The extent and variability of storm‐induced temperature changes in lakes measured with long‐term and high‐frequency data

Abstract

The intensity and frequency of storms are projected to increase in many regions of the world because of climate change. Storms can alter environmental conditions in many ecosystems. In lakes and reservoirs, storms can reduce epilimnetic temperatures from wind-induced mixing with colder hypolimnetic waters, direct precipitation to the lake's surface, and watershed runoff. We analyzed 18 long-term and high-frequency lake datasets from 11 countries to assess the magnitude of wind-vs. rainstorm-induced changes in epilimnetic temperature. We found small day-to-day epilimnetic temperature decreases in response to strong wind and heavy rain during stratified conditions. Day-to-day epilimnetic temperature decreased, on average, by 0.28 C during the strongest windstorms (storm mean daily wind speed among lakes: 6.7 AE 2.7 m s −1 , 1 SD) and by 0.15 C after the heaviest rainstorms (storm mean daily rainfall: 21.3 AE 9.0 mm). The largest decreases in epilimnetic temperature were observed ≥2 d after sustained strong wind or heavy rain (top 5 th percentile of wind and rain events for each lake) in shallow and medium-depth lakes. The smallest decreases occurred in deep lakes. Epilimnetic temperature change from windstorms, but not rainstorms, was negatively correlated with maximum lake depth. However, even the largest storm-induced mean epilimnetic temperature decreases were typically <2 C. Day-to-day temperature change, in the absence of storms, often exceeded storm-induced temperature changes. Because storminduced temperature changes to lake surface waters were minimal, changes in other limnological variables (e.g., nutrient concentrations or light) from storms may have larger impacts on biological communities than temperature changes.

Classifying Mixing Regimes in Ponds and Shallow Lakes

“…One mechanism for this could come from the direct contribution of colder water to the pond. For example, 25.4 mm of precipitation would directly increase volume of our study ponds by 1.4%-8.4% depending on pond depth, but only represent an additional 0.4% of volume in a larger lake with a mean depth of 7 m. Consequently, while water temperatures in lakes may not respond to small precipitation events (Andersen et al, 2020;Doubek et al, 2021), ponds may have a greater response as they take less energy to mix. In addition to precipitation, storms could also reduce stratification strength through drops in air temperature, reduced solar radiation, and increases in wind speed (Jennings et al, 2012;Song et al, 2013).…”

Experimental thermocline deepening alters vertical distribution and community structure of phytoplankton in a 4‐year whole‐reservoir manipulation

“…There were several differences between the effects of our experimental thermocline deepening manipulations and extreme storm effects on lake ecosystems. First, we were unable to reproduce storm effects such as increased inflow and nutrient loading or changes in epilimnetic water temperature (e.g., Doubek et al, 2021; Klug et al, 2012; Stockwell et al, 2020). Second, FCR's engineered mixing system is installed at a depth of 5 m, or at approximately the middle of the water column, so mixing action is initiated from the middle of the water column rather than the surface, as would occur due to a storm.…”

“…To determine whether our thermocline deepening manipulations approximated naturally occurring storms, we calculated daily sums of precipitation and daily mean wind speed during the 4‐year study period to identify extreme storm events. Extreme storms were defined as when both daily mean wind and summed precipitation were at or above the 95th percentile of all observation days (total n = 572) across the study period (following Doubek et al, 2021). Following this, we identified two extreme storm events during our 4‐year study period: one on 5 May 2016 and one on 8 June 2019.…”

Drivers of phytoplankton responses to summer wind events in a stratified lake: A modeling study

“…Upwelling of nutrient‐rich water during mixing can alleviate nutrient limitation, potentially causing phytoplankton blooms (Soranno et al 1997; Kasprzak et al 2017; Whitt et al 2019). At the same time, surface temperature tends to slightly decrease during storms (Mesman et al 2020; Doubek et al 2021), potentially reducing growth rates of light‐saturated phytoplankton (Trombetta et al 2019). In addition, a deeper mixed layer can increase light limitation for growth (Diehl et al 2002) and deepening dilutes concentrations by mixing phytoplankton over a larger volume of water (Kuha et al 2016).…”