This is important because to correctly parameterize kinetic models, it is critical that total spiraling values be used. This is demonstrated in conceptual Figure 2D, which shows uptake concentration curves for total (Utot) and added nutrient (Uadd). Because spiraling measured during a nutrient addition experiment is that of added nutrient, the measured uptake at zero-added nutrient concentration (i.e., ambient concentration with no influence of added nutrient) will appear to be 0 μg m–2 min–1 (Fig. 2D).
However, this neglects to recognize that Uadd occurs in addition to Uamb also occurring in the stream reach (Fig. 2D). For this reason, if kinetic models are parameterized using Uadd instead of Utot data, the parameter values will be incorrect.