This is similar to enzyme kinetic experiments performed in a laboratory where uptake is measured across a range of substrate concentrations from zero substrate to near saturated (or saturated) conditions (e.g., Voet and Voet 1995). Next, the BTC of the tracer addition must be sampled across the entirety of the nutrient concentration range (i.e., across BTC) with substantial resolution to characterize spiraling at all concentrations experienced across the BTC. We have also found that longer stream reach distances, larger grab sample volumes (e.g., 250–1000 mL), and collecting samples from a fixed location in the channel (i.e., sampling through a tube attached to a post driven into the streambed) help to decrease sampling induced variability in spiraling curve data. This is particularly relevant in highly advective systems and/or those with substantial gains and losses to and from groundwater.