Measurement of Nutrient Transport and Uptake Parameters in Streams Using a Pulse Injection

Calculation of transport and uptake parameters in streams such as As/A, ts, Sw, and Vf is usually accomplished with a steady-state injection and a transport simulator such as OTIS [Runkel, 1998]. A steady-state injection is infeasible if ts is large or if discharge is high. However, a pulse injection measured at one or multiple downstream locations makes the experiment feasible even for high discharge [Tank et al., 2008], but creates challenges for data interpretation. We generate a set of simple equations for calculation of transport and uptake parameters from a pulse injection without the need for a transport simulator by extending the method of moments. The moment equations include decay parameters that are different between the channel and the transient storage zone. Moment equations can also be written for decay products, multiple timescales of exchange, and multiple decay rates. The method of moments is less dependent on the details of the exchange model than transport simulators, and so some parameters can be calculated independently from any assumptions about exchange timescales.