Final answer:
The highest concentration of silicon in a stratified lake water column would be in the spring, due to the spring turnover that brings the nutrients from the lake bottom to the surface.
Step-by-step explanation:
The highest concentration of silicon in a stratified lake is typically found during the spring season. This occurs because of the spring turnover, which is initiated when the temperature of the surface water warms up enough to approach 4 °C, and this denser water then sinks displacing the water from the bottom upwards. As the deeper water containing sediments, nutrients, and silicon rises, it enriches the surface water. Conversely, during the summer the lake stratifies, and these layers prevent the bottom nutrients from mixing with the surface water. In the fall, as temperatures cool, another turnover can occur, helping to mix nutrients from the bottom to the top again. However, spring turnover is particularly significant because it follows a long winter period where nutrients have accumulated at the bottom.