Isotope tracers have substantially advanced our understanding of nitrogen flow through stream food webs, but few of these studies have been associated with reach-scale, experimental experiments. This is likely due to logistical difficulties associated with combining isotope additions with ecosystem-scale manipulations, but also reflects the lack of robust statistical tools to draw inferences from such experiments. We developed a Bayesian modeling approach (IsoTracer) to address this issue and apply it to isotope additions in stream reaches that were subjected to increased light (via canopy thinning) and fish introduction (guppy, Poecilia reticulata) to test hypotheses regarding N fluxes and food web topologies derived from laboratory and mesocosm experiments. Experimental methods followed LINX 1 protocols, except they were of shorter duration (10 days) and targeted a higher isotopic enrichment (~20,000 per mil). Each experimental reach had three sampling stations located approximately 25, 50 and 75 m downstream of the dripper. All ecosystem compartments were sampled prior to the addition, and on days 1, 3, 5, 7, and 10 during enrichment, and on five subsequent post-addition days. As predicted, our preliminary results indicate that the canopy-thinned streams, had enhanced NH4 flux to epilithon and seston, their primary consumers (Petrophila and Leptonema, respectively) and select secondary consumers (Eudaniela). In contrast, the impact of fish introduction on community standing stocks and nitrogen flow were substantially less than expected based on similar mesocosms experiments. We compared our approach with previously published results from these experiments using traditional empirical techniques and found that our model produced significantly different N-uptake rates for many of the primary uptake compartments and in both high and low-light treatments. Interestingly, both modeling approaches produced similar results for primary and secondary consumers under low-light conditions (within 95% credible intervals), but these approaches diverged for some consumers in the high-light treatment. The mechanisms driving these departures are currently being explored.