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WATER QUALITY CHANGES IN HYPORHEIC FLOW AT THE AQUATIC-TERRESTRIAL INTERFACE OF A LARGER RIVER
Citation:
Fernald, A. G., P. J. WIGINGTON JR, AND D H. Landers. WATER QUALITY CHANGES IN HYPORHEIC FLOW AT THE AQUATIC-TERRESTRIAL INTERFACE OF A LARGER RIVER. Presented at American Geophysical Union Spring 2000 Meeting, Washington, DC, May 30-June 3, 2000.
Description:
Exchange between river water and groundwater in hyporheic flow at the aquatic-terrestrial interface can importantly affect water quality and aquatic habitat in the main channel of large rivers and at off-channel sites that include flowing and stagnant side channels. With tracer studies on the Willamette River, Oregon, we identified high rates of surface water-groundwater exchange in bar deposits that were reworked by an active river channel. We instrumented six of these deposits with 20-30 wells each to study hyporheic flow paths and water quality changes. With water level data we determined the direction of subsurface flow, and we measured the distance from the river along the hyporheic flow paths to each sampling point. In river source water, hyporheic flow, and receiving off-channel surface water, we measured physical and chemical water quality characteristics.
Water physical characteristics show that riverine surface water is the primary component of water in hyporheic flow paths that have residence times of a few hours to a few days. Analyses of oxygen and hydrogen stable isotope signatures provide additional data on the riverine surface water and terrestrial groundwater components of hyporheic flow. At a majority of sites we found the following changes in hyporheic flow compared to river source water: dissolved oxygen, temperature, and ammonium decrease; and specific conductance, soluble reactive phosphorus, and nitrate increase. Our research shows that physical and chemical changes in hyporheic flow affect receiving off-channel surface water and the magnitude of this effect depends on site substrate porosity.
Sampling a range of sites is important for characterizing hyporheic water quality relationships over river reaches on the order of tens of kilometers long. In the river ecosystem as a whole, hyporheic flow appears to promote overall water quality stability while at specific sites it seems to create and maintain aquatic habitat diversity.