## 4 Discussion  
We studied nutrients, oxygen metabolism and bacteriplankton production before, during and after a simulated 1-month summer heat wave (HW) in shallow lake mesocosms run at contrasting nutrient concentrations and temperatures. As the mesocosms had already been in operation for 11 years prior to this experiment, we assumed that the different compartments (i.e., sediment, water and biota) have reached an equilibrium, allowing reliable comparison with natural systems. However, disentangling the effects of the HW from those of seasonality was not straightforward with our design lacking true controls. We, therefore, compared the data from the HW with those from the periods before \begin{table}
\begin{tabular}{c c} \hline \hline
**Data Set** & **With Chl-a TP and TN** \\ \hline Full & Log(GPP20) = 2.50(0.04) + 0.022(0.009) Log (Chl-a), \(p\) \(<\) 0.0001, \(n\) = 337 \\ Log(ER20) = 2.40(0.04) + 0.019(0.005) Log (Chl-a) \(-\) 0.026(0.007) Log(TN), \(p\) \(<\) 0.0001, \(n\) = 337 \\ Log(NEP20) = 2.43(0.01) + 0.031(0.009) Log(TN), \(p\) \(<\) 0.02, \(n\) = 337 \\ \hline LN & Log(GPP20) = 2.25(0.07) + 0.029(0.013) Log (TN) \(-\) 0.044(0.013) Log(TP), \(p\) \(<\) 0.0001, \(n\) = 168 \\ Log(ER20) = 2.28(0.03) \(-\) 0.033(0.008) Log (TN), \(p\) \(<\) 0.0001, \(n\) = 168 \\ Log(NEP20) = 2.27(0.07) + 0.055(0.013) Log(TN) \(-\) 0.041(0.013) Log(TP), \(p\) \(<\) 0.0003, \(n\) = 168 \\ \hline HN & Log(ER20) = 2.40(0.06) + 0.027(0.009) Log (Chl-a) \(-\) 0.058(0.016) Log (TP), \(p\) \(<\) 0.0001, \(n\) = 169 \\ GPP20 and NEP20 were not significantly related to these variables. \\ \hline Full and HN & GPP20, ER20 and NEP20 were not significantly related to PVI. \\ \hline \multirow{2}{*}{LN} & Log(GPP20) = 2.23(0.03) + 0.011(0.02) Log (PVI + 1), \(p\) \(<\) 0.02, \(n\) = 83 \\ Log(ER20) = 2.21(0.04) \(-\) 0.04(0.01) Log (TN) + 0.05(0.02) Log(PVI + 1), \(p\) \(<\) 0.0001, \(n\) = 83 \\ MEP20 was not significantly related to PVI. \\ \hline \end{tabular}
\end{table} 
Table 4: Multiple regression (backwards procedure) relating gross primary production standardized to 20 \({}^{\circ}\)C (Equation (1)), GPP20 and the same figures for ecosystem respiration (ER20) and NEP20 = GPP20-ER20 with chlorophyll a (Chl-a), total phosphorus (TP) and total nitrogen (TN) as explanatory variables and when also including the plant volume inhabited (PVI). Note that the dataset is smaller for the latter set (less PVI measurements). All \(p\) values are so low that even if they were corrected for multi-sampling, they would still be significant. Standard deviation is shown in brackets. \begin{table}
\begin{tabular}{c c} \hline \hline
**Data Set** & **With Chl-a TP and TN** \\ \hline Full & Log(BACPR) = \(-\)2.62(0.35) + 0.14(0.01) Log (Chl-a) + 1.03(0.11) Log (TEMP), \(p\) \(<\) 0.0001, \(n\) = 328 \\ \hline LN & Log(BACPR) = \(-\)4.97(0.80) \(-\) 0.16(0.04) Log (Chl-a) \(-\) 0.15(0.06) Log (TP) + 1.51(0.22) Log (TEMP), \(p\) \(<\) 0.0001, \(n\) = 160 \\ HN & Log(BACPR) = \(-\)0.66(0.19) \(-\) 0.024(0.011) Log(Chl-a) + 0.13(0.02) Log (TP) + 0.66(0.05) Log (TEMP), \(p\) \(<\) 0.0001, \(n\) = 168 \\ \hline \multicolumn{2}{c}{**With PVI, Chl-a TP, TN, and PVI Must Be included**} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Multiple regression (backwards procedure) relating bacteriplankton production (BACPR) with chlorophyll a (Chl-a), total phosphorus (TP), total nitrogen (TN) and water temperature (TEMP) as explanatory variables without and with inclusion of plant volume inhabited (PVI). Note that the dataset is smaller for the latter set (less PVI measurements). All \(p\) values are so low that even if they were corrected for multi-sampling, they would still be significant. SD is shown in brackets. and after, considering the changes in A0 having no artificial HW but warmer temperatures in July arising from a natural HW (Figure 1). We found a strong nutrient treatment effect on Chl-a, TP, TN and PO\({}_{4}\), as expected, given the major difference in nutrient loading of the LN and HN mesocosms.