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 406

TABLE 18.3
The.Origin.of.Various.Contributors.to.N.and.P.Contents.in.the.
Water.of.Taihu.Lake.Region

Human
Excrement

Domestic
Waste

Animal
Manure

FisheryWaste
(IncludingSludge) Origins

P.(%) 26.7 23.8 57.6 11.9 5.7

N.(%) 30.7 / 27.8 10.2 7.5

the.ratio.of.N.to.P.content.(N/P).in.water.is.over.7.then.it.will.dramatically.
cause. algae. blooming.. When. the. P. available. in. soil. reaches. a. certain. con-
centration,. its. movement. from. agricultural. soil. to. water. rapidly. increases.
either. via. runoff. and/or. leaching;. therefore,.a. warning. value. was. adopted.
(known.as.the.breakpoint),.in.which.higher.availability.of.P.in.soil.is.often.
used.to.evaluate.the.threats.of.the.surrounding.quality.of.the.shallow.body.
of.water.(Cao.et.al..2005,.Cao.and.Lin.2006,.Edwards.and.Withers.1998)..In.the.
4.years.of.continual.ield.experiments,.which.were.executed.in.four.various.
types.of.paddy.soils.in.the.Taihu.Lake.region,.the.breakpoint.of.25-30.mg/kg.
Olsen-P. (Figure. 18.10). was. obtained. for. the. available. P. in. the. soil. of. this.
region..However,.when.P.is.above.this.value,.it.will.be.dramatically.removed.
from.the.soil.through.an.increase.in.runoff.and/or.leaching..At.present,.the.
available.P.in.the.soil.of.the.Taihu.Lake.area.was.observed.to.be.in.the.range.

35

30

25

20

15

10

5

0 0 5 10 15 20 25 30 35 40 45 50 55 60
01sen-P in soil (mg/kg)

FIGURE 18.10
The.breakpoint.of.soil.P.runoff.from.the.paddy.ields.in.the.Taihu.Lake.Region.