2010 Volume 46 Issue 1 Pages 1-15
A simple mathematical biomass model was formulated based on the logistic growth equation. In the model, the growth rate parameter ‘rt’ was related to the daily environmental factors like temperature, light and nutrient. The environmental factors were represented in the model with their respective functional equations. The other parameter, maximum biomass density ‘Bmax’ was considered constant on long term. The test plants used for simulation were two floating macrophytes Eichhornia crassipes (Mart.) Solms and Spirodela polyrhiza; and two emergent macrophytes Lythrum anceps (Koehne) Makino and Phragmites japonicus. When applied, the model simulated cumulative biomass results matched fairly well with the observed cumulative biomass ranging from apparently no discrepancies to 8% discrepancies in 2006 and 2007. However, only one model simulated cumulative biomass result of E. crassipes in 2005 saw a discrepancy of 20% against the observed biomass. The Bmax parameter value of L. anceps and P. japonicus measured intermittently during 4 to 5 years of their establishment in the pond varied by several fold with the possibility of stabilization of their value measured in 2009. As an illustration, the model was used to simulate biomass at different biomass densities limits keeping lower limits to 50% of Bmax. The simulation results were in consistent with the notion of maximum sustainable yield (MSY). Similarly, the model was used to simulate cumulative biomass production by macrophytes under different climatic and water environment conditions. In general, the model is simple and flexible; parameters are easy to measure and could be obtained from public domains. However, in the present level of this study the estimated parameters of mortality and measured parameter Bmax needs revision until their values are stabilized.
