slow and inefficient there since the machine had to travel very
to the shore disposal sites.
Obviously, efficiency will be increased if dis-
posal sites are located near the harvesting site, or if a separate transporter
unit is used with the harvester.
In southern waters, particularly Florida, harvesting is seldom appli-
cable.
62 tons ha
Here, plant densities may often
and as much as
-1
370 tons ha
in dense waterhyacinth infestations, and regrowth rates can be
several hectares per day of new vegetation.
In these situations, harvesting
rates will be slow, disposal costs will increase, harvests will have to be
repeated very frequently, and exotic plant growth rates will exceed the rate
In these cases, harvest-
at which they can be harvested during some periods.
ing is not an effective management option, and reservoir managers may have to
rely on other procedures, such as herbicides, or an introduction of biological
controls following a harvest or herbicide application.
Harvesting could have an additional restorative or improvement effect
for a reservoir when large amounts of nutrients are removed as plant biomass.
Removal of nutrients would have to be sufficient to significantly lower the
net external nutrient loading or to significantly interfere with the nutrient
of plants.
Nutrient removal
release that occurs during the autumnal
Burton, King, and Ervin
to this extent is unlikely in many large reservoirs.
(1979) have listed the conditions that must be met to accomplish sufficient
nutrient removal:
(a) macrophyte densities must be high,
phosphorus load-
-2
(c) most of the
year
ing to the reservoir must be less than 1.0 g m
reservoir surface must be covered with plants, and (d) macrophytes must regrow
every year.
They provide a useful nomograph to estimate the macrophyte har-
vest required to equal net phosphorus income as a
of percent coverage
by plants.
While many reservoirs have nutrient loading in excess of the above
value, few have complete macrophyte coverage, and the harvest season may be
short.
As well, complete macrophyte removal could be detrimental to a sports
fishery, could contribute to increased turbidity through erosion of littoral
Harvesting is
sediments on windswept shores, or may stimulate an algal bloom.
therefore unlikely to be a factor in improving reservoir
state through
nutrient removal alone.
Harvesting may lead to improvement in dissolved oxygen conditions
through the removal of particulate and dissolved organic matter, which is con-
tinually produced by sloughing of plant tissue and by plant decay at summer's
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