Discharging grey and black water through dormant reed beds in winter - what happens?

What happens to discharged water from a home treatment plant when it passes through a reed bed in winter time?  I have tried to search for an answer but am obviously asking Google the wrong questions.

If the plants are dormant during the winter,  is the bacteria in the root zone of the plants enough to filter the water? I know about the uptake of the plants during months where the plants are activity growing and when designed correctly the discharge for the reed beds is clean water.  Does this still apply in winter months and the discharged water is all clean even though there are no green plants in the system?

I am in a warm area where the ground does not freeze but all water plants that I am aware of go dormant here in central mississippi.  

Great question Greg ! I know that several years ago Paul had a thread discussion with a guest "expert" here at permies, but it might take some time to find that thread. In the meantime I googled this link this link which says , "Cold climate constructed wetlands use native wetland vegetation to help naturally treat wastewater. In the winter, when plants are dormant, their roots still provide surface area for beneficial attacted growth bacteria that aid in the treatment process."
So I assume that there is more going on in the wetland than just the plants water treatment capabilities ?

Thanks Miles.

Yep,  seem the root zone on reeds hold enough bacteria to treat the water even though the reeds themselves are doing little during their dormant season.

Most interesting, what when the soil freezes for several months? Will the bacteria produce enough energy in conjunction with the remaining water temperature to fend off -10°C for ±3 months?

I know in Maine anyway, wetlands never get fully frozen. They have enough bacteria action to "heat up" and keep things cooking. My leach field (though of standard design) and my septic tank never have dirt frozen on top of them due to this heat.

Way in the back country where I log, I avoid wetland like the plague because it never fully freezes. Bogs and open water will freeze, but not where the edges where the reeds and cat tails are. It is possible to put a road over it to get wood out, but it requires shoving snow on very cold nights over the spots, packing it down, and doing that many times. then you can drive over it, but left to nature...it seldom freezes.

I am not advocating logging here, I am just explaining how difficult it is to get the ground to freeze in these area.

It stinks. You can have a nice overgrown pond in summer with frogs but in winter you'd rather fill it up with mulch otherwise it stinks!