Assessing food-web structure, matter fluxes, and system attributes of a Central European mountain stream by performing mass-balanced network analysis

Abstract

Trophic interactions and cycling of matter within the community in a soft-water mountain stream were analyzed on the basis of a compartment food-web model. The model describes (i) the structure of the food web, quantifying biomass, production, and consumption of individual elements as well as of the entire system, and (ii) the flow of matter between compartments as well as trophic levels. Detritus and primary producers sustain a broad variety of invertebrate consumers. Fishes are the top predators; sculpin (Cottus gobio) and a compartment consisting of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) are at the highest trophic level. Heterotrophic microorganisms (227.1 g dry mass (DW)·m–2·year–1) and aufwuchs algae (150.1 g DW·m–2·year–1) have the highest production. Secondary production of fishes and macroinvertebrates amounts to 2.56 and 19.9 g DW·m–2·year–1, respectively. Total consumption amounts to 1136.41 g DW·m–2·year–1. Main flows occur between the lower trophic levels. Food intake is greatest for microorganisms and Ephemeroptera. A relatively high fraction of invertebrate production is consumed by predators. For 10 of 19 compartments, over 95% of production is used as food by other organisms. Transfer efficiencies are generally low (<10%). A large proportion of matter transfer occurs at the lower discrete trophic levels of the stream.