| |
Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Landscapes
Geomorphic and hyporheic controls on water temperature in fluvial landscapes
G.C. Poole1,2, S. O''Daniel3,4, S.A. Thomas1, L.A.K. Mertes4, W.W. Woessner5, B.R. Boer5, and A.S. Arrigoni4. 1Eco-metrics, Inc., Tucker, GA and Pendleton, OR, 2Institute of Ecology, University of Georgia, Athens, GA, 3Confederated Tribes of the Umatilla Indian Reservation, Pendleton, OR, 4Department of Geography & ICESS, University of California, Santa Barbara, CA, 5Department of Geology, The University of Montana, Missoula, MT
Stream temperature is an important variable influencing lotic ecosystems. In many alluvial rivers of the Pacific Northwest, seasonal floods scour the bank-full channel, creating expansive unvegetated gravel bars exposed at low flows. Thus, in these systems, shade from streamside vegetation is a less important driver of the thermal regime than in smaller, more confined headwater streams. In the Umatilla River, Oregon, evidence from remote sensing, modeling, and hydrologic field studies suggests that water exchange between the channel and hyporheic zone has a major influence on the spatio-temporal patterns of temperature at multiple scales across and along the fluvial landscape. Beyond creating a diversity of thermal conditions including patches of cool water ("thermal refugia"), hyporheic exchange influences the longitudinal pattern of stream temperature in the main channel, at times even reversing the expected downstream warming trend. Further, evidence suggests that channel engineering (e.g., dredging and straightening the river) reduces hyporheic exchange by simplifying spatial geomorphic patterns, thereby eliminating hydraulic gradients that drive hyporheic fluxes. Subsequent reductions in hyporheic exchange rates are correlated with accelerated rates of downstream warming. Thus, in some fluvial landscapes, restoration of channel and flood plain morphology may be an important tool for recovery of degraded thermal regimes.
|
|
