# Nitrates Inhibiting Aquatic Plants



## dwalstad (Apr 14, 2006)

Interesting new information to share, folks....I have always considered nitrates essentially harmless, but then I was always thinking in terms of fish. I never thought of plants....

I have just come across three references that clearly show substantial and significant growth inhibition of 3 aquatic plant speciess (marine eelgrass, alpine pondweed, and a Salvinia).


Burkholder JM, Mason KM, and HB Glasgow Jr. 1992. Water-column nitrate enrichment promotes decline of eelgrass Zostera marina: evidence from seasonal mesocosm experiments. Marine Ecology Progress Series 81: 163-178.
Boedeltje G, Smolders AJP and JGM Roelofs. 2005. Combined effects of water column nitrate enrichment, sediment type and irradiance on growth and foliar nutrient concentrations of Potamogeton alpinus. Freshwater Biology 50: 1537-1547.
Jampeetong A and Brix H. 2009. Nitrogen nutrition of Salvinia natans: Effects of inorganic nitrogen form on growth, morphology, nitrate reductase activity and uptake kinetics of ammonium and nitrate. Aquatic Botany 90: 67-73.

The papers are compelling. (Dr. Burkholder is a top-level scientist, famous for her work with toxic marine dinoflagellates.) For her eelgrass paper, plants were rooted in ordinary sediment and got their nitrogen from sediment-generated ammonia. When these plants were continuously fed just 0.22, 0.45 and 2.2 ppm nitrates, they immediately "greened up", but over time they started to decline. After 4-5 weeks, the investigators were surprised to see that the nitrate-fed plants actually fell apart when handled.

The alpine pondweed grew significantly less when exposed to 32 ppm nitrates under 4 different growing conditions. For example, when grown on sandy sediment, plants given nitrates grew at least 50% less than control plants without added nitrates.

Salvinia growth rate was reduced almost 40% by 32 ppm nitrates. Fronds were smaller and paler than those fed ammonium.

The 3 investigators attribute the inhibition to a "metabolic disturbance" within the plant, which I won't go into here. It is not an outright toxicity, but the results are the same-- inhibited plant growth.

Reason for these studies...There's been a general decline in some aquatic plant species associated with high nitrate levels in some polluted waterways. Plant decline was thought to be due to stimulation of algae or light reduction due to turbidity associated with the pollution. So these investigators were surprised to find that the nitrates _alone_ inhibited the plants.

I am curious to hear what you all have to say on this important topic.


----------



## mudboots (Jun 24, 2009)

These are great finds!!! One of the main issues in my line of work is allowing the world's kidneys, the wetlands, an opportunity to remove the "stuff" we don't want, ultimately, in our waters. There seems to be a very heavy emphasis on pesticides, turbidity, light, algae, phosphates, nitrates, and the usual list of culprits...with a lot of weight put on ag-related chemicals (and for good reason). It is really wonderful that these studies focused on nitrates and came up with these results. I have to admit that I am a bit surprised, as I would have thought that nitrates is one name on "the list" that plants would not have as much of a problem with relative to others.

Thank you for posting this; I am anxious to find these and give them a read.


----------



## bartoli (May 8, 2006)

dwalstad said:


> The 3 investigators attribute the inhibition to a "metabolic disturbance" within the plant, which I won't go into here. It is not an outright toxicity, but the results are the same-- inhibited plant growth.


It would be interesting to know the pathway through which nitrate disturbed the metabolic process. Did any of the papers trace the pathway?

When it is not an outright toxicity, does that mean it is a case of "too much of a good thing"? Did they mention any threshold beyond which nitrate started to inhibit plant growth?

Thanks for the info. Very interesting!


----------



## snooze (Apr 10, 2008)

Thanks for posting references to these articles. I read Rodney Barker's book regarding Dr. Burkholder's research of a toxic dinoflagellate (Pfiesteria piscida) for one of the botany courses I took as an undergraduate. I highly recommend this book to anyone interested in aquatic sciences, epidemiology, or the practice of science (esp. with regard to policy). The title is "And the Waters Turned to Blood."

edit: fixed the title.


----------



## dwalstad (Apr 14, 2006)

Snooze, I really enjoyed that book, too. A scientific thriller!

Dr. Burkholder kindly supplied me yesterday with information and some more recent papers. Here are two more papers that have some interesting information.


Burkholder JM, Glasgow Jr, HB and JE Cooke. 1994. Comparative effects of water-column nitrate enrichment on eelgrass Zostera marina, shoalgrass Halodule wrightii, and widgeongrass Ruppia maritima. Marine Ecology Progress Series 105: 121-138.

Burkholder JM, Tomasko DA and BW Touchette. 2007. Seagrasses and eutrophication. J Expt Marine Biology 350: 46-72.

The first paper shows that _Zostera marina_ (eelgrass) is again inhibited (actually killed) by a 14 wk exposure to 10 uM NO3 (0.62 ppm nitrate). One thing interesting here is that Burkholder (1994) also tested plants pre-exposed to low level nitrates a few months earlier (12 weeks at 0.31 ppm nitrate). You might think that the pre-exposed plants could have adapted "learned" to deal with nitrates, but they were actually inhibited _more_ than unexposed plants.

The two other plant species responded much better to the nitrate addition (14 wk at 0.62 ppm) than "Zos". That is, _Halodule wrightii_ showed a small and significant increase in shoot production; but _Ruppa maritima_ increased shoot production 300%. Thus, "Zos" is gradually being replaced by species that can handle NO3 pollution better.

The second paper is a review paper where the authors (Burkholder 2007) provide theory to explain why nitrates inhibit _Zostera marina_.

"Zos" apparently doesn't have a feedback mechanism to regulate NO3 uptake. Unlike other plants, it takes up nitrates day or night (most aquatic plants limit nitrate uptake to daytime when they have photosynthetic energy to process the nitrates).

This unregulated NO3 uptake and processing (i.e., assimilation) depletes the plant of energy (nitrate processing consumes energy) and carbohydrates, including structural carbohydrates (that's probably why the plants gradually fall apart). Unregulated NO3 uptake would be an advantageous strategy (physiological mechanism) in nitrogen-depleted waters, but would become disadvantageous as coastal waters become more nitrate-polluted.

I would agree with Dr. Burkholder's statement that some of the more oligotrophic species of freshwater aquatic plants (those from and adapted to nutrient-depleted habitats) should be susceptible to nitrates. I have had a few plant species die out in my tanks where nitrates are _a lot_ higher than 0.62 ppm. I suspected iron deficiency, allelopathy, etc, but never nitrate inhibition.


----------



## JeffyFunk (Apr 6, 2006)

Well, this is most definitely interesting new information that raises some interesting new questions. More specifically, I'm wondering if the scientists thought about the presence of NO3 causing a nutrient deficiency in Carbon or any other nutrients for that matter? 

From what I understand, most high tech tanks are generously supplied w/ an abundance of nutrients in the form of CO2 fertilization and daily dosing, including nitrates. In this fertilizer regime, I would expect that the depletion of carbon from the plant structure would not be a problem since carbon is already generously supplemented. 

That said, I also find it interesting that the presence of the previously thought inert nitrates would be the cause of such plant issues. I look forward to hearing more about what you find in the literature this from you.


----------



## dwalstad (Apr 14, 2006)

Excellent question! It is one that the investigators have commented on.

_Zostera marina_ can use bicarbonates as a carbon source very effectively, and seawater is full of bicarbonates.

Thus, the nitrate inhibition shown was not due to carbon limitation, lack of CO2, etc.


----------



## tames (Apr 18, 2008)

Specifically related to aquariums, how do nitrates get into the water?

Some ideas for comment:

1. Through the bacteria cycle. In a well planted tank, this should be less of an issue since the simple ammonia forms are taken up by the plants.

2. Present in the tap water.

3. Fertilizers and Water Conditioners.

4. Present in the soil?

5. Aquarium decorations such as driftwood?

6. Animal waste?


----------



## dwalstad (Apr 14, 2006)

In my case, nitrification. At times, I've measure over 50 ppm nitrates in established tanks!

It is not that plants don't take up ammonia; it is just that nitrifying bacteria (in the biofilter and in the tank itself) get to the ammonia first. 

I've ordered a nitrate test kit and will measure the nitrates in my tanks with water circulation (more oxygenation and probably more nitrification) and those with no water circulation.

Stay tuned!


----------



## Johnriggs (Jun 26, 2009)

As I've said before, mine run between 20-40 ppm if I don't change the water regularly. But my tank is a 6 gallon and is just under 3 months old, so has barely ripened.

Frogs are messy eaters. They shred food all over the place and it goes into the substrate, which I'm sure adds to the nitrifiction. But I figured this was good for the soil nutrition and I understand vacuuming is neither necessary nor really practical.

J


----------



## Supercoley1 (May 28, 2007)

I use EI on mine and never vacuum. Never had a problem with high nitrates.

I do think it sounds more like the high nitrates causing a defficiency of something else though. Not necessarily CO2. It could be anything else. this is why dosed tanks work. We add more of everything than is needed and remove all defficiencies. We don't suffer any toxicity problems though.

It is a little naive to add 1 thing and then assume it is a toxicity from that 1 thing that is the cause. changing 1 thing means everything else is altered too. There may have been enough Fe for example to match N, suddenly N rises and Fe is defficient etc. So any traces, K, P who knows.

AC


----------



## brenmuk (Oct 7, 2008)

This is very interesting stuff indeed. It would be interesting to know a bit more about the controls that were used in the experiments. I think Supercoley makes an interesting point about adding a single fert in isolation - I can't help think that the conclusion jars a bit with the EI method and all the lush growth that people have using that method.
Also how applicable are the results to the hobby where plants are bought that are probably grown with plenty of ferts and where their physiology is not adjusted to low nitrates. 

Is nitrate at high levels inhibiting or is a high degree of fert inbalance inhibiting ie nitrate on its own?

I suppose the classic fert imbalance is high phosphates with very low nitrates for example that promotes bga - its not high levels of phosphate are bad but more that nitrate soon becomes limiting.


----------



## dwalstad (Apr 14, 2006)

What's EI?

I'm not sure that the documented nitrate inhibition of 3 plant species has any practical implications for aquarium plants. The majority of aquarium plants (grown under nursery conditions) are probably not nearly as sensitive as _Zostera marina_. Otherwise, they would be dead! In Burkholder's 1994 paper, _Zostera marina_ was severely inhibited by as little as 0.6 ppm nitrates, while _Ruppia maritima_ was stimulated 300% by the same concentration.

It is hard for me to say anything further until we get feedback from people who have actually done experiments on aquarium plants or those who grow aquarium plants for a living.


----------



## Supercoley1 (May 28, 2007)

dwalstad said:


> What's EI?


I figure this is a tongue in cheek comment. lol

However just in case....EI is where we dump in NPK and maintain nitrate at levels of 20ppm+, phosphate at 5ppm+ etc. then do a large water change at the end of the week.

Some people with very heavily planted high light tanks dose 3x this. No 'ill' effect on any plants at all unless shiny lush growth is an 'ill effect' 

AC


----------



## prBrianpr (Nov 18, 2007)

Supercoley1 said:


> I figure this is a tongue in cheek comment. lol
> 
> However just in case....EI is where we dump in NPK and maintain nitrate at levels of 20ppm+, phosphate at 5ppm+ etc. then do a large water change at the end of the week.
> 
> ...


I think that a lot of all not is the best idea ever but also deficency are bad. When the plants receive the needed nutrients and are very healthy they can survive some conditions. When you have healthy looking plant it can live in high temps, one or two degree more that the temp that everybody says that it will die. I think that will happend to some (not all) plants that live in EI fertilised aquarium. If the High nitrate can inhibite grow to some plant but it are healthy the plant make the way to continue growing maybe have the sufficient energy to grow fast and to convert the nitrate to ammonium.

Brian


----------



## dwalstad (Apr 14, 2006)

Supercoley1 said:


> I figure this is a tongue in cheek comment. lol
> 
> However just in case....EI is where we dump in NPK and maintain nitrate at levels of 20ppm+, phosphate at 5ppm+ etc. then do a large water change at the end of the week.
> 
> ...


Thanks for the clarification. No tongue in cheek; I was dead serious. After all, this is the El Natural forum where fishfood (not chemicals) provides plant nutrients.


----------



## prBrianpr (Nov 18, 2007)

In my tanks I have a lots of guppies but thats seems that the guppies and substrate not do all the work needed. I check today the nitrates in a 10G 5 tanks row and the nitrates are near 0 (I check because I saw cyanobacteria growing in some rocks) so I broken the rule one more time to dose KNO3. Maybe there are a lot of light (sun) that makes that the plants works faster and consume all the nitrate.


----------



## f1ea (Jul 7, 2009)

Great topic, and in fact something i was very curious about. Because at my local gardening shop they have a very good 'foliar' fertilizer (20-10-20 + all traces)... however, the label states 38% of the total N is in ammonia form.

Based on the discussion here, it seems we would be better off dosing 'some' ammonia (as mentioned above) rather than say, KNO3 as a source of N... in fact i was even thinking of using this fertilizer to encourage a fishless cycle (adding the ammonia through the fertilizer). 

Would it also be possible to do this with fish in the the tank (carfeully dosing to make sure not to reach an ammonia concentration of 0.1 ppm) ??

Regards


----------



## dwalstad (Apr 14, 2006)

f1ea said:


> Great topic, and in fact something i was very curious about. Because at my local gardening shop they have a very good 'foliar' fertilizer (20-10-20 + all traces)... however, the label states 38% of the total N is in ammonia form.
> 
> Based on the discussion here, it seems we would be better off dosing 'some' ammonia (as mentioned above) rather than say, KNO3 as a source of N... in fact i was even thinking of using this fertilizer to encourage a fishless cycle (adding the ammonia through the fertilizer).
> 
> ...


Ammonia is very toxic to both plants and fish. I would never recommend adding ammonia to tanks. Also, foliar fertilizers are designed for terrestrial plants and usually are loaded with sufates. Again not recommended... In the submerged environment of an aquarium, sulfates get converted to toxic hydrogen sulfide.

Soil (assuming its unsterilized) already contains plenty of nitrifying bacteria that will work in the tank. Hopefully, the soil you choose will contain organic matter, which decomposes and slowly releases the ammonia that plants like and that will stimulate nitrifying bacteria. Fishfood and fish waste will rapidly add more nitrogen.

I took nitrate measurements on my 8 tanks today. They all contain 10-20 ppm nitrates, and all plant species seem to be growing well right now. (I don't see the inhibition I saw in some plants when nitrates were much higher.)

If you're injecting CO2 and see symptoms of nitrogen deficiency, you may need to add KNO3. But there's no need to add KNO3 (or any other fertilizers) to an El Natural tank. In general, I've found fertilizers to be counter-productive. Once in "a blue moon" I'll squeeze a small root tab in for a big Swordplant that looks hungry, but that's it.


----------



## f1ea (Jul 7, 2009)

Of course, good organic soil already has all the 'ingredients' we should be looking for 
No need to be so skeptical about Nature's formula....


----------



## Supercoley1 (May 28, 2007)

dwalstad said:


> Thanks for the clarification. No tongue in cheek; I was dead serious. After all, this is the El Natural forum where fishfood (not chemicals) provides plant nutrients.


Indeed it is but always good to have knowledge of other methods too. I run an 'almost El Natural' in that it does get some added NPK but not much and also a hi tec full CO2 injection full dosing tank so I ee both sides of the coin here.

AC


----------



## Dave Spencer (Mar 4, 2007)

This is very interesting information, but I would personally struggle to find this process in action in any of my tanks, all of which are dosed as per the EI method.

I have always struggled with Hygrophila corymbosa "Siamensis" 53B, as it constantly shows healthy new growth, but the leaves are soon full of pin holes and turn brown. At least I now have something to blame for my failings.

Dave.


----------



## Dave Spencer (Mar 4, 2007)

dwalstad said:


> Ammonia is very toxic to both plants and fish.


Do you have any figures on this Diana? I know that there is a whole genre of people out there adding ammonia at 5ppm in order to cycle a tank (without fish of course). I am constantly recommending that they don`t cycle with the plants in the tank, because so many end up an algified mess with dead plants.

Would the 5ppm of ammonia be toxic to most aquatic plants? Sorry to go off tack a bit.

Dave.


----------



## tug (Jul 23, 2009)

Dave Spencer said:


> I know that there is a whole genre of people out there adding ammonia at 5ppm


I added a 1/4 tsp of Liquid Grow 7-9-5 once.


> 4/15 Dose.
> 1/4 tsp. Lquid Grow with last 40% WC, (1 tsp AmQuel).
> Cu, (0.09 ppm) No testing, just a guess based on survival rate of the RCS -vs- algae
> RCS, (Hardy little sp.) not effected if water flow is well circulated.
> ...


I was starting a 20 gal. planted tank and didn't have anything else to try, so gave it a shot. Shrimp made out fine and the copper knocked back the algae big time. I didn't have a way of measuring it, but copper levels around 0.1 ppm starts to become an effective algaecide. Just get the water circulating and oxygenated. I have heard NH4 causes BGA, a problem for any planted or unplanted tank. Mine had plants, (yellow decrepit looking things) and algae. Thats why I tried it. The plants improved and I then moved on to other sources of NPK. I'm staying around 10 ppm and range up to 20 ppm around the time I start seeing that yellow water in my 10 gal tank. Then it's time to change the water in both tanks. I truthfully do not know what levels of NO3 and PO4 (for example) cause problems for plants or induce algae in a fully planted tank. NO3 levels above 40ppm can cause fish health issues. PO4 at very high levels can influence alkalinity (KH) above 5ppm-10ppm.

:emptybath
EI Natural Planted Aquarium


----------



## dwalstad (Apr 14, 2006)

Dave Spencer said:


> Would the 5ppm of ammonia be toxic to most aquatic plants? Sorry to go off tack a bit.
> 
> Dave.


Sensitive plant species would be harmed by 1 ppm (my book, p. 21).


----------



## LVKSPlantlady (Oct 4, 2009)

Supercoley1 said:


> I figure this is a tongue in cheek comment. lol
> 
> However just in case....EI is where we dump in NPK and maintain nitrate at levels of 20ppm+, phosphate at 5ppm+ etc. then do a large water change at the end of the week.
> 
> ...


this method seems very wasteful. do the plants even have a chance to use half the frets you add before you dump them down the drain, the ferts not the plants?


----------

