Dual Root Zone - Unique Application

[Jeremiah Robinson]

I'm working on a project to grow in "nutrient rich" (not by aquaponic standards) but otherwise nontoxic river water.  I want to remove phosphorous from the water and also grow sale-able plants.  

I am legally forbidden to add any fertilizer to the river water.  If my plants could remove some phosphorous, however, the DNR would be happy about that.  

What I'm curious about is whether I can use Vlad's Dual Root Zone technique to add "fertilizer" (this can be compost, organics, or whatever) to the plants without any measurable amount of that fertilizer getting into the water.  

I would make my fertilizer mix phosphorous limiting so the roots would still be searching for P from the river water.

One other issue is that this will have to be done in such a way that the upper portion of the "root zone" can be watered without a person standing there doing it, for labor reasons.  I've thought of using drip irrigation, but I'm worried that it would so easy to mess it up and drip nutrients into the water.  This could be mitigated somewhat by using slow release fertilizer and just dripping water onto the upper root zone.

I'm wondering if a small string used to wick up river water would also wick down nutrients?  The water-wicking would be one-directional with the upper root zone always being dryer than the river, but the concentration of nutrients would be higher in the upper root zone than in the river, so the nutrients would want to go down.  I wonder if there's any way to ensure that the water wicks up fast enough that the nutrients never make it into the river?