Title: The stream subsurface: nitrogen cycling and the cleansing function of hyporheic zones
Author: Mazza, Rhonda; Wondzell, Steve; Zarnetske, Jay;
Source: Science Findings 166. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 6 p.
Publication Series: Science Findings
Description: Nitrogen is an element essential to plant growth and ecosystem productivity. Excess nitrogen, however, is a common water pollutant. It can lead to algal blooms that deplete the water's dissolved oxygen, creating "dead zones" devoid of fish and aquatic insects.
Previous research showed that the subsurface area of a stream, known as the hyporheic zone, regulated amounts of waterborne nitrogen, but the nature of that role was unclear. Forest Service and university scientists undertook a suite of experiments to learn what factors determine if the hyporheic zone will be source or a sink for nitrogen.
They conducted a field study using a nitrogen isotope to monitor the flow path of water through the hyporheic zone of a gravel bar in a Willamette Valley stream. This experiment confirmed that the hyporheic zone can be either a net source or a net sink of nitrate--a reactive bioavailable form of nitrogen. Further analysis revealed that the residence time of water and uptake rate of oxygen by microorganisms in the hyporheic zone determine if this subsurface area functions as a nitrate source or sink.
The scientists then developed a theoretical framework to predict this nitrate source or sink potential of any hyporheic zone. Using this kind of information, stream restoration projects could be designed to maximize the selfcleansing process of hyporheic zones and help control water pollution.
Keywords: nitrogen, hyporheic zone, aquatic system, Steve Wondzell
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Mazza, Rhonda; Wondzell, Steve; Zarnetske, Jay. 2014. The stream subsurface: nitrogen cycling and the cleansing function of hyporheic zones. Science Findings 166. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 6 p.
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