(榮譽)學位課程 Bachelor of Social Sciences (Hons) in Environment and Resources Management

EFFECTS OF HEAVY METAL ON MUDFLAT ECOSYSTEM BY LEUNG MAAN SZE, MICHELLE STUDENT NO.:14677040

環境及資源管理社會科學學士 (榮譽)學位課程 BACHELOR OF SOCIAL SCIENCES (HONS) IN ENVIRONMENT AND RESOURCES MANAGEMENT

April/2016

畢業論文 PROJECT

Effects of heavy metal on mudflat ecosystem

LEUNG MAAN SZE, MICHELLE STUDENT NO. 14677040

AN HONOURS PROJECT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

BACHELOR OF SOCIAL SCIENCES (HONOURS) IN ENVIRONMENT AND RESOURCES MANAGEMENT

HONG KONG BAPTIST UNIVERSITY

APRIL / 2016

HONG KONG BAPTIST UNIVERSITY

April /2016

We hereby recommend that the Honours Project by Miss. Leung Maan Sze, Michelle entitled "Effects of environmental pollutants on intertidal mudflat ecosystem" be accepted in partial fulfilment of the requirements for the Bachelor of Social Sciences (Honours) in Environment and Resources Management.

Dr. Wei Xi Chief Adviser Second Examiner

Overall Grade :

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Acknowledgements

I would like to express my gratitude to Dr. X. Wei who gave valuable advice and guidance on my Honours Project and provided assistance in laboratory work. Thanks are given to Dr. H. C. Chim and Dr. K. L. Chow whose provided assistance in laboratory work also. I would also like to thanks Mr. C. H. Yeung, technician of Geography Department who provided equipment for conducting fieldwork. And thanks are given to my friends: Vicky Lau and Vitus Li who offered assistance in my fieldwork described in this Honours Project.

______Student’s signature

Date:______

Abstract

Environmental pollutants like heavy metals can have different pathways to discharge into water and sediment. Impact of heavy metal on the mudflat’s ecosystem was studied in Ha Pak Nai and San Tau. Concentration of heavy metal in water, composition of grain size in sediment were tested and number of species and individual of crabs and snails were counted in this study. The concentrations of heavy metal in water were similar in Ha Pak Nai and San Tau.

The physical parameters of water in two study areas was similar while the amount of conductivity was higher in San Tau than Ha Pak Nai by 13161.5

µS/cm. Mean percentage of silt sediment in Ha Pak Nai was more than in San

Tau by 29.7%. Both the communities of crabs and snails were different in the two study area. More crabs species were investigated in Ha Pak Nai while more snails species were investigated in San Tau. Dominance index was also calculated by using the crabs and snails. Dominance index was 0.76 in Ha Pak

Nai and 0.21 in San Tau. To reduce the heavy metal contamination in mudflat, a better management is needed.

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TABLE OF CONTENT Page Acknowledgement i Abstract ii Table of Content iii List of Tables v List of Figures vi CHAPTER 1 INTRODUCTION 1.1 Background 1 1.2 Introduction of Study Area 3 1.2.1 Ha Pak Nai 3 1.2.2 San Tau 3 CHAPTER 2 LITERATURE REVIEW 2.1 Global Situation of Heavy Metal Contamination in Mudflat and 5 Mangrove 2.2 Hong Kong Situation of Heavy Metal Contamination in 6 Mangrove 2.3 The effect of sediment on heavy metal contamination 7 2.4 Biological Effect 8 2.5 Ecological Effect 10 2.6 Filling the Gap 13 2.7 Objectives 13 2.8 Hypothesis 14 CHAPTER 3 METHODOLOGY 3.1 Fieldwork 15 3.2 Water Sample Collection 15 3.2.1 Date and Time 15 3.2.2 Sampling Sites 16 3.2.3 On-site Preparation 16 3.3 Sediment Samples Collection 16 3.3.1 Date and Time 17 3.3.2 Sampling Sites 17 3.3.3 On-site Preparation 17 3.4 Sampling of Organisms 17 3.5 Laboratory Analysis 18 3.5.1 Grain Size Analysis 19 3.5.2 Heavy Metal in Water 20 3.6 Calculation and Statistical Analysis 20

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CHAPTER 4 RESULTS 4.1 Physical Parameters in Water 21 4.1.1 Dissolved Oxygen 21 4.1.2 Conductivity 22 4.1.3 pH Value 23 4.2 Composition of Grain Size in Sediment 24 4.2.1 Gravel 24 4.2.2 Sand 25 4.2.3 Silt 26 4.3 Heavy Metal Concentrations in Water 27 4.3.1 Chromium (Cr) 27 4.3.2 Arsenic (As) 28 4.3.3 Cadmium (Cd) 29 4.3.4 Lead (Pb) 30 4.3.5 Mercury (Hg) 30 4.4 Abundance of Species 31 4.4.1 Abundance of Crabs 31 4.4.2 Abundance of Snails 32 4.4.3 Biodiversity Index 32 CHAPTER 5 DISCUSSION 34 CHAPTER 6 CONCLUSION 46

List of Tables Table 1 (a) Species and total number of individual of crabs in study 34 areas Table 1 (b) Species and total number of individual of snail in study 34 areas Table 2 Simpson’s Index of Ha Pak Nai and San Tau 34 Table 3 Data of different parameters in monitoring station DS3 44 and NS6

List of Figures Figure 1 Location of study areas 4 Figure 2 Transect setting for the sampling of organisms 18 Figure 3 Dissolved oxygen level at the two study areas during 22 October and November (PN: Ha Pak Nai; ST: San Tau) Figure 4 Conductivity at the two study areas during October and 23 November (PN: Ha Pak Nai; ST: San Tau) Figure 5 pH value at the two study areas during October and 24 November (PN: Ha Pak Nai; ST: San Tau) Figure 6 Mean percentage of gravel in sediment samples at the 25 two study areas (PN: Ha Pak Nai; ST: San Tau) Figure 7 Mean percentage of sand in sediment samples at the two 26 study areas (PN: Ha Pak Nai; ST: San Tau) Figure 8 Mean percentage of silt in sediment samples at the two 27 study areas (PN: Ha Pak Nai; ST: San Tau) Figure 9 Mean concentration of chromium in water samples at 28 the two study areas (PN: Ha Pak Nai; ST: San Tau) Figure 10 Mean concentration of arsenic in water samples at the 29 two study areas (PN: Ha Pak Nai; ST: San Tau) Figure 11 Mean concentration of cadmium in water samples at the 30 two study areas (PN: Ha Pak Nai; ST: San Tau) Figure 12 Mean concentration of Lead in water samples at the two 31 study areas (PN: Ha Pak Nai; ST: San Tau) Figure 13 Mean concentration of Mercury in water samples at the 32 two study areas (PN: Ha Pak Nai; ST: San Tau) Figure 14 Spatial distribution of heavy metal in marine sediment 39 in Hong Kong

CHAPTER 1 INTRODUCTION

1.1 Background

Mudflat, also as tidal flat, is a type of coastal wetland. It is a flat and low-lying habitat. Most mudflats are finding in intertidal areas because they are affected by the tidal and so called intertidal mudflat. They are exposed during low tide and submerged during high tide (Pande and Nayak, 2013). In Hong Kong, there are many intertidal mudflats in different district such as Luk Keng in New

Territories, Tsim Bei Tsui in Deep Bay area, Nai Chung in Sai Kung and Tai Ho

Wan in Lantau Island (Tam and Wong, 2000). Water and sediments with mud, silt, clay and some gravel are the major elements of mudflat, the sediments are originated by land and sea (Pande and Nayak, 2013). Mudflat is one of the biomes having high productive.

Mudflat has a very high biodiversity because it supports many animals such as crabs and worms etc. and plants such as mangroves and seagrass can also be found in intertidal mudflat. Infauna inside mudflat support the feeding species such as crustaceans, fish and molluscs (Cheung et al., 2008), which provide food sources to these higher trophic level of organisms (Rahmanpour,

Ghorghani and Ashtiyani, 2014). Mudflat is important to different organisms especially migratory birds and shorebirds. Migratory birds will migrate a long

1 distance to breed and take rest, they stop at mudflats or estuaries to refuel in winter. As mudflat has a high biodiversity, crustaceans, infauna organisms and fish are the food sources for those migratory birds and shorebirds. In Hong

Kong, about 50000 wintering waterbirds fed on Deep Bay intertidal mudflat when they passing through Hong Kong in every winter (WWF, unknown).

However, rapid expansion of population size had occurred and causing urbanization and industrialization in Hong Kong. Due to the rapid development, pollution problem is serious from the past until now. Some of the mudflats are near the human activities and thus they are receiving many environmental pollutants. Heavy metals, excess nutrients are some of the environmental pollutants. Heavy metals are one of the environmental pollutants that mudflats are received. Due to heavy metals have persistent toxic effect, they are classified as hazardous pollutants in environment, even they are at a low concentration (Marcovecchio and Ferrer, 2005). Heavy metals will uptake by different organisms and accumulate in their bodies. Heavy metal bioaccumulation occurs with the food chain structure. In Hong Kong, people like going to estuarine environment such as Tung Chung Bay and Shui Hau to dig clam. They will uptake the heavy metal if they eat the seafood which contain high concentration of heavy metals. There are various factors to affect the

2 concentration of heavy metals in mudflats like the sediment size. This study is examining the heavy metal in water and assessing the effect of heavy metal on mudflat ecosystem of two mudflats in Hong Kong

1.2 Introduction of Study Area

The mudflats in Ha Pak Nai and San Tau were chosen for studying the heavy metal contamination and their ecosystem. Ha Pak Nai and San Tau are both located the western part of Hong Kong. The location of Ha Pak Nai and San

Tau is shown in Figure 1.

1.2.1 Ha Pak Nai

Ha Pak Nai is located at Yuen Long. It is in the district of Deep Bay (Tam and

Wong, 2000). Also, it is near Sheng Zheng Bay and Pearl River. The area of Ha

Pak Nai is about 18 ha.

One seagrass species can be found in Ha Pak Nai. There are mangroves in Ha

Pak Nai. However, the area of mangroves in Ha Pak Nai is small, it has 0.71 ha only (Tam and Wong, 2000).

1.2.2 San Tau

San Tan is located at the west of Tung Chung Bay on north Lantau Island. The area of San Tau is about 2.7 ha. It is a mix of silt and sand. Also, it was

3 designated as a ‘Site of Special Scientific Interest’ (SSSI) in 1994 (Green Power, unknown).

Two seagrass species can be found in San Tau -- Halophila ovalis and Zostera japonica. The seagrass bed provide food and shelter for snails, crabs and mudskippers etc. (Green Power, unknown). Apart from seagrass bed, mangroves are also found in San Tau. The area of mangroves in San Tau contain 2.14 ha of the total area (Tam and Wong, 2000).

Figure 1. Location of study areas

CHAPTER 2 LITERATURE REVIEW

2.1 Global Situation of Heavy Metal Contamination in Mudflat and

Mangrove

Heavy metal contamination in both mudflat and mangrove were studied in many countries.

In Singapore, six types of metals including Cd, Cr, Cu, Ni, Pb and Zn were tested in the sediment of mangrove. The mean of concentration of Cd, Cr, Cu,

Ni, Pb and Zn were 1.87 µg/g, 84.7 µg/g, 344 µg/g, 38.3 µg/g, 158 µg/g and

313 µg/g respectively (Cuong et al., 2005).

The fluxes of Cd, Cu, Hg, and Pb were investigated from the sediment of intertidal mudflat in the three coastal lagoons in Mexican Pacific

(Ruiz-Fernández et al., 2009).

In the upper gulf of Thailand, Chaiyara et al., (2013) found that the concentration of Zn was the highest metal concentration in the sediment.

Concentrations of heavy metals were different in dry season and wet season.

Concentration of Cu was highest in dry season while concentration of Pb was highest in dry season.

The rapid growth of economic development in China resulted by increasing the pollution in mangrove. Concentrations of different metals including Cu, Zn,

Cd and Pb in the sediment of mangrove in Guangdong and Fujian were higher than in Guangxi and Hainan (Wang et al., 2013).

2.2 Hong Kong Situation of Heavy Metal Contamination in Mangrove

In Hong Kong, heavy metal contaminations in the surface sediment of 18 mangrove swamps distributed in different region were studied by Tam and

Wong (2000). Different location of mangrove swamps had different concentration of heavy metals. The 18 mangrove swamps were divided into four groups. Three mangrove swamps located in Deep Bay region were in the first group. The mangrove swamps in this group had high heavy metal concentration. Ho Chung, Sam Mun Tsai, Tolo Pond and Nai Chung were the second group. These four mangrove swamps were the polluted swamps which receiving different anthropogenic effluent. The third group were relatively clean including Tai Ho Wan and Yi O. Both of them located at Lantau Island.

Nine of the mangrove swamps were the fourth group which were uncontaminated such as Hoi Ha Wan and Lai Chi Wo. These mangrove swamps were having the lowest concentration of heavy metals because they were far from urban area or within the country park area, so they received less human influence (Tam and Wong, 2000).

2.3 The Effect of Sediment on Heavy Metal Contamination

Sediment acts a sink of different environmental pollutants so it has an important role to assess the metal contamination in aquatic environment.

Sediment type, organic content were the factors to influence the concentration of metals in sediment (Ahn et al., 1994). Heavy metal contamination was found in both mudflat and mangrove sediment in India. The mudflat in Ulhas

Estuary was dominated a high value of total nitrogen while the mangrove in

Thane Creek was dominated by total organic carbon and total phosphorus.

There was strong correlation between total nitrogen and the metals found in

Ulhas Estuary. This was because adsorption, formation of organic complexes and biological degradation etc. were causing deposition and remobilization of trace metals in the environment rich in organic matter (Fernandes and Nayak,

2012). However, worms might be more tolerant to the metal-originated stress in a higher organic content of sediment because the bioavailability of metals could be reduced and the sediment had higher organic carbon to had a better nutritional conditions stated by Ahn et al. (1994).

2.4 Biological Effect

Heavy metal contamination in sediment would cause the accumulation of heavy metal in organisms. Heavy metal accumulation in organisms were investigated in different studies.

In Hong Kong, heavy metal contamination was found in bivalves at Ting Kok

(Chen, 2003). But higher metal concentration in molluscs in Pearl River Delta

Region was higher than in Hong Kong (Fang et al., 2001). The highest concentration of heavy metal found in bivalves was the oysters. For any organisms, absorption of Cu and Zn was stronger than Pb and Ni, the sequence was Zn>Cu>Pb>Ni. Thus, the contamination level of Zn was higher than Cu

2.5 to 18 times at the same organism. However, the absorption of heavy metal of various organisms were different. The oysters had a high level concentration of Zn. Other organisms such as clams under bivalves had a lower level of heavy metal that oysters. Bivalves especially oyster, was absorbed heavy metals easier than the other types of organisms. Oyster had a higher level of heavy metal contamination than others bivalves organisms because of the different of feeding. Oysters were filter feeder, they would absorb a large amount of water and feed the algae. As they absorbed very large amount of water, they would also absorb heavy metal from water more easily.

Although the heavy metal contamination at Ting Kok was relatively lower, the heavy metal would accumulate in the bivalves (Chen, 2003). Size of organisms could affect the concentrations of heavy metals in their bodies. Ahn et al. (1994) stated that smaller polychaetes accumulated more metals per unit body weight that the larger polychaetes.

Some organisms could appear in high heavy metal contamination. Ahn et al.

(1994) found that a dominant polychaete species was disappeared in a lower metal contamination of the sediment while appeared in a higher heavy metal contamination of the sediment. It was because many factors could affect the availability for biological uptake the metals and the survival of affected organisms (Ahn et al., 1994). Gender was the other factors to affect the accumulation of heavy metal (Na and Park, 2012). There were differences of the mean concentration of heavy metals in the gender of crabs investigated by

Na and Park (2012). Some of the non-essential metals (As, Cd and Pb) were higher in females than in males.

However, some of the organisms were expected to have a high concentration of heavy metal. Raising levels of Cu and Zn in shellfish and Cu level in crustaceans were expected because these metals play an important role in the metabolic processes (Cuong et al., 2005).

Bioaccumulation was another effect to influence the uptake of heavy metal by organisms. Higher bioaccumulation factor ranges were found in Cd, Cu and

Zn and there was potential biomagnification. Cu and Zn were essential for hemocyanin and enzymatic activities for the crustaceans. Bioaccumulation factor of Cd was high because Cd was not regulate and accumulation was not occur at all concentrations. There was positive correlation between the levels of Cd, Cu, Ni and Pb in crabs and those levels of metals in sediments found in the study. Thus, crabs could also be the bioindicators of environmental systems where having the diverse and variable pollution sources (Na and Park,

2012).

2.5 Ecological Effect

Heavy metal contamination in sediment would also affect the communities and ecosystem of mudflat and mangrove. Benthic communities such as gastropod and crabs were contributed in monitoring the environment and assessment of heavy metal and organic contamination in estuaries (Amin et al.,

2009). In Indonesia, strong negative correlations were found between the concentrations of Cd, Cu, Zn and Ni in sediments and the numbers of gastropod species and abundance of gastropod in the study by Amin et al.

(2009). When the concentration of heavy metals increased, decline of the

10 abundance of gastropod occurred. Moreover, only two species of polychaete were sampled in the sampling sites of a tidal flat of Korea (Ahn et al., 1994).

Metals could reduce the abundance, reduce the species diversity and change the community composition to the benthic communities. The significance impact of contaminated sediments to the benthic communities was the death of organisms (Amin et al., 2009).

Bioavailable concentration of heavy metals from sediment, vegetation and organisms was transferred by food chains (Villhena and Coasta, 2013).

Concentrations of Ni, Cu, Zn, As and Hg etc. in crabs were higher than the leaves, indicated the bioaccumulation of those metals (Villhena and Coasta,

2013).

Some of the crustaceans were sensitive to the pollution including heavy metal.

Absence of two important species – C. volutator and C. carinata in Fal estuary was investigated by Warwick (2000). The reason of absence of these two species was the pollution and resulted in the change of microbenthic assemblages in Fal estuary.

Mai Po, located in the northwestern part of Hong Kong, was facing heavy metal contamination also. Lizhe et al. (2003) found that intertidal mudflats at

Mai Po were slightly polluted by using species diversity index, biotic

11 coefficient and macrofauna pollution index. There were heavy metal contamination in both mangrove, benthic microgastropods and waterbirds found in Mai Po.

High level of Cu and Zn contamination in sediment was found. The northern and southern ends of wetland in Mai Po were identified as hot spots of contamination. Different organisms and mangrove roots were having the heavy metal contamination. Heavy metals contaminations were found in mangrove root by Ong che (1999). Concentrations of different metals were vary in different mangrove species because their uptake systems were not the same.

Mai Po mudflat infauna community had a low species richness. Only two species of gastropod found in the mudflat including Sermyla riqueti and

Stenothyra devalis. High Zn accumulation in Sermyla riqueti had found in the study by Lai et al. (2005). Accumulation of Cu was especially high in the species of Stenothyra devalis, showing bioaccumulation. There were two factors affecting bioaccumulation of heavy metal in the microgastropod. One was the physical factors in sediment. Another was the metabolic factors.

Growth of organisms reflected the environmental condition. Pollution and organic matter in the sediments were major toxicity factors in the survival and growth of gastropod like Sermyla tornatella (Liang, 2007). Apart from the

12 mangrove organisms, feathers of Ardeids in Mai Po was also discovered that having heavy metal contamination. The concentration of Pb and Hg were higher than the other metals in Ardeids’ feathers found by Connell et al. (2001).

2.6 Filling the Gap

Heavy metal contamination had been investigated lots in Hong Kong. Effect of heavy metal on mudflat ecosystem had investigated in other foreign countries while there is no study in Hong Kong.

2.7 Objectives

There are seven objectives in this study:

1. To assess the concentration of heavy metal in water of the two mudflats.

2. To compare the concentration of heavy metal in water of the two mudflats.

3. To assess the grain size distribution in sediment of the two mudflats.

4. To study the relationship between grain size of the sediments and

concentration of heavy metal.

5. To identify the impact of heavy metal on mudflats’ ecosystem and compare

the differences of crabs and snails’ communities.

6. To identify other factors that influence the concentration of heavy metal

which did not cover in the study.

7. To evaluate the policy on mudflat protection and give suggestions to

improve heavy metal pollution in Hong Kong’s mudflats.

2.8 Hypothesis

Six hypothesis were made:

1. The concentration of heavy metal in water in Ha Pak Nai is higher than in

San Tau.

2. Pollution is high in both Ha Pak Nai and San Tau.

3. Physical parameters of water do not have relationship with the heavy metal

concentration.

4. Sediment in Ha Pak Nai will have a higher percentage of fine particles.

5. More species and individual of crabs find in Ha Pak Nai.

6. More species and individual of snails find in San Tau.

CHAPTER 3 METHODOLOGY

3.1 Fieldwork

Sampling of organisms, water samples and sediment samples were collected in low tide mainly in October and November. Fieldwork days were decided by tidal change according to Hong Kong Observatory. With the reference of tidal change given by Hong Kong Observatory, eight days were decided for the fieldworks. The tidal of those eight days were also lower than 0.5 m. Four days were decided in October and four days were decided in November. The two field sites -- Ha Pak Nai and San Tau, both would go for four times. In the fieldwork, one water sample and two sediment samples were taken in the two field sites respectively. Also, sampling of organisms was conducted after the collection of water sample and sediment samples.

3.2 Water Sample Collection

One water sample was collected for heavy metal analysis in each field site.

Volume of 800 mL of water would collect. Water sample was collected when the tide was not in the lowest.

3.2.1 Date and Time

Eight dates in October and November were selected for water sample collection at each field site, which were 10th, 24th of October and 7th, 21st of November in

2015 would go to Ha Pak Nai for sampling and 11th, 25th of October and 8th,

22nd of November in 2015 would go to San Tau for sampling. No specific of time for water sampling and the time of water sample collection were different in each date because the collection time was according to the tidal changes.

3.2.2 Sampling Sites

Sample site of water sample in the first time of fieldwork was selected randomly in both field site. Then, GPS was recorded for the remaining fieldworks. The remaining fieldworks of the two field sites would use the same sample site as the first time of collection.

3.2.3 On-Site Preparation

Apart from water sample collection for heavy metal analysis, four parameters would collect using multi-prob including temperature, dissolved oxygen, conductivity and pH.

3.3 Sediment samples collection

Two sediment samples were collected for grain size analysis in each field site.

Around 700 g of sediment would collect. Sediment samples were collected after the water sample collection.

3.3.1 Date and Time

The dates for the sediment samples collection were same as the water sample collection. Same as collection of water sample, there was no specific of time for collection and the time of sediment samples collection were different in each date because the sediment samples were conducted in the lowest tide on that date when the sediment was not covered by water.

3.3.2 Sampling Sites

Sample sites of sediment samples in the first time of fieldwork were also selected randomly in both field site and GPS was recorded for the remaining fieldworks. The remaining fieldworks of the two field sites would use the same sample sites as the first time of collection same as water sample collection.

3.3.3 On-site Preparation

Sediment samples were collected the surface sediment, 5 cm of the surface sediment (Tam and Wong, 2000) would collect by using shovel for the grain size analysis.

3.4 Sampling of Organisms

A systematic sampling was used to count the organisms. Two transects would be used for organisms sampling at each field site. Same as waster sample and sediment samples collection, the locations of two transects were selected

17 randomly in the first time of sampling at the two field sites and GPS was recorded for the next field dates. 25 m of transect was used in each sampling. In each transect, a 0.5 m x 0.5 m of quadrat was used for the sampling of organisms. Ten quadrats would place in each transect, sampling would conduct in the separation 2.5 m of the previous quadrat. Transect setting is shown in

Figure 2. There were two main types of organisms which were crabs and snails were counted in this study. The individual number of crabs and snails and the number of species of crabs and snails would counted within the quadrats at both field sites. Sampling of organisms was used for comparison of their assemblages between Ha Pak Nai and San Tau.

Figure 2. Transect setting for the sampling of organisms

3.5 Laboratory Analysis

Two laboratory analysis are focused in this study. One is the heavy metal analysis for the water samples. Another is the grain size analysis for the sediment samples. 18

3.5.1 Grain Size Analysis

The grain size analysis of the sediment samples were tested with the shaker. Six size of sieves including 10 mm, 4 mm, 3 mm, 2 mm, 0.5 mm, 0.25 mm, 0.212 mm and base pan were used in grain size analysis. Before sieving the sediment, there were some pretreatments. Because there were some non-geological materials inside the sediment samples such as wood and snails. The first step was to take away all the materials that were not the silt and sand in each sample.

After taking away all the non-geological materials, put the sample in a large beaker, one beaker for one sample, and wash the sediment samples using tap water. After washing the sediment samples, weighed the tin trays and poured the sample in the tin tray and weighed again. Put all the trays in oven set at 70

℃ for a week. Once two days, shake the trays to ensure even drying across each tray.

After drying, put the selected size of sieves in order, the smallest mesh size

(0.212 mm) on the base pan and the biggest mesh size (10 mm) on the top.

Poured the sample into the 10 mm sieve. Closed the lid and put the stack onto the shaker. Tightened with the belt and shake for 2 minutes. After 2 minutes, poured the samples on each sieve onto a paper and recorded the weight of the

19 samples on each sieve and base pan. Cleaned the sieves and repeated the steps with other sediment samples (Reddy, unknown).

3.5.2 Heavy Metal Concentration in Water

For the analysis of heavy metal concentration in water, HNO3 was added to dilute in a suitable concentration. The suitable concentration for testing cadmium, chromium, lead, arsenic was 1.0 µg/mL while the suitable concentration for testing mercury was 0.10 µg/mL. ICP-MS was used to test the concentration of heavy metal in water sample.

3.6 Calculation and Statistical Analysis

Simpson dominance index was used to calculate the biodiversity index of two study areas in this study:

∑ D = 푛(푛−1) , where D is biodiversity index; n is the total number of 푁(푁−1) organism of a particular species, N is the total number of organisms of all species (Simpson, 1949)

CHAPTER 4 RESULTS

4.1 Physical Parameters in Water

The record of three physical parameters (dissolved oxygen, conductivity and pH) in water in each study area are shown in Appendix 1 and 2.

4.1.1 Dissolved Oxygen Level

Figure 3 shows that the dissolved oxygen varies in each field date. In all of the fieldworks at Ha Pak Nai, the highest dissolved oxygen recorded was 7.5 mg/L and the lowest dissolved oxygen recorded was 5.34 mg/L, with the mean of 6.81 mg/L. At San Tau, the highest dissolved oxygen recorded was 8.04 mg/L and the lowest dissolved oxygen recorded was 5.8 mg/L, with the mean of 7.41 mg/L.

Generally, there was a decreasing trend of dissolved oxygen and increased little in the last field date at Ha Pak Nai while there was an increasing trend of dissolved oxygen and decreased little in the last field date at San Tau.

DISSOLVED OXYGEN LEVEL

PN ST

9 8 7 6 5 4

DO (MG/L) DO 3 2 1 0 10- 11/10/15 24- 25/10/15 7 - 8/11/15 21- 22/11/15 DATE

Figure 3. Dissolved oxygen level at the two study areas during October and

November (PN: Ha Pak Nai; ST: San Tau)

4.1.2 Conductivity

Figure 4 shows that the conductivity varies in each field date. In all of the fieldworks at Ha Pak Nai, the highest conductivity recorded was 41440 µS/cm and the lowest conductivity recorded was 18907 µS/cm, with the mean of

25274.5 µS/cm. At San Tau, the highest conductivity recorded was 45200

µS/cm and the lowest conductivity recorded was 31500 µS/cm, with the mean of 38436 µS/cm.

Generally, the trend of conductivity between Ha Pak Nai and San Tau is similar. Both Ha Pak Nai and San Tau had the highest conductivity at the first week of November.

CONDUCTIVITY

PN ST

50000

40000

30000

20000

10000 CONDUCTIVITY (ΜS/CM) CONDUCTIVITY 0 10- 11/10/15 24- 25/10/15 7 - 8/11/15 21- 22/11/15 DATE

Figure 4. Conductivity at the two study areas during October and November

(PN: Ha Pak Nai; ST: San Tau)

4.1.3 pH Value

Figure 5 shows that the pH value varies in each field date. In all of the fieldworks at Ha Pak Nai, the highest pH value recorded was 8.25 and the lowest pH value recorded was 7.95, with the mean of 8.095. At San Tau, the highest pH value recorded was 8.48 and the lowest pH value recorded was

7.81, with the mean of 8.05.

Similar to the conductivity, the trend of pH value between Ha Pak Nai and San

Tau is similar. Both Ha Pak Nai and San Tau had the highest pH value at the first week of November.

PH VALUE

PN ST

8.5 8.4 8.3 8.2 8.1

PH 8 7.9 7.8 7.7 7.6 10- 11/10/15 24- 25/10/15 7 - 8/11/15 21- 22/11/15 DATE

Figure 5. pH value at the two study areas during October and November (PN:

Ha Pak Nai; ST: San Tau)

4.2 Composition of Grain Size in Sediment

Tables of percentage of gravel, sand and silt of each field date at two study areas are shown in Appendix 3 and 4.

4.2.1 Gravel

Figure 6 shows that the mean percentage of gravel in the sediment samples at the two study areas. Mean percentage of gravel was higher at Ha Pak Nai than at San Tau. The mean percentage of gravel in the sediment was about 7.7% at

Ha Pak Nai and about 3.7% at San Tau.

Gravel 9 8 7 6 5 4

Percentage (%) Percentage 3 2 1 0 PN ST

Figure 6. Mean percentage of gravel in sediment samples at the two study areas (PN: Ha Pak Nai; ST: San Tau)

4.2.2 Sand

Figure 7 shows that the mean percentage of sand in the sediment samples at the two study areas. Mean percentage of sand was higher at San Tau than at

Ha Pak Nai. The mean percentage of sand in the sediment was about 37.6% at

Ha Pak Nai and about 71.1% at San Tau.

Sand 80

30 Percentage (%) Percentage 20

0 PN ST

Figure 7. Mean percentage of sand in sediment samples at the two study areas

(PN: Ha Pak Nai; ST: San Tau)

4.2.3 Silt

Figure 8 shows that the mean percentage of silt in the sediment samples at the two study areas. Mean percentage of silt was higher at Ha Pak Nai than at San

Tau. The mean percentage of silt in the sediment was about 54.8% at Ha Pak

Nai and about 25.1% at San Tau.

Silt 60

Percentage (%) Percentage 20

0 PN ST

Figure 8. Mean percentage of silt in sediment samples at the two study areas

(PN: Ha Pak Nai; ST: San Tau)

4.3 Heavy Metal Concentrations in Water

Five heavy metals including chromium(Cr), arsenic (As), cadmium (Cd), lead

(Pb) and mercury (Hg) were tested from the water sample at the two study areas. The concentration of heavy metals of each water sample in two study areas are shown in Appendix 5 and 6.

4.3.1 Chromium (Cr)

Figure 9 shows that the mean concentration of chromium in water samples at the two study areas. Mean concentration of chromim in water at Ha Pak Nai was higher than at San Tau. The mean concentration of chromium in water was 0.001 mg/L at Ha Pak Nai and 0.0005 mg/L at San Tau.

Chromium (Cr) 0.0012

0.001

0.0008

0.0006

0.0004 Chronmium (mg/L) Chronmium 0.0002

0 PN ST

Figure 9. Mean concentration of chromium in water samples at the two study areas (PN: Ha Pak Nai; ST: San Tau)

4.3.2 Arsenic (As)

Figure 10 shows that the mean concentration of arsenic in water samples at the two study areas. Mean concentration of arsenic in water at San Tau was higher than at Ha Pak Nai. The mean concentration of arsenic in water was 0.00275 mg/L at Ha Pak Nai and 0.003 mg/L at San Tau.

Arsenic (As) 0.00305 0.003 0.00295 0.0029 0.00285 0.0028

Arsenic (mg/L) Arsenic 0.00275 0.0027 0.00265 0.0026 PN ST

Figure 10. Mean concntration of arsenic in water samples at the two study areas (PN: Ha Pak Nai; ST: San Tau)

4.3.3 Cadmium (Cd)

Figure 11 shows that the mean concnetration of cadmium in water samples at the two study areas. Mean concentration of cadmium in water at Ha Pak Nai and San Tau were the same. The mean concentration of cadmium in water was

0.0005 mg/L at Ha Pak Nai and San Tau.

Cadmium (Cd) 0.0006

0.0005

0.0004

0.0003

0.0002 Cadmium (mg/L) Cadmium

0.0001

0 PN ST

Figure 11. Mean concentration of cadmium in water samples at the two study areas (PN: Ha Pak Nai; ST: San Tau)

4.3.4 Lead (Pb)

Figure 12 shows that the mean concentration of lead in water samples at the two study areas. Mean concentration of lead in water at Ha Pak Nai and San

Tau were the same. The mean concentration of lead in water was 0.0005 mg/L at Ha Pak Nai and San Tau.

Lead (Pb) 0.0006

0.0005

0.0004

0.0003

Lead (mg/L)Lead 0.0002

0.0001

0 PN ST

Figure 12. Mean concentration of lead in water samples at the two study areas

(PN: Ha Pak Nai; ST: San Tau)

4.3.5 Mercury (Hg)

Figure 13 shows that the mean concentration of lead in water samples at the two study areas. Mean concentration of lead in water at Ha Pak Nai and San

Tau were the same. The mean concentration of lead in water was 0.000025 mg/L at Ha Pak Nai and San Tau.

Mercury (Hg) 0.00003

0.000025

0.00002

0.000015

0.00001 Mercury (mg/L) Mercury

0.000005

0 PN ST

Figure 13. Mean concentration of mercury in water samples at the two study areas (PN: Ha Pak Nai; ST: San Tau)

4.4 Abundance of Species

The whole data of the number of individual and species recorded in fieldwork were shown in Appendix 7 to 10.

4.4.1 Abundance of Crabs

Table 1 (a) shows that the species of crabs and the number of individual of that crabs found at Ha Pak Nai and San Tau. The table of sampling of crabs in the transect and quadrat in all fieldworks are shown in the Appendix. There were three species found in Ha Pak Nai including Metaplax longipes, Philyra carinata and Uca borealis. Uca borealis was the highest abundance found in

Ha Pak Nai than the other others. At San Tau, only one species of crab found which was Clibanarius longitarsus. Both the number of species and the total

32 number of individual of crabs were higher at Ha Pak Nai than at San Tau.

4.4.2 Abundance of Snails

Table 1 (b) shows that the species of snails and the number of individual of that snail found at Ha Pak Nai and San Tau. The table of sampling of snails in the transect and quadrat in all fieldworks are also shown in Appendix. Only one species of snail found at Ha Pak Nai which was Cerithidea cingulata.

There were five species of snails found at San Tau including Cerithidea cingulata, Cerithidea djadjariensis, Clithon oualaniensis, Lunella coronata and Batillaria multiformis. Batillaria multiformis had the highest abundance compare with other species in San Tau.

4.4.3 Biodiversity Index

Table 2 represents the biodiversity index of crabs and snails’ species in Ha Pak

Nai and San Tau by using simpson’s index. The biodiversity index of Ha Pak

Nai was 0.76 while biodiversity index of San Tau was 0.21. The biodiversity index of San Tau was lower than Ha Pak Nai.

Table 1 (a) & (b). Species and total number of individual of crabs and snails at Ha Pak Nai and San Tau

Table 1 (a). Species and total number of individual of crabs in study areas

Study area Species name Number of individual Ha Pak Nai Metaplax longipes 4 Philyra carinata 26 Uca borealis 342 San Tau Clibanarius longitarsus 87

Table 1 (b). Species and total number of individual of snails in study areas

Study area Species name Number of individual Ha Pak Nai Cerithidea cingulata 21 San Tau Cerithidea cingulata 1293 Cerithidea djadjariensis 1265 Clithon oualaniensis 457 Lunella coronata 928 Batillaria multiformis 1422

Table 2. Simpson’s Index of Ha Pak Nai and San Tau

Study area Simpson’s Index Ha Pak Nai 0.76 San Tau 0.21

CHAPTER 5 DISCUSSION

Abundance of crabs and snails Total number of individual and species of crabs counted more at Ha Pak Nai than at San Tau. Uca spp. was the dominant species of crab found at Ha Pak Nai in the four field dates. Although Ha Pak Nai is near

Shenzhen and receives pollutants discharging from Shenzhen, the sewage did not stress the abundance of crabs. Same finding in East Africa was represented in the research by Cannicci et al. (2009), higher biomass of crabs founded in peri-urban sites which received urban wastewater than non-urban sites and the abundance of crabs was increased in peri-urban sites. The research was also found that the dominance of Uca spp. was increasing in the sewage dumping areas. There were two reasons of the large number of fiddler crab at Ha Pak Nai.

The first reason was the characteristics of sediment, which could influence the distribution of crabs (Cannicci et al., 2009). Uca spp. of the fiddler crabs are mainly existing in muddy sediment. Smaller Uca borealis occurred sediment s with fine particles (Shin et al., 2004). The second reason was the nutrient concentration of the sewage discharging from Shenzhen City and river.

Increasing the concentration could increase the bacteria and benthic diatoms and the fiddler crabs would feed them. Discharging suitable sewage could stimulate the growth of benthic organisms (Penha-Lopes et al., 2009).

Moreover, some crabs such as sesarmid crabs had a high tolerance to the sewage (Cannicci et al., 2009) and heavy metal could influence the distribution of fiddler crabs (Mokhtari et al., 2015). Crustaceans had the detoxification storage mechanisms in some organs by using physiological and biochemical to protect the tissues and other organs from the harmful effects of the metals

(Marsden and Rainbow, 2004). But sesarmid crabs did not discover in the sampling sites at both Ha Pak Nai and San Tau.

Total number of individual and species of snails counted more at San Tau than at Ha Pak Nai. Negative relationship between heavy metal concentration in sediment and the number of gastropod and number of gastropod species

Indonesia was found by Amin et al. (2009). It was meaning that when metals concentration increased, the number of gastropod decreased. If the snails exposure to the toxic environment in a long period, mortality would increase

(Ramakritinan, Chandurvelan & Kumaraguru, 2012). Moreover, biodiversity index could reflect the pollution status. Smaller number of Simpson Index represents higher species diversity. High species diversity represented low impact or unpolluted status. Simpson Index in San Tau was lower showed that

San Tau had higher species diversity than Ha Pak Nai. Higher heavy metal contamination at Ha Pak Nai than at San Tau researched by Zhou et al. (2007).

Because heavy metals contamination in sediment was higher at Ha Pak Nai, the abundance and the number of species was lower than San Tau. Gastropod had contact with sediments directly. Also, they were immobile and had fewer capacity to escape the impacts caused by pollutants. On the other hand, Cu and

Zn were the most harmful metals to the population of gastropod and contaminated sediments which had high toxicity would cause the death of gastropod.

The findings of the biomass of crabs and snails were same as the hypothesis.

Concentration of heavy metal might not affect the number of crabs while affect the number of snails.

Sediment grain size The mean percentage of silt in the sediment at Ha Pak Nai was more than at San Tau. Fine particles are the major element in sediment at

Ha Pak Nai while sand is the major element in sediment at San Tau. Particle size of the sediment is one of the methods to assess the metal contamination in aquatic systems. Because the sampling sites at Ha Pak Nai and San Tau were also located on intertidal mudflat, these areas would be covered by water when there were high tide. Many metals were deposited into sediment under the water

(Chaiyara et al., 2013). On the other hand, many studies found that higher contamination of heavy metals occurred in the sediment which had more clay

37 and fine particle in both mudflat and mangrove. For example, Tam and Wong

(2000) stated that heavy metals were easier to bond in clay and silt fraction of sediment than sand fraction of sediment. Heavy metal contamination is occurred in sediment with high percentage of silt and clay because the fractions of these types of sediments are more chemically active than larger sediment

(Rahmanpour et al., 2014). Moreover, heavy metals will be removed from water and transported to the sediment rapidly (Rahmanpour et al., 2014) and absorbed by clay and silt.

Zhou et al. (2007) were using the GIS to find out the spatial distribution of heavy metals including Zn, Pb, Cd, Cu, V and Fe of the marine sediments in

Hong Kong. Results showed that the concentration of these heavy metals were higher at Ha Pak Nai than at San Tau. The findings studied by Zhou et al. (2007) is shown in Figure 14.

The percentage of silt in sediment was larger at Ha Pak Nai found in this study same as to the hypothesis. Because fine particles have a potential to absorb heavy metals (Rahmanpour et al., 2014) and concentration of metals are increasing from sand to silt (Tam and Wong, 2000). It is estimated that metals contamination in sediment was higher at Ha Pak Nai than at San Tau. Although concentration of heavy metals in sediment did not conduct in this study, higher

38 metals contamination in sediment at Ha Pak Nai was showed in the research by

Zhou et al. (2007) and have this inference.

Figure 14. Spatial distribution of heavy metal in marine sediment in Hong

Kong

(Source: Zhou et al., 2007)

Heavy metals in water The mean concentration of each heavy metal in water was similar at Ha Pak Nai and San Tau. Also, the findings were low and not significant. The findings were different with the hypothesis. There are two possible reasons of the low metal concentration in water. The first reason is the variation of daily and seasonal fluctuations (Lau and Chu, 1999) such as tidal and monsoon. The water sampling sites of the two study areas were near the sea

39 also, the metal levels would be decreased because of the seawater. Seawater had a lower metal content than fresh water and had a dilution effect (Lau and Chu,

1999). On the other hand, the magnitude of the concentration of contaminants was lower in water than in sediment (Fernandes and Nayak, 2012). In the study conducted by Chaiyara et al. (2013), they found that the concentration of heavy metals including cadmium, Copper, Lead and Zinc in water in the three rivers of the upper Gulf of Thailand were lower than in the sediment. The statement stated by Fernandes and Nayak (2012) supported the finding in this study.

Furthermore, the possible reason of the concentration of heavy metal in water was similar at both Ha Pak Nai and San Tau might be the concentration of heavy metals in water at San Tau were increasing in the recent year.

Construction of Hong Kong-Zhuhai-Macao Bridge aims to connect Hong Kong,

Zhuhai and Macao. Hong Kong Link Road was near the mudflat at San Tau. A layout plan of Hong Kong Link Road is shown in Appendix 11. The construction of Hong Kong Link Road was started in 2012 (Highways

Department, 2016). There was a news about the illegal discharge of sewage and construction materials during the construction works in 2015 (Apple, 2015).

Those sewage might contain toxic pollutants such as heavy metals. Moreover, dredging of seabed would conduct during the construction. Dredging would flip

40 the sediment, suspended sediment would increase and the contaminants would release to the water (Lau and Chu, 1999), so causing water pollution and contamination. Thus, the construction of Hong Kong Link Road may cause water pollution and contamination and increase the concentration of heavy metals in the water near San Tau.

Although the findings of heavy metals in water were not significant and different with the expectation. The findings showed that heavy metal contamination in water was not serious at both Ha Pak Nai and San Tau during

October and November. Dilution effect by the seawater would affect the concentration of heavy metal and the construction of Hong Kong Link Road may increase the concentration of heavy metals in water at San Tau in the future.

Relationship between water parameters and heavy metals Although the results of the correlation of water parameters and heavy metal were not comparable, the physical parameters of water were having effect on the concentration of heavy metal. In overall data, dissolved oxygen in San Tau were higher than in Ha Pak Nai except the first field date. The amount of dissolved oxygen would affect the metals release. From the experiment done by Atkinson et al. (2007), releasing of lead from the sediment was greater in low dissolved

41 oxygen. They found that the concentration of dissolved lead remained less than

5 µg L-1 in high and middle dissolved oxygen while remained a mean of 50 µg

L-1 in low dissolved oxygen. This observation was explained by slower rate of oxidative precipitation and removing of Fe(II) and Mn(II) ions since they diffused by the sediment-water interface (Atkinson et al., 2007). The mean conductivity in San Tau was higher than in Ha Pak Nai. Electrical conductivity increased when discharging of industrial wastes (Yalcin et al., 2008). High conductivity in San Tau might cause by the sewage and pollutants from the construction of Hong Kong-Zhuhai-Macao Bridge while the result of the conductivity in Ha Pak Nai might cause by the sewage discharge from Pearl

River and Shenzhen River. The mean of pH value in Ha Pak Nai and San Tau were similar (Figure), both study areas had mean of pH value of 8. Kar et al.

(2008) investigated that no significant correlation between concentration of heavy metals and the pH value of water.

Organic matter in sediment Organic content in sediment could affect the heavy metal contamination in sediment. Organic matter includes nitrogen, phosphorus and organic carbon. Although organic content in sediment did not test in this study, Environmental Protection Department (EPD) had the data of different parameters of marine sediment. Ha Pak Nai is located in Deep Bay Water

Control Zone while San Tau is located in North Western Water Control Zone.

The nearest monitoring station of Ha Pak Nai is DS3 and nearest monitoring station of San Tau is NS6. The data of concentration of different metals, ammonia nitrogen and total phosphorus in monitoring station DS3 and NS6 in

Table 3. From the table, the amount of ammonia nitrogen in monitoring station

NS6 was lower than DS3 while total phosphorus m was higher than DS3. In overall, the organic content in monitoring station NS6 was higher than DS3.

Also, concentration of those heavy metal in monitoring station NS6 were higher than DS6. It might due to the high organic content. Higher organic matter content in sediment would absorb heavy metal easily. Deposition and remobilization of trace metals occurred in the sediment which abundant in organic matter (Fernandes and Nayak, 2012). Some of the metals such as copper, lead and cadmium have high affinity with organic matter (Ahn et al.,

1994). It means that sediment with abundant organic matter will absorb more

Cu, Pb and Cd.

In the past, the organic content (ammonia nitrogen and phosphorus) in monitoring station DS3 near Ha Pak Nai were much higher than in 2014 and higher than the monitoring station NS6. In recent year, the pollution situation was improved because Shenzhen government collaborate with Hong Kong

43 government to reduce the pollution and reduce the operation of pig farms in

2005 to 2008 (Environmental Protection Department, 2014).

Table 3. Data of different parameters in monitoring station DS3 and NS6

As Cd Cr Cu Fe Pb DS3 8.55 0.05 24.5 24 35500 26 NS6 15 0.15 36 30.5 38000 39

Hg Ni V Zn N P DS3 0.085 15.5 30 101 6 235 NS6 0.12 21 49.5 100 3.47 250

*Units for both metals, N and P are mg/kg

(Source: Environmental Protection Department, 2014)

Source of heavy metal Sources of heavy metal can be come from both natural and anthropogenic activities. Cu, Cr and Zn were coming from anthropogenic impacts; Al, Ba, Mn, V and Fe were coming from natural sources; Cd, Hg, Ni and Pb were coming from anthropogenic activities or rock materials (Zhou et al.,

2007). Both Ha Pak Nai and San Tau are located at the western part of Hong

Kong. The pollutants of San Tau were mainly from local discharges and surface run-off from North Lantau (Environmental Protection Department, 2014).

Apart from local discharges, the western part of Hong Kong is receiving discharges from Shenzhen River (Environmental Protection Department, 2014).

More anthropogenic impacts occurred in Ha Pak Nai than San Tau (Zhou et al.,

2007) because Ha Pak Nai is nearer to the Shenzhen River. Due to the rapid 44 economic development in Shenzhen, many factories were built to increase the industrial activities. Sewage from factories would discharge into river and flew into Hong Kong’s water zone through Shenzhen River and Pearl River.

Management and sustainable use of mudflat in Hong Kong Even heavy metal contamination do not have the impact on the ecosystem immediately, heavy metal can stay in the sediment in the long time and will affect the communities and ecosystem. Although San Tau was listed as SSSI, there was no specific protection strategies to these SSSIs in Hong Kong (Chen, 2003). In EU, there were different strategies to strengthen the protection of SSSIs. For example, establishment of the Countryside and Rights of Way Act (Foster et al., 2014). In the case of Hong Kong, government should establish different strategies to protect the SSSIs. Also, one of the study areas -- Ha Pak Nai, should also list into SSSI. Moreover, to reduce the pollutants into water and sediment, sewage should be treated first and monitor the illegal discharge.

Several improvements were discovered in this study. Results found from this study were not significant because the sample numbers were not much enough.

The limited time and storage materials resulted fieldworks were conducted four times in each study areas. On the other hand, concentration of heavy metal and

45 organic content in sediment did not cover in this study because of the limited laboratory equipment.

In this study, crabs and snails were the two organisms that studied in terms of biological and ecological aspects. Sampling could conduct more if there was enough time and benthic communities can be studied in the further study to have more comprehensive study on mudflat ecosystem.

Those parameters that did not study are important to investigate the heavy metal contamination and will consist in the further study.

CHAPTER 6 CONCLUSION

Three physical parameters (dissolved oxygen, conductivity and pH) of water, grain size analysis of sediment, heavy metal in water and biomass of crabs and snails were studied. A better understanding of various factors could influence the concentration of heavy metal in water and sediment, the effect of heavy metal to the distribution of crabs and snails and different sources of heavy metals were investigated from this study.

No relationship amongst the physical parameters of water and heavy metal concentrations could be investigated in this study. But the amount of electrical conductivity could show the level of waste discharge while the level of dissolved oxygen could affect the release and remain of metal ions. There was only no relationship between the pH value of water and concentration of heavy metal.

Concentration of heavy metals in water were not high found in this study as there were various factors to influence the heavy metal concentration. However, the construction of Hong Kong Link Road might increase the heavy metal concentrations in water.

Grain size of the sediment and organic matter content were the major factors to affect the adsorption of heavy metal. Sediment especially with more fine

47 particles and high organic matter content would adsorb more heavy metals due to the surface area and the affinity.

The level of heavy metal contamination would affect the communities and ecosystem of mudflat in long term. Many organisms could be the bioindicators to reflect the heavy metal contamination. The community of crabs might not be changed due to their detoxification mechanisms and their tolerance. However, the level of heavy metal contamination would affect the community of snails because they had a direct contact with sediments.

Sources of heavy metal were vary in different mudflat, could be anthropogenic and natural. Anthropogenic impacts were the major source of heavy metal in this decade due to the rapid development like the two study areas in this study.

Organisms are having many connections between sediment and other organisms and have a chain effect. Government should take an active role to have a better management and reduce the releasing of toxic environmental pollutants into mudflat which aims to have a sustainable use of mudflat.

Table of physical parameters in water recorded Ha Pak in Nai water parameters in physical of Table

Appendix 1

San Tau San

Table of physical parameters in water recorded in water parameters in physical of Table

Appendix 2.

diment in Ha Pak Nai Pak Ha dimentin

Table of composition of grain size of se of size grain of ofcomposition Table

Appendix

Table of composition of grain size of sediment of sizeTau San in grain of ofcomposition Table

Appendix 52

Concentration of heavy metal in water sample of Ha Pak Nai Pak Ha sample of water in metal heavy of Concentration

5. Appendix is mg/L. concentration metal heavy *Unitof

ter sample of San sampleTau of ter

Concentration of heavy metal in wa in metal heavy of Concentration

6. Appendix is mg/L. concentration metal heavy *Unitof

Table of number of crabs counted in Ha Pak Nai in Pak Ha counted ofcrabs of number Table

Appendix

Table of number of crabs counted in Tau San counted ofcrabs of number Table

Appendix

Table of number of snails counted in Ha Pak Nai Pak Ha in ofsnails of number counted Table

Appendix

Table of number of snails counted in San Tau San in snails of number of counted Table

10.

Appendix 58

Layout plan of Hong Kong LinkRoad Kong ofHong plan Layout

Appendix 11. 11. Appendix

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(榮譽)學位 課程 Bachelor of Social Sciences (Hons) in Environment and Resources Management

(榮譽)學位課程 Bachelor of Social Sciences (Hons) in Environment and Resources Management