
0.12
0.10
0.11
-
12
0.3
0.13
0.21
0.11
0.11
0.08
0.08
0.08
0.09
-
21
0.3
0.11
0.17
0.26
0.12
0.11
0.10
0.11
0.11
-
-------
TABLE 6
CONCENTRATION OF CERTAIN ELEMENTS IN VARIOUS AQUATIC PLANTS
FROM LAKE SALLIE, MINNESOTA, SEPTEMBER 16, 1968
Plant
Part
1/3 Concentration
-------
TABLE 6 —Continued
Plant Description
Potamogeton
Microcystis
Periphyton
richardsonii
scum
removed
from Vallisneria
Plant
Part
1/3
Q)
a T3 s ' • '
Oi -r-l O
P S >J p N C H
x 0.33 2.8 27.9 3.7 45
x 0.31 2.8 27.3 3.7 44
x 0.34 2.5 25.7 3.2 44
N.A.a 0.72 8.1 43.0 6.2 3
N.A. 0.46 2.7 22.9 3.8 46
Concentration
Ca
.0
.0
.0
.9
.0
Mg
3.2
3.2
2.7
2.0
3.7
Na
0.70
0.80
1.10
0.60
0.36
K Co
5.0 0.100
5.5 0.009
9.0 0.009
3.5 0.018
1.5 0.022
mg/g
Cu
0.015
0.024
0.020
0.023
0.023
Fe
0.870
0.940
1.040
0.780
1.06
Mn
0.441
0.451
0.270
0.223
0.510
Mo
<0.065
<0.065
<0.065
<0.065
-------
00
TABLE 7
CHEMICAL ANALYSIS OF AQUATIC MACROPHYTES FROM
SELECTED AREAS IN LAKE SALLIE, MINNESOTA
Date
12 July 1971
20 July 1971
27 July 1971
30 July 1971
5 August 1971
10 August 1971
10 August 1971
16 August 1971
16 August 1971
16 August 1971
16 August 1971
Sample
Transect 3-1
Transect 5-2
Area 3
Transect 1-1
Area 6
Transect U-l
Transect 5-3
Transect 6-1
Transect 6-1
Transect 6-1
Transect 6-1
Remarks
Almost entirely Potamogeton pectinatus
Mixture of Ruppia maritiuia and
P. pectinatus
From 0.283 TO. sample
Mixture of Myriophyllum exalbescens
and P. pectinatus
From 0.283 m^ sample
Mixture of M. exalbescens and
P. pectinatus
Mixture of M. exaTbescens and
P. pectinatus
0-15 m from Pelican R. , mostly
M. exalbescens
30-^5 m from Pelican R., mostly
M. exal~bescens
75-90 m from Pelican R. ,
M. exalbescens and P. pectinatus
90-105 m from Pelican R., mostly
P. pectinatus
Total
C
g/kg
336
311
29^
286
250
305
315
307
305
328
312
Total
N
g/kg
18.3
23.7
21.0
28.7
2^.0
23.7
21.3
25.3
25.0
28.3
25.3
Total
P
g/kg
2.25
2.60
2.135
2,lh
2.5^
2.295
2.165
2.515
3.02
2.50
2.683
-------
TABLE 8
PRIMARY PRODUCTIVITY OF SUBMERGED VASCULAR PLANTS AND
ASSOCIATED PLANKTON, LAKE SALLIE, MINNESOTA
Date
12 August 1970
19 August 1971
20 August 1971
5 September 1971
Location Time
Ac 1100-1145
1145-1600
Bd 2230-0800
Bd 1100-1500
1500-2030
2030-1130
Ce 0715-0915
0915-1215
1215-1415
1415-1615
1615-1815
Totala
1187
587
- 375
713
250
- 411
238
475
119
475
0
Net
Production
Rooted Plank-
Plants21 tona
780
84
-375
475
216
-388
119
158
-119
237
0
407
503
0
238
43
- 24
119
317
238
238
0
Rooted
Plants13 Planktonb
_
-
-6.0
7.6
3.5
-6.2
3.7
5.0
3.7
7.4
0
_
-
0
68.0
12.3
- 6.9
92.2
245.7
184.5
184.5
0
10 September 1971
1700-1900
- 119
-119
- 41.9
-------
TABLE 8—Continued
Net Production
Date Location Time
11 September 1971 Df 0700-0900
0900-1200
1200-1530
Totala
178
911
950
Rooted
Plantsa
0
594
679
Plank-
tona
178
317
271
Rooted
Plantsb
0
15.2
17.4
Plankton
62.7
111.6
95.4
00
o
amg C/m3/hr.
bmg C/g dry weight/hr.
C250 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
P. pectinatus and R. maritima (43.5 g combined dry wt) . Dominant algae were M. aeruginosa,
A. spiroides and Lyngbya sp. (17.5 mg/1 dry wt). Depth 1 m.
e25 m NW of Station 1. Enclosed M. exalbescens (31.9 g dry wt). Dominant alga was
O_. curviceps (12.9 mg/1 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/1
dry wt). Depth 1.1 m.
-------
TABLE 9
WATER AND NITROGEN AND PHOSPHORUS BUDGETS IN LAKE SALLIE 1968-69 TO 1970-71
WATER YEAR
A.
B.
C.
D.
E.
In Lake Sallie
Water
Weeds
Fish
Sediment
Total
Input
Pelican R.
Fox Lake
Monson L.
Total
Outflow
Net Gain
or Loss
(B-C) to
Lake
Removed by
Harvest
Fish
Weeds
Total
1968-69
Total Total Water Total
N P Flow N
kg kg m xlC)6 kg
24,740 2,270* - 5,070
- - - 8,149**
7,210 1,980 - 4,270
1,014 95 - 748
32,494 4,345 - 21,412
11,360 10,020 18.96 5,590
200 80 0.78 180
90 20 0.48 80
11,650 10,140 20.22 5,850
9,720 5,810 22.71 2,640
1,930 4,330 -2.49 3,210
1,590
- - - 721
- - - 2,311
1969-70
Total Water
P Plow
kg m3x!06
9,690
1,038**
1,220
73
12,415
7,060 16.77
310 0.66
100 0.41
7,470 17.84
2,510 19.08
4,960 -1.24
406
100
506
Total
N
kg
21,231
2,810
11,594
738
36,729
10,568
393
217
11,178
7,217
3,961
786
248
1,034
1970-71
Total
P
kg
16,513
358
3,152
89
20,112
15,169
305
169
15,643
7,758
7,885
207
26
233
Water
Flow
m3x!06
-
-
-
-
—
16.88
0.62
0.35
17.85
20.81
-2.96
-
-
* Soluble P
**Approximation from
1971 standing crop data and 1970 harvest.
-------
APPENDIX
82
-------
LIST OF PLANKTERS OBSERVED 1968-71
Bacteria
Division Schizophyta
Class Schizomycetes
Sphaerotilus natans Kutz.
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 planetonica (W. and W.) Lem.
Sphaerocystis Schroeteri Chod.
Order Ulotrichales
Stichococcus bacillaris Naeg.
83
-------
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.
Selenastrurn 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.
Order Zygnematales
Closterium moniliforme (Bory) Ehr.
84
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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
Stephanodi scus astraea (Ehr.) Grun.
Stephano discus astraea var. minutula (Kutz.) Grun
Order Pennales
Amphiprora sp. Ehr.
Asterionella 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
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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. 0. 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. P. Mull.) Duj
Glenodinium berolinense (Lem.) Lindem.
Peridinium sp. Ehr.
Class Cryptophyceae
Cryptomonas sp. Ehr.
86
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Division Cyanophyta
Class Myxophyceae
Order Chroococcales
Aphanocapsa sp. Naeg.
Aphanothece nidulans Naeg.
Chroococcus cispersus (Keissl.) Lem.
Chroococcus limneticus Lem.
Coelosphaerium dubiurn Grun.
Coelosphaerium Kutzingianum Naeg.
Coelosphaerium Naegelianum Ung.
Dactylococcopsis Smithii Chod. and Chod,
Gomphosphaeria aponina Kutz.
Marssoniella elegans Lem.
Merismopedia punctata Meyen
Microcystis aeruginosa Kutz.
Microcystis flos-aquae (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.
Phormidium sp. Kutz.
Spirulina major Kutz.
Animals
Phylum Protozoa
Class Sarcodina
Order Testacea
£ejvt£0pyxis aculeata (Ehr.) Stein
Difflugia sp. Lecl.
Difflugia lebes Pen.
87
-------
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.
Stronibilidium 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.
-------
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
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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 (O. F. Mull.)
Daphnia longiremis Sars
Simocephalus sp. Sch0d.
Order Podocopa
Ostracod sp.
Order Eucopepoda
Cyclops sp. O. F. Mull
Diaptomus sp. Westw.
Nauplii
Miscellaneous
Division Chlorophyta
Volvocalean spores
90
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Division Eumycophyta
Fungal spores
Division Tracheophyta
Pollen grains
Phylum Rotifera
Rotifer eggs
Phylum Annelida
Class Oligochaeta
Aeolosoma sp. (eggs)
Phylum Arthropoda
Class Crus_tacea
Order Cladocera
Ephippia
frU.S. GOVERNMENT PRINTING OFFICE: 1973-540-309/44 1-3 91
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Report So.
3. Accession No,
w
4. Title
WEED HARVEST MD LAKE NUTRIENT DYNAMICS
7. Author(s)
Neel, Joe K., Peterson, Spencer A., and Smith, Wintfred L.
S. Organization
Department of Biology
University of North Dakota
12. Sponsoring Organization Environmental Protection Agency
is. Supplementary Notes Environmental Protection Agency report
number EPA-660/3-73-001, July 1973.
5. Report Date
S.
S. Performing Organization
Report No.
10. Project No.
11. Contract I Grant No.
16010 DFI
13. Type of Report and
Period Covered
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 3W 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 $0.61; 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
i?b. Identifiers Eutrophication, Pelican River, Minnesota, Weed harvest and nutrient
removal
17c. COISRR Field & Group Q5 C
18. Availability
19. Security Class.
(Report)
20. Security Class.
(Page)
21. No. of
Pages
22. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OFTHE INTERIOR
WASHINGTON. D. C. 20240
Abstractor Joe ft. Neel
\institutiop University of North Dakota
WRSIC102(REV JUNE 1971)
EP 0 913.251
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