Effects of Rainfall and Topography on Total Phosphorus

Effects of Rainfall and Topography on Total Phosphorus Loss

from Purple Soil under Simulated Rainfall Conditions

Presenter: Xue Y.North China Electric Power University

Email: [email protected]

2016 SWAT Conference

North China Electric Power University

01

Importance

MaterialsExperiment deviceExperiment design

Analysis and discussionEffects of precipitation on TP lossEffects of rainfall intensity on TP lossEffects of slope on TP loss

Conclusions

Contents

02 03

04

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PART 1 Importance

2016/8/2 2

North China Electric Power University2016/8/2 3

Heavier nonpoint source pollution

Importance


Sichuan Basin

Purple soil is an important kind of unirrigated tilth soil and accounting for 68% of the total cultivated area in Sichuan Basin of China.

Importance


Properties of purple soil

• Rich in phosphorus, potassium, and other nutrients

• Fast soil erosion and fast weathering

• Shallow soil

Easily eroded

Importance


PART 2 MaterialsExperiment deviceExperiment design

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Soil box for experiment

Experiment device

Photos were took in January 2015.

1.0×0.6×0.25 mTwo wheelsApertures at the bottom of boxExtended 0.1 mSet a groove with small holesA regulating screw


Norton nozzle-type rainfall simulatorExperiment device

Photos were took in January 2015.

The height of the nozzle was 2.5 m and the hydraulic pressure was 0.04 M Pa, which made the distribution and size of raindrops were similar to those in nature.

Rainfall intensity could be set in different levels by changing the frequency of nozzle flaps and was stable under a determined condition.


Pretreatment steps• Passed by a 7-mm sieve to avoid sticky soil jammed meshes• Air-dried to make water content rate of soil reduced to about 12%• Mixed thoroughly

• Physical and chemical properties

Soil layers (cm)

Unit weight (g cm-3)

Initial water content (%)

Organic matter (g kg-1)

TN(g kg-1)

TP(g kg-1)

0-20 1.30 12.16 8.75 0.76 0.68

Experiment design

North China Electric Power University 102016/8/2

Process procedure before experiment

Five 5-cm layersof soil werecompacted in a soilbox to prevent thesoil stratification,and the surface ofthe lower soil layerwas loosed beforethe upper soil layerwas filled in.

Experiment design


Designed scenarios for experiment

RainfallIntensity (B)

Slope (A)

30 mm h-1 60 mm h-1 90 mm h-1 120 mm h-1

5° A1B1 A1B2 A1B3 A1B410° A2B1 A2B2 A2B3 A2B415° A3B1 A3B2 A3B3 A3B420° A4B1 A4B2 A4B3 A4B425° A5B1 A5B2 A5B3 A5B4

Experiment design


Analysis and discussionEffects of precipitation on TP lossEffects of rainfall intensity on TP lossEffects of slope on TP loss

PART 3

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1) Effects of precipitation on TP loss--load



The total phosphorus loadwas increased with theincrease of precipitation ateach slope.

It could be explained thatthe more the precipitationfell, the larger amount ofrainfall runoff and theeroded soil increased, andthe more the TP was carried.


An initial runoff-yielding timecould be found before runoffgeneration in this figure.

The water content rate wasrelatively low at the beginning ofrainfall. With the increase ofprecipitation, the infiltrationeffect led the water content tosaturation, the runoff formed,and the TP began to loss bywashing and carrying of rainfallrunoff as well as soil erosion.

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2) Effects of precipitation on TP loss--concentration

It could be found that totalphosphorus concentrationpresented an increasetrend with the increase ofprecipitation.

During the process of rainfall, dissolvedphosphorus, including dissolved organicphosphorus, orthophosphate andpolyphosphate, was melted and carried by therainfall runoff. Meanwhile, the more wasadsorbed phosphorus was combined with soilsediments and then transported in the processof water and soil loss.


3) Effects of rainfall intensity on TP loss--concentration

The five slopes in certain rainfallintensity were integrated as valueby calculating mean in order toeliminate the influence of slope onTP concentration in this figure.

TP concentration rose when therainfall intensity increased.

The higher the rainfall intensitywas, the more the rainfall runoffand sediments transported, whichcarried more TP adsorbed onsediments and made theconcentration increased.


4) Effects of rainfall intensity on initial runoff-yielding time

The relationship betweenrainfall intensity and theinitial runoff-yielding timewas a negative correlation.

The difference of slopesreduced as the rainfallintensity increased whichstood for rainfall intensityplayed a more and moreimportant role in affectingthe initial runoff-yieldingtime with the rise of rainfallintensity.


5) Effects of slope on TP loss--load

When slope increased, TP load grewgenerally under various rainfallintensity conditions.

It could be explained that the effectof scouring was more powerful atsteeper slopes, a larger amount ofrainfall runoff would generated,more sediments would be carried,and more serious TP loss occurred.


6) Effects of slope on TP loss--concentration

Five rainfall intensities in certainslope were integrated an averagevalue, in order to ignore the influenceof rainfall intensity on TPconcentration.

TP concentration showed a positivecorrelation with the increase of slopebefore degree 15, and then TPconcentration decreased with theincrease of slope.


6) Effects of slope on TP loss--concentration

There was a critical slope of TP loss and the critical slope was degree 15 in this research.


7) Effects of slope on initial runoff-yielding time The relationship between

the slope and the initialrunoff-yielding time was anegative correlation.

For a steeper slope, contactangle between rainfall andground was smaller, lessunconsolidated soil wasgenerated by splash erosion,rainfall infiltration wasmore weakened, and theslope runoff was easier toform, hence the initialrunoff-yielding time wasshorter.


PART 4 Conclusions

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Precipitation Rainfall intensity Slope

TP load Positive Positive Positive

TP precipitation Positive Positive Positive before 15°

Initial runoff-yielding time Uncorrelated Negative Negative

The critical slope of TP loss appeared at degree 15 in this research.

Conclusions


Extension

• The research on critical slope of TP loss from purple soil • Influential mechanism of underlying surface on nonpoint

source pollutants under multiple continuous precipitation scenarios

Conclusions


THANKS!

Documents

Effects of Rainfall and Topography on Total Phosphorus