Changes in the Flux of Nitrate during Storms in an Eastern Shore, Virginia Stream

During a storm event, transient changes in the hydraulic gradient can result in very different discharge rates, residence times of bank storage, and ultimately NO₃^- concentrations in the stream. During varying storm events, water samples were collected with an automatic storm sampler and hydraulic gradient fluctuations between the stream and stream bank were measured with pressure transducers. In the nine storms sampled, NO₃^- concentrations generally decreased during the passing of a flood wave. Furthermore, flood wave height and duration together controlled NO₃^- flux during the storm as there was a strong positive relationship between the change in NO3- flux when compared with base flow and the total storm discharge when compared with base flow. Small flood waves with small discharges resulted in a decrease in NO₃^- flux during the storm. Slower discharges created longer residence times for more NO₃^- removal. Large flood waves ultimately resulted in an increase in NO₃^- flux, although large flood waves with different flood durations had vastly different increases in NO₃^- flux. Short durations created high rainfall intensities which reduced head gradients, discharge and NO₃^- flux. Conversely, long durations created low rainfall intensities which increased head gradients, discharge and NO₃^- flux. These results provide better insight into NO₃^- transport into streams and will inform better models to help predict future watershed NO₃^- budgets.