# Ecological Stoichiometry & Algae.



## Tim Harrison (6 May 2012)

Does the conversion of organic compounds to inorganic nutrients favor the growth of algae due to the carbon*:*nutrient ratio found in organic matter such as plant detritus etc?


----------



## plantbrain (6 May 2012)

No.

Where large plant biomass exists, there is no correlation between between nutrients in the water and algae presence.

That said, seasonally, there can be correlation in northern/far southern lakes/rivers etc, when the plants die off in the Fall, or prior to their seasonal new growth in the spring. But this precludes having any plants, which is not representative.

Let's take another case: aquatic weed control. Something not popular in Europe/UK etc.
Very popular here in the USA. We actually go out and kill aquatic weeds.

A lake is infested with say Hydrilla. They call me out for treatment options. I suggest Copper sulfate initially, then followed a couple weeks later with Fluridone herbicide(Copper is cheap, Fluridone is $$$). The copper will kill off the algae on the plants. Then later, we add the fluridone. This is a slow acting herbicide that is 1000X less toxic than caffeine, and we only need parts per BILLION.

This takes roughly 8 to 20 weeks to slowly kill the plants. If I chose Diquat, a fast acting herbicide, it would kill the plants in 3-5 days. But then all this dead organic matter would be produced and bacteria would bloom.
When this happens the O2 levels will drop near zero, this leads to a lake full of dead fish floating up to the top and a mad lake owner.

They say the herbicide was TOXIC AND DEADLY. But it's not the herbicide that's toxic, it was the environmental conditions that killed off the biomass way to fast.

End result using diquat: huge algae bloom/dead fish
End result of the Fluridone: slow milder algae bloom/happy fish

In both cases, if you remove the plants, you get pea soup.
If you add ferts to the lakes with plants, you get more aquatic weed growth.

Many people want to remove the weeds and have nice clear water......... then only get something worse with the pea soup algae after killing off the weeds. All that lawn fertilizer and bug spray they use right next to the lake does not help one bit either.


----------



## Tim Harrison (7 May 2012)

plantbrain said:
			
		

> No.
> 
> Where large plant biomass exists, there is no correlation between between nutrients in the water and algae presence.
> 
> ...



Hi Tom and thanks for answering, although I must admit to being a little confused still. If the DOM from the dead plants causes a massive algal bloom then surely the answer to my question is yes.

I'm in no doubt that inorganic nutrients encourage plant growth and not necessarily algal growth, the question I was asking is...does the carbon:nutrient ratio of decomposing organic matter favor algal growth over macrophyte growth (through bacterial and algal stoichiometry)?


----------



## sWozzAres (7 May 2012)

I doubt it. Indirectly though decomposing organic matter usually happens in places with low flow where the local nutrient balance is fluctuating due to decomposition. This favours algae.


----------



## Tim Harrison (7 May 2012)

Exactly...same difference. 

Ok...I'll confess, I have a theory that actually it does, and I have read a few papers that support my theory but I wanted to know if anyone had the same inkling. 

It's all really about getting to the bottom of why inorganic eutrophic dosing does not cause algal blooms and why a lot of decomposing organic matter (bad husbandry) often does. Do you see where I am coming from?

I guess I'm trying to find the Holy Grail of the planted Tank world...for what it's worth...call me a crusader or a hopeless romantic, if you will.


----------



## sWozzAres (8 May 2012)

It doesn't matter if the organic matter decomposes in your tank, or in the filter - the c:n end result will be the same. Only difference is that there is no light in the filter.

So what's your theory?


----------



## dw1305 (8 May 2012)

Hi all,


> A lake is infested with say Hydrilla. They call me out for treatment options. I suggest Copper sulfate initially, then followed a couple weeks later with Fluridone herbicide(Copper is cheap, Fluridone is $$$). The copper will kill off the algae on the plants. Then later, we add the fluridone. This is a slow acting herbicide that is 1000X less toxic than caffeine, and we only need parts per BILLION. This takes roughly 8 to 20 weeks to slowly kill the plants. If I chose Diquat, a fast acting herbicide, it would kill the plants in 3-5 days. But then all this dead organic matter would be produced and bacteria would bloom. When this happens the O2 levels will drop near zero, this leads to a lake full of dead fish floating up to the top and a mad lake owner.......Many people want to remove the weeds and have nice clear water......... then only get something worse with the pea soup algae after killing off the weeds. All that lawn fertilizer and bug spray they use right next to the lake does not help one bit either.


Tom that is really funny, talk about "_shoot the messenger_", on the bright side it should keep you in a job for life.

I don't know the answer to the "_Ecological Stoichiometry & Algae_" question, you can have naturally eutrophic conditions, with calcareous water, where you have abundant macrophyte growth and little in the way of planktonic algae, although this often to do with zooplankton abundance rather than nutrients <http://www.econ-ecology.co.uk/restoration.php>.  Even in these cases you often get occasional blooms, particularly of planktonic cyanobacteria. See "the breaking of the Meres" <http://www.eco-challenge-xtra.org/fieldstudies/documents/vol1.4_27.pdf>.

cheers Darrel


----------



## Brenmuk (8 May 2012)

Hi Tom - When you dose Copper sulphate do you have to consider the ecological impact that will have on invertebrates?


We spend alot of the thinking about algae & nutrients but what about the relationship between algae & ammonia/O2 levels in the water column and substrate? 
Also as Darrel alluded to what effect the numbers and types of crustacia have. In my cherry shrimp tank I have hardly any algae to speak of and a host of wierd and wonderful 'critters' that I never see in tanks with fish. It has made me think that the traditional fish tank with lots of fish is very top heavy in terms of predators vs algae eating herbivores (in the form of daphnia, copepods, small shrimp etc).


----------

