# Ecosystem Metabolism in Small Ponds: The Effects of Floating-Leaved Macrophytes
## 2 Materials and Methods
### Pond Dissolved Oxygen Levels and Ecosystem Metabolism  
From 17 May 2018 to 29 October 2018 (except in Warner when our instrument failed after 27 September 2018), we measured O\({}_{2}\) concentration every 10 min in each pond using HOBO(r) Model U26-001 optical dissolved oxygen sensors fitted with copper antifouling guards. Oxygen sensors were placed in the center of the pond and maintained at 10 cm below the water surface. In Stickleback and Warner ponds we placed a second sensor at 0.75 m in depth (approximately halfway to the bottom of the ponds) starting on 22 June 2018, to examine vertical variability in O\({}_{2}\) levels. We also deployed HOBO(r) weather stations at each pond. These weather stations were outfitted with photosynthetically active radiation (PAR) (HOBO(r) Model S-LIA-M003), wind speed (HOBO(r) Model S-WSB-M003) and barometric pressure sensors (HOBO(r) Model BPB-CM50). Finally, we placed water depth sensors (HOBO(r) model U20 L-04) in each pond. We compared the differences in O\({}_{2}\) level (arcsine-transformed% saturation) of the surface located sensors among ponds over the course of the sampling period using a mixed-model ANOVA with O\({}_{2}\) as the dependent variable, pond as the independent variable and date as the random variable. Tukey's tests were conducted to examine which ponds were significantly different. We also compared the O\({}_{2}\) level of the surface and 0.75 m deep sensors in Stickleback and Warner ponds, again using a mixed model ANOVA followed by a Tukey's test. The components of ecosystem metabolism include gross primary production (GPP), respiration (R) and net ecosystem production (NEP = GPP - R). While some authors prefer to use net aquatic production (NAP) rather than NEP since emergent macrophytes and floating-leaved macrophytes would not contribute to estimates of primary production [37; 41], we have continued to use the NEP terminology which is more widely used. Daily changes in GPP and R in aquatic systems can be estimated by daily changes in O\({}_{2}\)[42]. If R is constant throughout the day and GPP only occurs during daylight hours, then the differences in oxygen levels between daylight and night hours can be used to estimate R and GPP. Taking O\({}_{2}\) measurements throughout the day allows the components of ecosystem metabolism to be estimated as:  
\[\frac{dC}{dt}=GPP-R+k(C_{s}-C)+GWA\]  
\[NEP=GPP-R\]  
where, \(C\) = concentration of oxygen, \(Cs\) = concentration of oxygen at saturation, \(k\) = reaeration coefficient and \(GWA\) = oxygen accrual from groundwater. The reaeration coefficient allows for the computation of O\({}_{2}\) changes due to the exchange of O\({}_{2}\) between the atmosphere and the water. We made calculations of daily values of GPP, R and NEP using the R-script LakeMetabolizer [43]. The R-script provides estimates based on five different models of fitting the oxygen, light and temperature data collected (bookkeeping, Bayesian, Kalman, maximum likelihood estimation and ordinary least squares). It also provides the possibility of calculating each model using different methods of estimating the reaeration coefficient. With the data we collected we were able to estimate the reaeration coefficient with three different methods--[PERSON] and Caraco [44], Crusius and Wanninkhof [45] and Vachon and Prairie [46]. [PERSON] et al. [43] details the assumptions behind both the different models and reaeration coefficients. We were able to generate 15 estimates of daily GPP, R and NEP (5 models with 3 estimates of reaeration coefficients each). [PERSON] et al. [43] did not provide information on the best model to use. They did comment on the issues surrounding the modelsproviding \"impossible\" values, i.e., values where GPP \(<0\) or R \(>0\), both of which are biologically unreasonable.