Sains Malaysiana 46(9)(2017): 1513–1520 http://dx.doi.org/10.17576/jsm-2017-4609-21 The Evaluation of Spatial Variation of Water Quality in Sungai Setiu Basin, Terengganu (Penilaian Perubahan Reruang terhadap Kualiti Air di Lembangan Sungai Setiu, Terengganu) IZYAN MUNIRAH M. ZAIDEEN, SUHAIMI SURATMAN & NORHAYATI MOHD TAHIR* ABSTRACT This study investigates the spatial variation of water quality parameters in Sungai Setiu Basin at ten different locations from March 2010 to February 2011. The water quality was assessed using the Water Quality Index by Malaysian Department of Environment (DOE-WQI) and classified according to the Malaysia Interim National Water Quality Standard (INWQS). Six water quality parameters embedded in the DOE-WQI were dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), pH, ammoniacal nitrogen (AN) and total suspended solid (TSS). In addition, this study also examined the changes in water quality over the past 10 years by comparing the present water quality to the previous works. The overall mean WQI value obtained was 84.0 which indicate that the Sungai Setiu basin is in clean condition and all measured water quality parameters gave value within the permissible limits of the INWQS classification except for pH which fall in Class III. It can be concluded that water quality in Sungai Setiu does not varies greatly over a decade. Hence continuous monitoring is needed to improve the water quality and minimize water pollution. Keywords: DOE-WQI; INWQS classification; physical parameters; Sungai Setiu basin (Malaysia) ABSTRAK Kajian ini dijalankan untuk mengkaji variasi reruang bagi parameter kualiti air antara sepuluh lokasi yang berbeza di lembangan Sungai Setiu bermula pada Mac 2010 hingga Februari 2011. Kualiti air dinilai menggunakan Indeks Kualiti Air oleh Jabatan Alam Sekitar, Malaysia (IKA-JAS) dan dikelaskan mengikut Piawaian Interim Kualiti Air Kebangsaan, Malaysia (INWQS). Enam parameter yang digunakan dalam IKA-JAS telah dianalisis iaitu oksigen terlarut (DO), permintaan oksigen biokimia (BOD), permintaan oksigen kimia (COD), pH, ammoniakal nitrogen (AN) dan jumlah pepejal terampai (TSS). Di samping itu, kajian ini juga menentukan perubahan kualiti air sejak 10 tahun yang lalu melalui perbandingan dengan kajian yang terdahulu. Hasil kajian menunjukkan bahawa nilai purata IKA yang diperoleh adalah 84.0 dan ini menunjukkan lembangan Sungai Setiu adalah dalam keadaan bersih dan semua parameter kualiti air yang diukur telah memberikan bacaan dalam had yang dibenarkan mengikut pengklasifikasian INWQS kecuali nilai pH yang berada dalam kelas III. Dapat disimpulkan bahawa kualiti air di lembangan Sungai Setiu tidak menunjukkan perubahan yang ketara untuk tempoh sedekad. Walau bagaimanapun, pemantauan berterusan diperlukan untuk meningkatkan kualiti air dan mengurangkan pencemaran air. Kata kunci: IKA-JAS; lembangan Sungai Setiu (Malaysia); parameter fizikal; pengklasifikasian INWQS INTRODUCTION The quality status of a river can be examined using River is the most important freshwater resource for human Water Quality Index (WQI) in accordance to its specific and it is essential for many purposes such as agricultural, interest and for a variety of uses such as agriculture, recreational, irrigation and industrial activity. The quality aquaculture and domestic use (Naubi et al. 2016). WQI of river water is identified in terms of its physical, chemical was initially developed by Brown et al. (1970) which later and biological parameters thus the river quality status improved by the National Sanitation Foundation (NSF) in will act as an indicator of river condition and potential 1975. WQI is a mathematical instrument used to relate a for beneficial uses. Nowadays deterioration in river group of parameters to a common scale and combining water quality is a prominent issue throughout the world them into a single number (Lescesen et al. 2015) and so far and probably a serious threat to the nation. Pollution of this practice has successfully overcomes many problems river water originated from both organic and inorganic and allows the public and decision makers to receive water pollutants, as pollutants often enter into river systems quality information (Pesce & Wunderlin 2000). and are ultimately transported to the marine environment WQI intended to provide a simple and understandable (Suratman et al. 2016) thus may lead to hazardous risks to tool for managers and decision makers on the quality and humans, animals and also plants and also affect economic possible uses of given water body (Bordalo et al. 2006) development and social prosperity (Milovanovic 2007). and act as an indicator of water quality changes and as a 1514 tool for a clearer public view on river water quality subject. the pollution load categorization while INWQS provides the It has been considered as one criterion for river water classification according to beneficial uses. classifications, based on the use of standard parameters for The DOE-WQI is being practiced in Malaysia more water characterization (Bordalo et al. 2006; Fawaz et al. than 30 years since it was first introduced in 1978 and the 2013) and also act as a management tool in water quality calculation of WQI is an opinion-poll formula. DOE-WQI assessment and it integrates complex data to generate a outlined six parameters to define the status of surface score that describes the status of water quality to the public water quality and those parameters are dissolved oxygen as well as decision and policy makers (Bharti & Katyal (DO), pH, chemical oxygen demand (COD), biological 2011; Terrado et al. 2010). oxygen demand (BOD5), total suspended solids (TSS) and The degradation of water quality is a clear indicator ammoniacal nitrogen (AN). The WQI is derived by entering in the diminishing of the river basin environmental health. the six water quality parameters mean values into the In Malaysia, according to the environment quality 2013 calculation using the following formula: reported by the Department of Environment, 5.3% of a total 473 rivers were polluted with 36.6% slightly polluted. WQI = 0.22*SIDO+0.19*SIBOD+0.16*SICOD+ The sources of pollution normally come from domestic 0.15*SIAN + 0.16*SITSS+0.12*SIpH and industrial sewerage, effluents from livestock farms, manufacturing and agro-based industries, suspended solids The value of those parameters are transformed into from mining, housing and road construction, logging and sub-indices (SI) before applying to calculate the WQI and clearing of forest and heavy metals from factories. For Table 1 shows the calculation of the sub-indices of WQI instance, the lack of awareness, unconsciousness and the parameters. A river with a WQI value in the ranges of 0-59%, attitude of people could potentially become a serious threat 60-80% and 81-100% would be considered as polluted, to the river quality. slightly polluted and clean, respectively (DOE 2006). The Department of Environment (DOE) is the Malaysia INWQS is a standard which was orientated responsible body to monitor the condition of Malaysian on quality of water according to the beneficial uses which rivers and also to develop a guideline in water quality can be considered to be suitable for a specific use as long together with identification of pollution sources. The level as it is within the range specified for the designated classes of water quality in Malaysian rivers was calculated based and the definition of each class shown in Table 2. It focused on Malaysian Department of Environment Water Quality on water for domestic water supply, fisheries and aquatic Index (DOE-WQI) and classified according to the Malaysia propagation, livestock drinking, recreation and agricultural Interim National Water Quality Standard (INWQS). The use (DOE 2006). The standards also help in identifying DOE-WQI is the core for river water assessment related to water quality problems causes such as improper treated TABLE 1. Calculation of WQI (DOE 2006) Sub-indices DO (% saturation) × ≤ 8 SIDO = 0 × ≥ 92 SIDO = 100 8 < × < 92 SIDO = -0.395 + 0.03×2 - 0.0002×3 Sub-indices BOD (mg/L) × ≤ 5 SIBOD = 100.4 - 4.23x × > 5 SIBOD = 108-0.055x - 0.1x Sub-indices COD (mg/L) × ≤ 20 SICOD = -1.33× + 99.1 × > 20 SICOD = 103e-0.0157x - 0.04× Sub-indices ammonia, AN (mg/L N) × ≤ 0.3 SIAN = 100.5 - 105× 0.3 < × < 4 SIAN = 94e-0.573x - 5|×-2| × ≥ 4 SIAN = 0 Sub-indices TSS (mg/L) × ≤ 100 SITSS = 97.5e-0.00676x + 0.05× 100 < × < 1000 SITSS = 71e-0.0016x - 0.015× x ≥ 1000 SITSS = 0 Sub-indices pH x < 5.5 SIpH = 17.2 - 17.2x + 5.02x2 x ≤ x < 7 SIpH = -242 + 95.5x - 6.67x2 7 ≤ x < 8.75 SIpH = -181 + 82.4x - 6.05x2 x ≥ 8.75 SIpH = 536 - 77x + 2.76x2 1515 TABLE 2. Definition of Classes for INWQS (DOE 2006) Class Uses Class I Conservation of natural environment Water Supply 1 - practically no treatment necessary (except by disinfection or boiling only) Fishery 1 - very sensitive aquatic species Class IIA Water Supply II - conventional treatment required Fishery II - sensitive aquatic species Class IIB Recreational use with body contact Class III Water Supply III - extensive treatment required Fishery III - common, of economic value, and tolerant species; livestock drinking Class IV Irrigation Class V None of the above wastewater discharges, fertilizers runoff and chemicals from the basin 12 times with one month interval. There from agricultural areas. The classification ofINWQS divided were ten sampling locations selected from the upstream to into five classes namely Class I WQI( > 92.7), Class II