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In Lake Geneva Switzerland, the whitefish population was
restored, game fish increased, and the water clarified by stocking,
eliminating overfishing, and reducing phosphate input.
The Sand Lake Observer
Vol. 1, No. 4,
May 20, 2012
The Draw of Big Sand: Wisconsin, to our Native Americans, means a good place to live. A big factor is
the abundant lakes: one twenty-fifth of our area is covered by water. In Burnett County, Big Sand is the
second largest lake. Food and clothing was supplied by its abundant fish, rice, and animals. As European
settlers moved in, fishing provided a respite for vacationers from the south. Then as resorts gave way to
summer homes, the lake was prized for its clear water, clean beaches, and the north-woods experience.
Abundant small panfish along with an occasional lunker sustained interest in fishing.
Changes: During the transition between subsistence and recreation over the twentieth century,
changes were substantial. But they were often unnoticed because they were gradual. Culverts under
Highway 70 and Sand Lake Road allowed easy spearing of walleye and suckers. Altered drainage to the
south reduced flow through Sand Creek. Farms and cabins added phosphate increasing the amount of
living material in the lake. And selective harvesting of big fish reduced the size distribution of all. These
and other changes affected how the lake functions in basic ways.
Gainers and Losers: Some populations on the rise were small panfish, bass, geese, snails, and the beds
of weeds called macrophytes. Also some interesting little balls of dark fluff can be seen rolling around on
the sand bottom. These appear to be microbial communities held together with beautiful strands of
Spirogyra-like algae. Migrating populations of geese, swan, and pelicans have returned. Losers include
large northern pike as they were replaced by underfed dwarfs, walleye which are now nearly gone, and
suckers and bullheads which fed apex piscivores up to large size. Others reduced were the swarms of
mayflies whose larvae were a major food source for growing fish, clams which fed the bullheads, and
the standing crop of phytoplankton. Small zooplankton filter these barely visible green specks from the
water. Their nutrients and energy then passes up through the food chain from small herbivores on to
large piscivores, i.e. predatory fish. However the macrophytes of weed beds, unlike phytoplankton, do
not transfer much of their energy up the food chain. Since both are limited in amount by phosphate, an
increase in macrophytes is balanced by less phytoplankton and thus fewer fish. Fish productivity
depends ultimately on phytoplankton so their loss is important. The large bodied piscivores prefer
cylindrical prey such as bullheads and suckers. However the overabundance of panfish limits
invertebrates which reduce the production of preferred prey, so the excess bass and bluegill populations
indirectly reduce the amount of walleye and large northern pike. Moreover, bluegill the size and shape
of silver dollars provide little energy, and larger ones are spiny and hard to swallow.
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Wild rice was lost from the west bay and to most of the lake as well. Other communities have probably
disappeared as well because the rice has exceptional nutrient value which supported a wide range of
wildlife. The main cause for these changes is almost certainly anthropogenic, that is human caused.
Cascades: The abundance of life forms in most ecosystems is regulated by a top piscivore. Removal of
this predator usually changes the whole system. In lakes it is generally a large bodied fish-eating fish. A
trophic (feeding) cascade is a series of steps from the top predator down to primary plant life such as
phytoplankton (algae) where each member alternates in population. The top piscivore consumes its
prey down to a low level. Its prey, such as a smaller fish, is reduced in population.
So food for the small fish, zooplankton for example, may rise in abundance and keep aquatic plants in
check. Figure 1 show how the trophic cascade may have changed in Big Sand in response to increased
fishing during the mid twentieth century according to information available. The original food chain was
from phytoplankton to zooplankton, to forage fish, to large breeding fish. This is shown on the left. The
likely change was from macrophytes (weeds) to invertebrate herbivores, and finally on to dwarfed
breeding fish on the right. The change in the cascade was thus the classical change of four major
components to three as the system was impacted by over harvesting of big fish and alterations to
drainage of the lake.
Fig. 1 Proposed changes in the trophic cascade in the 1900's
When more than 30% of the fish of a particular type is regularly harvested, the sustained catch becomes
smaller than it would be if the harvest was smaller. When caught down to about 15% and held there by
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continued overfishing, the system is overexploited. But when fished down to about 10% of normal
levels, recovery is unlikely because the link in the food chain is generally replaced by something else.
This happened to the world class Atlantic Cod fishery on the east coast, the clam fishery on the
California coast, and to other fisheries world over. In Big Sand, overfishing increased the population of
northern pike, but the individuals remained small. Low on food but abundant in numbers, some species
sustain by switching from growth mode to reproduction at small size. The physiological cause of
dwarfing is a hormonal change. So the abundant small bass you may catch may be old in age.
Restoration of a lost population can be difficult because their "niche" generally becomes occupied by
another species. In the case of the Atlantic Cod, replacement was by crabs and lobsters; serendipity
indeed! Introduction or restoration of walleye has been successful in many lakes, but has failed in many
others including Big Sand.
In an important water system study, McIntosh (Ecology, 1994) showed how a difference in top predator
can change the trophic cascade in a way similar to that shown in Fig 1. One system had brown trout as
the top piscivore. The other had Galaxias, a small New Zealand fish of mountain streams. The trout fed
on mayfly larvae which eat algae, while the Galaxias are night feeders that eat zooplankton. The mayfly
larvae from trout-containing streams, even in the absence of trout, spent most daytime hours hiding
under rocks. So the algae had a better chance to grow in the presence of trout than when Galaxias was
around. Algae was the main primary producer and at base of the food chain in these ecosystems. The
productivity of the streams with trout turned out to be six times higher because algae-grazing by mayfly
larvae was limited. This and other measurements showed some interactions that allowed a change in
the apex predatory fish to affect a whole ecosystem.
Phosphate: As discussed in Vol. 1, Issue 3, the water clarity of Big Sand has increased over the years
despite continued addition of dwelling-added phosphate. This may seem puzzling because phosphate is
the cardinal limiting nutrient in our lakes. It is also the main cause of eutrophication, i.e. choking by
plant life due to excess nutrients. Phosphate is a rather conserved mineral with little mobility. It mostly
cycles between plants and the water. The concentration stays about the same in the water and what is
left over makes more plants. The plants are eaten by herbivores like insects. But if there are lot of little
fish around such as small bluegills, they eat the insects, and the weeds can accumulate. Because the
lightly grazed weeds are not removed, have lots of surface area to absorb the phosphate, and time to
collect most of it because they can grow slowly, they can extract most of the phosphate from the water.
Thus the weeds can starve out the phytoplankton. The phytoplankton better support the food chain
leading to fish, reduce the clarity of the water, so excess weeds can lead to a tipping point. That is where
lakes switch between weed rich and clear, to phytoplankton rich and turbid.
The Demise of Wild Rice: Rice, once a staple food for Native Americans, has all but disappeared. It also
supports many of the lakes more visible species including birds and mammals. In the west bay, the
demise of rice is shown below to be due to infertile water. The low fertility is mostly due to the loss of
flushing caused by surrounding roads which blocked normal movement of water. Also the blocked outlet
drowned out some of the rice in the main body of Big Sand. The removal of emergent aquatic plants
along the lakeshore eliminated wave barriers causing one whole rice bed to disappear because the
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disturbance lifts out seedlings during the critical "floating stage" in the spring. Power boat traffic can
damage rice in this way as well. And the thirst for corn-based ethanol has come with an expanded farm
crop that attracts geese, grass-eating waterfowl that can ravage stands of rice. Excess phosphate was
probably one of the biggest reasons for the loss of rice in much of Wisconsin.
Phosphate Starvation: In 2010 large transparent cylinders were set in the sediment in the west bay,
seeded, and amended with phosphate. Growth and productivity of the rice was good. Last year the
effective component in garden fertilizer was identified in the same way. It was phosphate as shown in
Table 1. Seed production was similar in enclosures amended with phosphate or nitrogen plus
phosphate. Growth was absent with nitrogen alone, as well in unamended controls. In August, the
diameter of the tillers (stems) measured at the water level is shown in Table 1. The addition of
phosphate was clearly critical. However there was no significant effect of nitrogen, rice-straw, or
sediment disturbance. Sometimes riling the sediments can liberate phosphate and stimulate rice.
Repeated this year, findings were the same.
Table 1 Phosphate requirement for wild rice production in the west bay
Treatment
None
Nitrogen added
Phosphate added
Tiller (stem) diameter, mm
± standard error.
No growth
No growth
7.1 ± 1.3
Nitrogen and
phosphate added
8.2 ± 2.1
Is the lake phosphate starved or in excess leading to the weediness now present? Both. In the lake,
most of the phosphate is in the weeds, not the water. The weeds, with their large leaves, can extract
what they need. But the rice, a root-feeding grass, cannot compete. Where the beds are thick enough to
avoid uprooting by waves, the flowing water brings enough phosphate by for growth. But in the west
bay, the low flow did not bring phosphate by fast enough for the rice extract what they need. This is of
interest because when wild rice is nutrient starved it is usually thought to be due to insufficient
nitrogen.
Fish Kill and Carp: There was concern that blockage of Sand Creek might cause an oxygen deficiency due
to absence of flushing during ice cover because of recent restrictions to Sand Creek. The creek connects
the west bay to Yellow River where carp have been present for 20 years. There had been two previous
possible sightings of carp. This is now problematic because they can survive low-oxygen water while
game fish cannot. Bluegill are thought to be a main agent of carp control because they follow spawning
carp around and consume eggs as they are released. This spring there was a fish kill as shown in Fig. 2.
Unknown in recent history, it was confined to the north side of the west bay away from the main
outflow of water from the lake. Dead frogs also littered the bottom of the bay. The likely cause was
oxygen starvation. The bacteria in detritus (dead plant material) washed into the bay probably
consumed oxygen faster than oxygen-rich water from the lake could replace it. In winter, oxygen
produced by growing plants is low, and ice cover restricts the other input, absorption from the air. That
oxygen deficiency caused the fish kill is consistent with the finding that wild rice in the west bay was
starved lut due to insufficient phosphate.
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Fig 2 Fish Kill. Left; Dead fish in marsh grass. Center; species recovered: bowfin, bullhead,
bluegill, large mouth bass, perch, and frogs (not shown). Right; swirls from large wary fish,
presumably common carp.
Last year Upper Clam Lake was overrun with perhaps 100 tons of common carp. They decimated a
prized rice stand by rooting for invertebrates in lake sediments. Other macrophytes were reduced as
well allowing excess phosphate in the water. This led to more phytoplankton and greater turbidity. The
weed beds were then shaded out in a downward spiral. Bluegill and bass populations were probably
starved out as well due to diminished weed beds; at least their populations in 2003 were very low.
Bluegill and bass prey on the eggs and larvae of carp, the low populations of bluegill means fewer are
looking for them, and the murky water makes the eggs and larva harder to find. This is a classic regimen
shift which Big Sand residents would probably prefer to avoid.
This spring, there appeared to be a significant carp population in the west bay of Big Sand at ice out
(March 20) as shown, but the bluegill were absent. They returned around May 3. Hopefully the
improved drainage anticipated will help maintain aerobic conditions, continued clear water will facilitate
predation on eggs by small fish, and the scenario of carp overrun in Clam Lake can be avoided
Alternate Stable States: Some lakes are full of weeds, but have quite transparent water. Others are less
clear with more phytoplankton and fish. These conditions seem to be temporarily stable but can switch
back and forth over time. One tipping point can be the loss of top piscivores as mentioned. There seems
to have been some jockeying for position among steps in the trophic cascade in Big Sand over the last
half century. Northern Pike became small, abundant, and quite skinny. Hordes of one- and two-inch
panfish appeared. Now the pike, bass and bluegill seem to have stabilized at an intermediate rather
small size. With the growing load of phosphate in the weeds the lake is at risk of suddenly becoming
overly rich. Such eutrophification can lead to low oxygen, fish kills, and expansion of the population of
common carp into shallow weed-rich areas of the lake. The fish kill actually happened as shown above.
Interestingly it was predicted here; this paragraph was written before the fish kill occurred. However the
problem was poor drainage rather than infestation by an invasive such as Eurasian Water-Milfoil which
could have had an even more deleterious effect.
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Weed beds: Bass and bluegill spawn in depressions whisked out of the sand, then stand guard during
incubation. The preferred location for nests is near weed beds where newborn fry can hide. The
abandoned nests provide sites for new plants to establish. The result is a patchy mosaic of macrophyte
species that improves the ecology of the lake. Perch spawn among them and then hide near the
boundaries to ambush prey. In Big Sand, northern pike are near their upper temperature limit. Water
temperatures reached 83 degrees last year, but the weed beds provide a cooler respite.
Zooplankton use weed beds as a refuge when not actively feeding on phytoplankton. But small bluegills
are over abundant in Big Sand so that the zooplankters are held in check. Thus the weed beds are only
lightly grazed. Free to grow, the large beds of weeds extract phosphate from the water starving out
pelagic (open water) phytoplankton as mentioned. The result is clear water with an underabundance of
zooplankton to support mid-sized fish. Plant diversity with many species improves the productivity of a
lake. However invasive plants, unknown in Big Sand, can turn weed beds into monocultures which are
conducive to oxygen starvation, smelly weed beds, and fish kills. A particular problem is the tendency of
some invasive macrophytes such as Eurasian Water-milfoil to sprout early, overgrow the native species,
clog waterways, die in mid-summer, and deplete oxygen supplies when the warm water holds little
oxygen even when saturated with air.
Macrophytes add new oxygen to the water during growth. If the weed beds are large, they can
contribute to fish kills because bacteria use oxygen to digest weeds thereby suffocating the fish. Some of
the minerals accumulated by the plants such as phosphate become buried in the sediments which helps
limit accumulation of weeds in the lake. If phosphate loss due to burial and flushing is exceeded by
terrestrial runoff or rivers, a lake is likely to become overpopulated with weeds. If the excess weeds are
over-grazed by fish or invertebrates, the phosphate liberated can lead to excessive populations of
phytoplankton. As described above, this can foster a regimen shift.
The nymphs of many insects depend on the microorganisms fed by decaying weeds in the sediments
below weed beds, and adults use emergent weeds to dry off and fly away. Mayfly larvae, for example,
are large and nutritious. But the short but intense annual swarms are gone, perhaps also due to the
abundant undersized panfish. Waterfowl depend on the seeds as well as the greens of macrophytes
during migration. Emerging wild rice is a favorite aquatic macrophyte for migrating geese. Attracted by
corn fields, large stands of rice can survive them, but depleted beds can be hard to restore. Thus well
integrated weed beds are an important ingredient of a productive lake.
Algae: Toxic blue-green algal blooms have caused warnings to be posted in other near-by lakes. Having
but one molecule of DNA, they are really bacteria. Called cyanobacteria because of their bluish color,
they frequent slow moving water. The common genera in lakes are Aphanizomenon, Anabena, and
Microcystis. They were responsible for the oxygen in early Earth thus the beginning of animal life.
Moreover they are one of the few living groups strong enough to convert the abundant dinitrogen (N2)
in air to a form (-NH2) used in the construction of proteins. However some contain powerful toxins.
These include neurotoxins and others that sometimes affect beach-going dogs. Iridescent scums of
cyanobacteria have appeared in Big Sand but the areas observed were small.
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With many molecules of DNA phytoplankton are true algae. They are the main organisms that reduce
visibility in water. Moderate populations are best for fishing because they dominate the base of the food
chain.
Bacteria: Except for viruses, true bacteria are our most abundant swimming partners. Their main role is
to recycle the organic material formed. When living organisms die, it is mostly bacteria that separate the
remaining biochemicals. These bacteria contribute some to the food chain, but more importantly they
release the minerals necessary for plants to begin another carbon cycle. Thus they control much of
water chemistry. Very few bacteria affect humans but some fish diseases are known which is why
unused minnows should be discarded, not dumped into the lake.
It takes about a trillion of the more commonly recognized bacteria such as those of compost piles,
excrements, and disease to weigh a gram; more than 100 could span a human hair. Aquatic bacteria are
only a tenth as big, and too small to be seen with the best light microscope. Each drop of lake water
contains about 100,000. But this is not enough to significantly restrict water clarity. With the help of his
laboratory and others, this author increased the sensitivity of a commercial flow cytometer so that it can
count, size, physically sort, and chemically analyze these small organisms. He named them oligobacteria
for their ability to survive on the very small nutrient concentrations in water. An analysis of the bacteria
in the water from Big Sand Lake taken with this instrument is shown in Fig. 3. He is using these data help
develop the mathematics that describe how aquatic bacteria control the chemistry of water such as
oceans and lakes.
Fig. 3 Bacteria in the water of Big Sand Lake. The three broad peaks are three different groups
of bacteria in about one drop of lake water. It shows their population, DNA content, and size of
each bacterium. The sharp tall peak is from latex beads used as an internal standard.
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Restoration: progress and plans. The variation among area lakes is large so restoration efforts are most
efficient when targeting the appropriate lakes. Restoration plans treat Big Sand as a large lake that is
free of invasive species, dammed up with poor flushing, very clear water, and has appropriate depths for
ample weeds. It is over-fished with excessive juvenile and dwarfed game fish, and has a large bay that is
starved for phosphate and sometimes oxygen that will no longer grow wild rice. There are chronic
beaver problems and potential for the establishment of invasive species and for regimen shift. The
relationships among aquatic vary from lake to lake and few are well understood. Therefore additional
measurements and consultations are intended.
Progress:
1.
Good progress in understanding the ecology of Big Sand as demonstrated by Fig. 1.
2.
A much improved understanding of the demise of wild rice as demonstrated by Table 1.
3.
Interactions with those setting specifications on lake flushing.
4.
A better understanding of the need to restore adequate flushing as demonstrated by the
accurate prediction of fish kills in Fig. 3.
5. Support and involvement by our Native American community on issues involving Big Sand.
6.
Installed four new signs at the public landing which will help to prevent invasive species.
7.
Continued public education with articles in several media including The Sand Lake Observer.
8.
With elections, the Sand Lake Preservation Association (SLPA) officers--- Don Button president,
Deb Loots secretary, and Susan Raisanen treasurer, helped make these efforts possible.
Plans:
1. Better Fishing. To improve fishing success in Big Sand the Sand Lake Preservation Association is
considering a variety of efforts. One is to facilitate a better size distribution of northern pike
through size or slot limits similar to those successful in Canada and elsewhere. Another is to
restore a walleye population through stocking. Minnesota stocks about 1000 lakes per year at a
cost of about $3,000 per lake. The return of these large-bodied predators could have the added
benefit of culling the population of dwarfed panfish and allow more of these to mature at larger
size. Seven inch walleye are available in Spooner at about $500 per hundred. Research from
twenty-four lakes in northern Wisconsin (North American Journal of Fisheries Management
2009, page 996) has shown that it is more cost effective to stock walleye of this size than either
fry or smaller fingerlings. Most walleye caught in lakes that are stocked are a combination of
both stocked and naturally produced so stocking is seen in part as ecological remediation. Big
Sand, once a good producer of native walleye, appears to be a reasonable candidate for
stocking. It has sand beaches for spawning (although gravel is better), weed beds for cover,
deep water for respite, few aggressive piscivores able to consume seven-inch stock, and newly
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available perch for food. They can also prey on small bluegill if perch run low but prefer roundbodied fishes.
2. It is unclear exactly what goes on in the weed beds of lakes like Big Sand, so the Association
plans direct observation by video and to survey the contents of fish stomachs to improve the
understanding of the trophic cascade shown in Fig. 1 and thus fine tune these restoration efforts
as we proceed.
3. Organization of additional efforts to understand lake ecology including participation in the
SWIMS program.
4. Staffing of the public landing to encourage good lake stewardship that includes day users.
5. Writing of proposals to obtain additional funding for these efforts.
6. Continue efforts to restore some beds of wild rice in Big Sand.
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The Observer is provided by the Sand Lake Preservation Association as an educational service to the Big
Sand Lake Community. Don Button, editor: [email protected]
Donations may be addressed to Susan Raisanen, Treasurer, 1276 Balsam Trail E, Eagan MN 55123. Uses
include funds for education, scientific measurements and equipment, data mining and collection,
matching funds for grants, restorations, and operation funds.
We thank The Pour House, Robert's Roadhouse, Diamond Collision Center, and Association members for
support.
Annual meeting
Robert's Roadhouse, Saturday morning, June 9 at 10:00
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