IN-STREAM MANAGEMENT OF AN ESTUARINE BAY
In-stream management uses devices and techniques for treatment and flow management directly within control structures and receiving waters. One challenge facing watershed management is the large volumes of sediments already stored in receiving waters. When coupled with poor circulation, these conditions result in hypoxic events that impede benefits from upland restoration efforts. From September 2000 to August 2001, three InStreem™ water units were installed in Wilson Bay, North Carolina, USA to enhance circulation as part of a multi-phase effort to restore Wilson Bay. Prior to InStreem™, bay sediments supported macroinvertebrates only in the cooler months of the year. During the late spring to fall, anoxic conditions at the bottom of the bay were widespread as indicated by the lack of benthos, black surficial sediments, and a septic smell. The bay experienced extended periods of hypoxia, and currents ranged from 2 cm/s at the bay mouth to <0.3 cm/s in the N and NE sectors of the bay. After InStreem™, surficial sediments changed from black to a light brown color and the septic smell was eliminated. Apparent redox potential discontinuity (RPD) layer depth increased from zero to several millimeters within one month of InStreem™ operation. Current direction was reversed during falling tide conditions, increasing to 3 cm/s at the bay mouth and to 2–4 cm/s in the N and NE sectors. In August 2001, the methodology changed to benthos evaluation when RPD layers at most sites were too complex for visual tabulation. Benthos in the areas of enhanced flow were comparable to the positive control areas – areas with natural flow. With induced circulation and mixing, hypoxic events (12- hour averages of dissolved oxygen near the bottom) decreased nearly three-fold. The results of this study indicate that in-stream water management offers an effective addition to integrated watershed management.
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Document Type: Research Article
Publication date: 2002-01-01
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