Origin of Paddy Fields and Functions for Environmental Remediation in the Urbanized Areas of Yangtze River Delta - Environmental Contamination: Health Risks and Ecological Restoration - page 407

of.12-15.mg/kg,.suggesting.that.under.the.existing.fertilization.regime.P.loss.
from.paddy.soils.will.not.be.a.serious.risk.to.water.bodies.for.at.least.the.next.
5-10.years..But.there.is.still.room.for.phosphorus.contents.to.be.increased.in.
paddy.soils.(Cao.et.al..2005,.Cao.and.Lin.2006,.Lin.et.al..2004).

Treatment of Domestic Wastewater

Paddy.ields.can.be.adopted.as.artiicial.wetlands.(Cao.and.Lin.2006,.Xu.
et.al..1998).and.be.used.for.domestic.sewage.treatment..Results.from.ield.
experiments.(Figures.18.11.and.18.12).(Li.et.al..2009a,b).show.that.both.total.
N. and. P. in.the.loodwater.of.paddy.ields.tend.to.reach.zero.before.har-
vest,.when.irrigated.with.both.gray.and.black.water..It.has.been.revealed.
that. rice. plants. and. paddy. soils. are. very. eficient. in. removing. most. of.
the. N. and. P. from. domestic. wastewater.. Another. similar. study. (Zhang.
et. al.. 2008). indicated. that. during. the. rice. growing. season,. the. removal.
of. NH 4 + -N,. NO 3 − -N,. and. total. P. from. wetland. paddy. ields. were. 10.7. to.
12.3,.6.8.to.9.2,.and.−1.2.to.2.0.kg/hm 2 ,.respectively..The.output.of.NH 4 + -N,.
NO 3 − -N,.and.total.P.from.drainage.was.signiicantly.lower.than.the.input.
during.the.irrigation.of.sewage.water,.which.was.attributed.to.the.uptake.
of.rice.as.well.as.the.absorption,.transformation,.ixation,.and.iltration.of.
paddy.soils..This.suggested.that.paddy.ields.can.be.used.as.a.resourceful.

30

25

CK
SW
GW
DW
BW

20

15

10

5

0

16-Jul 22-Jul 10-Aug 1-Sep

Sampling data (day-month)

1-Oct 1-Nov

FIGURE 18.11
Total.N.(TN).content.in.loodwater.during.the.rice.growing.season,.with.various.treatments.of.
wastewater.and.fertilizers.