# Multi-Year Monitoring of Ecosystem Metabolism in Two Branches of a Cold-Water Stream
## 3 Results
### Physical-Chemical Parameters
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Variable** & **Factor** & **F Ratio** &
\begin{tabular}{c} **Degrees of** \\ **Freedom** \\ \end{tabular} & **Probability \textgreater{} F** \\ \hline \multirow{3}{*}{Water depth} & Year & 128,744.2 & 2, 154,114 & \textless{}0.0001 \\  & Location & 10,356.5 & 1, 154,097 & \textless{}0.0001 \\  & Year * Location & 25,347.5 & 2, 154,083 & \textless{}0.0001 \\ \hline \multirow{3}{*}{Discharge} & Year & 188.4 & 1, 690 & \textless{}0.0001 \\  & Location & 1445.9 & 1, 1446 & \textless{}0.0001 \\  & Year * Location & 9.3 & 1, 573 & 0.002 \\ \hline \multirow{3}{*}{Temperature} & Year & 599.8 & 2, 148,717 & \textless{}0.0001 \\  & Location & 311,070.6 & 1, 311,070 & \textless{}0.0001 \\  & Year * Location & 56.5 & 2, 148,707 & \textless{}0.0001 \\ \hline \multirow{3}{*}{\% DO} & Year & 5143.7 & 2, 125,124 & \textless{}0.0001 \\  & Location & 21,036.5 & 1, 125,129 & \textless{}0.0001 \\  & Year * Location & 2807.5 & 2, 125,066 & \textless{}0.0001 \\ \hline \multirow{3}{*}{GPP} & Year & 12.8 & 2, 809 & \textless{}0.0001 \\  & Location & 578.2 & 1, 808 & \textless{}0.0001 \\  & Year * Location & 23.5 & 2, 795 & \textless{}0.0001 \\ \hline \multirow{3}{*}{ER} & Year & 38.0 & 2, 844 & \textless{}0.0001 \\  & Location & 1.3 & 1, 845 & 0.3 \\  & Year * Location & 67.0 & 2, 832 & \textless{}0.0001 \\ \hline \multirow{3}{*}{NEP} & Year & 5.4 & 2, 855 & 0.0046 \\  & Location & 128.6 & 1, 859 & \textless{}0.0001 \\ \cline{1-1}  & Year * Location & 33.9 & 2, 846 & \textless{}0.0001 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mixed-model ANOVAs of location and year on water temperature, water depth, arcsine-transformed percent dissolved O\({}_{2}\) (DO), and measures of ecosystem metabolism—In (gross primary production—GPP), In (ecosystem respiration—ER), and In (net ecosystem production—NEP). Discharge was more variable in the North Branch than the South Branch (coefficient of variation 11.8 versus 3.9%, respectively). The conductivity, measured in both locations in 2017 was higher in the North Branch than the South Branch (Table 1, \(t\)-test \(-\) t\({}_{39222}\) = 51.9, \(p\) < 0.0001). From data provided by the St. Croix Watershed Research Station (Science Museum of Minnesota--Table 1), there was no significant difference in dissolved P levels between the branches or years (two-way ANOVA--location: \(F_{1,11}\) = 6.8, \(p\) = 0.6; year: \(F_{2,11}\) = 1.3, \(p\) = 0.3; location*year: \(F_{2,11}\) = 0.7, \(p\) = 0.5). There was a significant difference in dissolved N between branches with the South Branch having higher levels of N but no difference between years (two-way ANOVA--location: \(F_{1,11}\) = 249.9, \(p\) < 0.0001; year: \(F_{2,11}\) = 1.2, \(p\) = 0.4; location*year: \(F_{2,11}\) = 1.0, \(p\) = 0.4). There were no significant differences between years in the amount of light reaching the streams (mixed-model ANOVA--\(F_{2,327}\) = 0.6, \(p\) = 0.5). However, for PAR levels measured in the forested part of the stream, there were significant differences (mixed-model ANOVA--\(F_{2,288}\) = 3.1, \(p\) = 0.04) with PAR being significantly lower in 2018 than in 2017 or 2019 (Figure 3). There was a large change in PAR values in the forested site over the seasons, with light levels decreasing greatly in early spring (May) and then remaining fairly constant after leaf-out (Figure 3). There was not as much change in PAR in the spring at the open site, used in calculating stream metabolism parameters, but a decline in the fall as the sun angle decreased. The North Branch is a gaining stream in the section of the Creek where the DO levels were measured, while the water in the South Branch is close to being in equilibrium with the groundwater (Figure 4) at the sampling location. For both branches, the exchange between surface and groundwater was fairly stable in 2017 and 2018 with a drop in the gradient in both streams in 2019 (Figure 4). The percent saturation of dissolved oxygen (DO) was significantly different between locations and years (Figure 5, Tables 1 and 2).