# Effect of Extreme Climate Events on Lake Ecosystems
###### Abstract
During an average summer storm, the lake number dropped by an order of magnitude, the thermocline deepened by an average of 2.8 m, water column stability decreased, and the epilimnion temperature decreased by a factor of five compared to the average change in response to winter storms (0.5 \({}^{\circ}\)C vs. 0.1 \({}^{\circ}\)C). The results suggest that any projected increase in summer storm frequency may have important implications for lake physics and biological pathways. In the Arctic and Alpine areas, the frequency of glacial lake outburst floods (GLOF) is increasing due to climate change, and this may also have strong effects on circulation patterns and biota in downstream aquatic ecosystems. [PERSON] et al. [16] explored the response of circulation and zooplankton abundance in a Patagonian fjord to GLOF events between 2008 and 2014 based on measurements of current velocities, density, in-situ zooplankton samples, and volume backscatter (Sv) derived from an acoustic profiler. They found an increase in Sv in late winter and spring, which coincided with a high species richness of zooplankton. In addition, diel vertical migrations were recorded during this seasonal increase. These events combined with wind forcing that deepened the pycnocline led to peaks in zooplankton abundance, indicating that mixing conditions could favor secondary production. The concentration of dissolved organic carbon (DOC) in freshwater catchments has implications for the carbon availability in downstream lakes and for water supplies. [PERSON] et al. [17] used high-frequency fluorescence data, a proxy for DOC, to investigate the relationship between stream discharge and DOC in a blanket peat catchment during extreme high flows, as well as the relationship between inflow and in-lake DOC concentrations. They found that for approximately 2/3 of extreme events, there was a decrease in stream DOC concentrations on the rising limb of the hydrograph rather than an increase. Events where DOC concentrations increased dominated only in spring and summer. In comparison to the stream, concentrations in the downstream lake were less variable, and peaks and troughs were damped and lagged. [PERSON] et al. [18] also evaluated the effects of extreme events on the quality of DOC that exported to lakes by measuring changes in DOC concentration and quality in boreal lakes following storm events in different seasons. They found differences in the response of DOC quality metrics between an early summer and an autumn storm, with changes in DOC quality being dependent on lake features. During the early summer storm, greater changes in various DOC quality metrics were observed in deep lakes with longer residence times, whereas during the autumn storm, lakes with large watershed area to lake area ratios experienced the greatest changes. Land cover was highly correlated with changing DOC quality metrics in the early summer storm but did not play a significant role in the autumn storm response. They concluded that seasonal differences in the effects of storms on boreal lakes are mediated by a combination of lake and watershed characteristics as well as seasonal differences in climate such as solar radiation and antecedent weather conditions. [PERSON] et al. [19] conducted a study in Lough Feeagh, Ireland, during an exceptional heatwave in 2018, which broke long-term temperature and drought records. These calm, stable conditions were abruptly interrupted by a second extreme storm event in late June. Using high-frequency monitoring data, coupled with fortnightly biological sampling, they showed that the storm resulted in an intense mixing event that changedthe stratification pattern of the lake, even though stratification re-established quickly after the storm as the heatwave continued. During the storm, there was a three-fold reduction in Schmidt stability, with a mixed layer deepening of 9.5 m coinciding with a two-fold reduction in chlorophyll \(a\) and a three-fold increase in total zooplankton biomass.