The Potential of in the Treatment of Shrimp Aquaculture Effluent on the Eastern Coast of Thailand

7 Nina Fancy B. Sc.(Horn), Queen's University, 1999

A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCE

in the Department of Geography

O Nina Fancy, 2004

University of Victoria

AII rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author. Supervisor: Dr. Mark Flaherty

ABSTRACT

This thesis examines the potential of low-cost, low-maintenance mangroves in the

treatment of nutrient-rich effluent originating from a shnmp fmon the coast of

Thailand's Chanthaburi province. The objective of this thesis is to identify the

environmental impact of shnmp aquaculture effluent and to determine if

can be used as effective biofiltration areas to remove significant quantities of

, ammonia and nitrite from shrimp wastewater. The study mangrove was found

to remove an average of 44.5% of nitrate, 46.6% of ammonia and 59.0% of nitrite

from shrimp effluent. The ratio of mangrove treatment area to shrimp fmrequired

to adequately treat daily effluxes of wastewater from shrimp fmswas calculated to

. be 1: 14. This ratio is significantly less spatially demanding than ratios calculated by

.-: P 0 previous researchers and reveals the potential of mangroves to be used as large-scale

areas in shrimp-producing nations. TABLE OF CONTENTS .. ABSTRACT ...... 11 ... TABLE OF CONTENTS ...... UI LIST OF TABLES...... vi .. LIST OF FIGURES ...... WI ... ACKNOWLEDGEMENTS ...... WIN CHAPTER 1 ...... 1 INTRODUCTION ...... 1 1.1 NATUREOF THE PROBLEM ...... 1 1.2 PURPOSE OF THE STUDY...... 4 1.3 THESIS OUTLINE ...... -5 CHAPTER 2 ...... 7 BACKGROUND...... 7 2.1 GLOBALAQUACULTURE TRENDS ...... 7 2.2.1 Geographical ShiJi...... 13 2.2.2System %iJi ...... 16 2.3 MANAGEMENTPRACTICES ...... 17 2.3.1 Site Selection...... 17 2.3.2Pond Preparation and Stocking ...... 19 2.3.3 Feeding ...... 20 2.3.4 Aeration and Water Exchange ...... 22 2.3.5 Harvesting ...... 23 2.4 ENVIRONMENTALIMPACTS ...... 23 2.4.1 Land Requirements ...... 23 2.4.2 Water Supplies ...... 26 2.4.3 Chemical Discharge ...... 26 2.4.4 Organic Outputs ...... 27 2.5 BESTMANAGEMENT PRACTICES ...... 30 2.5.1 Planning and Management ...... 31 2.5.2 Physical Techniques...... 31 2.5.3 Feed Related Practices...... 33 2.5.4 Policy Options ...... 34 2.5.5 Biological Practices ...... 35 2.6 SUMMARY...... 38 CHAPTER 3 ...... 40 MANGROVE ...... 40 3.1 DEFINITION...... 40 3.2 GEOGRAPHICALDISTRIBUTION ...... 41 3.3 BIOL~GYOF MANGROVES...... 42 3.3.1 Anatomy ...... 42 3.3.2 Environmental Adaptations ...... 44 3.3.3Nutrient Dynamics ...... 47 3.3.4Associated Hora and Fauna ...... 49 3.3.5 Natural and Anthropogenic Impacts ...... 52 3.4 USESOF MANGROVES...... 54 3.4.1 Local Subsistence...... 54 3.4.2 Coastal Function ...... 55 3.4.3 Tourism...... -56 3.4.4 Wastewater Filtration ...... 56 3.5 CONSTRUCTED AND MODIFIED MANGROVES ...... 60 3.5.1 Design...... 60 3.5.2 Can Mangroves be Constructed?A Question of Environmental Feasibility ...... 61 3.5.3 Economic Feasibility...... 64 3.6 SvMMARY ...... 66 CHAP'lXR 4 ...... 67 STUDY AREA AND METHODOLOGY ...... 67 4.1 REGIONAL CONTEXT...... 67 4.2 FARMAREA ...... -70 4.3 MANGROVEDESCRIPTION ...... 74 4.4 EXPERTMENTALDESIGN ...... 76 4.5 DATACOLLECTION OVERVIEW ...... 77 4.5.1 Pre-TreatPnent Samples: Mondays ...... 77 4.5.2 Post-Treatment Samples: Wednesdays ...... 78 4.6 INSTRUMENTATION AND LABORATORYANALYSES ...... 79 4.7 LIMITATIONS...... 80 CHAPTER 5 ...... 82 RESULTS AND DISCUSSION ...... 82 5.1 SAMPLEID~CATION ...... 82 5.2 PH AND RAWFALLDATA...... 83 5.3 BOD ANALYSIS...... 86 5.4 PJUSE ANALYSIS ...... 89 5.5 PRE-TREATMENT DATA:EFFLUENT SAMPLES ...... -92 5.6 PRE-TREATMENT DATA:MANGROVE ...... 97 5.7 POST-TREATMENTDATA ...... 98 5.8 COMPARISONOF PRE-TREATMENT AND POST-~XI~ATMENTNITROGEN DATA.. 103 5.8.1 Nitrate...... 104 5.8.2Ammonia ...... I07 5.8.3 Nitrite ...... 108 5.9 PERCENTREMOVAL OF NUTRIENTS...... 109 5.10 NITROGENLOADING OF THE COASTOF CHANTHABURI...... 111 5.1 1 L~ATIONSAND FUTURE RESEARCHNEEDS ...... 113 5.12 MANAGEMENTIMPLICATIONS ...... 116 5.12.1.Mangrove to Shrimp Ratio ...... 116 5.12.2Recirculation ...... I21 5.12.3 Global Impacts ...... 122 5.13 SVMMARY...... 123 CHAPTER 6 ...... 125 CONCLUSION ...... 125 6.1 SUMMARY ...... 125 6.2 MAJORRESEARCH FINDINGS ...... 126 6.3 FUTURE RESEARCHDIRECTIONS ...... 127 REFERENCES ...... 129 LIST OF TABLES

Table 2.1 : Comparison of extensive, semi-intensive and intensive shrimp farms in Thailand...... , ...... 18 Table 2.2: Common chemical and biological compounds used in intensive shrimp culture in Thailand...... 2 1 Table 2.3: Optimum water quality parameters for culture of P. monodon...... 24 Table 2.4: Concentrations of key nutrients in shrimp farm effluent from an intensively managed shrimp pond in Thailand...... 29 Table 2.5: Regulations for shrimp farming issued by the Thai government, November 1991...... -36 Table 3.1 : Examples of mangrove loss in Asia and Oceania...... 43 Table 4.1 : Land use practices along the coast of Chanthaburi in 1991...... 70 Table 5.1: Mann-Whitney tests to detect differences between nitrate, ammonia and nitrite concentrations in the 2 distinct phases ...... 91 Table 5.2: Pretreatment mean concentrations of nitrate, ammonia and nitrite in effluent...... -93 Table 5.3: Mean concentrations of nitrate, ammonia and nitrite during weeks 1-4 and weeks 5-8...... 93 Table 5.4: Mann-Whitney test to detect if differences in nitrate, nitrite and ammonia concentrations exist between weeks 1-4 and 5-8...... 93 Table 5.5: Comparison of mean nitrate, ammonia and nitrite concentrations in eMuent in this study (averaged over 8 weeks)...... 96 Table 5.6: Post-treatment mean concentrations of nitrate, ammonia and nitrite in the mangrove...... -100 Table 5.7: Concentration of nitrate, ammonia and nitrite in well samples...... lo0 Table 5.8: Comparison of pre-treatment values of nitrate, ammonia and nitrite compared to the upper bound of the 95% confidence interval of post-treatment values...... 106 vii

LIST OF FIGURES

Figure 2.1: Aquaculture production of shrimp (by weight) in 1998 ...... 10 Figure 2.2. Aquaculture production (by weight) of P.monodon in Thailand ...... 15 Figure 3.1. Photo of Avicennia marina pneumatophores...... 46 Figure 3.2. Simplified nitrogen cycle in mangrove ecosystems...... SO Figure 4.1 : Map of Chanthaburi with approximate location of the study site...... 68 Figure 4.2. Average monthly temperature in Chanthaburi, Thailand ...... 69 Figure 4.3. Average monthly rainfall in Chanthaburi, Thailand ...... 69 Figure 4.4. Layout of the shrimp farm and mangrove study site...... 72 Figure 4.5: Magnified view of the modified mangrove area with approximate location of the submersible pump ...... 75 Figure 5.1. Field schedule with sample week and day identification ...... 84 Figure 5.2. pH values for pre and post-treatment samples ...... 85 Figure 5.3. BOD2 data for pre-treatment effluent samples ...... 87 Figure 5.4: Residual Dissolved Oxygen concentration after 2-day incubation period ...... 87 Figure 5.5. Average nitrate concentrations for effluent and mangrove samples ...... 99 Figure 5.6. Average ammonia concentrations for effluent and mangrove samples ....99 Figure 5.7. Average nitrite concentrations for effluent and mangrove samples ...... 99 Figure 5.8: Concentration values for all pre-treatment samples - plotted in ascending order...... -105 Figure 5.9: Percent of nitrate, ammonia and nitrite removed from effluent by the treatment mangrove throughout the field season ...... 110 ... Vlll

ACKNOWLEDGEMENTS

There are a number of people I would like to thank for making this research possible. Thank you to CIDA for providing the funding for the field research portion of this thesis. My warmest thanks also goes to my supervisor, Dr. Mark Flaherty whose support throughout this degree has been invaluable. To my committee, your knowledge and insight enabled me to delve further into my results to uncover the true value of my research.

There are a few people without whom both my sanity and smile would have been lost long ago. Michey, your endless laughter, your overwhelming understanding of all my quirks, your cleverness and your adoption into the Fancy Family has made you the better halfmanx I never thought I'd find. Without you Operation Man-Grove and

Operation My-Probe would have been a disastra rather than a pleasure. I can't thank you enough for getting me through this! Krissy - you always know how to make the whole world seem right again, even when I don't know whaaahappened and the walskis crumble, thanks sweets! Curls, ahhh, sweet Curls, the autumn leaves blow in the wind and I wonder what we all would have done without the brains of the operation! Billy, my friend through thick and thm, armed with bevvies and a huge smile at every turn of life - cheers to the next chapter. And to J-cks, my muse for everything un-academic and my reminder that magic truly exists. To my family - no words exist for the thanks I'd like to express. You have all been my rock when I wavered in the wind, you've shown me the paths and walked beside me as I choose my way, even when I make wrong turns. I thank you not just for your support throughout this degree, but for your unfaltering knowledge, wisdom and love. Thanks for always believing in me and making me realize I can move mountains - I just have to put a little heart into it! CHAPTER 1

INTRODUCTION

1.1 Nature of the Problem

Aquaculture has traditionally been viewed as a low-impact technique for rearing aquatic species with little alteration to their natural environments (Csavas 1993). The ever-increasing demand for aquatic protein on international markets, coupled with declining global finfish and shellfish stocks, however, has transformed aquaculture from a low-intensity farming practice, capable of sustaining small rural communities, into a thriving industry contributing over 27% to world fisheries production ( FA0

2002). The economic success of the recent boom in aquaculture has brought much needed foreign exchange and employment opportunities into previously impoverished areas (Flaherty and Kamajanakesom 1995). Unfortunately, as with many industries that expand at such a high rate, this so-called "Blue Revolution" does not come without some negative political, social and, of most concern, environmental repercussions (Moss et al. 2001).

Yields obtained from low-impact, extensive practices are minimal and farm expansion is neither spatially nor financially feasible (Hopkins et al. 1995b, Nunes and Parsons 1999). In order to increase production, given land scarcity and monetary constraints, intensive high-input farming techniques were developed. However, the degree of nahual system manipulation necessary for intensively rearing aquatic species renders this farming technique unsuitable for many animals sensitive to environmental fluctuations (Folke and Kautsky 1992, Boyd 2001). Of the aquatic species harvested for human consumption, shrimp appear to be the most resilient to variations in environmental conditions and are also a highly profitable commodity, making them one of the most commonly intensively farmed aquatic animals (FA0

2002).

The widespread adoption of intensive shrimp farming has provided financial benefits to numerous communities. However, when environmental degradation is considered, the true costs of such high input practices are generally much greater than their monetary benefits (Folke and Kautsky 1992, Naylor et aZ. 2000). The increased popularity of intensive shrimp aquaculture, along with a lack of environmental regulations in most of the producer nations, allowed for the establishment of high input fmsadjacent to sensitive tropical coastlines and estuarine waters (De Silva

1998). Although many of the effects of intensive practices were initially unknown, the environmental impacts of shrimp farming have since been extensively researched and include mangrove destruction, the introduction of exotic species and land salinisation as common side-effects of these techniques (Pbz-Osuna 2000, Dierberg and Kiattisimkul 1996). These impacts all degrade the ecological integrity of surrounding ecosystems to varying degrees. The most serious of these result from the large effluxes of untreated nutrient-rich waters released into neighbouring waters

(Dierberg and Kiattisimkul 1996).

Shrimp farm effluent contains high concentrations of organic compounds containing nitrogen and phosphorus (Funge-Smith and Briggs 1998). The continuous draining of such eutrophic waste into surrounding irrigation canals and coastal waters is extremely handid to the health of proximal ecosystems. of receiving waters is of primary concern where shrimp farms are densely situated along coastlines that serve as nursery and breeding grounds for numerous marine species.

This is most prevalent in Thailand, the largest producer of farm-reared black tiger shrimp (Penaeus monodon) in the world (Kongkeo 1994, FA0 2002). The environmental effects of the unmonitored disposal of organically rich effluent into coastal regions of Thailand has recently received widespread attention (Funge-

Smith and Briggs 1998). The excessive discharge of polluting effluent onto

Thailand's coastlines has resulted in toxic algal blooms and anoxic waters unable to sustain healthy species assemblages leading to a detrimental decrease in floral and faunal diversity (Paez-Osuna 2001).

The large-scale impacts of coastal eutrophication are predicted to reach all levels of the thereby disrupting the dynamics of many aquatic and terrestrial ecosystems (Paez-Osuna 2001). The gravity of the situation has resulted in the creation of environmental regulations aimed at increasing the quality of aquaculture effluent as well as financial penalties for farmers not adhering to healthy effluent standards (Kongkeo 1997). Unfortunately, these attempts to improve effluent quantity and quality have been unsuccessll thereby revealing the need for research focusing on biological treatment of shrimp fmwastewater.

Studies have been conducted exploring the potential use of bivalves, seaweed and other aquatic flora and fauna in reducing the harmful impacts of shrimp effluent (e.g.

Macintosh and Phillips 1992b; Jones et al. 2001). Although promising results have been obtained from such research, these biological treatments are often seen as practical solutions only for small subsistence aquaculture farms. Large-scale operations require extremely efficient and rapid nutrient cycling areas such as those of wetlands. Until recently, little attention was given to wastewater treatment

(Redding et al. 1997). However, the employment of constructed wetland systems for the treatment of eutrophic waste has received tremendous support owing to the high nutrient assimilative capacities of many wetlands as well as the minimal financial and labour inputs required to maintain these areas (Schwartz and Boyd 1995, Wong et al. 1997). The wastewater treatment capacities of natural and constructed freshwater wetlands have been examined with respect to industrial and agricultural wastes as well as domestic sewage, but little research has been conducted on the potential of mangroves in the treatment of saline and brackish aquaculture effluent (Schwartz and

Boyd 1995).

Mangroves are renowned for their efficient nutrient cycling dynamics and have the ability to transform leaf-litter and other organic matter influxes into biologically available forms imperative for the growth and survival of a myriad of aquatic and intertidal species (Ellison 2002, Jennerjahn and Ittekkot 2002). Pilot studies examining the potential of mangroves in the treatment of eutrophic effluent have produced encouraging results, but further research is required to determine the specific benefits of mangrove biofiltration (Rivera-Monroy et al. 1999, Tilley et al. 2002).

Low-impact, inexpensive treatment of aquaculture effluent is of vital concern as more nations throughout the world adopt intensive shrimp aquaculture practices and attempt to reap their financial benefits. Environmentally sustainable effluent treatment systems may be the only solution to ensuring a healthy future for many of the world's coastal regions.

1.2 Purpose of the Study

The purpose of this thesis is to investigate the efficiency of modified mangroves in the treatment of aquaculture effluent. This is accomplished through an experiment in which effluent concentrations of ammonia, nitrate and nitrite are measured before and after exposure to a modified mangrove. The specific objectives of this study are: To review recent trends in shrimp aquaculture so as to identifj the main

environmental impacts of farming practices, and to document the need for

effluent treatments

To investigate the potential of natural, constructed and modified mangroves as

effluent filtration areas, with focus on their nutrient assimilative capacities

To determine if one modified mangrove can effectively reduce BOD,

ammonia, nitrate and nitrite concentrations in effluent originating from one

shrimp farm off the coast of Chanthaburi province in Thailand

To quantify the amount protein one modified mangrove can process into

ammonia over a 48-hour period

To quantify the ratio of mangrove to shrimp pond required to effectively treat

effluent

To determine the average nitrogen loading along the coast of Chanthaburi

originating from shrimp farm effluent and the number of hectares of mangrove

required to treat efnuent in this region

1.3 Thesis Outline

The thesis has seven chapters. Chapter 2 provides background information on shrimp aquaculture outlining fanning practices in Thailand and their negative environmental impacts. A review of best management practices that have attempted to reduce the harmful effects of shrimp aquaculture is presented and the need for more sustainable effluent treatment is identified. Chapter 3 provides a synopsis of general mangrove ecology and investigates the potential of mangroves as wastewater filters.

The economic and environmental costs and benefits of natural and constructed mangroves as biofilters are assessed and modified mangroves are identified as feasible effluent treatment areas. Chapter 4 gives a description of the study site and the procedures followed throughout the duration of the field component. Methods of data analysis and limitations of the research are also outlined. The results of the experiment are presented in Chapter 5 with focus on ammonia, nitrate and nitrite. The local and regional implications of the findings are discussed in Chapter 6. Chapter 7 summarises important conclusions, addresses issues of feasibility and identifies future research needs. CHAPTER 2

BACKGROUND

This chapter provides a broad overview of global aquaculture trends and then focuses on the development of shrimp farming in Thailand. The management practices of intensive shrimp farming are discussed along with the environmental impacts of such techniques and current attempts at minimising these eff'ects. The need for hrther research exploring environmentally friendly solutions is expressed and constructed mangroves are introduced as one possible option.

2.1 Global Aquaculture Trends

Throughout history rural peoples have relied on aquatic species for both their nutrition and livelihoods, depending on wild catch and extensive aquaculture practices to meet their needs. Today, the FA0 (2000) estimates that aquatic species supply over one billion people with their primary source of protein, providing 16% of the animal protein consumed globally. In addition to their nutritional value, and aquatic invertebrates are also economically and socially important, trading at levels of approximately US $50 billion per year and providing income to over 230 million people (FA0 2000). Although most of the benefits from aquatic food sources are gained from wild capture marine fisheries, the demand for aquatic protein has far exceeded the sustainable yields available from natural waters. Exploitative harvesting has led to a severe depletion of wild stocks and has created a niche for aquaculture to supply the ever-growing need for aquatic species (Phillips and Macintosh 1996).

Aquaculture is differentiated from wild catch fisheries in that stocks are owned and the production cycle of the species of interest is intentionally altered or controlled (Meade 1989). The movement towards the rearing of aquatic species is aimed at raising nutritional standards, providing employment and income and improving food security, especially amongst developing nations (FA0 2002).

The expansion of aquaculture has proceeded at the highest rate of any food- producing industry in the world. Between 1987 and 1997 the weight and value of farmed species supplied to the global market doubled (FA0 2000). Worldwide, more than 220 species of finfish and shellfish are farmed in marine, brackish and fresh waters with Asia contributing approximately 90% to total global aquaculture production (Naylor et al. 2000). Most aquatic products are used for human consumption, but it should be recognised that a small portion is harvested for aquariums and pharmaceutical purposes (Bezard and Maigret 1990).

AquacuIture has proven beneficial on both national and regional scales, providing a significant source of foreign exchange and bringing wealth into areas previously experiencing extreme poverty (Funge-Smith and Briggs, 1998). Although the

Einancial successes of aquaculture endeavours have been outstanding, reaching levels of over US $50 billion in 1997, as is the case with many industries that intensify rapidly, the boom has not arisen without its share of negative impacts, both environmental and social (FA0 1999; Folke and Kautsky 1992).

Traditional aquaculture activities depend on natural processes to rear a number of finfish and shellfish in so called extensive systems. Tidal action and naturally occurring blooms provide the necessary water exchange and feed required to cultivate aquaculture crops (Csavas 1993). With the rising demand for fmed species, techniques to increase were developed. These primarily involved larger inputs of feed, fertiliser, chemicals and skilled labour as well as increased frequencies of water exchange (Hopkins et al. 1995b). The intensification of farming practices has brought with it much wealth, but the rapid shrift from minimal to high input processes has resulted in degradation of coastal and public water supplies, destruction of (specifically mangrove forests), salinisation of soils on neighbouring lands and spread of bacterial and viral diseases

(Naylor et al. 2000; Bevendge et al. 1994; Boyd 2001). These impacts not only cause significant social strife among rural peoples, but also negatively affect the aquaculture industry itself (Macintosh and Phillips 1992a).

The most controversial of all the marine aquaculture industries is that of shrimp farming. The demand for shrimp on the international market has skyrocketed since the late 1970's. hl98O the annual global production of all farmed species of shrimp was estimated at 200 000 T. This number rose to 744 000 T by 1993 and by 1998 was calculated at 840 200 T (Rosenbeny 1998 in Paez-Osuna 2001; Briggs and Funge-

Smith 1994). Using this data Rosenbeny (1 998 in Paez-Osuna 2001) projects that the global yield of fanned shrimp will reach approximately 2.1 million T by 2005. The estimated maximum sustainable yield of wild catches of shrimp is 1.6 - 2.2 million T revealing that by 2005, the shrimp aquaculture industry may be producing more shrimp than available from wild catch (Paez-Osuna 2001). Intensive crustacean culture, specifically of the black tiger prawn, Penaeus monodon, is extremely prevalent in Southeast Asia where over 50% of the world's production, by weight, are produced. Since 1994, Thailand has been the world's largest producer of cultured shrimp (Figure 2.1). Thailand Indonesia Philipppines Malaysia Countries

Figure 2.1: Aquaculture production of shrimp (by weight) in 1998 (Rosenbeny 1998 in Paez-Osuna 2001) 2.2 Shrimv A~uaculturein Thailand

Prior to 1985 Thailand had a small niche in the international shrimp market. By

the mid-19807s,however, Thailand had replaced Taiwan as the largest exporter of

shrimp in the world (FA0 1999). Numerous natural and economic factors made

Taiwanese farmers unable to produce more than one shrimp crop a year. Taiwan had

long supplied to Japan, the largest consumer of shrimp, but with rising electricity

costs, Japan was no long able to feasibly cold store Taiwanese shrimp to ensure year

round availability (Kongkeo 1994). In addition, Taiwanese crops suffered high

mortality and losses in 1987 due to bacterial and viral shrimp pathogens causing their

billion dollar industry to almost come to a halt (Csavas 1993; Kongkeo 1997). As a

result, Japan started to encourage suppliers from other countries to boost production, forcing the price of shrimp to rise from US $2.50 to US $8-10 per kg (Kongkeo 1994).

Many Southeast Asian nations, specifically Indonesia, Taiwan, Vietnam and the

Philippines, were potential rivals for Thailand. However, Thailand's political,

economic, social and environmental climates were ideally suited for the development

of shrimp aquaculture. Recognising the potentially enormous economic benefits of leading the world's shrimp exports, the Thai government offered loans and grants to provide capital for new aquaculture establishments, in addition to encouraging large businesses to invest in upcoming shrimp farms (Kongkeo 1994). Thailand soon became the largest exporter of farmed shrimp contributing over 30% to global farmed shrimp production in 1998 (FA0 1999).

Among the factors leading to Thailand's dominance in the global shrimp market are the climate, geology and biology of the country's coastlines as well as the availability of materials and technical expertise in the field of aquaculture. Typhoons and cyclones are extremely rare along the coast and the water temperature is non- fluctuating making the region ideal for shrimp farming (Kongkeo 1994). The high clay content of many soils allows for minimal seepage and is therefore a suitable material for grow-out (Hambrey and Lin 1998). With respect to infrastructure,

Thailand is more advanced that its neighbouring competitors. Electricity is widely available and comparatively reliable (Kongkeo 1994). This is important for daily farm operations such as aeration, pumps and lighting and is imperative for freezing and packaging procedures (Tookwinas 1994). Telephones are also common in most areas allowing for rapid communication and consultation should a problem arise during a culture cycle. Equally important is Thailand's extensive network of paved roads (Kongkeo 1994). This facilitates the transport of materials (e.g. construction goods, feed, chemicals) as well as providing easy access for trucks transporting shrimp to packaging and freezing .

Shrimp farms can not survive as isolated entities and therefore rely on numerous support industries for their success. Prior to the shrimp "gold rush" in the 19807s,

Thailand was already producing and exporting fish and poultry products (Csavas

1993). When the demand for shrimp increased, Thai farmers were able to obtain formulated feed from previously established chicken feed suppliers. This not only provided low cost feed but reduced the risk of toxicity associated with imported feed which may have expired or been stored incorrectly in humid conditions (Kongkeo

1994). Preexisting fish processing plants were also quickly and cheaply modified to package and freeze shrimp. In addition, equipment, such as pumps, tanks and heavy machinery required for pond construction, was readily available (Harnbrey and Lin

1998). Compared to developed nations, skilled labour in Thailand is relatively cheap allowing for profitable export of a variety of shrimp: head-o$ head-on, peeled and specialty (Kongkeo 1994). Despite all these conditions conducive to success in the shnmp aquaculture industry, Thai farmers experienced mass shrimp mortalities resulting fiom poor site selection. This resulted in frequent geographic shifts of shrimp farming areas. Large- scale crop losses were most often attributed to farm establishment on acidic coastal soils and self-pollution in areas densely populated by shrimp farms.

2.2.1 Geoaaphical Shift

Extensive shrimp aquaculture has been practiced on Thailand's coasts for centuries. The sheltered calm seas along the 2700 lcm of coastline provide an ideal setting for aquaculture operations as does the abundance of natural seed in these temperate waters (Tookwinas 1996). Historically, Penaeus merguensis were harvested in the dry season and Metapenaeus species were farmed in the wet season

(Tookwinas 1994). This was achieved through the construction of dykes on the perimeter of rice fields allowing wild shrimp to enter though sluice gates that subsequently retained the animals until they reached maturity (Tookwinas 1994). The surge in popularity of shrimp products awakened the need for techniques that would increase production yields. As a result, supplementary feeds were introduced in the

1970's while the 1980's gave rise to technological advancements enabling intensive systems to come into fruition. The most significant of these new technologies was the

Department of Fisheries' (DOF) success in hatchery producing Penaeus monodon or black tiger shrimp at commercially demanded quantities (NACA 1996). This species of shrimp is the most widely cultured owing to its rapid growth rate and high tolerance to temperature and salinity fluxes (Chanratchakool et al. 1995).

Intensive shrimp fanning began in the upper Gulf of Thailand replacing salt pans and extensive aquaculture sites (Flaherty and Vandergeest 1998). Low yields were frequently observed in the upper Gulf as these cultivation activities require large

amounts of high quality water, which is rarely available in these areas

(Chanratchakool et al. 1995). Water supply canals are narrow and muddy and subject

to pollution from upstream industries, agricultural lands, domestic sewage and other

shrimp farms. These conditions have resulted in severe losses of shrimp from disease

and unexplained mortality (Hambrey and Lin 1998). The upper Gulf also experienced

an industrial boom causing land prices to soar thereby pushing shrimp fanners out of

the region and, either out of the industry altogether, or onto the east coast.

Farmers achieved varied success along the eastern coastline due to poor soil

quality (acidic with high concentrations of iron and aluminum, characteristic of many

mangrove soils), variable salinity and pesticide runoff from neighbouring fruit plantations (Hambrey and Lin 1998).

In the early 1990's the hghest concentration of shrimp aquaculture operations

could be found in the southeast (NACA 1996). Shrimp farmers were quite successful in this area as soils are more suitable for cultivation and the coastline is straight with deep waters of stable salinity. As industry had not yet inundated this area, there was little upstream pollution. Another possible reason for the success of intensive farms in the southeast is that farmers gained experience and knowledge from their previous attempts further to the north and improved upon existing culture practices and techniques (NACA 1996).

Despite the near optimum conditions in the east, Thailand was unable to escape the same fate as Taiwan and suffered a crash in production in 1996 due to disease outbreaks (Figure 2.2). Thailand's shrimp indust~ydid not completely collapse, however, as many farmers had already begun to move from diseased, polluted coastal farms to inland areas owing to the recent discovery of low salinity fanning. Year

Figure 2.2: Aquaculture production (by weight) ofP.monodon in Thailand (FA0 2001) 2.2.2 Svstem ShiR

In addition to a geographical shift, there has also been a noticeable movement fiom open to semi-closed and occasionally closed intensive culture systems. These methods of shrimp farming primarily differ by the amount and frequency of water exchange through a culture cycle. Open farming systems exchange 20-30% of pond water per day during the initial stages of the culture cycle but increase these rates to

50% in the final month (Hambrey and Lin 1998). Farmers discovered that with such high water exchange rates, effluent from upstream aquaculture operations could easily pollute and even spread disease to their ponds (Dierberg and Kiattisirnkul1996). The most popular solution to this was the adoption of semi-closed systems characterised by limited water exchange throughout the 90-120 day grow out period (Funge-Smith and Briggs 1998). This practice, however, did not receive unanimous support as farmers must construct settling or biological treatment ponds for both incoming and recycled water in order to maintain water quality at optimum levels, (Dierberg and

Kiattisimkul 1996). Although the yields of semi-closed intensive systems are similar to that of open systems, treatment ponds occupy space that could be used as grow out ponds and many farmers are unwilling to sacrifice this potentially productive land.

Closed system farms have not been readily adopted by farmers in Thailand due to the capital and skill required f%r efficient operation. Closed water systems do not release any effluent but do require water input as some is lost to evaporation and seepage during a production cycle (Funge-Smith and Briggs 1998). As this technique uses recycled water, solids must be continuously removed and nutrients kept at suitable concentrations. This can be achieved with polyculture areas, water treatment or settling ponds, and through the use of filters (Dierberg and Kiattisirnkul 1996). 2.3 Management Practices

There are three types of farming practices, extensive, semi-intensive and intensive

systems. These differ by feeding and water exchange practices, stocking densities and

production potential (Table 2.1). The largest contributors to commercial shrimp

supplies, and thus the operations of greatest concern, both economically and

environmentally, are intensive farms. Accordingly, the culture practices of intensive

establishments are discussed from the time of site selection to pond preparation,

through stocking, rearing and finally harvesting.

2.3.1 Site Selection

The first and arguably most important step in establishing a shrimp aquaculture

operation is selecting an appropriate site. Location must be considered with respect to

water quality and availability as well as soil composition and infrastructure. Supply

water should contain minimal amounts of suspended solids and pollutants originating

from upstream activities as these substances create a stressful environment for shrimp

(Boyd and Tucker 1998). In addition, to achieve optimal growth and survival rates, pH levels should range from 7.5 to 8.5 and salinity should be maintained between 10-

30 ppt. (Chanratchakool et al. 1995).

With respect to soil, clay or loamy substrates with a pH higher than 5 are ideal.

Sandy soils are less desirable as they have a low organic content making it difficult to start and sustain phytoplankton blooms. Ponds established in sandy areas also experience high seepage rates and therefore require constant filling to ensure water remains at optimum levels. This high demand for water is not of great concern in coastal areas but poses a problem in inland areas where water is often a limited Size 2-20 ha 1-5 ha 0.1-1 ha

Management Minimal attention Continuous and Continuous and required semi-skilled skilled

Water exchange Tidal Tidal and pump Pwnp and aeration

Feed Natural Natural and Formulated diet supplement

Stocking density 0.1-1.0 PL/~~ 1-5 PL/~~ 15-100 pvm2

FCR 0 4.5 1.5-2.0

1Yield 4000-15000 k a/

Table 2.1 : Comparison of extensive, semi-intensive and intensive shrimp fanns in Thailand (modified from Phil et al. 1993; Thongrak et al. 1997;Chanratchakoolet al. 1995; Lorenzen et al. 1997)

Note: FCR refers to feed conversion ratio (a measure of shrimp per kg of food supplied) resource (Bangkok Post 1999). Acid sulphate soils, such as those present in mangrove forests, are also sub-optimal as they cause water pH levels to decrease and are not suitable for phytoplankton blooms (Tookwinas 1994).

When selecting a farm site, access is of vital concern. In order to decrease post- larval stress and ensure high quality shrimp for export, the distance from hatchery to grow out pond should not exceed 6 hours while that between the farm and processing should remain less than 10 hours (Chanratchakool et al. 1995).

2.3.2 Pond Preparation and Stocking

The average size of grow out ponds in Thailand is between 0.16 and 1.0 ha

(NACA 1996). Each of these ponds must be thoroughly cleaned between culture cycles to ensure optimum water quality and decrease the risk of disease outbreaks in subsequent crops (NACA 1996). This process begins on the day of harvest. Once the pond has been drained and the shrimp harvested, a layer of sludge weighing between

185-199 tomes dry weightha remains on the pond bottom (Briggs and Funge-Smith

1994). This fouled layer is composed of shrimp faeces, uneaten food, dead phytoplankton and solids originating from pond wall erosion (Funge-Smith and Briggs

1998). In the dry season this sediment can be removed by bulldozers or excavators and packed on pond banks to dry. In the rainy season, heavy machinery cannot be operated so sludge is often flushed out by high pressure hoses (Kongkeo 1997).

Despite government efforts to ensure that sediment is retained in settlement ponds so as to prevent water contamination, in practice, most farmers dispose of this fouled substrate directly into public water canals (Tiensongrusmee and Phillips 1994 in

Dierberg and Kiattisimkul 1996). Once the sludge layer has been removed, ponds are left to dry for approximately one month to oxidise toxic gases such as and ammonia (Macintosh and Phillips 1992). The bottom is then ploughed to expose deeper layers of soil and eliminate more toxic gases. Prior to stocking, the pond bottom is often treated with a barrage of chemicals to neutralise acidic soils as well as disinfect and eliminate predators (Table 2.2).

Once the pond bottom has been treated, a small amount of water is added which, when stimulated by organic and inorganic fertilisers, results in the formation of a phytoplankton bloom (Funge-Smith and Briggs 1998). Phytoplankton provide oxygen and uptake excess nutrients in the . They also provide a shaded pond environment that deters harmful benthic algae and reduces flues in water temperature

(Chanratchakool et al. 1995). Once the phytoplankton population is stable, a total of

120-15Ocm of water is allowed to enter the pond and hatchery reared 15-20 day old post-larvae (PLIS-PL20) are stocked at a density of 30-100 PL/~~(NACA 1996).

These juvenile shrimp must be acclimatised to conditions in the grow-out pond before stocking. This is achieved by putting larvae in a tank near the pond with an equal mixture of their hatchery water and pond water, or by placing the plastic bag in which they are transported into pond water for an hour before releasing them into the grow out area (Chanratchakool et al. 1995).

2.3.3 Feeding;

Shrimp grown under intensive conditions require inputs of commercial pellet diets high in nitrogen and phosphorus, These pellets contain attractants to encourage food uptake as well as prophylactic doses of antibiotics to decrease the risk of disease outbreaks (Tookwinas 1996). Schedules vary from farm to farm but feeding usually occurs between 4 to 6 times over a 24-hour period (NACA 1996). As shrimp are a nocturnal species, more feed is distributed at night than during daylight hours. The Treatment Type Compounds Commonly Used _.______.__.__.__..... _.______.__.__.__...______.______.__.__.__...______...... ,-- ...... -- ...... -...-...-...... -----.--. Soil and water treatments Lime Dolomite Zeolite Chlorine Microbial preparations Laundry detergent

Pesticides, piscicides and molluscicides Teaseed cake (saponin) Derris root extract (rotenone) Calcium hypochlorite Ammonium sulphate

Chemotherapeutants to prevent disease Malachite green Formalin Chloramphenicol Oxytetracycline Tetracycline

Plankton growth stimulators N-P-K fertilizers

Table 2.2: Common chemical and biological compounds used in intensive shrimp culture in Thailand (adapted from NACA 1996; Macintosh and Phillips l992b; Prirnavera 1993) feed conversion ratio (FCR) in intensive ponds should not be higher than 2 although levels exceeding 5.5 have been documented, resulting in mass accumulations of waste

(Macintosh and Phillips 1992b). Feed is commonly scattered by hand with attempts to disperse the majority of feed in areas where the pond bottom has been swept clean by aerator-induced currents (Chanratchakool et al. 1995). This concentrates shrimp in areas with minimal waste buildup thereby reducing exposure to infectious sediment dwelling pathogens. The amount of feed supplied to ponds is determined by placing feed in nets, submersing them in ponds and estimating the rate of consumption

(Chanratchakool et al. 1995; NACA 1996).

2.3.4 Aeration and Water Exchange

High stocking densities and large feed inputs result in increased concentrations of phytoplankton and a high biological oxygen demand (Csavas 1993). In order to maintain Dissolved Oxygen concentrations at suitable levels, both in the water column and at the sediment surface, and to facilitate the decomposition and mineralisation of organic debris, aerators are used to produce water currents (Boyd and Tucker 1998).

Aeration has proven to be very effective in concentrating wastes in the centre of the pond, keeping most of the pond bottom clean and increasing oxygen levels in the water column. However, it has also been shown to aggravate pond wall erosion resulting in high levels of suspended solids (Dierberg and Kiattisimkul 1996). As aeration is most important when Dissolved Oxygen levels decrease and wastes accumulate, aerator use increases as grow out progresses and are operated 24 hours a day in the final stages of production (Chanratchakool et 01. 1995).

As previously mentioned, water exchange rates vary depending on the fanning system in use (open, semi-closed or closed). The rate and amount of water exchange is dependent on the tabulated characteristics of pH, salinity, Dissolved Oxygen, visibility, hydrogen sulphide and unionised ammonia along with visual observations of water colour and the presence of bubbles or foam on the pond surface (Table 2.3)

(Boyd and Tucker 1998).

2.3.5 Harvesting

The average grow-out period for P. monodon is 100-120 days after which time environmental conditions become stressful resulting in slower growth and higher probability of disease (NACA 1996 and Funge-Smith and Briggs 1998). At the time of harvest, shrimp weigh approximately 30g (Chanratchakool et al. 1995). The two most common methods of harvesting are manually netting shrimp by wading into the pond or draining the pond and collecting shrimp in a bag net attached to an outlet pipe. Any shrimp remaining in the sediment are collected by hand (NACA 1996).

Shrimp should be harvested as quickly as possible, graded according to size and placed on ice in packing boxes and transferred rapidly to processing plants.

2.4 Environmental Imvacts

It cannot be refuted that shrimp farming has been an astronomical success for many rural and urban peoples. Along with this "gold rush',, however, comes an array of negative impacts. The most well documented of these focus on the degradation of coastal ecosystems, inland areas and ground and surface waters.

2.4.1 Land Requirements

Shrimp aquaculture has arisen in many geographic regions of Thailand owing to the conversion of fields, salt-pans, rice paddies and mangroves into shrimp Water Parameter Optimum Level PH 7.5-8.5 Salinity 10-30ppt Dissolved Oxygen 5-6 ppm Secchi Disk 30-40 cm 0H2s <0.03 ppm

Table 2.3: Optimum water quality parameters for culture of P. monodon (adapted from Chanratchakool et al. 1995) farms. By 1997 productive shrimp farms occupied roughly 70 000 ha, although this figure does not account for many of the recently established inland farms or numerous

abandoned sites (Tookwinas and Songsangjinda 1999). The majority of these farms are situated on converted rice fields and mangroves.

Shrimp farmers have long been labelled as destroyers of mangroves, but such a claim is often unfounded. Although shrimp aquaculture can be observed along a large portion of Thailand's coastline where mangroves used to be abundant, most of these farms occupy land previously cleared for charcoal and timber production (Primavera

1998). This is supported by statistics describing the increase in shrimp production areas by 37 760 ha between 1986-1989 while the corresponding decrease in mangroves was less than half this value (15 867 ha) (Kongkeo 1994). Although shrimp farms may not be the sole cause of the decrease in mangrove coverage, they have significantly contributed to the overall decline of rnangal abundance in Thailand.

Increased awareness regarding the detrimental effects of mangrove removal has resulted in the creation of policies preventing further mangrove destruction and banning the establishment of shrimp farms in most mangrove areas. These regulations coupled with increased shrimp disease prevalence in coastal regions have led to the creation of inland shrimp farms. Inland aquaculture techniques have received little attention as the widespread adoption of low salinity practices has only occurred in the last 5 to 7 years (Flaherty et al. 1999). Shrimp fanns are being established in agricultural areas the majority of which are amongst rice fields and fruit orchards. At present, there is not a shortage of viable land for agricultural use, but the establishment of aquaculture operations in these areas has raised concern, specifically with regard to salinisation of inland areas (Flaherty et al. 1999). 2.4.2 Water Supplies

Coastal aquaculture operations primarily draw water from the sea Owing to the abundance of source water, water use on coastal farms can be considered negligible.

With the emergence of inland shrimp farms, however, attention has been directed towards the potential impacts on availability and quality of surface and used for domestic and agricultural purposes (Flaherty et al. 1999). Thailand's central plain has an extensive irrigation network and has long enjoyed an abundance of and therefore has no regulations controlling water use. Few studies have assessed the water requirement for shrimp farms but it is estimated that 1kg rice uses

5m3 of water whereas an equal amount of shrimp (assuming 3.75TIha) uses 8.8m3 water (International Rice Research Institute 1998 in Flaherty et al. 1999; Flaherty et al. 1999). In addition, it is important to recognise that the creation of ponds exposes a large surface area of water to the atmosphere causing evaporation rates to increase from those in canals (Beveridge et al. 1994). With the increased occurrence of drought conditions and a heightened urban and agricultural demand for water in recent years, it is not unreasonable to hypothesise that freshwater supplies will be insufficient to meet future requirements. At present, however, the water supply is still sufficient to meet the needs of its users thus concern is focused on the composition and quality of output water.

2.4.3 Chemical Dischawe

Semi-intensive and intensive aquaculture operations manipulate natural systems in such a way that chemical additions are often necessary to ensure the health of cultured species. Fertilisers are commonly used to promote phytoplankton growth while pesticides and piscicides are applied to prevent unwanted species from competing with cultured shrimp. Previous research suggests that standard chemotherapeutant applications are lethal to many marine species and may also have deleterious effects on overall ecosystem health (Macintosh and Phillips 1992b).

The recent popularity of highly intensive aquaculture farms has led to greater demands on water resources, higher effluent loads and a necessity for extremely frequent water exchange. These practices have degraded source and pond water resulting in weakened shrimp immune systems and providing an optimum environment in which shrimp pathogens thrive (Kongkeo 1994, Flaherty and

Vandergeest 1998). Farmers have responded to diseases by applying antibiotics, both as a prophylactic present in most commercially available feed products and in concentrated doses during times of acute disease outbreaks (Flaherty and Vandergeest

1998). The effects of unregulated antibiotic seepage into surrounding ecosystems are poorly understood, but evidence suggests that widespread use of such medications may encourage the emergence of antibiotic resistant strain . This has the potential to harm natural ecosystem processes, fisheries and may even pose a risk to human health (NACA/FAO 2000).

2.4.4 Organic Outputs

Shrimp aquaculture requires significant organic inputs in order to hction at optimum levels. These organic materials are added to the system in the form of fertilisers and feed and are either incorporated into shrimp body mass or remain in the pond as uneaten feed or shrimp excreta (Briggs and Funge-Smith 1994). The amount of uneaten feed in a pond depends on the individual practices of each farmer.

Intensive practices, specifically those with high FCRs, severely degrade pond water quality and necessitate frequent water exchange. Daily water exchange and seepage result in discharges of 1 050 to 23 188 m3/ha depending on the production stage

(Briggs and Funge-Smith 1994). The concentrations of key nutrients present in this

discharge are described in Table 2.4.

Shrimp effluent is not as toxic as waste from other sources such as sewage, when

compared in terms of milligrams of toxic substance per litre of effluent (Macintosh

and Phillips 1992b). It is, however, extremely hazardous as it is typically discharged in large volumes due to the synchronized harvesting cycles of fmswithin a region or province (Macintosh and Phillips 1992b). This leads to large effluent discharges into neighbowing ecosystems at key points during the shrimp culture cycle. The most common way to assess the polluting potential of effluent is to monitor nitrogen and phosphorus concentrations in wastewater. Of specific concern are nitrate, nitrite and ammonia. At low levels, nitrate is not hadto ecosystems and is in fact a major contributor to growth and survival of a number of species. At high concentrations, however, this nutrient is responsible for disrupting ecosystem dynamics by encouraging rapid growth of microorganisms that increase primary productivity

(Moriarty 1986 in Phil et a1. 1993). This in turn alters community structure and can lead to harrml/toxic phytoplankton blooms. The increase in respiring organisms, along with the breakdown of organic material and waste products in effluent, disturbs dynamics at the very bottom of marine food chains in addition to reducing Dissolved

Oxygen in canals and (Phil et al. 1993). The resulting anaerobic environment can suffocate and severely diminish, if not completely destroy, fauna and flora present in nearby habitats (Nunes and Parsons 1998). Nitrite and ammonia are also of concern as they are toxic to many marine species even when present at very low concentrations...... ------~.-~~~ Parameter Concentration in Effluent

. it rite-nitrogen- 0.04 * 0.06 Nitrate-nitrogen 0.11 * 0.19 Total Nitrogen 3.45 =t 1.69

Table 2.4: Concentrations of key nutrients in shrimp farm effluent from an intensively managed shrimp pond in Thailand (stocking density of 80 to 100 PLI~~)(Briggs and Funge-Smith 1994) Of particular importance is the potential degradation of sensitive estuarine, coral

reef and habitats that are home to a plethora of , many of which

are commercially important. The large sediment loads of effluent discharged at

harvest not only lead to eutrophication in receiving water ways, but can also cause

severe blockage in neighbouring canals resulting in decreased water supplies,

flooding and lethal anaerobic conditions (Paez-Osuna 2001). Eutrophication and

sedimentation of neighbouring waters are also of concern to aquaculturalists. As

shrimp farms are usually established in close proximity to each other, wastewater

discharge from one fann often serves as inflow water for a neighbowing farm. If

effluent quality is extremely poor owing to high nutrient content and minimal or non-

existent waste treatment facilities, the potential for a farm to pollute all other farms in the vicinity is extremely high Self-pollution has been responsible for low harvest yields and a rapid spread of disease in many coastal areas. (Dierberg and Kiattisimkul

1996)

2.5 Best Management Practices

The seemingly endless array of potentially negative impacts of intensive shrimp farming have given rise to a remarkable number of mitigation options and suggested best management practices. Unfortunately each of these options comes with a price, either financial, temporal or spatial, and have therefore not been widely accepted.

Despite this, many are worthy of consideration and a combination of a number of practices may prove to be the most viable and effective solution for ensuring long- term sustainability of these operations. 2.5.1 Planning and Management

One of the most imperative steps in reducing the negative impacts of intensive

shrimp aquaculture is proper site selection. Farmers must be educated to conduct risk

analysis prior to establishing shrimp farms. It is essential that they view their farm as part of a larger, dynamic whole as opposed to an isolated entity. By considering the suitability of a site, with respect to soil and water quality and the potential impacts both on and from the surrounding environment, farmers will be able to decrease the frequency of site abandonment and disease outbreaks (Macintosh and Phillips 1992a).

Such a holistic approach could have helped prevent the destruction, degradation and subsequent abandonment of many lands (Phillips et al. 1993). For example, through careful assessment regarding the suitability of mangrove forests for shrimp culture, farmers would have soon realised that the pH of mangrove soils is too low to sustain shrimp culture, and therefore that mangroves are not ideal areas in which to establish ponds (Chanratchakool et al. 1995).

2.5.2 Physical Techniques

As a significant amount of solids enter ponds through soil erosion aggravated by aerators, separating the pond bottom from the water column is an effective way to decrease the amount of the accumulated sediment (Funge-Smith and Briggs 1998).

This can be achieved through the use of bitumen impregnated geotextile or PVC pond liners (Chanratchakool et al. 1995). This practice reduces the amount of solids remaining on the pond bottom after harvest, while minimally affecting the total nutrient load, as the majority of organic matter originates fiom feed inputs. As a result, the remaining liquid contains high levels of organic matter and can be sold as an agricultural fertiliser after the salt is removed (Funge-Smith and Briggs 1998). In addition to decreasing sediment outputs, liners can halt the seepage of pond water thereby eliminating the risk of chemicals and salt leaching into agricultural lands and underground aquifers (Macintosh and Phillips 1992b). The separation of pond bottom from water also allows farms to be situated in sub-optimal areas with porous, acidic soils (Dierberg and Kiattisimkul 1996).

Although pond liners are quite costly, the initial investment is negligible when the benefits are considered (Dierberg and Kiattisimkul 1996). The average time to clean and treat an earthen pond varies from four to eight weeks depending on weather, disease, soil condition etc. This time is decreased to ten days when using lined ponds thereby reducing costs by up to 50%. It is estimated that the cost of liners, which are guaranteed for ten years, can be recovered within five to eight years of installation

(Macintosh and Phillips 1992b).

Unfortunately there a few problems associated with PVC and geotextile liners.

Firstly, organic phosphorous concentrations tend to increase in lined ponds. This is attributed to the blocking of potential phosphorus binding sites in pond soil (Dierberg and Kiattisimkul 1996). Secondly, cannibalism and high FCRs have been reported.

The smoothness of the substrate and aerator induced water circulation facilitate the buildup large concentrations of feed in the centre of the pond. This makes feed inaccessible to shrimp. The relationship between pond soil and shrimp nutrition is not well understood but it is thought that pond liners could potentially hinder nutrient uptake (Funge-Smith and Briggs 1998).

Liners themselves also have physical drawbacks as they are sensitive to sunlight and extended exposure between crops can dramatically reduce the length of their service life (Funge-Smith and Briggs 1998). If pond lining becomes standard management practice, the disposal of used materials will become an important environmental issue. No effective pond liner recycling programme exists in Thailand

and many fanners may simply opt to bum them, which would release noxious gases

into the atmosphere, while others may dump them or bury them on site.

2.5.3 Feed Related Practices

Most best management practices revolve around remediating, minimising and

even terminating the impact of effluent on surrounding lands and water sources. Feed

is the source for the largest input of nutrients into shrimp ponds. Commercial pellet

diets account for 92% of nitrogen and 51 % of phosphorus input in pond water (Briggs

and Funge-Smith 1994). As these nutrients can cause the disruption of neighbouring

ecosystem structures when drained into irrigation canals, many management strategies that are concerned with reducing environmental effects of effluent, focus on ways to

decrease the impact of feed. A number of researchers have recommended the

production of highly digestible, low pollution diets (e.g. Thongrak et al. 1997; Burford

and Williams 2001). Although the cost of such feed would be higher than diets

currently available, the FCR will decrease thereby reducing both the quantity of feed

required and subsequent wastage. Unfortunately, owing to the reluctance of feed manufacturers to cooperate with government and academic researchers, it is difficult to determine the current ingredients in feed and therefore to suggest more suitable formulas (Kongkeo 1994).

Thai shrimp farmers have been widely criticized for the extremely haphazard ways in which they feed their crops resulting in frequent overfeeding and high wastage

(Funge-Smith and Briggs 1998). Nunes and Parsons (1998) suggest the development of a feeding model based on shrimp behaviour and physiology. They propose that feeding frequency, distribution and feed quantity should be adjusted according to an animal's varied requirements dependent on rates of ingestion and digestion as well as

size, age, life stage, light intensity and spatid patterns.

2.5.4 Policv Options

Along with the variety of physical and biological management options, there are a number of policies that can aid in decreasing the environmental impact of intensive shnmp cultivation. In November 1991 the Thai government established a number of rules and regulations in an attempt to control the imminent spread and impact of shrimp farms (Table 2.5). Unfortunately, the government does not have the money, the manpower and as if ofien speculated, the desire, to effectively enforce these regulations. Thongkrak et al. (1997) suggested some additional policies, some of which do not require such intensive use of government resources. Many farmers overstock grow-out ponds simply because of a belief that more initial stock results in higher yields. In reality, shrimp yields are approximately equal due to lower survival in higher stocked ponds as a result of competition and decreased water quality. High stocking rates also increase organic waste fiom farms. One option, then, will be to impose a tax on fry which would result in more appropriate stocking densities while minimally affecting production. Taxation, however, is likely to be extremely unpopular among farmers. It was also suggested that the government distribute loans and grants to farmers interested in adopting environmentally friendly practices

(Thongkrak et al. 1997). This type of funding would require close monitoring to ensure funds are being used appropriately and for designated purposes. Thongrak et al. 's (1997) suggestion of communal water treatment areas is also worthy of consideration. This involves separating water source and discharge canals and ensuring that effluent passes through communal sedimentation and treatment ponds. This idea is of interest as it decreases the amount of land an individual farmer must

sacrifice to establish treatment areas and gives farmers access to high quality source

water. However, all farmers in an area must be willing to participate in this practice in

order for treatment to be effective. As an additional incentive to adopting

environmentally sustainable practices, shrimp reared on farms following such

guidelines could be certified and labelled as "eco-friendly" and therefore warrant higher price tags.

2.5.5 Biological Practices

If pond liners are not used, suspended solids in influent and effluent waters can be rapidly removed in settling ponds (Corea et al. 1995). A 1 ha pond can effectively settle-out solids in 1000m3of effluent per day (Kongkeo 1994; Teichert-Coddington er al. 1999, in Paez-Osuna 2001). The unavoidable drawback to this form of treatment is that shrimp effluent contains large amounts of phytoplankton which are naturally buoyant and will therefore not easily settle (Macintosh and Phillips 1992b).

For this reason, settling ponds are often used in conjunction with biological treatment ponds which filter solids and improve overall water quality.

Biofiltration experiments in Thailand revealed that Perna viridis (green mussels) are capable of reducing biological oxygen demand, organic solids and phytoplankton levels (Macintosh and Phillips 1992b). Gracilaria, a common seaweed, has also been effective in removing dissolved nutrients and sea cucumbers and macroalgae efficiently uptake settled particulate matter (Lin et al. 1991 in Macintosh and Phillips

1992a). Similarly, oysters are capable of removing fine organic particles in suspension through ingestion, coagulation and egestion in the form of pseudofeces Regulation Problems with Enforcement No new mangrove destruction - all existing farms in mangrove areas must leave by 1994 Shrimp farmers must register with the DOF Exporters may only buy shrimp from =* Lack of manpower and hds registered farms

Shrimp farms over 8 ha must have wastewater treatment areas not less than 10% the size of production area Effluent released into receiving waters must have BOD less than 1Omg/l Mud and sedimmt is not permitted to =Waste water generally drained at be released into natural water sources night --> difficult to monitor or public areas S& water must not be drained into neighbouring freshwater or farming areas

Table 2.5: Regulations for shrimp farming issued by the Thai government, November 1991 (modified fiom Kongkeo 1994) (Jones et al. 2001). An added benefit to adopting biological treatment techniques is

the secondary use of these marine species as food for humans and other organisms.

The main drawback to biological treatments is that the organisms used require

extremely specific environmental conditions for optimal functioning and survival. For

example, unlike P. monodon which are tolerant to a wide variety of salinities, green

mussels cannot survive with even minimal fluxes. In addition, bivalves have low

sediment assimilation capacities and are therefore sensitive to heavy loads of sediment

present in shrimp farm effluent (Jones et al. 2001). Another area of significant

concern to shrimp farmers is ammonia, a harmM by-product of biological treatment.

Although bivalves absorb some dissolved nutrients and suspended solids,

approximately 27% of absorbed nitrogen is excreted as ammonia, a compound that is

toxic to shrimp. If, however, bivalve treatment is used in conjunction with macroalgal

absorption, ammonia can be reduced to non-toxic levels (Jones et al. 2001).

Artificial bacterial suspensions are also an avenue of increasing interest. Microbes

have proven successful in treating sewage and industrial wastes but have achieved

minimal success in fish and shrimp ponds. This has been attributed to a lack of

understanding of microbial processes and their specific environmental requirements

(NACA 1996). As a result, their potential benefit in treating shrimp fann effluent has

not yet been disregarded.

Salt-tolerant plants, or halophytes, are another possible source of water treatment.

The water discharged from 1 ha of intensive shrimp farms can irrigate 18 ha of halophytes for one week, assuming water is only discharged at harvest (Brown and

Glenn 1999 in Paez-Osuna 2001). Salicornia bigelovii, Atriplex bardyana and Suaeda esteroa are efficient biofilters capable of removing a significant amount of nitrogen

and phosphorus from intensive shrimp fmeffluent as well as providing forage straw for ruminants. The hypersaline, nutrient poor water end product of halophyte

processes can serve as a habitat for the growth ofArtemia, brine shrimp, or be

manipulated to produce salt (Brown and Glenn 1999 in Paez-Osuna 2001).

Wetlands also serve as effective nutrient sinks and filtration sites and have been

used in a number of temperate regions to treat an array of domestic, agricultural and

industrial wastes (Gopal 1999, Summerfelt et al. 1999, Nzengy'a and Wishitemi

2001). Most wetland treatment areas consist of salt-intolerant reeds and are therefore unsuitable as biofilters for aquaculture effluent (Summerfelt et al. 1999). Of

increasing interest in saline and brackish wastewater treatment is the use of mangrove wetlands.

Mangroves are one of the most productive ecosystems in the world capable of recycling large influxes of organic matter from both anthropogenic and natural sources (Tam 1998). The dynamics of mangal environments are complex, but preliminary examinations of mangrove effluent treatment have produced encouraging results that demand further research to unveil the true potential of these intertidal forests as biofilters (Wong et al. 1997, Rivera-Monroy et al. 1999). If mangroves prove to be efficient at removing large quantities of nutrients from shrimp fm effluent, without being negatively affected by influxes of organically rich wastewater, they may become a primary source of effluent treatment for coastal farms around the world.

2.6 Summary

Shrimp aquaculture is an ever-expanding industry driven by the global demand for marine species and has not yet been curbed by government policies, social strife or environmental degradation. Thailand is the leading producer of shrimp worldwide and has therefore experienced the brunt of negative impacts arising ffom aquaculture's

popularity. It is imperative that the practices of aquaculture establishments be

improved to decrease their harmful effects on surrounding ecosystems before these habitats are altered past the point of feasible remediation. Several solutions have been

suggested to decrease the magnitude of aquaculture's impacts but none have been unanimously popular due to financial, spatial and temporal requirements. Mangroves may prove effective as wastewater treatment wetlands, but detailed examinations of their nutrient cycling capacities, such as those undertaken in this thesis, are essential before finite conclusions can be made.

The following chapter explores the ecology of mangroves and provides a background of the current uses of mangal habitats and their potential as biofilters for aquaculture effluent. CHAPTER 3

MANGROVE ECOLOGY

Mangrove ecology is outlined in this chapter with specific attention to ecosystem

biology and nutrient cycling. Mangal susceptibility to a variety of anthropogenic and

natural stressors is examined, followed by a description of the uses of mangroves and

their potential as effluent biofilters. Recent studies of mangroves as wastewater treatment areas are reviewed and the limitations in current research are identified. A

discussion of the environmental and financial issues surrounding the use of natural

and constructed is presented and modified mangroves are introduced as an interim

solution to current feasibility concerns.

3.1 Definition

Mangroves are defined as woody plants that thrive in the intertidal zone along many tropical and subtropical coastlines. The trees and shrubs that grow in the interface between land and sea have developed a number of adaptations so that they

can endure a variety of environmental extremes, ranging from high temperatures and anaerobic sediments to strong winds, forcefid tides and fluctuating salinities (Hogarth

1999). The specialised mechanisms adopted by mangrove trees enable them not only to flourish in seemingly inhospitable environments, but also to provide a rich habitat for a number of marine and terrestrial organisms. Mangrove forests and their semi- permanent and permanent residents are sometimes referred to as mangal, while mangrove usually denotes plant species. However, the terms mangrove and mangal are commonly used interchangeably. Mangroves occur primarily in humid eutrophic and oligotrophic estuaries with

well-drained alluvial soils that experience regular tidal flushing as well as freshwater influxes from inland sources (Gopal and Krishnamurthy 1993). There are three types

of mangroves: true mangroves, consisting mainly of Avicennia and Rhizophora species, minor mangroves and associate mangroves (Kathiresan and Bingharn 2001).

True mangroves are classified as either black, red or white mangroves and occur exclusively in mangal areas. Minor mangroves and mangrove associates grow in the terrestrial regions of mangals as well as in freshwater swamps and inland rainforests

(Hogarth 1999).

Mangrove trees and shrubs provide a number of physical and biological services to surrounding ecosystems. These include, but are not limited to, physical coastal protection, nursery grounds for juvenile organisms, nutrients for estuarine dwelling species and products for commercial exploitation (Bashan and Holguin 2002).

Despite the array of contributions mangroves make to neighbouring systems, their ecological significance has consistently been overlooked or underestimated which has led to the destruction of a significant proportion of the world's mangroves (Adeel and

Pomeroy 2002).

3.2 Geographical Distribution

Mangroves occur in 112 countries and temtories between the latitudes of 30% and 30's (Kathiresan and Bingham 2001). Their distribution appears to have a correlation with oceanic temperatures, with increased abundance in regions experiencing winter sea temperatures above 20'~(Hogarth 1999). It is difficult to obtain exact values of global mangrove coverage but it is estimated that they occur on more than 8% of the world's coastlines, covering a total area of 10 to 24 million hectares (Adeel and Pomeroy 2002, Bunt 1992, Twilley et al. 1992). These numbers are forever fluctuating as mangroves are being lost at rates of 2%to 8%per year as a result of human encroachment into intertidal areas, pollution and altered sedimentation patterns resulting from inland anthropogenic activities (Adeel and

Pomeroy 2002, Gopal and Krishnarnurthy 1993). National mangrove losses range from 8% to 84% with the greatest natural cover decrease in Southeast Asian countries

Mackinnon 1997) (Table 3.1).

3.3 Biology of Mangroves

This section describes the anatomy of mangroves as well as the environmental adaptations and nutrient cycling dynamics displayed by intertidal forests. It also reviews their sensitivities to natural and anthropogenic stresses.

3.3.1 Anatomv

There are between 50 and 75 species of mangroves in 20 to 26 genera in 16 to 20 families (Kathiresan and Bingham 2001). Although anatomical differences exist between these mangrove varieties, several physical features are unique to all mangrove species, in that they are not present in any non-mangal woody vegetation

Mangrove trees are typically greater than half a metre in height at maturity. Exact height and age correlations, however, are difficult to determine due to anomalous or absent growth rings in mangrove wood (Tomlinson 1986). All woody tissues, however, do possess specialised vessels to help them adjust to osmotic pressure changes resulting from fluctuating external salinities (Kitaya et al. 2002). These vessels passively open and close to increase and decrease flow resistance through Country Percent Manprove Loss Period Covered Brunei 20 Original extent to 1986 Indonesia 55 Original extent to 1980s Malaysia 74 Original extent to 1992-3 Myafmar 74 Original extent to 1992-3 Thailand 84 Original extent to 1993 pPa ua New Guinea

Table 3.1 : Examples of mangrove loss in Asia and Oceania (Mackinnon 1997) mangrove tissues thereby allowing mangroves to regulate water uptake and loss through an array of environmental conditions (Tomlinson 1986).

Mangrove leaves also possess adaptive characteristics to optimise photosynthesis and evapotranspiration rates. Moderately-sized leathery leaves are arranged to prevent self-shading thus enhancing photosynthetic rates (Tomlinson 1986).

Specialised salt-excreting structures and leaf size further aid mangroves with water retention (Tomlinson 1986, Naidoo and Von-Willert 1995).

The most highly developed anatomical structures of mangroves are their root systems. In order to survive periods of tidal inundation and submersion as well as frequently anoxic sediments, mangrove trees have developed specialised roots that elevate them above the sediments. Unlike the roots of terrestrial plants that grow deep into underground soils, mangrove roots remain a few centimetres below the substrate surface (Hogarth 1999). They grow out of the substrata due to elongation behind the apical meristem and are therefore able to serve as areas of gas exchange to prevent trees from suffocating under low oxygen conditions (Kathiresan and Bingham 2001).

These aerial root structures are discussed in further detail in the following section.

3.3.2 Environmental Adaptations

As previously mentioned, mangroves have developed numerous adaptations to not only survive, but thrive, in the intertidal of subtropical and tropical coastlines. They are constantly challenged by salinity fluxes resulting from variations in seasonality, freshwater runoff and evaporation rates. Salinity changes pose difficulties for mangrove trees that are constantly attempting to maintain adequate water absorption rates. Mangroves typically regulate salt in one of four ways: by exclusion, excretion, accumulation or tolerance (Hogarth 1999, Kathiresan and Bingham 2001). In addition to serving as areas of gas exchange, the structure of exposed roots of some mangrove species also facilitate water absorption while excluding all salts present in surrounding waters (Kitaya et al. 2002). Although the exclusion of salts during water exchange prevents direct salt acquisition, it results in hypersaline soils around the base of mangroves which cause strong osmotic pressures capable of pulling water out of the roots and resulting in fatal desiccation. To prevent severe water loss from hypersaline soils, plants produce highly viscous sap to decrease internal water flow and transpiration rates and increase water retention (Zimrnerman et al. 1994). Mangrove species that are unable to exclude all salts present in tidal water, absorb a small percentage and excrete them through modified leaves containing salt glands (Azocar et al. 1992). To regulate osmotic balance, absorbed salts may also be shunted into bark or senescent leaves or accumulated and converted into organic compounds such as glycine and betaine (Tomlinson 1986, Ashihara et al. 1997). The mangrove trees that do not possess any of the aforementioned structures or mechanisms appear to be very efficient at using and retaining water over a wide range of osmotic gradients. They do not actively sequester water and exclude salts but rather passively absorb low salinity surface water and use it sparingly (Medina et al.

1990, Lin and Sternberg 1994).

Continuous tidal flushing results not only in salinity fluctuations but also in a decrease in the amount of oxygen in mangrove sediments. To respond to low oxygen availability, mangroves have developed elaborate above-ground root systems, referred to as stilt roots in Rhizophora species and pnewnatophores in Avicennia species

(Figure 3.1) (Toledo et al. 1995, Tomlinson et al. 1986). These roots are abundant in air breathing cells, or lenticels, that adjust in size in order to regulate the degree of gas Figure 3.1 : Photo of Avicennia marina pneumatophores exchange between mangrove trees and the surrounding environment (Kathiresan and

Bingham 2001). Mangrove roots also have non-lenticellular structures that promote

oxygen exchange (Hovenden and Allaway 1994). These are particularly important for

Avicennia species as pneumatophores grow at rapid rates in oxygen limited

environments and newly-formed tips require a few days to develop lenticels

(Hovenden and Allaway 1994). Without non-IenticelluIar gas exchange, this species

would experience high mortality rates in areas of decreased oxygen concentrations. In

addition to the stresses of anoxic, saline sediments, mangroves are often subject to

poor nutrient availability. Mangal growth is commonly limited by either nitrogen or

phosphorus in areas that do not receive eutrophic runoff from agriculture or industry.

Mangroves are able to ff ourish in nutrient-depleted environments as a result of various

adaptations including low photosynthetic capacities, low levels of nutrient loss from

plant tissue, slow growth and long life-spans (Aerts et al. 1999, Bryant et al. 1983).

Mangrove trees also rarely use nutrient stores for regeneration as they experience

minimal losses to herbivory owing to the production of toxic, protective compounds

such as acrid latex (Kathiresan and Bingham 2001). The nutrient cycling mechanisms

of mangroves are analysed in detail in the next section

3.3.3 Nutrient Dynamics

The vegetated intertidal mudflats bordering land and sea are some of the most productive ecosystems in the world. They contribute large amounts of carbon to coastal estuaries and inlets by way of leaf-litter, which can reach quantities of 10 tomes per hectare per year (Adeel and Pomeroy 2002). It is unclear if mangrove- originating carbon affects oceanic carbon cycles but the trophic contribution of carbon is thought not to extend much beyond the mangal habitat where it provides a primary source of nutrition for juvenile organisms and sediment-dwelling bacteria (Lee 1999,

Jennerjahn and Ittekkot 2002). Understanding how leaf-litter is processed into suitable forms for microbial and plant uptake in nutrient-poor mangal environments requires a close look at the nutrient cycling capacity of mangroves.

Nutrient retention in mangroves is influenced by an assortment of abiotic and biotic conditions such as light intensity, temperature, salinity, substrate type and detritivore and microbial diversity (Alongi et al. 1992, Toledo et al. 1995). Although all these factors have the potential to affect nutrient dynamics, the most influential players in the achievement of adequate nutrient processing and retention rates are the microbial communities (Holguin et al. 1992, Holguin et al. 2001). Microbes attach themselves to mangrove detritus, roots and submerged structures as well as line sediment surfaces in the form of cyanobacterial mats (Gotto and Taylor 1976, Zuberer and Silver 1979, Holguin et al. 1992). They fhction in symbiosis with mangrove trees by converting incoming nutrients into forms suitable for plant uptake while receiving energy from root exudates and enjoying optimal plant-mediated soil salinities, pH and oxygen concentrations (Holguin et al. 2002, Nedwell et al. 1994).

As mangrove growth is frequently limited by nitrogen or phosphorus availability, it follows that these nutrients are of great importance to mangal-dwelling species.

Nitrogen usually enters natural mangrove ecosystems in the form of leaf-litter. Crab species mechanically break down plant matter which is then processed by bacteria and sediment-dwelling fungi (Smith et al. 1991). These microbes synthesize enzymes capable of degrading plant materials such as lignin and cellulose resulting in partially decomposed organic litter, or detritus (Bremer 1995). Detritus is broken down fiuther by other microbial communities and then consumed by a number of organisms (e.g. crustaceans, molluscs, insect larvae, fish and resident plant species). Mangrove flora also utilise nitrogenous products of microbial processes, specifically nitrate (N03-)

and ammonium (NI%+)(Holguin et al. 2001) (Figure 3.2).

Phosphorus is usually present in low concentrations in mangrove waters. A small

percentage of this nutrient is available for plant primary productivity, but the majority

is immobilised as iron, calcium or aluminium phosphates in acidic mangrove soils

(Robertson and Phillips 1995). Few studies have analysed phosphorus dynamics in

mangal regions, but it is thought that phosphate-solubilising bacteria are involved in

freeing up sediment-bound phosphate thereby making it available to plants (Davis et

al. 2002, Tam and Wong 1999, Holguin et al. 2001). Under anaerobic conditions,

sulphate-reducing bacteria are also involved in the production of soluble iron and

phosphorus that is then used by a number of mangrove organisms (Sherman et al.

1998).

Although nitrogen and phosphorus are repeatedly identified as the most imperative

components of basic mangrove nutrient cycling, it is worthwhile recognising other

important nutrients, such as potassium and sodium, which contribute to mangrove

production. In order to maintain suitable permeability for mangrove survival during

salinity fluctuations, a high potassium-to-sodium ratio in leaf and root cells is

required. This ratio also ensures that potassium is prevalent in greater concentrations than sodium which results in high flowering and reproduction rates (Ukpong 1997).

3.3.4 Associated Flora and Fauna

As is evident fiom the nutrient cycling relationships between mangroves and microbial communities, mangrove trees could not survive in isolation They depend on a number of other mangal-dwelling species that in turn require some of the services provided by mangroves. Plant Growth

Mangrove Stand

Leaf litter Uptake

NH,+--b NO,- -+ NO,--+ NO, -bDenitrification

Nitrification

N, fixatiodoxidation

Anthropogenic Inputs

Figure 3.2: Simplified nitrogen cycle in mangrove ecosystems (modified from Schulze 2000) In addition to a myriad of bacterial assemblages, mangals are also home to an

abundance of algal species. Macroalgae are commonly found on hard mangrove

substrates, such as roots and tree trunks, while microalgae preferentially reside on soil

surfaces (Hogarth 1999). These photosynthetic algae contribute between 20% and

50% of total net mangrove production (Kathiresan and Bingham 2001).

Mangroves are home not only to a variety of floral species but also to plentiful marine fauna. Along with the short-term transient organisms that use mangroves only in juvenile life stages, a number of species permanently reside in mangroves. Many bivalves and snails as well as crustaceans and feed off organic detritus provided by mangroves and use the multitude of niches in these environments for protection from predators and abiotic stresses (Hogarth 1999). Sponges attached to prop roots, for example, provide mangroves with a source of nitrogen while receiving carbon from root structures (Ellison et al. 1996). In addition, they provide coastal trees with anti-predator defence against a number of pathogenic organisms

(Kathiresan and Bingham 2001, Ellison et al. 1996).

Of all the associated mangal fauna, crabs appear to provide the greatest number of benefits to coastal forests. There are four distinct types of mangrove crab: detritivores, that obtain nutrition from sediments, herbivores, that feed directly on leaf debris and seek leaves from the tree canopy, active predators and opportunistic scavengers (Twilley et al. 1997). Herbivorous crabs provide the vital service of harvesting leaf-litter that would otherwise build up on forest floors and cause root suffocation (Lee 1999). Crabs are capable of collecting the equivalent of one day's fallen leaves in under an hour vwilley et al. 1997). These leaves are stored in burrows to decrease tannin concentrations and are later masticated into a more suitable form for detritivorous crabs and microbial processing (Holguin et al. 2001, Lee 1999). Crabs further aid microbial activity by providing a low tannin microbial substrate in the form of faeces and also have a role in the growth and reproduction of mangrove trees (Lee 1999). Their complex burrow systems improve sediment water flow, facilitate removal of toxic compounds and increase soil aeration thereby decreasing levels of ammonium and sulphide in mangrove soils (Smith et al. 1991, Holguin et al.

2001, Howes and Goehringer 1994).

3.3.5 Natural and Anthropogenic Im~acts

The intertidal zone is an area &ected by natural weather fluctuations and tidal regimes. Mangroves must endure the stresses of these daily variations as well as acute and violent coastal storms and changes in global climate patterns. The shallow root systems of mangroves, coupled with their unsheltered coastal environment, make these forests extremely susceptible to high winds fiom typhoons and cyclones.

Mangroves commonly experience uprooting and defoliation as well as hindered propagation rates resulting from seedling damage (Kathiresan and Bingham 2001).

Freefloating mangrove seedlings are frequently suffocated by sediment build-up or killed by high concentrations of toxic sulphides released during soil disturbance

(Smith et al. 1996). Mangal habitats are also indirectly affected by mass mortalities of key species imperative to mangrove health.

Mangroves are not only sensitive to climatic variations induced by local storm fronts but also to global climatic changes. Increasing carbon dioxide concentrations are expected to cause a rise in atmospheric temperatures and a subsequent increase in sea level. Changes in tidal levels and rainfall affect hydrological regimes and have the potential to both enhance and hinder mangal health (Lee et al. 1996). Small variations in atmospheric temperatures will minimally affect mangrove survival, but may result in changes in species assemblages and an increased prevalence of intertidal forests along subtropical shores (Ellison 2002). Increased water levels may negatively influence mangrove growth rates although mass mortalities are not predicted as mangroves have been shown to display inland migration in response to rises in water levels (Sayed 1995).

In addition to the stresses induced by natural impacts, mangroves experience severe stress from a variety of anthropogenic sources. A lack of understanding about the ecological importance of mangroves has resulted in worldwide exploitation by charcoal, timber and aquaculture industries as well as unregulated waste disposal, unrnonitored oil spills and altered hydrological patterns (Adeel and Pomeroy 2002).

Some regions of South America and Southeast Asia have experienced mangrove losses of as much as 90%, resulting mostly from industrial, agricultural and aquacultural expansion (Holguin et al. 2001, Twilley et al. 1997). Mass clearance of mangroves affects neighbouring ecosystems by altering coastal sedimentation patterns which results in increased erosion rates and a decrease in the amount of organic material available to organisms living in the intertidal zone (Jennerjahn and Ittekkot

2002).

In recent years, high inputs of eutrophic waste have been labelled as one of the main culprits of mangrove degradation. The global expansion of shrimp aquaculture operations has resulted in large effluxes of nutrient-rich waste into mangrove areas.

Although some researchers predict that high loads of aquaculture effluent are detrimental to mangroves (e.g. Feller 1995, Madeira et al. 1999), at present there is no conclusive evidence that shrimp farms negatively affect mangrove dynamics. Some studies actually suggest that shrimp farms may contribute to increased growth and survival rates (Raj endran and Kathiresan 1996). Altered patterns of freshwater influxes are also of concern as they compromise

mangrove health and survival. Dam and highway construction in Brazil and

Columbia has diverted or blocked freshwater channels that naturally empty into

coastal regions and resulted in mass mortalities in affected mangal areas (Lacerda et

al. 1993 a in Holguin et al. 2001).

Although the cumulative impacts of anthropogenic stresses over extended periods

are unknown, it is hypothesised that even slight alterations to natural mangrove

functions will have far-reaching impacts owing to tbe intricate interconnections

between mangroves and numerous other ecosystems (Lee 1999).

3.4 Uses of Manmoves

The uses of mangroves are examined in this section with respect to the material

and protective benefits of mangal habitats for coastal communities. The potential for mangroves as tourist venues is also explored followed by and an in-depth discussion of mangrove biofiltration efficiency.

3.4.1 Local Subsistence

Coastal communities in tropical and subtropical regions acquire a myriad of benefits from mangroves that allow them to both sustain and improve their quality of life. Forested coastlines serve as natural barriers between oceans and land. During tropical storms, vegetated intertidal fringes decrease the speed of water flooding into terrestrial areas thereby minimising property damage and associated fatalities (Adeel and Pomeroy 2002, Ewe1 et al. 1998). Intact mangroves also prevent the destabilisation of coastal soils and consequently increase the stability of neighbouring homes often at risk of being pulled into the ocean during flood periods.

From a consumer perspective, mangroves provide an array of domestic products, such as honey, sugar, alcohol, tea, cigarette wrappers and musical instruments, as well as wood-derived construction materials for local or commercial uses (Hogarth 1999,

Tomlinson 1986). In addition to timber, other mangrove derivatives including charcoal and rayon are important commercial products (Ewe1 et al. 1998). A few unexplored mangrove by-products with great potential for national and international markets include UV-screening extracts and anti-viral medicines that may attenuate viruses such as HIV and hepatitis B (Kathiresan and Binghamm 2001).

3.4.2 Coastal Function

Mangal habitats are permanent homes to a multitude of terrestrial and marine organisms and a temporary refuge for over 90% of all marine species (Holguin et al.

2001). Mangroves directly benefit juvenile fish, crabs, shrimps, molluscs, jellyfish and birds by providing grounds for spawning, nursing and feeding (Tomhson 1986,

Lee 1999). They also provide indirect benefits to organisms in nearby waters by trapping excess sediments and nutrients originating fiom terrestrial regions thereby impeding the accumulation of suffocating soils and decreasing the occurrence of detrimental algal blooms. In addition, mangroves may be effective in neutralising or precipitating toxic chemicals in pesticides and other chemotherapeutants thus protecting mangal species fiom the deleterious effects of chemical additions (Clough et al. 1983). 3.4.3 Tourism

Although mangroves are often thought to be fetid swamps abundant in insects,

reptiles and pungent odours, the presence of many popular species of wildlife, such as

alligators, monitor lizards and wading and migratory birds, has the potential to benefit

the tourism industry. Boardwalks raised above tree canopies and guided kayak or

canoe tours through mangrove waters allow tourists to catch a glimpse of wildlife in their natural environment while minimally impacting their habitat. Examination of the

revenue-generating potential of mangroves as tourist attractions is in its infancy, but in the few regions where this has been tested, such as the forests of Juala Selangor in

Malaysia, the results are encouraging (Hogarth 1999).

3.4.4 Wastewater Filtration

Freshwater wetlands have been analysed for their wastewater treatment capacity for many years, but very little research has focused on saline wetlands, specifically mangroves. There are several reasons for the lack of information regarding mangrove biofiltration. Until recently, mangroves were regarded as barren wastelands suitable

only for clearing. With the realisation of the ecological importance of mangroves, efforts have been made to protect these coastal forests. The establishment of shrimp farms in mangrove areas as well as the dumping of sewage and eutrophic or industrial pollutants into mangal habitats has been discouraged if not prohibited in many countries such as Australia, the United States, Thailand and parts of Indonesia

(Kathiresan and Bingham 2001, Kongkeo 1994). The complexity of mangrove systems and their interrelationships with other ecosystems, along with newly-enforced regulations regarding mangrove management, has probably deterred many researchers from conducting experiments in mangal regions. Despite the difficulties inherent in mangrove analyses, some have realised the potential benefits these intertidal forests

may provide and have pursued studies in this field. The research specific to

mangroves as wastewater treatment wetlands has produced both indeterminate and

promising results.

One of the most complete investigations of mangrove filtration capacities involved

300 hectares of natural mangrove subjected to thrice-weekly influxes of sewage over a

one-year period (Wong et al. 1997). Constant sewage loading in the mangrove had no negative effect on mangrove trees. On the contrary, the loading appeared to decrease the death rates of trees. No significant differences in growth, species composition or

leaf nutritive status were observed between test and natural tree stands (Wong et al.

1997). These results are also supported by previous research (Rajendran and

Kathiresan 1996, Yates et al. 2002). In addition, the treatment mangrove appeared to

effectively process applied inorganic nitrogen as only a small percentage accumulated in the sediments. Tidal action may have aided the export of nitrogen into surrounding waters, but its contribution was considered negligible in this experiment. As a result, it was concluded that the majority of nitrogen in the wastewater was processed by plants or microbes and released into the atmosphere as nitrogen gas (Wong et al.

1997). In addition to metabolising nitrogen, sediments near effluent discharge pipes contained high concentrations of phosphorus post-wastewater application. This indicates the effectiveness of mangrove sediments in trapping and irnmobilising phosphorus (Wong et al. 1997). The effectiveness of mangroves in the treatment of nitrogen and phosphorus wastes is also supported by Ye et al. (2001). This study revealed that when livestock waste was applied to a mangrove, the system was capable of removing over 80% of the nitrogen and 70% of the phosphorus from the effluent. Mangroves not only filter nutrients, but also serve as heavy metal sinks, for cadmium, zinc, manganese and copper, and are effective sediment traps (Tam and

Wong 1998,Robertson and Phillips 1995). Concentrations of suspended solids present in wastewaters have been reported to decrease by as much as 95% after treatment by natural mangroves (Sansanayuth et al. 1996, Gautier et al. 2001). Vegetated biofilters decrease the flow rate of incoming effluent thereby allowing time for suspended sediments to settle-out of wastewater (Gautier er al. 2001). The impact of large sediment loads on mangroves over extended time-periods has not been determined, but no detrimental effects have been reported as yet.

The nutrient uptake capacity, heavy metal irnmobilisation and sediment-trapping properties of mangroves resemble that of other wetland systems currently used for freshwater effluent treatment (e.g. Johnson 1991). Mangroves may, however, prove more efficient than vegetated inland biofilters as they are adapted to tidal inundation at all times throughout the year. Most freshwater wetlands are naturally subject to wet and dry seasons and require periods of drying in order to function optimally (Gopal

1999). Mangroves may therefore be able to process wastewater at more frequent intervals than freshwater treatment lands.

Although mangrove filtration studies have yielded promising results, it is important to consider the potential problems and limitations of such systems. Large inputs of eutrophic effluent cause severe oxygen depletions resulting from increased biological activity. Decreased oxygen availability often induces an aerobic-anaerobic environment to shift to a completely anaerobic system characterised by less efficient nutrient cycling ability (Holguin et al. 2001, Robertson and Phillips 1995). In order to maintain adequate nitrification rates, external aeration techniques may be required to manually increase oxygen levels (Tilley et al. 2002). If sufficient oxygen is available, the addition of nitrogen-rich waste will cause nitrification and rates to

increase. These processes are benign, but in anaerobic environments lead to the

production and release of nitrous oxide NO), a compound that may contribute to the

destruction of the ozone layer (Corredor et al. 1999). In addition, heavy loadings of

nitrogen-rich effluent have the potential to hinder the completion of microbial

nitrification processes. Excessive ammonia inputs can lead to nitrite (Nod

accumulation, a substance toxic to all marine organisms (Figure 3.2). Mangroves

may, however, be able to assimilate large quantities of ammonia without

compromising nitrification rates. Inputs of eutrophic emuent may also stimulate

methanogenic sediment bacteria and cause the release of toxic amounts of methane

(Strangmann et al. 1999 in Holguin et al. 2001, Giani et al. 1996).

As previously mentioned, mangals are typically low-nutrient environments,

limited by nitrogen or phosphorus. A few researchers have suggested that increasing the availability of a naturally scarce nutrient may decrease the efficiency of mangroves to process that nutrient (e.g. Feller 1995, Madeira et al. 1995). This hypothesis has, however, been refuted by others who claim that altering nitrogen

andlor phosphorus levels has little or no effect on nutrient transformations (e.g.

Baddeley et al. 1994, Bowman 1994).

Other factors that must be considered are the hydraulic residence time (HRT) and the wetland area required for adequate water treatment. Longer HRT allows less wetland area to be used to treat the same amount of effluent as a larger area with shorter HRT (Tilley et al. 2002). Studies examining the potential of saline wetlands in the treatment of shrimp pond effluent suggest that, with HRTs of two to five days, the ratio of pond area to required wetland area is between 0.14 and 22 (Gautier et al.

2001, Tilley et al. 2002, Robertson and Phillips 1995). The study yielding the higher estimate assumed that plant uptake was the only sink for nutrients (Robertson and

Phillips 1995). As sediment processes are known to significantly contribute to nutrient processing, this value is probably greatly overestimated (Kristensen et al.

1998).

Due to the rapid decrease in global mangrove coverage, the unknown effects of anthropogenic stresses on mangal areas and the great ecological importance of natural mangroves, it is important to acknowledge their unsuitability as experimental treatment wetlands. Although they appear to be unharmed by, and may even benefit from, wastewater influxes, no long-term studies have been conducted to assess the cumulative effects of nutrient-rich applications. Until mangrove destruction ceases and the percentage of global mangal coverage increases, it is probably wise to refrain from tampering with these complex tidal forests.

3.5 Constructed and Modified Mangroves

A possible procedure to ensure the longevity and health of natural mangroves while also allowing wastewater producers to benefit from mangrove nutrient biofiltration efficiency is to develop constructed or modified mangroves. At present, few researchers have attempted to construct mangroves although there are numerous examples of constructed freshwater treatment wetlands (e.g. Johnson 1991, Brix

1999).

3.5.1 Design

Constructed wetlands have typically been designed in one of two ways: surface flow or sub-surface flow. Surface flow wetlands consist of basins or channels with soil substrates that often possess sub-surface liners to prevent seepage. Wastewater is directed through the system at shallow depths and treated by submerged macrophyte

tissues and associated microbes (Brix 1999). Sub-surface flow wetlands possess sand

or gravel substrates with sub-surface passages into which water is channelled and

processed primarily by microbial activity (Brix 1999). Theoretically, it should be

possible to construct mangrove treatment areas following designs similar to those of

constructed fieshwater wetlands.

3.5.2 Can Mangroves be Constructed? A Question of Environmental Feasibility

Most efforts to grow mangroves have focused on replanting trees in areas that were once abundant in mangroves but have since suffered significant losses due to human or natural disturbances. In order to ascertain if mangroves can be grown, it is useful to examine their reproductive biology. Mangroves display both self-pollinating and cross-pollinating mechanisms (Kathiresan et al. 2001). Following pollination, a few species produce seeds while the majority display vivipary. Vivipary is characterised by the growth of embryos on the parent plant. Propagules remain attached to parents for a few months after which they are released into surrounding waters for dispersal. Following a period of one to three months, propagules settle and grow roots (Hogarth 1999).

It was initially thought that rooted propagules could be transplanted fiom one site to another with minimal negative impact on growth or survival, but attempts to move these structures have been unsuccessful (Kathiresan and Bingham 2001). Researchers have also made efforts to collect fiee-floating propagules for manual planting, but high rates of crab and insect herbivory often render a large proportion of propagules obsolete (Famsworth and Ellison 1997). Other studies of attempts to replant mangroves destroyed by anthropogenic stressors revealed that if sufficient numbers of healthy propagules are available, rapid recolonisation can be achieved (Panapitukkul et al. 1998 and Walters 2000). Propagule survival rates can be dramatically improved if grown in nurseries for a few months before replanting (Hogarth 1999). Cultivation of certain species from seeds has also proven successful, but growth rates are slower owing to high biological requirements of free-standing seedlings (Hogarth 1999).

One of the most extensive and successful mangrove reforestation efforts was undertaken in Pakistan with Rhizophora species. Propagules were grown in nurseries for one year and then replanted along the coastline. Manual algae removal and replanting of toppled seedlings was maintained for two years resulting in a survival rate of 95%. After three years, all 12 000 hectares of replanted mangroves reproduced naturally (Qureshi 1996). Although these mangrove stands are healthy and fecund, they do not display the same diversity as natural mangroves. When mangroves are replanted, growers tend to plant only one or two species whereas natural stands typically consist of 10 to 20 species (Walters 2000). The species chosen by growers are usually of local importance, providing wood for fishing apparatus, ~~nstruction and fuel. Little research has been done on the internal dynamics of replanted mangroves, but a lack of diversity in such stands may result in the development of sub-optimal ecosystem relationships compared with those of natural mangroves.

Reforestation efforts, therefore, should attempt to maintain natural species' diversity

(Walters 2000).

Given the success of pilot replanting projects it is reasonable to assume that, with sufficient care and monitoring, mangrove trees can be grown in areas where they recently occurred naturally. The dificulty facing mangrove construction is whether this knowledge can be extrapolated to non-mangal areas. Owing to the lack of understanding surrounding natural mangrove dynamics, it may not be wise to place constructed mangroves in sensitive estuaries if they are to be used as wastewater filtration systems.

Natural mangroves occur in environments that experience constant changes in temperature, salinity, tidal flushing and oxygen availability. The mechanisms they possess to ensure survival in such varying conditions may also enable them to grow in regions where they do not occur naturally. As previously mentioned, mangroves can grow under a variety of salinities without compromising their nutrient cycling efficiency. In addition, certain species, such as Avicennia marina are also unaffected by light or temperature variations (Tam 1998, Tam and Wong 1999, Clarke and

Allaway 1993). Although some species are sensitive to environmental variations during early development, plant growth-promoting bacteria (PGPB) may enhance growth in sub-optimal environments (Bashan and Holguin 1997, Bashan and Holguin

2002). Tidal inundation and tidal levels are also important to certain species, but if this requirement is known in advance, effluent inputs can be controlled to mimic natural tidal fluxes.

Another important consideration in mangrove construction is the presence of key mangal species. Microbial communities are not thought to be of concern as they occur in all environments throughout the world, Vital crab species, although not ubiquitous, may naturally migrate into areas where mangroves are being grown, be transferred from areas with natural mangrove stands or be cultured in captivity and added to constructed mangroves (Alongi ef al. 2000).

There are a number of tropical coastlines around the world with well-drained alluvial soils in which mangroves do not grow. Researchers initially suspected that unidentified environmental or anthropogenic stresses prevented mangrove residence in these areas, but dispersal strategies were soon identified as the limiting variables (Tomlinson 1986). A promising example of the potential of mangroves to grow in

areas where they are not native can be seen on the islands of Hawaii. Hawaii has no

natural mangal areas but manually transplanted seedlings have established and

flourished on many islands revealing that mangrove absence in certain geographical

areas may be due to dispersal limitations, not unsuitable environments (Tomlinson

1986).

3.5.3 Economic Feasibility

Assuming mangroves can be constructed, the question of economic feasibility is raised. If mangroves are to be grown from either seeds or propagules, the amount of manpower and time investment required to nurture seedlings must be considered. If the highly labour-intensive example in Palastan foreshadows the inputs required to successfully construct mangroves, then this form of natural wastewater treatment may prove too costly to gain widespread popularity. If, however, future planting efforts show encouraging results with minimal financial investment, mangroves could be the key to effective natural wastewater treatment.

As previously mentioned, there are major discrepancies concerning the ratio of mangrove area to wastewater area to successfully treat nutrient-rich effluent. Most countries requiring wastewater treatment facilities, specifically for sewage and aquaculture effluent, are in the developing world where available land is scarce and hence extremely valuable. More accurate measurements must be obtained regarding the amount of mangrove area required for effluent treatment before conclusions can be drawn about whether these natural filters are economically feasible for communities in developing countries. When economic concerns are considered, along with the uncertainty about the

long-term efficiency of mangroves as wastewater filters and the ecological importance

of natural mangroves, there appears to be a need for an interim mangrove treatment

area that is not as ecologically important or sensitive as natural mangroves nor as potentially labour intensive to produce as constructed mangroves. The development of lower-cost modified mangroves may provide further insight into mangrove treatment capacities while minimally affecting coastal ecosystems. Modified mangroves can be created from small plots of natural or replanted mangroves along subtropical and tropical shores. These plots are sectioned off from natural tidal inundation through the creation of banks. Levees directing incoming water may be constructed throughout the mangrove as long as the development of these channels does not require removing a large proportion of mangrove vegetation. If levees are created, treated water can be directed into an outflow pipe or ditch from which samples can be taken to ascertain the quality of outgoing water. If levee construction necessitates severe mangrove clearance, water can be shunted into mangroves to naturally disperse throughout the treatment area Ditches can also be created around the perimeter of the mangrove to collect all treated water. Depending on the quality of the treated water, it can either be recirculated into the wetland area for further treatment, discharged into the ocean or reused by industries such as aquaculture.

Monitoring water quality in modified mangroves will provide data that can be used to determine if mangroves are effective biofilters and if their environmental benefits outweigh the investments required for their construction Cost-benefit analyses can then reveal if efforts should be made to construct mangrove treatment lands. 3.6 S-

Mangroves are complex ecosystems with the ability to endure extreme environmental conditions while also providing vital niches for numerous marine and terrestrial organisms. Their importance often extends beyond the boundaries of the intertidal zone as they serve as effective nutrient sinks and sediment traps thereby protecting ocean-dwelling species from pollutants (Hogarth 1999).

The potential of these intertidal forests to extend their nutrient cycling capacities to the treatment of effluent originating fiom anthropogenic sources has only recently become of interest. The few studies that have been conducted show great potential for mangroves as wastewater filters. Until in-depth research reveals the intricacies underlying natural mangrove dynamics, it may be more suitable to examine the biofiltration capacity of modified or constructed mangroves. This research examines the efficiency of a modified mangrove as an effluent filtration system and attempts to provide insight into the potential of this form of natural wastewater treatment and its significance for many coastal regions throughout the world. CHAPTER 4

STUDY AREA AND METHODOLOGY

This chapter provides a brief description of Chanthaburi, the Thai province in

which the study site was located, as well as detailed information about the shrimp farm and mangrove under study. Procedures followed throughout the field season are presented along with the water sampling strategies and specific laboratory analyses employed during the study.

4.1 Renional Context

Chanthaburi lies 260 km east of Bangkok, bordered by the Thai provinces of Trat,

Chachoengsao, Sa Kaeo, Chonburi and Rayong as well as Battambang, one of

Cambodia's western provinces (Figure 4. I). The region experiences two distinct seasons: monsoonal weather dominates between May and October and hotter, drier conditions emerge during the months of November to April (see Figure 4.2 for average monthly temperatures). The average annual rainfall in Chanthaburi is estimated at 21 00mm with monthly averages presented in Figure 4.3 (Raine 1994).

For many years, the region's economy was primarily supported by the gem trade and secondarily by revenues fiom fruit orchards and rice crops. In 1991, however, shrimp farming emerged as the leading source of income in the province. Shrimp aquaculture operations were established in areas previously allocated to salt-pans, fruit orchards and rice paddies as well as pristine coastal lands bordering mangrove forests

(Raine 1994). The boom in shrimp aquaculture coincided with a dramatic decrease in mangrove cover in the area, but it is unclear whether a direct correlation between the two events exists. The decrease in mangrove coverage has significantly changed Figure 4.1: Map of Chanthaburi with approximate location of the study site Jan Feb Mar Apr May Jun Jul Aug Sep &t Nov Dec Months

Figure 4.2: Average monthly temperature in Chanthaburi, Thailand (Global Historical Climatology Network, 1990)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months

Figure 4.3: Average monthly rainfall m Chanthaburi, Thailand (Global Historical Climatology Network, 1990) and sedimentation patterns causing much of the coastline to become covered

in duck layers of alluvial, humus rich soils. This has not only decreased the aesthetic

appeal of the area but has also decreased coastal water quality and thereby negatively

impacted fisheries and aquaculture operations.

An examination of the land use practices in the coastal zone of Chanthaburi

province reveals the dominance of shrimp aquaculture in the region (Table 4.1).

Current land use data for Chanthaburi is unavailable, but it is assumed that the present

coverage of shrimp ponds in the region is higher than 45.3%, the documented

percentage in 1991.

Most of the shrimp fmsin the province are situated adjacent to coastal lands and, as with those throughout Thailand, are small-scale backyard farms consisting of 1 to

10 ponds of 0.1 6 to 1.0 ha each (NACA 1996). A number of large-scale operations existed in the province until the mid 1990s when large farms were rendered financially risky due to an increased incidence of disease outbreaks and subsequent mass mortalities.

4.2 Farm Area

The shrimp farm studied in this thesis is located on the coast of Chanthaburi province near the town of Laem Sing latitude 12" 28' 27" N, longitude 102" 03' 45" E

(Figure 4.1). The farm consists of 37 ponds, stocked with 50 to 80 PLI~~.Each pond is approximately 2 to 3 rai (0.32 to 0.48 ha) in size and all are arranged within a 1 km by 0.2km area A reservoir borders the west side of the farm, beginning at the farm access and continuing down to the coastline (Figure 4.4). The reservoir is filled twice weekly by opening a floodgate at the coastal end of the channel and allowing seawater to flow in freely at high tide. The coastal area directly south of the farm has Land Use as of 1991, Percent Coverage

Mangroves Shrimp farms Upland forest Rice paddy Fruit orchard Rubber plantation Scrub Marsh Salt pan Beach

Table 4.1 : Land use practices along the coast of Chanthaburi in 1991 (Raine 1994) Gulf of Thailand

7/-----7--

\

Emuent gate

Reservoir

,

Mangrove (1hmp pond

fgj... Access road

Effluent canal

Figure 4.4: Layout of the shrimp fmand mangrove study site (not to scale) experienced a recent decline in its mangrove coverage and as a result is susceptible to

large influxes of sediment. Tidal action agitates much of the flocculent sediment

layer, decreasing the suitability of tidal water for shrimp cultivation. As a result, the

reservoir is used as a settling area for any suspended sediments in influent waters that

may hinder farm productivity. Once sediments have settled, reservoir waters are used to replace water in ponds lost to seepage, evaporation and occasional water exchange.

The ponds are maintained by local fmers, each of whom is responsible for 4 or 5 ponds. The fmers monitor shrimp growth and disease and vary medication, chemical application, feed quality and quantity and water exchange according to the particular requirements of each pond. The exact management practices of each farmer were not documented but it is assumed that they are representative of most farms in the region with the exception of sludge removal and disposal techniques. Throughout

Thailand, sludge that accumulates on the pond bottom throughout a shrimp culture cycle is typically removed by pressure hose at the time of harvesting and drained into effluent canals which filter into the coastal waters. The owners and managers of the farm under study, however, are aware of the damaging effects of such practices, and have developed their own sIudge management techniques. Sludge is removed by a backhoe following every shrimp harvest, piled onto a flatbed truck and transported to the northern end of the fmwhere a sludge pile has been created. This mound of sludge is extremely fertile. Following a fdow period of 6 to12 months, during which natural processes dilute and remove salts fiom the soils, the area becomes viable for the cultivation of many fhits and vegetables.

As with many coastal farms, water exchange is not practiced on a regular basis.

Water exchange is commonly required to maintain water quality in inland farms with day-lined ponds as this substrate is relatively non-porous allowing for very little outflow of water from the pond area. This results in high nutrient loadings in pond water and gradual degradation of water quality that is improved by manual water exchange. In coastal areas, however, porous sands replace clay soils and result in high seepage rates of approximately 2 cm per pond per day. The loss of water due to seepage is rectified by frequent top-ups from coastal waters in the reservoir.

All water outputs from the ponds, via seepage and pond emptying, drain into an effluent canal that runs along the east side of the farm. This canal is approximately

1.8 m deep and 3.1 m wide and stretches 1 krn from where the farm meets the local access road to the coastline. Due to the close proximity of the farm to the ocean, a tidal gate has been placed at the coastal end of the effluent canal. This gate is usually kept open when the tide is out but when tide levels reach 1.5 m, seawater begins to enter the canal causing an overflow into nearby shrimp ponds. As it is undesirable to have wastewater re-enter the ponds, effluent gates are usually closed during high tide, approximately 8 hours a day.

4.3 Mangrove Description

At the southern end of the farm there is an area of mangrove, 25 by 55 m, that local farmers replanted in 1996 following mass destruction of the nahual mangroves in the resulting from a variety of anthropogenic and natural factors.

The mangrove is composed of approximately 95% Avicennia marina and 5%

Rhizophora mangle. The trees range in height from 2.5 to 4.5 m with an average density of 10 trees/m2. There is also a large population of mud crabs in the area with approximately 60 crab burrows/m2.

In order to ensure that the inputs to the study area could be controlled a plot of 25 by 35 m of mangrove was sectioned off (Figure 4.5). By excluding 20 m of the Constructed bank I

Mangrove area not used in the Mangrove Study Area study

Effluent Gate

Figure 4.5:Magnified view of the modified mangrove area with approximate location of the submersible pump (not to scale) mangrove area directly bordering the effluent canal, though the creation of a 2 m deep

trench, I prevented tidal waters from entering the mangrove during rough tides as this

would have interfered with the processes under study. Banks were also built on the

southern and eastern side of the mangrove area under study to prevent tidal waters and

effluent overflow from entering the mangrove. Unlike many mangrove areas, tidal

action did not cause seawater to enter the mangrove from beneath the sediments as the

mangrove was built on a raised area approximately 2 m higher than sea-level, A

plastic graduated cylinder rain gauge was also placed in the mangrove to collect

rainfall throughout the field season. By ensuring that the inputs to the study area were

controlled and monitored, it was possible to reduce the number of variables affecting

the mangrove system.

4.4 Experimental Desim

A submersible pump was placed in the effluent canal, 100 m south of the tidal gate

(Figure 4.5). The pump was elevated by four bamboo sticks arranged in a tent-like

fashion. The sticks were joined together with bailing twine and a plastic basket was

suspended from the sticks with rope. The basket was adjusted to a height

approximately 60 crn above the canal bottom. The pump was then placed inside the

basket which served to filter out debris originating from surrounding foliage as well as

large influxes of sediment that could become entangled and break the pump. 60 m of

PVC tubing with a diameter of 8 cm was attached to the pump with the output end 20

m from the north-eastem edge of the mangrove and approximately 5 m towards the centre of the area. Water was pumped into the mangrove at an approximate rate of

170 L per minute. A well-like structure was built in the centre of the mangrove area A 30 L plastic bucket with holes drilled into the bottom was placed in a 1.5 m deep hole dug into the mangrove sediments.

4.5 Data Collection Overview

Field visits to the study site began on July 1, using the first three weeks to prepare the mangrove area and document management practices and daily events. Beginning

July 22, visits were made to the area twice a week until September 18 when the field season ended. The site was visited at 8am every Monday and Wednesday during the aforementioned weeks and data was collected on 8 Mondays and 7 Wednesdays.

4.5.1 Pre-Treatment Sam~les:Mondays

Upon amvaI at the site qualitative data were collected. This included discussing with farmers whether or not any ponds had recently been drained or were going to be drained within the next 24 hours, documenting the position of the effluent gate (i.e. open or closed), the tide level and precipitation levels. If a pond had recently been emptied or was scheduled for draining within 24 hours it was decided that data collection for the week would be cancelled as pond drainage introduced too many uncontrollable variables. Once qualitative observations of the fann were made, a check for visual anomalies or disturbances in the mangrove, such as flooded soils, excess garbage or destruction of any sort, was carried out. The pump was also checked to ensure that no debris was lodged in the apparatus that could hinder functionality. Once it was determined that the site was in good order, the submersible pump was turned on and water fiorn the effluent canal was directed into the mangrove area Water samples were collected directly fiorn the effluent pipe in non-sterilized, plastic 2 L bottles rinsed with effluent water before samples were collected at three different time intervals: one sample when the pump was turned on, one sample three hours following this, and one sample six hours from initial pumping. After a total of three samples were collected from the effluent pipe, three more samples were collected from three random areas within the mangroves. Random areas in the mangrove were determined by mapping out a 1m by lm grid, throughout the area of the mangrove that had been flooded in the previous six hours, and selecting sampling areas using a random number table. As the depth of water after only six hours of filling was quite low, a 200cc syringe was used to collect these samples.

A11 of these samples were measured for in-situ Dissolved Oxygen, pH, salinity, conductivity and temperature. Following this, each sample was divided into two 300 mL bottles: one without a preservative and one with H2S.The non-preserved samples were used to analyse nitrate and nitrite concentrations while the preserved samples were used to determine ammonia concentrations. The 1.4 L of water remaining in each of the six 2 L sample bottle was stored on ice and transported back to Burapha

University where they were prepared for the analysis of biological oxygen demand.

Once all the samples were collected and analysed for in-situ parameters and divided into appropriate bottles, the fmers were asked to ensure the pump remained free from debris and was always submersed in water and were instructed to turn the pump off in 24 hours.

4.5.2 Post-Treatment Samples: Wednesdays

Upon arrival at the site, discussions were carried out with one of the farm managers to determine if any unexpected events had occurred in the 48-hour period since the initial samples were collected. The exact time that the pump was turned off was also determined from a logbook where farmers recorded their activities. The amount of precipitation was recorded from the rain gauge and three water samples

were collected fiom three random locations withn the mangrove, with the use of a

200cc syringe. One sample was also collected from within the well. All samples

were analysed and stored in accordance with the methods previously mentioned for

the Monday samples.

4.6 Instrumentation and Laboratory Analyses

Dissolved Oxygen was measured using a Hach SensIon 6 portable Dissolved

Oxygen probe, pH was determined using a Horiba D-21 portable pH meter and

salinity, conductivity and temperature were assessed by a YSI 85 portable probe.

Conductivity measurements were all corrected to 25'~.All instruments were

calibrated once a week in accordance with manufacturers instructions.

Laboratory analyses were also conducted for biological oxygen demand, nitrate,

nitrite and ammonia with the assistance of NCA Laboratories Co. Ltd. (Thailand).

Each sample obtained in the field was divided into three equal portions and analysed

for the aforementioned parameters. All samples were filtered and triplicate laboratory

analyses were conducted to ensure analytical errors did not skew results.

Biological oxygen demand (BOD) was analysed in accordance with APHA

(1992). The only variation to these methods is that, given the poor water quality and

subsequent high demand for Dissolved Oxygen, along with the rudimentary laboratory

facilities and lack of dilution solution, Dissolved Oxygen measurements were taken

over a two-day period instead of the standard five-day period. It is understood that

BOD2 values are not comparable to BOD5 values recorded in most of the literature

and, as a result, the obtained values were only to be used for comparisons within this

study. Nitrate (N03-N) was analysed using the APHA cadmium reduction method (1992) with lowest reporting limits 0.05 mg/L.

Nitrite (NO2-N) was analysed using conventional APHA standard methods (1992) reported to a minimum of 0.003 mg/L.

Ammonia (NH3-N) was analysed in accordance with APHA standard methods ammonia-selective electrode method (1 992) using with a 0.1 mgk reporting limit.

4.7 Limitations

It is important to note that there are several limitations to this study that must be taken into account when analysing and interpreting the data. The most profound of these is that water samples were only taken for the first 6 hours of the 24 hour mangrove filling period. Due to great distances between study site and laboratory, the specific storage requirements of each sample and the time required to analyse each parameter, it was not feasible to collect samples over a longer time period. Given the nature of the farm, 37 ponds all at different stages during the production cycle, and the efforts made to avoid sampling on days that would yield unusual effluent values (e.g. days of pond drainage and harvest), it is assumed that effluent data collected on different weeks can be averaged and considered representative of what was pumped into the mangrove over each 24 hour filling period.

Post-treatment measurements were determined fiom water samples collected within the mangrove 48 hours after initial filling began. These samples are not representative of what is leaving the mangrove and filtering into the ocean, but rather provide information on how above-sediment processes alter the qudity of water for the parameters of interest. Although sediment processes are thought to significantly contribute to lowering nutrient concentrations (Kristensen et al. 1998), it was not possible to manipulate the mangrove to enable collection of samples that had been exposed to sediment processes. In order to do this, concrete levees and an outlet pipe would have needed to be constructed and it was feared that such large disturbances would negatively affect mangrove flora and fauna and compromised nutrient cycling processes. CHAPTER 5

RESULTS AND DISCUSSION

This chapter presents the results of this study and compares data collected in the field with those from previous research. In-depth analyses of the findings of the research provide explanation for any disparities between the results of this study and those of other researchers. The major findings from the field investigation are then used as a basis for assessing the feasibility of mangrove wastewater treatment on a large-scale basis, and to identifl key areas in the field of mangrove biofiltration that require further research. The management implications of mangrove treatment areas are discussed on a local scale and also in a more regional context to display the wide range of benefits mangrove treatment areas could provide to nations participating in the shrimp farming industry.

5.1 Sample Identification

Prior to describing statistical analyses conducted on the data collected, the labels used for sample week and day identification are defined. Data were collected for an

8-week period between July and September 2002.

Three samples were collected on each sampling day and, for ease of sample identification, they are referred to in the following manner: 1A-l,1A-2, 1A-3, 1B-1,

1B-2, 1B-3,2A-1,2A-2,2A-3 etc. For example, 1A-1 signifies the sample was collected in week 1, that it was a pre-treatment sample (A) and that it was the first of the 3 samples collected. Note that samples collected from the effluent and mangrove on sample days A will be referred to as e.g. effluent 1A-1, mangrove 1A-1. 1B-2 signifies the sample was collected in week 1, that it was a post-treatment sample (B)

and that it was the second of three samples collected (see Figure 5.1).

Mangrove samples on day 4A and 8A and post-treatment samples collected on day

7B and 8B are not included in data analyses owing to on-site difficulties that resulted

in misrepresentative measurements. Sample storage difXculties on day 4A and 8A

prevented the collection of reliable data. On day 7B, the pump used for filling the

mangrove was left on for 48 hours instead of the desired 24-hour period. On day 8B,

farmers drained the entire volume of a nearby pond into the mangrove before sample

collection began. With the exclusion of 7B and 8B, there are 8 days of pre-treatment

data collection and 6 days of post-treatment data collection.

5.2 pH and, Rainfall Data

The pH of all pre- and post-treatment samples remained consistent throughout the

study (Figure 5.2). Extreme variations in pH have the ability to affect numerous

biological processes and it is therefore important to note that there were no severe

fluctuations in pH in values in any of the samples.

Rainfall also has the ability to alter mangal processes by causing fluctuations in

salinity levels. This is of specific concern during monsoonal weather as salinity

values can reach very low levels thereby inhibiting many estuarine and marine processes that require a certain level of salinity for optimal functioning. Rainfall

entering the mangrove during each 48-hour treatment period measured less than 1mrn throughout the field season. The dense foliage of mangal vegetative cover prohibited most rain from reaching the under story of the mangrove study area Its effect on samples, with respect to dilution, is considered negligible in this study. It should, however, be noted that throughout the field season there were numerous days of heavy 84 sun Thu Fri Sat

5

Sun Sat

3

WEEK 3 AUG

WEEK 4

WEEK 5

WeeklD Sun Mm Tue Wed ?%u Fn' Sat

1 2 3 4 5 6 7 WEEK 6 6A 6B 8 9 10 11 12 13 14 WEEK 7 7A 7B SEPT. 15 16 17 18 19 20 21 WEEK 8 8A 8B 22 23 24 25 26 27 28

29 30

Figure 5.1: Field schedule with sample week and day identification (A signifies pre- treatment data collection, B signifies post-treatment data collection) Sample ID

Figure 5.2: pH values for pre- and post-treatment samples rainfall that affected salinity levels within ponds and resulted in samples having lower

salinity levels than the surrounding coastal waters.

5.3 BOD Analysis

Measurements for BOD were analysed for all samples throughout the field season.

Shrimp pond effluent is known to have a high organic content which results in a very

high oxygen demand. It was clear that if BOD samples were incubated for the

standard 5-day period, the samples would become anoxic and it would be impossible

to make any BOD calculations. As a result, BOD was monitored over a 2-day period

to avoid low or undetectable residual oxygen readings. BOD2 measurements for pre-

treatment effluent data are described in Figure 5.3. BOD2 for all effluent samples was

greater than 13 mg/L. Even though it is not possible to compare these values to BOD5

values reported in the literature, the BOD2 values calculated in this study suggest an

extremely high organic load in effluent water. Due to the design of the study area and the sampling technique, it is thought that the organic particulate matter in effluent

originated from the effluent canal rather than from within the shrimp ponds and was therefore not affected by farm activities such as large-scale pond drainage at harvesting. The effluent canal in which the submersed pump was placed was composed of sand, clay and a large amount of organic material produced by neighbouring shrimp fanns and other coastal activities. The history of the effluent canal is not known, but the visible algal cover and the presence of fish and reptilian species within the channel suggest that the composition of the lining is richer in organic material than the average shrimp pond.

As can be seen in Figure 5.4, oxygen levels in post-treatment samples after 2 days7 incubation were often below 1 mg/L and for weeks 4,5 and 6 were 0 mg/L. Sample week Figure 5.3: BOD2 data for pre-treatment effluent samples

+Effluent --:$-- Mangrove (A)

1 2 3 4 5 6 Sample Week

Figure 5.4: Residual Dissolved Oxygen concentrations after 2-day incubation period (note that data collected in week 3 are not considered reliable due to laboratory error) These values indicate that within 2 days, the biological oxygen demand of the samples

exceeded the available oxygen. Although it is not possible to calculate BOD for the

majority of post-treatment samples, it is interesting to examine why the residual

Dissolved Oxygen measurements for post-treatment samples reached 0 mg/L so

quickly. One hypothesis is that effluent is not the only source of organic material.

Organic matter may have been introduced into the mangrove from unknown human

activities prior to the study's commencement. In addition, carbonaceous matter may have originated from within the mangal ecosystem from litterfall and resident animal species (Madeira er al. 1995). A more likely hypothesis is that the organic matter pumped into the mangrove in week 1 was not fully metabolised by bacteria As a result, BOD data collected in the second week represents the amount of oxygen required to breakdown both the organic matter pumped into the mangrove in week 2 and the residual material left over from week 1. This hypothesis provides an explanation for the increasing oxygen demand in the mangrove over the 6-week period.

It is important to note that these results do not signify that mangroves increase the biological oxygen demand of effluent water and are therefore not suited for effluent treatment. The mangrove under study was analysed with respect to its above-ground processes, that is, the samples collected were only exposed to processes on the surface of mangrove soils and roots. Mangrove soils are known for being anoxic, but this does not lead to the conclusion that effluent that is fblly processed by mangroves must also be oxygen depleted. Future studies should examine water that has filtered through mangal sediments in order to determine if mangroves are capable of improving the biological oxygen demand of organic effluent. 5.4 Phase Analysis

As mentioned in the Methodology chapter, effluent was pumped into the mangrove for 24 hours. For approximately 8 hours of the 24-hour pumping period, tide levels were high enough to force tidal water into the effluent canal, often resulting in an overflow from the effluent canal into bordering shrimp ponds. In order to prevent self-pollution, farmers closed the effluent gate for 8 hours during high tide. It was observed that during the 24-hour pumping period, there were 3 phases of effluent composition; pure effluent (low tide, effluent gate open), a mixture of seawater and effluent @gh tide, effluent gate open) and seawater (h~ghtide, effluent gate closed).

The position of the effluent gate and tidal levels were monitored during sample collection to ensure that samples could be identified as originating from the ei3luent, a mixture of effluent and seawater or pure seawater phases. Despite this, it was often dificult to differentiate between pure effluent and a mixture of effluent and seawater samples. When the tide reached the level of the pump, it was unclear if samples consisted of equal amounts of effluent and seawater or if their source was primarily effluent or seawater. As a result, conductivity measurements for all pure effluent and mixture samples were compared to determine if samples collected during these two phases could be treated separately. Statistical analyses revealed no significant difference between conductivity values of pure effluent and mixture samples (Mm-

Whitney U = 180, p =O. 144). The lack of difference in conductivity between these two phases can most likely be attributed to tidal regimes. During low tide, the tide recedes approximately 1 km from the effluent gate. Effluent from the study farm is continuously discharged into this open coastal area and pools on sands exposed at low tide levels. As tidal levels rise, it was observed that previously discharged effluent was flushed back into the canal, at least to the location of the pump, with the tide. The similarity of conductivity measurements for effluent and mixture samples, coupled

with the visual observations of tidal activity resulted in the pure efnuent and mixture

samples being grouped together and treated as a single phase for the purpose of this

experiment.

Conductivity values for samples collected during this amalgamated phase were

then compared to those obtained during the seawater phase. It was determined that all

samples with conductivity measurements of 27 mS/cm and higher were collected

during the seawater phase and measurements of 25 mS/cm were obtained during the

grouped effluent and mixture phase.

Conductivity measurements for seawater are most probably higher than those of

effluent due to monsoonal rainfall. As shrimp ponds cover a much smaller area

relative to the ocean, they are much more susceptible to dilution than the ocean which

results in lower conductivity values for effluent samples than for seawater samples.

Analyses were then conducted to determine if the composition of these two

distinct phases differed, with respect to concentrations of nitrate, nitrite and ammonia.

Separate Mann-Whitney tests were conducted for data collected during weeks 1-4 and

weeks 5-8 (an explanation of the two 4-week blocks is discussed in the following

section). It was determined that there was no significant difference between the nitrate, nitrite and ammonia concentrations of samples collected during either of the

phases throughout the field season (Table 5.1). This rather unexpected result can be

attributed to the same factors that explained the similarity of conductivity values for pure effluent and mixture samples. During low tide, the study farm is one of many farms on the coast that discharges effluent. Hence, when the tide rises the majority of the water being pushed landward is emuent which was previously discharged from all Weeks Nitrate Ammonia Nitrite 14 Mann-Whitney U 11.000 15.000 18.000 p-value 0.262 1.000 0.63 1 5-8 Mann-Whitney U 17.000 13.000 15.500

Table 5.1: Mann-Whitney tests to detect differences between nitrate, ammonia and nitrite concentrations in the 2 distinct phases (eMuent and effluentkeawater mixture compared to seawater for Weeks 1-4 and 5-8) fmsin the vicinity. This also explains why seawater samples have higher

conductivity values than samples consisting primarily of effluent. Effluent samples

originate from pond waters that are exposed to high evaporation rates and should

therefore have higher conductivity values than incoming seawater. However, the

samples that have been classified as originating from seawater in this study actually

consist of farm discharge that has been laying in open coastal lands during low tide.

High evaporation rates on coastal lands result in seawater samples having higher

conductivity values than effluent samples collected immediately after pond discharge.

5.5 Pre-Treatment Data: Effluent Samples

Data were grouped and analysed in 4-week blocks (weeks 1-4 and weeks 5-8).

Pre-treatment data were averaged for each of the 4-week blocks to provide a better

representation of what entered the mangrove during the 24-hour pumping period. The

4-week grouping was decided upon because between weeks 4 and 5,15 shrimp ponds

were harvested. As shrimp grow, the amount of nitrogen present in the pond typically

increases and it was hypothesized that the overall effluent composition would change after week 4 owing to a great decrease in the number of shrimp ponds in the final stages of the culture cycle. Note that BOD data were not affected by this large-scale harvesting as the organic matter represented by the data originated from sediment in the effluent canal and not shrimp pond effluent.

The mean concentrations of nitrate, ammonia and nitrite for each week are presented in Table 5.2 and mean concentration for each of the 4-week groups are presented in Table 5.3. Statistical analyses revealed a significant change in effluent composition for nitrite and ammonia values between weeks 1-4 and 5-8 and the data were subsequently divided into 4-week groups (Table 5.4) Sample NOS-N (mg/L) i SD NH3-N (mglL) NO2-N (mg/L) & SD Day *SD 1A 0.1985 * 0.1742 0.05 i .09 0.2790 i 0.2489

Table 5.2: Pre-treatment mean concentrations of nitrate, ammonia and nitrite in effluent

Variable Weeks 1-4 Weeks 5-8 Mean Concentration (mg/L) * Mean Concentration (mg/L) * SD

Table 5.3: Mean concentrations of nitrate, ammonia and nitrite during weeks 1-4 and weeks 5-8

Nitrate Ammonia Nitrite Mann-Whitney U 678.000 250.000 173.000

Table 5.4: Mann-Whitney test to detect if differences in nitrate, nitrite and ammonia concentrations exist between weeks 1-4 and 5-8 The concentrations of all three variables are higher in the first 4-week group than the second 4-week group, but only ammonia and nitrite concentrations dispIay significant differences. It is important to consider the causes of these significant changes. The main sources of ammonia in pond water are shrimp waste and bacterial breakdown of organic sediment that builds up on pond bottoms throughout culture cycles (Funge-Smith and Briggs 1998). As shrimp reach a harvestable size, fecal matter and sludge accumulate in the ponds thereby increasing in-situ ammonia concentrations. Between weeks 4 and 5, 15 ponds were harvested resulting in a dearth of older ponds (i.e. ponds with shrimp nearing the end of their culture cycle). As of week 5, most of the ponds were stocked with young shrimp that excrete low levels of ammonia, which in turn results in low levels of nitrite and nitrate originating fiom the synthesis of ammonia It is unclear why nitrate levels did not significantly decrease between weeks 4 and 5. It is hypothesized that nitrate concentrations in influent water are high, owing to excessive nutrient loading along the Chanthaburi coast, and therefore make significant changes in nitrate levels of effluent seeping from older and younger ponds harder to detect.

The quality of effluent water sampled throughout this experiment was hypothesized to be higher than that of pond water analysed in previous studies owing to the management practices of farmers at the study site. Shrimp pond managers at the site are extremely well educated and have both the knowledge and the desire to minimise the environmental impacts of shrimp farming. As a result, they make every

attempt to prevent feed wastage and avoid the use of pesticides and fertilisers until they are deemed essential for the survival of the shrimp. As mentioned, they have also adopted an environmentally sustainable technique of sludge disposal at harvest. By removing the organic layer that accumulates on the pond bottom throughout a

culture cycle, fmers have attempted to improve in-situ pond water quality.

Despite these factors, when nitrate, nitrite and ammonia concentrations of samples

collected in this study are compared with those from Briggs and Funge-Smith (1994)

who examined poorly-managed high-density shrimp ponds in Thailand, the values

obtained in this study actually appear to be equivalent if not higher than those previously documented (Table 5.5). There are two plausible explanations for the similarity in eMuent composition between the data collected at the study fmand those documented in previously published data The first is that the main contributor to poor effluent quality may be shrimp fecal matter and that effluent composition is affected minimally by environmentally friendly farm management practices such as low fertilser application, pesticide use and feed wastage. This hypothesis seems unlikely, however, as several researchers have found overfeeding to be the primary source of high concentrations of nitrogenous waste (Briggs and Funge-Smith 1994).

The second and more likely explanation for the high concentrations of nitrogenous waste at the field site can be attributed to sampling methodology. Effluent samples are commonly collected from within shrimp ponds or from an outlet pipe attached directly to the shrimp pond (e.g. Briggs and Funge-Smith 1994, Robertson and

Phillips 1995). The samples analysed in this study were taken from an effluent canal fed by seepage fiom shrimp ponds. When the study farm was first established in the late 1980s, there was linle consideration given to the potential impact of unmonitored effluent discharge. For the first 5 years, farmers removed sludge from pond bottoms at harvest with high-pressure hoses and disposed of it directly into the effluent canal.

Although this practice was halted approximately 8 years ago, organic sludge remains Variable Current Briggs and Funge- Briggs and Funge- Study Smith (1994) (50- Smith (1994) (80- 60 PLI~') lo0 pL/m2) NOS-N (mg/L) * SD 0.20 * 0.15 0.04 * 0.10 0.11 0.19

Table 5.5: Comparison of mean nitrate, ammonia and nitrite concentrations in effluent in ths study (averaged over 8 weeks) with Brig@ and Funge-Smith (1 994). in the canal with an approximate depth of 2.5 m. Pond water quality was not

measured by collecting samples directly from the ponds, but rather from the effluent

canal where leaching of dissolved nutients from organic sludge into effluent water

may have occurred. It is therefore possible that the quality of pond water at the study

site is higher than that revealed by sample values.

Regardless of why the concentrations of nitrate, ammonia and nitrite at the study

farm are higher than that of poorly-managed sites documented in the literature, the

levels of these nutrients have the potential to harm surrounding environments. If the

field site existed in seclusion, the impact of the effluent produced would be minimal.

Concern is raised when the density of shrimp farms and subsequent loading of the

coastline is considered. This is examined in further detail in the section exploring

management implications.

5.6 Pre-Treatment Data: Mangrove

The purpose of collecting three samples in the mangrove was to determine if

changes in the water quality parameters under study could be detected after only 6 hours of treatment. If changes were observed, a time-series data set could be

generated to describe concentrations of nutrients at time = 0 (effluent), time = 6 hours

(mangrove-A) and time = 48 hours (mangrove B). Testing water quality parameters after 6 hours of treatment was intended to give some insight into the rate at which the study mangrove processed nutrients. This information, along with the data collected after 48 hours of treatment, could then be used to determine the approximate residence time required for effluent to remain in the mangrove to significantly improve effluent quality. It was only possible to obtain samples at these three times due to time and logistic constraints. After 6 hours of pumping, the mangrove was only partially full, i.e. the sampling area was less than the 25 m by 35 m plot. This resulted in a number

of samples being taken within very close proximity of other samples, often very near

the effluent pump. As the flow of the pump was quite strong, samples collected

within 5 to 10 m of the pump were also subject to movement and mixing with

incoming effluent. This sampling technique introduced bias into the study as samples

did not accurately represent effluent that had been in the mangrove for 6 hours, but

rather were a mixture of incoming effluent, often consisting primarily of effluent

recently pumped into the mangrove. Figures 5.5,5.6 and 5.7 show a comparison of

mean nitrate, ammonia and nitrite values for pre-treatment effluent and mangrove

sample concentrations. Although some mangrove sample concentrations are less than

effluent concentrations, there are no patterns that emerge from the data The

inconsistencies in the data set may be introduced from the biased sampling technique

and it was therefore concluded that meaningful analyses could not be performed on

pre-treatment mangrove samples. As a result, they have been omitted from further

analyses.

5.7 Post-Treatment Data

The means of post-treatment mangrove data for each week are presented in Table

5.6.

The nitrogen data for samples collected in the well are presented in Table 5.7. The nitrate and nitrite concentrations of samples within the well are similar to those of post-treatment samples while the ammonia concentrations are significantly higher than those of the samples collected within the mangrove. The water present in the well is pore water that has been exposed to sediment microbial activity as it seeped from the surface of the mangrove soils through the sediment and finally into the well.

9 1B 0.1596 * 0.05 14 0.35 * 0.12 0.0361 0.0054 2B 0.0925 * 0.1388 0.56 * 0.06 0.01 19 f 0.0008 3B 0.1155 * 0.0153 0.22 =t0.03 0.0076 f 0.0006 4B 0.0806 0.0140 0.48 * 0.15 0.0071 * 0.0010 5B 0.1571 * 0.0184 0.15 * 0.08 0.0093 * 0.0019 6B 0.1002 * 0.0130 0.05 * 0.07 0.0061 0.0006 Overall mean 0.1 176 * 0.0675 0.30 * 0.21 0.0194 * 0.0290

Table 5.6: Post-treatment mean concentrations of nitrate, ammonia and nitrite in the mangrove

Sample Day NO3-N (mgL) f SD NH3-N (mgIL) f SD N02-N (mg/L) A SD 1B 0.0554 * 0.0010 2.34 f 0.12 0.0287 * 0.0000 2B 0.1313 * 0.0400 3.90 * 0.26 0.03 18 * 0.0002 3B 0.0751 * 0.0013 4.23 * 0.06 0.0079 * 0.0001 4B 0.0757 f 0.0037 1.60 * 0.00 0.0096 * 0.0000 5B 0.0758 * 0.0020 2.13 * 0.15 0.0073 * 0.0003 6B 0.1350 * 0.0017 1.10 * 0.10 0.0462 * 0.0003 Overall mean 0.0914 * 0.03 14 2.56 * 1.18 0.0219 * 0.0151

Table 5.7: Concentration of nitrate, ammonia and nitrite in well samples In order to determine the cause of such high ammonia readings, it is important to analyse the reactions involved in the breakdown of organic matter.

BOD data collected from effluent samples in this study reveal that a large amount of organic particulate matter, both carbohydrates and protein, enters the mangrove during each 24-hour pumping period. Proteins are metabolised into amino acids which are further broken down, through the process of deamination, into NH3.

Although the exact composition of the particulate matter pumped into the mangrove is unknown, it is reasonable to assume that much of it is protein originating &om shrimp feed, feces and meat as well as a number of other anthropogenic and natural sources.

There is no empirical data to quan@ the amount of protein in typical shrimp pond effluent. However, it is thought that the protein content of the effluent pumped into the mangrove in this study is much higher than emuent sampled directly from a pond due to the excessive amount of particulate organic matter present in the effluent canal.

To accurately determine the amount of protein the mangrove is capable of metabolising, all other sources contributing to the high ammonia concentration in the well must be subtracted from the average value of 2.56 mg/L m-N. The well was home to a number of small shrimp present at a density of approximateIy 200 shrimp/L. The exact weight of the shrimp was not calculated but each organism is estimated to weigh 0.1 mg. Assuming an excretion rate similar to that of mussels

(0.000192 mg NH3-N per mg of mussel per hour), 200 shrimp weighing 20 mg total would produce 0.18 mg/L of NH3-N in 48 hours (Aldridge et al. 1995). In addition to the inputs of resident shrimp populations, post-treatment mangrove water has an average concentration of 0.30 mg/L of NH3-N. The rationale behind subtracting post- treatment mangrove ammonia values instead of pre-treatment eMuent values is that nitrate and nitrite values in the well are similar to post-treatment mangrove samples suggesting that water entering the well has been exposed to surface nutrient uptake processes before seeping into the sediments. Taking both of these values into consideration, the well has an average concentration of 2.08 mg/L of NH3-N or 1.14 mg/L of NH3. The deamination process is described by one mol of protein (CHON) being metabolised to release one mol of ammonia (MI3). Using this equation, 2.88 mg/L of protein is required to produce 1.14 mg/L of NH3. The amount of water pumped into the mangrove over a 24-hour period was 242 240 L yielding a total of

699 g of protein entering and being processed by the 875 m2 mangrove over a 48-hour treatment period. Using these figures, a 1 lan2 plot of mangrove can metabolise 799 g of protein, or 1.8 kg of shrimp feed in 48 hours (protein content of commercial shrimp feed is approximately 45.4% dry weight, Funge-Smith and Briggs 1998). No previous research has examined the efficiency of mangroves as sinks of protein so comparative analyses are not possible at this stage.

Although the results of the well data show promising results for the role mangroves may play in protein metabolism, the limitations of this research must be explored. The study mangrove was shown to process 699 g of protein and produce

2.56 mg/L or a total of 620 g of NH3-N over a 48-hour period. This concentration of ammonia is extremely toxic to a number of estuarine-dwelling species. Although the samples collected in the well had passed through some sediment, it was not possible to determine if the composition of these pore water samples was similar to that of water leaving the mangrove and entering the surrounding coastline. Further research must analyse the path of this pore water and the concentration of ammonia being discharged into surrounding ecosystems to determine the suitability of mangroves as protein sinks. Data collected in the well will not be included in pre- and post-treatment nitrogen

comparisons or in extrapolation analyses as the high ammonia concentrations present

in the well data are a reflection of the abnormally high levels of organic matter

originating from the effluent canal and not from pond water itself Typical shrimp ponds in Thailand do not discharge the large amounts of particulate matter seen in this study. In order to ensure the widespread applicability of the study, mangrove nutrient uptake will be analysed only with respect to dissolved nitrogen in pre- and post- treatment samples. The unusual organic load of the effluent does not affect post- treatment samples as, unlike water collected from the well, these samples are subject only to above-ground processes and are therefore not influenced by the metabolism of organic matter that takes place in the sediments.

5.8 Comarison of Pre-Treatment and Post-Treatment Nitrogen Data

Pre- and post-treatment samples are not analysed using standard statistical methods owing to the way in which data were collected. The variation between individual pre-treatment samples is very large due to a number of factors including tide levels and daily shrimp feeding schedule along with a myriad of unknown environmental variables. The characteristics and behaviours of these variables are not considered of vital importance as, for this study, it is assumed that they are cyclical in nature, varying over a 24-hour period. The variance that is of concern is the variance between the 24-hour pumping periods (i. e. the variance between sample days 1A-4A and 5A-8A). As it was neither financially nor temporally feasible to sample for the entire pumping period, it was not possible to obtain a measurement of this variance. In this study, it is assumed that the overall composition of effluent pumped into the mangrove over each 24-how: period is the same for weeks 1-4 as it is for weeks 5-8. As the variance between the individual samples collected in this study is much larger than the variance of concern, it is not considered a good substitute for the purposes of statistical analyses. When the concentration values for all three variables are plotted in ascending order, it can be seen that samples were collected at most points of the curve (see Figure 5.8). This signifies that the samples collected are balanced, that is, there were an equal number of samples collected for each of the three variables at all concentration values along the curve. From this, it can be concluded that the mean values calculated for pre-treatment samples are representative of what entered the mangrove over a 24-hour pumping period. As a result, the overall mean of pre- treatment data for each of the 4-week groups is calculated and compared to post- treatment values.

The mean of pre- and post-treatment data are compared using a 95% confidence interval. If pre-treatment means fall outside the upper 95% confidence interval of post-treatment means, the pre- and post-treatment means are considered significantly different. See Table 5.8 for a summary of results.

5.8.1 Nitrate

Nitrate levels in treated water were significantly less than those in effluent water for weeks 3-6, Mangroves are typically nutrient deficient, limited either by nitrogen or phosphorus (Yates et al. 2002). Although the addition of nutrient-rich waste has been observed to increase nutrient cycling capacities, it is possible that mangroves require some time to adjust to influxes of effluent with high levels of nitrogen and phosphorus (Boto et al. 1985, Yates et al. 2002). Nitrate is primarily taken up by plants and used for growth and reproduction (Feller 1995). Plants may need to acclimatise to increasing nutrient loads before being able to synthesise high Pre-Treatment Samples Weeks 1-4

Pre-Treatment Samples Weeks 5-8

Figure 5.8: Concentration values for all pre-treatment samples - plotted in ascending order Sample NOS-N pre- NO3-N post-treatment value (mg/L) Day treatment value 95% Confidence Interval Upper Bound

Sample N&-N pre-treatment m-Npost-tremtmen t value (mg/L)

Day value (mg/L) 95% Confidence Interval Upper- - Bound 1B 0.69 0.44*

Sample NO2-N pmtreatment NO2-N post-treatment value (mg/L) Day value (mg/L) 95% Confidence Interval Upper Bound 1B 0.0628 0.0403' 2B 0.0628 0.0125* 3B 0.0628 0.0081* 4B 0.0628 0.0079* 5B 0.0177 0.0108* 6B 0.0177 0.0066*

Table 5.8: Comparison of pre-treatment values of nitrate, ammonia and nitrite compared to the upper bound of the 95% confidence interval of post-treatment values * denotes that the upper bound of post-treatment values are significantly less than pre- treatment values levels of nitrate resulting in a lag time between nitrate input and efficient nitrate

absorption. This may explain why the treatment mangrove did not significantly

decrease nitrate concentrations during the first 2 weeks of the field study.

Another possible explanation for the inability of the mangrove to significantly

decrease nitrate levels at the onset of this experiment is oxygen availability.

Nitrogenous inputs into the mangrove are used by mangal-dwelling bacteria and fungi

which release ammonium as a by-product of metabolic processes. Ammonium is then

available for plant uptake or, if present in excessive concentrations can be converted

into nitrate by nitrifjmg bacteria and absorbed by plants. Nitrate uptake occurs

primarily in anoxic conditions. During the first 2 weeks of the field season, mangrove

soils potentially had high oxygen content as the area had been isolated fiom tidal

waters and had been allowed to dry out for approximately one month with only 2 flooding episodes during that time. Mangroves may require frequent submersion and resulting anoxic conditions in order to adequately process nitrate,

There are currently no standards of acceptable nitrate levels in coastal waters, but it is advisable to decrease the concentration of this nutrient in eMuent as excessive loading can result in unwanted phytoplankton blooms that result in deleterious effects in intertidal communities.

5.8.2 Ammonia

The concentration of ammonia in effluent water was significantly lower following treatment by the mangrove for all of the treatment weeks. Although ammonia itself is not harmful to aquatic environments, the unionised form of the nutrient (NH3) is highly toxic. When analysing the content of ammonia in effluent in the laboratory, the equilibrium of ammonium and ammonia (NH4' +-+ NH3) is shifted towards NH3 and hence all ammonia readings are recorded as NH3. In reality, the concentration of NH3 present in natural waters is dependent on pH and temperature fluctuations. Due to the unstable nature of ammonia, it is preferable to decrease its presence in effluent (Moore

1991). No stringent rules exist for the limit of ammonia allowed in shrimp farm effluent but it is suggested that at a pH of 8 and temperatwe of 30 OC, ammonia (NH3-

N) levels should not exceed 0.5 mg/L (Moore 1991). The pre-treatment concentrations of NH3-N in effluent exceeded 0.5 mg/L for the first 4 weeks of the field season, but the concentration of ammonia-nitrogen in post-treatment water was reduced to less than 0.5 mgL for weeks 1,3 and 4. These results demonstrate that the mangrove at the field site was able to synthesise enough ammonia to significantly decrease its presence in effluent water samples over a 24-hour period. There are two possible pathways for the uptake of ammonia One is through bacterial metabolism by microbes residing in aerial pneumatophores and the second is the settling of ammonia on mangrove soils. The ammonia binding to mangrove soils has the potential to be processed by surface dwelling microbes or seep into pore water where it may be metabolised by sediment bacteria or taken up by mangrove trees for use in photosynthesis.

5.8.3 Nitrite

After exposure to the mangrove, nitrite concentrations in effluent water decreased significantly for all of the treatment weeks. The suggested maximum concentration of

N02-N in coastal waters is less than 0.06 mgL as levels exceeding this result in an increase in fish mortality rates (Moore 1991). Effluent nitrite concentrations in the first 4 weeks of this study were greater than 0.06 but after mangrove treatment were significantly reduced to acceptable concentrations. This demonstrates that mangal processes were capable of taking up nitrite and converting it into a less noxious form

of nitrogen. As nitrite is toxic, if not lethal, to many marine organisms, this result

shows the potential of mangroves to decrease the concentration of a polluting nutrient

that can devastate coastal habitats.

5.9 Percent Removal of Nutrients

In addition to reporting significant differences in pre- and post-treatment

concentrations, it is also usefid to discuss the percent of each nutrient removed fiom

effluent by the mangrove treatment area Throughout the entire experimental period,

an average of 28.8% nitrate, 46.6% ammonia and 59.0% nitrite was removed by the mangrove. When considering percent removal on a weekly basis, it can be seen that there are variations in the degree of treatment between weeks (Figure 5.9). The percent treatment for sample 1B for nitrate is extremely low and is more likely the result of laboratory error than low nitrate cycling efficiency of the mangrove. When thts value is removed, the average percent of nitrate removed by the mangrove is

44.5%. The variation of percent treatment values reveal some of the difficulties involved in using natural systems to treat wastewater. Mangrove wetlands are subject to a number of abiotic and biotic fluctuations that have yet to be thoroughly researched and understood. Despite the variation in treatment capabilities of the study mangrove, it is important to re-emphasise that post-treatment concentrations for all three variables, with the exclusion of nitrate in the first 2 weeks, were significantly lower than pre-treatment values. Treatment Weeks

Figure 5.9: Percent of nitrate, ammonia and nitrite removed from effluent by the treatment mangrove throughout the field season 5.10 Nitrogen Loading of the Coast of Chanthaburi

As discussed earlier, effluent discharged fiom one farm does not pose a severe

threat to sensitive coastal ecosystems. The impact of shrimp farms on marine

environments must be evaluated by calculating the cumulative discharge of all shrimp

farms in a given region.

Chanthaburi has approximately 3 989 ha of shrimp farms that discharge effluent

along the province's coastline. Assuming an average pond depth of 1.5 m and a seepage rate of 2.0 cm/day, the daily effluent discharge on the coast would be 797 809

L. It should be noted that the seepage rate and pond depth were determined through communication with fmers in the region and are not measured values. There are no published estimates for either of these values in the Chanthaburi province and it is not possible to extrapolate seepage rates fiom previous studies as they are measured either inland or in clay-bottomed ponds (e.g. Braaten and Flaherty 2000, Briggs and Funge-

Smith 1994). Using the mean concentrations of nitrate, ammonia and nitrite obtained in this experiment (Table 5.5), the daily load of nitrogen fiom shrimp farm effluent into Chanthaburi's coastal waters is 282 kg. Annual loading, including drainage at harvest (assuming 2 cropslyear and 120 day grow-out cycle) is 152 222 kg Nlyr.

Bergheim, Siversten and Selmer-Olsen (1982) estimated that the waste of one human consisted of 1 1.88 g Nlday. Using this figure, the annual load of nitrogen from shrimp effluent on the Chanthaburi coast is equivalent to the waste produced by 12.8 million people. Briggs and Funge-Smith (1994) determined that, per tonne of shrimp produced, intensive shrimp farms discharge effluent equivalent to the waste of approximately 85 people. Using the value that 1 ha of shrimp farm can produce 3.46 tomes of shrimp, calculated by Briggs and Funge-Smith (1994), the 3 989 ha of shrimp farm in Chanthaburi would produce 13 817 tonnes of shrimp that would

discharge nitrogenous effluent equivalent to 1.17 million humans.

The two values for human-equivalent waste production are extremely different.

The larger number of 12.8 million was calculated using the volume of eMuent seeping

daily into coastal waters as well as effluent drained from ponds at harvest whereas the

smaller number only took into account the tonnes of shrimp produced per hectare of

land. This number can be very misleading as it was calculated from the total weight

of intensively produced shrimp in Thailand divided by the total number of hectares of

shrimp farms in the country. The value for the total weight of shrimp is susceptible to

large variation as exact numbers are extremely hard to obtain owing to a number of

small-scale farms that are not registered and may therefore be unknown to institutions

calculating average shrimp production per unit area In addition, many ponds throughout the country succumb to disease and, although producing effluent, do not

contribute to the nation's production of shrimp.

The major difficulty with comparing these two values is that Briggs and Funge-

Smith (1994) do not describe how they calculate that 1 tonne of shrimp produces an

equivalent amount of waste to 85 people. It is unclear what values they use to determine effluent loading per hectare or tonne of shrimp produced and it is therefore not possible to pinpoint where the discrepancies in the data arise. It is, however, reasonable to assume that Briggs and Funge-Smith greatly underestimated the magnitude of nitrogen entering coastal waters from shrimp farms as they did not calculate amounts of waste based on effluent volume but rather on quantity of shrimp produced per hectare.

Assuming that the values calculated in this study are accurate, the total nitrogen load of the coastline from shrimp farm effluent receiving no treatment is 152 222 kg Nlyr. Using the average percent removal capacity for nitrate, ammonia and nitrite determined in this study, if all effluent was to be treated by a mangrove wetland, the total loading of the coastline would decrease to approximately 7 1 097 kg N/yr

(equivalent to the waste of 5.98 million people). Although this figure is still high, it is considerably less than the untreated value. At present, there are few effluent treatment systems that have the capacity to reduce nutrient concentrations to this extent. In order to determine the long-term feasibility of mangrove wetlands on a large scale, it is imperative to recognise the weaknesses of this study and identify key focus areas for future research in this field.

5.1 1 Limitations and Future Research Needs

The findings of this study demonstrate that mangroves have the potential to be used as efficient effluent treatment areas. Before discussing the management implications of these results, it is important to acknowledge the limitations of this study and fbrther research needs on this topic.

The nutrient uptake capacity of a modified mangrove was analysed with respect to three nitrogen-based nutrients in this experiment. There are also a number of other constituents in shrimp effluent that need to be reduced in order to improve effluent quality. Of specific importance is phosphorus. Previous research has commended the use of mangroves in phosphorus treatment, but little analysis has been conducted on the assimilative capacities of mangal forests with respect to phosphorus or nitrogen

(Wong et al. 1997, Ye et al. 2001). For the purposes of this experiment, it was assumed that the concentrations of nitrate, ammonia and nitrite in the effluent were the maximum concentrations the treatment area could process. Loading studies should be carried out to reveal the carrying capacity of mangrove forests with respect to the nutrients of concern

It is also important to recognize that, in this study, the treatment area was only exposed to effluent pumped in from the adjoining shrimp farm. Coastal lands throughout Thailand and a number of other developing nations are typically inundated with waste originating from a myriad of agricultural, urban and industrial sources.

When assessing the area of mangrove required to treat shrimp farm effluent, all nutrient-laden inputs must be included so that the assimilative capacity of the mangal region is not exceeded.

This study was carried out over a 10-week period. During this time, there were no visible detrimental effects of pumping nutrient-rich effluent into the mangrove.

Farmers at the site have continued to use the treatment area on a weekly basis and have reported no adverse effects. Wong et al. (1 997) also documented insignificant changes in natural tree growth and mortality rates in a 300 ha mangrove forest in

Shenzen that was flooded with sewage discharge three times a week for a 2-year period. The effluent dispersed in Wong et al. 's large treatment area had concentrations of nitrate and nitrite similar to those of shrimp waste collected in this study, but the concentration of ammonia was considerably higher in the Shenzen study. These findings suggest that mangroves will be able to assimilate nutrients at concentrations typically found in intensive shrimp farm effluent, with little to no detrimental repercussions on the health, fecundity or survival of mangal flora. Lf, however, mangrovp are to be used consistently for long-term effluent treatment, the health of mangroves exposed to shrimp effluent loading must be monitored over extensive time-periods in a variety of environmental conditions. In addition to mangrove vitality, the health of mangal-dwelling species must also be considered. The mangrove used in this study was modified to prevent coastal water from penetrating the soils. This was done to decrease the number of variables affecting the mangrove in order to increase experimental control and also to ensure that sensitive aquatic species that use mangroves for nurseries, breeding and foraging were not able to enter the test area By isolating the mangrove from the intertidal zone, it was hoped that there would be minimal disturbance to natural habitats. If, however, mangrove wastewater treatment is to become widely used, it is important to determine if effluent influxes would negatively affect species that inhabit mangroves and neighbowing intertidal environments.

The flooding regime of this experiment is also noteworthy. The mangrove was flooded once a week for 24 hours and then left to dry out for 6 days. If this form of effluent treatment were to be used on a large-scale basis, studies must be conducted to determine how much time mangroves require to dry out between treatments. Natural mangroves are exposed to daily tidal fluctuations and those along the coast of

Chanthaburi are typically submersed for 12 hours a day. Flooding regimes of modified mangroves should probably mimic natural tidal action in order to achieve maximum nutrient uptake potential.

Residence time of wastewater in the mangrove is also a source of variability in mangrove nutrient cycling efficiency. Effluent pumped into the study treatment area had a residence time of approximately 2 to 4 days. In highly-branched systems fbrther inland, residence time may be significantly greater thereby increasing the area of mangrove required to adequately treat wastewater. The morphology and hydrology of mangrove forests must be considered when determining the suitability of a site for effluent treatment. 5.12 Management Im~lications

Assuming that the nutrient cycling capacity of the study mangrove is representative of intertidal forests in other geographic regions, there are a number of management implications that must be considered to ensure the feasibility and long- term success of mangrove biofiltration.

5.12.1. Mangrove to Shrimp Pond Ratio

Thai shrimp farmers are very much aware of the negative effects of nutrient-rich effluent loading along their country's coastlines. For a number of years many appeared to turn a blind eye to the problem, but recent government regulations concerning effluent discharge coupled with international criticism and complaints fiom coastal water users have made coastal eutrophication impossible to ignore.

Farmers are not adverse to making their farms environmentally sustainable, as this improves their chances of successful crops and increases the longevity of their shrimp farm operations. Unfortunately, shrimp farmers have not been provided with any feasible management options that will enable them to effectively decrease the had effects of excessive effluent discharge.

In order for an effluent treatment system to be widely adopted, the benefits of the system must outweigh the costs, financially, spatially and environmentally. Using the results of this study the spatial feasibility of mangal treatment areas is assessed. The modified mangrove in this study was 875m2and capable of treating 242 240 L of effluent per day (when the average concentrations of NOS-N, NI%-N and N@-N

0.2023mg/L, 0.46mgL and 0.0403mgL respectively). Given that these values are representative of other farms along the Chanthaburi coastline and that the amount of effluent treated by the study mangrove is near the assimilative capacity of the mangrove, the ratio of shnmp pond to mangrove treatment area required to significantly increase effluent quality with respect to the three aforementioned nitrogenous variables can be calculated.

When pond drainage at harvest is excluded from the equation, 1 ha of mangrove can treat effluent seeping from approximately 28 ha of shrimp ponds if the mangrove is flooded continuously for 24 hours a day. If effluent is only discharged into the mangrove for 12 hours a day, this ratio is decreased to 1:14.

If pond drainage is included in the equation, with the average pond depth assumed to be 1Sm, then the volume of effluent drained along the coastline at harvest would be

5.98 x 10" L. The ratio of mangrove treatment area to shrimp pond at harvest would be approximately 5: 1. When excluding the effluent drained at harvest, a ratio of 1: 14, mangrove to shrimp pond, seems spatially feasible. The inverse relationship of 5: 1 mangrove to shrimp pond required to treat harvest drainage is problematic. It is, however, entirely feasible for farmers to drain their harvested ponds at a slower rate rather than emptying the entire pond in one day. This would greatly decrease the amount of mangrove required to treat this effluent.

All of these ratios are significantly less spatially demanding than the 7:l

(mangrove to shrimp pond) ratio calculated by Roberston and Phillips (1995). Using estimates of nitrogen required for primary production in a Rhizophora forest, they calculated the area of mangrove required to remove nitrogen from shrimp farm effluent. There are a number of reasons for the disparity in the aforementioned ratios.

Due to the theoretical nature of Robertson and Phillips7(1995) study, it was possible to calculate the area required to remove all nitrogenous matter from shrimp waste.

Although complete removal of nitrogen is ideal, it is obvious from the high ratio of mangrove to shrimp pond that the area of mangrove necessary to achieve this is not spatially feasible. From a management perspective, it is still extremely usefbl to significantly decrease inorganic nitrogen concentrations even if complete removal is not attainable.

When determining the composition of shrimp farm effluent that would be entering the mangrove, Robertson and Phillips (1995) also included nitrogenous inputs from sediment drained at harvest. As previously mentioned, sediment at the study farm is not flushed into neighbouring canals. Jf this practice was widely adopted by shrimp farmers, the area of treatment land required to treat shrimp &uent could be greatly decreased. If sediment nitrogen inputs are excluded from Robertson and Phillips'

(1995) calculations the ratio is still approximately 1: 1.

Another possible explanation for the drastic differences in the ratios calculated in this study and those determined by Robertson and Phillips (1995) is that the latter assumed that plant uptake was the only source of nitrogen removal. Microorganisms residing on pneumatophores and other exposed mangrove structures are capable of high levels of denitrification as well as serving as sinks for nitrate and ammonium

The discrepancy in the ratio of treatment area to pond area in these two studies may reveal the currently unknown role of these organisms in mangrove nutrient assimilation. It is important to note that neither this experiment nor that of Robertson and Phillips (1995) accounted for the contribution of deniwng bacteria in mangrove sediments. In order to prevent massive disturbance to the study mangrove, this experiment was designed to only monitor nutrient cycling from above-ground processes. Rivera-Monroy et al. (1999) estimated that denitrification rates in mangrove soils can reach levels of 1 -49 kgfhdday. If sediment denitrification rates had been examined, it is hypothesized that the percent treatment of all three variables would have increased sigdicantly.

From a spatial perspective, if future research supports the 14: 1 shrimp pond to mangrove ratio, farmers in Chanthaburi should have minimal difficulty obtaining enough land to sustain an adequate mangrove treatment area. Along most of the province's coastline there is a 1 km expanse during low tide that used to flourish with mangroves. Due to a number of anthropogenic and natural stresses, the presence of these intertidal forests have severely diminished. These lands, however, are suitable for mangrove reforestation and, as they are currently unused, would not infringe on farming areas. The length of Chanthabwi's coastline is approximately 70 km (PCL

Map Collection 1988). If mangroves were replanted in the 1 km area along the coast that used to be abundant in mangal vegetation, there would be a total of 7 000 ha of mangrove. Given that Chanthabwi has 3 989 ha of shrimp farms, there would only need to be 285 ha of mangrove to effectively treat effluent discharged from all existing coastal farms. As is evident from these figures, mangrove treatment areas are spatially feasible in Chanthaburi.

There are very few studies that have analysed mangrove wastewater treatment in a real situation, that is, most researchers have modelled mangrove nutrient cycling capacities using primary productivity data and average shrimp effluent compositions rather than flooding mangroves and testing effluent composition before and after treatment from the wetland area As this experiment is one of the pioneer studies analysing mangroves in situ, it is unclear whether it is representative of the capabilities of mangroves in general. It does, however, provide very promising results for the potential of these intertidal forests in the treatment of nutrient-rich waste. From a financial perspective, mangroves require little cost and minimal

maintenance to thrive. Mangroves have long been known to provide a vital habitat to

a multitude of marine species, but only recently have they been thought of as nutrient

sinks. Governments of several tropical countries have made efforts to reforest mangal

areas (e.g. Pakistan and the Philippines), but resources and man-power along with

limited community involvement oRen hinder large-scale reforestation successes

(Qureshi 1996, Walters 2000).

This study shows the potential for mangroves to be effkctive nutrient sinks for

organic effluent originating from the shrimp farming industry. If low cost, low

maintenance techniques to replant mangroves are discovered, governments could create regulations to facilitate mangrove reforestation throughout their country. If all shrimp farms in coastal regions that were previously bordered by natural mangroves are required to replant these forests then not only would mangrove reforestation be achieved with little cost to the government, but shrimp effluent would also be passively treated by perimeter mangroves. Governments could establish nurseries and disseminate seedlings and information regarding their care. Incentives such as tax deductions could also be given to farmers who begin reforestation in less than one year to ensure rapid results.

Using replanted mangrove forests for wastewater treatment assumes that natural mangroves can be used as effluent filters. If large effluent loading is found to be detrimental to the health of mangrove-dwelling species, that is to biotic components other than mangrove trees, governments will have to ensure that a portion of the reforested mangrove remains isolated fiom tidal inundation and is the only region used for effluent treatment. This will increase the spatial requirements of mangrove treatment areas, but may still be feasible in a number of areas. If, however, the spatial demands of mangrove biofilters outweigh their environmental benefits, it may also be possible to use these treatment wetlands in conjunction with other biological treatments such as settling ponds. Combining two forms of effluent treatments may not only decrease the amount of land required for adequate mangrove filtration but may also increase the percentage of nutrients removed from effluent prior to discharge into coastal waters. This would not only decrease the impact of effluent on marine ecosystems but could also benefit farmers who are interested in creating closed- system fmsthat use water recirculation to decrease the risk of crops acquiring diseases from neighbouring farms.

5.12.2 Recirculation

The increased popularity of shrimp farming in the last decade has led to high densities of farms in areas that are environmentally and logistically suitable for the production of shrimp. One of the key requirements of these farms is clean influent water. Unfortunately, the availability of suitable water to fill ponds prior to stocking shrimp and for daily pond refilling due to evaporation and seepage, is becoming scarce. Coastal waters are used both as a dumping ground for effluent and a source area for influent water. With increased wastewater discharge, estuaries are often unable to adequately process effluent loads and hence influent water is essentially of the same composition as effluent water. As mentioned, farmers have adapted new techniques, semi-closed and closed systems, to minimise water requirements of farms, but high quality water is still required at the beginning of a shrimp cycle.

If the treatment capacity of the mangrove in this study is representative of many, if not all mangroves, these wetlands could be used to not only treat effluent water to improve the health of coastal ecosystems, but also to improve the quality of influent water for shrimp farms. Many fmers are also concerned about introducing fatal

viruses into their ponds through contamination from influent water. If mangroves are

capable of improving effluent water quality to the degree that it is suitable to be re- introduced into the ponds, farmers could essentially re-circulate their own water thereby creating a closed system that is less susceptible to viral invasion from neighbouring farms' wastewater.

5.12.3 Global Im~acts

Shrimp farming is a lucrative business in many countries throughout Asia and

South America. Thailand, Indonesia, Taiwan and the Philippines are the major exporters of shrimp worldwide, primarily owing to their large production capacity which has been achieved through the adoption of intensive farming practices

(Rosenberry 1998 in Paez-Osuna 2001). These intensive practices have provided wealth to a number of previously impoverished areas, but are also responsible for a significant proportion of the eutrophic eMuent that is constantly flushed into sub- tropical and tropical waters.

Environmentally sustainable shrimp farming practices must be mandated in these regions if the health of coastal ecosystems is to be maintained. Currently there are no policies in existence that state acceptable limits of nitrate, nitrite and ammonia in shrimp farm effluent. Possible reasons for the lack of effluent composition regulations include minimal funds and man-power available to implement these regulations in addition to a dearth of feasible solutions for fmsthat have high concentrations of inorganic nitrogen in their effluent. If mangroves are found to be capable of significantly decreasing key nutrients that lead to eutrophication of receiving waters at a spatially undemanding ratio of 14:l mangrove to shrimp farm, mangroves could be used in many countries to improve the quality of estuarine waters.

As mangroves have once, and do still, occur in most regions with high concentrations of shrimp fanns, environmental conditions in these areas should be suitable for mangrove reforestation.

If governments of all countries with high densities of shrimp farms make mangrove wastewater treatment a prerequisite to intensive shrimp farm establishment, these wetlands could provide a natural solution to effluent management.

5.13 Summary

Previous research examining the potential of mangroves as biofilters for shrimp farm effluent determined mangrove nutrient cycling capacities based on theoretical values of mangal nutrient requirements and average shrimp wastewater composition.

This chapter presented results of one of the first in situ studies to monitor effluent quality pre- and post-exposure to a mangrove treatment wetland.

The composition of effluent in this study was similar to previously published values for intensive shrimp farms in Thailand. The mangrove treatment area was found to metabolise 699 g of protein into NH3 in a 48-hour period, significantly decrease effluent nutrient concentrations of ammonia and nitrite throughout the field season and also removed significant portions of nitrate for 4 of the 6 treatment weeks.

Overall, concentrations of nitrogen-based nutrients were significantly reduced indicating that mangroves have the potential to be effective low-cost, low- maintenance management tools for wastewater treatment. The ratio of mangrove to shrimp pond required to treat shrimp aquaculture effluent was calculated to be 1:14, which is both financially and spatially feasible in many shrimp farming regions.

Extrapolations fiom this study indicate that nitrogen loading on the coast of Chanthaburi could be as high as 152 222 kg Nlyr. The magnitude of this value highlights the need for rapid implementation of effluent wastewater treatment in many

shrimp-producing areas. CHAPTER 6

CONCLUSION

6.1 Summary

The ever-increasing popularity of shrimp farming has raised concern within

international communities due to the unknown detrimental effects of high effluent

loading on coastal ecosystems (Moss et al. 2001). Despite the global attention shrimp

farming has received in recent years, few studies have provided feasible solutions to

effluent management issues. The purpose of this study was to investigate the potential

of a modified mangrove in treating effluent originating from an intensive shrimp farm in Chanthaburi. Previous research has examined the theoretical potential of mangroves as wastewater treatment wetlands, but very few studies have examined their efficiency in real, natural environments.

The specific objectives of the study were: to examine the history of shrirnp

aquaculture and identify the environmental impacts of high density, high intensity farming practices and the need for feasible effluent treatment systems; to investigate the potential of mangroves in the treatment of nutrient-rich shrimp farm effluent ;to determine if a modified mangrove off the coast of Chanthabwi, Thailand could significantly reduce ammonia, nitrate and nitrite concentrations in effluent originating fiom an adjoining shrimp farm; to calculate the ratio of mangrove to shrimp pond required to adequately treat shrimp effluent and to determine the number of hectares of mangrove required to treat effluent originating from fanns along the coast of

Chanthaburi. 6.2 Maior Research Findinas

The most significant findings in this study were as follows:

The composition of effluent from the study farm was similar to previously

recorded effluent values fiom intensive shrimp farms with respect to nitrate,

nitrite and ammonia concentrations.

The mangrove study area metabolised 699 g of protein into NH3 over a 48

hour period

The mangrove treatment area significantly decreased concentrations of nitrite

and ammonia in effluent water throughout the entire field season.

The mangrove wetland ~i~cantlydecreased nitrate concentrations in

effluent for the last 4 weeks of the study.

The study mangrove was found to remove an average of 44.5% of nitrate,

46.6%of ammonia and 59.0% of nitrite fiom shrimp effluent.

Assuming mangroves can be flushed with effluent for 12 hours a day, and

assuming a pond seepage rate of 1.0 cdday, the ratio of mangrove to shrimp

pond necessary to significantly decrease nitrate, ammonia and nitrite

concentrations from shrimp farm effluent is 1: 14. This ratio is extremely

different from the 7: 1 ratio calculated by Robertson and Phillips (1995) and

suggests that mangroves may provide an environmentally, financially and

spatially feasible solution to current effluent management issues in many

nations around the world.

Although the effluent from one farm poses little to no threat: to coastal

ecosystems, constant flushing from shrimp farms along the entire length of

Chanthaburi's coastline has the potential to severely harm marine

environments. No standards exist at present for the limit of nitrate, ammonia and nitrite in shrimp effluent but there is a need to decrease the concentration

of all these parameters as the cumulative nitrogen loading of coastlines with

high densities of shrimp farms can severely disturb natural ecosystem

dynamics. The total nitrogen load generated by shrimp farms along the coast

of Chanthaburi was calculated to be 152 222 kg Nlyr. lbsvalue could be

decreased to as little as 71 097 kg N/yr if effluent was to be treated by 285 ha

of mangrove biofilters. If mangroves were to be replanted along the length of

Chanthaburi's coastline, they would cover an area of 7 000 ha, more than 24

times the amount of mangrove needed to adequately treat shrimp effluent fi-om

all farms along the province's coast.

6.3 Future Research Directions

The rapid expansion of intensive shrimp farming and the affiliated discharge of nutrient-rich effluent into surrounding coastal waters throughout the developing world has raised global concern about the environmental impacts of high intensity practices.

Research has identified the key effects associated with unregulated effluent flushing, but despite the undeniable fact that shrimp farming has the potential to harm coastal ecosystems if management techniques are not made more environmentally friendly, little to no feasible options for decreasing the impact of effluent have been discovered.

This study has revealed three areas that should be the focus of future research in this field:

The impact of long-term effluent loading on natural and modified mangroves

and mangal dwelling species Farm-scale studies analysing nutrient removal and assimilation capacities of

small mangrove wetlands, accounting for both above-ground and sediment

nutrient cycling processes

Techniques for low-cost, efficient mangrove cultivation and reforestation

Before finite conclusions can be made about the long-term efficiency of mangroves as wastewater biofilters, more research is required to enable researchers to predict mangal nutrient uptake capacities. Despite this, the findings of this study indicate that modified and natural mangroves show great promise as innovative, low- cost solutions to the harrml effects of shrimp farm effluent plaguing many of the world's tropical shores. REFERENCES

Aerts, R, Verhoeven, J.T.A. and Whigham, D.F. 1999. Plant-mediated controls of nutrient cycling in temperate and . Ecology 88: 2170-21 81.

Adeel, 2. and Pomeroy R. 2002. Assessment and management of mangrove ecosystems in developing countries. Trees 16: 235-238.

Aldridge, D. W., Payne, B. S. and Miller, A C. 1995. Oxygen consumption, nitrogenous excretion, and filtration rates of Dreissena polymorpha at acclimation temperatures between 20 and 32 degree C. Canadian Journal of Fisheries and Aquatic Sciences 52:1 76 1-67

Alongi, D.M, Boto, KG. and Robertson, AI. 1992. Nitrogen and phosphorus cycles. In Roberston, A.I. and Alongi, D.M. (eds.). Tropical mangrove ecosystem. American Geophysical Union, Washington, D.C. USA pp 25 1-292.

Alongi, D.M., Johnston, D.J. and Xuan, T.T. 2000. Carbon and nitrogen budgets in shrimp ponds of extensive mixed shrimp-mangrove forestry farms in the Mekong delta, Vietnam. Aquaculture Research 31: 387-399.

APHA (American Public Health Association). 1992. Standard methods for the examination of water and wastewater (18th edition). Washington, DC.

Ashihara, H., Adachi, K, Otawa, M., Yasumoto, E., Fukushima, Y., Kato, M., Sano, H., Sasamoto, H. and Baba, S. 1997. Compatible solutes and inorganic ions in the mangrove plant Avicennia marina and their effects on the activities of enzymes. Zeitschriftju Naturforschung 52(7-8): 433-440.

Azocar, A., Rada, R and Orozco, A 1992. Relaciones hidricas e intercambio de gases en dos especies de mangle, con mecanismos contrastantes de regulaci6n de la salinidad interna Ecotropicos 5(2) 1 1-1 9.

Baddeley, J.A., Woodin, S.J. and Alexander I. J. 1994. Effects of increased nitrogen and phosphorus availability on the photosynthesis and nutrient relations of three arctic dwarf shrubs fiom Svalbard. Functional Ecology 8: 676-685.

Bangkok Post 1999. Shrimp farmers say ban order is unfair. September 1.

Bashan, Y. and Holguin, G. 2002. Plant growth-promoting bacteria: a potential tool for arid mangrove reforestation. Trees 16: 159-166.

Bashan, Y. and Holguin, G. 1997. Azospirillium-plant relationships: environmental and physiological advances. Canadian Journal of Microbiology 43: 103-121.

Bergheim, A., Siversten, A. and Slemer-Olsen, A.R 1982. Estimated pollution loadings fiom Norwegian fish farms. I. Investigations 1978-1979. Aquaculture 28: 347-361. Beveridge, M.C.M., Ross, L.G. and Kelly, L.A. 1994. Aquaculture and biodiversity. Ambio 23(8):497-502.

Boto, K., Sailigna, P. and Clough, B. 1995. Role of nitrate in nitrogen nutrition of the mangrove Avicennia marina. Marine Ecology - Progress Series 21 (3):259-265.

Bowman, W. D. 1994. Accumulation and use of nitrogen and phosphorus following fertilization in two alpine tundra communities. Oikos 70:261 -270.

Boyd, C.E. 2001. Inland shrimp farming and the environment. World Aquaculture 32(1):10-12.

Boyd, C.E. and Tucker, C.S. 1998. Pond aquaculture water quality management. Kluwer Academic Publishers: Massachusetts.

Braaten, R.0,and Flaherty, M. 2000. Hydrology of inland brackishwater shrimp ponds in Chachaengsao, Thailand. Aquacultural Engineering 23: 295-3 13.

Bremer, G.B. 1995. Lower marine fungi (Labryinthulomycetes) and the decay of mangrove leaf litter Hydrobiologia 295: 89-95.

Briggs, M.RP. and Funge-Smith, S.J. 1994. A nutrient budget of some intensive marine shrimp ponds in Thailand. Aquaculture and Fisheries Management 25: 789-81 1.

Brix, H. 1999. How 'green' are aquaculture, constructed wetlands and conventional wastewater treatment systems? Water Science and Technology 40(3):45-50.

Brown, J.J. and Glenn, E.P. 1999. Reuse of highly saline aquaculture effluent to irrigate a potential forage halophyte, Suaeah esteroa. Aquaculture Engineering 20: 91-111.

Bryant, J.P., Chapin, F.S. and Klein, D.R 1983. Carbonlnutrient balance of boreal plants in relation to herbivory. Oikos 40: 357-386.

Bunt, J.S. 1992. Introduction. In Robertson, A.E. and Alongi D.M.(eds.). Tropical mangrove ecosystems. American Geophysical Union, Washington, D.C. USA. pp 1-6.

Burford, M.A. and William, KC. 2001. The fate of nitrogenous waste from shrimp feeding. Aquaculmre 198: 79-93.

Chanratchakool, P., Turnball, J.F., Funge-Smith, S. and Limsuwan, C. 1995. Health management in shrimpponds. Health Research Institute, Department of Fisheries Bangkok, Thailand. Clarke, P. J. and Allaway, W.G. 1993. The regeneration niche of the grey mangrove (Avicennia marina): effects of salinity, light and sediment factors on establishment, growth and survival in the field. Oecologia 93548-556.

Clough, B.F., Boto, KG.and Attiwill, P.M. 1983. Mangroves and sewage: a re- evaluation. In Teas, HJ. (ed.). Tasksfor vegetation science 8. Dr W.Junk, The Hague. pp 151-161.

Corea, A. S,L.E., Jayasinghe, J.M.P.K., Ekaratne, S.U.K. and Johnstone, R. 1995. Environmental impact of prawn farming on Dutch Canal: the main water source for the prawn culture indllstry in Sri Lanka Ambio 24(7-8): 423-427.

Corredor, J., Morell, J. and Bauza, J. 1999. Atmospheric nitrous oxide fluxes from mangrove sediments. Bulletin 38(6): 473-478.

Cowan, V.J., Lorenzen, K and Funge-Smith, S.J. 1999. Impact of culture intensity and monsoon season on water quality in Thai commercial shrimp ponds. Aquaculture Research 30: 123-133.

Csavas, I. 1993. Aquaculture development and environmental issues in the developing countries of Asia In Pullin, R.S.V., Rosenthal, H. and Maclean, J.L. (eds.). Environment and Aquaculhrre in Developing Countries. ICLARM Conf. Proc. 3 1. pp. 74-101.

Davis, S.E., Childers, D.L, Day Jr. J.W., Rudnick, D.T. and Sklar, F.H. 2002. Wetland-water column exchanges of carbon, nitrogen and phosphorus in a Southern Everglades dwarf mangrove. Esfuaries 24(4): 610-622.

De Silva, S.S. 1998. Tropical mariculture: current status and prospects. In De Silva (ed). TropicalMariculture. Academic Press: San Diego, California pp 1-16.

Dierberg, F.E. and Kiattisimkul, W. 1996. Issues, impacts and implicationsof shrimp aquaculture in Thailand. ESlvironmental Management 20(5): 649-666.

Dixon, J.A 1989. Valuation of mangroves. Tropical Coastal Area Management 4(3): 1a.

Ellison, A 2002. Macroecology of mangroves: large-scale patterns and processes in tropical coastal forests. Trees 16: 181-194.

Ellison, A, Famsworth, E.J. and Twilley, RR 1996. Facultative mutualism between red mangroves and root-fouling sponges in Belizean mangal. Ecology 77: 243 1- 2444.

Ewel, K, Twilley, R and Ong, J. 1998. Different kinds of mangrove forests provide different goods and services, Global Ecology and Biogeography Letters 7: 83-94.

FAO. 1999. Aquaculture production statistics 1988-1997. FA0 Fisheries Circular. 8 15 Rev. 1 1, Rome. 203 pp. FAO. 2001. FA0 yearbook. Fishery statistics: Aquaculture production 2001. 92:2.

FAO. 2002. Xhe state of the world's$sheries. Editorial Group FA0 Information Division: Italy.

Farnsworth, E.J., and Ellison, A.M. 1997.Global patterns of pre-dispersal propagule predation in mangrove forests. Biotropica 29(3): 3 18-330.

Feller, I.C. 1995. Effects of nutrient enrichment on growth and herbivory of dwarf red mangrove (Rhizophora mangle). Ecological Monographs 65: 477-505.

Flaherty, M and Kamjanakesorn, C. 1995. Mamie shrimp aquaculture and natural resource degradation in Thailand. EnvironmentalManagement 19(1): 27-37.

Flaherty, M. and Vandergeest, P. 1998. "Low-salt" shrimp aquaculture in Thailand: goodbye coastline, hello Khon Kaen! Environmental Management 22(6): 81 7-830.

Flaherty, M., Vandergeest, P. and Miller, P. 1999. Rice paddy or shrimp pond: tough decisions in rural Thailand. World Development 27(12): 2045-2060.

Flegel, T.W. and Alday-Sanz, V. 1998. The crisis in Asian shrimp aquaculture: current status and hture needs. Journal ofAppliedIchthyology 14: 269-273.

Folke, C. and Kautsky, Nils. 1992. Aquaculture with its environment: prospects for sustainability. Ocean and Coastal Management 17: 5-24.

Funge-Smith, S. J. and Briggs, M.RP. 1998. Nutrient budgets in intensive shrimp ponds: implications for sustainability. Aqaraculmre 164: 117-133.

Gautier, D., Amador, J., and Newmark, F. 2001. The use of mangrove wetland as a biofilter to treat shrimp pond effluents: preliminary results of an experiment on the Caribbean coast of Colombia Aquaculture Research 32: 787-799.

Giani, L. Bashan, Y., Holguin, G. and Stangmann, A. 1996. Characteristics and methanogenesis of the Balandra mangrove soils, Baja California Sur, Mexico. Geodem72: 149-160.

Global Historical ClimatoIogy Network 1990. Internet. www.worldcIimate.com Last retrieved January 2004.

Gopal, B. 1999. Natural and constructed wetlands for wastewater treatment: potentials and problems. Water Science and Technology 40(3): 27-35.

Gopal, B. and Krishnamurthy, K. 1993. Wetlands of South Asia. In Whigham, D.F., Dy Kyjova, D. and Hejny, S. (eds.). Wetlands of the World Kluwer Academic Publishers, Netherlands. pp 345-41 4. Gotto, J.W. and Taylor B.F. 1976. N2 fixation associated with decaying leaves of the red mangrove (Rhiwphora mangle). Applied Environmental Microbiology 31 : 781 -783.

Hambrey, J. and Lin, C.K. 1998. Shrimp culture in Thailand. Internet. http://www. aauafind,com/articles/shmcul. html Last retrieved May 2003. Hogarth, P.J. 1999. The Biology ofMangroves. Oxford University Press, New York, USA. Holguin, G., Buzman, M.A. and Bashan, Y. 1992. Two nitrogen-fixing bacteria from the rhizosphere of mangrove trees- their isolation, identification and in vitro interaction with rhizosphere Staphylococcus sp. FEMS Microbiology Ecology 101: 207-216.

Holguin, G., Vazquez, P. and Bashan, Y. 2001. The role of sediment microorganisms in the productivity, conservation and rehabilitation of mangrove ecosystems: an overview. Biology and Fertility of Soils 33: 265-278.

Hopkins, J.S., Browdy, C.L., Hamilton R.D. and Heffernan, J.A. 1995a. The effect of low-rate sand filtration and modified feed management on effluent quality, pond water quality and production of intensive shrimp ponds. Estuaries 18(1 a): 116- 123.

Hopkins, J. S., Browdy, C.L., DeVoe, M. R, Hooland, A.F., Sandifer, P. A. and Stokes, AD. 1995b. Environmental impacts of shrimp farming with special reference to the situation in the continental United States. Estuaries 18 (la): 25-42.

Hovenden, M.J. and Allaway, W.G. 1994. Horizontal structures on pneumatophores ofAvicennia marina (Forsk.) Vierh. : A new site of oxygen conductance. Annals of Botany 73(4) 377-383.

Howes, B.L. and Goehringer, D.D. 1994. Porewater drainage and dissolved organic carbon and nutrient loss through the intertidal creek banks of a New England , Marine Ecology Progress Series 1 14: 289-301.

International Rice Research Institute. 1998. The looming water crisis. Internet. ~~://www.cigar.ordirri/riceweb/researc~es issloom.htm Last retrieved June 2003

Jennerjahn, T.C. and Ittekkot, V. 2002. Relevance of mangroves for the production and deposition of organic matter along tropical continental margins. Naturwissenschajen 89: 23-30.

Johnson, C.A. 1991. Sediment and nutrient retention by freshwater wetlands: effects on surface water quality. Critical Reviews in Environmental Con&ol215(5,6): 491-565. Jones, A.B., Dennison, W.C. and Preston, N.P. 2001. Integrated treatment of shrimp effluentby sedimentation, oyster filtration and macroalgal absorption: a laboratory scale study. Aquaculture 193: 155-178.

Kathiresan, K. and Bingham, B.L. 2001. Biology of Mangroves and Mangrove Ecosystems. In Southward, A. J., Tyler, P. A., Young, C.M. and Fuiman, L. A. (eds.). Advances in Vol. 40. Academic Press, London, U.K. pp 84- 251.

Khatun, S. and Flowers, T. 1995. Effects of salinity on seed set in rice. Plant Cell and Environment 18(1): 61 -67.

Kitaya, Y., Yabulu, K., Kiyota, M., Tanni, A., Hirano, T. and Aiga, I. 2002. Gas exchange and oxygen concentrations in pneurnatophores and prop roots of four mangrove species. Trees 16: 155-158.

Kongkeo, H. 1994. How Thailand became the largest producer of farmed shrimp in the world. Infoj?sh January.

Kongkeo, H. 1997. Comparison of intensive shrimp farming systems in Indonesia, Philippines, Taiwan and Thailand. Aquaculture Research 28: 789-796.

Kristensen, E. and Suraswadi, P. 2002. Carbon, nitrogen and phosphorus dynamics in creek water of a southeast Asian mangrove forest. Hydrobiologia 474: 197-211.

Lacerda, L.D., Conde, J.E., Alarcon, C., Alvarez-Leon, R, Bacon, P.R, D'Corz, L.D., Kjerfve, B., Polania, J. and Vannucci, J. 1993a Ecosistemas de manglar de America Latina y el Caribe: synopsis. In Lacerda, L.D., Polania, J. (eds.). Conservation y aprovechamiento sostenible de bosques de manglar en las regions America Latina y AJLica. International Tropical Timber Organization and International Society for Mangrove Ecosystems. Okinawa, Japan pp 1-38.

Lacerda, L.D., Carvalho, C.E.V., Tanizaki, KF., Ovalle, A.RC. and Rezende, C.E. 1993b. The biogeochernistry and trace metals distribution of mangrove rhizoshperes. Biotropica 25: 25 1-256.

Lee, S.Y. 1999. Tropical mangrove ecology: physical and biotic factors influencing ecosystem structure and function. Australian Journal of Ecology 24: 355-366.

Lee, S.K, Tan, W.H. and Havanond, S. 1996. Regeneration and colonization of mangrove on clay-filled reclaimed land in Singapore. HNrobiologia 319: 23-25.

Lin, C.K., Ruamthaveesub, P., and Wanuchsoontom, P. 1991. Wastewater of intensive shrimp farming and its potential biological treatment. Unpublished paper. Asian Institute of Technology. Bangkok, Thailand.

Lin, G.H . and Sternberg, L.D.S.L. 1994. Utilization of surface water by red mangrove (Rhizophora mangle L.): An isotopic study. Bulletin ofMarine Science 54(1): 94- 102. Lorenzen, K., Struve, J. and Cowan, V.J. 1997. Impact of farming intensity and water management on nitrogen dynamics in intensive pond culture: a mathematical model applied to Thai commercial shrimp fanns. Aquaculture Research 28: 493- 507.

Macintosh, D.J. and Phillips, M. J. l992a. Environmental issues in shrimp farming. LNFOFISH International 4: 38-42.

Macintosh, D. J. and Phillips, M.J. l992b Environmental issues in shrimp farming. Paper presented at Shrimp '92: 3"' Global Conference on Shrimp Industry. Hong Kong.

Mackinnon, J. 1997. Protected areas systems review of the Indo-Malayan realm. Asian Bureau for Conservation, Canterbury, U.K.

Madeira, M., Araujo, M.C. and Pereira, J. S. 1995. Effects of water and nutrient supply on amount and on nutrient concentration of litterfall on forest floor litter in Eucalptus globulus plantations. Plant and Soil 168-169: 287-295.

McKinnon, A.D., Trott, L.A, Alongi, D.M. and Davidson, A. 2002. Water column production and nutrient characteristics in mangrove creeks receiving shrimp farm effluent. Aquaculture Research 33: 55-73.

Medina, E., Garcia, V. and Cuevas, E. 1990. Sclerophylly and oligotrophic environments: relationships between leaf structure, mineral nutrient content and drought resistance in tropical rain forests of the Upper Rio Negro region Biotropica 22: 5 1-64.

Moore, J.W. 1991. Inorganic contaminants of surface water: research and mohitoring priorities. Springer-Verlag: New York.

Moss, S.M., Arce, S.M., Argue, B.J., Otoshi, C.A., Calderon, F.RO. and Tacon, A.G.J. 2001. Paper presented at Aquaculhrre 200I Conference. Lake Buena Vista, Florida: January 2001.

Moriarty, D. J.W. 1986. Bacterial productivity in ponds used for culture of penaeid prawns, Gelang Patah, Malaysia 12: 259-269.

NACA (Network of Aquaculture Centres in Asia Pacific). 1996. A survey of fiom coastal aquaculture. Final report to the Pollution Control Department. October 1996.

NACAEAO. 2000. Aquaculture development beyond 2000. The Bangkok Declaration and Strategy. Conference on aquaculture in the third millennium, 20- 25 February 2000, Bangkok, Thailand. NACA, Bangkok, FAO, Rome. 27 pp. Naidoo, G. and Von-Willert, D.J. 1995. Diurnal gas exchange characteristics and water use efficiency of three salt-secreting mangroves at low and high salinities. Hydorbiologia 295(1-3): 13-22.

Naylor, R.L., Goldburg RJ., Primavera, J.H., Kautsky, N., Beveridge, M.C.M., Clay, J., Floke, C., Lubchenco, J., Mooney, H., and Troell, M. 2000. Effects of aquaculture on world fish supplies. Nature 405: 1017-1 024.

Nedwell, D.B., Blackburn, T.H. and Wiebe, W.J. 1994. Dynamic nature of the turnover of organic carbon, nitrogen and sulphur in the sediments of a Jamaican mangrove forest. Marine Ecology Progress Series 1 10: 223-23 1.

Nunes A. J.P. and Parsons, G. J. 1998. Dynamics of tropical coastal aquaculture systems and the consequences to waste production. WorId Aquaculture 29(2): 27- 37.

Nzengy'a, D.M. and Wishitemi, B.E.L. 2001. The performance of constructed wetlands for, wastewater treatment: a case study of Splash wetland in Nairobi Kenya. Hydrological Processes 15: 3239-3247.

Paez-Osuna, F. 2001. The environmental impact of shrimp aquaculture: causes, effects and mitigating alternatives. Environmental Management 28(1): 131-1 40.

Panapitukkul, N., Duarte, C.M., Thampanya, U., Kheowvongsri, P., Srichai, N., Geertz-Hansen, O., Terrados, J. and Boromthanarath, S. 1998. Mangrove colonization: mangrove progression over the growing Pak Phanang (SE Thailand) mud flat. Estuarine, Coastal and ShelfScience 47: 5 1-61.

PCL Map Collection. 1988. Thailand provinces (political). University of Texas at Austin. Intemet.http://www.lib.utexas.edu/maps/middleeast and asiafthailand provinces 88.i~Last retrieved August 2003.

Phillips, M.J. 1998. Tropical mariculture and coastal environment integrity. In De Silva (ed). Tropical Mariculture. Academic Press: San Diego, California. pp 17- 69.

Phillips, M.J, Lin, C.K. and Beveridge, M.C.M. 1993. Shrimp culture and the environment: lessons fiom the world's most rapidly expanding warmwater aquaculture sector. In Pullin, RS.V., Rosenthal, H. and Maclean, J.L. (eds.). Environment and Aquaculture in Developing Countries. ICLARM Cod. Proc. 3 1. pp. 171-197.

Primavera, J.H. 1993. A critical review of shrimp pond culture in the Philippines. Reviews in l(2): 151-20 1.

Primavera J.H. 1998. Tropical shrimp fanning and its sustainability. In De Silva (4.). Tropical Mariculture. Academic Press: San Diego, California. pp 257-289. Profitt, C.E., Devlin, D. J. and Lindsey, M. 1995. Effwts of oil on mangrove seedlings grown under different environmental conditions. Marine Pollution Bulletin 30: 788-793.

Qureshi, M.T. 1996. Restoration of mangroves in Pakistsan In Field, C. (ed.). Restoration of mangrove ecosystems. International Timber Organisation and International Society for Mangrove Ecosystems, Okinawa, Japan pp126-142.

Raine, RM. 1994. Current land use and changes in land use over time in the coastal zone of Chanthaburi Province, Thailand. Biologiml Consewation 67: 201-204.

Rajendran, N. and Kathiresan, K. 1996. Effect of effluent from a shrimp pond on shoot biomass of mangrove seedlings. Aquaculture Research 27: 745-747.

Redding, T., Todd, S. and Midlen, k 1997. The treatment of aquaculture wastewaters - a botanical approach. Journal of Environmental Management 50: 283-299.

Rivera-Monroy, V.H., Twilley, RR., Boustany, RG., Day, W.J., Vera-Herrera, F. and Ramirez, M.C.1995. Direct denitrification in mangrove sediments in Terminos lagoon, Mexico. Mkrine Ecology Progress Series 126: 97-109.

Rivera-Monroy, V.H., Torres, LA, Bahamon, N., Newrnar, F., and Twilley, RR 1999. The potential use of mangrove forests as sinks of shrimp aquaculture and pond effluents: the role of denitrification. Journal of the World Aquaculture Society 30: 12-25.

Robertson, AI and Phillips, M.J. 1995. Mangroves as filters of shrimp pond effluent: predictions and biochemical research needs. Hydrobiologia 295 :649-666.

Rosenbeny, B. 1998. World shrimp farming. Shrimp Navs International. San Diego, California 328 pp.

Sansanayuth, P., Phadungchep, A., Ngammontha, S., Ngdngam, S., Sukasem, P., Hoshino, H. and Ttabucanon, M. S. 1996. Shrimp pond effluent: pollution problems and treatment by constructed wetlands. Water Science and Technology 34(11): 93-98.

Sayed, O.H.1995. Effects of the expected sea level rise on Avicennia Marina L; A case study in Qatar. Qatar University Science Journal 15(1) 91-94

Schulze, E.-D. 2000. The carbon and nitrogen cycle of forest ecosystems. In Schulze, E.-D. (ed.). Carbon and Nitrogen Cycling in European Forest Ecosystems. Springer-Verlag Berlin Heidelberg, Germany. pp 3-1 1.

Schwartz, M.F. and Boyd, C.E. 1995. Constructed wetlands for treatment of channel catfish pond effluents. Progressive Fish Culturist 57 (4):255-266. Sherman, R.E., Fahey, T.J. and Howarth, R. W. 1998. Soil-plant interactions in a neotropical mangrove forest: iron, phosphorus and sulfur dynamics. Oecologia 115: 553-563.

Smith, S.M., Yang, Y.Y., Kamiya, Y. and Snedaker, S.C. 1996. Effect of the environment and gibberellins on the early growth and development of the red mangrove, Rhizophora mangle L. Plant Growth Regulation 20(3): 215-223.

Smith, T.J., Boto, KG., Frusher, S.D. and Giddens, RL. 1991. Keystone species and mangrove forest dynamics: the influence of burrowing by crabs on soil nutrient status and forest productivity. Estuarine, Coastal and SheIfScience 33: 41 9-432.

Strangmann, A, Noorman, M., Bashan, Y. and Giani, L. 1999. Methane dynamics in natural and disturbed mangrove soils (tropical salt marshes) in Baja California Sur, Mexico (in German). Mitteilungen der Deutschen Bodenkundlichen Gesellschaft 91: 1549-1552.

Summerfelt, S.T., Adler, P. R ,Glenn, D. M., Kretschmann, R.N. 1999. Aquaculture sludge removal and stabilization within created wetlands. AquaculturaI Engineering 19: 8 1-92.

Tam, N.F.Y. 1998. Effects of wastewater discharge on microbial populations and enzyme activities in mangrove soils. Environmental Pollution 102: 233-242.

Tam, N.F.Y. and Wong, Y.S. 1999. Mangrove soils in removing pollutants from municipal wastewater of different salinities. Journal of Environmental Quulity 28: 556-564.

Teichert-Coddington, D.R, Rouse, D.B., Patts, A. and Boyd, C.E. 1999. Treatment of hasvest discharge from intensive shrimp ponds by settling. Aquaculture Engineering 19:147-1 61.

Thongrak, S., Prato, T., Chiayvareesajja, S. and Kurtz, W. 1997. Economic and water quality evaluation of intensive shrimp systems in Thailand. Agriculhtral Systems 53: 121-141.

Tiensongrusmee, B. and Phillips, M. J. 1994. The environmental management of coastal aquaculture. A study of shrimp culture in southern Thailand. Training course and semi-intensive shrimp culture operation and management, 4-24 July 1994. The Network ofAquaculture Centres in Asia-PaciJic (NACA), Kasetsart University, Bangkok, Thailand.

Tilley, D.R, Badrinarayanan, H., Rosati, R. and Son, J. 2002. Constructed wetlands as recirculation filters in large-scale shrimp aquaculture. Aquacultural Engineering 26: 81-109.

Toledo, G., Bashan, Y. and Soeldner, A. 1995. and black mangroves in Northwestern Mexico: colonization, and diurnal and seasonal nitrogen fixation on aerial roots. Canadian Journal ofMicrobiology 41: 999-101 1. Todinson, P.B. 1986. The Botany of Mangroves. Cambridge University Press, Cambridge, U.K.

Tookwinas, S. 1994. Intensive marine shrimp fanning techniques in Thailand. Unpublished report. Coastal Fisheries Resources and Environment Research Centre, Department of Fisheries, Chantaburi, Thailand.

Tookwinas, S. 1996. Environmental impact assessment for intensive marine shrimp farming in Thailand. Paper presented at the World Aquaculture Society Conference 1996. Bangkok, Thailand.

Tookwinas, S., Tabkaew, R and Srisapoom, P. 1997. An intensive marine shrimp culture in freshwater area (Suphanburi province): the preliminary investigation on impact assessment. Paper presented at the Asian Shrimp Culture Council meeting, March 15,1997, Bangkok, Thailand.

Tookwinas, S. and Songsangjinda, P. 1999. Water quality and phytoplankton communities in intensive shrimp culture ponds in Kung Krabaen bay, eastern Thailand. Journal of the World Aquaculture Society 30(1): 3645.

Twilley, R.R., Chen, R. and Hargis, T. 1992. Carbon sinks in mangroves and their implications to carbon budget of tropical ecosystems. Water, Air and soil Pollution 64: 265-288.

Twilley, R.R, Porn, M., Garcia, V.H., Rivera-Monroy, V.H., Zambrano, R and Bodero, A. 1997. Litter dynamics in riverine mangrove forest in the Guayas River , Ecuador. Oecologia 11 1 : 109-122.

Ukpong, I.E. 1997. Vegetation and its relation to soil nutrient and salinity in the Calabar mangrove swamp, Nigeria Mangroves < Marshes 1: 2 11 -2 18.

Walters, B.B. 2000. Local mangrove planting in the Philippines: are fisherfolk and fishpond owners effective restorationists? Restoration Ecology 8(3): 237-246.

Wong, Y.S., Tam, N.F.Y. and Lan, C.Y.1997. Mangrove wetlands as wastewater treatment facility: a field trial. Hydrobiologia 352: 49-59.

Yates, E. J., Ashwath, N. and Midmore, D. J. 2002. Responses to nitrogen, phosphorus, potassium and sodium chloride by three mangrove species in pot culture. Trees 16: 120-125.

Ye, Y., Tam, N.F.Y. and Wong, Y.S. 2001. Livestock wastewater treatment by a mangrove pot-cultivation system and the effect of salinity on the nutrient removal efficiency. Marine Pollution Bulletin 42(6): 5 13-52 1. Zimmerman, U., Zhu, J.J., Meinzer, F.C.,Goldstein, G.,Schneider, H., Zirnmerrnan, G., Benkert, R., Thuermer, F., Melcher, P., Webb, D. and Haase, A 1994. High molecular weight organic compounds in the xylem sap of mangroves: Implications for long-distance water transport. Botanzca Actu 107(4): 218-229.

Zuberer, D.A. and Silver, W.S. 1979. Nz-fixation (acetylene reduction) and the microbial colonization of mangrove roots. Nay Phytologist 82: 467-671.