The focus of this study is to refine the process-based understanding of riparian hollows as small-scale nitrogen-retention mechanisms. We used a multicomponent flow and reactive transport model to simulate the effects of hydrobiogeochemical perturbations on riparian hollow nitrogen cycling dynamics, using data from the East River watershed to constrain the model. Model results suggest groundwater upwelling and rainfall events act as significant hydrologic controls on the nitrogen retention capacity of riparian hollows. Future climatic perturbations related to these controls will likely increase the sink capacity of riparian hollows, enhancing their function as inhibitors to upland nitrogen reaching the stream.