Pond scum, also known as pond algae, blanket weed, and some far less appropriate terms that we will not include, is a hot topic right now. Probably about half of our questions this season relate to dealing with this messy mass. These questions came from one of our readers via email:
Question:
You say pond scum starts at the bottom of the pond or lake, then why do we always see it at the top?
Answer:
Pond scum starts at the bottom, always, every time. When you see the pond algae mats on the top of the water, you are seeing the end result of the growing cycle.
For it to grow, it has to have nutrients and light. The bottom provides the nutrients, the sun provides the light. It works it's way to the top because of photosynthesis. During the photosynthesis process the plants take in carbon dioxide (the plants need the carbon) and, as physicist Richard Feynman said, they "spit out the oxygen".
Some of the expelled oxygen gets trapped under the pond scum, and floats it to the top, where it gets more sunlight and carbon dioxide. The sunlight causes the carbon and oxygen molecules to break apart. Truly amazing design!
Question:
I always thought it was the temperature that started the process. I noticed that pond scum grows when the water warms up. Am I wrong?
Answer:
The temperature does play a role in the process, and since sunlight and heat both come from the same source, it is sometimes difficult to distinguish which is having which effect. You can heat pond water in the absence of light, and pond scum will not grow. Put that container of water in the sunlight and leave it alone for a few days, and you can start your own algae farm with the results!
Speaking of starting a pond algae farm, one of our readers is involved in the manufacture of fuel using pond scum, and we hope to write more on the subject soon.
Question:
If pond algae has to have sunlight to grow, won't one of the available dyes for ponds and lakes solve the problem?
Answer:
Yes, the dye will prevent the light from reaching the bottom, but it also prevents the light from encouraging the phytoplankton necessary for the life cycle of the pond or lake. The production of phytoplankton is the primary production necessary to feed everything else in your pond.
