IJERD – International Journal of Environmental and Rural Development (2010) 1–1

Research article
erd

Effect of Land Use Change on Land Quality and Water
Resources in Phatthalung Watershed, Thailand
ANISARA PENSUK
Faculty of Technology and Community Development,
Thaksin University, Phatthalung, Thailand
Email: anisara@tsu.ac.th

RAJENDRA P. SHRESTHA
School of Environment, Resources and Development, Asian Institute of Technology,
Pathumthani, Thailand

ROBERTO S. CLEMENTE
School of Engineering and Technology, Asian Institute of Technology,
Pathumthani, Thailand
Received 1 January 2010

Accepted 5 March 2010

Abstract A watershed scale study was conducted to assess the effect of land use change
on land and water quality using selected indicators in the Phatthalung watershed, Thailand.
The changes in water quality in the study area were assessed by computing a Water
Quality Index (WQI) using some important water quality parameters, including pH,suspended solids and plant nutrients. Water quantity was also assessed through estimating
soil moisture storage. Land quality was assessed by developing a Land Quality Index(LQI) based on indices of soil resource, land degradation status and water resource. Thequality of land from two different areas, i.e. where land use has changed, and where nochange has occurred, was assessed using the selected indicators. The computed WQI
decreased during the study period. The highest WQI was 97.5 in 1997 and 2003 and thelowest was 80.0 in 2005 and 2006. Suspended solids (SS) was the major factor influencing
WQI. Water quantity, in terms of soil moisture storage, showed positive results as thenumber of months of water surplus increased from one month per year in 1976 to 4
months in 2006. This was due to the decline in paddy field area. For LQI the indices ofsoil resource and land degradation status were higher, and water resource lower, in areas
where land use did not change compared to those where land use did change.
Keywords: Land use change, land quality, water quality, Phatthalung Watershed

INTRODUCTION
Recently the pressure on land and water resources has increased due to the expansion of populationand economic development. The major pressure on land is attempts to increase agricultural
production from land, as intensification of agricultural activities increases food production for anincreasing population. However this causes impacts on the agricultural inputs, such as soil andwater resources.
Land use change has positive and negative effects on land and water, the key resources for
agricultural production. Land use and land use change generally reflect changes in agriculturalactivities, and give rise to issues in land and water quality (Dalal and Mayer, 1986; Bushchbacher
et al., 1988; Fu et al., 1990). Excessive and careless use of fertilizers and pesticides can havenegative effects on land and water resources through impacts on groundwater and runoff andassociated ecological damage (George et al., 2002). Eventually such changes can be dangerous forhuman health. Moreover runoff of excess nutrients, especially phosphorus, leads to eutrophication
with taste and odour impacts on public water supplies and excess algae growth leading to© ISERD

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deoxygenation of water and fish kills (FAO, 1996). Using heavy machines also plays an importantrole in the deterioration of land and water resources due to soil compaction, decreased soil porosity,
increased soil erosion and loss of top soil nutrients and organic matter. Therefore recognition of thecurrent situation with regard to land use and its consequences can be useful for planning future land
uses to protect land and water resources.
Phatthalung watershed, a major agricultural area of southern Thailand has experienced land
use change, particularly the replacement of paddy areas by rubber plantations. These changes ofland use are driven by of internal and external factors, economic return being one of the major
drivers. Therefore, an assessment of quality of land and water is needed to understand the current
situation, and to provide an early warning and guide for future land resource management anddevelopment. The establishment of land and water quality indicators can measure changes in theland resource due to external disturbances; especially land use for agricultural activities.
METHODOLOGY
Water quality assessment
The water quality of Phatthalung watershed over the period 1994 to 2006 was determined on thebasis of the WQI proposed by Rodriguez de Bascaron (Pesce and Wunderlin, 2000; Sanchez et al.,2007; Wu et al., 2008) as follows:
WQI sub = k∑ i C i Pi
∑ i Pi(1)where, WQIsub is the water quality index of surface water of Phatthalung watershed, k is asubjective constant with a maximum value of 1 for good quality water and 0.25 for highly polluted
water (in this study the k value was not considered and hence assigned as 1), Ci is the value
assigned to each parameter after normalization (Table 1), and Pi is the relative weight assigned toeach parameter. This weight was assigned as 1 in all cases in this study to account only forvariation due to measured parameters. The WQI used in this study included four parameters asfollows:
WQI =C pH + C SS + C P + C N(2)

4

where, CpH, Css, CP and CN are the values of pH, suspended solids (SS), and Phosphate andNitrate values after normalization, respectively.
Table 1 Values of normalization factor (Ci) for selected parameters of water quality
Parameter
pHSS
NitratePhosphorus

100
7
<20
<0.5<0.16

90
7-8
<40
<2.0
<1.680
7-8.5<60<4.0<3.270
7-9<80<6.0<6.4

Normalization factor (Ci)60504030
6.5-7
6-9.5
5-10
4-11
<100<120<160<240<8.0<10<15<20<9.6<16<32<64203-12<320<50<96102-13<400≤100<16001-14>400>100>160

All values, except pH, in mg/l (Pesce and Wunderlin, 2000; Sanchez et al., 2007)

Water quantity assessment
In this study, soil moisture storage was used as the indicator for water quantity assessment. Soil
moisture can be affected by various types of agricultural activities and changes in land use. Soil
moisture storage and its change were assessed in this study by using Eq. (3):ΔSM = P − ETc − q(3)© ISERD

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where, ∆SM is the change in soil moisture (cm), P is rainfall (cm), ETc is crop
evapotranspiration (cm), and q is runoff depth (cm).
Land quality assessment
The quality of land resource was assessed through the LQI. In this study the LQI was developed toaddress changes in land quality due to land use change. LQI consisted of major components of theland resource included soil properties, water resource, and land degradation status. The set ofindicators used is presented in Table 2.
Because of the different scale and unit of selected land quality indicators, it was necessary tostandardize the values in order to compare between land quality indicators for land use changes
compared to the no change area. Therefore the linear scaling method was used to normalize thedifferent scale values.
Table 2 Land quality indicators
Indicator suite

Component attributes

Measurement and method

Soil
Physical property
Nutrient status
Water resource
Land degradation status

Water holding capacitySoil texture (sand and clay content)
Cation exchange capacity (CEC)
Water sufficiency
Erosion status

Laboratory analysis
Laboratory analysis
Laboratory analysis
Effective rainfall
Erosion model

RESULTS AND DISSUSSION
Land use in Phatthalung watershed has been undergoing change, significantly so since 1976. The
major change has been the rise in rubber plantations, continuously increasing due to rapidly
increase in rubber prices in the local and global market during the period 1990 to 2006, The forest
area decreased continuously and significantly and the rubber plantation area rapidly increased(+37.3%), resulting in a decreasing of paddy field (-36.1%) and forest area (-12.4%). Fig. 1 shows

the areas where land use change occurred.
100

WQI90
80
7060501994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
YearFig. 1 Land use change area
during 1990-2006

Fig. 2 Computed WQI during 1994-2006

Water quality analysis
Based on the parameters presented in the above section, the computed WQI varied ranging from 80
to 97.5 in the study area (Fig. 2). The WQI declined in the period 1998 to 2003 and slightly
increased in 2003 due to lower amounts of suspended solid being loaded into water bodies. The© ISERD160

IJERD – International Journal of Environmental and Rural Development (2010) 1–1index decreased again from 2004 to 2006. The highest water quality was in 1997 and 2003 (WQI =97.5), and the lowest WQI (WQI = 80) was in the most recent years (2005 and 2006). The
computed WQI for all periods indicated that water quality is of “good” and “excellent” condition,
as described by Jonnalagadda and Mhere (2001). However, the WQI trend indicates declining
water quality during the study period, implying that the quality of water is degrading based on theparameters used in this study.
Water quantity analysis
The quantity of water can mean different things in different contexts. From an agricultural point ofview soil moisture is very important and was used in this study to refer to water quantity. Soil
moisture is important for agriculture as it is an input to plant production. It can be lost throughmany channels including runoff, deep percolation, evaporation and transpiration. Land use is amajor factor capable of controlling the level of moisture loss through its influence on surface runoff.
The soil moisture change of Phatthalung watershed during the study period was computed
using the concept of soil moisture balance. The number of months in which surplus water impliedhigh soil moisture increased during the study period. Surplus water was found only in November in1976 (Fig. 3) and 1990 (Fig. 4) but it had increased to four months (January, October, Novemberand December) in 2006 (Fig. 5).

Fig. 3 Soil moisture of Phatthalung watershedin 1976

Fig. 4 Soil moisture of Phatthalungwatershed in 1990

Note: The surplus water in January = 0.06 cm

Fig. 5 Soil moisture of Phatthalung watershedin 2006

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Fig. 6 The relationship of land use types
and the surface runoff

IJERD – International Journal of Environmental and Rural Development (2010) 1–1

The moisture of soil in 2006 increased because of the reduction in runoff. Fig. 6 shows therelationship between land use and annual runoff depth of the three main land uses. Note that theincreasing area of rubber plantation and decreasing area of paddy field resulted in the reduction inrunoff depth. Hence, the decline in paddy field area and the increase in area of rubber plantation
can cause positive effects on soil moisture storage
Land quality analysis
Land quality of the study area was assessed through three selected indicator sets, which included
soil, water resource and the status of land degradation. Four indicators were used to assess thequality of soil resource; those were sand and clay content, CEC and water holding capacity (WHC).
Water sufficiency and soil erosion rate were the selected indicators used to assess water resources
and land degradation status, respectively. Table 3 presents the detailed computed score for eachindicator under each land use scenario. The overall LQI, an aggregated index value for the wholestudy area, was 0.452 for the land use change area and 0.629 for no use change area. However,there was no statistically significant difference between the groups.
The no change land use areas have higher LQIs than the land use change areas. the overall soil
resource index of the two areas was significantly different, but the water resource and landdegradation indices were not significantly different. For the soil resource index, the score for the nochange area (0.785) was significantly higher (p<0.05) than for the area of land use change (0.708).
For individual indicators the area of no land use change has higher scores in most of theindicators, except for clay content. This was because the soil sample points that represented theland use change were mostly located in the areas that had been paddy field in the past, and whichusually contain higher clay content.
This is to note here that the computed land quality scores of no change area were higher thanthe area where land use change occurred in terms of the selected indicators.
Table 3 Land quality assessment
Land quality indicators
Soil resource
Physical property%Sand%Clay
Water holding capacity
Nutrient status
CEC
Overall soil resource index
Water resource
Water sufficiency
Land degradation status
Soil loss
Overall LQI

Land use change

No change

Significance

0.705
0.965
0.468

0.804
0.827
0.689

0.051
0.025*
0.277

0.675
0.708

0.819
0.785

0.361
0.045*

0.327

0.337

0.065

0.643
0.452

0.878
0.629

0.086
0.377

CONCLUSION
Land and water resources of the Phatthalung watershed are influenced by various factors, and land
use is the influencing factor investigated in this study. The computed WQI indicated that theoverall water quality of Phatthalung watershed has declined during the observed period (1994 to2006). Suspended solid has been increasing over the years. Overall the water quantity status ofPhatthalung watershed has increased during the study period because about half of paddy field area
was replaced by rubber plantation, with positive impacts on the water quantity in terms of increasedwater storage. The reason is that paddy field areas have the capability to generate higher surface
runoff compared to rubber plantation and forest areas, which can reduce the amount of the moisturein soil.
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The computed LQI of the no change in land use areas tended to have better land quality interms of the selected factors, however the changes were not significantly different between twoareas. In the individual indicator level, no land use change areas had relatively better scores formost of the land quality indicators compared to the area where land use changed, except for water
sufficiency and clay content. The rubber plantation area has higher water sufficiency as it canutilize higher amounts of rainfall with lower water loss through surface runoff. In other words,
rubber plantation areas which have not undergone land use change may exhibit higher LQIs in
terms of water sufficiency. Similarly, the long term rice cultivation areas can have higher clay
content compared to the areas where soil disturbance occurred due to land use change.
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