# Multi-Year Monitoring of Ecosystem Metabolism in Two Branches of a Cold-Water Stream
## 3 Results
### Ecosystem Metabolism  
Rates of ecosystem metabolism were calculated for 1068 days. Of these, 73 days (7%) were excluded from the analysis because the model did not converge or the R\({}^{2}\) values for the model fit were less than 0.5. Of these, 21, 23, and 29 days were excluded for 2017, 2018, and 2019, respectively, and 70 of the 73 were for the North Branch location. There were significant differences for GPP, ER, and NEP between years and locations and their interaction (Figure 6, Table 2). A Tukey test indicated that GPP was significantly lower in 2017 than in 2018 or 2019 (Table 3). GPP was greater in the South Branch than the North Branch (Table 3). The significant interaction term (Table 2) showed that GPP was highest in 2019 in the North Branch, but highest in 2018 for the South Branch (Table 3). GPP was also highest in May in most years (Figure 6). For ER, there were significant differences between years but not between locations (Figure 6, Table 2). However, there was a significant interaction between location and year; thus, location did play a role in the differences between years. For ER, there was no significant difference between years for the South Branch, while for the North Branch, ER was significantly lower in 2019 than in 2017 or 2018 (Table 3). Generally, ER was lower in the South Branch than the North Branch except for 2019 (Table 3). NEP was generally \(<0\) for both locations and all 3 years (Figure 6). There were significant differences between locations and years in NEP (Figure 6, Table 2). NEP was generally greater (less negative) in the South Branch than the North Branch except for 2019 (Table 3). NEP was greatest in the South Branch in 2018, while it was lowest in 2018 for the North Branch, demonstrating the importance of the interaction term (Tables 2 and 3). An ANCOVA showed that water temperature had a significant impact on GPP and through significant interaction terms on ER and NEP (Table 4). Since there was no significant interaction term for GPP, thus, the temperature impacts on GPP were similar although small (Figure 7). There was an increase in ER with temperature in the North Branch but a small but negative effect in the South Branch (Figure 7). For NEP, the increased temperature had a positive effect on NEP in the South Branch but a negative effect in the North Branch (Figure 7). Light intensity, measured as PAR, had a significant impact on GPP, and this impact varied by location (Figure 7, Table 5). The impact was greater for the North Branch than the South Branch (Figure 7). PAR did not have a significant effect on either ER or NEP except through its interaction with location (Figure 7, Table 5). For the North Branch, there was a slight positive effect of PAR on ER but a slight negative effect in the South Branch. For NEP, the effects of PAR were just the opposite; slightly negative for the South Branch and slightly negative for the North Branch (Figure 7). PAR used in these calculations were from a sensor in full sunlight. \begin{table}
\begin{tabular}{c c c c c} \hline
**Variable** & **Factor** & **F Ratio** & **Degrees of Freedom** & **Probability \textgreater{} F** \\ \hline \multirow{4}{*}{GPP} & \(\ln\) (temperature) & 15.5 & 1, 868 & \textless{}0.0001 \\  & Location & 97.8 & 1, 868 & \textless{}0.0001 \\  & \(\ln\) (temperature) & \multirow{2}{*}{0.5} & \multirow{2}{*}{1, 868} & \multirow{2}{*}{0.47} \\  & \(\ast\) location & & & \\ \hline \multirow{4}{*}{ER} & \(\ln\) (temperature) & 3.5 & 1, 868 & 0.06 \\  & Location & 0.7 & 1, 868 & 0.4 \\  & \(\ln\) (temperature) & \multirow{2}{*}{22.9} & \multirow{2}{*}{1, 868} & \multirow{2}{*}{\textless{}0.0001} \\  & \(\ast\) location & & & \\ \hline \multirow{4}{*}{NEP} & \(\ln\) (temperature) & 3.5 & 1, 868 & 0.06 \\  & Location & 75.3 & 1, 868 & \textless{}0.0001 \\  & \(\ln\) (temperature) & \multirow{2}{*}{22.9} & \multirow{2}{*}{1, 868} & \textless{}0.0001 \\  & \(\ast\) location & & & \\ \hline \end{tabular}
\end{table}