Procedia Environmental Sciences 30 ( 2015 ) 358 – 363

1878-0296 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of organizing committee of Environmental Forensics Research Centre, Faculty of Environmental Studies, Universiti Putra Malaysia.doi: 10.1016/j.proenv.2015.10.064

Available online at www.sciencedirect.com

ScienceDirect

International Conference on Environmental Forensics 2015 (iENFORCE2015)

Spatiotemporal variations in groundwater chemistry of a small tropical island using graphical and geochemical models

Nura Umar Kuraa, Mohammad Firuz Ramlia,b*, Wan Nor Azmin Sulaimana, Shaharin Ibrahima, Ahmad Zaharin Arisa,b, Tahoora Sheikhy Naranya

a Department of Environmental Sciences, Faculty of Environmental Studies, Universiti Putra Malaysia, 43400 UPM Serdang, Malaysia

b Environmental Forensics Research Centre, Faculty of Environmental Studies, Universiti Putra Malaysia, 43400 UPM Serdang, Malaysia

Abstract

In this work, the spatial and temporal variations in the groundwater chemistry of Kapas Island were assessed using geochemical and graphical models. The Durov diagram classifies the groundwater of the island into three water types; Ca- HCO3

-, Na- HCO3-,

and Na-Cl types with Ca- HCO3- as the dominant water type. The Schoeller diagram reveals that the order of abundance in ions

was Ca2+ > Na+> K+> Mg2+, for cations and HCO3- > Cl- > for anions. These findings would help in creating a sustainable

management plan through strategizing visitations and pumping periods to ensure that the island’s aquifer and other smaller islands with similar characteristics are well protected. © 2015 The Author. Published by Elsevier B.V. Peer-review under responsibility of organizing committee of Environmental Forensics Research Centre, Faculty of Environmental Studies, Universiti Putra Malaysia.

Keywords: Spatiotemporal; groundwater; hydrochemistry; geochemistry models; Tropical Island

1. Introduction Groundwater chemistry varies over space and time as a function of the hydro-geological state and seasonal fluctuations, land use and geology of the area [1]. It is important to include spatial assessment of hydrochemistry in any management plan to avoid error which may lead to a catastrophic effect not only on human health and socioeconomic developments but also on the entire ecosystem.

* Corresponding author. Tel.: +603-8946-6753; Fax: +603-8943-8109 E-mail address: firuz@upm.edu.my

© 2015 The Authors. Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of organizing committee of Environmental Forensics Research Centre, Faculty of Environmental Studies, Universiti Putra Malaysia.

359 Nura Umar Kura et al. / Procedia Environmental Sciences 30 ( 2015 ) 358 – 363

These potential effects would be more severe on small islands such as Kapas Island due to their limitation in natural resources, such as freshwater, where, in most cases, groundwater is the only source of freshwater due to the unsuitability of the topography to generate surface water. This is further compounded by the complexity in the mineralogy, geology and hydrogeological minerals and complexity in geological and hydrogeological structures, such as high permeability or impervious rocks, which limits the storage capacity of the aquifer [2]. Moreover, temporal variations in groundwater chemistry, even in small quantities, can have a considerable effect on the transport of solutes and pollutants yet, most studies of small islands groundwater hydrochemistry in Malaysia prioritized the spatial changes of the hydrochemistry only [3], with no account given to the temporal changes, perhaps due to the general perception that tropical islands receive rainfall almost throughout the year. However, rainfall events vary significantly over space and time as most of the rainfall is received during the monsoon season which can have a tremendous effect on the concentrations of ions and total dissolved solids (TDS) in the groundwater [4].

Researchers have used different techniques to evaluate the spatio-temporal variations of groundwater chemistry. For example, researchers like Reddy et al. [5] used ionic ratio techniques to characterize and determine the spatio-temporal variations of groundwater hydrochemistry in India. While Desa et al. [6] used modelling techniques to assess the usability of the Gulf of Kachchh waters based on spatial and temporal variations in dissolved oxygen as a target indicator. This work attempt to evaluate the spatio-temporal variations of Kapas Island hydrochemistry. This will empower the policy makers and environmental managers to come up with a reliable and justifiable management plan that would ensure the sustainability of the island’s groundwater and environmental protection of the entire ecosystem.

2. Materials and methods 2.1. Study area

Kapas Island (Fig. 1) is situated between 5° 13.140′ N and 103° 15.894′ E, at a distance of about 3km from Marang coastal area with a total area of about 2 km2, bordered by South China Sea, under Terengganu State, in the north-eastern part of Malaysia. Most of the island (80%) is hilly with a maximum elevation of 100 m above sea level and is covered by forest. The lithology of the island is dominated by inter-bedded sandstone, siltstone, mudstone and shale. The southern part of the island consists of shaly siltstone, conglomerate with quartzite siltstone and weathered tuff. The island’s climate is tropical in type, receiving over 2,800 mm of rainfall annually, mostly during the monsoon season between November and February. The temperature fluctuates between 28 and 31°C, with a humidity of about 80%. 2.2. Sampling and analysis Before any sampling exercise, Polyethylene bottles which were used as the water containers underwent an acid wash with 5% nitric acid (HNO3

-) and rinsed with distilled water. A total of 16 sampling sites (15 boreholes, and one open well) were utilized. The sampling surveys were carried out on monthly bases for the months of August and September 2012 (pre-monsoon) and then March and April 2013 (post-monsoon). Three replicates of groundwater samples were collected during each sampling exercise from each of the 16 sampling sites and the water level (W/L) was always measured at each sampling site before sampling was done. The In-situ parameters as well as the measure ions were strickly measured in accordance with the APHA standard [7]. 3. Results and discussion

3.1. Groundwater classification

Durov’s diagram [8] is used to determine the processes influencing groundwater chemistry such as salinity and recharge for the pre- and post-monsoon seasons (Fig. 2a and b). In both periods, the groundwater is generally dominated by Ca2+– HCO3

- water type, whereby 11 of the 16 sampling sites in the pre-monsoon period (Fig. 1a) fall under Ca2+– HCO3

- type, while, in post-monsoon period, the number increases to 13 sampling sites which is likely due to increase in rainfall which flushes most of the saline water out of the aquifer (Fig. 2b).

360 Nura Umar Kura et al. / Procedia Environmental Sciences 30 ( 2015 ) 358 – 363

Two sampling sites, namely C3 and CMW which initially fall under the mixed water type Na+– HCO3- in the pre-

monsoon period, shifted to Ca2+– HCO3- during the post-monsoon season which was most likely due to flushing of

the saline water by monsoon rainfall. Thus, it is expected that the aquifer undergoes reverse ion exchange which usually occurs when freshwater flushes out saltwater from the system [9]. Additionally, in the pre-monsoon period four sampling sites fall within Na+–Cl type but this is reduced to three in the post-monsoon season. The shifting of M5 sampling site to Na+–Cl type in the post-monsoon season is likely due to leaching from septic tanks near the sampling site or up coning. The concentrations of ions which are responsible for TDS [10] significantly decrease in the post-monsoon period compared to the pre-monsoon period. In the pre-monsoon season, the TDS values range between 100–1,000 mg/L while the value decreases to a maximum of less than 350 mg/L reflecting recharge [11] which dilutes the concentrations of ions in the groundwater. The Scholler diagram [12] was employed in order to understand the hydrochemical process controlling the groundwater system. Generally, the ions concentrations for both seasons are in order of abundance for cations: Ca2+ > Na+>K+> Mg2+ and HCO3

- >Cl > for anions (Fig. 2a and b) and the groundwater type for both seasons was mainly recharge water. However, the concentration of Na+-Cl significantly decreases during the post-monsoon season which is likely to be due to excessive recharge [13].

Fig. 1. Kapas Island showing lithology and sampling sites

361 Nura Umar Kura et al. / Procedia Environmental Sciences 30 ( 2015 ) 358 – 363

Fig. 2. (a) Durov diagram of groundwater types for pre-monsoon; (b) post-monsoon water types

Individually, M3 and M4 sampling sites were found to have the lowest concentration of HCO3- and Ca in both

seasons at the same time in having the lowest pH values. When carbonate minerals are dissolved in groundwater, they serve as the natural buffer to pH. That is why HCO3

- is usually the dominant ion in neutral pH among the CO32−

species, and therefore controlled the alkalinity of groundwater [14]. As such, a low pH which also coincides with low HCO3

- and Ca2+ indicates that the weathering processes in this area were not strong enough to absorb the hydrogen ions [15]. M3 and M4 sampling sites also show a different order of abundance in ions: Cl– – Na+– Ma facies in pre-monsoon, and Cl-–Mg– Na+– facies in post-monsoon season. The groundwater quality is generally influenced by three processes, namely rainfall, water-rocks interaction and rate of evaporation [16]. Therefore, the island’s groundwater for both pre-monsoon and post-monsoon periods was tested with the Gibbs diagram to evaluate the source of ions and variation in the island’s hydrochemistry. The resulting output of the Gibbs diagram (Fig. 4 a-d) for both cations and anions for the pre-monsoon season suggests that most of the samples are influenced by water-rock interaction. While K5 sample falls between the rock dominance and evaporation-precipitation dominance (Fig. 4 a and b).

Fig. 3. Scholler diagram for (a) pre-monsoon and (b) post-monsoon seasons

By comparison, in the post-monsoon season (Fig. 4 c and d), the K5 sampling site which was initially on the border between rock dominance and evaporation-dominance has now shifted completely to rock-dominance. This is likely to be due to the increase in rainfall during the post-monsoon season which dilutes the salinity in the affected

(b)

(b) (a)

(a)

362 Nura Umar Kura et al. / Procedia Environmental Sciences 30 ( 2015 ) 358 – 363

area. Similarly M3-M5 sampling sites in the post-monsoon season appear to move towards rainfall dominance. These sites have the lowest pH (3.5-5) in the entire island and are believed to be affected by multiple processes such as salinization due to up-coning, leaching from septic tanks, low weathering process and water lodging among other things. Moreover, both Gibbs diagrams for the cations and anions have shown a similar trend in terms of processes which further justify each another.

Fig. 4. (a and b) Gibbs diagram showing processes controlling groundwater chemistry pre-monsoon, (c and d) post-monsoon for cation and anions respectively

4. Conclusion Spatial and temporal variations of Kapas Island groundwater chemistry were assessed using geochemical graphical models and geostatistical tools based for pre- and post-monsoon seasons in the period 2012-2013 respectively. The classification of groundwater types and dominant ions for both seasons based on Durov and Schoeller diagrams were: Ca2+- HCO3

- type, Na+- HCO3- type, and Na+-Cl water type with Ca2+- HCO3

- as the dominant water type. The order of abundance in ions is Ca2+ >Na>K> Mg2+, for cations and HCO3 >Cl > for anions. In conclusion, it is advisable that future research in this area should focus on establishing threshold levels for groundwater pumping and other means of minimizing or preventing seawater intrusion such as creating artificial recharge areas and upgrading the sewage system of the island to prevent linkages.

1

10

100

1,000

10,000

100,000

0 0.2 0.4 0.6 0.8 1

TD

S

Na+K/Na+K+Ca CM2 CM3 CMW KP1 KP2 KP3KP4 KP5 KP6 KP7 LC MG1MG2 MG3 MG4 MG5

1

10

100

1,000

10,000

100,000

0 0.2 0.4 0.6 0.8 1

TD

S

Cl/Cl+HCO3

1

10

100

1,000

10,000

100,000

0 0.2 0.4 0.6 0.8

TDS

Na+K/Na+K+Ca

1

10

100

1,000

10,000

100,000

0 0.2 0.4 0.6 0.8 1

TDS

Cl/Cl+HCO3

Rock dominance

Rainfall dominance

(a) (b)

Rock dominance

Rainfall dominance

Evaporation-Precipitation dominance Evaporation-Precipitation dominance

Rainfall dominance

Evaporation-Precipitation dominance

Rainfall dominance

Evaporation-Precipitation dominance

(d) (c)

Rock dominance

TDRock dominance

363 Nura Umar Kura et al. / Procedia Environmental Sciences 30 ( 2015 ) 358 – 363

References 1. Chou, C. J. Assessing Spatial, Temporal, And Analytical Variation Of Groundwater Chemistry In A Large Nuclear Complex, USA.

Environmental Monitoring and Assessment, 2006; 119, p. 571–598. 2. Falkland, A. Hydrology and water resources of small islands: a practical guide, Paris, France: United Nations Educational, Scientific and

Cultural Organisation (UNESCO) 1991. 3. Lin, C. Y., Abdullah, M. H., Praveena, S. M. & Yahaya, A. H. B. Delineation of temporal variability and governing factors influencing the

spatial variability of shallow groundwater chemistry in a tropical sedimentary island. Journal of Hydrology 2012; 432–433 , p. 26–42. 4. Belkhiri, L., Mouni, L. & Boudoukha, A.,. Geochemical evolution of groundwater in an alluvial aquifer: Case of El Eulma aquifer, East

Algeria. Journal of African Earth Sciences 2012; 66-67, pp. 46-55. 5. Reddy, A., Saibaba, B. & Sudarshan, G. Hydrogeochemical characterization of contaminated groundwater in Patancheru industrial area,

southern India. Environ Monit Assess 2012; 184, p. 3557–3576. 6. Desa, E., Zingde, M. D., Vethamony, P., Babu, M. T., D’Sousa, S. N., & Verlecar, X. N. Dissolved oxygen––a target indicator in

determining use of the Gulf of Kachchh waters. Marine Pollution Bulletin 2005; 50, p. 73–79. 7. APHA, "Standard Methods for the Examination of Water and Wastewater.," American Public Health Association (APHA) and American

Water Works Association, Water Environment Federation,, Washington., 2005. 8. Durov, S. Natural waters and graphical representation of their composition. Dokl Akad Nauk USSR 1948; 59, p. 87–90. 9. Rina, K., Datta, P. S., Singh, C. K. & Saumitra Mukherjee, S. Isotopes and ion chemistry to identify salinization of coastal aquifers of

Sabarmati River Basin. Current Science 2013; 104(3), pp. 335-344. 10. Sundaray, S. K. Application of multivariate statistical techniques in hydrogeological studies-a case study of Brahmani-Koel River (India).

Environmental Monitoring and Assessment 2010;164, pp. 297-310. 11. Chang, J. & Wang, G. Major ions chemistry of groundwater in the arid region of Zhangye Basin, northwestern China. Environ Earth Sci

2010; 61, p. 539–547. 12. Scholler, "Hydrodynamique Lans Lekarst (Ecoulemented emmagusinement).," Doubronik,, 1965. 13. Hounslow, A. W. Water Quality Data Analysis and Interpretation. New York: CRC Lewis. 1995 14. Delgado, A. G., Parameswaran, P., Fajardo-Williams, D., Halden, R. U., & Krajmalnik-Brown, R. Role of bicarbonate as a pH buffer and

electron sink in microbial dechlorination of chloroethenes. Microbial Cell Factories 2012; 11(128), pp. 1-10. 15. Marques, E. D., Tubbs, D., Gomes, O. V. O. & Silva-Filho, E. V. Influence of acid sand pit lakes in surrounding groundwater chemistry,

Sepetiba sedimentary basin, Rio de Janeiro, Brazil. Geochemical Exploration 2012;112, pp. 306-321. 16. Gibbs, R. J.,. Mechanisms controlling world water chemistry. Science 1970; 170, pp. 1088-1090.