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 401

10

V= 0.0028x + 1.6068;
R 2 = 0.7948;

8

6

4

2

0

0 50 100

Cultivation years(a)

150 200

FIGURE 18.6
Natural.fertility.of.the.surface.layer.of.the.paddy.soil.chronosequence.

EcologicalFunctionsofRicePaddyFields
Sequestrate More Carbon

China. is. now. the. world's. largest. contributor. of. CO 2 . emissions,. having.
superseded. the. United. States. as. “Polluter. Number. 1”. due. to. the. rapid.
development.in.recent.years;.hence,.CO 2 .emissions.have.to.be.reduced.and.
carbon. sequestration. increased. for. the. planet's. sustainability.. Irrigated.
rice. cultivation. controls. the. oxidative/reductive. conditions. in. paddy.
soils,.where.a.bulk.of.the.paddy.soil.body.is.under.anaerobic.conditions..
However,.some.parts.of.soil.were.under.oxidative.conditions.when.either.
near. the. surface. of. a. very. thin. (2-3.mm). layer. or. within. the. rhizosphere.
close.to.the.roots.or.during.the.dry.period.created.as.a.result.of.exposure.
to. oxygen. (Cao. and. Lin. 2006,. Cao. and. Zhou. 2008,. De. Data. 1981,. Kögel-
Knabner.et.al..2010,.Li.1992,.Li.et.al..2007,.Xu.et.al..1998)..SOM.is.less.miner-
alized.and.more.stable.under.anaerobic.conditions;.therefore,.paddy.soils.
contain. much. more. SOM. than. upland. soils. (Cao. and. Lin. 2006,. Cao. and.
Zhou.2008,.De.Data.1981,.Kögel-Knabner.et.al..2010,.Li.1992,.Xu.et.al..1998),.
which. was. the. situation. revealed. by. the. last. two. National. Soil. Surveys.
conducted.40.and.25.years.ago..Organic.carbon.stock.has.been.found.to.be.
higher.in.paddy.soils.than.in.upland.soils.across.China,.with.the.average.
of.SOM.being.16.70.±.7.53.g/kg.and.10.89.±.8.36.g/kg,.respectively..Since.the.
1980s,.soil.organic.carbon.(SOC).of.paddy.soils.has.increased.signiicantly.
(151.±.24.Tg.C).and.still.has.a.large.potential.(estimated.at.112.1.±.23.1.Tg.C.
in. the. paddy. soils. of. subtropical. region. in. China). to. increase. (Liu. et. al..
2006).. When. the. SOC. content. in. the. surface. layer. of. paddy. soils. reaches.
the.ecological.balance.or.saturation.point.of.the.conditions.associated.with.
a.locality.(usually.about.21-23.g/kg.in.the.Yangtze.River.Delta),.dissolved.
organic.carbon.[DOC].will.increase.and.move.down.to.the.deeper.layers.
of. the. proile,.leading. to. a. steady. increase. in. SOC. storage.. The. results. of.