Document: JOH-3-15-1

Movement of organic matter and nutrients from stream to riparian zone: A reversal of fortune.

SCHADE, J.D.*, J.R.WELTER, N.B.GRIMM and S.G.FISHER

Arizona State University, Tempe, AZ 85287 USA ¹

Abstract:
In the classic model of stream ecosystems, materials move from the surrounding watershed to the stream. This classic model derives from mesic streams, characterized by a closed canopy, high leaf litter inputs and low instream productivity. Furthermore, rain infiltrates upland soils in mesic watersheds and groundwater tends to move from uplands through riparian soils to the stream. Arid land hydrology leads to a different direction and strength of aquatic-terrestrial material exchanges. Rain in the desert does not infiltrate upland soils, rather it flows overland into stream channels, generating flash floods. These spates prevent plants from establishing in the channel, thus the streams channels are wide and well lit. Floodwaters also infiltrate coarse channel sediments, and thence move from the stream out into the riparian zone. Because of the open canopy, leaf litter inputs are low, and algal production is high. Algal biomass increases during post-flood succession but as the stream contracts, stranded algae are exported laterally to the terrestrial system. High production rates also lead to high insect emergence, of which 3% is permanently exported. In Sycamore Creek, Arizona, lateral export of organic matter from the stream is on the same order of magnitude as leaf litter input, and there is a net export of dissolved nutrients as water moves subsurface from stream to riparian zone. In the desert, the stream in many ways rules the valley.

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This abstract is being presented at: 8:10 AM in session:
Symposium # 3: Linking Communities Across Ecosystem Boundaries: A Symposium in Memory of Gary A. Polis.