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The pump
house remains from farming days (see sign 6), because water level
management is still needed. Since the present fields and marsh and
Nielsen Stadium are below lake level, the pump must continue to
operate. This pump gives us an ideal tool for maintaining a healthy
marsh under urban conditions and demonstrating how to prevent
man-made nuisance problems such as: wide water level fluctuations,
weeds, mosquitoes, mud E turbidity, eutrophication, and the
accompanying anoxia.
Water levels:
Maintaining a healthy marsh here involves simulating the gradual
seasonal water level cycles of natural wetlands in rural
areas. Because
urbanization prevents water storage in soil by encouraging storm
runoff, the pump may be needed to dispose of flash floods that would
destroy plants and bird nests. Between rains, water may have to be
siphoned in from the lake to keep the water level from dropping too
much, now that many springs and seeps are dry. Managing the emergent
plants and muskrats to maintain interspersion of waterways and
vegetation may likewise be achieved by skillful control of water
level fluctuations.
Weeds
and trees on shores are a consequence of soil disturbance.
Constructing natural shallow shorelines will prevent wave and ice
action from causing undercutting or slumping of shores so that
natural plant succession will stabilize the vegetation. Here we will
remove persistent noxious weeds and invading pioneer trees and
shrubs that got started during construction. There should be a good
diversity of shore plants but no trees or shrubs. Cessation of
construction in the watershed will eventually stop the addition of
mud which favors undesired pioneer plants; a slight spring rise in
water, to cover exposed mud, can in the meantime prevent their
establishment.
Mosquitoes
require two conditions: rapidly fluctuating water levels and absence
of predators. The eggs, laid below the high water mark,
require both
freezing and drying before they will hatch, and the wrigglers need
only two weeks of continuous shallow water or moist mud to develop.
They are eaten by many predatory animals from small insects to fish.
Hence most problem mosquito areas are not the permanently wet
marshes but rather the river flood plain forests and the sedge
meadows where an alternation of flooding and drying triggers
hatching but prevents the
longer-lived
aquatic predators from living there. In this marsh, gradual shallow
edges harboring diverse animal life, coupled with attempts
to maintain
water levels evenly through a very gradual seasonal cycle, should
keep mosquito populations to a minimum.
Turbidity
--
muddy water
--
clogs the
gills of fish and some aquatic insects, prevents light penetration
necessary for plant growth and
oxygen
production, keeps ducks and other animals from finding food, and
hence also might favor mosquitoes. Prevention of soil erosion in the
watershed and on the shores, and keeping carp out, should lead to
clear water. Unlike clay and silt, the organic matter accumulating
on the marsh bottom does not stay in suspension for long when
stirred up. Until the bottom becomes organic, the marsh could be
temporarily pumped dry
in late
summer to settle the mud if it won't settle by itself. The silty
water could be pumped onto the grassy playing field, which could
absorb the silt as well as the fertilizer in the water.
(For
Eutrophication
and its
abatement, see Sign 7)
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