PRELIMINARY RESULTS OF STRATIFICATION STUDY IN SEMBRONG RESERVOIR, PENINSULAR MALAYSIA

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1 ID: PRELIMINARY RESULTS OF STRATIFICATION STUDY IN SEMBRONG RESERVOIR, PENINSULAR MALAYSIA Nor Bakhiah Baharim, Zulkifli Yusop, Muhamad Askari, Ismail Yusoff, Wan Zakaria Wan Muhd Tahir, Zainudin Othman, Mohamed Roseli Zainal Abidin Institute of Environmental and Water Resource Management Universiti Teknologi Malaysia, Johor, Malaysia Geology Department, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia Malaysian Nuklear Agency, Selangor, Malaysia Sultan Idris Education University, Selangor, Malaysia Humid Tropics Centre Kuala Lumpur, Kuala Lumpur, Malaysia The possible occurrence of stratification was assessed in Sembrong reservoir located in Kluang, Johor, Peninsular Malaysia. It is a man-made reservoir. Profile samplings were conducted at eight points. Water samples at each point were collected at discrete depth intervals of m. In situ measurement of Temperature, ph, Conductivity and Oxidation Reduction Potential (ORP) were carried out using Hydrolab DSX. Water samples were analysed in lab for Fe, Al and Mn using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES).The results show that ph, temperature and ORP tend to decrease after m depth. On the other hand, concentrations of Fe, Mn and Al slightly increased with depth as a result of reduction process. This phenomenon confirms the occurrence of reservoir stratification. Keywords: stratification, physical quality, heavy metals, reduction process Introduction Dam, reservoirs and lakes are important in the conservation of basic national resource-water. In recent years, monitoring quality of water body/reservoir has become a main concern for the determination of current condition and long term pattern for future management (Johnes, 999; Sharip and Jusoh, ; Gulati and Donk, ; Te and Gin, ). Although quite a number of lake water quality studies have been conducted, very limited work on limnological work has been reported in Malaysia (Shuhaimi Othman et al. 8; Prasanna et al. ; Toriman and Gasim, ; Ashraf et al. ). Furthermore, it should be noted that land clearing and subsequent agricultural activities especially oil palm plantation may enhance loading of non point source pollution and subsequently impair water quality (Bricker et al. 8; Toriman and Gasim, ). Previous studies show that climate and geomorphology play an important role controlling limnology and geochemical characteristic in reservoir (Mohammadreza, ; Ashraf et al. ; Mwuara, ; Kovac and Clement, 9; Odour et al. ).There are six classifications of lake mixing processes which differ in climatic condition and geomorphology (Dodson, ). For example, Lake Thonotosassa in Florida which has subtropical climate, maximum depth m is considered as polymictic condition (Dodson, ). On the other hand, Lake Washington with maximum depth of m illustrated a monomictic condition with the maximum depth m (Dodson, ).

2 ID: According to Dodson () vertical profiling studies could provide a robust tool to gain a better understanding of limnology and hydrogeochemical processes. Detailed studies of vertical sampling proved that stratification and lake mixing processes are controlled by climate and limnological characteristics (Dodson, 7; Bechmann et al. ; Macleod et al. ; Clement, ; Kotut et al. 999; Smith et al.99). These studies strongly suggested that individual characteristic of water body/reservoir needs to considered for reservoir management. Temperature plays significant roles that influence the water chemistry and biological activity in the reservoir. It has conclusively been shown that the chemical reactions increase at higher temperature and vice versa (Dodson, 7; Kotut et al. 999; Freeze and Cherry, 977). The relationship between dissolved oxygen and depth has been widely investigated (Koretsky et al. and Macleod et al. ). This study shows that dissolved oxygen decrease with depth possibility due diminishing photosynthesis activity with increasing depth. This preliminary study is important for interpreting the lake chemical processes especially stratification. Additionally, the data might provide an opportunity to examine land use impacts to the water body. Sites Sembrong Dam is located about km from Ayer Hitam, Johor. This floodcontrol dam is tapped by Syarikat Air Johor for water supply since 98. Geologically, the host rock of the reservoir is metamorphic rock which consists of shale, mudstone, siltstone, phylite and sandstone. The reservoir is surrounded by oil palm plantation. Other minor landuse are swamp forest, modern agriculture and husbandry. There are two major tributaries flowing into the reservoir, namely Sembrong River and Marpo River. Methodology Hydrographical Survey Hydrographical survey is very important to determine bed morphology and bathymetric status. Hydrographical operation was carried out from nd to rd November. A total of depth points were recorded using Echosounder Garmin C model. Kretau RSO Malaya Meter was used as projection system in the field survey and mapping the coordinates of the measurement points. Water Sampling Water samples were collected at 8 stations. Sampling was performed on rd November. Water samples were collected at different depths with m intervals using Horizontal Van Dorn sampler. Temperature, ph, DO, Conductivity and ORP were measured in-situ using a Hydrolab DSX from a boat. Water samples were acidified by concentrated HNO - to ph and filtered through.µm. The acidified samples were analysed for geochemical elements using Inductively Coupled Plasma Emission Spectrometer at the Hydrogeology Laboratory of University of Malaya.. Results and discussion Bathymetry map Figure (a) shows bathymetric map of Sembrong reservoir. The reservoir area is about 77 ha. The storage capacity calculated.8 million m. In particular, the depths range from m to 7m with a mean of.m. Figure (b) shows the bathymetric

3 ID: cross sections of the reservoir. It is obvious that the basin margins and the water body were modified by the dam construction a) b) A North m ScaleX/ TasikSembrong B South C South-West Tasik Sembrong 8m Scale X/ D North-East O South-West P North-East m Scale X/ M South-West N North-East m ScaleX/ Figure : Sembrong Lake Bathymetric map Water Quality Characteristic Table summarizes the physical and chemical quality of the lake water. As might be expected from temperature profile, ph values relatively decreased with depth (Figure ). The near surface water is moderately alkaline and become neutral at the bottom. The high ph values (above ) are not expected to occur in the agricultural area. The possible source of alkalinity in this agricultural area is from lime which is widely applied in the area to improve the soil quality. According to Dodson (7) temperature may become a good indicator to determine thermocline. However, in this study, temperature does not show a clear thermocline occurrence. ph, temperature, DO, ORP decreased with depth especially at m depth except conductivity. These results are consistent with other studies and suggest possible reduction in photosynthesis activities with depth (Koretsky et al. ; Macleod et al. ). Furthermore, the negative correlation of Conductivity and DO tends to support organic matter sink and decomposition at the bottom layer (Smith et al 99; Dodson, 7). Interestingly concentrations of Mn, Fe and Al tended to increase at m depth. According to Freeze and Cherry (977), the increases of heavy metals concentrations with depth were due to reduction process. This is supported with ORP profile which indicated the oxygen reduction potential start to occur at m depth.

4 ID: Table : A summary of physical and chemical parameter Statistic T Cond ph DO ORP Na K Ca Al Mn Mg Fe O C ms/cm mg/l mv mg/l Average Min Max Conclusion Though Semberong Lake is considered shallow, the preliminary results show stratification does take place. Stratification seems to play important roles in the chemical processes such as photosynthesis and reduction process. A detailed temporal study may be necessary to adequately characterize the reservoir stratification. Acknowledgement This research is funded by the Humid Tropical Centre Kuala Lumpur, Department of Irrigation and Drainage Malaysia (DID). The authors are grateful to all staff of the DID office of Batu Pahat for helping the data collection.

5 ID: a) 8 (ms/cm) Depth (m) Temperature ph 8 (C).. ORP(mV) Conductivity Dissolved Oxygen b) Depth (m) Legend S S S S S S S7 S8 c) Mg Mn Fe Al Depth (m) Ca 789 Na K Figure : Profiles patterns of a) physical and (b, c) chemical parameter

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