Phosphate in Marine Ecosystems

[mesocosm]

Greetings All !

I received a PM last week which included, "I would really enjoy one of your posts on phosphate. ... In our ecosystems, cycles, types and whatever interests you...."

Hehe ... ... the Chinese have a saying about this ...

What follows immediately are a few posts describing the behavior of phosphates in marine ecosystems. Hopefully these will get a discussion going. Rather than starting with my perspective, I thought it would be infinitely more useful to begin with a brief review of some of the commentary of true experts on the subject.

Enjoy ... and please don't hesitate to jump in with any questions or comments regarding the topic.

Many Thanks !

[mesocosm]

Greetings All !


It occurs to me that while we're very concerned with the behavior of phosphate in our aquaria, relatively little is ever posted about the phosphorous cycle in nature.



"Phosphorous enters the marine environment from the land. The breakdown of rock and sediments releases inorganic phosphorous to wash from land to sea. Phosphorous released from sewage and fertilizer also eventually finds the sea. Phosphorous occurs in three forms in marine waters: Dissolved Inorganic Phosphorous (DIP) as orthophosphate and phosphate, Dissolved Organic Phosphate (DOP) as part of dissolved organic compounds, and as Particulate Organic Phosphorous (POP) in organic particles, including components of detritus. Phosphorous is not a part of the atmosphere and there is no exchange toward equilibrium with atmospheric gas. However, dissolved inorganic phosphorous (DIP) readiuly leaves seawater incorporated in tiny droplets of salt spray along with other organic and inorganic compounds. DIP coats air bubbles in seawater, travels with bubbles to the surface, and leaves water with the transport of salt spray. This mechanism for phosphate loss from seawater is more of a factor in marine aquariums where spray particles are lost from the system than in the natural environment. In fact, the "aerosol particles" composed of phosphate and organic compounds form particles that are an important food source to planktonic organisms. DIP is converted to POP through air/water interaction at the sea surface."

(Martin Moe, 1992)

[mesocosm]

Greetings All !


While "real world" cycles are certainly important, it seems to me that what is really important is what phosphate is doing in our aquaria.

The following graphic ... aside from demonstrating why I am NOT a Photoshop advisor ... presents one perspective on phosphorous cycling in our aquaria. It is modelled after Wheaton (Wheaton, F. W. 1997. Aquacultural Engineering. Robert E. Kreiger Publishing Co., Malabarm Florida, USA.) and is a really bad reproduction of a graphic which appears in Delbeek and Sprung's The Reef Aquarium. Science, Art, and Technology (2005).

[mesocosm]

Greetings All !


Lots of red arrows ... hmmm. Some of you may have noticed that I'm oftentimes engaged in ranting about "bacterioplankton filtration." One of the key mechanisms has to do with the cycling of phosphorous through bacterial guilds. Here's a comment on the export of phosphorous utilizing bacteria ...

"All living creatures need phosphorous to survive, so the growth of any form of life within an aquarium can be a way to strip phosphate from the weater. The death and decomposition of this biomass returns phosphate to the system, so a complete removal of phosphate requires harvest of the living organisms. This is the principle behind algal filters, and it is the principle behind a novel approach to phosphate and nitrate management in aquaria: promoting the rapid growth in the water column of bacteria that assimilate phosphate and nitrate, and harvesting their biomass with a protein skimmer."

(Delbeek & Sprung, 2005)


Hardly an earth-shaking observation for ZEOvit methodology users, but I thought it was worth mentioning none the less. Oddly enough, this extract is taken from a section on vodka dosing.

[mesocosm]

Greetings All !


Okay ... all this babble about "cycling" is interesting enough, but what is ... precisely ... that's being cycled? Consider ...

"Phosphorous is dissolved in seawater as inorganic phosphorous, orthophosphate, and as organic phosphate, tied up in various organic phosphorous compounds, phospho-proteins, nucleo-proteins, and phospholipids."

Martin Moe, 1992




"... phosphate is present in many forms in the aquarium, and not all of them can be easily measured. The majority of the phosphate test kits used by aquarists measure only inorganic phosphate (orthophosphate) and ignore organic phosphates. In addition, algae, and the symbiotic bacteria that live on their surface can secrete phosphatase enzymes that liberte useable orthophosphate from organically bound phosphate."

(Delbeek & Sprung, 2005)

[mesocosm]

Greetings All !


"Precisely" ... hmmm ...

Phosphates and phosphate groups readily lose hydrogen ions (i.e., they are somewhat acidic). At physiological pHs phosphate groups are highly negatively charged due to their ionization (loss of hydrogen ions). On the other hand, phosphoric acid is typically referred to as inorganic phosphate (abbreviated, Pi) when not bonded to carbon. Phosphate groups play important roles especially in the structure of nucleic acids, many of the molecules that make up membranes (phospholipids), and in energy storage associated particularly with the molecule called ATP.


Phosphoric acid (aka PO4, inorganic phosphate or Pi):
..........OH
...........|
... HO - P = O
...........|
..........OH


Replace one H of phosphoric acid with carbon and you have a phosphate group (attached to that carbon).


Phosphate Group ...

.........OH..................... OH
..........|........................ |
...HO - P = O ---> C - O - P = O
..........|........................ |
.........OH..................... OH



The Role of Phosphate in Cellular Structure

Phospholipids are a variation on the triacylglycerol theme in which one fatty acid is replaced with a phosphate group, which in turn is bound to additional functional groups. Structurally and functionally, the important thing about phospholipids is that these molecules are simultaneously hydrophobic (at one end, the fatty acid end) and hydrophilic (at the other end, the phosphate end).

Phospholipids are amphipathic molecules meaning that they have both a hydrophobic and a hydrophilic end. Phospholipids can exist as bilayers in aqueous solutions. The hydrophobic portion of the phospholipid is shielded in middle of these bilayers. The hydrophilic portion is exposed on both sides to water.

The ability of the cell to discriminate in its chemical exchanges with the environment is fundamental to life, and it is the plasma membrane that makes this selectivity possible. The membranes that are found within cells (plus the plasma membrane surrounding cells) consist of phospholipids (and other lipids plus membrane proteins) arrayed by hydrophobic exclusion into two-dimensional fluids known as lipid bilayers. The plasma membrane contains proteins, sugars, and other lipids in addition to the phospholipids. The model that describes the arrangement of these substances in and about lipid bilayers is called the fluid mosaic model. Basically, membrane proteins are suspended within a two-dimensional fluid that in turn is made up mostly of phospholipids.

[mesocosm]

Greetings All !


When it comes to discussing the chemistry of things in marine aquaria, it's tempting just to post links to Dr. Randy Holmes-Farley's, Dr. Stephen Spotte's, and/or Dr. Craig Bingman's stuff ... and call it a day. But hopefully this is slightly more useful ...

Phosphate in the ocean and in marine aquaria is of tremendous importance because it is often a limiting nutrient for algae growth. In seawater, the amount of phosphate present is typically quite low (usually less than 0.05 ppm) and often varies significantly by location and depth. Much of the phosphate present in seawater is rapidly cycled through living organisms. In many marine aquaria, though, the phosphate concentration can be significantly higher (up to several ppm).

The ability to export phosphate from marine aquaria has been the topic of lengthy discussion and is the object of numerous commercial products. The nature of the inorganic phosphate present in seawater and in marine aquaria, however, is certainly more complicated than traditionally credited.

Inorganic phosphate can exist in a number of forms, in a manner analogous to carbonate:

H3PO4 <=> H+ + H2PO[4-] <=> 2H+ + HPO[4--] <=> 3H+ + PO4[3-]

Ignoring ion pairing and complex formation for the moment, phosphate is primarily found in the HPO42- and PO43- forms in seawater. This is quite different from the forms found in freshwater at the same pH, where the H2PO4- and HPO42- forms predominate.

Forms and Amounts of Phosphate in seawater at pH of 8.0:
H3PO ......... (4 trace)
H2PO[4-] .... (0.5 percent)
HPO4[2-] .... (79.2 percent)
PO4[3-] ...... (20.4 percent )



To a large extent, the high proportion of phosphate present in the PO4[3-] form in seawater is due to ion pairing, just as in the case of carbonate. The various phosphate species pair extensively with magnesium and calcium in seawater. PO4[3-] is nearly completely (96%) ion paired, while only 44% of HPO4[2-] is paired. This is what causes the shift in the equilibrium to more of the PO4[3-] form in seawater compared to freshwater (just as it does for carbonate).

Additionally, phosphate interacts with certain ions in a manner that is stronger than simple ion pairing. Phosphate can, for example, complex with a number of positively charged species, including both metals (e.g., iron) and organics. These interactions further serve to reduce the concentration of free phosphate and are the basis of many of the various phosphate-binding media sold to aquarists.

Phosphorus is also contained in dissolved organic compounds. While natural seawater has more inorganic phosphate than organic forms, this may not be true in aquaria where much higher organic levels may prevail.

Extracted from:
What is Seawater?
Dr. Randy Holmes-Farley
(Reefkeeping; November, 2005)

[Pikeman]

OK, I'll play. If the phosphate has ionic tendencies, would a protein skimmer have a minimal impact on phosphate ion removal given that the skimmer is primarily exporting hydrophobic compounds? Unless of course, the uptake of the phosphates into larger organisms, reducing the ionic tendency/increasing the hydrophobicity, makes the skimming process more effective. As such, would the introduction of a very weak solution of micelles improve the nutrient export capabilities of the skimmer and help lower the "unseen" phosphate levels? This is assuming that the phosphate concentrations in a closed system are higher than they would be in the wild. And that lowering the phosphates would maintain a level equal to or above the levels found in the wild. How this is measured would be a challenge, but conceptually our tanks hold unnaturally high levels. Food for thought!

Jeff

[mesocosm]

Greetings All !

OK, I'll play. ...

Very cool ... it's hard to tango alone ... :destroy:

... If the phosphate has ionic tendencies, would a protein skimmer have a minimal impact on phosphate ion removal given that the skimmer is primarily exporting hydrophobic compounds? ...

Ionic phosphate is part of the water column that is incorporated into the liquid component of air bubbles ... so it's definitely being exported by skimming. As noted in an earlier post, "... dissolved inorganic phosphorous (DIP) readily leaves seawater incorporated in tiny droplets of salt spray along with other organic and inorganic compounds. DIP coats air bubbles in seawater, travels with bubbles to the surface, and leaves water with the transport of salt spray. This mechanism for phosphate loss from seawater is more of a factor in marine aquariums where spray particles are lost from the system ... ."

Having said that, your assertion looks correct ... the impact of such an export mechanism would be minimal.


JMO ... HTH

[mesocosm]

Greetings All !

... Unless of course, the uptake of the phosphates into larger organisms, reducing the ionic tendency/increasing the hydrophobicity, makes the skimming process more effective. As such, would the introduction of a very weak solution of micelles improve the nutrient export capabilities of the skimmer and help lower the "unseen" phosphate levels? ...

Sweet! Questions like these are why I became involved with this site. A quick review of some prerequisite vocabulary ...

Micelle
In chemistry, a micelle (also micella, plural micellae) is an aggregate (or cluster) of surfactant molecules. Micelles only form when the concentration of surfactant is greater than the critical micelle concentration (CMC). Surfactants are chemicals that are amphipathic, which means that they contain both hydrophobic and hydrophilic groups. Micelles can exist in different shapes, including spherical, cylindrical, and discoidal.

Extracted from:
en.wikipedia.org/wiki/Micelle

Google search results ... for more definitions

Colloidial
Microscopic particles suspended in some sort of liquid medium. The particles are between one nanometer and one micrometer in size and can be macromolecules.

Extracted from:
naturalhealthcare.ca/medical_terms.phtml

Google search results ... for more definitions

Flocculation
The change which takes place when the dispersed phase of a colloid forms a series of discrete particles which are capable of settling out from the dispersion medium. In geological processes, flocculation is almost inevitably a result of a colloidal solution mixing with a solution containing electrolytes, eg, sea water.

Extracted from:
www.dto.com/hunting/glossary/index.jsp

Google search results ... for more definitions

Surfacant
Surfactants, also known as wetting agents, lower the surface tension of a liquid, allowing easier spreading, and the interfacial tension between two liquids. The term surfactant is a contraction of "Surface active agent". Surfactants are usually organic compounds that are amphipathic, meaning they contain both hydrophobic groups (their "tails") and hydrophilic groups (their "heads"). Therefore, they are typically sparingly soluble in both organic solvents and water. ...

Extracted from:
en.wikipedia.org/wiki/Surfactant

Google search results ... for more definitions

Amphipathic
An amphipathic (a.k.a. amphiphilic) molecule contains both hydrophobic and hydrophilic groups.The hydrophobic group can be a long carbon chain, with the form: CH3(CH2)n, with 4 < n < 16.The hydrophilic group falls into one of the following categories:# Ionic Molecules#* Anionic (with respect to the charge on the group maintaining hydrophobia). Examples are:#** fatty acids: RCO2-Na+;#** sulfates: RSO4-Na+;#** sulfonates: RSO3-Na+.#* Cationic. ...

Extracted from:
en.wikipedia.org/wiki/Amphipathic

Google search results ... for more definitions

Back to the question, "... As such, would the introduction of a very weak solution of micelles improve the nutrient export capabilities of the skimmer and help lower the "unseen" phosphate levels?" The answer is ... clearly.

During my own research into the ZEOvit methodology, I pursued a similar question tangent having to do with why the turbidity of water column would decrease when using the system. Strangely enough ... or not ... there are whole industries which are intensely concerned with the behavior of chemicals and particulates in solution. Waste water management corporations, and ... more pleasantly ... breweries, have contributed much in these area.

Why the definitions? Micelles are aggregations of surfactants ... surfactants are usually organic amphipathic molecules ... colloidial suspensions have components whose sizes range from macromolecules to 1 nm ... flocculation occurs with the mixing of collodial suspensions ("marine snow") ... "flocs" are exported through foam fractionation.

Guess what ... we don't need to add micelles. Bacterial-driven marine ecosystem filtration configurations (whether they are ZEOsystems or not) generate aggregations of micelles naturally. Although I would argue that an ecosystem which includes a bacterial culture chamber ... such as a ZEOreactor ... would generate them at significantly higher levels than ecosystems which do not include such a chamber. BTW ... it seems to me that the generation of a micelle-enriched water column can be easily generated ... although not as efficiently/effectively, IMO ... by something that Peter Wilkins documented back in the early 1980s: stirring the sandbed. No sand bed? ... no worries. Take out your trusty turkeybaster or small, handheld powerhead and perform a similar function on the surface of your live rock.

It seems to me that such aggregation-enriched water columns will necessarily demonstrate increased PO4 export, particularly those phosphate forms which we are currently unable to directly test for.

FWIW ... if someone wishes to tinker around with introducing inert micelles into their ecosystems, the brewers have made an interesting suggestion regarding their own "water columns" ...
... ...

... clay. Personally, I'll stick with the bacterioplankton.



Excellent question and conceptualization ... please play again!


JMO ... HTH

[mesocosm]

Greetings All !

For the record ... the "zeo-skeptics" were partially correct in their concerns about the "flocculation effect" of the ZEOvit methodology. Flocculation is in fact occurring. That observation was both astute and "well taken." But they were incorrect regarding the mechanism(s). Several inferred that it had to be some iron-oxy-hydroxide mechanism, or another mechanism related to the iron and/or aluminum content of the ZEOvit media. Sorry ... but we're not working with a "fancy-smancy aluminum based iron-phosphate binder" here.

The mechanisms for the siginificant improvement in water clarity associated with the ZEOvit system are twofold: (1) Flocculation around organic aggregations; and (2) The sequestration of DOCs within bacteria suspended in the water column ... and their subsequent export.


JMO

[Aged Salt]

Excellent review of Organic Chemistry, Gary[ ] as it relates to our aquaria I agree that the ZEOvit method's reduction in both N03's & P04's has no relation to any Al3 or iron-binding mechanism[release by the special zeolites] but more related to mechanisms that Jeff & you related above. ZEOvit's stones are an amazing factor in our nutrient reduction. Just stir up detritus, add a little Start2 & pump the reactor into overdrive Bob

[mesocosm]

Greetings All !

Effect of Substrate and Cell Surface Hydrophobicity on Phosphate Utilization in Bacteria
MJ Lemke, PF Churchill and RG Wetzel

We measured the rates of utilization of hydrophobic and hydrophilic phosphate compounds in gram-negative bacteria with different surface hydrophobicities, isolated from wetland habitats. Three hydrophobic and two hydrophilic bacterial species were selected for study by measuring cell adherence to hydrocarbons. The bacteria were grown under phosphorus-limited conditions with P(infi), hydrophilic (beta)-glycerophosphate, or hydrophobic phosphatidic acid as the phosphate source. Hydrophilic bacteria grew most rapidly on P(infi), followed by (beta)-glycerophosphate. Phosphatidic acid did not support growth or did so at a much later time (40 h) than did the other phosphate treatments. Although all hydrophobic species grew well on these substrates, the rate of growth of two Acinetobacter baumannii isolates on phosphatidic acid exceeded the rate of growth on phosphate or (beta)-glycerophosphate. A membrane phospholipid and lipopolysaccharide were used as a source of phosphorus by hydrophobic species, whereas hydrophilic species could not use the membrane phospholipids and used lipopolysaccharide to a lesser extent. Besides hydrophobic interaction between cells and substrate, phosphatase activity, which was cell bound in hydrophilic species but 30 to 50% unbound in hydrophobic species, affected cell growth. Dialyzed culture supernatant containing phosphatase from hydrophobic species increased the phosphate availability to hydrophilic species. Additionally, cellular extracts from a hydrophilic species, when added to hydrophilic cells, permitted growth on hydrophobic phosphate sources. Naturally occurring amphiphilic humic acids affected the utilization of P(infi) and (beta)-glycerophosphate in bacteria with hydrophilic surfaces but did not affect hydrophobic bacteria. Our results indicate that hydrophobic phosphate sources can be used by bacteria isolated from aquatic environments as the sole phosphorus source for growth. This utilization, in part, appears to be related to cell surface hydrophobicity and extracellular enzyme production.

Extracted from:
Appl. Environ. Microbiol., Mar 1995, 913-919, Vol 61, No. 3

Full Text Article (pdf)

FYI

[Pikeman]

Most excellent responses! Very helpful. I guess I won't have to throw a bunch of dish soap in my reef tank to get my phosphates down. I was aware that the bacteria would utilize the phosphates for growth, but was unaware of the flocculation effects of turkey basting your tank. Great insight. It's amazing what one can do when they understand the science behind the practice. Applause!!!

[mesocosm]

Greetings All !

Alkaline phosphatase activity in the phytoplankton communities of Monterey Bay and San Francisco Bay.
Nicholson, D., Dyhrman, S., Chavez, F. and Paytan, A.
Limnol. Oceanogr., 51(2), 2006, 874-883.


Abstract

Enzyme-labeled fluorescence (ELF) and bulk alkaline phosphatase (AP) activity enzyme assays were used to evaluate the phosphorus (P) status of phytoplankton communities in San Francisco and Monterey bays. Both regions exhibit spatial and temporal variability in bulk AP activity with maximum activities during the early spring and summer periods of high biological productivity. ELF analysis revealed pronounced differences in the makeup of organisms responsible for AP activity in these two environments. In Monterey Bay dinoflagellates are responsible for the bulk of the AP activity. Diatoms infrequently exhibited AP activity. Dinoflagellates that comprised only 14% of all cells counted in Monterey Bay accounted for 78% of AP-producing cells examined. The presence of AP activity in this group suggests that changes in P sources, concentrations, and bioavailability could disproportionably influence this group relative to diatoms in Monterey Bay. In San Francisco Bay, AP production, indicated by ELF, was associated primarily with bacteria attached to suspended particles, potentially used to hydrolyze organic compounds for carbon, rather than to satisfy P requirements. Our results highlight the importance of organic P as a bioavailable nutrient source in marine ecosystems and as a component of the marine P cycle.

Extracted from:
Reefkeeping Magazine (April 2006)

Also presented were comments by Habib Sekha ...

From the above abstract the following part is, in my opinion, the most interesting for aquarists:

"In San Francisco Bay, AP production, indicated by ELF, was associated primarily with bacteria attached to suspended particles, potentially used to hydrolyze organic compounds for carbon, rather than to satisfy P requirements. Our results highlight the importance of organic P as a bioavailable nutrient source in marine ecosystems…"

Phosphate, if chemically bound to organics, usually can't be taken up by bacteria. Bacteria excrete an enzyme called alkaline phosphatase for that purpose, which splits the phosphate from the rest of the organic molecule. This allows the phosphate to be taken up by bacteria as a source of phosphor. Bacteria usually do this (excrete the enzyme) if the free inorganic phosphate concentration is very low. The most striking part of the study is that bacteria used the enzyme not to make the phosphate part, but to make the organic part bioavailable. The bacteria (in that particular environment) were apparently not phosphor-limited but organic carbon-limited. That is, it appears as if enough inorganic phosphate (the type of phosphate measurable by hobby test kits) was present in the water, but simple organic carbon compounds were not.
If something like that occurred in an aquarium not limited in inorganic phosphate but limited in simple bioavailable organics, then it would have implications. The organic phosphate compounds would be split by bacteria to obtain the carbon part before most of them could be skimmed out. This would result in an increase in phosphate's concentration because the bacteria would not care about the extra phosphate released. That is, the bacteria would not take the phosphate up and would leave it in the water.

This could be prevented if sufficient simple, non-phosphate containing, organic carbon compounds were present so that bacteria would not be limited by them, reducing their need to split the phosphate-containing organic compounds just to use the organic part and not the released phosphate part. I would speculate that this might be one of the mechanisms for reducing, at least partly, the phosphate concentration by the addition of certain simple organic carbon compounds, e.g., ethanol.

A different mechanism proposed elsewhere is that organic carbon fuels bacteria's growth and multiplication. This growth and multiplication requires phosphor and nitrogen, thus reducing the phosphate and nitrate/nitrite/ammonia concentration.

The mechanism which I proposed (based on the above abstract) is, therefore, different. If organic carbon (but not phosphate), is limited, and if it is dosed, it may reduce the bacteria-driven breakdown of organic phosphate compounds. This would keep them intact for longer periods and might increase the likelihood of their removal by skimming.

Results for phosphate and nitrate concentrations over time during an ethanol (Vodka) dosing experiment, published by Michael Mrutzek and Jörg Kokott in 2004, if measured accurately, support the mechanism I suggested by the initial decrease in phosphate concentration only, and not by the nitrate concentration. This mechanism is probably followed (after a few weeks of dosing) by the bacteria growth/multiplication fueling mechanism. This "fueling mechanism" results in a decrease in both phosphate and nitrate concentrations as opposed to a reduction of only phosphate in the initial part. Note the initial drop in phosphate only, followed by a "steady-state" period and then a drop in both nitrate and phosphate, from a graph of their results:
http://www.korallenriff.de/wodka_diagramm_jk.jpg.

Extracted from:
Reefkeeping Magazine (April 2006)

Good stuff ... I'm also posting this in The "Mulm" Thread.



FYI