Nov. 21

Control of Aquatic Plants:

Industry - aquatic plants are often found in water intakes for power
plants and factories.  These areas need to be screened to prevent plant
material from getting into pipes and machinery and plugging them up.

Agriculture - plant growth is also seen in irrigation canals where it
blocks water flow.  If plants get established in the water delivery system
they may plug up and ruin siphons and pumps.

Recreation - aquatic plants have an adverse impact on fishing, boating,
swimming and sailing.   If a lake is covered with plant material, it will
use up all of the available oxygen at night, causing fish kills.

Control of aquatic plants (aquatic weeds) is a matter of reversing the
natural progression of a lake.

Causes of excessive plant growth:
1)  Nature - aquatic plants are simply found in bodies of water.
2)  Excess nutrients - most often the case.  These are made available from
erosion, pollution, or human and animal wastes.

Why try to control?  Aquatic weed control provides many jobs.  There are
several steps to follow for successful removal:  
1)  Look at the problem and determine what the intended use of the water
is.  Usually it is not necessary to get total elimination, just control of
growth.
2)  Determine the safety of the method to be used.  Concern about safety
is for the applicator, the users of the water, and the environment.  An
example of safety is not adding herbicides to drinking water.
3)  Determine how effective the method will be.  This takes into account
the percent removal, time to do work, longevity, cost-benefit analysis,
and side effects.  Some adverse side effects are damage to wildlife, water
storage capacity, and the increase of erosion.

Methods:
1)  Physical removal - pulling out by hand, rakes, cutting, or digging.
This method is effective for small areas such as docks, small beaches, and
boat houses.  The problem with this method is that usually it is only a
temporary fix (it is not possible to get rhizomes, roots, tubers) and it
can be expensive and time consuming.

2)  Mechanical methods - there are many types of machinery available now,
including underwater mowers, weed harvesters, and portable dredges (this
machinery is very expensive).  The problem here is that  tearing up the
bottom of a lake can release nutrients and pollutants from the substrate
which increases the turbidity.  Many wildlife habitats are also destroyed.

3)  Habitat modification - there are many methods available.
	a)  Line or cover the bottom when a pond is new or water levels
are low.  Concrete, soil-concrete, and plastic liners are used.  It is
also possible to dump sand, gravel or rock to bury plants.  Gravel
substrates make regrowth difficult.
	b)  Shading by the use of plastic sheets, pool covers, plastic
bottles, film cans, soluble dyes (for larger areas - products like
aquashade block certain wavelengths of light to prevent photosynthesis),
large floating structures such as docks and rafts, and overhanging trees.
Trees are good for control in shallow areas of a pond.
	c)  Drawdown methods dry out a lake to expose shallow areas which
will kill aquatic plants.  The lake is then filled back up.  This is
common with farmers.  It is also possible to flood a lake which will kill
vegetation by preventing gas exchange and shading plants from light.
	d)  Flushing is a process which knocks loose plants that are not
bound tightly to the substrate.  These are then washed down stream. 
	e)  Dredging destroys the substrate which also kills aquatic
plants.  the problem with this method is that you must then find a place
to dump dredged material.
	f)  Fertilization causes algal blooms which block enough sunlight
to kill aquatic plants.  This methods is common in fish farming.

4)  Management methods - 
	a)  By not fertilizing slopes, it is possible to prevent runoff
from providing too many nutrients to a lake.
	b)  Maintaining septic tanks also prevents nutrient build-up in a
nearby lake.
	c)  Prevent the dumping of ashes, leaves, or any other wastes into
a body of water.
	d)  Plant a buffer zone with native vegetation.  This will trap
sediment, provide a wildlife habitat, and shade the edges of a lake.
	e)  The use of a rock lining around a lake traps sediment and
prevents wave erosion.
	f)  Fence out livestock to keep animal waste out of a lake.
Livestock also tear up the substrate, releasing nutrients.
	g)  Overfeeding of fish also adds to the nutrient problem.

5)  Biocontrol - 
	a)  Use of ducks and geese (domestic or wild).
	b)  Tilapia can be used in polluted waters (but only warm water).
	c)  C tenopharyngodon idella (grass carp)  will feed off of
aquatic plants.  This may be an expensive method because the fish must be
certified for triploidy to stop reproduction.  Grass carp run $10-12 a
piece, and live for 7-15 years.  It is only necessary to have 5-25 fish
per acre for vegetation control.