Modeling Approach to Periphyton and Nutrient Interaction in a Stream

We propose a model of the development of a periphyton community in a stream under the influence of nutrients and light. Coupling the model with a nutrient transport model clarified the longitudinal distribution of both periphyton community and nutrients. The thickness of the periphyton mat, an important factor regulating nutrient exchange between the mat and overflowing water, was determined from water velocity and the periphyton biomass. We compared the results of this study with three observational data sets to overall validate our proposal: (1) a comparison of electrical conductance in two channels with different periphyton biomasses validated the model in the mass exchange between stationary and flowing water zones; (2) a comparison of the temporal variation in periphyton biomass and nutrient concentration in a once-through and a re-circulated water channel, validated the relationships among the periphyton biomass, the nutrient uptake rate, and the nutrient concentrations in the stationary water zone; and (3) a longitudinal distribution of the algal species composition of Stigeoclonium and Chamaesiphon, and the nutrient concentrations of a 140 m reach was reproduced and compared with measured data. The light intensity indirectly controlled the nutrient gradients along the stream by the periphyton biomass in the third application.