The goal of this project is to understand feedbacks between species assemblages and nutrient cycling, and how feedbacks change with stream size and stream network position. Stream networks comprise gradients in light and temperature from small shaded headwater streams to large open rivers. These gradients coincide with a shift in the energy source to aquatic organisms from terrestrial detritus to algal production. These changes may alter food quality (nutrient content) and consumer species composition that ultimately feedback on nutrient cycling. As a result of the tight linkage between nutrient availability, food quality, and consumer nutrient use efficiency, the effects of consumer-resource interactions may be transmitted downstream, with potential consequences for receiving systems. Examining how variation in network structure influences the downstream flux of nutrients provides the basis for understanding how food web effects are propagated in space and the potential impact of material subsidies in influencing ecosystem properties. Using both surveys and manipulative experiments (e.g. light, nutrients, grazing) in streams spanning a drainage area gradient from 0.5 - 150 km2, the results of this work will help us to better predict the consequences of environmental change for watershed nutrient fluxes.
This project is funded by an National Science Foundation Ecosystems Grant (DEB-0543363) with several collaborators and has supported a number of SCU student research projects.