## 4 Discussion  
The work described here gives an insight into how a deep monomotic dystrophic lake situated on the Atlantic coast of Europe responded to sequential extreme weather events. To our knowledge, it is the first study reporting on planktonic community responses relating to the 2018 European heatwave, when Western Europe, in particular, experienced notably increased summer surface lake water temperature [52; 64]. In turn, for the study site, Storm Hector was of particular interest, as it abruptly interrupted the heat wave conditions, with high temperatures and drought well outside the ranges normally recorded in Ireland. The physical structure of the Feeagh water column responded to the arrival of the first heat wave in the early summer season (late May-early June), with a rapid stratification of the water column (high Schmidt stability). Consequently, once Storm Hector arrived, Feeagh experienced a characteristic mixing event with a surface mixed layer deepening of 9.5 m at the end of June, never previously reported at this site [63]. Following Storm Hector, the anomalous pre-storm heat wave conditions returned, allowing an unprecedented isolated summer mixing episodic event in the middle of extremely high lake stability, for the site, to be examined. The unusual lake stratification pattern presented in this study differed from another episodic flood event which occurred on the 2 nd of July 2009 at the same site. Compared to the 2018 event, in 2009 there was a loss of Schmidt stability for the rest of the year and, despite the extreme nature of the event, the overall lake impact was considered relatively small [10]. In contrast, results from this study show that the mixing event induced by extreme continuous weather events drove a shift towards an increase in R and a decrease in NEP, despite the already natural heterotrophic conditions of the system [66]. In turn, a two-fold reduction in Chl \(a\) coincided with a three-fold reduction in lake Schmidt stability. In contrast, pre- and post-storm heat waves clearly encouraged fast growth of phytoplankton cells in the top water layers. As a consequence, an unexpected and atypical increase in cyanobacteria was observed at the end of July and beginning of August. In addition, observations of N:P imbalances for primary consumers in Lough Feeagh indicated a step change from P to N nutrient constrains following the mixing event in June. Furthermore, an increase in total zooplankton biomass during the intermediate period indicated a quick response to potential availability of more favourable food for primary consumers. Metabolism estimates can provide a concise summation of the many effects of extreme meteorological events. In this study, we observed a significant increase in ecosystem R and a decrease in NEP during the intermediate mixing period, compared to pre- and post-storm warm and stable periods, which resulted in a slight decrease in GPP following Storm Hector. Similar to our study, some authors have also reported a decrease in GPP and an increase in R after flooding events, coinciding with an increase in bacterial biomass and a decrease in phytoplankton biomass and Chl _a_[10; 44; 46]. In contrast, results from thermocline-deepening experimental mesocosms, simulating the effects of storm events, showed that surface water GPP responded more strongly than R as a consequence of increased autotrophy driven by the proliferation of filamentous cyanobacteria released from light and nutrient limitation, resulting in an increase in NEP [43]. Phytoplankton primary production and bacterioplankton secondary production are influenced by bioavailable nutrients and, in turn, both processes support fluxes of energy and matter to higher trophic compartments [105]. In freshwater ecosystems, a range of organic and inorganic species of N and P co-occur. Both the amounts and stoichiometry of the total bioavailable resources determine nutrient limitation patterns in planktonic communities [23].