IMPROVEMENTS TO THE DIURNAL UPSTREAM-DOWNSTREAM DISSOLVED-OXYGEN CHANGE TECHNIQUE FOR DETERMINING WHOLE-STREAM METABOLISM IN SMALL STREAMS

Whole-stream metabolism in a first-order stream was measured using ups tream-downstream changes in dissolved oxygen (DO) concentration measur ed at 1-min intervals over a 40-h period. The measured change in DO wa s corrected for reaeration flux using a reaeration coefficient determi ned from injections of conservative and volatile tracers. The whole-st ream metabolism measurement was compared in the spring with in situ ch amber measurements performed a few days later in the same stream reach . Chamber measurements of community respiration extrapolated to a 24-h period (CR(24)) were about one third the whole-stream measurements, w hile gross primary production (GPP) measured at midday in the chambers was roughly 20% less than the whole-stream estimate. Whole-stream GPP was higher during the spring just prior to forest canopy closure than in summer or autumn. Community respiration exceeded whole-stream GPP on all dates and was greatest during the summer. Our results suggest t hat this whole-stream approach provides a measure of total stream meta bolism that is relevant to other stream ecosystem processes measured o n reach scales, such as nutrient spiralling.