Author: Jorrit P Mesman,  PhD Student (University of Geneva)

Designation: 

Description:
Storm-induced mixing events can have a myriad of effects on lake ecosystems. Mixing may deepen the thermocline, cool the surface water, and bring up nutrients from the hypolimnion. All these changes have synergetic and antagonistic impacts on phytoplankton growth, and these are further influenced by lake morphology, trophic state, and phytoplankton functional traits. We applied a one-dimensional physical model, GOTM, coupled to a biogeochemical model, to study the effects of storms on phytoplankton biomass in Lake Erken, Sweden. We performed two model experiments. In the first, we explored potential regulating factors for the response of phytoplankton to wind mixing. In the second experiment, we scaled air temperature according to the RCP8.5 climate scenario and assessed potential future changes. Wind speed could have both increasing and decreasing effects on phytoplankton concentration. In case of high nutrient concentrations below the thermocline and sufficient incoming light, especially moderate wind speeds could promote phytoplankton growth. However, in case of stringent light limitation or low hypolimnetic nutrient levels, wind decreased phytoplankton levels, and higher wind speeds more so. Below a certain mixed layer depth, the impact of storms on phytoplankton was markedly reduced, and strength of stratification had no strong effect. The investigated climate scenario showed no strong changes in phytoplankton response to storms, despite changing in-lake conditions. These findings can inform studies on phytoplankton response to storms in other systems as well.

Category: Scientific Program Abstract > Special Sessions > CS17 Extreme Events