Impact of salinization on lake stratification and spring mixing

Abstract

Anthropogenic freshwater salinization affects thousands of lakes worldwide, and yet little is known about how salt loading may shift timing of lake stratification and spring mixing in dimictic lakes. Here, we investigate the impact of salinization on mixing in Lakes Mendota and Monona, Wisconsin, by deploying under‐ice buoys to record salinity gradients, using an analytical approach to quantify salinity thresholds that prevent spring mixing, and running an ensemble of vertical one‐dimensional hydrodynamic lake models (GLM, GOTM, and Simstrat) to investigate the long‐term impact of winter salt loading on mixing and stratification. We found that spring salinity gradients between surface and bottom waters persist up to a month after ice‐off, and that theory predicts a salinity gradient of 1.3–1.4 g kg−1 would prevent spring mixing. Numerical models project that salt loading delays spring mixing and increases water column stability, with ramifications for oxygenation of bottom waters, biogeochemistry, and lake habitability.

Lakes in Hot Water: The Impacts of a Changing Climate on Aquatic Ecosystems

“…An increase in salinity may also influence the physical environment of lakes—notably, by altering the vertical water density gradient and increasing the stability of stratification or influence seasonal mixing (Boehrer and Schultze 2008 , Ladwig et al. 2021 ). By altering the timing of seasonal stratification and mixing and, therefore, the duration of summer stratification, salinity changes in lakes represent a positive feedback on water level, which should be carefully considered in future climate change impact studies.…”

The aftermath of a trophic cascade: Increased anoxia following species invasion of a eutrophic lake

“…However, invasions are not the only drivers or stressors that force abrupt change (Turner et al, 2020). Climate change is shortening ice duration (Sharma et al, 2021), increasing water temperature (Woolway et al, 2022), decreasing wind speeds (Magee et al, 2016), and increasing intensity of rain events in the midwestern US (Kucharik et al, 2010); and road salt is shifting lake stratification regimes (Ladwig et al, 2021b). As climate change-caused disturbances increase the stochasticity of aquatic ecosystems, ecological consequences can be far-reaching, from affecting community composition to increasing the extent of oxygen-depleted waters, thereby further restricting organism habitat.…”

Winter inverse lake stratification under historic and future climate change

“…As we focused on the winter period, where temperature differences between surface and bottom water are quite small in comparison, other processes could also have an important effect. For example, under ice cover, chemical stratification (e.g., where solutes contribute to the density of freshwater) can be a key driver of hydrodynamic processes in some lakes (Malm et al 1998;MacIntyre et al 2018;Cortés and MacIntyre 2020), and salinization can delay or prevent turnover in spring (Ladwig et al 2021). In lakes with short residence times, chemical and thermal stratification can also be influenced by river and groundwater inflows (Pasche et al 2019;Cortés and MacIntyre 2020), which are not considered in our simulations.…”