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Biomass production and nutrient dynamics in an aquaponics system

ProQuest Dissertations and Theses, 2009
Dissertation
Author: Jason Licamele
Abstract:
The goal of this study was to prove that aquaponic systems can produce lettuce of equal growth and quality compared to hydroponic lettuce production and to determine the stocking density of fish required for plant growth. Aquaponics is the integration of recirculating aquaculture and hydroponic plant production. The project had four objectives. The first objective was to determine the biomass of fish required for plant growth to develop a fish to plant density ratio. The second objective was to compare lettuce grown with aquaponic water and a hydroponic solution under the same environmental conditions. The third objective was to compare the quality of lettuce grown with aquaponics water plus nutrient supplementation with a hydroponic solution. The fourth objective was to determine the nitrogen dynamics in the aquaponic system and to compare the nutrient composition of lettuce grown with aquaponics water with nutrient supplementation and hydroponic solution. It was determined that under the specified environmental conditions 5 kg m-3 of Nile tilapia ( O. niloticus ) fed 2% of their body weight daily yields on average 4.7 kg m-2 of lettuce (L. sativa cv. Rex) in 35 days. There was no significant difference (p≤0.05) in biomass or chlorophyll concentration index in lettuce (L. sativa cv. Rex) grown with aquaponics water and nutrient supplements versus a hydroponic solution. The aquaponics solution generated equal biomass and chlorophyll concentration indexes compared to the hydroponic solution. Aquaponics water plus supplementation can yield L. sativa cv. Rex with equal biomass accumulation and chlorophyll concentration indexes compared to hydroponics lettuce. Nutrients added to the aquaponics system consisted of iron, manganese, and zinc. These nutrient concentrations became depleted in the aquaponics water over time and were not replenished via the fish feed. Dolomite was added to the aquaponics system every two weeks to increase the buffering capacity of the water and maintain optimal pH levels. Aquaponics lettuce had similar nutrient composition to hydroponic lettuce. One head of L. sativa cv. Rex (176.75 ± 31.03) will assimilate approximately 5.96 grams of nitrogen (3.38% per dry gram lettuce). One kilogram of fish will yield 6.4 lettuce heads (1,128 grams) and fixate 38.13 grams of nitrogen.

TABLE OF CONTENTS

LIST OF FIGURES…………………………………………………………………….....9

LIST OF TABLES……………………………………………………………………….10

ABSTRACT……………………………………………………………………………...11

INTRODUCTION……………………………………………………………………….13

PROBLEM STATEMENT………………………………………………………13

LITERATURE REVIEW……………………………………………..................16 Aquaculture……………………………………………………................16 Lettuce Hydroponics………………………………………………...…...19 Aquaponics……………………………………………………................22

PROJECT GOALS AND OBJECTIVES……………………………..................30 Aquaponics Research Greenhouse Design………………………………36 Hypothesis and Specific Aims…………………………………………...42

PRESENT STUDY…………………………………………………………....................45

OVERALL SUMMARY………………………………………………………...45 OPTIMAL FISH (OREOCHROMIS NILOTICUS) TO PLANT (LACTUCA SATIVA CV. REX) RATIOS FOR A CONTROLLED ENVIRONMENT AQUAPONICS SYSTEM (APPENDIX A)………………………………………………..………...45 COMPARISON OF LETTUCE (LACTUCA SATIVA CV. REX) GROWN WITH TILAPIA (OREOCHROMIS NILOTICUS) EFFLUENT AND NUTRIENT SUPPLEMENTATION VERSUS A HYDROPONIC SOLUTION (APPENDIX B)…………………………………................48 NITROGEN REMEDIATION AND NUTRIENT DYNAMICS IN A CONTROLLED ENVIRONMENT AQUAPONICS SYSTEM (APPENDIX C)…………...………………...53

OVERALL CONCLUSIONS AND RECOMMENDATIONS…………………56

REFERENCES…………………………………………………………………..64

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TABLE OF CONTENTS Continued

APPENDIX A: OPTIMAL FISH (OREOCHROMIS NILOTICUS) TO PLANT (LACTUCA SATIVA CV. REX) RATIOS FOR A CONTROLLED ENVIRONMENT AQUAPONICS SYSTEM………………………………………………………………………...70

ABSTRACT……………………………………………………………...71 INTRODUCTION……………………………………………………….73 MATERIALS AND METHODS………………………………………...78 Experimental Design……………………………………………..78 Fish and Plants…………………………………………………...79 Environmental Parameters and Water Chemistry………………..81 Data Analysis…………………………………………………….82 RESULTS……………………..………………………………................86 Fish Biomass……………………………………………………..86 Plant Biomass………………………………………………........86 Water Chemistry…………………………………………………87 DISCUSSION………………………………………………..................97 REFERENCES……………………………………………....................103

APPENDIX B: COMPARISON OF LETTUCE (LACTUCA SATIVA CV. REX) GROWN WITH TILAPIA (OREOCHROMIS NILOTICUS) EFFLUENT AND NUTRIENT SUPPLEMENTATION VERSUS A HYDROPONIC SOLUTION……………………………………………………………………107

ABSTRACT…………………………………………………………….108 INTRODUCTION…………………………………………………..….109 MATERIALS AND METHODS……………………………………….114 Aquaponics System Design and Protocol……………………....114 Nutrient Supplementation……………………………………....117 Monitoring of Environmental Parameters……………………...118 Biomass and Chlorophyll Concentration Index...………………118 RESULTS………………..…………………………..............................122 Water Chemistry Analysis and Environmental Parameters…….122 Biomass Analysis and Chlorophyll Concentration Index……....123 DISCUSSION………………………………………………................134 REFERENCES……………………………………………....................136

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APPENDIX C: NITROGEN REMEDIATION AND NUTRIENT DYNAMICS IN A CONTROLLED ENVIRONMENT AQUAPONICS SYSTEM………...…………………………………………..140

ABSTRACT…………………………………………………………….141 INTRODUCTION……………………………………………………...143 MATERIALS AND METHODS……………………………………….148 Aquaponics System Design and Protocol……………………...148 Nutrient Supplementation………………………………………151 Monitoring of Environmental Parameters……………………...152 Data Collection and Statistical Analysis………………………..152 RESULTS………………………………................................................157 Environmental Parameters…………………………………..….157 Water Chemistry Analysis……………………………………...157 Biomass Analysis……………………………………………….158 Nutrient Analysis……………………………………………….158 Nitrogen Dynamics……………………………………………..159 DISCUSSION………………………………………………..................166 REFERENCES……………………………………................................170

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LIST OF FIGURES

Figure 1. Picture of the University of Arizona controlled environment greenhouse The greenhouse structure (A), the fish bay (B), and the hydroponic plant bay (C)……………………………………………………………..32

Figure 2. The filtration system for the University of Arizona controlled environment aquaponics greenhouse. A Polygeyser™ PG7PR filter from International Filter Solutions was used to remove particulate matter from the aquaponics water. A biological filter was constructed to supplement the PG7 filter. The sludge from the aquaponics system was collected…………………………………………………………..…34

Figure 3. Aquaponics research greenhouse fish section design. Figure legend lists the Fish and filtration system components…………………………………..38

Figure 4. Aquaponics research greenhouse plant section design. Figure Legend lists the schematics of the hydroponic plant beds. Yellow represents airlines for oxygen delivery, and blue represents water flowing to the hydroponic beds and back to the fish component.….……39

Figure 5. Flow chart of the inputs and outputs of an aquaponics system. The three primary outputs are fish, lettuce, and processed fish sludge. Inputs include water, feed (nutrients), and sunlight. Energy is also utilized for moving water and delivering oxygen to the water…………………...44

Figure 6. Picture of lettuce (L. sativa cv. Rex) grown with aquaponics water (A), aquaponics water plus supplementation (B), and hydroponic solution (C)……......................................................................................................57

Figure 7. Fish and lettuce grown in the University of Arizona Controlled Environment Aquaponics Greenhouse. Tilapia (O. niloticus spp.) was harvested on monthly basis (A). Varieties of lettuce were grown in the aquaponics system including romaine, red and green oak, and butterhead (B). An organic romaine cultivar of lettuce (L. sativa cv. Rom) (C)…………….58

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LIST OF TABLES

Table 1. Amount of water required to produce $100 output of different food commodities……………………………………………………………………24

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ABSTRACT The goal of this study was to prove that aquaponic systems can produce lettuce of equal growth and quality compared to hydroponic lettuce production and to determine the stocking density of fish required for plant growth. Aquaponics is the integration of recirculating aquaculture and hydroponic plant production. The project had four objectives. The first objective was to determine the biomass of fish required for plant growth to develop a fish to plant density ratio. The second objective was to compare lettuce grown with aquaponic water and a hydroponic solution under the same environmental conditions. The third objective was to compare the quality of lettuce grown with aquaponics water plus nutrient supplementation with a hydroponic solution. The fourth objective was to determine the nitrogen dynamics in the aquaponic system and to compare the nutrient composition of lettuce grown with aquaponics water with nutrient supplementation and hydroponic solution. It was determined that under the specified environmental conditions 5 kg m 3 of Nile tilapia (O. niloticus) fed 2% of their body weight daily yields on average 4.7 kg m 2 of lettuce (L. sativa cv. Rex) in 35 days. There was no significant difference (p≤0.05) in biomass or chlorophyll concentration index in lettuce (L. sativa cv. Rex) grown with aquaponics water and nutrient supplements versus a hydroponic solution. The aquaponics solution generated equal biomass and chlorophyll concentration indexes compared to the hydroponic solution. Aquaponics water plus supplementation can yield L. sativa cv. Rex with equal biomass accumulation and chlorophyll concentration indexes compared to hydroponics lettuce. Nutrients added to the aquaponics system consisted of iron, manganese, and zinc. These nutrient concentrations became depleted in the aquaponics water over time and were not

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replenished via the fish feed. Dolomite was added to the aquaponics system every two weeks to increase the buffering capacity of the water and maintain optimal pH levels. Aquaponics lettuce had similar nutrient composition to hydroponic lettuce. One head of L. sativa cv. Rex (176.75 ± 31.03) will assimilate approximately 5.96 grams of nitrogen (3.38% per dry gram lettuce). One kilogram of fish will yield 6.4 lettuce heads (1,128 grams) and fixate 38.13 grams of nitrogen.

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INTRODUCTION PROBLEM STATEMENT The world population is growing fast and as of November 2009 is approximately 6.8 billion, while 308 million people reside in the United States (U.S. Census Bureau 2009). Water and land resources for agriculture are diminishing and world fisheries are at or past their maximum sustainable yields. To feed humanity for the next 40 years it is speculated that more food must be produced than all the food produced since the beginning of recorded history (Parker 2002). Extractive resources are taken from nature and then consumed in some applications for food or energy. Renewable resources such as trees and fish exist in finite quantities at any point in time but can regenerate (Rasband et al. 2004). Fisheries are an extractable renewable resource when managed properly. Recent consumption and demand for seafood primarily driven by technological fishing development and market demand (arising from recent knowledge of the health benefits from fish and increasing populations) has led to a mismanaged system. There are multiple reasons for the mismanagement of fisheries. First, increases in consumer demand has skyrocketed past what natural fish stocks can support. Second, pollution, climate change and the lack of global enforcement in fisheries management has led to severely depleted fish stocks. Some predict commercial fish stocks to disappear within the next decade or even sooner if problems are not addressed (FAO 2007). The majority of commercially fished species are at or past their maximum sustainable yields meaning that fish populations can not naturally rebound on their own. Aquaculture yields promise for sustaining fishery resources. However this can not be done by simple mass production via aquaculture. Environmental problems that arise from aquaculture include: biological

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pollution (escaped fish); fish for fish feed ingredients, farm discharge pollution leading to eutrophication, habitat modification and chemical pollution from antibiotics and pesticides. Aquaculture practices must be coupled with sound environmental and fisheries policies to yield a productive and sustainable management system. Aquaculture is the fastest growing sector of food production producing over 60 million metric tons of products in 2005 (FAO 2007). This will only continue to rise as demand for seafood is increasing and fisheries are being depleted. In aquaculture, as with livestock or poultry, water is not consumed but the biochemical nature of water is altered. In the United States aquaculture has increased in importance. The U.S. imports more seafood than it exports resulting in a $9.2 billion seafood import deficit (DOC 2007). Seafood consumption in the U.S. has increased to over 16 pounds per person in 2005 and is now third in the world behind China and Japan respectively (FAO 2005). The recent growth of organic farming has supported the use of fish and fish byproduct fertilizers over conventional synthetically derived chemical fertilizers. Water is a precious resource and becoming a scarcity relative to human demand. Sustainability of agriculture and economic activities that require water can only be achieved through proper management practices (Postel 2002). Water is one of the essential commodities for sustaining life and producing food. Demand for food is increasing with an increase in human population. Water and land resources are decreasing and as demand for their utilization to produce food increases their value will increase. Resources used in farming of food consist primarily of water, land, and feed. All three of these resources are limited. Resources used in farming of food consist primarily of water, land, and feed. All three of these resources are limited. Agriculture accounts for approximately 70% of the global water

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use (Rogers 2008). Agricultural runoff contributes to phosphorous and nitrogen pollution of surface waterways (Fitzsimmons and Posadas 1997). Elevated nitrogen and phosphorous levels have been documented to pose negative impacts on aquatic ecosystems. Farm irrigation is one of the major sinks for freshwater in the world. It is speculated that a 10% drop in farm irrigation water can save more water than water used by municipalities and public consumers (Rogers 2008). Improving water use by agriculture and food production is critical in order to supply the demand for food in the future (FAO 2003). The FAO has addressed some primary issues in regards to food production and water use. Some of the target issues of the FAO are the sustainable development and management of rain fed and irrigated agriculture, the modernization of irrigation practices to demandoriented management, improving governance of agriculture water through integrated, efficient and equitable water resources, the development of international cooperation, and the development of research in the field of food production technologies to maximize water use efficiency. Establishing proper water management practices will lead to an increase in water use efficiency and a reduction in environmental pollution. Rainwater collection and utilization could help alleviate the demand for water. However, it will take multiple efforts on all fronts to have a significant impact on water use efficiency. Farm irrigation is one of the major sinks for freshwater in the world. Some aspects of agriculture that can be changed to help conserve water are the implementation of new technologies such as drip irrigation, stringent crop management techniques, proper fertilization applications and integrating farming systems. The face of farming is changing and the future of farming resides in the sustainable production of nutritionally substantial foods.

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Aquaponic systems and integrated farming practices will yield sustainable and environmentally sound farming methods.

LITERATURE REVIEW Aquaculture Tilapia is the fourth most consumed aquacultured product in the world (FAO 2005). Catfish and Salmon are the only two aquacultured fish consumed more than Tilapia (Kohler 2000). There are numerous types of commercial farming applications ranging from extensive systems to very intensive systems. The type of system developed for farming tilapia is dependent on the experience and knowledge of the farmer, geographic locale, resource acquisition, potential marketing and distribution as well as startup funding. Tilapias are native to Africa and the Middle East (Fitzsimmons and Posadas 1997). World wide production of Tilapia has increased from 855,000 metric tons (1.8 billion pounds) in 1990 to 1,100,000 metric tons (2.2 billion pounds) in 1994. South American countries primarily export Tilapia to the United States. Tilapia imports have increased steadily over the past decade. U.S. imports have increased from 7.5 million pounds in 1992 to 41.9 million pounds in 1996 (Fitzsimmons and Posadas 1997). In 1992 89% (0.8 million pounds) of the tilapia imports were whole frozen fish whereas in 1996 20% (8.4 million pounds) of the imports were fresh fish marketed to local fish markets (Fitzsimmons and Posadas 1997). The increase in Tilapia imports can be attributed to the decrease in wild fish populations as well as the advent of aquaculture operations. Tilapia consumption has steadily increased through 2002 to over 150,000 metric tons/year (Parker 2002). The primary marketing targets for commercially produced Tilapia are the

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United States, Europe and Japan. Tilapia has been successfully marketed to tourist areas, restaurants, and fish markets and is currently in demand in the United States. The majority of tilapia species farmed outside of Africa is of the genus Oreochromis. Nile tilapia (O. niloticus) comprise up to 90% of the species being commercially farmed (Popma and Masser 1999). Other commercially farmed tilapia species are the Blue tilapia (O. aureus) the Mozambique tilapia (O. mossambicus), and the Zanzibar tilapia (O. urolepis hornorum) (Popma and Masser 1999). Several species of Tilapia are raised in the United States. The most popular species are the Nile Tilapia (O. niloticus). Tilapia are laterally compressed, deep bodied and have an interrupted lateral line. Nile tilapias generally have prominent vertical bands while mature male Nile tilapia develops gray or pink pigment on the throat area. (Popma and Masser 1999). The Chinese have been practicing integrated fish and plant culture system for centuries. China is the leader in aquaculture production and one of the major importers of frozen and fillet tilapia into the United States. In the United States the majority of domestic aquaculture production of tilapia is sold to the live fresh fish market (Fitzsimmons 2006). Tilapia has many favorable characteristics for aquaculture production. Tilapia can tolerate poor water quality. Wide salinity ranges, water temperature ranges, low dissolved oxygen levels, and elevated ammonia concentrations have less effect on tilapia than other fish species grown in commercial farming operations (Popma and Masser 1999). Tilapia consumption has risen annually in the U.S. and is currently one of the top five fish consumed per capita (Fitzsimmons 2006). There has been a shift in consumption from red meat to fish because it contains higher quality proteins and is low in fat. A 100 gram serving of tilapia contains 96 calories and is a good source of protein (20 g) and Vitamin

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B12 that is low in total fat (2 g), sodium (52 mg), and cholesterol (50 mg) (www.nutritiondata.com). It is mild in flavor, consumed globally, absorbs seasonings well, is easy to raise and has a relatively quick turnover time compared to other species. In the U.S the majority of tilapia production is sold to live markets, or fresh on ice, to obtain a more competitive price. The physiology, behavior, nutrition and genetics of tilapia have been well studied over the years. Tilapia are a hardy fast growing fish with a low protein requirement making them a primary target for aquaponic recirculating systems. Tilapia fish are omnivorous and have a relatively low protein requirement in comparison to other carnivorous aquacultured fish (Fitzsimmons 2006). They are omnivorous consuming a wide range of organisms including phytoplankton, zooplankton, aquatic macrophytes, algae, benthic invertebrates, larval fish, detritus and decomposing material (Popma and Masser 1999). Tilapia require the standard ten amino acids that other fish species require. Protein quantity and quality are required for sufficient and optimal growth. Most commercial tilapia feeds comprise approximately anywhere from 2836% protein depending on life stage and age of the fish. Digestible energy of tilapia is estimated to be 8.2 to 9.4 kcal of digestible energy (DE) per gram of dietary protein (Popma and Masser 1999). Vitamin requirements are similar to that of other fish species as well. Protein is the most expensive feed ingredient in fish food and often consists of wild anchovy meals, yeast meals, and animal meals. Tilapia are able to digest plant based proteins allowing for substitution of plant based protein sources for more expensive animal based protein sources (Watanabe et al 2002). Fish aquaculture systems can provide a consistent organic

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source of nutrients for the hydroponics plants. Aquaponics and farm integration can reduce the environmental impacts from agriculture and aquaculture farming.

Lettuce Hydroponics Hydroponics is the culture of plants in a soil less media. There are numerous advantages of hydroponic food production systems over conventional agriculture. The ability to produce vegetables all year round enables growers to obtain high prices for vegetables out of season when supply is decreased. In hydroponic systems the plants roots reside in a hydroponic solution formulated for optimal plant growth (Hanan 1998). The solution can be tailored to a specific species to yield optimal growth. Plants grown in a hydroponic solution can yield greater growth rates and be of higher quality in comparison to conventional agriculture. Hydroponic systems will also produce more consistent crops. Production of hydroponic systems can be ten times greater than conventional agriculture production (Resh 2001). Another advantage of hydroponic production methods is that the risk of soilbourne viruses is reduced because the plants reside in an aquatic medium. There are many soilbourne viruses that effect crops of economic viability. Lettuce dieback is a disease caused by at least two soilbourne viruses in the family Tombusviridae: lettuce necrotic stunt virus (LNSV) and tomato bushy stunt virus (TBSV) (Obermeier et al, 2001). Symptoms include chlorosis and necrosis in older leaves and eventually plant stunting and death (Grube & Ryder 2003). Reports of lettuce dieback have been increasing in California and Arizona which account for over 95% of lettuce production in the United States (U.S. Department of Agriculture 2002). The Romaine lettuce industry has suffered from this virus and research into has not warranted

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a cultivar resistant to the disease. Red and green leaf lettuce cultivars have also suffered from dieback but have not yet been documented in iceberg lettuce. Lettuce is commonly cultured and grows well in hydroponic and aquaponic systems. Typical types of lettuce grown are bibb, looseleaf, iceberg, and romaine. Looseleaf varieties are the easiest to grow and can tolerate daytime temperature of 27 0 C without bolting, wilting or slow growth. Spacing can be 10 to 30 heads per square meter. Lettuce has a four to five week vegetative growth phase to harvest. A profit can be realized in short time in comparison to tilapia (46 weeks). Lettuce (Lactuca sativa) is a common plant used in hydroponic systems. It is a hardy plant that has a fast growth rate (Resh 2001). Lettuce is the first salad crop to be cultivated commercialized internationally. Lettuce has the ability to a accumulate nitrogen and phosphate. The nitrogen and phosphate is assimilated from the solution medium (Resh 2001). Lettuce also has a quick growth cycle and can be harvested within four to five weeks allowing for quick realized profit and turnover of nutrients in the system (Rakocy et al. 2006). This makes lettuce a good target crop for aquaponic systems with a heavy bioload and thus high nitrogen accumulation. Biotic (genetics, growth, and disease) and abiotic (temperature, light, water potential, nutrient availability) factors influence growth and development of plants. These factors can also influence pigment concentrations in plants. Lettuce grows best at air temperatures between 16 – 25 o C and will bolt in air temperature above 25 – 28 o C (Resh 2001). Day temperatures of 24 o C and night temperatures of 19 o C coupled with photosynthetic active radiation (PAR) levels of 17 mol/m 2 per day were found to produce marketable lettuce heads in 24 days after transplant (Both et al. 1994). Lettuce will bolt (flower) at high air temperatures (2528 0 C) thus making it hard to grow

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in warm climates and seasons (Resh 2001). Research has shown that by keeping the root zone temperatures at optimal levels even though air temperatures are high proper growth can be achieved. Iceberg lettuce was able to grow properly and form compact heads when root zone temperatures were kept at 1517 0 C even though air temperature was 2539 0 C (Marsic and Osvald 2002). Temperature affects the pigment stability of lettuce. Higher temperatures lead to increased pigment degradation (ShakedSachray et al 2002). Coloration and nutritional value are important marketing parameters of lettuce. Coloration (intensity and uniformity) and nutritional value are linked to chlorophyll and anthocyanin levels (Simonne et al, 2002). Anthocyanin and chlorophyll concentrations in lettuce are effected by the plants genetics as well as the growing conditions (Dela et al, 2003). Genotype, temperature, and light can influence the shifting of pigment levels independently of one another or synergistically (Crozier et al, 1997). Temperature can affect anthocyanin and chlorophyll levels in lettuce negatively impacting both quality and nutrition. Day and night air temperature fluctuations (30/20 0 C) result in higher anthocyanin and chlorophyll b concentrations than a constant (30 or 20 0 C) day/night air temperature (Gazula et al, 2005). This suggests that the effects on quality and nutrition from high day air temperatures can be mitigated with low night air temperatures. Temperature affects the pigment stability. Higher temperatures lead to increased pigment degradation (Shaked Sachray et al 2002). A marketable lettuce head weighs a minimum of 150 grams and can be achieved in 34 weeks after transplant under optimal growing conditions (Both et al. 1994; Resh 2001).

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Nutritional requirements of plants vary at different stages of development. Nitrogen is the most essential nutrient that drives plant growth and elongation. Nitrogen is part of a large number of vital organic compounds such as amino acids, proteins, coenzymes, nucleic acids, and chlorophyll (Resh 2001). Phosphorous levels greater than 1530 mg kg 1 are sufficient for most agronomic crops (Ludwick, 2002). Lettuce has a higher phosphorous requirement for maximum growth. Phosphorous plays a vital role in the synthesis of organic compounds such as sugar phosphates, ATP, nucleic acids, phospholipids and coenzymes (Resh 2001). Phosphorous requirement thresholds range from 35 mg kg 1 (Ludwick 2002) to 80 mg kg 1 (McPharlin et al, 1996) for lettuce. This can vary depending on growing media and season. A deficiency in phosphorous will stunt growth and flowering or fruit set. Iron has been found to be the limited nutrient in recirculating aquaponic systems (Fitzsimmons and Posadas 1997). Therefore a recirculating aquaponics system will need iron supplementation over an extended period of time. Iron is required for chlorophyll synthesis and is an essential part of cytochromes which are electron carriers in photosynthesis and respiration (Resh 2001).

Aquaponics Aquaponics is the integration of recirculating fish production systems with hydroponic plant production to utilize the fertilizers efficiently. The integration of these two systems leads to the removal of nutrients (primarily nitrates and phosphates) from the system omitting the need for water changes thus conserving water. However, water is needed to fill the initial system. Dissolved nutrients from fish are similar to the nutrients required for hydroponic growth of plants (Rakocy et al. 2006). Aquaponics is the most

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efficient food production system in terms of amount of product produced per volume of water (Table 1). It takes approximately 500 liters of water to produce $100 of product (fish and lettuce), whereas producing cattle takes more than 100 times as much water to produce a $100 of product (Rakocy et al. 2004). Aquaponic systems recirculate water to utilize nutrients efficiently thus producing food in a sustainable manner with little environmental impact. Removal of nutrients from fish effluent via plant nutrient uptake is an efficient and productive method of filtration. The production of fish and vegetables through the integration of fish aquaculture and plant production has been demonstrated (Fitzsimmons 1991; Fitzsimmons 1992; Rakocy et al. 1993; McMurtry et al. 1997; Chaves 2000; McIntosh and Fitzsimmons 2003; Sabidov 2004; Castro et al. 2006; Diver 2006). Coupling fish aquaculture with hydroponic plant culture is more sustainable than conventional agriculture systems (McMurtry et al. 1990; Fitzsimmons 1992; Rakocy et al. 1992; Rakocy and Nair 1987; Rakocy and Hargreaves 1993). Popular food crops such as lettuce, basil, tomatoes and strawberries, have been successfully cultivated with the use of fish effluent as the primary fertilizer (McMurtry et al. 1997, Takeda et al. 1997, Rakocy et al. 2004, Hanson et al. 2008). The integration of recirculating aquaculture systems (RAS) with hydroponic plant production is referred to as aquaponics. The primary resources used in animal or crop production are water, nutrients, light, and land. Intensive RAS can produce more fish per liter of water than other types of aquaculture systems (Timmons et al. 2002) therefore reducing water used. Greenhouse hydroponics production can produce from five to ten times more output compared to conventional agriculture (Resh 2001; Hannan 1998). It takes approximately 100 liters of water to raise a fish in a recirculating aquaculture

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Commodity Liters of Water Rice 470,000 Cotton 160,000 Milk 147,000 Sugar 123,000 Beef Cattle 81,200 Vegetables and Fruit (soil) 37,900 Wheat 24,500 Hydroponics 600 Aquaponics (fish and lettuce) 500 Aquaponics (fish and basil)

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Table 1. Amount of water required to produce $100 of output of commodity (Rakocy et al. 2004).

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system (Timmons et al. 2002). Water loss in fish systems occurs mainly from water changes and/or discharge or evaporation. In hydroponic lettuce production systems one liter of water will yield on average 3.5 grams of dry lettuce biomass (Gonnella et al. 2002; Gonella et al. 2001). Preliminary studies at The University of Arizona’s aquaponics research greenhouse determined that it takes less than a liter of water per lettuce head, or approximately 4.2 liters of water per kilogram of head wet weight of lettuce. The integration of fish and plant systems can potentially reduce the amount of water used per kilogram of food produced. Aquaponic systems can yield similar crop production to hydroponic systems (Sabidov 2004). Water from RAS systems can be used in greenhouse hydroponics to intensify production by utilizing resources more efficiently potentially reducing water usage by 2027% compared to conventional agriculture (Chavez et al. 2000). Lettuce (Lactuca sativa cv.) is commonly cultured in hydroponic and aquaponic systems. Lettuce has a four to five week vegetative growth phase to harvest. It is a hardy plant that has a fast growth rate (Resh 2001). It was found that lettuce can deposit a large amount of nitrogen to its leaves and the nitrogen deposition can be manipulated by plant density and nitrogen availability (Seawright 1998). Tilapia can tolerate a pH from acidic to alkaline (pH 511) (Chervinski 1982) and a wide range of salinity concentrations (Watanabe et al. 2002). Plants grow best and uptake nutrients at a lower pH (5.56.5) (Resh 2001). Specifically, lettuce will grow well in a pH range of 5.56.5 (Resh 2001, Islam et al. 1980). Nitrifying bacteria is inhibited below a pH of 6.5, with an optimum pH of 7.8 depending on bacterial species and temperature (Antoniou et al. 1990; Tyson et al. 2007). Lettuce will exhibit normal growth at oxygen levels of the solution greater than

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0.10 mM (Yoshida et al 1997). Lettuce is tolerant of lower oxygen levels in comparison to other plants. Tilapia can withstand low dissolved oxygen levels but optimal growth occurs with levels greater than 2 mg / l (Watanabe et al. 2002). Electrical conductivity levels range between 12 mS / cm

Full document contains 173 pages
Abstract: The goal of this study was to prove that aquaponic systems can produce lettuce of equal growth and quality compared to hydroponic lettuce production and to determine the stocking density of fish required for plant growth. Aquaponics is the integration of recirculating aquaculture and hydroponic plant production. The project had four objectives. The first objective was to determine the biomass of fish required for plant growth to develop a fish to plant density ratio. The second objective was to compare lettuce grown with aquaponic water and a hydroponic solution under the same environmental conditions. The third objective was to compare the quality of lettuce grown with aquaponics water plus nutrient supplementation with a hydroponic solution. The fourth objective was to determine the nitrogen dynamics in the aquaponic system and to compare the nutrient composition of lettuce grown with aquaponics water with nutrient supplementation and hydroponic solution. It was determined that under the specified environmental conditions 5 kg m-3 of Nile tilapia ( O. niloticus ) fed 2% of their body weight daily yields on average 4.7 kg m-2 of lettuce (L. sativa cv. Rex) in 35 days. There was no significant difference (p≤0.05) in biomass or chlorophyll concentration index in lettuce (L. sativa cv. Rex) grown with aquaponics water and nutrient supplements versus a hydroponic solution. The aquaponics solution generated equal biomass and chlorophyll concentration indexes compared to the hydroponic solution. Aquaponics water plus supplementation can yield L. sativa cv. Rex with equal biomass accumulation and chlorophyll concentration indexes compared to hydroponics lettuce. Nutrients added to the aquaponics system consisted of iron, manganese, and zinc. These nutrient concentrations became depleted in the aquaponics water over time and were not replenished via the fish feed. Dolomite was added to the aquaponics system every two weeks to increase the buffering capacity of the water and maintain optimal pH levels. Aquaponics lettuce had similar nutrient composition to hydroponic lettuce. One head of L. sativa cv. Rex (176.75 ± 31.03) will assimilate approximately 5.96 grams of nitrogen (3.38% per dry gram lettuce). One kilogram of fish will yield 6.4 lettuce heads (1,128 grams) and fixate 38.13 grams of nitrogen.