PARENT SESSION
Symposium 4: Ecosystem ecology at the watershed scale: Linking biogeochemical cycles across the terrestrial - aquatic divide
Organized by: ES Bernhardt and MH Valett
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 517 A, Level 5, Palais des congrès de Montréal
Streams in watershed ecosystems: A biogeochemical continuum concept.
Valett, H. Maurice*,1, Bernhardt, Emily2, Brookshire, E.N. Jack 1, 1 Virginia Tech, Blacksburg, Virginia, USA2 Duke University, Durham, North Carolina
ABSTRACT- Streams represent the last link in a hydrologic continuum that begins with precipitation, traverses the terrestrial uplands, converges on riparian zones, and exists via channel flow. Generically, streams are transport systems and conceptual and analytical models applied to stream biogeochemistry recognize this characteristic feature. Watershed landscapes include a number of subsystems (atmosphere, canopy, soil, regolith, riparian zone, hyporheic zone, stream channel) that are linked by the hydrologic continuum. Streams are better understood when viewed as components of watershed landscapes and compared and contrasted with other ecosystems contributing to watershed biogeochemical function. We propose a comparative approach that relies on 1) the velocity of water as a measure of transport potential, 2) kinetics of uptake representing biological activity, and 3) capacity for storage as a scheme for placing streams in a biogeochemical continuum that characterizes watersheds. Borrowing ideas from the nutrient spiraling and river continuum concepts we contend that streams occupy a critical position in watersheds that respond readily to changes in up-gradient conditions and act as control points for the river networks they feed. Under certain conditions, streams may feed back onto neighboring terrestrial environments, but they are typically donor-controlled and respond to inputs from the valleys that surround them. Not surprisingly, they may display very different successional trajectories than their terrestrial counterparts. At the same time, streams are active ecosystems and over shorter time scales they may alter the form, abundance, and timing of watershed losses.
Key words: stream, watershed, biogeochemistry, continuum