Sodium

[Sacha]

This is an issue that I've raised before, but I've never really got a definitive answer.

I use RO water in my planted (Co2) tank. I re- mineralize that water using JBL Aquadur.

JBL Aquadur contains:

Cations:

Calcium 45%
Sodium 32%
Potassium 13%
Magnesium 10%

Anions:

Hydrogen Carbonate 45%
Sulphate 32%
Chloride 23%

So it's nearly 1/3 Sodium.

Now, as far as I understand it, sodium is bad for plants (and possibly fish). My question is this: does the amount of sodium in the tank dissipate over time, i.e. does it get used up by the filter/ fish/ plants?

If the answer to that question is "no", then surely the amount of sodium in my tank will keep going up and up, until it reaches ridiculous levels.

For argument's sake, let's say I add 1 gram of Sodium to the water. There is now 1g in the water.

Water change day, I remove 50% of the water, and so the sodium level goes down to 0.5g.

Then I add 1 gram of sodium, bringing the amount up to 1.5g.

I suppose this works in a logarithmic way (inverse of exponential), so that the increase in sodium gets smaller and smaller each week?

However, the point is that no matter what, my sodium levels by now will surely have risen to a high level.

How is this actually bad for plants?

Every time I've asked this question in the past, I get linked to pages where people say "Sodium is bad for plants". That's it. No further explanation.

Does anyone actually know why or how sodium damages plants?

Thanks.

 

[dw1305]

Hi all,

If the answer to that question is "no", then surely the amount of sodium in my tank will keep going up and up, until it reaches ridiculous levels

The sodium levels will build up, basically the ocean is salty with sodium and chloride ions (NaCl) because plants don't need either element in any more than trace amounts.

Every time I've asked this question in the past, I get linked to pages where people say "Sodium is bad for plants". That's it. No further explanation. Does anyone actually know why or how sodium damages plants?

This paper summarizes the effects of Na on plants <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC139373/>.

cheers Darrel

 

[Sacha]

Thanks Darrel,

An interesting read. But I am still none the wiser as to what will actually happen to my aquatic plants because of sodium. Stunted growth, thin stems, discolouration, holes in the leaves?

What does an excess of sodium actually look like?

 

[dw1305]

Hi all,

What does an excess of sodium actually look like?

I don't know. In terrestrial plants you get yellowing and "scorching" of the leaf edges and tips (although this is a chloride as well as sodium effect). I'm not sure about aquatic plants.

cheers Darrel

 

[Sacha]

This is exactly the point I am making.

We hear plenty of talk about how sodium is harmful for aquatic plants. That paper shows that, in theory, the science states that sodium should indeed be detrimental to aquatic plants.

But where is the proof? Where are the unhealthy, dying plants that have been exposed to too much sodium?

 

[dw1305]

Hi all,

We hear plenty of talk about how sodium is harmful for aquatic plants. That paper shows that, in theory, the science states that sodium should indeed be detrimental to aquatic plants.
But where is the proof? Where are the unhealthy, dying plants that have been exposed to too much sodium?

You can't really separate the effect of Na+ ions on their own, but you can get values for tolerance to NaCl (Na+, Cl-). A few plants will be tolerant (often ones from naturally hard waters) <http://www.fishchannel.com/freshwater-aquariums/planted-tank/brackish-plants.aspx>, but many "soft" water plants will suffer damage at lower levels. If plants can't exclude Na+ ions they will interfere with the uptake of K+ ions. This is from Jampeetong & Brix (2009)
"Effects of NaCl salinity on growth, morphology, photosynthesis and proline accumulation of Salvinia natans"
Aquatic Botany 91:3, pp.181–186.

The effects of NaCl salinity on growth, morphology and photosynthesis of Salvinia natans (L.) All. were investigated by growing plants in a growth chamber at NaCl concentrations of 0, 50, 100 and 150 mM. The relative growth rates were high (ca. 0.3 d−1) at salinities up to 50 mM and decreased to less than 0.2 d−1 at higher salinities, but plants produced smaller and thicker leaves and had shorter stems and roots, probably imposed by the osmotic stress and lowered turgor pressure restricting cell expansion. Na+ concentrations in the plant tissue only increased three-fold, but uptake of K+ was reduced, resulting in very high Na+/K+ ratios at high salinities, indicating that S. natans lacks mechanisms to maintain ionic homeostasis in the cells. The contents of proline in the plant tissue increased at high salinity, but concentrations were very low (<0.1 μmol g−1 FW), indicating a limited capacity of S. natans to synthesize proline as a compatible compound. The potential photochemical efficiency of PSII (Fv/Fm) of S. natans remained unchanged at 50 mM NaCl but was reduced at higher salinities, and the photosynthetic capacity (ETRmax) was significantly reduced at 50 mM NaCl and higher. It is concluded that S. natans is a salt-sensitive species lacking physiological measures to cope with exposure to high NaCl salinity

Cheers Darrel