Plant density (dry basis) for Lesser Duckweed was reduced during
the experiment, independently of the treatment due to the climatic
conditions of the experiment which also negatively
influenced the growth rate. A more pronounced decrement was observed
in the treatment control (without As). In wet basis non-significant
differences were found between treatments. This could be
the consequence of a major humidity percentage in plants of the
control treatment. Respect to the Water Hyacinth, it was observed
an increment of plant density in dry basis between the first and
14th days and a decrement between the 15th and 21st days. This
could be a consequence of the reproduction of the plants during
the first period and the reduction of the available area and nutrients
in the vessels during the second period.
Density on a wet basis it was observed as an increment during
the entire experimental period. No significant differences were
found in the behavior of plants in treatment with As and without
As. The presence of the contaminant had no influence in the density.
The growth rate for Water Hyacinth was positive during the
first period (day 1 to 14th) and negative during the second period.
In this last period a competence for the area and nutrients was
higher. The presence of the element does not influence the agronomical
behavior of the Water Hyacinth plants.