## 4 Discussion  
Inflow and outflow concentrations of TDN from the dry detention basin were similar, indicating poor treatment of nitrogen by the basin. After the basin was converted to a wetland, the treatment efficiency of the SCM increased, and the quality of water entering Reedy Branch improved. More specifically, discharge from the wetland had TDN and DIN concentrations that were 63% and 81% lower relative to wetland inflow. Furthermore, median concentrations of TDN and DIN in outflow from the wetland were nearly 66% and 73% lower relative to outflow from the basin. While the authors did not have the analytical laboratory capacity to directly measure dissolved organic nitrogen (DON), an estimate of DON may be calculated by subtracting DIN (NH\({}_{4}\)\({}^{+}\) and NO\({}_{3}\)\({}^{-}\)) from TDN. Based on these estimates, the median influent and effluent concentration of DON for the dry basin were similar, with 0.01 mg L\({}^{-1}\) more DON entering in comparison to exiting the basin. Differences in the estimated median DON concentration entering and exiting the wetland were larger, with 0.09 mg L\({}^{-1}\) more DON leaving the wetland than entering. Therefore, while the wetland was most often a sink for DIN, it was a source of DON. Most of the reduction in TDN concentrations for the wetland could be attributed to NO\({}_{3}\)\({}^{-}\) reduction. There was a decrease in NO\({}_{3}\)\({}^{-}\) concentration of 0.24 mg L\({}^{-1}\) when comparing outflow to inflow concentrations for the wetland, while NH\({}_{4}\)\({}^{+}\) concentrations decreased by 0.08 mg L\({}^{-1}\). It is likely that the mechanism for NO\({}_{3}\)\({}^{-}\) removal within the wetland was denitrification. Denitrification is the conversion of NO\({}_{3}\)\({}^{-}\) to N\({}_{2}\) or N\({}_{2}\)O, and requires anaerobic conditions, NO\({}_{3}\)\({}^{-}\), a source of carbon to serve as the energy sources and electron donor, suitable environmental conditions (e.g., pH, temperature), and time for microbial activity [12, 19, 28]. These requirements were present in the wetland. For example, the median DO concentration in wetland outflow was 4.1 mg L\({}^{-1}\) lower than the median inflow concentration (Table 1). The median ORP of wetland outflow was almost 300 mV lower in comparison to the median basin outflow, and 141 mV lower than wetland inflow. Thus, the lowered (relative to inlet) DO and ORP values in the wetland outflow indicates that the wetland was a reducing environment, where conversion of NO\({}_{3}\)\({}^{-}\) to N\({}_{2}\) may occur [19, 28]. The median DOC concentration in wetland outflow was greater in comparison to wetland inflow, and dry basin inflow and outflow. The increase in DOC for wetland outflow may be related to leaves, pine straw, and other organic debris that enters the wetland and sinks or is too large to pass through the small outlet pipes and decomposes, releasing DOC. These processes may also have contributed to the net export of DON from the wetland. The median concentration of NO\({}_{3}\)\({}^{-}\) in wetland influent was 0.30 mg L\({}^{-1}\) and the median DOC concentration in wetland outflow was 7.1 mg L\({}^{-1}\), resulting in a DOC to NO\({}_{3}\) ratio of 23:1. Based on that ratio, denitrification would not likely have been limited by carbon in the wetland [20, 29]. Water temperatures exceeded 2 \({}^{\circ}\)C for each storm sampled during the study, thus environmental conditions including temperature were conducive in the wetland for the denitrification process [21]. The pH of wetland inflow and outflow was greater than 4.5, thus pH was in the range suitable for nitrogen transformations by microorganisms [21]. The residence time of water in the wetland was more than an order of magnitude greater in comparison to the residence time in the basin. There was more time and opportunity for carbon and nitrogen transformations in the wetland relative to the basin. There was also a reduction in the median concentration of NH4\({}^{+}\) when comparing outflow to inflow concentrations in the wetland.