In terms of hydrology, it is important to measure Q at both the head and base of the stream reach. Conservative tracer released at the head of the reach cannot be used to calculate Q at the base of the reach.
This is because conservative tracer mass loss (i.e., hydrologic loss) along the stream length will lead to incorrect overestimates of Q at the base of the reach (this is true for both slug and constant-rate releases) (e.g., Payn et al. 2009). Also we encourage the use of the mass-balance approach for calculating uptake because it is a direct measure of nutrient use across the reach. Mass-balance derived uptake measures can be converted to Sw and Vf values to provide a full suite of spiraling metrics. These considerations should help to improve data quality and facilitate application of the method.