## 3 Results and Discussion
### Results
#### 3.1.2 Model Evaluation against Observations  
The long-term record, which includes stream water discharge, and DON and DIN export is rare, and provides an opportunity to constrain model operation. A comparison of the time series records to the modeled result is included in Figure 5 and demonstrates that model effectively captures the seasonal pattern that is outlined by the measured discharge and DON. For these variables, the modeled Nash Sutcliffe efficiency [42] values are 0.71 and 0.53 respectively. The efficiency for DIN is \(-0.12\), which clearly indicates that the model does not capture the measured response. This apparent failure of the model is likely because we did not attempt to simulate impacts of the clear-cut harvest that occurred in 1975. The removal of the trees, and pre-treatment activity, led to elevated DIN export after the harvest. The effects on DIN of this disturbance have been explored by [43] and are clearly evident in the long-term record and has been attributed to reduced uptake of N by vegetation. It is worth noting that the calculated Nash-Sutcliffe for years prior to the management activity (1968 to 1973) is higher, 0.33, lending additional support to the suggestion. Evaluation of against Budget Estimates of N and C Fluxes  
Given that the model is capable of representing key long term output measurements of water, DIN and DON, and also the overall trends in storage, the next step is to evaluate the degree to which the model is working for the right reasons--this we accomplish through an evaluation of the internal rate terms. These rates include respiration, mobilization, immobilization, internal solute fluxes and the aquatic processes that follow from them. Here we return to the existing budget studies which provide a set of annual flux estimates which we utilize in calibration, and to better understand model function. Rate terms are broadly grouped into four categories representing carbon fluxes, the sources of nitrogen, SOM dynamics, and processes occurring in the aquatic environment. This division is not to suggest that these categories are independent of one another, but only to facilitate presentation of results. In all cases, we present continuous model results (Figures 6-9) and in addition, time-integrated average yearly values  
Figure 4: Model results for average annual storage of nitrogen and carbon. Results are normalized by the total sum of nitrogen and carbon. Figure 6: Key modeled rate terms associated with carbon cycling. (**a**) The plot represents the modeled time series, as indicated in the legend, across the 20 year simulation time frame. These data are summarized and presented as a box and whisker plot (**b**). Note that the \(y\) axis is log transformed in the upper plot, but is linear in the lower plot. The combination is provided to more clearly outline the range in variation. Figure 7: Key modeled rate terms associated with the input of nitrogen into the system. (**a**) The plot represents the modeled time series, as indicated in the legend, across the 20 year simulation time frame. These data are summarized and presented as a box and whisker plot (**b**). Note that the \(y\) axis is log transformed in the upper plot, but is linear in the lower plot. Figure 8: Key modeled rate terms associated with root zone SOM. (**a**) The plot represents the modeled time series, as indicated in the legend, across the 20 year simulation time frame. These data are summarized and presented as a box and whisker plot (**b**). Note that the \(y\) axis is log transformed in the upper plot, but is linear in the lower plot. Figure 9: Key modeled rate terms associated with SOM processing occurring below the root zone. (**a**) The plot represents the modeled time series, as indicated in the legend, across the 20 year simulation time frame. These data are summarized and presented as a box and whisker plot (**b**). Note that the \(y\) axis is log transformed in the upper plot, but is linear in the lower plot.