Hi all,
As an example; if a gardener had a veg patch and got weeds among the crop, he wouldn't remove all the nutrients to 'starve' the weeds, as obviously this would damage his crop. Surely it's much the same in our case where the aquatic plants are like the veg, and the algae like the weeds.
Not really, there are photosynthetic organisms across all the different taxonomic groups that are adapted to conditions of low or high nutrients, this means that some "plants" & "algae" occur only in nutrient rich (eutrophic) conditions, and some occur only in nutrient poor (oligotrophic) conditions, most are somewhere in the middle (mesotrophic). A similar range of organisms occur along pH and salinity gradients as well.
To use the vegetable analogy you might add lots of manure to your Brassicas and Potatoes, but you wouldn't to your Onions or Garlic. Brasiccas need lime, but it makes Rapsberries go chlorotic. Beet-root and Asparagus might appreciate a bit of sea salt, but other crops certainly wouldn't, and you can only grow non-containerised Blueberries or Cranberries if you garden on a peat bog.
One effect of adding nutrients in the natural environment is that aquatic eutrophic situations are characterised by huge algal blooms, and often have a total lack of macrophytes (higher plants). You get a similar result in agricultural situations (in silage, cereal fields etc.), where you ideally want a single palatable grass species with a high growth response to added nitrogen (Wheat, Rye-grass etc). The problem comes that high nutrient levels also favour the growth of other weedy plants from naturally eutrophic conditions, that are either unpalatable or actively poisonous, like Docks, Nettles, Hemlock, Wild Oats etc. and you can only sustain yields with active management (herbicides etc.)
In the aquarium what we describe as "low light" plants are really plants with fairly low potential growth rates, things like mosses, ferns,
Anubias, Cryptocoryne, Tonina, Eriocaulon, Blyxa, Utricularia etc. They won't grow very quickly whatever you do to them.
Other plants can make use of higher levels of PAR, nutrients and CO2, and will grow extremely quickly when grown high tech. As you add light, nutrients and elevated levels of CO2, you are adding the potential for faster growth, but you are also adding the potential for things to go wrong (become unbalanced) extremely quickly.
I'm not interested in "maximal" or "optimal", I want sustainable stability.
Low nutrient levels give you stability, as an analogy you can think of this as the orchid, bromeliad, fern, succulent or alpine growing approach, it is aimed at growing plants with low potential growth rates in nutrient poor conditions.
On my allotment I add fertilisers and do a lot of weeding. In the garden I practice nutrient deprivation on lawns, borders and pond, the outcome of this is that I don't do any weeding and only occasionally have to mow the lawn.
Have a look at these threads for some more discussion and images of my pond, tank and garden: <
Problem with El Natural | UK Aquatic Plant Society>
cheers Darrel