Redfield ratio or Redfield stoichiometry is the molecular ratio of carbon, nitrogen and phosphorus in phytoplankton. The stoichiometric ratio is C:N:P = 106:16:1. The term is named after the American oceanographer Alfred C. Redfield, who first described the ratio in an article in 1934 (Redfield 1934).Redfield described the remarkable congruence between the chemistry of the deep ocean and the chemistry of living things in the surface ocean. Both have N:P ratios of about 16 (atoms to atoms). When nutrients are not limiting, the molar element ratio C:N:P in most phytoplankton is 106:16:1. Redfield thought it wasn't purely coincidental that the vast oceans would have a chemistry perfectly suited to the requirements of living organisms. He considered how the cycles of not just N and P but also C and O could interact to result in this match. (From Wikipedia, the free encyclopedia)Having established this ratio back in 1934, several articles of authority on nutrient ratios appeared (eg: Tilman et al., 1982; Howarth et al., 1988a; Leppänen et al., 1988), but it would take 60 years before A.P. Levich of Moscow State University proposed an interpretation which allowed dominance control of planktonic communities of blue-green or green microorganisms by nutrient manipulation.Levich had found an effective way to fight algae.
The role of nitrogen-phosphorus ratio in selecting for dominance of phytoplankton by cyanobacteria or green algae and its application to reservoir management.
(by: A. P. Levich; Laboratory of General Ecology, Department of Zoology of Vertebrates and General Ecology, Biological Faculty, Moscow State University, 119899 Vorobyovy Gory, Moscow, Russia December 1994.)
The undesirable consequences of phosphorus enrichment in reservoirs are primarily connected with the emerging abundance of cyanobacteria which are not utilized by the consumers and form, as a rule, a trophic block in the majority of nutrition chains. Blooming of Chlorococcales does not produce these negative effects since they are actively consumed by grazers. The NT ratio turns out to be the factor which regulates the dominance of planktonic communities by blue-green or green microorganisms. Decrease of the N:P ratio, through the addition of phosphorus compounds, leads to cyanobacterial blooming.In order to replace blue-green dominance of eutrophic reservoirs by dominant greens, it is suggested that the addition of nitrogen, thus varying the N:P ratio (nutrient manipulation) to apply, is superior to the traditional phosphorus load decrease. Utilization of the redundant green algal biomass may occur in a natural way or be conducted with the aid of biomanipulation, i.e., by introduction of planktivorous fish into the reservoir.
Five years later Levich teamed with Bulgakov publishing a paper providing numerical limits to nutrient manipulation in the control of algae.
The nitrogen : Phosphorus ratio as a factor regulating phytoplankton community structure : Nutrient ratios
(by: BULGAKOV N. G. and LEVICH A. P. ; Moscow State University 1999.)
Shifts in phytoplankton species composition following changes in N: P ratio have been observed in artificial laboratory microcosms and natural phytoplankton communities in vitro and in situ. The experiments reported and reviewed here have shown that high N: P weight ratios (20-50: 1) can favor the development of Chlorococcales, while a reduction of the N: P ratio to values of 5 to 10 frequently leads to a community dominated by Cyanophyta. Model calculations predict that the relative abundance of different phytoplankton species depends only on the relative amounts of N and P in the environment, so that the optimal N: P ratio for a given species is equal to the ratio of its minimum cell requirements for these elements. An empirical test of this hypothesis showed that for several species of Chlorococcales and Cyanophyta the ratios of their cellular requirements for N and P determined experimentally were close to their optimal (for growth) environmental concentration ratios. For instance, an experimental increase in the N: P ratio from a value of 4:1 to 25-50: 1 by mass in the water of fish-breeding ponds led to an increased abundance of Chlorococcales. The species shift was due mainly to Scenedesmus quadricauda, which has a high optimal N: P ratio for growth.
In 2004, Ilmar Tõnno provides additional information on the nitrogen cycle involving Cyanobacterial Dominance. This article is of importance because of its emphasis on “how” and “why” of these processes.
The Impact Of Nitrogen And Phosphorus Concentration And N/P Ratio On Cyanobacterial Dominance And N2 Fixation In Some Estonian Lakes
(by:ILMAR TÕNNO; Institute of Zoology and Hydrobiology, University of Tartu, Estonia. 2004)
Nitrogen (N) is one of the main building blocks for the production of organic matter and it is required in great quantities (Stolp, 1996; Williams et al., 2002). Most of the nitrogen on Earth is present in molecular form (N2) being biologically unavailable except for organisms containing the enzyme nitrogenase.N2-fixation (N2fix) by micro-organisms is the only process in nature that counteracts the losses of nitrogen from the environment by denitrification (Fig. 1). Cyanobacteria appear responsible for most of planktonic N2fix in aquatic ecosystems, this ability gives a significant competitive advantage to these organisms during the periods of nitrogen limitation (Tilman et al., 1982; Howarth et al., 1988a; Leppänen et al., 1988). Many hypotheses have been presented to explain cyanobacterial dominance and blooms in lakes. One of the most common is resource ratio competition theory, predicting that cyanobacteria tend to dominate in lakes where the ratio of nitrogen and phosphorus (P) is low, mainly because of the ability of some of these species to use molecular nitrogen (Elser 1999). This theory has been proved both empirically and experimentally. Cyanobacteria, both fixing and not fixing N2, tend to dominate if the ratio of total nitrogen (TN) and total phosphorus (TP) in the water column is below ca. 5–10 by mass (Schindler 1977, Seip 1994, Michard et al., 1996, Bulgakov & Levich 1999), although some authors regard the critical TN/TP ratio to be much higher, even as much as 29 by Smith (1983). According to many authors (Smith et al., 1987, Willén 1992, Lathrop et al., 1998, Downing et al., 2001) cyanobacterial dominance and blooms couple more strongly to the variations in P and N concentrations, rather than changes in N/P ratio. Other factors such as water temperature, pH, light intensity and total carbon dioxide concentration are also important. Generally N2-fixing cyanobacteria are better nitrogen competitors, but poorer phosphorus competitors, than other groups of algae. In shallow lakes, however, cyanobacteria appear to be more efficient than other phytoplankton species in converting P into their biomass (Smith, 1983; Nixdorf & Deneke, 1997). Water in shallow lakes is permanently mixed up and therefore enabling more or less homogenous nutrient spreading in the water column. Unlike from shallow lakes, in stratified waterbodies phytoplankton (including cyanobacteria) takes up epilimnetic nutrients and transports them to the hypolimnion via sedimentation. Nutrients may accumulate in the hypolimnion during stratification period while nutrients deficiency may occur in the epilimnion if resupply from the inflows is limited (Scheffer, 1998). In earlier papers, however, it has not been studied whether cyanobacterial N2-fixation starts in lakes instantly after the set-up of favourableconditions or after some lag period.
- When nutrients are not limiting, the molar element ratio C:N:P in most phytoplankton is 106:16:1 (Redfield 1934)
- The NT ratio turns out to be the factor which regulates the dominance of planktonic communities by blue-green or green microorganisms. Decrease of the N:P ratio, through the addition of phosphorus compounds, leads to cyanobacterial blooming. (Levich 1994)
It is suggested that the addition of nitrogen, thus varying the N:P ratio (nutrient manipulation) to apply, is superior to the traditional phosphorus load decrease. (Levich 1994)
- Experiments reported and reviewed here have shown that high N: P weight ratios (20-50: 1) can favor the development of Chlorococcales, while a reduction of the N: P ratio to values of 5 to 10 frequently leads to a community dominated by Cyanophyta. (BULGAKOV N. G. and LEVICH A. P. 1999)
- Cyanobacteria, both fixing and not fixing N2, tend to dominate if the ratio of total nitrogen (TN) and total phosphorus (TP) in the water column is below ca. 5–10 by mass. (Ilmar Tõnno. 2004)
- According to many authors (Smith et al., 1987, Willén 1992, Lathrop et al., 1998, Downing et al., 2001) cyanobacterial dominance and blooms couple more strongly to the variations in P and N concentrations, rather than changes in N/P ratio. (Ilmar Tõnno. 2004)
- Other factors such as water temperature, pH, light intensity and total carbon dioxide concentration are also important. (Ilmar Tõnno. 2004)
Implications for aquaria – or how to avoid the onset of an algae bloom.
The maintenance of the Redfield Ratio in an aquarium is a means of avoiding the onset of algae blooms. However
“Other factors such as water temperature, pH, light intensity and total
carbon dioxide concentration are also important. (Ilmar Tõnno. 2004)”.
This ratio should be somewhere between 10 and 22 atoms to atoms. The statistical optimum is 16.This means we need to test for NO3 and PO4 regularly. Unfortunately these tests give you answers in ppm (mg/L), which leaves the question: What is the relation between atoms and ppm?To find the atom to atom ratio you have to divide the molar weights into each other.Molar weight NO3: [NO3 ppm]/62Molar weight PO4: [PO4 ppm]/95Redfield Ratio: ([NO3 ppm]/62)/([PO4 ppm]/95) or 1.53* [NO3 ppm]/[PO4 ppm], in other words: you divide your NO3-reading by your PO4-reading and then multiply the answer by 1.53.That last term is sometimes called the "Buddy Ratio" which equals ±RR/1.5. If the RR has to be between 10 - 22, then the BR should be between 6 - 14 to get the same ratios.It is easier to work with the BR.The whole idea is to check NO3 and PO4 - say - once a month. If the ratio is out of the safe zone you can do a number of things:
If the readings are high (NO3 > 10ppm or PO4 > 1ppm), do a water change. Then test again.
If the readings are low, then add phosphate or nitrate depending.
· phosphate (KH2PO4, 0.1% solution) per ppm, per gallon: 5.5mL
· nitrate (KNO3, 1% solution) per ppm, per gallon: 0.6mL
What to do when an algae bloom hits you.
Measuring the Redfield Ratio (or Buddy Ratio) is easy to do, although there is always a chance that it may not be the reason, refer: “Other factors such as water temperature, pH, light intensity and total carbon dioxide, etc . . .”.Even so, if - nevertheless - the RR is greater than 22 or less than 10 (BR > 14 or <6)>
SEE HERE FOR MORE INFORMATION
Redfield Ratio & Easy life To Help Combat Algae:
Above is an old method that seems to have been forgotten about for many years and is starting to come back slowly. Myself and woolfenrook (ADE) have been testing this out for the last few weeks or so with so far good results.
As most of you will know I have never been able to dose anything in my planted tanks with out getting an algae bloom of one sort or another. The basic concept of the Redfield Ratio is to balance N&P being in between 10 & 22.The optimum being 16:1.
I have on top of bringing my N&P into this band started dosing Easy life Profito and also easycarbo. At 3ml & 4mls per day respectively. (21mls & 28mls per week)
This is the only time I have been able to add any thing to my tank and so far no sign of any increased algae growth so I am at the moment more than happy to continue with this and to increase dosing if needed.