PARENT SESSION
Oral Session #7: Aquatic Ecology: Stream ecosystems. Presiding: T. Ehlinger.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.
Nutrient uptake length, channel structure, and transient storage in streams draining harvested and old growth watersheds.
HILL, BRIAN1, McCORMICK, FRANK2, HARVEY, BRET3, JOHNSON, SHERRI4, 1 2 3 4
ABSTRACT- Channel structure and transient storage were correlated with nutrient uptake length in streams draining old growth and harvested watersheds in the Cascade Mountains of Oregon and the redwood forests of northwestern California. Channel width and riparian canopy were measured at 10 equally spaced intervals along each 50m to 100m study reach. Stream depth was measured at 1m intervals along the study reaches. No significant differences were found in stream width and depth between streams draining old growth and harvested watersheds, but streams draining harvested watersheds had more open riparian canopies. Transient storage (As) was calculated as differences in area under the curves for predicted and actual Cl- transport through the study reaches. Few differences in As were measured between streams draining old growth and harvested watersheds. Nutrient uptake (NH4+1, PO4-3) was measured, along with the Cl- tracer, by depletion over stream distance. Phosphate (P) uptake lengths were not significantly different comparing stream draining old growth and harvested watershed, but were significantly longer where there was more riparian cover and where As was greater. Ammonium (N) uptake lengths were significantly longer in old growth compared to harvested watershed, and were significantly shorter where there was more riparian cover, stream channel area, or As. The opposing correlations of P and N uptake with riparian canopy and As suggest that P uptake is driven by autotrophic processes whereas N uptake is driven by heterotrophic processes.
KEY WORDS: nutrient, uptake, watershed, disturbance