Storm impacts on alpine lakes: Antecedent weather conditions matter more than the event intensity

Abstract

Extreme weather events may be just as important as gradual trends for the long-term trajectories of ecosystems. For alpine lakes, which are exposed to both exacerbated atmospheric warming and intense episodic weather events, future conditions might not be appropriately forecast by only climate change trends, i.e. warming, if extreme events have the potential to deflect their thermal and metabolic states from their seasonal ranges. We used high-frequency monitoring data over three open-water seasons with a one-dimensional hydrodynamic model of the high-altitude Lake Muzelle (France) to show that rainstorms or windstorms, notwithstanding their intensity, did not trigger long-lasting consequences to the lake characteristics when light penetration into the lake was not modified. In contrast, storms associated with high turbidity input from the watershed ("turbid storms") strongly modified the lacustrine hydrodynamics and metabolism for the rest of the open-water season through reduced light penetration. The long-lasting effects of turbid storms were related to the inputs and in-lake persistence of very light glacial suspensoids from the watershed. The occurrence of the observed turbid storms was not related to the wind or rain intensities during the events. Instead, the turbid storms occurred after dry and atypically warm spells, i.e. meteorological conditions expected to be more frequent in this alpine region in the upcoming decades. Consequently, storm events, notwithstanding their intensity, are expected to strongly imprint the future ecological status of alpine lakes under climate warming.

Storm impacts on phytoplankton community dynamics in lakes

“…Similarly, for lakes on a long‐term changing environmental trajectory such as increasing eutrophication, a storm may appear to have a lasting impact but merely accelerated a “natural” progression (Bachmann et al, 1999; Clugston, 1963; Havens et al, 2001; James et al, 2008). Many of the studies in our systematic review observed that the trajectory of the communities and the duration of storm effects was highly variable and could be related to antecedent conditions (Perga et al, 2018) or a consequence of sampling frequency (James et al, 2008; Padisák, Tóth, & Rajczy, 1990).…”

“…The same storm will impact different lakes in different ways (Klug et al, 2012; Kuha et al, 2016), and the same lake will respond to different storms in different ways depending on antecedent conditions (see below) and the incidence of compound climatic events (Leonard et al, 2014; Perga et al, 2018). Consequently, “strength” of a storm is necessary but not sufficient to understand the degree to which storms impact light, nutrients, and temperature and thus phytoplankton community dynamics.…”

“…Similarly, antecedent conditions related to weather, soil, and land use can greatly influence external nutrient and sediment loading to lakes. For example, extended warm, dry weather can promote buildup of glacial flour through glacial abrasion and lead to increased glacial flour runoff with subsequent rain events, which can alter the light environment and thermal stratification in lake systems (Collins, 1989; Perga et al, 2018). In cold climates, precipitation in the form of rain or snow will likely have varying impacts on lakes in terms of immediate versus lagged effects depending on lake and watershed conditions (e.g., ice, snowpack, frozen soil; Johnson & Stefan, 2006; Joung et al, 2017).…”

13 Years of Storms: An Analysis of the Effects of Storms on Lake Physics on the Atlantic Fringe of Europe

“…Conditions leading up to a storm event may also be significant in predicting the impact. Perga et al, for example, showed that antecedent weather conditions were important in determining storm impact on lake turbidity in alpine lakes [17].Untangling this web of drivers of storm impacts on lakes can only be achieved by investigating a large number of storms of varying strength and duration, occurring at times when internal parameters within the lake, such as thermocline depth, water temperature and water column stability, are also changing. It requires a long time series of high frequency data on water column temperature profiles, data archives that are scarce in Europe and globally [18].…”

“…It requires a long time series of high frequency data on water column temperature profiles, data archives that are scarce in Europe and globally [18]. Single storm events have been investigated before [6,13,15,16,19], some studies have investigated several storms occurring over months or few years [5,17,20,21], but to our knowledge no studies to date have looked at large numbers of storm events over many years in one lake.In the present study, we investigated the effect of storms on physical conditions in Lough Feeagh, Co. Mayo, Ireland (Figure 1), during fully mixed conditions in winter and in the stratified period in summer. We quantified the changes in a range of lake physical parameters including energy flow (heat fluxes), temperature change, water column stability and thermocline depth.…”