## 3 Results and Discussion
### Nutrient Concentrations from Preserved Samples
#### 3.2.1 Nitrate-N Results  
The nitrate-N concentrations are presented along with the percent change from the baseline concentration in Table 3. The baseline concentration is the concentration of the spiked source water, receiving no preservation, at time zero. The high and low daily temperatures are also presented for each of the time points collected. Nitrate-N concentrations are graphically presented in Figure 3, with error bars to represent the standard deviation from the mean of the three samples at each time point and for the respective preservation method. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Tile Water** & **Pond Water** & **Stream Water** \\ \hline pH & 7.72 & 8.36 & 8.23 \\ Conductivity (mS/cm) & 0.42 & 0.75 & 0.46 \\ Turbidity (FAU) & 4 & 13 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Water source characterization for each water source. Figure 3: _Cont._The high and low daily temperatures remained quite consistent throughout this study. The control treatment for tile water, which received no preservation, maintained the nitrate-N concentration quite well for the 14-day period. At the end of the study period, nitrate-N showed only a very slight increase (0.09%) in concentration. However, there was a greater variation throughout the 14 days. Nitrate-N concentrations tended to decrease, by as much as 6.07% on Day 5, showing that some heterogeneity in individual samples existed and denitrification could have impacted the stability of the samples, as microbial activity was not inhibited. The control treatment for pond water was also quite stable, showing a 2.27% increase in nitrate-N concentration at the end of the 14-day period, with only slight variations (0.06-1.44%) throughout the period. Stream water showed the highest change in nitrate-N concentration for the control treatment, increasing by 6.68% at the end of the 14-day study period. Figure 3: Comparison of the impact of the four preservation methods on nitrate-N concentrations for Day 0–14. Error bars represent +/\(-\) one standard deviation from the mean. Note the \(y\)-axis values are not the same for each water source for visual clarity. (**a**) Tile water; (**b**) Stream water; (**c**) Pond water. The filtered treatment for the tile water showed the largest Day 14 change (7.47% decrease) of any preservation method and water source tested in this study. Since the concentrations all decreased relative to the baseline, except for Day 2, it is possible that denitrification was occurring, as the sample was non-preserved up until the time of collection, at which time it was filtered. The filtered pond water showed a similar trend as the tile water. All nitrate-N concentrations decreased, with the exception of Day 0.5. In the case of the pond water, processes like adsorption to particulate matter may have caused variation in addition to denitrification, since the pond water had the highest conductivity and turbidity of the three source waters tested in this study. The filtered stream water held the baseline concentrations the best of the three source waters, with a 2.38% increase in nitrate-N concentration on Day 14. All time points, except Day 2 and Day 14, showed a decrease in concentration for the stream water. The tendency of concentrations to decrease with the filtration method is in contrast to other studies, where nitrate-N concentrations increased by as much as 3.7-fold when samples went unfiltered for 10 days [4]. The sulfuric acid preservation method is intended to eliminate microbial activity and lower the pH to less than two. Therefore, processes like denitrification or immobilization should not have impacted