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[APD] Periphyton in the Everglades and how low can PO4 go?

I just got back from a seminar on PO4 mitagation in the Everglades.
Many of you may not be aware but the Everglades is one of the few
Periphyton dominate ecosystems in the world.
In this case, periphyton is our friend and more PO4 causes plant ecological
shifts which cause a host of other problems.

Since the Army Core came in to do flood control back in the late
1940's/1950's things have changed. 
People and agriculture moved in. 
This brought high increases in PO4.

So how much PO4 is from the peat that in naturally accumulated at the lower
end of of the Lake Okeechobee over the last 10,000 or so years  when the
sugar cane growers drained this anaerobic peat layer and exposed it to O2
vs what PO4 in the form of fertilizers the sugar cane growers add for the
cane that ends up in the water downstream?

I asked and they just don't know but it's a good question. That has grant
money written all over it.  

Now you might initially assume that all the PO4 the cane growers apply goes
into the water and causes problems.
No, not really. 

They have contructed wetlands to mitagate the PO4 inflows, but the problem
is that the levels of PO4 need to be 10 ppb.That's parts per BILLION.
And it's total PO4, SRP and DOP(see below for these). 

The best Typha(cattails) can do is about removal down to around 20-30ppb,
Submersed aquatic do a little better 15-20ppb, but periphyton is the only
natural remedy that can remove PO4 down to under the 10ppb target.

Now, adding KH2PO4 etc vs fish food/peat etc(Organic sources) poses issues.
The form that is most readily available to plants, is called SRP, souble
reactive phosphorus, the dissolved organic portion is called DOP. Plants
quickly gobble up SRP. DOP is much more presistent. 

The SRP is easily removed down below the limits with catatils, submersed
aquatics, but the DOP is much harder to remove and presist in the system
much longer.

This organic fraction is bound/complexed etc and is very difficult to
remove by adding Al to form AlPO4 since there is so much tannins in the
water so you have to use huge amounts of AlCl to achieve any removal.

So back to DOP. DOP is readily used by periphyton and they can strip it out
of the water better than any plant in either SRP and especially low levels
of DOP which plants don't really mess with.Some periphyton species will
form Calcium phosphate and remove by precipitation.

So doing water changes removes this DOP(and DON as well) and selects for
the plants as far as nutrient availability. DOP and DON are like adding
algae food at high light which plants do not have access to. 

FYI, measuring PO4 at 10ppb, yes that's parts per BILLION, is extremely
difficult, and the error in testing at such small amounts becomes extremely
Even if you can measure that low, the error around 10ppb is around 8ppb,
they have delveloped in a couple of research labs where they are very
careful with each measurement etc gotten down to 2-3ppm which will be
useful for attempts to achieve the mandated 10ppb level of discharge into
the Everglades.

But contract laboraties cannot get this low(But I guess they will have to
work on better detection methods in the near future) and are what most
management disctricts must use for their testing and independent compliance.

So your test kits are not going to be able to tell you a damn thing as far
as limiting PO4 and limiting periphyton.
A couple of research labs in the state can do it, but it's doubtful any
Lamott kit is going to be able to give you any more than a rough guess. 
Many times people will test and find a presistent residual and assume that
their plants have enough of N or P when it's in this DON/DOP form and is
actually NOT available.

Changing large amounts of water removes this fraction and dosing back the
inorganic forms will add back the usable forms.
So plants need about 2-5x more PO4 than periphyton at least.
We don't know the PO4 limitation level in algae, testing methods simply do
NOT EXIST for such low levels of PO4.
Ulrich suggested less than 3ppb but it went beyond some of Europe's best
research labs as well. 

The South Florida water management disctrict that deals with the Everglades
is charged with supplying water at PO4 levels far below any other agency.
10ppb is rough, and consider how much water: 100 million acre feet a year. 

Generally the contructed wetlands flow into Typha/emergents=> Submersed
Aquatic Vegetation=> Periphyton.
Typha is PO4 limited at around 25-35ppb. It cannot remove any more than to
this amount.

Periphyton does not remove low levels of DOP if there is a peat layer so it
needs hard surface with out any peat to perform well.

Tom Barr

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