Tributary/mainstem interactions, the River Continuum Concept and the Grande Ronde River

ABSTRACT
The River Continuum Concept (RCC)(Vannote et al. 1980) applies theories of fluvial geomorphology to river ecology. Conceived as a biological analog to the energy equilibrium theory of the physical system, the RCC hypothesizes that a continuous gradient in physical conditions along the river should result in a continuum of ecology along the river. At river confluences there is a sudden increase in discharge and debris, and the river morphology must make adjustments to the sudden flux of materials. Thus confluences represent locations of sudden change in the gradient of physical conditions along the river, which in turn cause sudden changes in gradient of ecology along the river, contesting the continuous gradient proposed by the RCC. Future work must evaluate which confluences function as discontinuous steps in the gradient in ecology of the river, and which function as spikes in biodiversity, having no overall influence on a continuous gradient in the ecology of the river.