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ABSTRACT
Free floating aquatic macrophyte Pistia stratiotes Linn. were exposed to different concentrations of ballast water (0 %, 5 %, 10 %, 25 %, 50 % and 100 %) for 15 days. Ballast water is water usually taken in or unloaded from the ballast tank to improve ships' stability, balance, structural strength, and maneuverability during a voyage. Ballast water is seen as a pollutant that is hazardous to aquatic lives. Measurements were taken at 3 days interval during this period for the determination of changes in the leaf area, leaf number and root length. The chlorophyll content was determined at the beginning and on termination of the experiment. There was a general increase in root length on day 3 for all concentrations until day 9 when plants in higher levels of ballast water concentration such as 100 %, 50 % and 25 % died while there was a recorded increase for other concentration levels. There was a significant difference among the higher concentration (100 %, 50 % and 25 %) and the lower concentrations (10 %, 5 % and 0 %) (P < 0.05). The leaf area was observed to have generally increased in all plants before which there was an observable reduction in leaf area for plants in higher levels of ballast water concentration. Some plants had a constant leaf area measurement as there was no increase observed. The 0 % (control) values were significantly different from the 100 % and 50 % values (P < 0.05). The leaf number reduced rapidly for high concentration levels (100 %, 50 % and 25 %) while for the lower concentration levels (0 %, 5 % and 10 %), the leaf number increased slowly and began to reduce or remain constant over time. The results showed that high concentration of ballast water was toxic to the plants. All physico-chemical parameters of the ballast water were higher than the seawater except for nitrate.
