Although an increase in nitrogen level in water can cause an
increase of water hyacinth growth rate (Heard and Winterton,
2000), a significant difference (p < 0.05) in water hyacinth growth
rate was not observed in this study between the two groups of
experiments, the 9-tank system with a total nitrogen level of
around 25 mg/L and the 3-tank system with total nitrogen level
of about 50 mg/L. However, the overall average water hyacinth
growth rate in the 2-tank system with total nitrogen of 2mg/L was
significantly higher than those in the 9-tank system and the 3-tank
system. The primary reason might be the difference in water surface
area and water depth. The water surface area in the larger
tank was 2.54m2 in the 2-tank system and 0.23m2 in the other
two systems. The depth of the tanks in the 2-tank system is close
to twice that in the other systems, 0.67m and 0.3 m, respectively.
The leaf and body size was observed to be smaller in the 9-tank
system and the 3-tank system compared to those in the 2-tank
system.