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Monthly physicochemical variation of tropical island groundwater of Pulau Bidong, south China sea
Groundwater for Sustainable Development 10 (2020) 100358
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Research paper
Monthly physicochemical variation of tropical island groundwater of Pulau Bidong, south China sea Tan Jia Xin a, Hasrizal Shaari a, b, *, Adiana Ghazali a, Nor Bakhiah Ibrahim a a b
Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu, Malaysia Institute of Oceanography and Environment, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu, Malaysia
A R T I C L E I N F O
A B S T R A C T
Keywords: Tropical South China sea Water quality Island groundwater
The groundwater of Pulau Bidong, Terengganu, Malaysia was investigated to monitor the quality of freshwater source. Groundwater samples were collected from five sampling stations from June 2016 to October 2016. Physical parameters such as temperature, specific conductivity, dissolved oxygen (DO), pH, salinity, and DO saturation were measured in-situ by using handheld device. Meanwhile, total suspended solid (TSS), total dis 3 solved solid (TDS), nitrate (NO3 ), nitrite (NO2 ), ammonium (NHþ 4 ) and phosphate (PO4 ) were also analysed. þ 3 The inorganic nutrients of NO3 , NO2 , NH4 , and PO4 were ranged from 0.000 to 4.310 mg/L, 0.000–0.190 mg/ L, 0.000–0.807 mg/L and 0.003–0.028 mg/L, respectively. The monthly trends of specific conductivity, DO, salinity, DO saturation, NH4, NO3 and NO2 demonstrated significant variation in June (the lowest rainfall) compared to other months. Correlation matrix revealed that temperature was associated with the specific con ductivity, and NHþ 4 strongly correlated with DO, NO3 and NO2 . Nevertheless, there is a strong negative corre lation between physicochemical parameters and monthly rainfall distribution. The physicochemical parameters were within the recommended safe limits suggested by the World Health Organization (WHO) and National Drinking Water Quality Standard (NDWQS) except for pH. Nevertheless, pH of water does not directly impact on the human health. Environmetrics analysis demonstrated that NO3 and PO34 significantly influenced the groundwater quality spatially. Furthermore, the temporal variation of groundwater quality was affected by pH and salinity. Overall, the groundwater sources from Pulau Bidong are considered safe to be used as drinking water. Notably, future studies are required for long-term monitoring to ensure the good quality of groundwaters from Pulau Bidong.
1. Introduction Water is a natural resource that plays a significant role in sustaining human life. Groundwater is a freshwater that is widely used in our daily activities including drinking, domestic usage, agricultural and other purposes. Groundwater is essential in coastal areas with rapid popula tion growth where it is important for boosting the economic activities. As such, there is an increased demand for freshwater to the extent of its limit (Trabelsi et al., 2007). The accessibility to safe and reliable source of water is crucial for sustainable development. The estimated groundwater use in Malaysia is approximately 3.4% of total water use in which the estimated groundwater usage for domestic, industry and agriculture are 60%, 35% and 5%, respectively (Ismail and Karim, 2010). Understanding of the groundwater quality is important to sustain the potential future consumption of groundwater especially in
islands such as Pulau Bidong where groundwater has no substitute in providing freshwater for users. The reliability and quality of water for various purposes are affected by physical and chemical quality of water. Hence, several studies have evaluated the characteristics of groundwater by understanding physicochemical parameters as well as hydro chemistry of water (Martos et al., 1999; Subba et al., 2002; Bhardwaj and Singh, 2010; Rahamanian et al., 2015). In tropical island, the groundwater chemistry has shown to be influenced by several factors such as climate change, sea level rise, groundwater recharge and discharge, weathering, over-use and seawater intrusion (Praveena et al., 2010; Kura et al., 2013). Therefore, the groundwater studies in Malaysia have focused on investigating groundwater resources, management and seawater intrusion. Nonethe less, the investigation on groundwater in the islands of Malaysia has been scant and not well documented. It should be noted that there has
* Corresponding author. Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu, Malaysia. E-mail address: [email protected] (H. Shaari). https://doi.org/10.1016/j.gsd.2020.100358 Received 2 September 2019; Received in revised form 11 January 2020; Accepted 25 February 2020 Available online 29 February 2020 2352-801X/© 2020 Elsevier B.V. All rights reserved.
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Fig. 1. The map showing sampling stations in Pantai Pasir Cina (1, 2 and 3) and Pantai Pasir Pengkalan (4 and 5) in Pulau Bidong.
been increasing usage of groundwater in Pulau Bidong by visitors as the main freshwater resource. Hence, the current study was carried out to provide preliminary information on the groundwater quality in Pulau Bidong. This study provides a comprehensive understanding on the quality and suitability of existing groundwater for various purposes with regard to the perspective of locations, relationship between rainfall and the quality of physical-chemical parameters of groundwater. The study also offers the baseline data to monitor the water quality to sustain future water consumption in this island. The information obtained from this study could provide a reference for future studies in Pulau Bidong as well as other Malaysian tropical islands.
2. Methodology 2.1. Study area Pulau Bidong is located in the East Coast of Peninsular Malaysia (Fig. 1). The total land area of the island is approximately 230 km2. This island is hilly with steep slope where the maximum elevation is approximately 267 m. The freshwater supply in this island is mainly from groundwater. The water sources in this island inclusive of small streams in the flat land at the south of the island, which is covered by forest except for the steepest points along the water’s edge which are bare rock (Howard, 1979). Pulau Bidong consists of a research centre belongs to Universiti Malaysia Terengganu (UMT). There are few wells present in both UMT Marine Research Station and Pantai Pasir Pen gkalan. Besides, there is a dam collecting water in UMT Marine Research 2
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nutrients (NO2 and NO3 ) amounts were determined via ultraviolet spectrophotometric screening method at different wavelengths. The DRP was determined by ascorbic method and NHþ 4 was determined by phenate method (APHA, 1999). The standard solutions were prepared to obtain standard curve and reagents were prepared for the determination 3 of nutrients (NO2 , NO3 , NHþ 4 and PO4 ) concentrations in water sam ples respectively. The TDS and TSS concentrations in the sample were calculated using gravimetric method after filtration process.
Table 1 The coordinate of each sampling station in Pulau Bidong. Site
Station
Longitude (� E)
Latitude (� N)
UMT Research Station
1 2 3 4 5
103 103 103 103 103
5 360 5 360 5 370 5 370 5 370
Pantai Pasir Pengkalan
2 30 30 30 30 0
49.19 34.0100 29.2600 28.4700 29.2600 00
48.6700 54.5300 15.9600 16.7100 15.9600
2.6. Data and statistical analysis
Station during wet season in which the dam is connected to the main reservoir that provides water to the well during wet season. Pulau Bidong is an island with tropical rainforest climate and Northeast monsoon season from October to March where during this season, the study area is exposed to heavy rain spells of about 2000 mm of rainfall annually (MetMalaysia, 2016). Thus, the main source of groundwater recharge in Pulau Bidong is rainfall. The other factor that may affect the groundwater in Pulau Bidong is saltwater intrusion which normally occur during drought season when the rainfall is minimum. The sam pling activities were carried out during June to October as represent the transitional period from Southwest Monsoon to Northeast Monsoon since Peninsular Malaysia is expected to receive heavy rainfall during September to October (Suhaila and Jemain, 2009).
The SPSS version 20 was used to perform statistical analysis with respect to the monthly variation of physicochemical parameters and rainfall. The physicochemical parameters were analysed by calculating Pearson’s correlation coefficient (r) value. The correlation matrix was constructed by calculating the coefficients of different pairs of param eters and correlation for significance was determined using r-value. The significance is considered at the level of 0.01 and 0.05 (2-tailed analysis). The chemometrics techniques were applied to determine the signif icant parameters that affecting the groundwater quality of Pulau Bidong. The aforementioned parameters could be the factors or pollutants that may impair the Pulau Bidong freshwater sources. On that account, principal component analysis (PCA) and discriminant analysis (DA) were performed by using Microsoft Excel extension, XLSTAT version 2014.5.03 for Excel 16.0. The principal component analysis (PCA) was utilized to compare the compositional patterns between the measured groundwater parameters and identify the factors that influence each factor loading.
2.2. Selection of sampling points The sampling points were selected based on the criteria of proper well constructed at each sampling points. Three sampling points were located in UMT Marine Research Station and two sampling points were located in Pantai Pasir Pengkalan (Fig. 1, Table 1). The wells in Pulau Bidong mainly supply freshwater for various activities and purposes. The well at station 1 is currently active for freshwater usage, the well at station 2 acts as an alternative freshwater supply and the well at station 3 is inactive, whereas the wells at station 4 and station 5 are mainly used by fisherman for bathing purposes. The major groundwater sources of all stations are mainly from precipitation.
3. Results 3.1. Physical parameters Fig. 2 illustrates the monthly variation of physicochemical parame ters for groundwater samples. The temperature of the groundwater in Pulau Bidong was generally constant and ranged from 26.8 � C to 28.7 � C with an average value of 27.6 � C (Fig. 2a). Specific conductivity value was ranged from 0.010 S/m to 0.452 S/m with an average value of 0.059 S/m (Fig. 2b) where the minimum value was recorded at station 3 in July and the highest value was recorded at station 2 in June. Dissolved oxygen value was ranged from 0.26 mg/L to 7.45 mg/L (Fig. 2c) with an average value of 2.05 mg/L, the DO value was highest in June and generally low from July to October. The pH value was ranged from 5.2 to 7.6, which was between slightly acidic and neutral nature with an average value of 6.2 (Fig. 2d). The salinity value was ranged from 0.04 to 2.41 ppt with an average value of 0.31 ppt (Fig. 2e). The salinity values were highest in June and were below zero ppt from July onwards. The DO saturation was ranged from 0.61 to 60.60% with an average saturation of 15.70% (Fig. 2f) where saturation was generally highest in June except the extreme low saturation at station 3 in June. The TDS values were ranged from 0.086 to 6.840 mg/L with an average of 0.833 � 1.447 mg/L (Fig. 2g). The concentrations of TDS were generally higher in station 3 for solids. The TSS concentration in groundwater of Pulau Bidong were low with a minimum value of 0.001 mg/L and 0.011 mg/L with average concentration of 0.002 � 0.002 (Fig. 2h).
2.3. Sample collection A total of 25 water samples were collected from five sampling sta tions over a period of 5 months from June 2016 to October 2016. Groundwater samples were collected in triplicates at each sampling stations. The water level was measured followed by pumping the surface water out from the well for 15 min before taking water samples from each sampling stations (Isa et al., 2012). This was done to ensure that the samples collected represent the groundwater instead of the stagnant water, which would affect the quality of the samples. The samples were later collected using Niskin water sampler and were kept in 1 L and 5 L sampling bottles. The samples were then preserved in icebox to mini mize the changes of nutrients content prior to the laboratory analysis. 2.4. Physical parameters The physical parameters such as temperature, specific conductivity, dissolved oxygen (DO), pH, salinity and dissolved oxygen saturation (DO%) were measured in-situ during sample collection using Multipa rameter YSI Professional Plus. The Multiparameter was calibrated ac cording to manufacturer’s recommendations to ensure the accuracy of the reading.
3.2. Nutrient concentration The concentrations of nutrients were generally similar except for phosphate that was low and constant. Generally, NH4 , NO3 and NO2 were relatively higher in June and low from July onwards. The con centration of NH4 ranged from as low as 0.00–0.81 mg/L with an average of 0.05 � 0.16 mg/L (Fig. 3a). NO3 was ranged from 0.00 to 4.31 mg/L with an average of 0.46 � 1.15 mg/L (Fig. 3b) whereas NO2 was ranged as low as from 0.00 to 0.19 mg/L with an average of 0.01 �
2.5. Laboratory analysis The concentrations of nitrite (NO2 ), nitrate (NO3 ), ammonium 3 (NHþ 4 ) and phosphate (PO4 ) amounts were measured according to the standard methods recommended by American Public Health Association (APHA, 1999) and Environmental Protection Agency (EPA, 1983). The 3
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Fig. 2. Monthly variation of (a) Temperature, (b) Specific conductivity, (c) Dissolved oxygen, (d) pH, (e) Salinity, (f) DO Saturation, (g) TDS, (h) TSS in the groundwater in Pulau Bidong.
0.04 mg/L (Fig. 3c). Phosphate concentration was ranged from 0.00 mg/ L to 0.03 mg/L with average concentration of 0.01 � 0.01 mg/L (Fig. 3d).
Data scattering demonstrated that there was no difference in distri bution pattern between spatial and temporal distribution. Fig. 4 illus trates that data were consistently distributed except for DO and TDS. 4
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Fig. 2. (continued).
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Fig. 3. Monthly variation of the (a) NH4 -, (b) NO3 , (c) NO2 and (d) PO34 in the groundwater in Pulau Bidong.
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Fig. 4. Data distribution of Pulau Bidong groundwater.
(1964) demonstrated that the temperature of groundwater exists in the tropics vary within narrow limits. The specific conductivity was found to be directly related to tem perature as the mobility of ions in solution increased as temperature increased (Barron and Ashton, 2013). Nonetheless, results reveal that rainfall affected more towards specific conductivity in Pulau Bidong (r ¼ 0.623). This is consistent with a previous study that demonstrated that there was a significant difference between specific conductivity and rainfall events at shallow water depth of groundwater (Datry et al., 2004). The specific conductivity in Pulau Bidong, however, with the minimum value of 0.01 S/m and maximum value of 0.45 S/m, was in accordance with standard limit of the drinking water stated in National Drinking Water Quality Standard (NDWQS) guidelines (Table 4). The DO value demonstrated significant positive correlation with salinity (r ¼ 0.950), TSS (r ¼ 0.914), NO2 (r ¼ 0.959) and NHþ 4 (r ¼ 0.946). Furthermore, DO values were varied between June and the following months as the values were negatively correlated to each other (r ¼ 0.758). This could be due to the massive inflow of precipitation (Datry et al., 2004). Evidence has shown that DO content of water is also influenced by the source and water temperature (World Health Orga nization, 2004). Moreover, the water from Pulau Bidong was slightly acidic in which pH values was ranged from 5.2 to 7.6. The rainfall could possibly affect pH where it is the main source of recharge of ground water, which imparts acidity to groundwater as pure rainfall is slightly acidic in nature (Karanath, 1987). Besides, the high pH values may be due to process of chlorination. There were also several readings below the recommended pH value of 6.58, however, the pH value does not have any adverse health effect except the alteration of the taste of water. It should be noted that according to World Health Organization (2004), most of the natural and groundwater have pH from 4 to 9.
Table 2 The records of monthly rainfall amount from June to October 2016 at meteo rological station in Kuala Terengganu. Latitude: 5� 200 N Longitude: 103� 080 E Elevation: 35.1 m Rainfall amount (mm) Year
June
July
August
September
October
2016
94.7
157.7
182.7
165.7
278.4
The median value of both parameters reveal that the collected data were distributed towards the minimum value and only few data were recor ded at the high value. 4. Discussion Table 2 demonstrates monthly rainfall recorded at the nearest meteorological station to Pulau Bidong (MetMalaysia, 2016). The data revealed that the rainfall had increased from June to October 2016 and the highest level was recorded in October 2016. Table 3 demonstrates the correlation coefficient between water quality variables and rainfall with correlation matrix. Strong positive correlation (r ¼ 0.982) was observed between temperature and specific conductivity. Temperature is useful in evaluating the drinking water quality as it influences the overall water quality such as chemical re actions rate in water body, decreasing the gases solubility and improving the tastes and colour of water (Olajire and Imeokparia, 2001). Never theless, there was no variation in temperature of the collected water, which could be due to location of Pulau Bidong in the tropics. Mink
Table 3 Correlation coefficients between average monthly variation of physicochemical parameters in Pulau Bidong and rainfall. T SC DO pH Salinity DO% TDS TSS NO3 NO2 NH4 PO34 Rainfall a b
T
SC
DO
pH
Salinity
DO%
TDS
TSS
NO3
NO2
1 .982b 0.548 0.312 0.374 0.383 0.123 0.527 0.357 0.421 0.373 0.061 0.645
1 0.449 0.277 0.237 0.305 0.023 0.436 0.223 0.284 0.234 0.083 0.623
1 0.366 .950a .934a 0.015 .914a 0.541 .959a .946a 0.663 0.758
1 0.355 0.614 0.321 0.433 0.019 0.316 0.336 0.052 0.44
1 .921a 0.206 .918a 0.705 .998b 1.000b 0.715 0.681
1 0.07 .965b 0.608 .914a .911a 0.467 0.856
1 0.284 0.827 0.203 0.215 0.152 0.218
1 0.765 .919a .911a 0.389 -.912a
1 0.703 0.709 0.211 0.629
1 .999b 0.717 0.688
Correlation is significant at the 0.05 level (2-tailed). Correlation is significant at the 0.01 level (2-tailed). 7
NH4
1
0.725 0.668
PO34
Rainfall
1 0.022
1
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Table 4 The comparison of analytical results of the concentration of parameters with international and national standards. Parameters
Min
Max
Mean
WHO Guideline value (2011)
NDWQS Guideline value (2004)
Specific Conductivity (S/m) DO (mg/L) pH Salinity (ppt) DO Saturation (%) Nitrate (mg/L)
0.009
0.452
0.059
–
1.000
0.26 5.2 0.04 0.61
7.45 7.6 2.41 60.60
2.05 6.2 0.31 15.70
6.58 6.5–8.5 – –
– 6.5–9.0 – –
0.000
4.310
50
10
Nitrite (mg/L)
0.000
0.190
3
–
TDS (mg/L)
0.086
6.840
1000
1000
TSS (mg/L)
0.001
0.011
0.455 � 1.153 0.011 � 0.038 0.833 � 1.447 0.002 � 0.002
–
25
Table 5 Factor loadings, eigenvalue and percentage of variance after varimax rotation for Pulau Bidong groundwater quality. Parameter
PC1
PC2
PC3
PC4
T SPC DO pH Sal NHþ 4 NO3 NO2 POþ 4 TDS TSS
0.6672 0.8712 0.2906 0.1704 0.8647 0.1540 0.0335 0.0928 0.1209 0.4641 0.7448
0.0941 0.2699 0.5123 0.3303 0.2526 0.9562 0.8377 0.9530 0.1167 0.0307 0.0223
0.0502 0.1276 0.5871 0.5481 0.1723 0.0773 0.0818 0.0583 0.0653 0.5616 0.2278
0.1646 0.0678 0.2466 0.4166 0.0903 0.0170 0.0398 0.0041 0.8849 0.1768 0.3227
Eigenvalue Variability (%) Cumulative %
4.0869 34.06 34.06
2.3585 19.65 53.71
1.4254 11.88 65.59
1.1481 9.57 75.16
salinity (r ¼ 0.681), NO3 (r ¼ 0.629), NO2 (r ¼ 0.688) and NHþ 4 (r ¼ 0.668), DO saturation (r ¼ 0.856) and TSS (r ¼ 0.912). This reveals that rainfall is one of the factors affecting the physicochemical parameters of groundwater in Pulau Bidong. The findings were in agreement with a previous study by Mayer et al. (2005) which demon strated rainfall, geology and topography are essential with regard to groundwater. Table 5 demonstrates that PCA for temporal and spatial assessment were similar. Four principal components (PCs) were acquired for Pulau Bidong groundwater column with Eigenvalues larger than 1 and had 75.16% of the total variance in the data-set. The first PC revealed 34.06% of the total variance and had strong positive factor loadings on conductivity and salinity; moderate factor loadings on temperature and TSS as well as weak factor loading on TDS. In Pulau Bidong groundwater, dissolved salts such as sodium and chlo ride ions affect the water conductivity due to their ability to conduct electrical flow. Additionally, the aforementioned salt ions are known to influence the concentration of TDS and TSS in the water column (Lane et al., 2007; McNeil and Cox, 2000). In general, temperature may affect the TDS and TSS contents as higher temperature will cause the dissolved salt to form solid salt (Hall and Burns, 2003). The second PC had 19.65% out of the total variance with strong factor loadings on NHþ 4 , NO3 and NO2 as well as moderate and weak factor loading on DO and pH respectively. Frequently, NHþ 4, NO3 and NO2 are derived from fertilized agricultural land, domestic waste, animal waste, urban drainage, septic tanks, soil erosion, de tergents and sewage disposal systems (Buck et al., 2003; Lichtenberg and Shapiro, 1997; Dick, 1983). The aforementioned compounds are well-known as organic and acidic compound, therefore, their existence in the water column would reduce water pH. The existence of organic compound in the water column are shown to reduce DO value due to degradation process by the microorganisms (Vrzel et al., 2016; Gormly and Spalding, 1979). The findings of the present study indicate that domestic waste, animal waste, septic tanks, soil erosion and the usage of detergents affected the groundwater quality of Pulau Bidong. Meanwhile, the third and fourth PC had 11.88% and 9.57% of the total variance correspondingly. Furthermore, DO, pH and TDS reveal moderate factor loadings on PC3 whereas PO34 had strong factor loading and pH and TSS had weak factor loadings on PC4. Similar to the first and second PC; PC3 and PC4 had similar significant variables as the existence of the organic materials would reduce the value of DO and pH as well as the concentration of TDS and TSS in Pulau Bidong groundwater column. The discriminant analysis (DA) was applied to the collected water quality data to define the spatial and temporal variation of Pulau Bidong groundwater. In DA, groundwater quality data were designated as the independent variables. DA for both cases was performed via standard, stepwise forward and stepwise backward model. Table 6 demonstrates
Salinity is defined by the amount of salt content in a water column that is closely affecting the value of conductivity, TDS and TSS (Brown, 2016). The salinity of the groundwater sources of Pulau Bidong was between 0.04 and 2.41 ppt. The results reveal high salinity in ground water of Pulau Bidong in the month of June. This could be due to seawater intrusion in June caused by increased activities such as active usage and bathing while at drought, causing the groundwater overdraft. Besides, groundwater contains naturally occurring salts from organic material that would increase the salinity (Mayer et al., 2005). Table 3 reveals that the salinity in Pulau Bidong was significantly related with DO saturation (r ¼ 0.921), TSS (r ¼ 0.918) NO2 (r ¼ 0.998), and NHþ 4 (r ¼ 1.000). The strong positive correlation between NHþ 4 and salinity was caused by prevalent nitrogen inorganic species form of ammonium in groundwater. According to Mayer et al. (2005), freshwater for drinking and all irrigation purpose have salinity level less than 0.5 ppt, and high concentration of TDS will affects the taste and odour of water. The TDS are the inorganic matters that present as solution in water, therefore considered as an accurate measure of salinity. The recommended cutoffs for TDS in drinking water by WHO and NDWQS should not exceed 1000 mg/L. The TDS found in groundwater sources of Pulau Bidong were below the recommended cutoffs value with a value ranged between 0.086 and 6.840 mg/L, making it suitable for drinking. Total dissolved solid is highly correlated to NO3 , where nitrate is one of the ions in total dissolved solids parameters that determine the nature of water quality (Lukubye and Andama, 2017). According to Aris et al. (2009), ground water in small islands is often exposed to heavy pumping as a result of high demand for freshwater consumption. The TSS value in Pulau Bidong of 0.001 mg/L and 0.011 mg/L were lower than the NDWQS permissible limit. Additionally, r value of TSS and rainfall was 0.912, suggesting that the low TSS could be indicative of the wash off of surface pollutants by rainfall characteristics such as rainfall intensity, duration and depth (Gong et al., 2016). Moreover, low TSS also indicates that the groundwater in Pulau Bidong is not turbid. Nitrite is rarely present in significant concentrations except in a reducing environment, as nitrate is the highly stable oxidation state. The NO2 and NHþ 4 were highly correlated (r ¼ 0.999) as the aforementioned nutrients were relatively low in groundwater. The concentrations of NO2 and NO3 in groundwater of Pulau Bidong are within the recom mended limit suggested by WHO and NDWQS. The high intake of NO2 and NO3 in drinking water were found to cause methaemoglobinaemia, which is caused by the reaction between nitrite and haemoglobin in the red blood cells to form methaemoglobin that binds oxygen tightly and inhibit the release of haemoglobin (World Health Organization, 2011). In general, rainfall had strong negative correlation with temperature (r ¼ 0.645), specific conductivity with r ¼ 0.623, DO (r ¼ 0.758), 8
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Table 6 Confusion matrix of temporal DA for Pulau Bidong groundwater. from \ to Standard Mode August July June October September Total Stepwise Forward Mode August July June October September Total Stepwise Backward Mode from \ to August July June October September Total
August
July
June
October
September
Total
% correct
5 0 0 0 0 5
0 5 0 0 0 5
0 0 5 0 0 5
0 0 0 5 0 5
0 0 0 0 5 5
5 5 5 5 5 25
100.00% 100.00% 100.00% 100.00% 100.00% 100.00%
1 1 0 0 0 2
3 2 0 0 0 5
0 0 5 0 0 5
1 2 0 5 0 8
0 0 0 0 5 5
5 5 5 5 5 25
20.00% 40.00% 100.00% 100.00% 100.00% 72.00%
August 5 0 0 0 0 5
July 0 5 0 0 0 5
June 0 0 5 0 0 5
October 0 0 0 5 0 5
September 0 0 0 0 5 5
Total 5 5 5 5 5 25
% correct 100.00% 100.00% 100.00% 100.00% 100.00% 100.00%
Table 7 Confusion matrix of spatial DA for Pulau Bidong groundwater. from \ to
Station 1
Standard Mode Station 1 5 Station 2 0 Station 3 0 Station 4 0 Station 5 0 Total 5 Stepwise Forward Mode Station 1 4 Station 2 1 Station 3 0 Station 4 0 Station 5 0 Total 5 Stepwise Backward Mode Station 1 3 Station 2 0 Station 3 0 Station 4 0 Station 5 0 Total 3
Station 2
Station 3
Station 4
Station 5
Total
% correct
0 5 0 0 0 5
0 0 5 1 0 6
0 0 0 4 1 5
0 0 0 0 4 4
5 5 5 5 5 25
100.00% 100.00% 100.00% 80.00% 80.00% 92.00%
1 3 0 1 0 5
0 0 2 0 0 2
0 1 0 2 1 4
0 0 3 2 4 9
5 5 5 5 5 25
80.00% 60.00% 40.00% 40.00% 80.00% 60.00%
2 5 0 0 0 7
0 0 3 1 1 5
0 0 0 4 0 4
0 0 2 0 4 6
5 5 5 5 5 25
60.00% 100.00% 60.00% 80.00% 80.00% 76.00%
the classification matrix of temporal DA for Pulau Bidong groundwater. The temporal variation demonstrated that the calculated discrimi nant function analysis (DFA) for standard and stepwise backward mode were similar. There was 100% accurate classification of data with five discriminant variables for standard mode and three discriminant vari ables for stepwise backward mode. The standard mode DA revealed that conductivity, DO, pH, TDS and salinity were the significant variables that play role in temporal variation. On the other hand, only pH, salinity and TDS discriminated the groundwater quality throughout temporal changes. The stepwise forward DA indicated 72% accurate classification data as three datasets and one dataset of August were misclassified as July and October respectively. One dataset and two datasets of July were misinterpreted as August and October correspondingly. Moreover, findings demonstrate that only pH and salinity had high variation in terms of their temporal distribution. An increased flow of freshwater volume during the sampling period into Pulau Bidong groundwater would affect the pH and salinity value of the water column as the flushed out water or water seepage was acidic due to the existence of soil trace.
Furthermore, evidence has shown that freshwater contains less salt ions as compared to the groundwater (Wong et al., 2007; Waeles et al., 2005). The spatial variation based on DA was carried out using standard, stepwise forward and stepwise backward models. Table 7 demonstrates the classification matrix of spatial DA for Pulau Bidong groundwater. The standard mode of DA reveals 92% of accurate classification with three important variables, which are temperature, NO3 and PO34 . On the other hand, the stepwise forward and stepwise backward mode reveal 60% and 76% of correct classification of data respectively. Through the stepwise forward mode, two significant variables namely temperature and NO3 were identified whereas through the stepwise backward mode, only one parameter, temperature had high variability in terms of spatial distribution. Therefore, Pulau Bidong groundwater variables had significant variation in term of spatial distribution for temperature, NO3 and PO34 , which might be derived from domestic waste, animal waste, septic tanks, soil erosion and the usage of de tergents (Buck et al., 2003; Lichtenberg and Shapiro, 1997).
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5. Conclusion
Dick, W.A., 1983. Organic carbon, nitrogen, and phosphorus concentrations and pH in soil profiles as affected by tillage intensity. Soil Sci. Soc. Am. J. 47, 102–107. Environmental Protection Agency (EPA), 1983. Methods for Chemical Analysis of Water and Wastes. United States Environmental Protection Agency, Washington, DC. Gong, Y., Liang, X., Li, X., Li, J., Fang, X., Song, R., 2016. Influence of rainfall characteristics on total suspended solids in urban runoff: a case study in Beijing, China. Water 8 (7), 278–301. Gormly, J.R., Spalding, R.F., 1979. Sources and concentrations of nitrate-nitrogen in ground water of the Central Platte Region, Nebraska. Groundwater 17 (3), 291–301. Hall, C.J., Burns, C.W., 2003. Responses of crustacean zooplankton to seasonal and tidal salinity changes in the coastal Lake Waihola, New Zealand. N. Z. J. Mar. Freshw. Res. 37 (1), 31–43. Howard, J., 1979. Disaster technology: survey on water supply and sanitation for Pulau Bidong. Disaster 3 (4), 461–467. Isa, N.M., Aris, A.Z., Sulaiman, W.N.A.W., 2012. Extent and severity of groundwater contamination based on hydrochemistry mechanism of sandy tropical coastal aquifer. Sci. Total Environ. 438, 414–425. Ismail, C.M., Karim, M.H.A.K., 2010. Groundwater Availability and Quality in Malaysia. Mineral and Geoscience Department Malaysia. Karanath, K.R., 1987. Groundwater Assessment. Development and Management. Tata Mc Graw Hill Co. LTD, New Delhi. Kura, N., Ramlo, M.F., Sulaiman, W.N.A., Ibrahim, S., Aris, A.Z., Mustapha, A., 2013. Evaluation of factors influencing the groundwater chemistry in a Small Tropical Island of Malaysia. Int. J. Environ. Res. Publ. Health 2013 (10), 1861–1881. Lane, R.R., Day Jr., J.W., Marx, B.D., Reyes, E., Hyfield, E., Day, J.N., 2007. The effects of riverine discharge on temperature, salinity, suspended sediment and chlorophyll a in a Mississippi delta estuary measured using a flow-through system. Estuar. Coast Shelf Sci. 74 (1–2), 145–154. Lichtenberg, E., Shapiro, L.K., 1997. Agriculture and nitrate concentrations in Maryland community water system wells. J. Environ. Qual. 26 (1), 145–153. Lukubye, B., Andama, M., 2017. Physicochemical quality of selected drinking water sources in Mbarara municipality, Uganda. J. Water Resour. Protect. 9, 702–722. Malaysian Meteorological Department (MetMalaysia), 2016. Records of Monthly Rainfall Amount in Kuala Terengganu. Martos, F.S., Bosch, A.P., Calaforra, J.M., 1999. Hydrogeochemical processes in an arid region of Europe (Almeria, SE Spain). Appl. Geochem. 14 (6), 735–745. Mayer, X., Ruprecht, J., Bari, M., 2005. Stream Salinity Status and Trends in South-West Western Australia. Department of Envitronment. Salinity and land use impact series. Report No. SLUI 38. McNeil, V.H., Cox, M.E., 2000. Relationship between conductivity and analysed composition in a large set of natural surface-water samples, Queensland, Australia. Environ. Geol. 39 (12), 1325–1333. Ministry of Health (MOH), 2004. National Drinking Water Quality Standards for Malaysia (NDWQS). Engineering of Services Division, Ministry of Health Malaysia, Kuala Lumpur. Mink, J.F., 1964. Groundwater temperature in a tropical island environment. J. Geophys. Res. 69 (24), 5225–5230. Olajire, A.A., Imeokparia, F.E., 2001. Water quality assessment of osun river: studies on inorganic nutrients. Environ. Monit. Assess. 69 (1), 17–28. Praveena, S.M., Aris, A.Z., Abdullah, M.H., Bidin, K., 2010. Groundwater studies in tropical isands: Malaysian perspective. Episodes 33 (3), 200–204. Rahamanian, N., Hajar, S., Homayoonfard, M., Ali, N.J., Rehan, M., Sadef, Y., Nizami, A. S., 2015. Analysis of physiochemical parameters to evaluate the drinking water quality in the State of Perak, Malaysia. J. Chem. 2015, 1–10. Subba, R.N., Prakasa, R.J., Devadas, D.J., Srinivasa, R.K.V., 2002. Hydrogeochemistry and groundwater quality in a developing urban environment of a semi-arid region, Guntur, Andhra Pradesh. J. Geol. Soc. India 59 (2), 159–166. Suhaila, J., Jemain, A.A., 2009. Investigating the impacts of adjoining wet days on the distribution of daily rainfall amounts in Peninsular Malaysia. J. Hydrol. 368, 17–25. Trabelsi, R., Zairi, M., Dhia, H.B., 2007. Groundwater salinization of the Sfax superficial aquifer, Tunisia. Hydrogeol. J. 2007 (15), 1341–1355. Vrzel, J., Vukovi�c-Ga�ci�c, B., Kolarevi�c, S., Ga�ci�c, Z., Kra�cun, K., Kosti�c, J., Aborgiba, M., Farnleitner, A., Reischer, G., Linke, R., Paunovi�c, M., Ogrinc, N., 2016. Determination of the sources of nitrate and the microbiological sources of pollution in the Sava River Basin. Sci. Total Environ. 573, 1460–1471. Waeles, M., Riso, R.D., Corre, P.L., 2005. Seasonal variations of dissolved and particulate copper species in estuarine waters. Estuar. Coast Shelf Sci. 62, 313–323. Wong, G.T.F., Ku, T.-L., Mulholland, M., Tseng, C.-M., Wang, D.-P., 2007. The southeast asia time-series study (SEATS) and the biogeochemistry of the south China sea – an overview. Deep-Sea Res. II 54, 1434–1447. World Health Organization, 2004. Guidelines for Drinking Water Quality, third ed., vol. 1. WHO Press, Geneva, Switzerland. World Health Organization, 2011. Guidelines for Drinking Water Quality, fourth ed. WHO library, Geneva, Switzerland.
There were significant differences in physical characteristics and nutrients in June where the rainfall was lower than other months, and were similar from July to October, which were relatively higher, sug gesting that the aforementioned parameters were affected by the pre cipitation. There were low nutrients concentrations in Pulau Bidong due to non-point sources, and were safe to be consumed by the visitors. The physicochemical quality of groundwater in Pulau Bidong was superior except that pH was slightly lower than the local and international rec ommended drinking water guidelines. Based on chemometrics analysis, pH and salinity were significantly affected the changes of Pulau Bidong groundwater temporally due to the intrusion of high volume of fresh water during heavy rainfall. The spatial variation of the present study 3 reveals that NO3 , NO2 , NHþ 4 and PO4 significantly affected the changes of Pulau Bidong groundwater quality. Therefore, the proper manage ment of septic tanks is essential to improve the elimination of possible elevated concentration especially nitrate. Notably, the selected param eters are strongly interrelated and could be altered by human interfer ence. Besides, the seasonal variation also directly reflects the water quality of Pulau Bidong. This study provided the baseline data for future research. Nevertheless, long-term monitoring is essential for under standing the groundwater behavior in Pulau Bidong as this would facilitate proper management for preventing the effects of human ac tivities in order to ensure sustainable supply of groundwater to the users. Acknowledgement This research was supported by the Fundamental Research Grant Scheme (FRGS/1/2015/WAB09/UMT/02/1) of Ministry of Education Malaysia. This project was also funded by the Higher Institute Centre of Excellence (HICoE) Grant (Vote No. 66928) awarded to Institute of Oceanography and Environment (INOS). The authors would like to thank Malaysian Meteorological Department (MetMalaysia) for providing the rainfall data. The appreciation is also extended to the laboratory staff of Oceanography Laboratory, Faculty of Science and Marine Environment, Universiti Malaysia Terengganu. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.gsd.2020.100358. References American Public Health Association (APHA), 1999. American water works association (AWWA), & water environment federation (WEF). In: Standard Methods for the Examination of Water and Wastewater, twentieth ed. American Public Health Association, Washington, DC. Aris, A.Z., Abdullah, M.H., Kim, K.W., Praveena, S.M., 2009. Hydrochemical changes in a small tropical island’s aquifer: manukan Island, Sabah, Malaysia. Environ. Geol. 56 (8), 1721–1732. Barron, J.J., Ashton, C., 2013. The effect of temperature on conductivity measurement. Pract. Guide Accurate Conduct. Meas. 3, 1–5. Bhardwaj, V., Singh, D.S., 2010. Surface and groundwater quality characterization of deoria district, ganga plain, India. Environ. Earth Sci. 63 (2), 383–395. Brown, W.S., 2016. Physical properties of seawater. In: Dhanak, M.R., Xiros, N.I. (Eds.), Springer Handbook of Ocean Engineering. Springer Handbooks, Springer, Cham, pp. 101–110. Buck, O., Niyogi, D.K., Townsend, C.R., 2003. Scale-dependence of land use effects on water quality of streams in agricultural catchments. Environ. Pollut. 130, 287–299. Datry, T., Malard, F., Gibert, J., 2004. Dynamics of solutes and dissolved oxygen in shallow urban groundwater below a stormwater infiltration basin. Sci. Total Environ. 329, 215–229.
10
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Research paper
Monthly physicochemical variation of tropical island groundwater of Pulau Bidong, south China sea Tan Jia Xin a, Hasrizal Shaari a, b, *, Adiana Ghazali a, Nor Bakhiah Ibrahim a a b
Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu, Malaysia Institute of Oceanography and Environment, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu, Malaysia
A R T I C L E I N F O
A B S T R A C T
Keywords: Tropical South China sea Water quality Island groundwater
The groundwater of Pulau Bidong, Terengganu, Malaysia was investigated to monitor the quality of freshwater source. Groundwater samples were collected from five sampling stations from June 2016 to October 2016. Physical parameters such as temperature, specific conductivity, dissolved oxygen (DO), pH, salinity, and DO saturation were measured in-situ by using handheld device. Meanwhile, total suspended solid (TSS), total dis 3 solved solid (TDS), nitrate (NO3 ), nitrite (NO2 ), ammonium (NHþ 4 ) and phosphate (PO4 ) were also analysed. þ 3 The inorganic nutrients of NO3 , NO2 , NH4 , and PO4 were ranged from 0.000 to 4.310 mg/L, 0.000–0.190 mg/ L, 0.000–0.807 mg/L and 0.003–0.028 mg/L, respectively. The monthly trends of specific conductivity, DO, salinity, DO saturation, NH4, NO3 and NO2 demonstrated significant variation in June (the lowest rainfall) compared to other months. Correlation matrix revealed that temperature was associated with the specific con ductivity, and NHþ 4 strongly correlated with DO, NO3 and NO2 . Nevertheless, there is a strong negative corre lation between physicochemical parameters and monthly rainfall distribution. The physicochemical parameters were within the recommended safe limits suggested by the World Health Organization (WHO) and National Drinking Water Quality Standard (NDWQS) except for pH. Nevertheless, pH of water does not directly impact on the human health. Environmetrics analysis demonstrated that NO3 and PO34 significantly influenced the groundwater quality spatially. Furthermore, the temporal variation of groundwater quality was affected by pH and salinity. Overall, the groundwater sources from Pulau Bidong are considered safe to be used as drinking water. Notably, future studies are required for long-term monitoring to ensure the good quality of groundwaters from Pulau Bidong.
1. Introduction Water is a natural resource that plays a significant role in sustaining human life. Groundwater is a freshwater that is widely used in our daily activities including drinking, domestic usage, agricultural and other purposes. Groundwater is essential in coastal areas with rapid popula tion growth where it is important for boosting the economic activities. As such, there is an increased demand for freshwater to the extent of its limit (Trabelsi et al., 2007). The accessibility to safe and reliable source of water is crucial for sustainable development. The estimated groundwater use in Malaysia is approximately 3.4% of total water use in which the estimated groundwater usage for domestic, industry and agriculture are 60%, 35% and 5%, respectively (Ismail and Karim, 2010). Understanding of the groundwater quality is important to sustain the potential future consumption of groundwater especially in
islands such as Pulau Bidong where groundwater has no substitute in providing freshwater for users. The reliability and quality of water for various purposes are affected by physical and chemical quality of water. Hence, several studies have evaluated the characteristics of groundwater by understanding physicochemical parameters as well as hydro chemistry of water (Martos et al., 1999; Subba et al., 2002; Bhardwaj and Singh, 2010; Rahamanian et al., 2015). In tropical island, the groundwater chemistry has shown to be influenced by several factors such as climate change, sea level rise, groundwater recharge and discharge, weathering, over-use and seawater intrusion (Praveena et al., 2010; Kura et al., 2013). Therefore, the groundwater studies in Malaysia have focused on investigating groundwater resources, management and seawater intrusion. Nonethe less, the investigation on groundwater in the islands of Malaysia has been scant and not well documented. It should be noted that there has
* Corresponding author. Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Terengganu, Malaysia. E-mail address: [email protected] (H. Shaari). https://doi.org/10.1016/j.gsd.2020.100358 Received 2 September 2019; Received in revised form 11 January 2020; Accepted 25 February 2020 Available online 29 February 2020 2352-801X/© 2020 Elsevier B.V. All rights reserved.
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Fig. 1. The map showing sampling stations in Pantai Pasir Cina (1, 2 and 3) and Pantai Pasir Pengkalan (4 and 5) in Pulau Bidong.
been increasing usage of groundwater in Pulau Bidong by visitors as the main freshwater resource. Hence, the current study was carried out to provide preliminary information on the groundwater quality in Pulau Bidong. This study provides a comprehensive understanding on the quality and suitability of existing groundwater for various purposes with regard to the perspective of locations, relationship between rainfall and the quality of physical-chemical parameters of groundwater. The study also offers the baseline data to monitor the water quality to sustain future water consumption in this island. The information obtained from this study could provide a reference for future studies in Pulau Bidong as well as other Malaysian tropical islands.
2. Methodology 2.1. Study area Pulau Bidong is located in the East Coast of Peninsular Malaysia (Fig. 1). The total land area of the island is approximately 230 km2. This island is hilly with steep slope where the maximum elevation is approximately 267 m. The freshwater supply in this island is mainly from groundwater. The water sources in this island inclusive of small streams in the flat land at the south of the island, which is covered by forest except for the steepest points along the water’s edge which are bare rock (Howard, 1979). Pulau Bidong consists of a research centre belongs to Universiti Malaysia Terengganu (UMT). There are few wells present in both UMT Marine Research Station and Pantai Pasir Pen gkalan. Besides, there is a dam collecting water in UMT Marine Research 2
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nutrients (NO2 and NO3 ) amounts were determined via ultraviolet spectrophotometric screening method at different wavelengths. The DRP was determined by ascorbic method and NHþ 4 was determined by phenate method (APHA, 1999). The standard solutions were prepared to obtain standard curve and reagents were prepared for the determination 3 of nutrients (NO2 , NO3 , NHþ 4 and PO4 ) concentrations in water sam ples respectively. The TDS and TSS concentrations in the sample were calculated using gravimetric method after filtration process.
Table 1 The coordinate of each sampling station in Pulau Bidong. Site
Station
Longitude (� E)
Latitude (� N)
UMT Research Station
1 2 3 4 5
103 103 103 103 103
5 360 5 360 5 370 5 370 5 370
Pantai Pasir Pengkalan
2 30 30 30 30 0
49.19 34.0100 29.2600 28.4700 29.2600 00
48.6700 54.5300 15.9600 16.7100 15.9600
2.6. Data and statistical analysis
Station during wet season in which the dam is connected to the main reservoir that provides water to the well during wet season. Pulau Bidong is an island with tropical rainforest climate and Northeast monsoon season from October to March where during this season, the study area is exposed to heavy rain spells of about 2000 mm of rainfall annually (MetMalaysia, 2016). Thus, the main source of groundwater recharge in Pulau Bidong is rainfall. The other factor that may affect the groundwater in Pulau Bidong is saltwater intrusion which normally occur during drought season when the rainfall is minimum. The sam pling activities were carried out during June to October as represent the transitional period from Southwest Monsoon to Northeast Monsoon since Peninsular Malaysia is expected to receive heavy rainfall during September to October (Suhaila and Jemain, 2009).
The SPSS version 20 was used to perform statistical analysis with respect to the monthly variation of physicochemical parameters and rainfall. The physicochemical parameters were analysed by calculating Pearson’s correlation coefficient (r) value. The correlation matrix was constructed by calculating the coefficients of different pairs of param eters and correlation for significance was determined using r-value. The significance is considered at the level of 0.01 and 0.05 (2-tailed analysis). The chemometrics techniques were applied to determine the signif icant parameters that affecting the groundwater quality of Pulau Bidong. The aforementioned parameters could be the factors or pollutants that may impair the Pulau Bidong freshwater sources. On that account, principal component analysis (PCA) and discriminant analysis (DA) were performed by using Microsoft Excel extension, XLSTAT version 2014.5.03 for Excel 16.0. The principal component analysis (PCA) was utilized to compare the compositional patterns between the measured groundwater parameters and identify the factors that influence each factor loading.
2.2. Selection of sampling points The sampling points were selected based on the criteria of proper well constructed at each sampling points. Three sampling points were located in UMT Marine Research Station and two sampling points were located in Pantai Pasir Pengkalan (Fig. 1, Table 1). The wells in Pulau Bidong mainly supply freshwater for various activities and purposes. The well at station 1 is currently active for freshwater usage, the well at station 2 acts as an alternative freshwater supply and the well at station 3 is inactive, whereas the wells at station 4 and station 5 are mainly used by fisherman for bathing purposes. The major groundwater sources of all stations are mainly from precipitation.
3. Results 3.1. Physical parameters Fig. 2 illustrates the monthly variation of physicochemical parame ters for groundwater samples. The temperature of the groundwater in Pulau Bidong was generally constant and ranged from 26.8 � C to 28.7 � C with an average value of 27.6 � C (Fig. 2a). Specific conductivity value was ranged from 0.010 S/m to 0.452 S/m with an average value of 0.059 S/m (Fig. 2b) where the minimum value was recorded at station 3 in July and the highest value was recorded at station 2 in June. Dissolved oxygen value was ranged from 0.26 mg/L to 7.45 mg/L (Fig. 2c) with an average value of 2.05 mg/L, the DO value was highest in June and generally low from July to October. The pH value was ranged from 5.2 to 7.6, which was between slightly acidic and neutral nature with an average value of 6.2 (Fig. 2d). The salinity value was ranged from 0.04 to 2.41 ppt with an average value of 0.31 ppt (Fig. 2e). The salinity values were highest in June and were below zero ppt from July onwards. The DO saturation was ranged from 0.61 to 60.60% with an average saturation of 15.70% (Fig. 2f) where saturation was generally highest in June except the extreme low saturation at station 3 in June. The TDS values were ranged from 0.086 to 6.840 mg/L with an average of 0.833 � 1.447 mg/L (Fig. 2g). The concentrations of TDS were generally higher in station 3 for solids. The TSS concentration in groundwater of Pulau Bidong were low with a minimum value of 0.001 mg/L and 0.011 mg/L with average concentration of 0.002 � 0.002 (Fig. 2h).
2.3. Sample collection A total of 25 water samples were collected from five sampling sta tions over a period of 5 months from June 2016 to October 2016. Groundwater samples were collected in triplicates at each sampling stations. The water level was measured followed by pumping the surface water out from the well for 15 min before taking water samples from each sampling stations (Isa et al., 2012). This was done to ensure that the samples collected represent the groundwater instead of the stagnant water, which would affect the quality of the samples. The samples were later collected using Niskin water sampler and were kept in 1 L and 5 L sampling bottles. The samples were then preserved in icebox to mini mize the changes of nutrients content prior to the laboratory analysis. 2.4. Physical parameters The physical parameters such as temperature, specific conductivity, dissolved oxygen (DO), pH, salinity and dissolved oxygen saturation (DO%) were measured in-situ during sample collection using Multipa rameter YSI Professional Plus. The Multiparameter was calibrated ac cording to manufacturer’s recommendations to ensure the accuracy of the reading.
3.2. Nutrient concentration The concentrations of nutrients were generally similar except for phosphate that was low and constant. Generally, NH4 , NO3 and NO2 were relatively higher in June and low from July onwards. The con centration of NH4 ranged from as low as 0.00–0.81 mg/L with an average of 0.05 � 0.16 mg/L (Fig. 3a). NO3 was ranged from 0.00 to 4.31 mg/L with an average of 0.46 � 1.15 mg/L (Fig. 3b) whereas NO2 was ranged as low as from 0.00 to 0.19 mg/L with an average of 0.01 �
2.5. Laboratory analysis The concentrations of nitrite (NO2 ), nitrate (NO3 ), ammonium 3 (NHþ 4 ) and phosphate (PO4 ) amounts were measured according to the standard methods recommended by American Public Health Association (APHA, 1999) and Environmental Protection Agency (EPA, 1983). The 3
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Fig. 2. Monthly variation of (a) Temperature, (b) Specific conductivity, (c) Dissolved oxygen, (d) pH, (e) Salinity, (f) DO Saturation, (g) TDS, (h) TSS in the groundwater in Pulau Bidong.
0.04 mg/L (Fig. 3c). Phosphate concentration was ranged from 0.00 mg/ L to 0.03 mg/L with average concentration of 0.01 � 0.01 mg/L (Fig. 3d).
Data scattering demonstrated that there was no difference in distri bution pattern between spatial and temporal distribution. Fig. 4 illus trates that data were consistently distributed except for DO and TDS. 4
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Fig. 2. (continued).
5
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Fig. 3. Monthly variation of the (a) NH4 -, (b) NO3 , (c) NO2 and (d) PO34 in the groundwater in Pulau Bidong.
6
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Fig. 4. Data distribution of Pulau Bidong groundwater.
(1964) demonstrated that the temperature of groundwater exists in the tropics vary within narrow limits. The specific conductivity was found to be directly related to tem perature as the mobility of ions in solution increased as temperature increased (Barron and Ashton, 2013). Nonetheless, results reveal that rainfall affected more towards specific conductivity in Pulau Bidong (r ¼ 0.623). This is consistent with a previous study that demonstrated that there was a significant difference between specific conductivity and rainfall events at shallow water depth of groundwater (Datry et al., 2004). The specific conductivity in Pulau Bidong, however, with the minimum value of 0.01 S/m and maximum value of 0.45 S/m, was in accordance with standard limit of the drinking water stated in National Drinking Water Quality Standard (NDWQS) guidelines (Table 4). The DO value demonstrated significant positive correlation with salinity (r ¼ 0.950), TSS (r ¼ 0.914), NO2 (r ¼ 0.959) and NHþ 4 (r ¼ 0.946). Furthermore, DO values were varied between June and the following months as the values were negatively correlated to each other (r ¼ 0.758). This could be due to the massive inflow of precipitation (Datry et al., 2004). Evidence has shown that DO content of water is also influenced by the source and water temperature (World Health Orga nization, 2004). Moreover, the water from Pulau Bidong was slightly acidic in which pH values was ranged from 5.2 to 7.6. The rainfall could possibly affect pH where it is the main source of recharge of ground water, which imparts acidity to groundwater as pure rainfall is slightly acidic in nature (Karanath, 1987). Besides, the high pH values may be due to process of chlorination. There were also several readings below the recommended pH value of 6.58, however, the pH value does not have any adverse health effect except the alteration of the taste of water. It should be noted that according to World Health Organization (2004), most of the natural and groundwater have pH from 4 to 9.
Table 2 The records of monthly rainfall amount from June to October 2016 at meteo rological station in Kuala Terengganu. Latitude: 5� 200 N Longitude: 103� 080 E Elevation: 35.1 m Rainfall amount (mm) Year
June
July
August
September
October
2016
94.7
157.7
182.7
165.7
278.4
The median value of both parameters reveal that the collected data were distributed towards the minimum value and only few data were recor ded at the high value. 4. Discussion Table 2 demonstrates monthly rainfall recorded at the nearest meteorological station to Pulau Bidong (MetMalaysia, 2016). The data revealed that the rainfall had increased from June to October 2016 and the highest level was recorded in October 2016. Table 3 demonstrates the correlation coefficient between water quality variables and rainfall with correlation matrix. Strong positive correlation (r ¼ 0.982) was observed between temperature and specific conductivity. Temperature is useful in evaluating the drinking water quality as it influences the overall water quality such as chemical re actions rate in water body, decreasing the gases solubility and improving the tastes and colour of water (Olajire and Imeokparia, 2001). Never theless, there was no variation in temperature of the collected water, which could be due to location of Pulau Bidong in the tropics. Mink
Table 3 Correlation coefficients between average monthly variation of physicochemical parameters in Pulau Bidong and rainfall. T SC DO pH Salinity DO% TDS TSS NO3 NO2 NH4 PO34 Rainfall a b
T
SC
DO
pH
Salinity
DO%
TDS
TSS
NO3
NO2
1 .982b 0.548 0.312 0.374 0.383 0.123 0.527 0.357 0.421 0.373 0.061 0.645
1 0.449 0.277 0.237 0.305 0.023 0.436 0.223 0.284 0.234 0.083 0.623
1 0.366 .950a .934a 0.015 .914a 0.541 .959a .946a 0.663 0.758
1 0.355 0.614 0.321 0.433 0.019 0.316 0.336 0.052 0.44
1 .921a 0.206 .918a 0.705 .998b 1.000b 0.715 0.681
1 0.07 .965b 0.608 .914a .911a 0.467 0.856
1 0.284 0.827 0.203 0.215 0.152 0.218
1 0.765 .919a .911a 0.389 -.912a
1 0.703 0.709 0.211 0.629
1 .999b 0.717 0.688
Correlation is significant at the 0.05 level (2-tailed). Correlation is significant at the 0.01 level (2-tailed). 7
NH4
1
0.725 0.668
PO34
Rainfall
1 0.022
1
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Table 4 The comparison of analytical results of the concentration of parameters with international and national standards. Parameters
Min
Max
Mean
WHO Guideline value (2011)
NDWQS Guideline value (2004)
Specific Conductivity (S/m) DO (mg/L) pH Salinity (ppt) DO Saturation (%) Nitrate (mg/L)
0.009
0.452
0.059
–
1.000
0.26 5.2 0.04 0.61
7.45 7.6 2.41 60.60
2.05 6.2 0.31 15.70
6.58 6.5–8.5 – –
– 6.5–9.0 – –
0.000
4.310
50
10
Nitrite (mg/L)
0.000
0.190
3
–
TDS (mg/L)
0.086
6.840
1000
1000
TSS (mg/L)
0.001
0.011
0.455 � 1.153 0.011 � 0.038 0.833 � 1.447 0.002 � 0.002
–
25
Table 5 Factor loadings, eigenvalue and percentage of variance after varimax rotation for Pulau Bidong groundwater quality. Parameter
PC1
PC2
PC3
PC4
T SPC DO pH Sal NHþ 4 NO3 NO2 POþ 4 TDS TSS
0.6672 0.8712 0.2906 0.1704 0.8647 0.1540 0.0335 0.0928 0.1209 0.4641 0.7448
0.0941 0.2699 0.5123 0.3303 0.2526 0.9562 0.8377 0.9530 0.1167 0.0307 0.0223
0.0502 0.1276 0.5871 0.5481 0.1723 0.0773 0.0818 0.0583 0.0653 0.5616 0.2278
0.1646 0.0678 0.2466 0.4166 0.0903 0.0170 0.0398 0.0041 0.8849 0.1768 0.3227
Eigenvalue Variability (%) Cumulative %
4.0869 34.06 34.06
2.3585 19.65 53.71
1.4254 11.88 65.59
1.1481 9.57 75.16
salinity (r ¼ 0.681), NO3 (r ¼ 0.629), NO2 (r ¼ 0.688) and NHþ 4 (r ¼ 0.668), DO saturation (r ¼ 0.856) and TSS (r ¼ 0.912). This reveals that rainfall is one of the factors affecting the physicochemical parameters of groundwater in Pulau Bidong. The findings were in agreement with a previous study by Mayer et al. (2005) which demon strated rainfall, geology and topography are essential with regard to groundwater. Table 5 demonstrates that PCA for temporal and spatial assessment were similar. Four principal components (PCs) were acquired for Pulau Bidong groundwater column with Eigenvalues larger than 1 and had 75.16% of the total variance in the data-set. The first PC revealed 34.06% of the total variance and had strong positive factor loadings on conductivity and salinity; moderate factor loadings on temperature and TSS as well as weak factor loading on TDS. In Pulau Bidong groundwater, dissolved salts such as sodium and chlo ride ions affect the water conductivity due to their ability to conduct electrical flow. Additionally, the aforementioned salt ions are known to influence the concentration of TDS and TSS in the water column (Lane et al., 2007; McNeil and Cox, 2000). In general, temperature may affect the TDS and TSS contents as higher temperature will cause the dissolved salt to form solid salt (Hall and Burns, 2003). The second PC had 19.65% out of the total variance with strong factor loadings on NHþ 4 , NO3 and NO2 as well as moderate and weak factor loading on DO and pH respectively. Frequently, NHþ 4, NO3 and NO2 are derived from fertilized agricultural land, domestic waste, animal waste, urban drainage, septic tanks, soil erosion, de tergents and sewage disposal systems (Buck et al., 2003; Lichtenberg and Shapiro, 1997; Dick, 1983). The aforementioned compounds are well-known as organic and acidic compound, therefore, their existence in the water column would reduce water pH. The existence of organic compound in the water column are shown to reduce DO value due to degradation process by the microorganisms (Vrzel et al., 2016; Gormly and Spalding, 1979). The findings of the present study indicate that domestic waste, animal waste, septic tanks, soil erosion and the usage of detergents affected the groundwater quality of Pulau Bidong. Meanwhile, the third and fourth PC had 11.88% and 9.57% of the total variance correspondingly. Furthermore, DO, pH and TDS reveal moderate factor loadings on PC3 whereas PO34 had strong factor loading and pH and TSS had weak factor loadings on PC4. Similar to the first and second PC; PC3 and PC4 had similar significant variables as the existence of the organic materials would reduce the value of DO and pH as well as the concentration of TDS and TSS in Pulau Bidong groundwater column. The discriminant analysis (DA) was applied to the collected water quality data to define the spatial and temporal variation of Pulau Bidong groundwater. In DA, groundwater quality data were designated as the independent variables. DA for both cases was performed via standard, stepwise forward and stepwise backward model. Table 6 demonstrates
Salinity is defined by the amount of salt content in a water column that is closely affecting the value of conductivity, TDS and TSS (Brown, 2016). The salinity of the groundwater sources of Pulau Bidong was between 0.04 and 2.41 ppt. The results reveal high salinity in ground water of Pulau Bidong in the month of June. This could be due to seawater intrusion in June caused by increased activities such as active usage and bathing while at drought, causing the groundwater overdraft. Besides, groundwater contains naturally occurring salts from organic material that would increase the salinity (Mayer et al., 2005). Table 3 reveals that the salinity in Pulau Bidong was significantly related with DO saturation (r ¼ 0.921), TSS (r ¼ 0.918) NO2 (r ¼ 0.998), and NHþ 4 (r ¼ 1.000). The strong positive correlation between NHþ 4 and salinity was caused by prevalent nitrogen inorganic species form of ammonium in groundwater. According to Mayer et al. (2005), freshwater for drinking and all irrigation purpose have salinity level less than 0.5 ppt, and high concentration of TDS will affects the taste and odour of water. The TDS are the inorganic matters that present as solution in water, therefore considered as an accurate measure of salinity. The recommended cutoffs for TDS in drinking water by WHO and NDWQS should not exceed 1000 mg/L. The TDS found in groundwater sources of Pulau Bidong were below the recommended cutoffs value with a value ranged between 0.086 and 6.840 mg/L, making it suitable for drinking. Total dissolved solid is highly correlated to NO3 , where nitrate is one of the ions in total dissolved solids parameters that determine the nature of water quality (Lukubye and Andama, 2017). According to Aris et al. (2009), ground water in small islands is often exposed to heavy pumping as a result of high demand for freshwater consumption. The TSS value in Pulau Bidong of 0.001 mg/L and 0.011 mg/L were lower than the NDWQS permissible limit. Additionally, r value of TSS and rainfall was 0.912, suggesting that the low TSS could be indicative of the wash off of surface pollutants by rainfall characteristics such as rainfall intensity, duration and depth (Gong et al., 2016). Moreover, low TSS also indicates that the groundwater in Pulau Bidong is not turbid. Nitrite is rarely present in significant concentrations except in a reducing environment, as nitrate is the highly stable oxidation state. The NO2 and NHþ 4 were highly correlated (r ¼ 0.999) as the aforementioned nutrients were relatively low in groundwater. The concentrations of NO2 and NO3 in groundwater of Pulau Bidong are within the recom mended limit suggested by WHO and NDWQS. The high intake of NO2 and NO3 in drinking water were found to cause methaemoglobinaemia, which is caused by the reaction between nitrite and haemoglobin in the red blood cells to form methaemoglobin that binds oxygen tightly and inhibit the release of haemoglobin (World Health Organization, 2011). In general, rainfall had strong negative correlation with temperature (r ¼ 0.645), specific conductivity with r ¼ 0.623, DO (r ¼ 0.758), 8
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Groundwater for Sustainable Development 10 (2020) 100358
Table 6 Confusion matrix of temporal DA for Pulau Bidong groundwater. from \ to Standard Mode August July June October September Total Stepwise Forward Mode August July June October September Total Stepwise Backward Mode from \ to August July June October September Total
August
July
June
October
September
Total
% correct
5 0 0 0 0 5
0 5 0 0 0 5
0 0 5 0 0 5
0 0 0 5 0 5
0 0 0 0 5 5
5 5 5 5 5 25
100.00% 100.00% 100.00% 100.00% 100.00% 100.00%
1 1 0 0 0 2
3 2 0 0 0 5
0 0 5 0 0 5
1 2 0 5 0 8
0 0 0 0 5 5
5 5 5 5 5 25
20.00% 40.00% 100.00% 100.00% 100.00% 72.00%
August 5 0 0 0 0 5
July 0 5 0 0 0 5
June 0 0 5 0 0 5
October 0 0 0 5 0 5
September 0 0 0 0 5 5
Total 5 5 5 5 5 25
% correct 100.00% 100.00% 100.00% 100.00% 100.00% 100.00%
Table 7 Confusion matrix of spatial DA for Pulau Bidong groundwater. from \ to
Station 1
Standard Mode Station 1 5 Station 2 0 Station 3 0 Station 4 0 Station 5 0 Total 5 Stepwise Forward Mode Station 1 4 Station 2 1 Station 3 0 Station 4 0 Station 5 0 Total 5 Stepwise Backward Mode Station 1 3 Station 2 0 Station 3 0 Station 4 0 Station 5 0 Total 3
Station 2
Station 3
Station 4
Station 5
Total
% correct
0 5 0 0 0 5
0 0 5 1 0 6
0 0 0 4 1 5
0 0 0 0 4 4
5 5 5 5 5 25
100.00% 100.00% 100.00% 80.00% 80.00% 92.00%
1 3 0 1 0 5
0 0 2 0 0 2
0 1 0 2 1 4
0 0 3 2 4 9
5 5 5 5 5 25
80.00% 60.00% 40.00% 40.00% 80.00% 60.00%
2 5 0 0 0 7
0 0 3 1 1 5
0 0 0 4 0 4
0 0 2 0 4 6
5 5 5 5 5 25
60.00% 100.00% 60.00% 80.00% 80.00% 76.00%
the classification matrix of temporal DA for Pulau Bidong groundwater. The temporal variation demonstrated that the calculated discrimi nant function analysis (DFA) for standard and stepwise backward mode were similar. There was 100% accurate classification of data with five discriminant variables for standard mode and three discriminant vari ables for stepwise backward mode. The standard mode DA revealed that conductivity, DO, pH, TDS and salinity were the significant variables that play role in temporal variation. On the other hand, only pH, salinity and TDS discriminated the groundwater quality throughout temporal changes. The stepwise forward DA indicated 72% accurate classification data as three datasets and one dataset of August were misclassified as July and October respectively. One dataset and two datasets of July were misinterpreted as August and October correspondingly. Moreover, findings demonstrate that only pH and salinity had high variation in terms of their temporal distribution. An increased flow of freshwater volume during the sampling period into Pulau Bidong groundwater would affect the pH and salinity value of the water column as the flushed out water or water seepage was acidic due to the existence of soil trace.
Furthermore, evidence has shown that freshwater contains less salt ions as compared to the groundwater (Wong et al., 2007; Waeles et al., 2005). The spatial variation based on DA was carried out using standard, stepwise forward and stepwise backward models. Table 7 demonstrates the classification matrix of spatial DA for Pulau Bidong groundwater. The standard mode of DA reveals 92% of accurate classification with three important variables, which are temperature, NO3 and PO34 . On the other hand, the stepwise forward and stepwise backward mode reveal 60% and 76% of correct classification of data respectively. Through the stepwise forward mode, two significant variables namely temperature and NO3 were identified whereas through the stepwise backward mode, only one parameter, temperature had high variability in terms of spatial distribution. Therefore, Pulau Bidong groundwater variables had significant variation in term of spatial distribution for temperature, NO3 and PO34 , which might be derived from domestic waste, animal waste, septic tanks, soil erosion and the usage of de tergents (Buck et al., 2003; Lichtenberg and Shapiro, 1997).
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Groundwater for Sustainable Development 10 (2020) 100358
5. Conclusion
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There were significant differences in physical characteristics and nutrients in June where the rainfall was lower than other months, and were similar from July to October, which were relatively higher, sug gesting that the aforementioned parameters were affected by the pre cipitation. There were low nutrients concentrations in Pulau Bidong due to non-point sources, and were safe to be consumed by the visitors. The physicochemical quality of groundwater in Pulau Bidong was superior except that pH was slightly lower than the local and international rec ommended drinking water guidelines. Based on chemometrics analysis, pH and salinity were significantly affected the changes of Pulau Bidong groundwater temporally due to the intrusion of high volume of fresh water during heavy rainfall. The spatial variation of the present study 3 reveals that NO3 , NO2 , NHþ 4 and PO4 significantly affected the changes of Pulau Bidong groundwater quality. Therefore, the proper manage ment of septic tanks is essential to improve the elimination of possible elevated concentration especially nitrate. Notably, the selected param eters are strongly interrelated and could be altered by human interfer ence. Besides, the seasonal variation also directly reflects the water quality of Pulau Bidong. This study provided the baseline data for future research. Nevertheless, long-term monitoring is essential for under standing the groundwater behavior in Pulau Bidong as this would facilitate proper management for preventing the effects of human ac tivities in order to ensure sustainable supply of groundwater to the users. Acknowledgement This research was supported by the Fundamental Research Grant Scheme (FRGS/1/2015/WAB09/UMT/02/1) of Ministry of Education Malaysia. This project was also funded by the Higher Institute Centre of Excellence (HICoE) Grant (Vote No. 66928) awarded to Institute of Oceanography and Environment (INOS). The authors would like to thank Malaysian Meteorological Department (MetMalaysia) for providing the rainfall data. The appreciation is also extended to the laboratory staff of Oceanography Laboratory, Faculty of Science and Marine Environment, Universiti Malaysia Terengganu. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.gsd.2020.100358. References American Public Health Association (APHA), 1999. American water works association (AWWA), & water environment federation (WEF). In: Standard Methods for the Examination of Water and Wastewater, twentieth ed. American Public Health Association, Washington, DC. Aris, A.Z., Abdullah, M.H., Kim, K.W., Praveena, S.M., 2009. Hydrochemical changes in a small tropical island’s aquifer: manukan Island, Sabah, Malaysia. Environ. Geol. 56 (8), 1721–1732. Barron, J.J., Ashton, C., 2013. The effect of temperature on conductivity measurement. Pract. Guide Accurate Conduct. Meas. 3, 1–5. Bhardwaj, V., Singh, D.S., 2010. Surface and groundwater quality characterization of deoria district, ganga plain, India. Environ. Earth Sci. 63 (2), 383–395. Brown, W.S., 2016. Physical properties of seawater. In: Dhanak, M.R., Xiros, N.I. (Eds.), Springer Handbook of Ocean Engineering. Springer Handbooks, Springer, Cham, pp. 101–110. Buck, O., Niyogi, D.K., Townsend, C.R., 2003. Scale-dependence of land use effects on water quality of streams in agricultural catchments. Environ. Pollut. 130, 287–299. Datry, T., Malard, F., Gibert, J., 2004. Dynamics of solutes and dissolved oxygen in shallow urban groundwater below a stormwater infiltration basin. Sci. Total Environ. 329, 215–229.
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