Integrated agriculture and aquaculturefor sustainable food production

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Authors King, Chad Eric

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INTEGRATED AGRICULTURE AND AQUACULTURE FOR SUSTAINABLE FOOD PRODUCTION

By

Chad Eric King

A Dissertation Submitted to the Faculty of the

DEPARTMENT OF SOIL, WATER AND ENVIRONMENTAL SCIENCE

In Partial Fulfillment of the Requirements For the Degree of

DOCTOR OF PHILOSOPHY

WITH A MAJOR IN ENVIRONMENTAL SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

2 0 0 5

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THE UNIVERSITY OF ARIZONA

GRADUATE COLLEGE

As members of the Final Examination Committee, we certify that we have read the

dissertation prepared byj CHAD ERIC KING

entitled: INTEGRATED AGRICULTURE AND AOUACULTURE FOR

SUSTAINABLE FOOD PRODUCTION

and recommend that it be accepted as fulfilling the dissertation requirement for the

degree of Doctor of Philosophy.

Kevin Fitzsimmons

Edward P JSlenn

Thomas^^Tiompson

Stephen G. Nelson ( ^ / y ,

James Knight

Edward Franklin

Date

Date

Date

Date

Date

Date

Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copy of the dissertation to the Graduate College.

I hereby certify that I have read this dissertation prepared under my direction and recommend that iUfc accepted as fulfilling the dissertation requirement.

Dissertation Director Date

3

STATEMENT OF THE AUTHOR

This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department of the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from^he author.

SIGNE

ACKNOWLEDGEMENTS

4

Learning doesn't take place in a vacuum. Rather it is an interaction through

networks, communities and many small conversations. Through the sum of these

experiences, these small pieces, a project such as this can be accomplished with only a

minor loss of sanity. I would like to thank a number of people from whom I have

learned, who made the task of graduate school an enjoyable and manageable one. Kevin

Fitzsimmons for always having time to talk and lend advice, and for providing me with a

wide range of professional experiences. Dennis Mcintosh for providing an example of

what being a graduate student entails. Gary Dickenson for teaching from the wisdom of

experience, countless things not recorded anjwhere. And thanks to the numerous

individuals who shared a long drive to Gila Bend to see a shrimp farm in the desert and

lend a hand with hoses and meter sticks.

Thanks to Gary Wood for access to the Desert Sweet Shrimp Farm, as a location

for research. A special thanks to Craig Collins for teaching many informal lessons in

shrimp aquaculture and the assisting in many monumental tasks. Thanks to Dr. Rakocy

and everyone at the Agriculture Research Station in St. Croix, for answering questions

about their aquaponics systems.

Financial support for this research was provided by grant numbers OlR-08 from

the International Arid Lands Consortium and USDA Grant No. 00-38500-911 CFDA No.

10.200, awarded to Dr. Kevin Fitzsimmons of the University of Arizona's Environmental

Research Lab.

DEDICATION

Many thanks to the little one and the motivation you provided.

6

TABLE OF CONTENTS

Page LIST OF ILLUSTRATIONS 7

LIST OF TABLES 8

ABSTRACT 9

1 CAN SHRIMP AQUACULTURE BECOME A GREEN INDUSTRY? 11 Introduction 11 Greening of Existing Shrimp Farms 13 Planning for the Future 17 Clarification, Education and Regulation 20 Conclusions 23

2 IMPACTS OF EFFLUENT IRRIGATION ON SOIL PROPERTIES 24 Introduction 24 Plant Uptake 26 Impacts on Soil Properties 28 Financial Incentives for Water Treatment 31 Conclusions 33

3 USE OF LOW-SALINITY SHRIMP EFFLUENT AS AN IRRIGATION SOURCE FOR OLIVE TREES 34

Introduction 34 Materials and Methods 37 Results 40 Discussion 42

4 A COST BENEFIT ANALYSIS OF A SMALL-SCALE AQUAPONICS SYSTEM 53

Introduction 53 Materials and Methods 55 Results 59 Discussion 61

5 SUMMARY 74

LITERATURE CITED 77

7

LIST OF ILLUSTRATIONS

Figure 3.1, Experimental plot layout 47

Figure 3.2, Mean change in olive tree height over time as a response to water treatment 48

Figure 4.1, Schematic of the aquaponics system 64

8

LIST OF TABLES

Table 3.1, Procedures used to test water quality parameters 49

Table 3.2, Mean water quality parameters from treatments 50

Table 3.3, Total nitrogen additions per treatment 51

Table 3.4, Comparison of select water quality parameters from this study and data published for other inland shrimp farms 52

Table 4.1, Total startup costs for the small-scale aquaponics system 65

Table 4.2, Operating costs for the small-scale aquaponics system 67

Table 4.3, Daily water use for the aquaponics system 69

Table 4.4, Food production and revenue from the aquaponics system 70

Table 4.5, Cost and benefit analysis 71

Table 4.6, Overall value of this small-scale aquaponics system, without labor costs (3% discount rate) 72

Table 4.7, Overall value of the ideal model for this small-scale aquaponics system . . . . 73

9

ABSTRACT

As we have come to depend on aquacuhure to supplement natural fisheries,

intensive culture methods have increased production. Accompanying environmental

damage - non-point source pollution, loss of biodiversity and struggle for water - has

offset food and financial gains. Problems surrounding food production are amplified in

arid lands, as the potential of irrigated agriculture is weighed against the value of water.

Through the following research, I studied integration of aquaculture and agriculture

through multiple uses of water and nutrients, to reduce environmental impacts. When

managed properly, integration can provide multiple cash crops, increased food and fiber

production with reduced inputs.

Integration allows for groundwater and nutrients in water and solid waste to be

reused. Shrimp farms in Arizona use low-salinity ground water from aquifers for shrimp

ponds and agricultural irrigation. On one of these farms, effluent is reused for irrigation

of olive trees and other field crops. In Chapter 3,1 described an experiment designed to

quantify changes in the height of olive trees due to irrigation with shrimp effluent. Trees

receiving effluent grew an average of 61.0 cm over the two-year experiment, 70.4 cm

with fertilizer and 48.4 cm in the well water treatment. No negative effects due to

effluent irrigation were found, while increases in water use efficiency were realized by

producing two crops with the same irrigation water. Multiple uses of water are also

possible in smaller scale agriculture systems.

I performed a financial analysis of a small-scale aquaponics system, integrated

hydroponics and aquaculture, in Chapter 4. Biological viability of such systems is clear.

By building and managing this system for five months, I examined economic viability, by

analyzing annual costs and revenue. Calculating net present value showed that the

system was not financially viable unless labor costs were excluded. Financial returns

were between $3,794 and $10,640 over six years. In five months, this system produced

181.4 kg of food, with fish feed, iron and water as the only inputs. This study showed the

potential for using small-scale aquaponics as a hobby, in schools, and as a tool for

agricultural economics education, but not as a business opportunity.

11

CHAPTER 1

CAN SHRIMP AQUACULTURE BECOME A GREEN INDUSTRY?

Introduction

As trends in catch amounts for natural fisheries show a leveling off, signaling an

overexploitation of this fragile resource, demand for aquaculture products grows.

Aquaculture already provides around 30% of fisheries production (FAO, 2002), and in

1998, supplied 12% of marine production, with shrimp farms producing 25% of the total

harvested crustaceans (FAO, 1998). The international demand for shrimp and its

accompanying high market value has led to rapid expansion of shrimp aquaculture in

developing countries. This is evidenced in Bangladesh where shrimp farming grew from

20,000 ha in 1980 to 140,000 ha in 1995 (Deb, 1998). With competing demands on

water resources and coastal areas worldwide, public outcry from environmental groups

has drawn attention to mistakes made in aquaculture.

Unrestricted growth has caused the industry to be associated with many negative

environmental impacts. Some of the most serious are;

1) Disturbance and destruction of mangrove, wetlands and other sensitive

estuarine areas through pond construction, blockage of tidal creeks, and

alteration of the groundwater table and tidal flows (Alongi, 2002)

2) Conversion of agriculture land to saline ponds

3) Salinization of productive land due to salt water retention

4) Water pollution from effluents, especially through;

12

a. Eutrophication

b. Increased sedimentation from high levels of organic matter and other

suspended particulates

c. Reduced dissolved oxygen (DO) levels in receiving waters (Stanley,

2000)

Problems such as these must be resolved before shrimp aquaculture can be considered a

green industry and assure sustainability.

Greening of Existing Shrimp Farms

Aquaculture production is regionally concentrated, often coastally, discharging

large volumes of effluent in a non-point source manner. Aquaculture effluents are less

concentrated than effluents from other industries, and higher in volume (Beveridge et al.,

1991). Typical daily water exchange rates of up to 30% lead to estimates of water use

from 11,000-43,000 m^ per ton of shrimp produced (Stanley, 2000). It is also common

practice to drain ponds for harvest, increasing discharge rates and a flush of nutrients and

particulates. Intensive shrimp farming, with high stocking densities and manipulation of

water quality, elevates effluent nutrient levels.

Discharge water is often higher in nitrogen, phosphorus, carbon, total suspended

solids, bacterial oxygen demand (BOD) and bacteria than ambient levels in the water

body receiving the effluents (Jones et al., 2001; Samocha et al., 2004). Only 25-30% of

the nitrogen and phosphorus in feed inputs are harvested as shrimp biomass (Boyd and

Tucker, 1998), leading to much waste. High rates of biological activity in this water,

combined with high organic matter and suspended particulates cause eutrophication of

surrounding waters, increased sedimentation, and decreased DO levels. This also

changes the biological parameters of the receiving waters, increasing primary production

rates and zooplankton shifts (Burford et al., 2004). Reducing nutrient levels in effluent is

critical to maintain ecosystem integrity.

Recent studies have focused on management of effluent through reduction of

nutrient levels and volume of effluent. Feed formulation has provided high density, low

pollution feeds, where nutrients are more bioavailable for conversion to animal biomass.

14

Advances in feed storage, application and rate also serve to reduce both the food

conversion ratio (FCR) and effluent nutrient levels (Jory, 1995). Reducing effluent

volume by reducing water exchange rates and retaining harvest water also decreases

eutrophication of natural waters. Water exchange as low as 0-2.5% daily has been

attained with no difference in production or survival (Stanley, 2000; Menasveta, 2002;

Thakur and Lin, 2003).

Recirculating systems that treat and return culture water also achieve zero

exchange. Constructed wetlands may serve as a filter for recirculation. Experimentally,

a pond surface to wetland surface area ratio of 12:1 reduced total phosphorus (TP) by

31% and total suspended solids (TSS) by 65% while maintaining low levels of BOD

(<9mg/l), total ammonia (<1.8 mg N/1) and nitrate (<0.42 mg N/l)(Tilley et al, 2002),

with no discharge. Reducing water exchange limits self pollution on farms, and reduces

disease introductions. Other types of marine (Neori et al., 2000; Neori and Shpigel,

1999) and freshwater aquaculture (Rakocy, 1997) have used polyculture to reduce water

exchange or improve discharge water quality. Adding extractive species to recirculating

systems may achieve zero discharge while increasing marketable products.

Integrated culture with extractive species for pre-release treatment of the water

also shows promise for reducing environmental impacts. Algae (usually Gracilaria spp.

and Ulva spp.) and bivalves have both been used as extractive species, capable of

removing nutrients and particulates from culture water. These are grown either in

recirculating systems, or as an effluent treatment before release to the environment

(Chopin et al., 2001; Wang, 2003). Algae reduce dissolved nitrogen from 35-100%, and

15

grow well in most mariculture effluent (Troell et al., 2003). As a flow through treatment,

oysters reduced total nitrogen (TN) 36%, TP 45% and total particulates (<5 |xm in

diameter) 74% (Jones et al., 2002). In tandem, the bivalves can remove particulates and

phytoplankton, while macroalgae scrub nutrients from effluent to provide more complete

treatment. These extractive organisms provide a secondary cash crop for farmers, but

they also increase farm labor.

Sedimentation ponds are a simple, low-cost way to treat effluent before release or

reuse. These have been shown to reduce TSS by 60% with 0.6-1.9 day retention times

(Jackson et al., 2003). Collecting only a portion of pond water at harvest drainage may

optimize removal per retention time and basin volume. Teichert-Coddington et al. (1999)

collected the last 16% of pond volume into a settling basin for six hours, removing 100%

of the settleable solids, 88% of TSS, 63% of BOD, 31% of TN and 55% of TP. This

represents 61% of the settleable solids, 40% of TSS, 12% BOD, 7% TN and 14% of TP

for the whole pond, significant remediation with minimal operation cost. In flow through

systems, native mangroves have also been used to treat moderate streams of aquaculture

waste as it is returned to the estuary (Gautir et al., 2001).

These water treatment practices provide the potential for shrimp culture to

improve the environment. Many estuarine waters are already significantly impacted by

agriculture and other industries situated along rivers. Pond productivity, physical and

biological treatment and proper nutrient management may consume nutrients and settle

solids already present in river systems. Water quality monitoring programs of discharged

effluent from farms using innovative treatment techniques should be expanded to include

16

water entering the farm. Net changes to environmental systems can be measured in this

way, designing farms to make positive ecological impacts over time.

17

Planning for the Future

Learning from past mistakes can ensure that farms have low ecological and social

impacts. Unchecked, rapid expansion in the past led to mangrove destruction and

replacement of agriculture lands for pond construction. This is often followed by

collapses due to disease, poor planning and unsustainable practice, leading to farm

abandonment (Dierberg and Kiattisimkul, 1996). Abandoned farms require expensive

remediation to replace native habitat or treat for salt intrusion to allow for agriculture.

Planning for a green future in shrimp aquaculture must start in the design of each new

pond.

Careful aquaculture development has been demonstrated in Australia.

Geographic Information System (GIS) technology is used to determine optimal areas for

farms. State laws maintain a low farm density and require strict effluent control.

Settlement ponds, integration with extractive organisms and low stocking densities are

strongly encouraged (Johnson, 1997). Research is also focusing on shrimp growth in

evaporation ponds produced in an attempt to remediate poorly managed irrigated

agriculture lands. Using this water, and situating farms on estuary waters already

nutrient- and salt-enriched from irrigation practices is another way to incorporate

watershed level management use shrimp farms in water treatment. Such controlled

development ensures aquaculture doesn't exceed the environmental buffering capacity.

Many site-specific factors determine the capacity for an environment to assimilate

aquaculture effluent. Areas that might be encouraged for potential farming are those that

are perennially of medium to high salinity, incorporate buffer zones between mangroves.

18

and are built on salt flats or other naturally unproductive coastal areas. To reduce the

ecological footprint of aquaculture activities, it is logical mangroves and other natural

ecosystem filtration systems should no longer be removed, but incorporated.

Shrimp-mangrove integrated farming systems in Vietnam w^ith mangrove

coverage over 30-50% of the pond area gave increased economic return (Binh et al.,

1997), without further decreasing local biodiversity. Effluent fi'om small farms (30 ha

and 13.5 ha) in Australia discharging into mangrove streams is assimilated rapidly by

phytoplankton. No changes in nutrients or production were noted in the lower stretches

of the stream (McKinnon et al, 2002), indicating natural buffering capacities. Slightly

elevated nutrient levels in mangroves may increase production of ecosystem goods, such

as wood and wild fish. In a similar manner, effluent may be used to increase agriculture

production.

Pumping highly saline water inland, while reducing the impact on coastal

systems, clearly harms otherwise productive agricultural lands (Braaten and Flaherty,

2001). However, where groundwater is already being pumped for irrigation, savings can

be realized in reduced pumping and fertilizer costs. Inland shrimp farming in areas with

low-salinity ground water allows integration with agricultural irrigation (Mcintosh and

Fitzsimmons, 2003). In this way no water leaves the farm, eliminating contamination of

surface waters. If ground water is high in nitrates, biological uptake in ponds and

agriculture, through phytoplankton biomass, may actually reduce this contamination.

Further research in inland, low-salinity, shrimp farming is required to provide general

19

water budget guidelines. Better understanding the ratio of agriculture area required to

receive a given aquaculture volume will ensure optimal water use efficiency.

Designing farms with these reduced inputs is another critical step in reducing

economic and ecologic impacts. Allowing gravity to move most farm water, with only

one groundwater pump is one way of accomplishing this. Incorporating recirculation into

farms may also reduce energy use, as horizontal pumping requires less energy than

vertical pumping. Reducing stocking densities will produce less shrimp, but energy and

feed inputs are much lower, as are risk of disease and effluent nutrient levels.

Farm size and stocking rates need to be site specific, incorporating biological

carrying capacity into an otherwise economic formula. For example, the constructed

wetland Tilley et al. (2002) used to treat shrimp effluent is twelve times larger than the

ponds, while mangroves should be two to 22 times larger for adequate treatment.

Comparing shrimp pond area to the area required for effluent assimilation is described as

the ecological footprint (Kautsky et al., 1997). Production per ecological treatment area,

while requiring more research, may be more appropriate to evaluate economic and

environmental efficiency (Bunting, 2001). Ecological buffering capacity is site specific,

requiring monitoring and adaptation to reach a steady state condition where effluent

outputs equal environmental assimilation. The careful planning needed for shrimp

aquaculture development, requires the oversight of a group or individual to ensure

ecological foresight, and encouragement from educated consumers.

20

Clarification, Education and Regulation

Sustainability will not be reached in shrimp aquaculture unless research clarifies

the long-term benefits of improved water management, education changes common

perceptions of shrimp growers and consumers, and development and management

practices are regulated. While studies show that farm water exchange impacts water

quality in estuaries, long-term costs to soils, water quality and biodiversity have not been

quantified. Environmental benefits and disease reduction by reducing water exchange

with wetlands and recirculating systems is clear. However, there is no farm-scale proof

that installing and operating such systems is economically viable. Scientists have shown

that macroalgae, bivalves and fish can be grown with shrimp to reduce water pollution.

However, the quantity and quality of these secondary crops, methods for integration and

management, and level of economic gain in sales and lowered water treatment costs

requires more research and outreach. Defining gains from such alternatives must be

clearly defined to facilitate industry reform.

Education of farmers, investors and consumers is also critical for industry

transformation. Well-informed farmers may voluntarily change production methods if

they have knowledge of large-scale environmental impacts. Several well-informed

farmers may have the potential to initiate a domino effect in industry improvements.

Incentives to change may be provided to encourage best management practices (BMPs).

Taxing shrimp larva and feed, reducing subsidies on feeds and fuels, giving tax breaks on

organic feeds and subsidizing farms with low inputs all provide economic incentives for

21

farmers to change (Stanley, 2000). However, the fate of the industry will still lie with the

consumers.

Education of investors and consumer must not be forgotten. In this age of eco-

labeling, many consumers are aware of the impacts of unsustainable growing and/or

harvesting techniques. Labels such as dolphin safe tuna, shade grown coffee and organic

certified produce have shown that educated consumers are willing to pay a premium for

these foods. The Global Aquaculture Alliance (GAA) and the Aquaculture Certification

Counsel (ACC) are creating a unified, recognizable certification system for

environmentally sound shrimp culture, which should also provide an economic boost to

farmers willing to improve management techniques. Such labels may be expected to

raise prices for a niche market, given that if the whole industry changes there will be no

price differential. However, this motivation has the potential to initiate system-wide

change.

Understanding that voluntary changes are unlikely, laws regulating shrimp farm

construction and emissions may be necessary. Many voluntary codes of conduct exist in

aquaculture, providing basic outlines and guiding principles for management and

operations. These are created in hopes of improving the image of an industry. Best

management practices (BMPs) take codes of conduct one step further, giving the best

available means of addressing specific impacts while allowing efficient production.

BMPs provide general practices to achieve a goal, leaving the producer to implement the

details. Many BMPs are typically applicable to any given problem, allowing multiple

solutions.

22

Standards and permits define the most formal regulatory stance, requiring

producers to meet specified limits for water quality variables. These may quantify limits

such as the nutrient concentration in effluent or the total nutrient load leaving a farm per

day. Standards require monitoring, often by the farmer, in order to be effective.

Therefore, these are the most costly to impose, requiring samples to be analyzed and

reported to a management agency. Permits allowing aquaculture production may be

linked to meeting a set of standards (Boyd, 2003).

23

Conclusions

Shrimp aquaculture has the potential to move towards becoming a green industry,

greening the "blue revolution". To achieve green industry status would be an

achievement attained by few industries, including most land-based agriculture.

Production practice and intensity require alteration to reach such a lofty goal. The

scientific framework has been laid to reduce water use and effluent impacts,

environmental awareness is decrying fiirther destruction of mangroves and ecological

perception is ready for environmentally friendly shrimp. The winner in the battle

between economics and the environment remains to be seen, however. As long as

demand for shrimp is high, chasing after an instantly improved way of life through easy

production will continue to lay waste otherwise productive lands. Only with increased

scientific research and education, regulation, planned development, and incentives for

producers to change, can shrimp aquaculture reach sustainability.

24

CHAPTER 2

IMPACTS OF EFFLUENT IRRIGATION ON SOIL PROPERTIES

Introduction

Water use around the world grows with the global population. This brings a need

to treat and discharge more water with the least environmental impact. Terrestrial

application of pretreated sewage effluent is a common means of disposal (Jame et al,

1981; Jame et al., 1984; Fitzpatrick et al., 1986; Hayes et al., 1990; Vazquez-Montiel et

al., 1995; Schipper et al., 1996; Shatanawi and Fayyad, 1996; Bhuiyan et al., 1998). The

final treatment uses soil and plants. This is not limited to municipal water, but also treats

effluent from an assortment of sources, including slaughterhouses, industry, landfill

leachate (Revel et al., 1999), aquaculture (Adler et al., 2000; Edwards et al., 1981;

Hussain and Al-Jaloud, 1998; Valencia and Martin, 2001) and other agriculture.

Irrespective of the source, both benefits and concerns are associated with effluent

irrigation. Benefits include water reuse on release into the environment and the low cost

of soil as a tertiary treatment. Increased plant growth due to elevated nutrient levels in

effluent is another benefit. Concerns include long-term effects on the soil; soil salinity,

nutrient levels, microbial growth, and heavy metal accumulation. Immediate concerns

such as water runoff", leaching and groundwater contamination, and contamination of

edible crops must also be addressed.

To best summarize the use of effluent in irrigation, I focused on the fate of

effluent and its constituents when applied to various agriculture systems. This included

25

the potential impacts on microbial activity in the soil and projected long-term impacts on

soil properties that may decrease the efficacy of effluent reuse. I focused on arid land

applications. Reuse of treated municipal water for landscape and turfgrass applications is

now required in some arid regions. Long-term studies of effluent use on a variety of

crops must be examined in order to assure sustainability of these practices.

While the literature is full of such studies on municipal effluent, there is also a

groAving interest in the reuse of agricultural effluent from concentrated animal feeding

operations for agricultural crop production. These practices may be used to reduce

discharge from farms, and to lessen environmental impacts such as surface water

eutrophication, groundwater, and soil contamination. Comparing water quality of

varying effluent sources allows results from these studies to be used as a proxy for

agriculture wastewater and its impact on soils. I also examine tertiary water treatment

through the use of agricultural crops.

26

Plant Uptake

A number of plant species accumulate nutrients present in effluent, resistance to

salinity and heavy metals. These include maize (Edwards et al., 1981), turfgrass (Hayes

et al., 1990), alfalfa (Jame et al., 1984), soybean (Vazquez-Montiel et al., 1995; Bhuiyan

et al., 1998), barley (Hussain and Al-Jaloud, 1998), grass hay (Valencia and Martin,

2001), and tree species (Fitzpatrick et al., 1986). Research in effluent irrigation in arid

lands of the Southwest U.S. has also included oats (Avena sativa L.), small grain (Day

and Kirkpatrick, 1973), sorghum {Sorghum bicolor L.)(Day and Tucker, 1977), wheat

(Triticum aestivum L.)(Day et al., 1979) and cotton (Gossypium hirsutum L.)(Day et al.,

1981).

Some species are efficient at nutrient removal. Maize removes 46% of total

nitrogen (N) from raw sewage effluent, and 63% fi"om aquaculture effluent (Edwards et

al., 1981). Variance among species' ability to uptake nutrients highlights the importance

of selecting species based upon nitrogen needs (Vazquez-Montiel et al., 1995). Timing

effluent application may optimize nutrient uptake, as maize and soybeans increase uptake

during reproductive growth, as opposed to vegetative stages (Vazquez-Montiel et al.,

1995).

Effluent irrigation supplies a cheap source of nitrogen fertilizer. It provides

growth rates comparable to and higher than 60 kg per ha nitrogen application (Valencia,

2001). A three-year study by Valencia (2001) illustrates benefits of effluent as a time-

release fertilizer. One year after application, growth rates of grass hay are higher than

those in fields receiving 60 kg per ha of nitrogen fertilizer. Continuing elevated

27

production levels may be a direct result of organic matter in effluent. Organic material

slowly breaks down releasing nutrients. This decreases leaching loss and improves the

efficiency of applied nitrogen.

Aside fi"om direct nutrient additions, effluent has numerous other impacts.

Nitrogen-fixing plants such as soybeans have decrease root nodulation with the nitrogen

addition. Dry matter production also decreases due to increased soil salinity (Bhriyan et

al., 1998). However, many cases of effluent application demonstrate higher crop yields

due to additional nutrients, despite salinity levels that would otherwise cause yield

reductions (Edwards et al., 1981; Jame et al., 1984; Fitzpatrick et al., 1986; Vazquez-

Montiel et al., 1995). In this way effluent nutrient levels improve water use efficiency

(WUE). Effluent water produces more grain per unit than well water (Hussein and Al-

Jaloud, 1998).

28

Impacts on Soil Properties

Effluent irrigation management requires an understanding of effluent constituents

and their potential soil impacts. Impacts include chemical changes such as pH, electrical

conductivity (EC), exchangeable sodium percentage (ESP), cation concentrations and

nutrient loading; and changes in biological activity of soil microorganisms. Increases in

salinity in effluent, soil, and leachate are of main concern.

Shatanawi and Fayyad (1996) suggest restrictions on the direct use of treated

municipal effluent. They would limit crop selection to highly salt tolerant species that

are not consumed raw, due to elevated salt, sodium, chloride, and fecal coliforms levels.

However, blending effluent with river water improves the effluent water quality, diluting

these impacts and minimizing crop restrictions. Studies in arid regions have included

water quality analysis of irrigation water in the Jordan Valley (Shatanawi and Fayyad,

1996) and leachate quality from turfgrass applications in the Southwest U.S. (Hayes et

al., 1990).

Monitoring soil leachate is important as it directly affects groundwater quality.

Hayes et al. (1990) found that pH and bicarbonate levels in effluent leachate had no

significant increases compared to leachate from tap water irrigation. However, sodium

and EC levels in effluent treatments increase, raising concern of groundwater salinity and

sodicity contamination.

After irrigation with effluent, soil typically shows increased salinity and nutrient

loading. Five years of irrigation with secondary treated effluent dramatically increase

salinity near the soil surface, while salinity deeper in the soil column decreased (Jame et

29

al, 1981). However, with a leaching fraction of 0.1-0.16, yield still increase due to

higher nutrient levels. Hayes et al. (1990) observe increases of 1.0 dS m"' for EC, 3.2

mmol L"' for sodium, and ESP increases from 0.1 to 7.6 (near that of the effluent). While

ESP levels of the soil move to equilibrium with the irrigation water, an adequate leaching

fraction will maintain crop growth.

Effluent can alter soil biological activity. Schipper et al. (1996) irrigate Monterey

pine (Pinus radiata D. Don) with tertiary treated sewage effluent. Even with this highly

treated water, soil microbiology alters. No changes were observed in total nitrogen, total

carbon, basal respiration, microbial biomass, sulfatase activity or extractable ammonium,

but significant changes were reported in pH, invertase activity, denitrification,

mineralizeable nitrogen, and extractable nitrate. Most changes were attributed to the

change in nutrient levels. Altered nutrient cycling may change soil pH, and increased

root growth may alter invertase activity. Understanding soil microbiology is crucial to

reducing environmental impacts. Impairing the microbiological community may impact

treatment of applied effluent, increasing run off potential and groundwater contamination.

Long-term effects of the impacts of effluent irrigation must continue to be studied

to reduce negative environmental impacts. Soil and groundwater salinity will reach

equilibrium, with adequate leaching. In areas where groundwater is also used for

irrigation, evapotranspiration concentrates salinity in soil water. Leaching saline effluent

and irrigation waters increase aquifer salinity. Long-term leaching of slightly saline

water could therefore be devastating to the future of agriculture, as water composition

changes and reduces agricultural yields.

30

Financial Incentives for Water Treatment

There are several methods of lowering nutrient levels before release of effluent

waters. To lower phosphorus in trout farm effluent before discharge, Adler et al. (2000)

used it as a water source for hydroponic lettuce and basil crops. Using the nutrient film

technique (NFT), plants were grown in troughs. Plants were harvested from one end of

the trough and started at the other end. As on a conveyor plants were moved down the

trough, away fi"om the source water every several days. Plants nearest the incoming

water stored excessive nutrients (luxury consumption) for later use.

This method provided a cost efficient method of reducing nutrient loading, despite

high startup costs, requiring a greenhouse, heaters, lights and hydroponic trays. The

break-even cost for this system and location was determined to be $13.18 per box of

lettuce, or $0.53 per plant of basil, both values below market prices. Therefore it was

financially profitable to biologically clean water for discharge, as compared to costly

chemical or mechanical treatment.

Incorporating aquaculture and field application with municipal water effluent is

another financial alternative. Edwards et al. (1981) examine effluent treatment fi^om a city

of 10,000 residents. With the given effluent production and associated biological oxygen

demand; 63 hectares would be needed for a treatment. This included sewage stabilization

ponds, fish ponds for further water treatment, and maize fields for the final treatment, at a

size ratio of 1.86:1:10.25 respectively. This is a viable way to treat sewage, with $1,218-

$1,294 net income per hectare through the sale of the fish and maize produced (Edwards

et al., 1981). Disease control, public resistance to consumption of crops growth in human

31

effluent, and sizing for larger cities could obviously be problems for such systems, but

these examples show financial viability incorporating agriculture with effluent treatment.

32

Conclusion

Land applications are important for sewage effluent treatment, and provide cost-

efficient disposal of agricultural effluent. The EPA has strict limits on discharge fi-om

chicken, pork, and beef operations. In recent years these regulations lowered the

permissible nutrient loads in discharged aquaculture effluent from farms. This review

provides a starting point for understanding the fate of effluent applied to land for final

treatment.

Inland aquaculture farming raises similar questions of long-term impacts, with

high pumping and leaching rates. Large volumes of water leach from unlined ponds into

ground water, and upon harvest, whole ponds need to be drained rapidly. Evaporation

increases pond-water salinity, as much as 0.2 parts per thousand (Mcintosh and

Fitzsimmons, 2003). Land application of effluent can create an aquaculture facility with

no discharge, no eutrophication of surface waters or impacts to sensitive coastal habitats.

Agricultural crops benefit from the nutrient loading fi^om the aquaculture operation.

Without expanding land application of effluent, our water resources may be at

stake. This disposal of municipal, industrial and agricultural effluent is beneficial in the

short term. Additional studies must address management practices to ensure future

productivity from irrigated agricultural lands. Hu (1997) modeled sustainable irrigation

schemes examining the catchments level, and including inputs such as soil type, slope,

temperature, species present, and lowest allowable nutrient limits of the catchments in

question. Results comparing the model to field tests show that it is possible to accurately

33

predict long-term impacts of effluent irrigation. Tools such as this will need to continue

to be refined to define best management practices for effluent irrigation.

34

CHAPTER 3

USE OF LOW-SALINITY SHRIMP EFFLUENT AS AN IRRIGATION SOURCE FOR

OLIVE TREES

Introduction

Aquaculture provides around 30% of global fisheries production (FAO, 2002). In

1998, aquaculture produced 25% of the total shrimp supply (FAO, 1998). Demand for

shrimp and high market value have led to rapid expansion in shrimp aquaculture (Deb,

1998). Use of coastal areas for aquaculture often conflicts with other users, such as

recreationalists and homeowners, or impacts sensitive mangrove habitat (Alongi, 2002).

The high concentration of farms in coastal areas also leads to a self-polluting industry

(Corea et al., 1998), as nutrient rich waters or disease exit one farm near the intake of the

next. As a result of these factors, inquiries into the feasibility of inland low-salinity

aquaculture operations are becoming more common (Smith and Lawrence, 1990;

Flaherty and Vandergeest, 1998; Flaherty et al., 2000). Inland aquaculture reduces

coastal conflicts and the risk of disease (Menasveta, 2002), but requires a new approach

to water management.

Several studies have focused on water quality parameters and acclimation of

marine shrimp for inland growth in low salinity water (McGraw et al., 2002; McGraw

and Scarpa, 2003; Saoud et al., 2003). Lab and field experience has shown the

importance of maintaining proper mineral ratios in the water (Zhu et al., 2004), and has

identified potential areas to establish aquaculture facilities based on water quality.

35

Reduced water exchange in inland culture should not affect yields (Thakur and Lin,

2003), but total shrimp farm groundwater use has not been quantified.

In regions such as the arid Southwest, where aquaculture has been successfully

practiced, water is a precious commodity. Little work has been done to determine the

water consumption of inland shrimp farms. Recently, water supply for agriculture is

being reduced as urban centers, industrial and residential users consume greater

quantities. Reusing aquaculture effluent disposes of a nutrient-enriched waste stream,

while making multiple uses of water (Mcintosh and Fitzsimmons, 2003).

A fraction of the nutrients fed to aquaculture species are excreted into the culture

water. Much of this remains suspended in the water column due to aeration. Land

application on agricultural crops is a preferred method of aquaculture effluent disposal

(Olsen et al., 1993; Brown and Glenn, 1999; Brown et al., 1999; Adler et al., 2000;

Edwards et al., 1981; Hussain and Al-Jaloud, 1998; Valencia et al., 2001). Few studies

have investigated the contributions of irrigation with inland shrimp culture effluent

(Mcintosh and Fitzsimmons, 2003).

Characterization of low-salinity inland shrimp effluent shows slight nutrient

benefits to crops when it is used as an irrigation source. A previous study, examined

effluent from the same farm as in this experiment. While total nitrogen decreased,

ammonia-nitrogen (NHs-N), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N), total

phosphorus and reactive phosphorus all increased in water from the shrimp ponds

(Mcintosh and Fitzsimmons, 2003). In 2000, this farm contributed 0.41 kg of ammonia

nitrogen, 0.698 kg of nitrite nitrogen, 8 .7 kg of nitrate nitrogen and 0.93 kg of TP in

36

shrimp effluent each day of the shrimp growing season. When used for irrigation of

wheat, this effluent would contribute 20-31% of the required nitrogen (Mcintosh and

Fitzsimmons, 2003), but more importantly would also reuse water pumped for

agriculture.

In this study, we determine the effects of effluent irrigation on olive tree growth

and farm water use efficiency. We quantify nitrogen and salinity loads leaving shrimp

ponds. We determine economical and biological benefits of effluent irrigation, and

address potential negative impacts from effluent irrigation on an olive tree orchard over

time. Specifically, we will compare nutrient additions and tree growth in treatments

receiving effluent, well water and fertilizer.

37

Materials and Methods

Experimental Design

We hypothesized that the use of shrimp effluent as an irrigation source would

increase olive tree growth and water use efficiency over the use of well water, with no

detrimental effects on soil salinity and productivity. We compared differences in tree

height as a response to irrigation treatments between effluent, well water and irrigation

with standard fertilization. The goal was to determine changes in growth due to the

effluent irrigation and to compare those changes to growth expected with recommended

fertilizer application. The economic savings fi"om growing two crops with the same

water was also examined.

An experimental plot covering 0.133 ha (0.329 acres) was laid out on a

commercial shrimp farm growing Litopenaeus vannamei, the Pacific white shrimp, in

Gila Bend, Arizona. Soils in this area have been classified as a torrifluvent association

(Hendricks, 1985). The experimental plot was isolated from other olive groves, and the

top layer of soil had been removed and used as a source of soil during pond building.

Olive trees (one year old fi'om cuttings) were planted in ten rows of twelve trees (120

trees total)(Figure 3.1). The design was a randomized complete block. It was

unbalanced with respect to the effluent treatment in order to gain more knowledge about

response to effluent. The treatment assigned to each row was randomized by lottery and

trees to be planted within the rows were selected randomly, with order assigned by a

random number generator. Each row was an experimental unit, with data reported as

38

mean height for trees in each row. There was not a significant difference in tree height

between treatments at the beginning of the study (F2, n? = 0.31, /? = 0.73).

The experiment was designed to approximate farm conditions. For this reason,

trees were placed in rows receiving furrow irrigation. We planted as many rows as would

fit across the experimental plot, with the extra row assigned as an effluent replicate to

gain more information on response to effluent. Trees were planted in the bottom of a

single furrow 30 cm wide and 30 cm deep, and watered by flood irrigation. Tree height

was measured monthly, from a mark painted on the trunk, five cm above the original soil

level, to the end of the longest branch. Trunk diameter was also measured initially, but

was found to vary considerably depending on placement of the calipers. Due to this

variability, this measurement was abandoned.

Irrigation

Trees were irrigated every week in the summer and every third week in the

winter, approximating farm procedures. On the rest of the farm, trees were irrigated

weekly in the summer, and as trees showed signs of water deficiency the rest of the year.

Irrigation rates were 2.5 cm for each application from March through May and October

through December, and five cm for each application from May through October. During

shrimp production (approximately June to October), effluent from pond water discharge

was used to irrigate the effluent treatment rows. The well water + fertilization treatment

groups received urea fertilizer applications with the scheduled fertilizer applications for

39

the rest of the farm (March through April). The rest of the year, all trees received well

water.

Fertilizer was applied in four applications the first year and five during the

second, with a target of a total of 0.23 kg of N per tree per year, or 188 kg/ha. This is

half of what is recommended in the literature for large olive trees (Freeman et al., 1994),

to account for the small starting size. In year one, 1.64 kg of urea (45% N) was applied

per row in four applications, and a total of 10 cm of irrigation water (a rate of 112 kg/ha).

In year two, five fertilizer treatments totaling 5.56 kg urea/row were applied in 12.5 cm

of irrigation water (371 kg/ha), the full recommendation for olive trees. Urea was mixed

with well water in 7,571-L water tanks before application in irrigation water.

Duplicate water samples were taken for each treatment during every irrigation

event, to determine levels of nitrogen and salinity addition. A HACH DR-890

spectrophotometer (Hach Co., Loveland, CO) was used to analyze the samples (Table

3 .1) for ammonia-nitrogen (NH3-N), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N)

and total nitrogen. To confirm the nitrate-nitrogen results, a standard curve was

developed, and all nitrate-nitrogen samples were adjusted accordingly.

Statistical methods

We compared mean tree growth among treatments from beginning to end of the

experiment and the mean water quality parameters, using a one-way analysis of variance

(ANOVA). We performed all analyses with JMP IN 4 statistical software (SAS Institute

Inc., Pacific Grove, CA)

40

Results

Water Treatment Characterization

Mean nutrient content in irrigation waters varied considerably across treatments

(Table 3.2). NO2-N values for the effluent treatment were 0.3 mg/L and 0.5 mg/L higher

than the fertilizer and well water treatments respectively (Fj, 73 = 28.5, /KO.OOOl, one way

ANOVA). The fertilizer applications averaged 0.5 mg/L NH4-N higher than the effluent

and 1.0 mg/L NH4-N higher than well water values (F2,66 = 11.77, /?<0.0001). NO3-N

levels were comparable across treatments (F2,73 = 0.127,/? = 0.88). The TN was much

higher in the fertilizer treatment, 67.2 mg/L compared to 6.87 mg/L for the effluent

treatment, and 8.53 for the well water (F2,66= 60.5,/?<0.0001). TN levels reveal that urea

additions had not converted to other forms of nitrogen during application. While TN was

lower than the sum of the nitrogen components for the effluent and well water treatments,

given the standard error for each measurement, this difference is insignificant. Salinity

varied little among the treatments throughout the study, ranging from 1.63 ppt to 1.86 ppt

(F2,67= 1.46,/? = 0.24).

Total water applied was 159 cm (2,460 m^ for the whole experimental plot).

Total evapotranspiration (ET) over the two-year experiment was 405 cm, giving a crop

coefficient (Kc) was 0.39. There was a total of 38.4 cm of rainfall. Effluent irrigation

contributed 113 cm (71% of the total irrigation). In the first year, the fertilizer treatment

received a total of 1.64 kg of urea per row (112 kg/ha) in 10 cm of well water over four

applications. In the second year, 5.76 kg of urea was added per row (392 kg/ha) in 12.5

41

cm of well water over five applications. Water with fertilizer contributed 14.5% of the

total irrigation for this treatment.

Nitrogen additions were extrapolated from water quality parameters and total

water applied. Total nutrient additions - a summation of nutrients in the treatments and in

the well water the rest of the year - were highest in the fertilizer treatment, with the well

water treatment providing slightly more TN than the nitrate-rich well water treatment.

NO3-N and TN additions were comparable across treatments, while NO2-N and NH4-N

were highest in the effluent treatment (Table 3.3).

Tree Grrowth

Irrigation with shrimp effluent did not harm the olive trees. Growth of trees

receiving effluent was not different than the fertilizer or well water treatments (Figure

3 .2). The well water treatment grew substantially less than the fertilizer treatments when

comparing changes in growth from the beginning to the end of the experiment (F2,62 =

3.19,/? = 0.048, one-way ANOVA). Overall, trees receiving effluent averaged 61.0 cm

of growth over the experiment, compared to 70.4 cm for the fertilizer and 48.4 cm for the

well water treatment.

42

Discussion

Water Treatment Characterization

Nitrogen parameters in the water were similar to levels from previous studies

(Table 3.4). However, high nitrate-nitrogen levels in the groundwater distinguish well

water at this site from other inland farms. Effluent supplied 159 kg/ha NO3-N, 6.3 kg/ha

NO2-N, 5.04 kg/ha NH4-N and 116 kg/ha TN over the two-year experiment (Table 3.3).

While total nitrogen additions were highest in the fertilizer treatment, the effluent

treatment contained the highest nitrate, nitrite and ammonia additions (Table 3.3). TN

additions were not different in the well water and effluent treatments, despite nitrogen

additions in shrimp feed, possibly due to phytoplankton nitrogen assimilation. Since

salinity levels in effluent were not significantly different from well water, salinity in

effluent is not considered to be harmful.

The timing of these additions likely impacts tree growth more than the total

nitrogen contributions. Fertilizer was applied in the spring, as temperatures warmed,

stimulating an increase in the rate of tree growth (Figure 3.2). Effluent became available

for irrigation in July, when tree growth rate was not at its highest levels, suggesting trees

were assimilating fewer nutrients. However, the slow addition of plant available NO3-N

and NH4-N over the course of the growing season may allow for constant nutrient uptake

and more efficient assimilation.

43

Tree Growth

Effluent irrigation did not significantly increase olive tree growth over the two-

year study. While we did not reject the null hypothesis, we also found no significant

difference between trees receiving fertilizer and those receiving effluent. Despite the fact

that the effluent treatment TN additions were not different than the well water treatment,

tree growth was not different than the fertilizer treatment with its higher TN levels.

Effluent from low salinity inland shrimp culture can be reused as a source of irrigation

water, increasing water use efficiency in arid lands as water is pumped once and used

twice, without detriment to either crop.

In retrospect, a number of changes could have strengthened this experiment.

Testing a broader range of water and soil nutrient parameters to include micronutrients,

organic matter and ash could provide fiirther understanding of contributions of effluent to

field crops. This may help quantify contributions of algal biomass to soil nutrients and

composition. Sampling soil and leaf nutrients from each experimental unit would have

quantified nutrient uptake and deposition. Randomly selecting trees from each row for

removal to determine surface leaf area and total biomass every six months would have

also provided relative growth rate, a better measure of tree growth. Decreasing the

number of trees in each row, while increasing the number of rows would increase the

number of experimental units, improving statistical power without increasing the number

of trees. More experimental units would have also allowed the addition of another

treatment of a blend of effluent and fertilizer, to quantify fertilizer savings and potential

44

fertilizer-effluent interactions. Small test plots of other field crops could have provided

more complete information on water use and production with effluent irrigation.

Water Use Efficiency

Integrating shrimp aquaculture into farm production cycles reduces water costs

and increases water use efficiency. On this farm, water is constantly pumped from May

to October to provide water for aquaculture production. Early in the season much of this

is lost to seepage, before algae and fine solids seal the ponds. Evaporation losses are also

great, with evapotranspiration averaging 90 cm during the course of the growing season.

Water exchange in the shrimp ponds is estimated at 1% per day. Previously, it was

determined that this would contribute 2,725 m^ of water for irrigation daily (Mcintosh

and Fitzsimmons, 2003). Over the course of the 100-day shrimp growing season, this

provides approximately 2,700 ha cm of irrigation water. As the ponds are drained at

harvest, another 2,700 ha cm of irrigation water is made available. This is enough water

to irrigate nearly 48 ha of mature olive trees (Kc=0.75) annually, without having to pump

any additional water on the farm.

Reducing water consumption will lead to economic savings in electrical or water

costs. Average pumping costs for this irrigation district was $2.10 per ha cm ($26 per

acre foot). By using discharge water twice, the farmer can realize over $5,000 of

pumping savings if the farm is designed to gravity drain from ponds to agriculture fields.

If the farm has the capacity to hold the harvest water for use in irrigation, the farmer can

attain another $5,000 in savings. Economic gains can be even greater if the aquaculture

45

portion of the farm is financially successful, effectively subsidizing agriculture water

costs.

In the last year of this study, approximately 55.5 metric tons of shrimp were

produced, with a gross farm gate value of over $246,000. This valuable secondary crop

more than pays for the pumping cost of the water lost to seepage and evaporation.

Producing shrimp in water that is already being pumped for agriculture irrigation

increases water use efficiency, with greater production per unit of water than agriculture

alone. Any increase in field crop growth due effluent irrigation also increases water use

efficiency without any financial input by the farmer. So while nutrient addition from

inland shrimp effluent is minimal, financial savings in water costs and increased water

use efficiency make inland shrimp production a valuable option for integration with

existing irrigated agriculture.

Benefits of integrated shrimp culture and irrigated field crops are based on pond

water exchange and financially viable shrimp production. As shrimp producers in

Arizona have looked for ways to maximize production with reduced inputs, they have

decreased water exchange. Some are not exchanging any water, simply replacing

seepage and evaporation losses. In these cases, no water is available for reuse during the

summer months, with a large amount available at harvest when plant growth and ET is

reduced. Griven the decrease in shrimp prices over the last five years, production costs

are often higher than wholesale prices, leading to a net financial loss in aquaculture

production on most of the farms. Water management practices, shrimp prices and

46

production costs will therefore dictate the viability of effluent reuse for field crop

irrigation.

47

Figure 3.1. Experimental plot layout. Rows marked with a W = Well water treatment, F = Fertilizer treatment, and E = Effluent treatment. Flexible PVC hose was used from effluent ditch to pump to tree rows, and from the water tanks to rows.

Pipe from well

Effluent Ditch

Water Pump

Water Meter

W F E E F W E w F E

o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o

48

Figure 3.2. Mean change in oHve tree height over time as a response to water treatment. Standard error bars shown.

1.7

1.6

s

1.3

1.2

o o o o m

o

Time

Effluent Fertilizer —Well Water

49

Table 3.1. Procedures used to test water quality parameters.

Parameters Method Ammonia nitrogen (NH4-N) HACH method #8155, salicylate method Nitrite nitrogen (NO3-N) HACH method #8507, diazotization method Nitrate nitrogen (NO2-N) HACH method #8039, cadmium reduction method Total nitrogen (1^ HACH method #10071, persulfate digestion method Electrical Conductivity Markson 15/16 EC meter

Table 3 .2. Mean water quality parameters from treatments.

Effluent Fertilizer Well water Parameter (SEM) (SEM) (SEM) Nitrate-Nitrogen (mg/L) 8.4(1.06)" 9.5 (1.86)" 8.9 (0.90)"

Nitrite-Nitrogen (mg/L) 0.46 (0.05)" 0.16(0.09)'' 0.012 (0.39)"

Ammonia-Nitrogen (mg/L) 0.49 (0.11)" 0.96 (0.20)" 0.01 (0.09)"

Total Nitrogen (mg/L) 6.87 (2.66)" 67.2 (5.12)" 8.53 (2.26)"

ECw (mmhos/cm) 2.9 (0.08)" 2.5 (0.24)" 2.9 (0.09)"

Salinity (ppt) 1.9(0.06)" 1.6(0.12)" 1.8(0.05)"

Different letter superscripts designate significant differences between treatments.

Table 3.3. Total nitrogen additions per treatment. Includes nitrogen in the treatments and in well water

Fertilizer Effluent Well water Nitrate-Nitrogen (kg/ha) 148 159 148 Nitrite-Nitrogen (kg/ha) 0.49 6.3 0.19 Ammonia-Nitrogen (kg/ha) 2.25 5.04 0.13 Total Nitrogen (kg/ha) 288 116 128

52

Table 3.4. Comparison of select water quality parameters from this study and data published for other inland shrimp farms.

Intensive Farm lb

Semi-Intensive Farm

Parameter

Same farm This Study previous South Texas 1° South Texas 2

(S.E.M) study'^(S.E.M) (S.E.M) (S.E.M) Ammonia-Nitrogen 0.49(0.11) 0.17(0.022) 1.36(0.088) (mg/L) Nitrite-Nitrogen 0.46(0.05) 0.26(0.0095) 0.41 (0.033) (mg/L) Nitrate-Nitrogen 8.44(1.06) 9.8(0.73) 0.67(0.041) (mg/L) a Mcintosh and Fitzsimmons, 2003 b Samocha et al., 2004

0.04 (0.014)

0.01 (0.006)

0.65 (0.022)

53

CHAPTER 4

A COST BENEFIT ANALYSIS OF A SMALL-SCALE AQUAPONICS SYSTEM

Introduction

The aquaculture industry is typically characterized by intensive, large-scale,

monoculture production. Research tends to focus on maximizing single species growout.

A number of studies have examined methods for the polyculture of several aquatic

species, such as shrimp and fish (Erler et al., 2004), or multiple fish species (Yi et al.,

2003). Polyculture of aquatic species and fowl or livestock is practiced at the household

and community scale (AIT, 1986). Research has also found benefits of integrating fish

and algae (Chopin et al., 2001), and fish and plant culture (Azim and Wahab, 2003).

Integrating hydroponic plant production with fish culture (known as aquaponics) is

financially beneficial as a water treatment (Adler et al., 2000), but is not commonly

practiced at a commercial scale due to the perceived intricacies of managing two different

culture systems.

Research has defined requirements for maximizing production in aquaponics

systems. The study of nutrient dynamics has provided guidelines for size ratios of fish

tank to plant production (Rakocy, 1999; Rakocy, 1997), and for the daily amount of fish

feed required to provide adequate plant nutrients (Rakocy, 1997). Common nutrient

deficiencies have been identified, the most common being iron (Rakocy and Hargreaves,

1993). Financial analysis has also been performed on commercial systems producing up

to 3,096 kg of fish and 1,248-1,694 cases of lettuce annually (Rakocy et al., 1997).

54

Aquaponic systems are financially viable at this scale, depending on the vegetable crops

grown, as they are the main cash crop of the system. The viability of commercial

aquaponics is based on filling niche markets that command higher prices, and requires a

substantial capital input (approximately $30,000 US).

Small aquaponics systems are quite popular, as is evident in any search of the

gray literature. Internet searches identify a number of small vegetable and fish growers,

and several short courses and numerous school programs based around science or

agricultural education through the use of aquaponics systems. These small systems

increase household food security through the production of vegetables and fish. While

this is a hobby for many people, there is little published regarding the financial viability

of these systems as an additional source of household or community income. This study

provided an economic evaluation and a model for their use in agriculture economics

classrooms. We examined the financial returns of a small-scale aquaponics study by

determining costs, revenues and net present value (NPV) of a representative system. We

hypothesized that due to the high startup costs for these systems, small aquaponics

systems are not financially viable, despite the many marketing ploys that would suggest

otherwise.

55

Materials and Methods

In this study, we constructed and maintained a small aquaponics system for over

five months. Inputs and outputs for the system were quantified and priced during this

time. Feed and water inputs were measured as they were added. A strain of red tilapia

(Oreochromis spp.), red leaf lettuce (Lactuvia sativa), basil (Ocimum basilicum),

tomatoes (Lycopersicon esculentuni) and chilies {Capsicum annuum) were grown in the

system. Management followed a low maintenance approach, as nutrient deficiencies

were monitored through plant responses and treated as needed.

The aquaponic system was a closed, recirculating system, consisting of a 2.74-m

diameter metal fish tank (approximately 8.1-m^) with a liner, a 208-L conical tank, two

rectangular tanks and two 20.3-cm deep hydroponic trays with a total surface area of 11.9

m^ (Figure 4.1). The conical tank served as a settling basin for removing large solids,

receiving water from the bottom of the fish tank. A partition across the center of the top

half of the conical tank forced water to slowly move from the inlet at the top of the tank

to the bottom of the tank before exiting from the top, dropping solids as the water sank.

The first rectangular tank (208-L) contained one 4.57 m x 15.2 m roll of vinyl bird

netting as a substrate of high surface area for microbiological growth of nitrifying and

heterotrophic bacteria. The netting trapped fine solids and acted as a biological filter. As

water moved through the net tank, bacteria on the net converted ammonia to nitrate, and

under anaerobic conditions caused denitrification. The second rectangular tank (100-L

capacity) served as a head tank to distribute water evenly to the two hydroponic trays.

56

The hydroponic trays had wood sides and a plywood bottom, lined with 6 ml

black plastic. Water entered one end and exited from the other. Plant starts were placed

in holes drilled through high density Styrofoam insulation that floated on the water

surface. A standpipe at the drain maintained the water at a constant level.

Water leaving the hydroponic trays drained into a sump. A 1/3 hp pump in the

sump returned water to the fish tanks. The sump pump had an automatic shutofF, turning

off after draining the sump. All tanks were placed to maintain water levels at decreasing

heights, the fish tank maintained the highest water level, allowing gravity flow through

the system to the sump.

All inputs to the system were measured. Red tilapia were counted, weighed

before stocking. Fish were fed ad libitum twice a day. Feed was measured and recorded

at each feeding. Chelated iron was added to the culture water as plant leaves began to

yellow, indicating an iron deficiency, at a rate of 62 grams per application an average of

once a month. Water was added as the gravity flow through the system slowed due to

lack of hydraulic head. The amount added was measured using a water meter.

Labor for maintaining production was minimal after initial setup. Daily tasks of

draining solids from the conical tank and feeding the fish required less than six hours of

work per week. Weekly tasks included cleaning of the net filter, planting, and harvesting

plants. Seeds were started in peat until leaves sprouted, at which time we placed the peat

in the Styrofoam. Vegetables and herbs were usually planted in batches, with half to all

of the trays maturing simultaneously.

57

Crops from the system were harvested as they reached maturity. The wet weight

for each crop was recorded. After five months, the tilapia reached an average size

adequate for sale on the live market (0.68 kg). At this time the fish were sold, and the

experiment ended.

Costs of all materials, inputs and outputs from the system were determined.

Materials were priced as they were purchased. Because this research was carried out at a

university setting, many of the tanks and other materials were already present. Prices for

these were taken from aquaculture catalog listings that best matched the item. Labor

costs were calculated at student wages, as in the university setting where the tests were

performed. Product prices were based on actual sales or market values.

Electricity and water rates were gathered from local residential rates as provided

by the Tucson Electric Power Company and the City of Tucson water service. As this

was an analysis of a household system, it was assumed that monthly meter service rates

were already being paid for both services. Variable rate schedules for services were

incorporated into the pricing.

Annualized and ideal scenarios were projected using the costs and benefits from

running the experimental system for five months. We created annualized scenarios by

determining monthly input costs and extrapolating these for twelve months. The ideal

scenario was based on growing basil, the most profitable crop for the local niche market,

and assuming 85% survival rate for the amount of fish used in this study, with a food

conversion ratio of 1.5 (both common values for tilapia). Because this was designed as a

small-scale system, scenarios with and without labor costs were calculated, assuming that

58

a household member as a hobby could perform the average of six hours of labor per week

required for maintenance.

Economic analysis was performed to determine the annual benefits of operating

this system. This included an itemization of all costs and revenues to find net gains. Net

present value of the system was also calculated for an operating time of six years at a

discount rate of 3%. These calculations were carried out for this study, for annualized

and ideal annual costs and benefits, with and without labor costs. After six years it is

assumed that many of the system components will need replacing, increasing system

costs.

59

Results

This study quantified startup and operating costs as well as revenue for 22 weeks.

Startup costs for an aquaponics system of this size were $2,676, with the largest portion

of that being $2,191 for materials and $510 for labor costs (Table 4.1). The operating

cost for this study was $2,036, which includes electricity, labor, water, materials and fish

costs (Table 4.2). We established average monthly costs and extrapolated them over a

year to determine annual costs. Annual operating costs were extrapolated to be $3,847,

but only $1,284 without including labor. Electricity contributed to a large portion of the

operating costs at $566 annually.

In the second full month of the trial, all of the tilapia in the research facility were

attacked by a dinoflagellate outbreak. This rare occurrence was caused by the

introduction of a different fish species to another part of the research facility without

proper quarantine. This led to survival rates of only 53%, severely reducing final fish

yield and value. The disease also impacted the FCR (2.55). As a treatment for the

dinoflagellate, the hydroponic and fish production areas were decoupled and copper

chlorate and salt were applied in conjunction with high water exchange. Daily water use

was 1,154.5 L during the disease treatment, compared to 87.1 L during the winter and

136.3 L during the summer (Table 4.3). In the last 20 years, this was the first disease

outbreak of this magnitude at the research facility. Therefore this was considered an

anomaly and was not incorporated into extrapolated annual water use or fish production.

In just over five months, this system produced nearly 181.4 kg of food.

Vegetables and herbs amounted to 83.9 kg, wet weight. Fish harvest was 91.2 kg. This

60

totals a farm gate value of $962.66. Annualized this is over $1,677 (Table 4.4). Herbs

and vegetables provided a larger portion of the revenue than the fish. An ideal model

was created to project maximum total benefits fi-om this system. This model was based

on the sole production of basil, rather than the mixture of basil and other vegetables we

used in this study. The ideal model also assumed typical tilapia growout rates and FCR,

calculating out the rare disease outbreak that affected our fish. Following these

assumptions, the ideal model projected annual revenue nearly doubles that for the system

as studied, over $3,500 compared to $1,677.

61

Discussion

This study confirmed that small-scale aquaponics systems are not financially

viable business options. Only if labor costs were excluded could the system be

minimally beneficial. Therefore, it is logical to build and operate these systems as

hobbies or for use in schools or prisons where labor costs aren't considered, but

aquaponics is not recommended as a for profit business venture. Ideal annual costs and

benefits were calculated after finding the growth rates and revenue values for basil, the

most valuable crop in the system. This assumed plant production of only basil, with

typical tilapia growth. In this way, considerable financial gains can be realized.

Regardless of the economic analysis performed, this system will lose money in

the first year. Due to the high startup costs, first year losses will range from $5,342 for

this study to $3,473 for the ideal setup with labor included. Excluding labor costs, first

year losses will be between $2,269 and $399. For the next five years, the system will

become profitable if labor costs are excluded. Financial gains from $317 to $2,241 can

be expected (Table 4.5). Over a six year span at a discount rate of 3%, considering

annualized costs and benefits while excluding labor costs, the net present value (NPV) of

the system still projects a loss of -$569 (Table 4.6). Maximized yields in the ideal

scenario over six years at the same discount rate raise the NPV of the system to $9,864

(Table 4.7).

Several of the assumptions made in this study have a considerable impact on the

financial outlook for family scale aquaponics operations. This system was located in a

research greenhouse, which though minimally heated and cooled, maintained adequate

62

temperatures for fish and vegetable growth. This type of temperature control is required

to meet the ideal expectations from this system, as basil won't survive Arizona winters

without protection from frost, and fish growth will slow. Cooling costs during summer

months were not incorporated into the economic analysis, but all crops grown in this

study will grow well in high summer temperatures as experienced in Southern Arizona.

At the high NPV for the ideal scenario, investment in a small greenhouse may be

warranted. Even after construction and maintenance for three large greenhouses, Adler et

al. (2000) projected annual profits of $12,350 - $27,750 for an aquaponics system large

enough to treat 109 m^ of effluent daily. Energy and water values are also based on city

rates, and don't consider other household uses on the same meters, which could drive up

these costs. On the other hand, these costs would be reduced for a landowner with

agricultural service rates.

Decreasing materials costs is one way to increase the net benefits of aquaponics

systems. Construction of tanks and growing trays out of local materials with regional

building styles could drastically reduce startup costs. In this study, the fiberglass and

metal tanks with liners account for over 40% of the total materials cost. In many areas,

materials such as concrete blocks and stucco could be used to build cheap waterproof

tanks. Or pallets and liners could be used to assemble hydroponic trays. Alternatives

such as these could produce cheaper and more durable systems, increasing net benefits.

This study documents the financial viability of aquaponics systems, a tangible

means of measuring benefits. With a six-year NPV approaching more than $10,500, this

produces significant supplemental income. Decreasing household food insecurity by

63

producing supplemental food is another substantial benefit. In the course of a year, this

small system would produce over 160 kg of fish and 160 kg of leafy vegetables, more

than 3 kg of each per week. Despite the lack of economies of scale at this size, these

examples demonstrate significant economic and nutritional benefits.

Educationally, aquaponics systems continue to provide a number of benefits. A

high school student working independently on a science fair project has also used the

system described in this study. This project has allowed for project-based science

learning. Not only does aquaponics facilitate hands-on, experiential learning of topics

from animal husbandry to nutrient cycling, but they also provide the potential for studies

in agricultural economics.

This model could be replicated in educational research, incorporating aquaponics

systems in several agricultural education classrooms, to have students learn the

management and economics of the system. By comparing the learning in agriculture

economics in these classes to that to classes taught using traditional, non-experiential

methodology we could quantify impacts of aquaponics systems as economics classroom

tools. Student innovation could also be encouraged to increase economic viability

through improvements in materials, operational or labor costs.

64

Figure 4.1. Schematic of the aquaponics system. Arrows indicate direction of water flow.

Head Biological tank filter

Settling tank

Fish Tank

Sump

Table 4.1. Total startup costs for the small-scale aquaponics system.

Labor Hours Rate Cost Initial Construction 60 $8.5/hr $510

Water Liters Cost Fish Tank 6,625

Conical Tank 208 Net tank 208

Head tank 100 Grow trays 909

Total water 8,050 2.85 $2.94

Materials

PVC Fittings Number Price each

Total Price

2" 90 8 $0.88 $7.04 2" 45 4 $1.18 $4.72 2"T 2 $1.07 $2.14

2" Male threaded to female slip 11 $0.56 $6.16

2" PVC valve 3 $11.00 $33.00 2" bulkhead 9 $30.00 $270.00

1.5" male thr to female slip 2 $0.43 $0.86

1.5" 45 2 $0.92 $1.84 1.5" 90 9 $0.56 $5,04

1.5" PVC valve 1 $7.61 $7.61 1.5" 1.5-1" reducer 1 $0.40 $0.40

1" T 2 $0.46 $0.92 1" 90 6 $0.30 $1.80

1" cap 3 $0.24 $0.72 1" PVC valve 1 $3.65 $3.65

Tanks large tank 1 $305.00 $305.00 tank liner 1 $275.00 $275.00

conical tank 1 $149.00 $149.00 rectangle tank 1 $187.00 $187.00

head tank 1 $117.00 $117.00

trash can 1 $25.00 $25.00

Pipe 2" 50 $0.68 $34.00 1" 35 $0.32 $11.20

1.5" 15 $0.52 $7.80

Trays wood - 5.1 X 20.3 X 488cm 4 $16.00 $64.00

wood - 5.1 X 20.3 X 244 cm 2 $12.00 $24.00

plywood - 122 x 244 x 1.9 cm 4 $25.00 $100.00

1 pack 6.35 cm coarse screws 1 $4.00 $4.00

61 X 244 X 2.5 cm styrofoam 8 $4.00 $32.00

Air air valves 16 $0.72 $11.52 air stones 16 $0.58 $9.28

lead weights 16 $0.15 $2.40 0.32 cm airline (m) 61 $0.25 $50.00

Mechanical blower 1 $299.00 $299.00

pump 1 $110.00 $110.00 Total Materials $2,163.1

Totals $2,676.04

Table 4.2. Operating costs for the small-scale aquaponics system.

Ave weekly hours Weekly Cost Cost This Study Annual Cost

Labor Feeding 1.3 $11.05 $274.70 $574.60

Maintenance 2.5 $21.25 $528.28 $1105.00 Harvest/Planting 2 $17.00 $422.62 $884.00 Labor Totals 5.8 $49.30 $1,225.60 $2563.60

Electricity* Daily Use

(kwh) Monthly Cost Cost This Study Annual Cost Pump 9.12 $16.81 $92.45 $201.71

Blower 16.49 $30.39 $167.14 $364.67 Electricity Totals 25.61 $47.20 $259.60 $566.38

Water** Daily Use (L) Monthly Cost Cost This Study Annual Cost Winter Months 86 $0.94 $11.27

Summer Months 138 $1.50 $18.03 Water Totals $21.20 $29.30

Feed Daily Use (g) Monthly Cost Cost This Study Ideal Annual

Cost*** 370 $24.45 $134.48 $284.17

Iron Monthly Use

(g) Monthly Cost Cost This Study Annual Cost 62 $1.36 $7.48 $16.32

Materials Item Number Cost Each Annual Cost Pump 1 $110 $110.00

Airstones 32 $0.58 $18.56 Airlines 200 $0.25 $50.00

Peat pellets 1000 $0.09 $90.00 Seeds

(packages) 1 $24 $24.00 Materials Totals $292.56

68

Tilapia Fry Shipping Number Cost Each Annual Cost Hybrid 0. aurea X 0. nilotica $50.00 300 $0.15 $95.00

Total Costs this Study: $2,035.91

Total Annualized Operating Costs: $3,847.33

Total Annualized Operating Costs without Labor: $1,283.73

* Electricity use determined from pump (@12 hrs/day) and blower (@ 24 hrs/day) labels, with rates taken from Tucson Electric Power R-201 pricing plan ** Water rate taken from Tucson Water residential rate of $1.03/ccf (748 gallons, 2,832 liters) for the first 15 ccf *** Ideal feed cost based on same starting number of fish at 85% survival for annual growout from 45g to 681g at an FCR of 1.5

Table 4.3. Daily water use for the aquaponics system.

Dates Days L/day

Winter 2/11-4/4 54 86

Summer 5/7-7/31 86 138

Diseased 4/5-5/6 32 1,156

70

Table 4.4. Food production and revenue from the aquaponics system.

Weight (kg) Price/unit Revenue Annual Ideal Model* Fish 91.36 $5.50 $452.25 $452.25 $794.64

Vegetables Lettuce 36.60 $1.34 $49.28 $118.27 Basil 46.48 $9.90 $460.13 $1,104.31 $2,730.00 Tomatoes 0.45 $0.50 $1.20 Peppers 0.57 $0.50 $1.20 Totals 84.10 $510.41 $1,224.98 $2,730.00

Totals 175.46 $962.66 $1,677.23 $3,524.64

* Assumes same initial number of fish, at 85% survival rate to same growout size in one year. For vegetables assumes fiill system in basil production at 15.9 kg every 3 weeks.

Table 4.5. Cost and benefit analysis.

This Study This Study Annualized

This study years 2-

6** Ideal System

Annual Year 2-6** Materials $2,946.04 $2,946.04 n/a $2,946.04 n/a

Labor $510.00 $510.00 n/a $510.00 n/a Water $2.94 $2.94 n/a $2.94 n/a

Startup Totals $3,458.98 $3,458.98 n/a $3,458.98 n/a

Water* $21.20 $42.40 $42.40 $29.30 $29.30 Electricity $259.60 $566.38 $566.38 $566.38 $566.38

Feed $73.08 $293.40 $293.40 $284.17 $284.17 Materials $95.00 $95.00 $403.88 $95.00 $403.88

Labor $1,225.60 $2,563.60 $2,563.60 $2,563.60 $2,563.60 Total Operating Costs $1,674.48 $3,560.78 $3,869.66 $3,538.45 $3,847.33

Total Costs with Labor $5,133.46 $6,992.01 $3,869.66 $6,982.78 $3,847.33 Total Costs without Labor $3,397.86 $3,918.41 $1,306.06 $3,909.18 $1,283.73

Benefits Fish Profit $452.25 $452.25 $452.25 $794.64 $794.64

Vegetable Profit $510.41 $1,224.98 $1,224.98 $2,730.00 $2,730.00 Total Benefits $962.66 $1,677.13 $1,677.13 $3,524.64 $3,524.64

Net Benefits with Labor -$4,170.80 -$5,342.53 -$2,192.43 -$3,472.79 -$322.69 Net Benefits without Labor -$2,435.20 -$2,268.93 $371.17 -$399.19 $2,240.91

•Annualized water cost for this study was determined for averages of six summer and winter months, the disease affected time was not included. ** For years 2-6, there are no startup costs. Operating materials costs are higher due to needing to replacing materials such as the pump, airstones and airlines. After 5 years other materials such as the liner and floating styrofoam trays may need replacement.

72

Table 4.6. Overall value of this small-scale aquaponics system, without labor costs (3% discount rate).

Year Revenue Costs Profit 0 1677.23 3946.16 -2268.93 1 1677.23 1306.06 371.17 2 1677.23 1306.06 371.17 3 1677.23 1306.06 371.17 4 1677.23 1306.06 371.17 5 1677.23 1306.06 371.17

PV $9,358,452 $9,927.53 -$569.08

NetPV -$569.08

73

Table 4.7. Overall value of the ideal model for this small-scale aquaponics system. Annual without labor costs (3% discount rate, ideal conditions as described in Tables 4.2 and 4.4).

Year Revenue Costs Profit 0 3524.64 3923.83 -399.19 1 3524.64 1283.73 2240.91 2 3524.64 1283.73 2240.91 3 3524.64 1283.73 2240.91 4 3524.64 1283.73 2240.91 5 3524.64 1283.73 2240.91

PV $19,666.46 $9,802.94 $9,863.52

NetPV $9,863.52

74

CHAPTER 5

SUMMARY

As water resources in arid lands are stressed due to rapidly growing populations,

agriculture will likely receive a reduced allotment or costs will increase. In order to

maintain productive farms and continue to meet food and fiber needs, agriculture must

become more efficient with its water use. One means to accomplish this is through the

multiple uses of water, growing several crops with the same water, or continuously

recycling water until evaporation losses leave it too salty to be of benefit. Combining

aquaculture production with traditional production agriculture is one way to realize this

methodology. This has potential for large industrial agriculture as well as for backyard

gardeners, as illustrated experimentally in Chapter 4.

Inland shrimp culture removes considerable risk factors faced by shrimp farmers.

Disease, water contamination, bird control and storm damages are more manageable

away from other farms and coastal ocean waters. Recently developed management

practices allow shrimp to be acclimated to slightly saline waters that are marginal for

most terrestrial crops. Chapter 3 describes how wastewater from these operations can be

applied to field crops with no apparent detrimental effects, even slight increases in plant

growth. These are ways wastes from low-salinity shrimp culture can be returned to

beneficial uses in agricultural operations.

The biological feasibility of integrated fish and hydroponic vegetable production

is well documented, while the financial potential of small-scale aquaponics systems has

75

been overlooked. Chapter 4 provides a detailed analysis of the costs, benefits and net

values of such a system. While this size of a system won't provide large business

opportunities, for family operations, there is potential for use in food production or

income supplementation.

Savings in water and nutrient benefits were previously described. Now financial

opportunities and risks are better explained. More research into materials used in these

systems is necessary to lower costs. Providing a science-based, understanding of long-

term ftinctionality and feasibility will aid in public awareness of the best management

practices for aquaponics. This study also provides a model for expanding the use of

aquaponics systems as teaching tools in agricultural education, especially agriculture

economics.

Chapter 2 defines literature addressing the impacts of the application of various

types of effluent on soil characteristics and plant responses. Relatively little work has

focused on inland shrimp aquaculture effluent reuse in agriculture. Due to the recent

development of low-salinity culture of marine shrimp such as Litopenaeus vannamei,

future research into integrating this culture with agriculture can encourage sustainable

practices that have little net negative impact on the environment. Impacts on soil

characteristics due to the application of nutrient enriched aquaculture wastes will differ

based on the characteristics of the receiving soil, another field for future research.

Determining water budgets for integrated agriculture and aquaculture farms will provide

means for sizing terrestrial and aquatic components, and provide a better concept on

impacts on aquifers due to leaching and groundwater pumping.

76

The environmental disasters of agriculture and aquaculture practices are well

documented. The damages from the "green revolution" and the later "blue revolution"

still scar nature. Food production has the potential to return to an ecological base,

incorporating natural nutrient cycles in ways that minimize resource consumption. These

studies show multiple uses of water in aquaculture and agriculture as a way these

industries may become more "green", reducing inputs while increasing water use

efficiency. This work indicates the need for more study and education, and the principle

that aquaculture water management and economic viability will drive the potential for

integrating aquaculture and agriculture in Southwestern Arizona.

77

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