Look at the velocities.
As you get up to above 1-2 mph, then the weeds are ripped out.
So biomass will go down, this is mechanical shear, there's a trade off as we know between good current and uprooting plants all over.

Typically, in natural water ways, no flood control etc, the weeds are blasted out each year, if not, then the weeds clogged canals, rivers etc.

This is more what they where looking at.
At high areas/regions of flow, would expect sedimentation to occur? Accumulation of detritus?

Nope.

In areas of low flow, eg, inside the weed beds, would you expect to see more sedimentation and thus more dertrial accumulation and thus more richer composted soils?

I would.

So the data and conclusion makes pretty good sense.

I'm not suggesting to add more than 1mph of flow in our tanks
This gave the upper limits.
A general graph would show a bell shaped curve for plant biomass(Y axis) and flow velocities(x axis).

This same general bell shape is also true for species diversity(intermediate disstubance hypothesis, (Joe O connell)) and most organisms in flowing water.


As far as CO2 in real plant beds, this is virtually never measured.
Seems weird to me that they have not, perhaps the water samples vs real time data and the availability of a 2000$ probe.meter etc caused this.

They mostly do O2 meter readings and relate that to in situ growth rates.
As plants fix CO2, they give off a fixed ratio of O2.

Still, it does not tell you what the CO2 levels is.........

Regards,
Tom Barr

one mile per hour seems to be a very slow flow velocity, but that is about 18 inches per second, which doesn't seem nearly as slow.

To relate this to water movement, consider a tank in which all of the water flows uniformly from one side to the other at 18 inches per second. I calculate that this means a flow rate of:
for a typical 29 gallon tank, 3800 cubic inches per second, or 59,000 gallons per hour.
for a typical 55 gallon tank 4700 cubic inches per second, or 72,000 gallons per hour.
for a typcial 125 gallon tank, 9100 cubic inches per second, or 144,000 gallons per hour.

A #2 Koralia powerhead moves 600 gallons per hour.

Obviously, we can't move all of the water in the tank at that velocity!!

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This explains the retention of nutrients within the beds.
Settlement of detritus is an inverse function of flow rate.

Boundary-layers around bladed aquatic macrophytes

A factor of 10 in differences by waves and other flow related drivers.
Also, nutrient uptake is discussed a lot, but little about CO2 uptake, demand, changes etc in any of the papers really.

Surprising really.

Regards,
Tom Barr

But we can move a lot of it by using the boat propeller style reef powerheads.
18 inches a second is not much, think about it in cm/sec, then it's pretty good really.

We are not trying to deposit sediment either, which influences soil fertility and plant distribution.

So applying this is not quite what the research had in mind, but it does show how too much flow is bad and not enough causes sedimentation, algae epiphytes etc.

It also shows how aquatic plants modify their environment and greatly reduce/restrict water movement within the plant beds.

How this influences CO2, it is a real question and an area that ought to be of strong interest to researchers.

Regards,
Tom Barr

One of Wetzal's group did this study where the differences where 7X in CO2 concentrations from the edge to the center of the mats.

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You can also see how O2 and growth is affected as well.

Quite dramatic.
However, we do not know the current and flow, important information.
Still, as you can see, there is a large difference due to plant uptake of CO2.

The CO2 meter may be able to take many more spacial measurements of a plant bed and how the CO2 varies in complex species communities and be able to relate that....................to CO2 competition and answer why or why not a species is present, increasing or declining based on CO2.

Regards,
Tom Barr

If you had the time and inclination you could spend most of your time doing this research, writing it up, and all of us would benefit greatly. I'm impatient to see the results!

Be awhile. You can still draw some conclusions about the potential results and predict, but not really verify.

Still, the expectations seem fairly clear in these old measurements.
what I find incredulous is how some aquarist cherry pick the research when it suits them, say with PO4 water column levels without measuring/even considering the plant's internal PO4 critical values, then use that as some poorly thought out argument for PO4 limitation, and without testing it, yet make huge assumptions about CO2, again, without testing.

I understand the lack of testing in most all cases for the hobbyists, however, the cherry picking of research that supports their contention is really troublesome.
I look for a good article that's well done and run across some that are not as well done, or less specific to what I'm researching.

Some cases have conflicting results and conclusions.
With Barley Straw, there was about 50% saying it worked to varying degrees, and 50% said nope, got nothing.

Looking further into methods, we see they used few controls algae bloom germination(none). So unless you can compare the effectiveness fairly across all treatments and add the right life stage of the pest(in this case algae) it's impossible to say much about how the straw might work.

This is why I first induce algae, then I test(both before and after inducement).

Often times it can take many searches for various key words or a friend mentions a paper etc, you get tired of searching etc, then come back later refreshed.

Insight takes time, at least in my thick skull. I'm stubborn, hard headed as anyone.
But knowing that, I can let the mind wander and perhaps it'll find something worth looking at closer.

The other measurement that can be looked at closer and is rarely done is O2 readings which are excellent for a non destructive plant growth rate measurement. I've been using the LDO probes and Hach meters for this. Very pricey like the CO2 meter, but..........also very accurate and easy to use.

Adding a good current flow sensor to this, now we can really see the effects of gas and flow dynamics.

I have a couple of PAR light meters, so that's covered as well.
NO3, PO4 etc are easy to measure, sediments can be sent off to the lab for analysis for relatively decent pricing.

So now you can cover about 99.5% of things that influence growth in a planted tank.

Regards,
Tom Barr

I've just got my hands on a cost-effective NDIR direct measurement CO2 sensor & I want to see how useful it is for measuring the CO2 in my tank (this is just for fun - I currently have a pH controller, solenoid valve doing it for real!). The sensor is designed for air measurements & reports percentage CO2. I'm trying to find the formulae (in a REALLY easy to understand format!) which relates dissolved CO2 as ppm or mg/L to the percentage CO2 which would exist in a closed sample of gas in contact with the water surface (via Henrys Law presumably). Can anyone help with that? Does the question even make sense? - Regards, Kevin

Unfortunately the air vs dissolved does not work the same.
Using a small destructive sample run through an IR might be good, not a good in situ method really, but could be done if the water/CO2 sample was vaporized for the IR reading...............

The dissolved CO2 meter is really the tool that we need.

A good flow meter would be nice, but simply using the micro bubbles to measure and see how flow works is pretty easy, a ruler and stop watch is all you need.

I think you will find a huge difference within the plant beds vs open areas in the tank.

Regards,
Tom Barr

Hi Tom,

Don't keep us waiting, we want to look at some results =D

Anyway, I was wondering, considering a tank with good flow on the right of the tank.

Obviously, CO2 / Nutrients / Dirt is distributed well at the right side.
What about the left? Wont it have slightly higher CO2 (along with all the dirt) since it's all stuck and not moving?

Since in EI we aim to 'overfeed' our plants, isn't it be better if CO2 is done the same way? I know that gas/liquid move from areas with high concentration to areas with low concentration to reach equilibrium so mixing it around does not seem to be that much problem (IMHO)

On the other hand, I agree with having good flow as it removes dirt from plant leaves. I'm still struggling to have good flow in my tank so if there's good enough reason for me to be lazy, I would

Regards,
Ryan