4.1. Lakes

Try these first

1. 1.

   Define molecular diffusion.

   Hint

   Think about how smell spreads in a room.

2. 2.

   What is bulk flow?

   Hint

   Consider how a river carries debris downstream.

3. 3.

   What is the primary mechanism of mass transfer in a deep lake with low flow?

   • Advection
   • Molecular Diffusion
   • Thermal Convection

   Hint

   Consider what happens when water isn’t flowing.

4. 4.

   True or False: Advection is always present in lakes.

   • True
   • False

   Hint

   Think about conditions where water remains still.

5. 5.

   A chemical spills on the surface of a stratified lake in winter. Predict the timeline for how the chemical will reach the bottom of the lake considering diffusion and thermal convection.

   Hint

   Consider how long it takes for diffusion depending on the concentration gradient and water’s temperature.

6. 6.

   Evaluate the effectiveness of removing pollutants from a lake through a pumping system versus natural diffusion. Analyze potential impacts of bulk flow and stratification.

   Hint

   Think about how mixing can enhance pollutant removal compared to simple diffusion.