Friday, June 8, 2012

Assimilation of Nutrients

Wishing to understand water chemistry I began reading about REDOX and pH but the topics became overwhelming.  So I decided to take notes starting with definitions, because so many acronyms were being thrown at me all at once.

Then I tried to get my head around why it's called Reduction and what was being reduced.

Finally I began to understand that most of this water chemistry topic is about electricity and ions.   So here are my notes.  I've had some help along the way from a couple experts and Dr. George B. Brooks Jr. helped me convey the acidic reaction even better than I had.

Beyond the text I've quoted from various internet sources I have added some commentary in red italic. 

Without the ability to gain electrons many minerals cannot be absorbed and properly assimilated.


Ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.   [1]
Ionization is the process of gaining or losing electrons from a neutral atom or molecule  [1]
anion is a negatively charged ion 
cation is a positively charged ion  [1]

Oxidation - involves the loss of electrons or hydrogen OR gain of oxygen OR increase in oxidation state.  [2]
Reduction - involves the gain of electrons or hydrogen OR loss of oxygen OR decrease in oxidation state.
The species that gains electrons is said to be reduced because it has less voltage and less potential to oxidize.

CEC or Cation Exchange Capacity, refers to the quantity of negative charges in soil existing
on the surfaces of clay and organic matter. The negative charges attract positively
charged ions, or cations, hence the name ‘
Cation Exchange Capacity.

ORP stands for Oxidation Reducing Potential and is sometimes referred to as REDOX (Reduced oxidation).
is the tendency of a chemical species to acquire electrons and thereby be reduced [3]

TDS stands for Total Dissolved Solids. 
creates the pathway for the “ionization” (or more correctly electrolysis) to occur. [4]

pH stands for "potential hydrogen”.
measures alkalinity or acidity on the pH scale that runs from pH0 to pH14

Alkaline describes situations where pH levels exceed 7.0.
Alkalinity is a measure of a water’s capacity to neutralize acids
The term “alkalinity” should not be confused with the term “alkaline,” which describes situations where pH levels exceed 7.0.  [15]

Chelate is a substance whose molecules can form several bonds to a single metal ion

ORP is a potential energy measured in millivolts.  When Reduction occurs the potential energy (Voltage) is reduced. 

A “reducing” agent is simply something that inhibits or slows the process of oxidation. The reducing agent does this by “donating” an electron. When we measure something’s oxidation reduction potential, it is expressed in terms of –ORP and measures the concentration of OH- ions or reducing agents. [5]

Low PH water generally has High ORP

ORP measures the presence of oxidizing or [oxidation] reducing agents by their specific electrical charge, thus Oxidation Reduction "Potential". [4]
Oxidation in simple terms is what turns an apple brown after it is cut, or causes metal to rust. [4]  This is the electrolysis and ionization of iron.
The ORP of most tap water in the USA is between +150 to +600mv, and so is an oxidizing agent. [8]
High pH ionized water demonstrates a –ORP and so is a reducing agent or “antioxidant”.

Acid (Low PH) or low potential hydrogen has a High Oxidation Reducing Potential and has potential to Oxidize other atoms, and causes metal to rust, but ionization is dependent upon a third variable called TDS (Total Dissolved Solids)..  

OK to review the above information which still gets me confused.
High ORP tends to make a Low pH, and it promotes oxidation. 

We now know that oxidation involves an exchange of electrons between two atoms. The atom that loses an electron in the process is said to be "oxidized." The one that gains an electron is said to be "reduced." In picking up that extra electron, it loses the electrical energy that makes it "hungry" for more electrons. 
Thus we get the term Oxidation (losing an electron) Reduction (gaining and electron) Potential.[16]      

When the pH is not at the proper level the plant will lose its ability to absorb some of the essential elements required for healthy growth. For all plants there is a particular pH level that will produce optimum results (see chart 1 below). This pH level will vary from plant to plant, but in general most plants prefer a slightly acid growing environment (between 5.5-6.0), although most plants can still survive in an environment with a pH of between 5.0 and 7.5. When pH rises above 6.5 some of the nutrients and micro-nutrients begin to precipitate out of solution and can stick to the walls of the reservoir and growing chambers. For example: Iron will be about half precipitated at the pH level of 7.3 and at about 8.0 there is virtually no iron left in solution at all. In order for your plants to use the nutrients they must be dissolved in the solution. Once the nutrients have precipitated out of solution your plants can no longer absorb them and will suffer deficiency and death if left uncorrected. Some nutrients will precipitate out of solution when the pH drops also. Chart 2 (below) will give you an idea of what happens to availability some of the nutrients at different pH levels:[13]

Chart 2
pH Values For Different
Hydroponic Crops
Availability Of Nutrients
Available At Different
pH Levels
(From Hydroponic Food Production
by Howard M. Resh
Woodbridge Press, 1987)

This chart is for soiless (hydroponic) gardening only and
does not apply to organic or dirt gardening.
Plant pH Range

Buffers play an important role in pH balance, as they are substances that are found in living organisms that help them maintain a certain range of pH. It is a chemical or combination of chemicals that keep the pH within its normal limits. This happens because it is able to resist a pH change by either taking up excess hydrogen ions or hydroxide ions. [11]

An example of a buffer is bicarbonate ions.  They take up extra hydrogen ions forming carbonic acid, which keeps the pH from going too low. However, if the pH gets too high, carbonic acid breaks apart to release some hydrogen ions, which brings the pH back into balance. [12]

TDS (Total Dissolved Solids) creates the pathway for the “ionization” (or more correctly electrolysis) to occur [5]as ions from the dissolved solids create the ability for water to conduct an electrical current.
The most common chemical constituents are calcium, phosphates, nitrates, sodium, potassium and chloride.
The importance of Total Dissolved Solids can not be emphasized enough. [5]

For hydroponic uses, total dissolved solids is considered one of the best indices of nutrient availability for the aquatic plants being grown, [9] but these nutrients will not be available unless the pH and ORP are also correct.

Water without mineral content or TDS, like reverse osmosis or distilled water, will not conduct the current and therefore can not be “ionized”.
Oxidation-reduction reactions are vital for biochemical reactions such as converting Ammonia (NH3+H) to Nitrite (NO2) then Nitrite (NO2) to Nitrate (NO3) through a process called fixation which makes nitrogen available to plant life.

The electron transfer system in cells, and oxidation of glucose are examples of redox reactions. [2

These three variables ORP, pH,
and TDS affect the assimilation of nutrients in plants and animals, the electron transfer system in cells, and oxidation of glucose. 

Oxidation-reduction reactions are also vital for biochemical reactions such as converting ammonia into nitrite and Nitrate.  

This is done by bacteria which prefer to live in a pH of 5.8 to 7.5. Without these bacteria  the  nutrients which plants require would become locked up with unusable salts.  

But a sufficient amount of TDS to conduct the ion exchange is also required, and each of these three components must be kept in balance.
I have not even touched upon Hard Water yet, but Hard water has a lot of buffering capacity and soft water has almost none.. 

Read more:

So understanding performance is like understanding a dance between the three variables. [5]

This topic goes even deeper:
Many essential biological chemicals are chelates. Chelates play important roles in oxygen transport and in photosynthesis. Furthermore, many biological catalysts (enzymes) are chelates.  A chelating agent is a substance whose molecules can form several bonds to a single metal ion.
Another biologically significant chelate is vitamin B-12. It is the only vitamin that contains a metal, a cobalt(II) ion bonded to a porphyrin-like chelating agent. As far as is known, it is required in the diet of all higher animals. It is not synthesized by either higher plants or animals, but only by certain bacteria and molds. These are the sources of the B-12 found in animal products. Because vitamin B-12 is not found in higher plants, vegetarians must take care to include in their diets foods or supplements that contain the vitamin.  [10]

1.  Increase the availability of nutrients.  
Chelating agents will bind the relatively insoluble iron in high pH soil and make it available to plants.
2.  Prevent mineral nutrients from forming insoluble precipitates.
The chelating agents of the metal ions will protect the chelated ions from unfavorable chemical reactions and hence increase the availability of these ions to plants.  One example is iron in high pH soil.  In high pH soil, iron will react with hydroxyl group (OH-) to form insoluble ferric hydroxide (Fe(OH)3) which is not available to plants.

Fe+3 + 3 OH- --------> Fe (OH)3
Soluble Insoluble
Chelation will prevent this reaction from happening and hence render iron available to plants.
3.  Reduce toxicity of some metal ions to plants.
Chelation in the soil may reduce the concentration of some metal ions to a non-toxic level.  This process is usually accomplished by humic acid and high-molecular-weight components of organic matter.
4.  Prevent nutrients from leaching.
Metal ions forming chelates are more stable than the free ions.  Chelation process reduces the loss of nutrients through leaching.
5.  Increase the mobility of plant nutrients.
Chelation increases the mobility of nutrients in soil.  This increased mobility enhances the uptake of these nutrients by plants.
6.  Suppress the growth of plant pathogens.
Some chelating agents may suppress the growth of plant pathogens by depriving iron and hence favor plant growth.
4. Salinity - Salinity is usually expressed in terms of its specific gravity in science labs, but in the pond and Koi world it is more common to see it as the total percent of salt in a solution.

Water Salinity Based on Percentage of Dissolved Salts
Koi function best with just ever so slight brackish water.
Fresh Water Brackish Water Saline Water Brine
< 0.05% 0.05-3.0% 3.0%-5.0% > 5%
Range in Green Perfect for Koi Ponds  0.15-0.20%
Perfect for Koi Hospital Tanks  0.25 - 0.30%
Measure Salinity Level with Easy to Use Digital Readout Meter
Measure Salinity Level with Easy to Use Digital Readout Meter

This is an excellent article which i will list again at the bottom

How does Water Hardness relate to Ionization?
Hard water has a lot of buffering capacity and soft water has almost none.

Hard water is water that has high mineral content.
The higher the mineral content or Total Dissolved Solids the higher the levels of pH and ORP. [5]
The lower the mineral content the lower levels of pH and ORP. [5]

There are two types of water hardness.  GH (General Hardness) and KH (Calcium Hardness).

Temporary hardness
(Calcium Hardness) is a type of water hardness caused by the presence of dissolved carbonate minerals (calcium carbonate and magnesium carbonate). Unlike the permanent hardness caused by sulfate and chloride compounds, this “temporary” hardness can be reduced  by the addition of lime (calcium hydroxide) through the process of lime softening. [6]

Permanent hardness
Permanent hardness
(General Hardness) is hardness (mineral content) that cannot be removed  by the addition of lime. It is usually caused by the presence of calcium and magnesium sulphates and/or chlorides in the water.  Despite the name, the hardness of the water can be removed using a water softener, or ion exchange column. [6]

Classification hardness in mg/L hardness in mmol/L hardness in dGH/°dH
Soft 0–60 0–0.60 0–3.36
Moderately hard 61–120 0.61–1.20 3.42–6.72
Hard 121–180 1.21–1.80 6.78–10.08
Very hard ≥ 181 ≥ 1.81 ≥ 10.14
Table [7]

Here is an important quote: “The presence of free (ionic) calcium at relatively high concentrations in culture water helps reduce the loss of other salts (e.g. sodium and potassium) from fish body fluids (i.e. blood). Sodium and potassium are the most important salts in fish blood and are critical for normal heart, nerve and muscle function. In low calcium water, fish can lose (leak) substantial quantities of these salts into the water.” See reference below.
Understanding Water Hardness.


Common ions

Common Cations
Common Name Formula Historic Name
Simple Cations
Aluminium Al3+
Calcium Ca2+
Copper(II) Cu2+ cupric
Hydrogen H+
Iron(II) Fe2+ ferrous
Iron(III) Fe3+ ferric
Magnesium Mg2+
Mercury(II) Hg2+ mercuric
Potassium K+ kalic
Silver Ag+
Sodium Na+ natric
Polyatomic Cations
Ammonium NH+

Oxonium H3O+ hydronium
Mercury(I) Hg2+
Common Anions
Formal Name Formula Alt. Name
Simple Anions
Chloride Cl
Fluoride F
Bromide Br
Oxide O2−
Carbonate CO2−

Hydrogen carbonate HCO
Hydroxide OH
Nitrate NO

Phosphate PO3−

Sulfate SO2−

Anions from Organic Acids
Acetate CH3COO ethanoate
Formate HCOO methanoate
Oxalate C2O2−
Cyanide CN
Table [7]

A special thanks to Dr. George B. Brooks, Jr. for corrections and this explanation of acidic effects of REDOX,

"The nitrification process does indeed acidify the water. The process takes the hydrogen from NH3+ and exchanges them with Oxygen in NO2 and NO3. (NH3 + 2 O2 => NO3- + H+ + H2O). Free protons or hydrogen is the definition of acid so the process decreases your pH. It also uses a lot of oxygen. So in your aquaponics system, oxygen in your media beds is not only critical to your roots remaining healthy but also to the keeping the bacteria alive and to mediating the nitrification reaction they do. The more O2 the better off you are (in general)."


And finally here is a site that you may find to be a handy reference

For more very good articles 
    Understanding pH, KH, GH in Home Aquariums

No comments:

Post a Comment