Episodic wind events induce persistent shifts in the thermal stratification of a reservoir (Rappbode Reservoir, Germany)

Abstract

Stratification dynamics in reservoirs have a great impact on ecosystem functioning and biogeochemical cycling, and can be strongly influenced by wind events. In this study, a well‐established one‐dimensional hydrodynamic model (GLM) was used to investigate the response of stratification dynamics in Rappbode Reservoir to different wind conditions, in particular to episodic strong wind events. In years with increased wind speed, stratification duration and intensity were reduced. Episodic wind forcing by strong wind events are important determinants of thermal structure and can induce persisting shifts in the thermal structure that remain over the season until the next overturn. The results showed that reductions in stratification intensity were particularly distinct when the strong wind occurred in early summer. Strong wind events outside of this sensitive time window did not exert an important impact on the thermal dynamics of the reservoir. Our research confirms the decisive impact of wind speed on stratification of lakes and reservoirs. It effectively illustrates the sensitive time window of thermal dynamics to episodic wind events.

Variable withdrawal elevations as a management tool to counter the effects of climate warming in Germany’s largest drinking water reservoir

“…Our study emphasizes such effects on the thermal structure in winter, which were not addressed by Kerimoglu and Rinke [23]. A changing wind condition in a warmer climate may be able to modify stratification further (compare [30]), but only very high winter storms could prevent the occurrence of inversed stratification due to high mixing intensities.…”

“…Based on the stratification patterns [5], most of the freshwater systems in temperate regions are either dimictic or warm monomictic: a dimictic water body can be ice covered in winter and is generally stratified both in summer (direct) and winter (inverse) with turnover mixing in spring and autumn; a warm monomictic water is never ice covered and undergoes only one mixing period in winter in addition to being stratified during the rest of the year. Currently, when evaluating the stratification dynamics in this area, most studies focus on the summer stratification with three identifiable layers, epilimnion, metalimnion and hypolimnion, and distinct water temperature differences along the vertical direction during this period [18,22,23,30,37]. However, little attention has been specifically given to the winter inversed stratification in dimictic waters and its influencing factors.…”

glmGUI v1.0: an R-based graphical user interface and toolbox for GLM (General Lake Model) simulations

“…GLM is able to simulate the thermal dynamics of lakes in their temporal and spatial (vertical) characteristics. The model code is open source and applied in numerous studies to a broad variety of different lakes and research questions (e.g., Bueche et al, 2017;Bucak et al, 2018;Bruce et al, 2018;Fenocchi et al, 2017Fenocchi et al, , 2018Fenocchi et al, , 2019Robertson et al, 2018;Ladwig et al, 2018;Mi et al, 2018). Carey and Gougis (2017) present the usage of GLM beyond the research application by incorporating it into a teaching tool for students.…”

Assessing vertical diffusion in a stratified lake using a three‐dimensional hydrodynamic model

“…Stratification models have been developed for more than 30 years (Imberger, ; Riley & Stefan, ). Meanwhile, temperature variations, both in depth and time, achieve high coefficients of determination in many cases (often above 95%, see Arhonditsis & Brett, ; Mi, Frassl, Boehrer, & Rinke, ) when simulations are compared with observed data as several model tools and case studies have described (e.g. Frassl et al, ; Mi, Sadeghian, Lindenschmidt, & Rinke, ; Perroud, Goyette, Martynov, Beniston, & Anneville, ; Wahl & Peeters, ).…”