Physical constraints on the distribution of macrophytes linked with flow and sediment dynamics in British rivers

Abstract Aquatic vegetation plays a role in engineering river channels by altering patterns of flow velocity, sediment dynamics and, consequently, development and turnover of habitats. This could potentially aid in the rehabilitation of over‐widened, straightened channels, and, less desirably, reduce channel conveyance and contribute to flooding problems. Therefore, it is important to understand the environmental conditions in which in‐stream and marginal vegetation can reach sufficient abundance for these engineering roles to have a significant impact on the physical environment. Macrophyte and environmental data from 1653 river reaches across Great Britain were collated. Specific stream power (SSP) was calculated to represent hydrological disturbance and a median bed calibre index and percentage sand and finer sediment were used to characterize substrate size, since stream energy and sediment properties are two major physical controls on aquatic vegetation. Correlation and Principal Component Analysis (PCA) revealed subtly different physical habitat ‘preferences’ between species of contrasting morphology. Correlations of additional environmental data with SSP indicated that this physical disturbance variable also reflects gradients in stress variables describing nutrient availability and latitude and so is a useful integrator of a number of important pressures on plant survival. A conceptual model was produced which indicates ranges of SSP which may determine the significance of aquatic macrophytes in channel engineering processes. This model could contribute to predicting the potential for macrophyte growth within a given reach thus indicating its capacity for self‐restoration or the likelihood of weed problems. Copyright © 2010 John Wiley & Sons, Ltd.