Why do water changes cause plants to grow faster?

[Solcielo L]

Why do frequent water changes cause aquatic plants to grow faster? In an aquarium, the more frequent the water changes the faster flora grow. But why is that?

 

[Borek]

Looks like a homework type question to me.

What do plants need to grow?

 

[Solcielo L]

Any plants. It's not a homework question because there is no literature as to why this occurs so it's highly improbable anyone can cite a source. I'm looking to see if any botanist/biologists who have knowledge of this can provide an answer. Is is something about fresh water?

 

[Borek]

What do plants need to grow?

 

[HallsofIvy]

"In the wild", water flows that means that whatever nutrients are taken from the water are replace by nutrients from the "fresh" water that flows in. In pots or an aquarium, the nutrients are not replaced until you replace the water.

 

[Solcielo L]

We are dosing the water column as part of our regular fertilizing regimen. We add macro and micronutrients (which are low to nonexistent to begin with) to tap or reverse osmosis water. Plants will still grow much faster if we perform frequent water changes. So it's not an issue of fertilization.

Allelochemicals have been ruled out as activated carbon should remove these organics.
I've tested the effects of pressure and have tentatively ruled this out.

Tap water often contains high O2/CO2 so it may be this. However, if we let the water degas and reach equilibrium with normal atmospheric pressure, then there shouldn't be inordinate amounts of these gasses.

 

[chemisttree]

you might have a competing organism using up your fertilizer inputs before the plants can get to them. Changing the water reduces their number and gives the plants a window of opportunity to get the fertilizer. Look at a sample of the water before and after a water change under a microscope to be sure.

 

[Solcielo L]

If microorganisms are present, then the water should become turbid as they multiply. However, this is not necessarily the case. Fertilization is done on a regular basis, daily or 2-3x a week.

The nutrients are NPK and maybe micros (which include Fe, Mg, Mn, B, Cu, Zn, and Mo.)

UV sterilizers should remove any free floating organisms, as well as deactivate certain chelated nutrients such as Fe chelate, if added to the water column.

I should add that fish keepers have found that the more frequent the water changes, the faster they grow and the healthier the fish. This is why many fish farms do daily 100% water changes. The reason why, according to this article, may be the result of nanobubbles, though nanobubbles are purposefully added to the water.
Oxygen and Air Nanobubble Water Solution Promote the Growth of Plants, Fishes, and Mice
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065339

Whether or not nanobubbles are present in tap water and/or reverse osmosis water is yet to be determined, which is why I asked in the physics forum about the formation of nanobubbles.