A portable flow chamber for in situ determination of benthic metabolism

1. Many stream ecologists are interested in determining the metabolic rates of benthic organisms, particularly those of production and respiration. It is often necessary to make these measurements on fresh material in the field at remote sites. Recirculating chambers are commonly used for this purpose. 2. A broad variety of recirculating chambers are described in the literature, but each design has inherent limitations. The most common are inability to control flow in the chamber and match it with external flow rates, and a lack of the power required to do this for extended periods. Alteration of spectral irradiance, temperature rise and elevated internal chamber pressures are additional limitations that have received little attention. 3. We have designed and constructed a flow chamber that eliminates some of these problems. The chamber utilizes a DC motor-driven propeller as an efficient recirculator (axial impeller), minimizing power requirements and it is constructed of UVB transparent acrylic to allow a full spectral complement of solar irradiance in the interior. Modular components allow the chamber to be taken apart quickly for cleaning and replacement of parts, making it more functional than some previous designs. 4. The axial impeller chamber was compared to a similar sized conventional chamber that had a small diameter return line and a high capacity centrifugal pump. The axial impeller chamber had less of a temperature rise during field incubations, lower power consumption and less internal pressure in the return line when producing equivalent water velocities. 5. The reported axial impeller design had relatively homogeneous velocity across the working section relative to other chambers and was capable of water velocities in excess of 1 m s–1.