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Becker, George C. / Fishes of Wisconsin
(1983)

Wisconsin waters,   pp. 3-17 PDF (5.6 MB)


Page 15

Wisconsin Waters   15 
Acid Precipitation 
Acid precipitation, resulting from wind-borne sulfur oxides from coal-burning
industries and nitrous oxides from automobile exhausts, is a potential threat
to 
fish life in approximately 80% of the lakes in the Northern Highland region
of 
Wisconsin (Eilers et al. 1979, Staats 1979). Too much acidity in water can
kill or 
deform fish; and, as has already occurred in 90 lakes in New York's Adirondack
Mountains, a pH of about 4.5 renders waters fishless. Acid water releases
toxic 
heavy metals such as mercury copper, lead, manganese, nickel, zinc, and alu-
minum from the bottom sediments and permits them to get into the fatty tissues
of fish. High levels of mercury in inland lake fish of the Lake Huron basin
have 
already been linked with acid rain, and high levels of toxic metals in tributaries
are known to deter Great Lakes fish from using those streams for spawning.
The problem of acid precipitation in Wisconsin is currently (1980) being
studied 
by state and federal agencies. 
Eutrophication: Enrichment of Waters 
In its infancy a lake contains sterile waters which are clear, low in minerals,
and 
low in algae and aquatic plants. The bottom water strata carry a good supply
of 
oxygen all year round, along with low numbers of coldwater fishes. Such bodies
of water are oligotrophic (low in nutrient levels). The Great Lakes up to
the 
1900s were good examples of oligotrophic waters, and Lake Superior is still
clas- 
sified as oligotrophic. 
   Over a period of time, however, as large quantities of nitrogen and phospho-
rus compounds wash into a lake (from natural sources, but also very largely
from organic wastes produced by man and his activities), the water turns
cloudy 
and heavy algal blooms and thick mats of aquatic plants overrun the shallows.
The bottom water strata in this now eutrophic (enriched) lake carry a poor
sup- 
ply of oxygen, and eventually will sustain only the most tolerant of warmwater
fishes, such as bullheads and minnows. Materials are deposited rapidly upon
the bottom of a eutrophic lake, the depth of the lake decreases, and eventually
the lake fills in and disappears. This is the inevitable history of all lakes.
  Fortunately, most Wisconsin lakes are only moderately eutrophic. Yet even
Lake Michigan is becoming eutrophic in Green Bay and around the populated
southern end of the lake. Numerous lakes in southern and central Wisconsin,
and some in northern counties, are becoming choked with weeds and algae 
during the growing season. This process interferes with boating, swimming,
fishing, and other recreational pursuits, and may lead to a sharp reduction
in 
property values as desired lake values disappear. It is responsible for winterkills
and summerkills of fishes. 
  Millions of state and federal dollars are being spent to slow down or reverse
the eutrophication process. In Wisconsin a number of techniques have been
used to control eutrophication. Lake flushing and dilutional pumping of Snake
Lake (Vilas-Oneida counties boundary) have resulted in lowered phosphorus
concentrations, the elimination of nuisance blooms of duckweed, and deepened
littoral areas where compaction of the bottom followed drainage (Born et
al. 
1973a). The Marion Millpond (Waupaca County) generally exhibited less plant


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