Quote:
Originally Posted by Dan_P
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Where I think we missed an important point in this discussion is that the ratio of heterotrophic:autotrophic may be predictive of a system’s propensity to grow nuisance photoautotrophs such as diatoms, dinoflagellates, cyanobacteria and algae. The notion that nitrate and phosphate are predictive or are the cause of nuisance organism growth needs to be revisited. It might be more useful to think in terms of inadequate heterotrophic activity or a low C:N ratio as the cause of nuisance organism growth.
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It is a fact that the nitrate level has nothing to do with the total nitrogen produced in a system. As ammonia is used directly by a lot of organism it is difficult to determine how much is used by heterotrophic and autotrophic bacteria and how much is denitrified. Nitrate is the product of autotrophs but the denitrification ratio is not known.
As most organisms prefer ammonia, also nuisance organism growth, on has to make a study of there needs. As example the C:N:P ratio for bentic algae differs a lot from the ratio needed by phytho plankton. When carbon is provided the competition will be for nitrogen and phosphate. When carbon is not provided heterotropic growth is limited by the availability of organic carbon and nitrification and denitrification will be normal which means that nitrogen may be removed from the system and not stored into the food chain and not be reused by nuisance organisms after decay. Photoautotrops will use ammonia by preference and nitrite and nitrate as emergency nitrogen source, some cyno's have one more pathway and can take up nitrogen to produce ammonia bringing nitrogen within the organic carbon chain. They will only do so to survive, when no other nitrogen source is available.
http://www.baharini.eu/baharini/doku...o-chemie:cyano Study of the pathways of the different nuisance organisms may bring more information about there typical needs.
When heterotrophic growth is responsible for limiting nuisance growth it may be due to the competition for ammonia and phosphate as the growth rate using nitrate is a lot less. I think cyno's are in favour in the competition for nitrogen as they are Phototautotropic. The limiting factor may be phosphate or other building materials. Limited availability of phosphate and building materials will have influence on all live forms.
As most organisms are in competition for the same building materials one organism my switch sooner to another pathway as an other organism according to there needs.