Hi all,
Why is phosphate so dangerous in the environment at elevated level? What damage does it do?
It naturally occurs at low levels in most environments, and because it doesn't have a gaseous phase (and very low solubility), it remains in the place where it was deposited. This allowed large deposits to build up where you combined a dry climate with ocean up-welling zones and lots of colonial sea-birds. In the 19th and early 20th Century these deposits of "guano" were mined as a source of PO4, and most phosphate fertilisers are still obtained from rock deposits laid down in fossil seas.
Phosphates are really a fossil resource like fossil fuels, and <"
we are using them at a rate thousands of times quicker"> than they are naturally being replenished.
Nutrient limitation leads to biodiversity, and plants have evolved symbiotic mycorrhizal relationships to <"
scavenge scarce PO4"> from the soil. As soon as PO4 is freely available, conditions change and and a much more limited range of organisms benefit. These include grasses, both perennial pasture grasses and annual cereal crops, and many non-palatable weeds like Stinging Nettle, (
Urtica dioica) and Docks (
Rumex spp.). Once you've added the PO4 you can't put the genie back in the bottle and you are locked into a cycle of fertilisers and herbicides to remain productive. This is fine in most agricultural situations, but if that PO4 ends up in non-agricultural situations it leads to a change in plant community, which is why many of our rivers are now bordered by <"
huge stands of Stinging Nettles">.
Aquatic plant growth has been known to be phosphate limited for some time, and the addition of PO4 leads to "blooms" of phytoplankton, that reduce light to submerged macrophytes, leading to a situation where you get a cycle of huge algal blooms followed by algal death and de-oxygenation, followed by an algal bloom etc.
cheers Darrel
