Case study on Impact of Land use Change on soil & water in mountainous catchment of Lao PDR.

Oroth Sengtaheuangoung (DALaM), Lao P.D.R.) Olivier Ribolzi, Anneke de Rouw, Christian Valentin (IRD, France)

Alain Pierret, Emmanuel Bourdon, Jean-Luc Maeght, Jean-Pierre Thiébaux (IRD, Lao P.D.R.) Olga Vigiak (DPI, Australia), Tran Duc Toan (SFRI, Vietnam), Andrew Nobel (IWMI, Lao P.D.R.)

Cultivation practices vs erosion rates

Experimental catchment in Northern Lao PDR

Pho

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. Les

trel

in, I

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Houay Pano

Discharge

Meteo

0.64 km2

Bed- and suspended-load measurement

Hydrological monitoring

Improved fallow and contour lines

Improved fallow

Conventional slash and burn

No tillage cultivation

Land use monitoring / mapping / GIS

Soil losses at the catchment scale (full cropping cycle including fallow years)

Altered 2-year fallow + 1-year crop

Maize 5.8 ton/ha/year

Shifting cultivation systems

Conservation systems

Upland rice

Traditional ∼ 8-year fallow + 1-year crop

Rotations with improved fallow Continuous direct sowing

0.7 ton/ha/year

0.9 ton/ha/year

0.1 ton/ha/year

Riparian zone management for

water quality

� During floods, there are often massive increases in turbidity and suspended solid loads, which are frequently interpreted as an indication of bacteriological contamination (e.g. Maniphousayand Souvanthong, 2004).

______________

Maniphousay, N. and Souvanthong, B. 2004. Application of a household water storage chronination project in the RWSS Programme of Lao PDR. In: S. Godfrey (edit.), People-centre approaches to water and environmental sanitation. 30th WEDC International Conference, Vientiane, Lao PDR, 656-659.

How could the riparian vegetation be helpful in that matter ?

Bamboo-dominated riparian vegetation

Riparian zone management for water quality

Slope gradient (%)

So

il er

osi

on

(M

g/h

a/ye

ar)

(modified from Dupin et al., 2002)

70%

8 Mg/ha/an Tillage erosion

Stream

Riparian zone management for water quality

______________Dupin B., et al. 2002. The Lao Journal of Agriculture and Forestry. 4:52-59.

Riparian zone management and tillage erosion

Land covers vsvsstream annual runoff

Impact of fallow regrowth on annual runoff and low flow?

Pho

to, O

livie

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One of the hydrological stations (S3) along the stream of the Houay Panocatchment during the dry season (February 2003).

Land cover vs stream flow regime

Rotational cycles of the shifting cultivation system

� Variations with time and space

Houay Pano catchment almost entirely covered by fallow (2001)

Houay Pano catchment after slashing and burning (2007)

Land cover vs stream flow regime

Annual runoff vs fallow area

5976 m3/ha 3251 m3/ha

2002 2003 2004 2005 2006

400

800

1200

1600

Rai

nfa

ll, s

trea

mfl

ow

(m

m)

0.2

0.3

0.4

0.5

An

nu

al r

un

off

rat

io (

-)S

trea

mflo

w/R

ainf

allRain

Stream/Rain

Stream

0

40

80

Fal

low

(%

)

______________

Ribolzi, O., Thiébaux, J.P., Sengtaheuanghoung, O., Bourdon, B., Chaplot, V., de Rouw, A., Huon, S., Mouche, E., Pierret, A., Briquet, J.P., Marchant, P. Robain, H., Soulileuth, B., Valentin, C. - Effect of fallow regrowth on stream water yield in a headwater catchment submitted to shifting cultivation, Northern Lao PDR. The Lao Journal of Agriculture and Forestry (ongoing).

Land cover vs stream flow regime

Groundwater recharge (steam water yield) vs Root extraction

Interception

Precipitation

Through fall

Sap flow

Transpiration

Evaporation

Root extractionStream flow

Groundwater recharge

Infiltration

Soil water Evaporation

Land cover vs stream flow regime

In summary� A change of land cover from lower to higher cover

results in decreasing of volume of surface water run off.

� Fallow regrowth decreases water run off and stabilize groundwater recharge and stream water yield by: � extracting water from the soil profile to transpire through their

leaves, � intercepting parts of the rainwater and then infiltrating it directly

into the soil� Using of appropriate agricultural techniques can reduce soil loss

and maintain soil fertility and also reduce pollution to stream water by sediment and bacteria

Land cover vs stream flow regime