Improvements to the Diurnal Upstream–Downstream Dissolved Oxygen Change Technique for Determining Whole-Stream Metabolism in Small Streams

TLDR

Whole‑stream metabolism was quantified by measuring 1‑min interval upstream–downstream dissolved‑oxygen changes over 40 h, correcting for reaeration with tracer‑derived coefficients, and comparing spring results to nearby chamber measurements taken a few days later. Whole‑stream estimates were roughly three times higher than chamber‑derived community respiration, with gross primary production 20 % greater, and showed higher spring GPP before canopy closure, while community respiration consistently exceeded GPP, peaking in summer, indicating the method captures total stream metabolism relevant to ecosystem processes such as nutrient spiralling.

Abstract

Whole-stream metabolism in a first-order stream was measured using upstream–downstream changes in dissolved oxygen (DO) concentration measured at 1-min intervals over a 40-h period. The measured change in DO was corrected for reaeration flux using a reaeration coefficient determined from injections of conservative and volatile tracers. The whole-stream metabolism measurement was compared in the spring with in situ chamber 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, while 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 that this whole-stream approach provides a measure of total stream metabolism that is relevant to other stream ecosystem processes measured on reach scales, such as nutrient spiralling.