Evaporation Experiment

Incredible Results

I've had a theory about plants and water loss for a while now. I have been wanting to perform this experiment --they say there is no time like the present.

The Experiment
Thursday, September 23, 2010 at 10:00am
Two identical pots sitting next to each other were filled with water to a height of 17mm. The pots were placed in a location that was shady in the morning, sunny during the day and shady in the evening.  The water temperature in each pot was 65 degrees Fahrenheit.  In pot "A" I placed one healthy water hyacinth that encompassed approximately 75 percent of the pot surface.  Pot "B" had no plants. There was no pump or fountain of any kind in either pot. Other than the breeze, the water was perfectly still.

(My theory is that although plants shade the water, they still are comprised of mostly water themselves and they will absorb large amounts of water in order to grow and thrive.  So the faster a plant grows, like hyacinth, the more water it will take from the feature.)

The Results
Friday, September 24, 2010 at 9:00 am
Pot "B" (no plants) had only 14 mm of water.  That is an 18% water loss in 23 hours!
Pot "A" (with water hyacinth) had only 13.5 mm of water in it.  I did drain the roots of the plant so there was no water left on them.  That resulted in a loss of 21% in 23 hours.
Therefore, my theory is correct. Pot "A" with the plant had 15% more evaporation than Pot "B" with no plant.
Please don't misunderstand, I am not advocating taking out the plants during dry weather.  This is simply a way of judging water loss.  Keep this in mind...the weather conditions right now in Indiana are unlike any that we have had in a long time.  The relative humidity in dangerously low and we have had very little rain in the past two months.  In the meantime our temperatures are drastically above normal.  In more favorable weather we won't experience such great percentages of water loss, but for now, it would not be inconceivable to loose 18% of your water due to evaporation without a waterfall running.

How does that equate to the average pond?
Let's take a pond that is approximately 8' by 10' by 2' deep.  The gallons in that total pond would be approximately 1000, assuming curved sides and boulders and gravel within the pond.  Each inch of water would equate to approximately 42 gallons.  (1000 gallons divided by 24") An 18 percent water loss (what we experienced in our experiment with no plants) would be 180 gallons over 24 hours. (1000 gallons times 18%) That would be 4.28 inches of water in an 8' by 10' pond in 24 hours.  (180 gallons divided by 42 gallons per inch) So if you are experiencing a lower rate than that then you are staying ahead of our experiment results. With plants in the water feature, it could be 15% more water loss.

Hang in there folks, before you know it I will be experimenting here to see how much snow fall it will take to keep a feature topped off in the winter.  I believe 10 inches of snow equals 1 inch of water, right?

--Written by Cool Ponds staff member Steve       


francies26 said…
I too have experienced greater than usual evaporation over the past few weeks. Here is another theory for you to test! Assume that two ponds are of equal volume, but one pond is deeper, with less surface area and the other is more shallow with greater surface area. I would assume that the pond with the greater surface area would have greater water loss. Happy experimenting! And thanks for all your info!

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