Soil substrate pond

[Nepen]

Nepen, I don't know if you are interested, but this is a beautiful plant that has large lace like leaves that also have allelopathic characteristics ( algae doesn't grow on the leaves).

SPATTERDOCK Nuphar Japonica

View attachment 86603

That's petty!! Wher can I get that? I'll just look from eBay first.

 

[Meyer Jordan]

I am speaking about both new and old ponds with only gravel and rock on the pond floor.
Gravel and rock will have organic matter accumulate in it's large crevices, but that organic matter alone does not contain any mineral composition (clay) that adsorbs heavy metals and phosphorus. Periphyton must be exposed to the water column, otherwise once it is buried by detritus accumulation, it only becomes more decaying organic matter.
When I refer to substrate, I'm including both the organic and mineral components of the sediment layer on the bottom of the pond.

If you consider the three tanks that I have running:

Test tank has significant string algae and cold water, no plant filter
320 gallon tank has no string algae and cold water, with a plant filter
600g tank has no string algae and warm water, no plant filter

All 3 tanks have identical garden soil substrate and little to no water circulation. The 2 cold water tanks receive identical feedings of identical food. 600g tank receives heavy feedings daily. No tanks have a mechanical filtration device. The plant filter on 320g tank has a substantial clay component to it's media.

Because test tank and 320g tank are the most similar and both having slow to moderate plant growth, my observation is that the presence of clay in the 320g tank is preventing phosphorus from being available for string algae.
My explanation for no string algae growth in the 600g tank is that the warmer water is allowing for more vigorous plant growth, including some plants that are blooming, therfore incorporating excess phosphorus into the plant tissues. Frequent prunings have been required, so at that point phosphorus is exported from the system.

So - warm water may allow for more vigorous plant growth, preventing the growth of nuisance algae, but when there is cold water and low plant growth, the presence of clay is an important component for keeping a pond clear of string algae.
Because clay is a composition of minerals, it does not float, so it becomes a part of the substrate.

Yes, clay is well known as being the prime material for Phosphorus adsorption. Water Hardness (Calcium Carbonate) also plays a large part in regulating this adsorption rate.
Rock and/or gravel substrate is, of course, not the prime choice of Benthic substrates, but it is better than no sub-strate at all.

 

[Lisak1]

So would regular additions of bentonite or montmorillonite clay to a gravel bottomed pond contribute to the composition of the substrate?

 

[Meyer Jordan]

So would regular additions of bentonite or montmorillonite clay to a gravel bottomed pond contribute to the composition of the substrate?

Yes, but adding clay on a 'regular' basis may not be advisable. It will accumulate over time and would eventually become too deep to be totally beneficial. Also when it is added, it should be done with no plans to disturb or remove it at a future date. What one is attempting to do here is the creation of an approximation of the Benthic layer at the bottom of a Natural earth-bottom pond. Over time this layer (substrate) will become colonized with a wide diversity of micro-, meio-, and possibly some macro-organisms which only add to the total diversity of the whole pond environment.

 

[Lisak1]

eventually become too deep

We add about 4-6 tablespoons at a time. And my "regular" schedule is "whenever I think of it" - ha! I'm not much for regularly scheduled anything these days! At that pace it will take me many years to even get a few inches of clay, but it's good to know in theory is can be adding to the health of my pond.

 

[MitchM]

I would suggest, if you have a "bog" filter, that the clay is added to the surface of the bog filter and watered into the lower layers.
Make sure that the water flowing through the bog is not so strong that it simply forces the clay out and into the main pond.
When the clay is contained in the bog filter, then the nutrients that the clay adsorbs are available to the bog plant roots.
As you trim excess plant growth, you will be exporting excess nutrients from your pond.

 

[Lisak1]

I would suggest, if you have a "bog" filter

I do have a bog filter! I am going to consider that. We add "koi clay" directly to the pond whenever we've done anything to stir up the pond - the fish LOVE it. Some information that I read early on suggested putting the clay in the same spot in the pond every time in an attempt to create a clay bed. I add the clay in our "feeding spot" but so far there's no evidence that's happening.

So if I have an inch or two of water over the gravel in my bog filter, any suggestions on the best way to apply the clay?

 

[MitchM]

Hmm.
Bentonite clay will clump when it gets wet, so it might be a matter of turning off water supply to the bog, applying the clay and letting it settle into the bog media.
It would be best if you could somehow mix it into the media, closer to the plant roots.

 

[MitchM]

Yes, clay is well known as being the prime material for Phosphorus adsorption. Water Hardness (Calcium Carbonate) also plays a large part in regulating this adsorption rate.
Rock and/or gravel substrate is, of course, not the prime choice of Benthic substrates, but it is better than no sub-strate at all.

Another consideration is that you incorporate strong water flow into your designs, whereas I have no or minimal water flow.
Your designs would prevent excess detritus buildup for possible export to an external mechanical filter, or plant filter media.
I am trying to encourage detritus accumulation so that the detritus can filter it's way back down into the substrate, to be utilized by the plants.

 

[Meyer Jordan]

I would suggest, if you have a "bog" filter, that the clay is added to the surface of the bog filter and watered into the lower layers.
Make sure that the water flowing through the bog is not so strong that it simply forces the clay out and into the main pond.
When the clay is contained in the bog filter, then the nutrients that the clay adsorbs are available to the bog plant roots.
As you trim excess plant growth, you will be exporting excess nutrients from your pond.

I strongly disagree with this suggested application method. 'Bogs' (constructed wetlands) utilize, by design, an upflow system. For this to function properly, any and all materials that may induce clogging of this system should be excluded. If these materials are allowed to accumulate, water 'channeling' will occur which will result in less than optimum performance of the 'bog' and the development of anoxic areas within the 'bogs' sub-strate.
'Bogs' are of a completely fabricated design that is completely unknown in nature in that form. Upflow seepage may be quite common, but we are talking about flow rates of gallons per week (or month) and where anoxic conditions are not an issue.
The clay that is added should be allowed to accumulate on the bottom of the main pond basin which is the natural location for a Benthic layer. It is also suggested that it be mixed with equal parts of coarse sand.
In addition, a 'bog' should not have "strong water flow". The longer the 'resident time' of the water within the 'bog' the more efficient the filtering process.

 

[MitchM]

Fair enough.
So should these bog systems that are being used consist of clean gravel with 100% flow through?
Essentially the plant roots would be suspended in clear water.

My understanding of plant roots is that they prevent the substrate from becoming toxic by releasing oxygen from the root tips.
Anoxic areas developing in the bog should not become a problem.
Does it matter if the bog is upflow or down flow? The plants don't care.
I'm using the term bog because that is what seems to be the common name, accurate or not.

 

[Meyer Jordan]

So should these bog systems that are being used consist of clean gravel with 100% flow through?

Yes.

My understanding of plant roots is that they prevent the substrate from becoming toxic by releasing oxygen from the root tips.
Anoxic areas developing in the bog should not become a problem.

This is correct but this Oxygen release is confined to the immediate microscopic area surrounding the plants root system. Areas of the 'bog's' substrate that are free of root infiltration that become clogged will become anoxic.

Does it matter if the bog is upflow or down flow? The plants don't care.

Not really, though the vast majority of 'bogs' are upflow. The actual terminology used in wetlands construction is sub-surface flow and surface flow.

 

[MitchM]

If an area develops and becomes anoxic, will plant root growth expand into that area and eventually cause it to become oxic?

 

[MitchM]

Do your pond designs include external filtration?

 

[Meyer Jordan]

If an area develops and becomes anoxic, will plant root growth expand into that area and eventually cause it to become oxic?

Yes.