Spatial structure and populations of a periphyton community: a model and verification

An ecological model of periphyton dynamics was designed to simulate the dev elopment of periphyton communities. From morphological differences in the g rowth patterns of filamentous and non-filamentous algae, the model simulate d the vertical structure of a periphyton mat. The effects of shear stress o n the colonization and the detachment process, and the overall response of the community to water flow were formulated. Provided that nutrients were s ufficient for periphyton growth, a light index, representing the light avai lability for photosynthesis, was assumed to indicate not only the reproduct ion ability of an algal cell, but also the tensional strength of a cell aga inst the drag force. The thickness of the periphyton mat, which determines dynamically the light attenuation in the periphyton mat, was also evaluated . The model was verified with three cases. First, without detachment of per iphyton community, the process of growing mat was addressed under a constan t light index, and thus a constant reproduction rate. The vertical structur e of the periphyton community was simulated using different light indexes. Second, the growth rate and vertical light distribution inside the periphyt on mat were simulated with three values of the biotic light attenuation coe fficient. Third, the time of detachment, detachment effects on community gr owth, etc., were investigated at three different water velocities: 10, 20, and 30 cm s(-1). Finally, the model was applied to experimental results in a stream, successfully reproducing the important characteristics observed i n the experiment of the succession of communities, such as the variation of filamentous and non-filamentous cell densities related to the light distri bution and the detachment of filamentous species. (C) 2000 Elsevier Science B.V. All rights reserved.