Abstract
The present study aims to evaluate the growth and seasonal allocation of the biomass of water hyacinth (Eichhornia crassipes) under natural conditions in the south Mediterranean region (the Nile Delta, Egypt). In this study, the population characteristics (density, morphology and primary production) over a one-growing-season cycle were described. In the Nile Delta, the biomass of the shoot and root systems of E. crassipes was sampled monthly along three water courses from April 2014 to November 2014 using five quadrats (each of 0.5 m x 0.5 m) at each water course. The shoot system started to grow in April (121 g/DM/m(2)), reached a maximum biomass of 887 g/DM/m(2) in July, and then decreased until reaching a minimum of 299 g/DM/m(2) in November. The biomass of the root system increased from 75 g/DM/m(2) in April to a maximum of 235 g/DM/m(2) in August and decreased to a minimum of 100 g/DM/m(2) in November. Water hyacinth allocated ca. 2% of its total biomass to stolons, 22% to laminae, 24% to roots and 52% to petioles. Peak density as high as 144 individual/m(2) occurred in May, but it reduced to 33-50 individual/m(2) during July to November. The average rate of change of biomass was maximum (17.3 g/DM/m(2)/day) during April and May and minimum (-8.9 g/DM/m(2)/day) during October and November. Relative growth rates were found to be lowest during the cooler months, October and November (-0.017 g/DM/g /day), whereas highest yields were recorded during the spring months, April and May (up to 0.044 g/DM/g/day). The correlation coefficients between the water characteristics and the first two canonical correspondence analysis axes indicated that the separation of the population parameters of water hyacinth along the first axis was negatively influenced by Zn. On the other hand, the second axis was positively correlated with electric conductivity, total N, total P, Mg, Na, K and Mn and negatively with pH.