The investigators will study the extent to which a stream ecosystem is a source or sink for energy and nitrogen in the larger desert landscape. Energy flow will be summarized as the ratio of primary production to respiration (P/R) and nitrogen cycling as the ratio of dinitrogen fixation to denitrification (F/D). Judgments of whether a system is a source or sink will be generated for nested hierarchys, ranging from the algal assemblage to the entire drainage. Results will test in part the utility of hierarchical approaches to steam ecology. Disturbance effects generated by flash flooding and drying, each characteristic of a different hydrologic extreme, will be studied in the context of the hierarchy. Stability of subsystems will be evaluated in the face of each disturbance and combinations of the two. Detailed study of interactions between surface and hyporheic zones involving organic carbon and inorganic nitrogen will be used to explore how subsystem interaction influences the stability of each. The hypothesis is that vertical exchange enhances resilience of both subsystems. Finally, a simulation model will be used To simulate the effect of disturbance regimes on the whole drainage system. Results will show how disturbance regimes of several years length influence the linkage of streams with adjacent ecosystems: downstream reservoirs, groundwater aquifers, or parallel riparian communities. The investigators are well qualified to run the proposal research program, have adequate facilities and have an excellent publication record.
