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

An ecological model of periphyton dynamics was designed to simulate the development of periphyton communities. From morphological differences in the growth patterns of filamentous and non-filamentous algae, the model simulated the vertical structure of a periphyton mat. The effects of shear stress on the colonization and the detachment process, and the overall response of the community to water flow were formulated. Provided that nutrients were sufficient for periphyton growth, a light index, representing the light availability for photosynthesis, was assumed to indicate not only the reproduction ability of an algal cell, but also the tensional strength of a cell against 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 periphyton community, the process of growing mat was addressed under a constant light index, and thus a constant reproduction rate. The vertical structure of the periphyton community was simulated using different light indexes. Second, the growth rate and vertical light distribution inside the periphyton mat were simulated with three values of the biotic light attenuation coefficient. Third, the time of detachment, detachment effects on community growth, 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 in the experiment of the succession of communities, such as the variation of filamentous and non-filamentous cell densities related to the light distribution and the detachment of filamentous species.