The effect of population density of waterhyacinth on the growth and the absorption of nitrate nitrogen was studied under natural condition.
The effect of population density on waterhyacinth growth could be showed by logistic equation. Based on logistic growth equation, the following linear relation between the reciplocal after growing (1/S) and initial population density (1/S₀) of waterhyacinth was derived by Shinozuka (1956) and found to satisfy the experimental results at any stage of growth of waterhyacinth,
1/S=A+B1/S
in which A and B are the constants whose values depend on time, t. The growth rate of waterhyacinth was found to be directly proportional to the absorption rate of nitrate nitrogen. Therefore the absorption rate of nitrate nitrogen by waterhyacinth was found to be approximatly showed by logistic equation.
In order to remove 1 gram of nitrate nitrogen, 300-400grams of waterhyacinth might be produced from solar energy in water.

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Particulate matter suspended in the water of Hiroshima Bay was collected from 1980 to 1983 in sediment traps and estimations of the settling fluxes and comparison with net photosynthesis rates were made.
The concentrations of particulate matter reaches a maximum in the summer, when the quantity collected in the traps in the 5m layer was small but increased rapidly in the autumn. From this result, it is supposed that the settling of particulate matter seldom occurs as a result of gravitational sinking, and is mainly governed by vertical circulation of the sea water.
Apparent settling velocities of particulate matter calculated from quantities of trap catches were mostly less than 0.5m/d but increased to 46m/d in October, when the ratio of TOC/(Chl. a+phaeo.) of trap catches ranged from 2040, and corresponded with the composition ratio of phytoplankton.
As most of all trap catches probably originate in primary production by phytoplankton considering the composition ratio and the measurement of net photosynthesis in Hiroshima Bay, the decomposition rates of particulate matter in the settling process were calculated to be about 6080% from comparison of the trap catches in the bottom layer with net photosynthesis. The sedimentation rates for each of TOC, TON and T-P in Hiroshima Bay estimated from bottom trap catches were respectively 100, 14 and 3g/m²·y.

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The characteristics of phosphorus uptake and growth were studied in cultures of water hyacinth [Eichhornia crassipes (Mart.) Solms] growing outdoors in continuously flowing nutrient solutions.
Specific growth rate of about 0.02-0.13 (1/day) was determined, which was affected significantly by mean air temperature. The maximum rate of phosphorus removal was about 164mg-P/m²/day in the summer experiment. The relationship between specific uptake rate of phosphorus and phosphate concentration in culture container offered the analogy of a Langmuir adsorption isotherm. Phosphorus contents of tops and roots of water hyacinth on a dry weight basis were 0.20-1.20(%) and 0.17-0.76(%) respectively. Phosphorus content of whole plant was related to external phosphate concentration with a hyperbolic form.

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