Transient storage and gas transfer in lowland stream

Conservative and gaseous tracers are used in conjunction with several models to characterize transport and gas transfer for a small, sluggish lowland stream, the Piako River, in New Zealand. Results obtained with the transient storage model indicate that storage zones make up a significant proportion of the total stream cross section. This result is consistent with the fact that the river is lined with profuse marginal vegetation. However, because of their high density, exchange between these areas and the main channel is minimal. Hence, their net impact is to increase velocity and depth, rather than to trap pollutants. Measurement of gas exchange indicates that, although storage zone models fit tracer profiles better, the effect of transient storage on the estimation of gas transfer rates is negligible for systems like the Piako.