Stream typology and dynamics of leaf processing

Abstract

Is it possible to link leaf decomposition and associated invertebrates with the typological character of an heterotrophic stream ? This is an important question because it is related the spatial dynamics of the functioning low order streams, in the sense that it considers the use and interactions of allochthonous organic material along the horizontal axis of the stream. In the autumn/winter of two successive years, alder leaf breakdown rates and their nutrient variation (N, P, K) were estimated in a stream with energetically increasing dependence on POM inputs in the upstream direction. The succession of invertebrates colonizing the incubated leaves was observed and related to the characteristics of this organic substrate. Though extremely variable in time, the coefficients of decomposition revealed a spatial gradient in close association with the specific heterotrophic character of the different sites. Invertebrate trophic groups colonizing the leaves exhibited a pattern similar to their typological distribution in the stream : shredders were dominant in the upper stations and they were replaced by collectors in the lower ones. We concluded that a longitudinal pattern of decomposition of exogenous organic materials exists in streams that show a predictable typological shift along this gradient.