Abstract
Between May and July 2018, Ireland experienced an exceptional heat wave, which broke long-term temperature and drought records. These calm, stable conditions were abruptly interrupted by a second extreme weather event, Atlantic Storm Hector, in late June. Using high-frequency monitoring data, coupled with fortnightly biological sampling, we show that the storm directly affected the stratification pattern of Lough Feeagh, resulting in an intense mixing event. The lake restabilised 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 but a three-fold increase in total zooplankton biomass. Epilimnetic respiration increased and net ecosystem productivity decreased. The ratio of total nitrogen:total phosphorus from in-lake versus inflow rivers was decoupled, leading to a cascade effect on higher trophic levels. A step change in nitrogen:phosphorus imbalances suggested that the zooplankton community shifted from phosphorus to nitrogen nutrient constraints. Such characterisations of both lake thermal and ecological responses to extreme weather events are relatively rare but are crucial to our understanding of how lakes are changing as the impacts of global climate change accelerate.
Highlights
Extreme-weather-related episodic events are becoming more frequent as a consequence of global climate change [1]
After Storm Hector, from the 21st June to the 12th July, high pressure stretching from the Azores to Scandinavia brought very warm and dry conditions, during which a maximum air temperature of
We observed a significant increase in ecosystem R and a decrease in net ecosystem productivity (NEP) during the intermediate mixing period, compared to pre- and post-storm warm and stable periods, which resulted in a slight decrease in gross primary production (GPP) following Storm Hector
Summary
Extreme-weather-related episodic events are becoming more frequent as a consequence of global climate change [1]. Lake ecosystems are excellent sentinels of change as they respond directly to meteorological episodic events, incorporating the catchment effects and integrating responses over time at different trophic levels [6]. Responses to climate change in lake ecosystems operate on various temporal scales, and disentangling driver–response relationships impacting freshwater aquatic ecosystems is complex [7]. For this reason, understanding the responses of single climatic forcing events in the context of longer-term dynamics (e.g., seasonal patterns) is important and requires ecological variables
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