Summary Limnology Chapter 3: Understanding Molecular and Eddy Diffusion

Chapter 3, the Movement of Light, Heat, and Chemicals in Water, discussed the different types
of water movement and the different factors that affect diffusion. Diffusion is what makes life of
single celled organisms possible and is the primary mode of molecular transport near surfaces.
Plants developed xylem and phloem and animals developed vascular tissue so that they could
continue to grow in size beyond the limit of diffusion. This ties closely with the topic of how water
movement shapes organisms and helps me understand why bacteria are not streamlined. It
also explains why bacteria jiggle and humans do not in water. (Brownian motion) Fick’s law is a
good way to calculate the rate that a chemical will diffuse into water. Factors that affect this
include particle size, temperature, and the rate of mixing of water. Eddy diffusion is much more
effective than molecular, but can only occur where they can form. Sediment structure also has a
huge effect on how chemicals then integrate into the groundwater. I found sidebar 3.2 very
interesting in its discussion of how different things can impact the color of a body of water as
well as the extinction coefficient related to cyanobacteria and sediments.