Abstract
The present study aims to develop a dynamic numerical model to describe the growth and interactions between the shoot and root systems of Eichhornia crassipes along the irrigation canals in the Nile Delta, Egypt. While carrying out this study, the shoot and root biomasses of E. crassipes were sampled monthly from April to November 2014 over three irrigation canals in the Nile Delta using five randomly distributed quadrats (each 0.5 x 0.5 m) at each canal. Two state variables, shoot and root systems biomasses, were considered to follow the growth of E. crassipes. The biomass of each organ was simulated to incorporate the net growth of the plant as a function of photosynthesis, respiration, mortality and translocation from the shoot to the root system. After validating the model with data from the Nile Delta, it was verified using four independent sets of published field data: 19A degrees 50'S (Brazil), 19A degrees 57'N (Mexico), 29A degrees 38'N (USA) and 30A degrees 33'N (China). The level of agreement between the simulated values and actual field data indicated that the model was capable of simulating the total biomass of E. crassipes over a wide range of latitudes. Global sensitivity analysis showed that of all the parameters that were used, the model was most sensitive to the maximum photosynthetic growth rate. Based on our results, we recommend the following: first, if E. crassipes is used to remove water pollution or in animal feed, manure, mulch, or the production of biogas, pulp and paper, then E. crassipes stands should be harvested at peak net production. Second, if the main purpose of E. crassipes management is to suppress its growth or eradicate the plant from an irrigation canal, then the harvest should be at the point of the minimum net production.