# Effect of Extreme Climate Events on Lake Ecosystems
###### Abstract
Epilimnetic respiration increased and net ecosystem productivity decreased. The ratio of total nitrogen:total phosphorus in the lake surface waters versus that in the inflow rivers followed different patterns after the storm, a change that led to cascading effects on higher trophic levels and emphasized the key role that extreme weather may have on lake ecosystems. In the same lake and during the same time period, [PERSON] et al. (2020) studied the bacterial community composition using high-throughput sequencing to explore the bacterial community composition in this humic oligotrophic lake and to assess the impacts on composition dynamics related to extreme weather events. Filtration was used to separate free-living and particle-associated bacterial communities and amplicon sequencing was performed for the 165 rRNA V4 region. Two storms, six high discharge events, and one drought period occurred during the sampling period. They found that the particle-associated community was more likely to respond to physical changes, such as mixing, while the free-living population responded to changes in nutrient and carbon concentrations. Generally, however, a high stability of the bacterial community was observed, suggesting that the bacterial community is relatively resilient to extreme weather events. Using an experimental mesocosom approach, [PERSON] et al. (2021) studied the effect of simulated extreme precipitation on submerged macrophytes based on three different community treatments. These included six species of various growth forms in various combinations. Two levels of extreme precipitation treatment were simulated, one simulating a sudden increase of water level from 75 cm to 150 cm within one day and the other a gradual increase to the same water level within 3 months. They found that the macrophyte community biomass was resilient to the disturbances, while species-specific variations in responses, in terms of biomass, maximum height, and sexual reproduction, were found. They concluded that freshwater ecosystems with high coverage of submerged macrophytes may be overall resilient to extreme precipitation under nutrient-limited conditions, especially communities with diverse growth forms. Three papers in this issue deal with the ecological effects of a 5 \({}^{\circ}\)C simulated heatwave. Using the world's longest-running shallow lake experiment facility, investigations were conducted in mesocosoms adapted to three different temperature treatments (ambient, IPCC A2 scenario, and A2+50% and two levels of nutrient loadings (high and low)) for 11 years prior to the initiation of the additional 5 \({}^{\circ}\)C heatwave. Thus, each mesocosom was adapted to different conditions prior to the onset of the experiment. [PERSON] et al. (2021), [PERSON] et al. (2023), and [PERSON] et al. (2024) studied the effects of the simulated one-month summer heatwave in the A2 and A2+50% mesocosoms on phytoplankton, zooplankton, and metabolism, respectively. [PERSON] et al. (2021) found major differences in the phytoplankton community and biomass between the low and high nutrient mesocosoms, while the effects of the temperature treatments as well as the heatwave were modest and clearest in the high temperature scenario in the low nutrient treatments. Stability analyses revealed that the high nutrient mesocosoms were less affected by the heatwave press disturbance, most likely because the dominant algae group, cyanobacteria, is rather tolerant to variations in temperature. The authors concluded that the phytoplankton community was strongly affected by the nutrient level but less sensitive to the heatwave-induced changes in temperature in these systems that had already adapted to long-term temperature differences prior to the experiment. Also for zooplankton, the nutrient effect was much stronger than that of temperature in this experiment ([PERSON] et al., 2020). Before the heatwave, taxon richness was higher and functional diversity and evenness were lower in the high nutrient tanks.