## 2 Experimental Section
### Quantification of Lake Metabolism  
To estimate the lake metabolism, DO mass balance model is used here. It includes the following equations [12]:  
\[\Delta\mathrm{O_{2}}/\Delta t=\mathrm{GPP-R-\mathit{F}}/Z_{\mathrm{mix}}-\mathit{A} \tag{1}\]  
where \(\Delta\mathrm{O_{2}}/\Delta t\) is the change in DO concentration over time (mg O\({}_{2}\cdot\mathrm{L^{-1}}\cdot\mathrm{h^{-1}}\)), GPP is the primary production (g O\({}_{2}\cdot\mathrm{m^{-3}}\cdot\mathrm{h^{-1}}\)), R is the ecosystem respiration (g O\({}^{2}\cdot\mathrm{m^{-3}}\cdot\mathrm{h^{-1}}\)), \(\mathit{F}\) is the oxygen exchange with the atmosphere (g O\({}_{2}\cdot\mathrm{m^{-2}}\cdot\mathrm{h^{-1}}\)), it is negative (positive) for downward (upward) flux of O\({}_{2}\). \(Z_{\mathrm{mix}}\) (m) is the mixed layer depth (m). Since Lake Taihu is a shallow lake and is not subject to thermal stratification, \(Z_{\mathrm{mix}}\) is assumed equal to the mean depth of 1.9 m. The term \(\mathit{A}\) includes all the other processes that change DO concentration, such as horizontal and vertical advection within the lake. For simplicity, it is omitted in this study. Following [PERSON] _et al._[12], the oxygen exchange with the atmosphere (\(\mathit{F}\)) is computed as:  
\[\mathit{F}\,(\mathrm{g\ O_{2}\ m^{-2}\ h^{-1}})=\mathit{k}\,(\mathrm{O_{2\ meas }-O_{2 sat}}) \tag{2}\]  
where O\({}_{2\ meas}\) is the actual DO concentration (mg\(\cdot\mathrm{L^{-1}}\)); O\({}_{2 sat}\) is the oxygen saturation (mg\(\cdot\mathrm{L^{-1}}\)) as a function of water temperature (T, kelvin). The equation of [PERSON] [29] which is used to calculate O\({}_{2 sat}\) has been corrected for altitude according to the United States Geological Survey (USGS) Water Quality Technical Memoranda 81.11 and 81.15 [30]. The coefficient \(\mathit{k}\,(\mathrm{m\cdot h^{-1}})\) is estimated using the Schmidt coefficient (\(\mathit{Sc}\)) and gas piston velocity corresponding to a Schmidt coefficient of 600 (\(\mathit{k}_{600}\)):  
\[\mathit{k}\,(\mathrm{m\cdot h^{-1}})=\mathit{k}_{600}\times(\mathit{Sc}/600)^{ \mathrm{-n}} \tag{3}\]  
where \(\mathit{n}\) is equal to 2/3 for wind speed at 10 m height (U\({}_{10}\)) \(<\) 3.7 m\(\cdot\)s\({}^{-1}\) and is equal to 0.5 for U\({}_{10}\)\(>\) 3.7 m\(\cdot\)s\({}^{-1}\). The Schmidt coefficient is calculated from water temperature (T, Celsius) using the equation of Wanninkhof [31]:  
\[\mathit{Sc}=1800.6-120.1\ \mathrm{T}+3.7818\ \mathrm{T^{2}}-0.0476\ \mathrm{T^{3}} \tag{4}\]  
The coefficient \(\mathit{k}_{600}\) (m\(\cdot\mathrm{h^{-1}}\)) depends on wind speed at 10 m height and is calculated using the equation of [PERSON] [32]:  
\[\mathit{k}_{600}\,(\mathrm{m\cdot h^{-1}})=(2.07+0.215\ \mathrm{U_{10}}^{1.7})/100 \tag{5}\]  
U\({}_{10}\) is calculated according to [PERSON] [33]. Other equations from [PERSON] _et al._[12] which are used to calculate metabolism are the following:  
\[\mathrm{NEP_{hr}}\,(\mathrm{g\ O_{2}\cdot m^{-3}\cdot h^{-1}})=\Delta\mathrm{O _{2}}-\mathit{F}/Z_{\mathrm{mix}} \tag{6}\]  
\[\mathrm{NEP_{daytime}}\,(\mathrm{g\ O_{2}\cdot m^{-3}\cdot daylight\ period^{-1}})= \mathrm{mean\ NEP_{hr}}\,\mathrm{during\ daylight\ \times\ day\ fraction\ \times 24} \tag{7}\]  
\[\mathrm{R_{hr}}\,(\mathrm{g\ O_{2}\cdot m^{-3}\cdot h^{-1}})=\mathrm{mean\ NEP_{hr}}\, \mathrm{during\ darkness} \tag{8}\]  
\[\mathrm{R_{daytime}}\,(\mathrm{g\ O_{2}\cdot m^{-3}\cdot daylight\ period^{-1}})= \mathrm{R_{hr}}\times 24\ \mathrm{h\ \times\ dayfraction} \tag{9}\]  
\[\mathrm{R_{day}}\,(\mathrm{g\ O_{2}\cdot m^{-3}\cdot d^{-1}})=\mathrm{R_{hr}} \times 24\ \mathrm{h} \tag{10}\]  
\[\mathit{F}\,(\mathrm{g\ O_{2}\ m^{-2}\ h^{-1}})=\mathit{k}\,(\mathrm{O_{2\ meas }-O_{2 sat}}) \tag{2}\]0  
The DO concentration changed with temperature and biological activities. Driven by seasonal temperature changes, the saturation DO had a significant seasonal pattern, with lower values in summer and higher values in winter, and with the opposite tendency with respect to temperature.