Groundwater flux and open-channel estimation of stream metabolism: response to Hall and Tank

James H. McCutchan, William M. Lewis

Limnol. Oceanogr. Methods 4:213-215 (2006) | DOI: 10.4319/lom.2006.4.213

ABSTRACT: Rates of metabolism for a stream can be estimated from open-channel measurements of dissolved oxygen at 1 or 2 stations, provided that reaeration flux and groundwater flux to the channel are quantified, and the underlying assumptions of the mass-balance method are satisfied. Hall and Tank (Limnol. Oceanogr. Methods 3:222-229, 2005) challenge our previous work on open-channel estimation of oxygen metabolism (McCutchan et al., Limnol. Oceanogr. 47:321-324, 2002) on grounds that our principal mass-balance equation is incorrect. However, Hall and Tank have misrepresented our equation by considering the oxygen mass-balance for an entire reach rather than for a parcel of water moving downstream and by presenting volume as a constant rather than a function of time. Because Hall and Tank incorrectly reformulated our mass-balance equation, their conclusions are not relevant to our work.