Multivariate Analysis on Heavy Metals Distribution in Tropical Reservoir

Chemical properties of bottom sediment in manmade reservoir were analyzed. Principal component analysis and factor analysis were conducted to differentiate the sources of heavy metals. The mean concentrations of heavy metals decrease in the following order: Mn>Pb>As>Zn>Cr>Cu. The spatial distribution of heavy metals shows that oil palm plantation and modern agricultural activities influence heavy metal distribution. Heavy metal contents were higher in the west wing and could be associated with micronutrient fertilizer from oil palm plantation with remarkable increases, especially for Zn, Cu and Mn.


INTRODUCTION
Heavy metal contamination in sediments could have long-term implications on human health because surface water is the main source of water supply.Heavy metal contamination can cause toxicity as well as harm the aquatic environment (Ghrefat and Yusuf, 2006;Çevik et al., 2009;Tabari et al., 2010;Chen et al., 2007).The accumulation of heavy metal in reservoirs is controlled by complex physical and chemical adsorption mechanisms that are triggered by natural processes or human activities (Spencer and MacLeod, 2002;Abraham, 1998;Ghrefat and Yusuf, 2006;Çevik et al., 2009).Anthropogenic sources of heavy metals in sediments mainly come from agricultural activities, urbanization, industrialization and mining (Micó et al., 2006;Dragović et al., 2008;Cai et al., 2012;Krami et al., 2013).
Previous studies in Wadi Al-Arab Dam, Jordan and Seydan Dam, Turkey show that the application of fertilizer and pesticide in agricultural activities is the main source of anthropogenic input, particularly Zn and Cd (Ghrefat and Yusuf, 2006;Çevik et al., 2009).Studies on risk assessment and ecological risk of heavy metals in reservoir sediment have been conducted by previous researchers (Çevik et al., 2009;Ghrefat et al., 2011;Dou et al., 2012;Prasanna et al., 2012).
Two main rivers flow into the reservoirs, namely, Sembrong River and Marpo River.As heavy metal pollution poses a serious threat to human health and ecosystems, studying sediment quality has become a major concern to many researchers.This study aims to address this issue and achieve the following objectives: • To determine the chemical properties in bottom sediment cores • To determine the spatial distribution of heavy metals in Sembrong Reservoir.
Five bottom sediment cores were collected at different stations in Sembrong Reservoir by using the UM core sampler.This core sampler was designed for bottom lake sediment and equipped with two transparent acrylic tubes (Gharibreza Gharibreza et al., 2013a).The sampling s chosen carefully based on the bathymetry map.Bottom sediment cores were obtained from the deepest possible depth to ensure that the sediment contains the finest grains of clay (Hakanson, 1980).After sampling, the sediment samples were frozen at sliced at 2-cm intervals.The samples were dried at 80°C and weighted.
The acid digestion procedure was conducted by using the Multiwave 3000 oven and following Method 3052.For each slice, a 0.25 g powder sample was mixed with acid mixture that contains 9 UM core sampler.This core sampler was designed for bottom lake sediment and equipped with two (Gharibreza et al., 2013b, c; .The sampling stations were chosen carefully based on the bathymetry map.Bottom sediment cores were obtained from the deepest possible depth to ensure that the sediment contains the finest .After sampling, the at -10°C before being cm intervals.The samples were dried at The acid digestion procedure was conducted by using the Multiwave 3000 oven and following Method g powder sample was mixed with acid mixture that contains 9 mL HNO 3 ,  -------------------------------------------------------------------------------------------------------------------------------------------------- In addition, a dendogram shows the similarities and dissimilarities among heavy metals divided into two classes (Fig. 3).Class 1 consists of the element As only and Class 2 represents the strong correlations between Cu, Cr, Mn, Pb and Zn.Class 2 is divided into two clusters, with the first cluster comprising Cu and Mn and the second cluster comprising Cr, Pb and Zn.Both clusters are linked to each other and appear to be associated with natural and anthropogenic sources.Cu and Mn are associated with each other because both have a strong bond with organic matter (Loska and Wiechuła, 2003;Bhuiyan et al., 2010).In addition, Mn is subject to oxidation that triggers mobilization of Cu from the sediment.Therefore, the increments of Cu in sediments are proportional with Mn.Geologically, Cr, Pb and Zn primarily come from lithogenic origins, especially from chalcophylic nature.As such, Cr, Pb and Zn might be derived from natural sources and enriched by human-induced sources.The relationships between Cr, Pb and Zn suggest that these heavy metals originated from similar sources and were deposited together.Multivariate analyses have successfully distinguished the sources of heavy metals in the  reservoir.Cu, Cr, Mn, Pb and Zn can be classified as an "anthropogenic factor" that most likely originates from micronutrients in chemical fertilizer (Micó et al., 2006;Sun et al., 2013;Dou et al., 2012;Huang et al., 2007).Chemical fertilizer is extensively used in agricultural cropss to replenish soil quality.The application of micronutrient fertilizers, such as borate, copper and zinc sulfates, especially in oil palm plantation (Sabri, 2009;FOA, 2004) might be responsible for the presence of heavy metals in the northwest and southwest of the reservoir.By contrast, Cai et al. (2012) and Dou et al. (2012) explained that As could also be associated with other heavy metals, such as Zn and Cd, that originated from phosphorous fertilizer.However, the result indicates that Cd is absent and As did not associate with other heavy metals.Therefore, As may originate from a single source, most likely from geological substrates.

CONCLUSION AND RECOMMENDATION
Identifying and quantifying heavy metals are important for environmental studies.The results indicate that agricultural activities have contributed to heavy metal influxes at Sembrong Reservoir.The rapid expansion of the area that surrounds the oil palm plantation seems to cause high heavy metal contents in sediment, especially in the eastern part of the reservoir.The additional sources of heavy metals, especially Mn, Cu, Cr, Zn and Pb, most likely come from micronutrient fertilizer.The distribution of sediment particles and chemical properties in the reservoir is influenced by the physical mixing process.

Fig. 2 :
Fig. 2: Loading plot of the principal component of heavy metals in Sembrong Reservoir

Table 1 :
Changes in land use compositions in Sembrong Reservoir from 1966 to 2010

Table 2 :
Descriptive statistics of heavy metal concentrations in the bottom sediment in Sembrong Dam

Table 3 :
Factor analysis of heavy metal concentrations for bottom sediment at Sembrong Reservoir