Modeling the lateral variation of bottom-attached algae in rivers

The lateral distribution of benthic algae in flowing waters is an overlooked but important component of river water-quality management. A number of workers have described the spatially variable structure of bottom algae in the field, yet rarely has it been reproduced using mechanistic models. In this study, we develop a simple numerical model that describes lateral biomass accrual of bottom-attached algae in rivers and illustrate how gradients in light through the water column can be an important consideration in nutrient regulatory management. We then present a comparison of simulated and observed results on the Yellowstone River in the northern United States where the model was applied to compute maximum steady-state biomass. Following calibration to site-specific data, algal simulations yielded satisfactory outcomes with root mean square error and percent bias of 21.8 mg chlorophyll a m−2 and 51.9%, respectively for four different river transects totaling n = 36 observations. The general distribution of periphyton was well-represented. In this regard, we suggest that the tool is useful for management of light-limited rivers where depth varies significantly across the channel. However, accumulations of filamentous algae and confounding effects such as velocity and substratum influence community spatial structure and warrant further investigation with respect to the proposed model.