Effects of pulse events at different spatial scales on arid land and alpine stream and river ecosystems

V. Acuña^1,2, C.N. Dahm¹, K. Tockner², P. Reichert², and U. Uehlinger².¹Department of Biology, University of New Mexico, ²EAWAG, Swiss Federal Institute of Aquatic Sicence and Technology

The primary objective of this project is to investigate the effect of spatial and temporal scales on ecosystem stability to pulsed flow events. Stream metabolism (primarily gross primary production and ecosystem respiration) is used to evaluate ecosystem stability, because both processes integrate energy flow though the components of an ecosystem. Stability encompasses the capacity of minimal response (resistance) and the ability for rapid recovery after disturbance (resilience). Despite several disturbance studies in streams, information is still lacking concerning how floods affect entire river systems. The spatial scale effect is assessed at two climatically contrasting systems, the upper Gila catchment (New Mexico, USA) and the Thur catchment (Switzerland) in order to attain more robust conclusions. Our hypotheses are 1) with increasing scale, the system becomes more resilient to floods, while resistance has a maximum in low order and in high order reaches, 2) increasing stability with increasing scale is related to a larger hyporheic compartment, and 3) extreme flow events may change the importance of heterotrophy along the continuum and so affect the predictions of the River Continuum Concept (RCC). Extended goals and preliminary results from the Upper Gila are presented in this poster.