Effects of water produced by aquaponic

and reptoponic systems on leafy

vegetables and herbs.

S.E. FERGUSON, D.J. HEITMEIER, L.F. MCELHANEY, C.R. MICHAELS, M.K. SAWDY, S. F. WASILKO, A.L. WYLAND

2

Aquaponics is a recirculating soilless system that uses the waste of fish for crop production.

Research has been done on aquaponics systems, but the use of turtles in a recirculating system

has not been documented. In an approach unique to Westminster College, this research will

introduce a reptoponics system that uses turtles as the aquatic organism, rather than fish. A dual

system will provide the opportunity to examine differences between the efficacy reptoponics

and aquaponics. The water quality from each system and its effects on the production of lettuce,

Swiss chard, basil, and cilantro will be observed. Water parameters to be measured are pH,

temperature, ammonia, nitrates, dissolved oxygen, phosphorous, and total dissolved solids. Plant

growth will be measured by dry weight, chlorophyll content, and plant height.

Correlations among the water parameters and plant growth were analyzed. The bacteria were

over nitrifying the system resulting in nutrient overloading which may have caused nutrient

toxicity; this is supported by the observed success of a no nutrient added hydroponic control.

Introduction

Amidst economic crises, oil shocks, and apprehension of global climate change in an

already resource-strained and conflict-ridden world, food security has become one of

humankind’s most pressing problems (Metcalf and Widener 2011). Sustainable agriculture is

the process of harvesting or using resources in such a way that the resource is not depleted or

permanently damaged. Scientists and researchers have yet to identify a planet that can sustain

life in the same way that earth does. Because of this and other factors that impact the

environment, such as climate change, population growth, poverty, and government corruption,

resource utilization and distribution is a topic that warrants serious discussion. In an effort to

become more sustainable as well as to potentially restructure the food distribution system,

many individuals, colleges, universities, and communities are experimenting with the science

of aquaponics while taking note of the environmental, social, and economic benefits that come

with the use of these systems.

Introduced by researchers from North Carolina State University in the 1970s, aquaponics

is a combination of aquaculture and hydroponics that allows for soilless crop production

(Turcious and Papenbrock 2014). Aquaculture is the production and harvesting of aquatic

3

organisms. On the other hand, hydroponics is the culture of plants in soilless water (Liang and

Chien 2013). In aquaponic systems, waste and organic matter that are toxic to the animals are

converted by microbes into soluble nutrients for the plants. Toxicants such as ammonia and

nitrite are derived from decomposition of unconsumed feed and metabolites or waste of the

animals (Liang and Chien 2013). The water needs to be treated whenever toxicants have built

up beyond the recommended level (Liang and Chien 2013). The hydroponics system cleanses

and treats the water to make it safe for the animals, and then recirculates it back into the

aquaculture system. (Liang and Chien 2013). These systems are a closed-loop eco-culture

where a symbiotic relationship is created in which water and nutrients, utilized by the plants,

are recirculated and conserved for the health of the animals. While system design and

construction can vary, most systems address the following key water treatment functions: solid

waste removal, nutrient removal or detoxification, carbon dioxide removal, dissolved oxygen

supplementation, and bacteria and pathogen sterilization (Klinger 2012).

Intensive agriculture and the increasing use of herbicides and pesticides has led to the

contamination of soil and irrigation water, which poses problems when trying to meet the

increased food demands that come with a growing global population (Turcious and Papenbrock

2014). Aquaponics offers a solution to these problems and many others associated with

traditional farming. These systems do not require added fertilizers, herbicides, or pesticides

because all nutrients are provided by the waste of the aquatic organisms, as well as the fact that

added chemicals pose a serious risk to the health of the organisms. In addition to its ecological

merits, aquaponic systems also allow for economic advantages such as: saving cost on water

treatment for aquaculture systems, saving cost on formulated fertilizer for hydroponic systems,

and financial benefits from the harvest of plants and animals by a single input (Liang and Chien

4

2013). Today, commercial aquaponics production exists primarily in controlled environments,

such as greenhouses or outdoor locations with favorable conditions.

Previous studies have documented the productivity of research-scale aquaponics, and in

2013, the United States Department of Agriculture began collecting updated production data as

part of the Census of Aquaculture (Love et al. 2014). Many operations surveyed resembled

small farms with little gross sales revenue, which have utilized more direct sales outlets to sell

their produce compared to other typical small farms (Love et al. 2014). With an increased

interest in locally produced food that is sold directly to consumers, aquaponics is a form of

aquaculture that easily fits into the local and regional food system models in part because it can

be practiced in or near largely populated areas (Love et al. 2014). The survey conducted by

Love et al. in 2014 reported findings that indicated the need for more research and development

are needed to determine if aquaponics will evolve into a profitable food production method.

Recent estimates suggest that there are more than 1,500 aquaponic operations in the United

States. This technology is currently used by commercial, research, educational, and not-for-

profit organizations, as well as by private hobbyists (Klinger 2012). Many studies today are

focused on the ratio between the hydroponic and rearing tank components (Lam et al. 2015),

the effect of plant species on nitrogen recovery (Hu et al. 2015), and the effects of photoperiod

and feeding frequency on water quality and crop production (Liang et al. 2015).

The elements of a general recirculating aquaponics system includes a rearing tank for

animal production, a component that removes suspended solids, a biofilter, and a hydroponic

component. A biofilter and solids-removal method are crucial components to aquaponic

systems because accumulation of too many solids and other harmful matter can be detrimental

to the health and production of the plants and fish. When organic matter accumulates it can

5

depress dissolved oxygen levels and produce carbon dioxide and ammonia while decaying

(Rakocy et al. 2006). After the water is treated and transported to the grow beds, plants uptake

the remaining dissolved nutrients and the cleaned water is finally returned to the rearing tank.

There are many variations of these systems, as the design and materials used are often modified

to fit the scale of the production, the overall project budget, and the cost required to set up more

complex systems. These systems can include the use of floating rafts or gravel mediums for

grow beds or the use of clay materials to act as the biofilter (Love et al. 2014). In traditional

aquaponic systems there are various species of freshwater fish that can be used for production.

Tilapia, the fish used in this study, are the most commonly used fish in aquaponic systems

because of their high availability, fast growing nature, resistance to stress and disease, and easy

adaptation to indoor environments (Hussain 2004).

A lesser-known type of recirculating system similar to aquaponics is called reptoponics.

Developed at Westminster College, reptoponic systems draw on the design and construction of

aquaponic systems, but rather than using fish reptoponics uses turtles. Because reptoponics has

not yet been researched by the larger scientific community and is relatively unique to

Westminster College, this study has potential to significantly contribute to the growing field of

aquaponics and the largely unknown field of reptoponics. It will provide some of the very first

literature, data, and analysis of reptoponic systems as well as help to determine if there are

significant differences between aquaponic and reptoponic systems. The scope of this study is

small and limited by time, but provides a foundation for future research.

In addition to its scientific merits, this research also has potential to impact the

community surrounding Westminster College. As a form of urban gardening, aquaponics has

been used as a community outreach tactic to foster a sense of community, worth, and respect

6

while also helping to repair the disconnect that exists between people and the production of the

food they eat. An example of such a program is called the Massachusetts Avenue Project,

based in Buffalo, NY. Here, aquaponics is used in an urban farm setting to help disadvantaged

youth realize their worth while providing opportunities for entrepreneurship, economic

development, and community engagement (Metcalf and Widener 2011). Westminster’s

neighboring community of New Castle, Pa has a poverty rate of approximately 26%. That is

nearly double the state level (U.S. Census Bureau 2013). The research outlined here provides a

foundation for community members and organizations to design their own systems, and on a

larger scale restructure food production and distribution systems so that fresh and healthy

produce is easily accessible to a wider audience.

This study aimed at gathering preliminary research on aquaponic and reptoponic

systems by comparing the possible differences between them as well as their potential effects

on the production of Swiss chard, lettuce, basil, and cilantro. This experiment used two separate

rearing tanks to house the animals. Each rearing tank was connected to two separate grow beds

that contained lava rocks. There was a constant flow of water and effluent transported from the

rearing tank to the grow beds by submersible pumps. Each grow bed contained a bell siphon

that sent the excess water not used by the plants back to the rearing tank. A basking area was

created for the turtles using basking lights and cinderblocks. Each experimental tank also

contained an 800-Watt submersible water heater. Along with the reptoponic and aquaponic

systems, there were two separate controls. The first was a soil control where plants were grown

in soil and watered once a day. The second control was a hydroponic control where plants were

placed into a grow bed that was connected via bell siphon and submersible pump system to a

40 gallon water container. This water container had no animals living within it.

7

Methods

Aquaculture: Fish and Turtles

Two 300-gallon galvanized steel tanks were used for rearing tanks, one for fish and the

other for the turtles. The rearing tanks were heated with

Finnex Titanium Heater (TH-800 Plus, 800W). Forty-six Blue

Nile Tilapia (Oreochromis aureus) were used for the

aquaponics treatment group. The Tilapia were each 7.62 to

10.16 centimeters in size at the time of purchase. Three red-

eared sliders (Trachemys scripta elegans), one yellow-bellied slider (Trachemys scripta

scripta), and one Mississippi Map (Graptemys pseudogeographica kohni) turtle were used for

the reptoponics treatment group. The turtles had been used in a previous, novel reptoponic

system, but were transferred into this experimental reptoponic system. The turtles were

weighed using an analytical balance, and the weights were recorded in Table 1.

Turtle Weight (g)

PICTURE 1. BLUE NILE TILAPIA

PICTURE 2. TURTLES USED IN EXPERIMENT: THE THREE RED-EARED SLIDERS, THE MISSISSIPPI MAP, AND THE

YELLOW-BELLIED SLIDER

8

Table 1. Turtle Weights.

Red-eared Slider 1 1243.2

Read-eared Slider 2 1800.5

Red-eared Slider 3 467.5

Mississippi Map 696.9

Yellow-bellied Slider 1736.2

Both the Tilapia and the turtles were transferred into the system on 13 March 2015. The

system then ran for two days before placing the plants into the system. Before being placed into

the system, the Tilapia were contained in an aerated, filtered tank while the turtles were kept in

a separate tank with heat lamps. The water was monitored and kept between 21-24C, which

was optimum for Tilapia and turtle health and growth.

System Design

Four 40-gallon TuffStuff oval tanks were used as the experimental grow beds. For the

aquaponic and reptoponic systems, four beds placed atop tables that were positioned at opposite

ends of the rearing tanks (Figure 1). These beds were each filled with approximately 10 bags

of lava rock. Water was delivered to the grow beds through submersible pumps, Ponics Pumps

(Model PP40006). Each grow bed had one pump with a ¾ inch PVC piping attached to it in

order for the water to travel vertically to the beds. A 76.2 centimeter pipe was attached to this

piping and was set diagonally across the tanks. Each diagonal pipe had twenty holes drilled in

it and a cap on the end in order to ensure even distribution of water into the grow beds. Two

control beds were set up in two additional 40- gallon TuffStuff oval tanks, but lacked the

effects of animal waste on the water that they received. The first control was a hydroponic

9

control which also contained 10 bags of lava rock, a bell siphon, a tank that contained untreated

tap water beneath it, a pump, and PVC piping for water to be transferred between the tank and

the grow bed. A bell siphon was also used in this control in order to replicate the water flow in

the experimental beds. The second control was a soil control which contained a layer of soil, a

layer of a manure/compost mixture, and a layer of perlite at the bottom. The soil control was

watered every night to allow for plant growth.

Figure 1. Diagram of design and layout of the experimental space Where Grow beds (GB) 1 –

4 are Experimental beds. GB 5 is the hydroponic control and GB 6 is the soil control.

A bell siphon (Figure 2) was made for each experimental grow bed and for the

hydroponic control. The siphons were used to control the water draining back into the rearing

Figure 2. Bell siphon diagram

10

tanks based off of the water levels in the grow beds. The siphons were made out of a 24.13

centimeter tall inner ¾ inch PVC pipe with an expanded drain cap and a surrounding 3-inch

PVC pipe and end-cap that was 40.0 centimeters in height with

4 triangles cut into the bottom. These triangles, referred to as

teeth, controlled the suction and timing of water drainage.

Finally, a 46.7 centimeter tall 6-inch PVC pipe encased the

entire siphon and had alternating slits cut into the sides from the

bottom to about 8 inches from the top. This PVC pipe had

encased the entire siphon in order to assist in suction. From the

bell siphon, the water was returned into the rearing tanks by a

15.24 centimeter ¾-inch PVC pipe, elbow joint, and a 12

centimeter ¾-inch PVC pipe extension. As the water level rose

in the grow-bed, water was forced through the teeth on the bottom of the bell and up between

the walls of the standpipe and bell. As the water level exceeded the height of the standpipe and

the drain began to fill, a siphon was created (Fox et al. 2010). The siphon then drained most of

the water in the grow-bed until the water level reached the height of the teeth (Fox et al. 2010).

Once the water drained thoroughly and air reached the teeth the siphon was broken, resulting in

the siphon beginning to fill again: the cycle then repeated itself (Fox et al. 2010).

Plants: pre-planting and randomization

Before being placed into the system, the plants were watered once a day using either a

spray bottle or garden hose on the mist setting. The All-Star Mix lettuce and Bright Lights

11

Swiss chard were grown from seed in separate growing containers under grow lamps in a lab.

The leafy greens were transferred into the system after 35 days. The herb seeds, Vegan Seeds

basil and Vegan Seeds cilantro were soaked in water for 12 hours prior to being planted, in

accordance with the company instructions. The herbs were grown in separate growing

containers in the greenhouse before they were transferred into the system after 32 days.

All plants were transferred into the grow beds on 20 March 2015 to begin the

experimental phase. The four experimental and two control grow beds were labeled one

through six. For randomization purposes, a die was rolled to determine which grow bed a plant

was placed into. The die was then rolled again to determine which side of the grow bed a plant

was planted in. This process was repeated until 4 plants of each type were placed into all six of

the grow beds, with two on each side.

Sample Preparation

Vernier probes came with pre-made calibration standards. However, standards were

made for ammonium and nitrate (six standards ranging from 0.1 ppm – 100 ppm NH4Cl and

NaNO3 respectively), and a standard curve was made to test accuracy and precision of the

probes. The ion selective ammonium (ISE) probe from Vernier was selected because detected

levels of NH3 are converted into NH4+. The Nitrate-ISE probe was used to detect NO3

- in

samples.

Sample Analysis

Two daily water quality measurements were taken in 12 hour cycles at 8 A.M. and 8

P.M. Vernier lab quest probes were used to measure nitrates and total ammonia nitrates (TAN),

12

a YSI 55 dissolved oxygen meter recorded dissolved oxygen (DO) levels, and a LaMotte sensor

measured pH, total dissolved solids (TDS), and temperature. Measurements were taken in both

the fish and turtle tank after discharge cycles so as to represent an upwelling of nutrients and

homogenization of the water samples.

Plant measurements were taken weekly. The plant measurements included were plant

height, plant diameter, and chlorophyll content. Plant height and diameter were measured using

a ruler to the nearest millimeter. These parameters were chosen in order to track the plants’

growth throughout the experiment. Both were measured because while the herbs grew more

vertically, plants like the lettuce would reach a certain height and then grow only in diameter.

Chlorophyll content was measured using an atLEAF chlorophyll meter. With this tool, plant

relative chlorophyll concentration was measured by inserting a leaf into the device aperture.

Once the leaf was inserted, a button was pressed and the measurement appeared on the screen

in SPAD units. At the end of the experiment, plant fresh weight and dry weight were taken. The

plants were removed from the systems and weighed with an analytical balance. After taking the

fresh weight, the plants were kept in an oven for approximately forty-eight hours, and then the

dry weights were recorded with an analytical balance.

Weekly water samples for phosphorus measurements were taken and frozen at 0°C.

Sample analysis of phosphorous was taken for each week at the end of the study by Ascorbic

acid method (APHA) detailed by the Environmental Protection Agency. The total phosphorous

test measured all the forms of phosphorus in the sample (orthophosphate, condensed phosphate,

and organic phosphate). This was accomplished by first digesting (heating and acidifying) the

sample to convert all the other forms to orthophosphate. Then, the orthophosphate was

measured by the ascorbic acid method. Because the sample was not filtered, the procedure

13

measured both dissolved and suspended orthophosphate. A calibration curve was prepared by

using 5 standards. Distilled water containing the combined reagent was used to blank the

spectrophotometer before taking measurements of the standards and samples. Absorbance

versus phosphate concentration was plotted in order to obtain the calibration curve. Twenty-

five mL of deionized water was added to 25 mL of the sample. Then 50 mL of deionized water

was then added to the sample after digestion and transferred in order to raise the volume to 100

mL.

Feed rate

Fish and turtles were fed twice daily based on a 1% fish biomass following water quality

measurements. This rate was consistent with a daily-recommended feed rate for turtles, in

which daily feed amount for turtles was based on the approximate size of the head. A 20 mL

vial was used as an approximation for the turtle’s head size, and the mass of food contained

within was estimated to be the required daily feed for each turtle. Both of these biomass-based

feeding estimates resulted in 18 ± 0.03 grams per feeding. During week five, the feeding rate

was increased to 22.5g per feeding to accommodate the growing biomass of fish and, to a

smaller degree, turtles with a consistent a morning feeding of Reptomin and a night feeding of

Aquamax 4000 tilapia food, to both the turtles and fish.

Results

Data shows that there is a significant difference among treatment groups for each water

quality parameter. The only difference in the water quality parameters between the aquaponics

14

and reptoponics was that of TDS and Nitrates. In both cases the aquaponics treatment had

higher levels of both. The hydroponic treatment was statistically different among all parameters.

Hydroponics had lower temperatures, higher pH, lower TDS, lower TAN, lower nitrates, and

higher DO (Table 2). As expected correlations of pH versus TDS, Temperature versus DO, and

pH versus Nitrates were all negative (Table 3). A Pearson’s correlation of TAN to nitrates of

the aquaponics and reptoponics treatments resulted in a correlation of -0.282 (P = 0.002)

(Figure 2). Hydroponics was excluded as it had no organisms to contribute the ammonia cycle

and therefore we did not expect a correlation and there was not one. Mean study TAN

concentrations were reported from the aquaponics, reptoponics, and hydroponic systems as

follows: 3.0 ± 1.51 mg/L, 3.5 ± 2.78 mg/L, and 0.8 ± 0.16 mg/L. Mean study nitrate

concentrations were reported from the aquaponics, reptoponics, and hydroponic systems as

follows: 54.4mg/L, 35.8 mg/L, and 8.6 mg/L. Aquaponics and reptoponics systems had a high

source of variability over the course of the study.

Table 2: ANOVA analysis resulting P values and Tukey comparison results of the water quality

data.

ANOVA P value Tukey comparison

Temp P < 0.001 hydroponic < aquaponic = reptoponic

pH P < 0.001 hydroponic > aquaponic = reptoponic

TDS P < 0.001 aquaponic > reptoponics > hydroponic

TAN P < 0.001 aquaponic = reptoponics > hydroponic

Nitrates P < 0.001 aquaponic > reptoponic > hydroponic

DO P < 0.001 hydroponic > aquaponic = reptoponic

P-value Pearson’s correlation

variables

15

Table 3: The correlations of water

quality parameters.

Figure 2: The correlation of Nitrates versus TAN (p = 0.002, Pearson’s correlation = -0.282)

Figure 3: Averaged weekly TAN levels measured over a 5 week period in aquaponic,

reptoponic, and hydroponic systems. Error bars represent standard error.

-20.0

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0

Nit

rate

s

TAN

p < 0.001 -0.673 pH v TDS

p < 0.005 -0.481 Temp v DO

P < 0.001 -0.442 pH v Nitrates

16

Figure 4: Averaged weekly nitrate levels (ppm) measured over a 5 week period in aquaponic,

reptoponic, and hydroponic systems. Error bars represent standard error.

The chlorophyll content between the groups was not different. Some plants exhibited

higher percent survival than other (Table 4). Because of its low survival rate, the Swiss chard

was left out of the analysis. None of the plants (Cilantro, Basil, or Lettuce) grew significantly

different between the aquaponic, reptoponic, and hydroponic treatments. However, the soil

control was different, having higher growth. Though there was a lack of difference in plant

growth, there were some correlations of the water quality parameters and the plant growth

parameters. Lettuce height and diameter correlated negatively with pH and positively with

nitrates (Table 5). This was expected since plants uptake nitrates as a nutrient. What was

unexpected was that the other plants did not also correlate statistically this way. In regards to

basil, the basil diameter correlated negative with TDS (Table 5).

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

1 2 3 4 5

Nitrates

Aquaponics Reptoponics Hydroponics

17

Table 4: Percentage of survival for each species of plant in each system. 100% of the plants

survived in the hydroponic and soil control systems

Plant % Plant Survival

Aquaponics

% Plant Survival

Reptoponics

Swiss chard 12.5 0.0

Lettuce 50.0 62.5

Basil 25.0 75.0

Cilantro 87.5 75.0

Lettuce, basil, and cilantro dry weights were only statistically different in the soil treatment

(Figure 6).

Figure 6: Average dry plant weights with standard error bars.

-2

-1

0

1

2

3

4

5

6

7

8

lettuce Basil Cilantro

Ave

rage

Dry

wei

ght

(g)

System

Reptoponic Aquaponic Hydroponic Soil Control

18

Table 5: Pearson’s correlations of the water quality parameters versus the plant growth

measurements of the heights and diameters of each plant. Where S = Swiss chard, C = cilantro,

L = lettuce, B = basil, MHG = mean height growth, and MDG = mean diameter growth

Spearson’s ρ correlation significant variables

0.675 0.118 N pH v CMHG

0.043 -0.527 Y pH v LMHG

0.553 -0.166 N pH v BMHG

0.242 -0.322 N TDS v CMHG

0.218 0.338 N TDS v LMHG

0.718 0.102 N TDS v BMHG

0.558 0.164 N DO v CMHG

0.226 -0.332 N DO v LMHG

0.751 0.089 N DO v BMHG

0.558 0.164 N nitrates v CMHG

< 0.001 0.281 Y nitrates v LMHG

0.311 0.281 N nitrates v BMHG

0.191 -0.357 N ammonium v CMHG

0.761 -0.075 N ammonium v LMHG

0.170 -0.374 N ammonium v BMHG

0.196 -0.354 N Temp v CMHG

0.362 0.254 N Temp v LMHG

0.408 0.231 N Temp v BMHG

0.652 -0.127 N pH v CMDG

0.036 -0.545 Y pH v LMDG

0.311 0.281 N pH v BMDG

0.894 0.038 N TDS v CMDG

0.137 0.402 N TDS v LMDG

0.052 -0.510 Y TDS v BMDG

0.405 0.232 N nitrates v CMDG

0.044 0.525 Y nitrates v LMDG

0.337 -0.266 N nitrates v BMDG

0.451 -0.211 N ammonium v CMDG

0.781 0.079 N ammonium v LMDG

0.461 0.227 N ammonium v BMDG

0.791 -0.075 N DO v CMDG

0.226 -0.332 N DO v LMDG

0.245 0.320 N DO v BMDG

0.405 -0.232 N Temp v CMDG

0.296 0.289 N Temp v LMDG

0.491 -0.193 N Temp v BMDG

19

Total phosphorus was analyzed by Ascorbic Acid Method to determine total

phosphorus PO4-. The mean phosphorus concentrations of the aquaponic, reptoponic, and

hydroponic systems are as follows: 0.158 ± 0.018 µg PO4- /mL, 0.198 ± 0.013 µg PO4

- /mL, and

0.021 ± 0.00003 µg PO4- /mL (Figure 8). Beginning samples fluctuated in the first week for

aquaponic and reptoponic. After week three, an upward trend between total phosphorus in

waters was found in aquaponic and reptoponic systems. In the hydroponic system, a downward

trend was seen in total phosphorus concentrations. Determined by Tukey’s Multiple

Comparisons Test, total phosphorus levels were significantly higher in the reptoponic system

than in the hydroponic (p=0.021).

Figure 7: Standard curve for phosphorus analysis.

Figure 8: Phosphorus analysis between aquaponics, reptoponics, and hydroponics systems.\

y = 0.1063x R² = 0.8885

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Ab

sorb

ance

Standard Concentration (µg P/mL)

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0.500

1 2 3 4 5 6

µgP

/mL

Week

Hydroponics

Aquaponics

Reptoponics

20

Discussion

Data from this study showed no significant difference of chlorophyll content among

treatments for each plant type. Other studies have shown similar results of no significantly

different chlorophyll content among differing fish density treatments in lettuce crop (Pantanella

et al. 2010). Plant growth, measured by height and diameter, was only significantly different in

the soil control, which exhibited more growth than the aquaponic, reptoponic, and hydroponic

systems. In 2009, Graber and Junge conducted a study that compared the growth of tomato,

aubergine, and cucmber in soil, aquaponic, and hydroponic systems. In this study, the tomato

yield equaled productivity in traditional soil cultures but was significantly lower than in soil-

less cultures (Graber and Junge 2009). It was also noted that an important lack in fish water

was its low potassium concentration, which was 45 times lower than in hydroponic (Graber and

Junge 2009). This resulted in a lower quality tomato plant in aquaponic compared to the soil

and hydroponic systems (Graber and Junge 2009). As potassium is not needed by fish, it is not

added to fish feed and thus to the system in adequate amounts (Graber and Junge 2009). In

future studies, potassium could be supplied through potassium hydroxide (KOH) while also

being used to stabilize decreasing pH values that occur due to permanent nitrification (Graber

and Junge 2009).

There was a high death rate of plants. In the reptoponic system only 53% of the plants

survived the entire five week study while only 40% survived in the aquaponic system. However,

100% of the plants survived in the hydronic and soil control systems. This difference could be

due to many different reasons. It is most likely due to the physical set up. The area in the

greenhouse where the hydroponic and soil system were placed received more light throughout

the day due to the location if being placed by and outside wall. The reptoponic and aquaponic

21

systems were located on the other side of the room close to a dividing wall. This could have

caused them to receive less sunlight from the outside wall. Also, the placement of the bell

siphon in both the in the reptoponic and aquaponic systems caused some shade which limited

the sunlight received by the plants that surround it. Another reason could be that in the lava

rock there was significant space between rocks due to their large size and it is possible that the

roots did not have anything to grow around to keep them stable, as they did in the soil.

Water temperature in the hydroponic tank was significantly different from the

temperature in the reptoponic and aquaponic tanks. This was expected due to the fact that the

reptoponic and aquaponic tanks both contained submersible water heaters in order to keep the

water at a safe temperature for the organisms. A submersible heater was not placed in the

hydroponic control because prior research showed that the temperature of water did not impact

plant health and growth. There was no significant difference between the aquaponic and

reptoponic systems, which was expected due to the submersible heaters being used at the same

temperature setting. The hydroponic control was also significantly different in pH levels. The

hydroponic control had a higher pH than the aquaponic and reptoponic systems. A possible

reason for this is the presence of the aquatic organisms. When organisms breathe in oxygen,

they release carbon dioxide into the environment. This aqueous carbon dioxide can lower the

pH. In heavily stocked fish ponds, carbon dioxide concentrations can become high as a result of

respiration. The free carbon dioxide released during respiration reacts with water, producing

carbonic acid, and pH is lowered as a result (Wurts 1992).

Total dissolved solids (TDS) in the hydroponic control significantly differed from the

aquaponic and reptoponic systems. This was expected, because total dissolved solids

accumulated due to waste from the organisms and the organisms’ food. A previous study done

22

by Roosta and Hamidpour conducted in 2011 reported TDS measurements as 327 ± 12 mg/L in

their aquaponic system. After week one, TDS in the reptoponic and aquaponic systems

remained above the average range found in the Roosta and Hamidpour study. All of the

hydroponic TDS measurements were well under the average for the Roosta and Hamidpour

study. This is a possible reason that the hydroponic control performed better. In the study

conducted by Roosta and Hamidpour, both a hydroponic system and an aquaponic system were

observed. However, all of the hydroponic TDS measurements in our study were hydroponic

system in this study also performed better, but TDS measurements of the hydroponic system

were not reported in their study. High concentrations of nutrients can negatively impact the

growth of plants. A study done by Almuktar et al. in 2015 resulted in poor overall growth and

development of sweet peppers due to high concentrations of nutrients and trace minerals

(Almuktar et al. 2015).

Dissolved oxygen levels were significantly different only in the control. Dissolved

oxygen was higher in the hydroponic control than in the reptoponic and aquaponic systems.

This was expected for two reasons. First, the reptoponic and aquaponic systems had a 300

gallon rearing tank that held the water, while the hydroponic control held water in a 40 gallon

bucket. Due to the smaller volume, the dissolved oxygen would have a higher concentration.

Second, there were no organisms in the bucket to use the dissolved oxygen. This resulted in the

higher dissolved oxygen levels in the control.

Over the five week period, Figure 2 showed sinusoidal characteristics, suggesting that

TAN levels in each system had a periodic cycle. This means that concentrations begin at a

higher level, and decline over the course of the week, and then a rise in concentrations follows

after the lowest point of decline. Concentrations of the reptoponic and aquaponic systems posed

23

to be similar in results; however, they were both significantly higher than the hydroponic

system. Recommended nitrate levels in aquaponics are suggested to be less than 150 mg/L.

Although this is not toxic as 250 mg/L, a lower concentration keeps a safe balance between the

three organisms being grown in systems: aquaculture, plants, and bacteria (Small-scale

aquaponics food production, Ch. 3, PP 21-25). Regulating nitrate concentration is important in

the nitrifying process from ammonium. The pH is a significant factor in the nitrification of

NO3- from NH4

+.

Lettuce height and diameter were found to be negatively correlated with pH. This was

expected, due to the solubility of nutrients at certain pH levels. When the pH increased, the

lettuce was unable to absorb nutrients from the water, and therefore growth slowed. Also,

availability of micronutrients such as manganese, iron, copper, zinc, and boron tend to decrease

as soil pH increases (McKenzie 2003). The exact mechanisms responsible for reducing

availability differ for each nutrient, but can include the formation of low solubility compounds

and the conversion of soluble forms to ions that plants cannot absorb (McKenzie 2003). Lettuce

height and diameter were found to be positively correlated with nitrates which was expected.

As the amount of nitrates in the water increased, the lettuce’s height and diameter increased in

size. Organic nitrogen in the water is decomposed and converted to ammonia by various

heterotrophic microorganisms in the water. The ammonia is then oxidized to nitrate by

nitrifying bacteria, and the plants rely on these nitrates formed for its major source of nitrogen

(Tokuyama 2004).

The level of total dissolved solids in the water was found to be negatively correlated

with the growth of the basil. There are multiple possible reasons for this. The total dissolved

solids is an estimate of the nutrient and bacterial content of the water, but the TDS meter also

24

will measure the accumulation of organic matter present in the water, such as animal waste. An

accumulation of ammonia in the grow bed brought in from the rearing tank could have

occurred and the nitrogen-fixing bacteria could not keep up with the rate. If this was the case,

there would be a buildup of ammonia in the grow beds, possibly being toxic to the plants. A

possible solution to this would be to adjust the plant density in the growing beds. Insufficient

plant growing area can result in an accumulation of nutrients in recirculating systems or the

excessive release of nutrients in a flow through systems. Too large a plant growing area may

improve water quality but will also lead to slower plant growth rates and reduced production of

plant crops (Buzby and Lin 2014).

Recommended nitrate levels in aquaponics are suggested to be less than 150 mg/L, and

throughout the study, these levels were exceeded in the aquaponic and reptoponic system at the

end of week 3 and beginning of week 4. Once these levels were reached, 75 gallons of water

was replenished in each system to ensure concentrations decreased. A concentration over 250

mg/L is considered toxic to plants. Therefore, having lower concentration keeps a safe balance

between the three organisms being grown in systems: aquaculture, plants, and bacteria (Small-

scale aquaponic food production, Ch. 3, PP 21-25).

Based on the findings of this study, there were no significant differences in the leafy

vegetables and herbs produced between the aquaponic and reptoponic systems. Future research

should focus on ensuring flow rate consistency, increasing plant density, developing methods to

ensure bacterial health, and using distilled water to ensure the concentration of nutrients. The

results in this study indicated the bacteria were over nitrifying the system resulting in nutrient

overloading which may have caused nutrient toxicity; this is supported by the observed success

of a no nutrient added hydroponic control.

25

References

Almuktar, S.A.A.A.N., Scholz, M. Al-lasawi, R.H.K., and A. Sani. 2015. Recycling of domestic

wastewater treated by vertical-flow wetlands for irrigating Chillies and Sweet Peppers.

Agricultural Waste Management. 149: 1-22.

Buzby, L., and L. Lin. 2014. Scaling Aquaponic Systems: Balancing plant uptake with fish

output. Aquacultural Engineering 63: 39-44.

Edwards, Peter. 2015. Aquaculture Environment Interactions: Past, present, and likely future

trends. Aquaculture. Asian Institute of Technology.

Fox, B.K, Howerton, R., and C.S. Tamaru. 2010. Construction of Automatic Bell Siphons for

Backyard Aquaponic Systems. Biotechnology. College of Tropical Agriculture and

Human Resources.

Hu, Z., Lee, J.W., Chandran, K., Kim, S., Brotto, A.C., and S.K. Khanal. 2015. Effect of plant

species on nitrogen recovery in aquaponics. Biosource Technology 188: 92-98.

Hussain, M.G. 2004. Farming of Tilapia: Breeding Plans, Mass Seed Production and

Aquaculture Techniques. Bangladesh Fisheries Research Institute.

Klinger, D. 2012. Searching for Solutions in Aquaculture: Charting a Sustainable Course.

Annual Review of Environment and Resources 37.

Lam, S.S., Ma, N.Y, Jusoh, A., and M.A. Ambak. 2015. Biological nutrient removal by

recirculating aquaponic system: Optimization of the dimension ratio between the

hydroponic and rearing tank components. International Biodeterioration and

Biodegradation.

Liang, J. and Y. Chien. 2013. Effects of feeding frequency and photoperiod on water quality and

crop production in Tilapia-water spinach raft aquaponics system. International

Biodeterioration and Biodegradation 85: 693-700.

Love, D.C., J.P. Fry, L. Genello, E.S. Hill, J.A. Frederick, X. Li., K. Semmens. 2014. An

International Survey of Aquaponics Practitioners. PLOS ONE.

26

McKenzie, M. 2003. Soil pH and Plant Nutrients. Alberta Agriculture and Rural Development.

Metcalf, S.S., and M.J. Widener. 2011. Growing Buffalo’s capacity for local food: A systems

framework for sustainable agriculture. Applied Geography 31: 1242-1251.

Pantanella, E., Cardarelli, M., Colla, G., Rea, E., Marcucci, A. 2010. Aquaponics vs.

Hydroponics Production and Quality of Lettuce Crop. Proceedings of the International

Symposium on Greenhouse 2010 and Soilless Cultivation 927:887-893.

Rakocy, J.E., M.P. Masser, and T.M. Losordo. 2006. Recirculating Aquaculture Tank

Production Systems: Aquaponics-Integrating Fish and Plant Culture. Southern Regional

Aquaculture Center 454.

Roosta, H.R. and M. Hamidpour. 2011. Effects of foliar application of some macro- and micro

nutrients on tomato plants in aquaponic and hydroponic systems. Scientia Horticulturae,

3 (27): 396-402.

Somerville, C., Cohen, M., Pantanella, E., Stankus, A. & Lovatelli, A. 2014. Small-scale

aquaponic food production. Integrated fish and plant farming. FAO Fisheries and

Aquaculture Technical Paper No. 589. Rome, FAO. 262 pp.

Timmons, M. B., J. M. Ebeling, F. W. Wheaton, S. T. Summerfelt, and B. J. Vinci. 2002.

Recirculating aquaculture systems, 2nd Edition. Northeast Reg. Aquaculture Center Publ.

No. 01-002.

Tokuyama, T., Mine, A., Kamiyama, K., Yabe, R., Satoh, K., Matsumoto, H., Takahashi, R.,

and K. Itonaga. 2004. Nitrosomonas communis Strain YNSRA, An Ammonium-

Oxidizing Bacterium, Isolated from the Reed Rhizoplane in an Aquaponics Plant.

Journal of Bioscience and Bioengineering, 98 (4):309-312.

27

Turcious, A.E., J. Papenbrock. 2014. Sustainable Treatment of Aquaculture Effluents- What

Can We Learn from the Past for the Future. Sustainability 6: 836-856.

United States Census Bureau. 2009-2013. State and County QuickFacts: New Castle (city),

Pennsylvania.

United States Environmental Protection Agency. 2012. Water Monitoring and Assessment:

Phosphorus.

Wurts, W.A. and R.M. Durborow. 1992. Interactions of pH, Carbon Dioxide, Alkalinity, and

Hardness in Fish Ponds. Southern Regional Aquaculture Center, 464.