Final Report for LNE05-224
Project Information
A market survey of aquatic plants revealed that 125 ornamental plant species ranging in value from $2.00 – $19.00, 270 plant species ranging in value form $0.27 to $3.50 are cultured for the restoration or mitigation markets. A variety of product forms are sold including tubers, bare root, 2 inch plugs, and several container sizes (pint, 4-6 inch and gallon). Three pilot scale demonstration systems were evaluated: trout raceways/aquatic plants; a brackish water recirculating striped bass tank/aquatic plant system; and a baitfish pond/aquatic plants system in West Virginia, Maryland and Delaware respectively. Plant growth and nutrient uptake using fish waste was measured and results varied depending on the system. The greatest plant growth was observed in the recirculating tank system where fish feeding rate, and subsequent dissolved nutrients, was higher. In that system, cord grass -Spartina biomass production was 25% greater than in constructed marshes and nitrogen uptake was twice that of natural marshes. Preliminary economic analysis showed that the plant production can generate supplementary income as the plants have relatively high value. Sizing the aquatic plant section to filter out the nitrogen and phosphorus from the fish system will be needed. This study generates preliminary nutrient uptake rates to assist farmers in estimating plant to fish ratios. Workshops, tours, presentation and publications were well attended. However, only one farmer was observed to employ the technology to date.
Introduction:
Aquaculture in the Northeast is dominated by three primary production technologies: raceways, recirculating systems and ponds. These systems are relatively expensive to operate and are faced with increasing environmental regulations associated with effluent management. Species diversification, shifting to higher value species, integrating additional crops and polyculture are all useful strategies for farms to improve profitability. Aquatic plant culture for ornamental and restoration markets has proven to be an emerging industry with high value crops. In addition, aquatic plants can be an important means of nutrient uptake. Delaware State University (DSU), University of Maryland and West Virginia University are collaborating to demonstrate the potential economic and environmental benefits of integrating aquatic plant culture with aquaculture.
This project provided aquaculture producers in the Northeast an opportunity to understand the variety of aquatic plant species and their market potential; learn how to integrate plants into their production systems through tiered workshops, training and applied research and demonstration projects utilizing the three productions systems: raceways or flow-through (WVU) , recirculating tank systems (UMD) and ponds (DSU); understand the economic potential by review of economic analyses of each demonstration project; and receive implementation support through targeted technical support programming. The three system projects will be directly applicable to over 420 fish producers in the Northeast who employ one of the three culture systems, and secondarily to state and federal fish hatcheries. Through a series of milestones, including plant market surveys, workshops and training, tours, and implementation instruction and support, Farmers were able to evaluate this integration approach for integrating aquatic plant production in their operations and increase farm income through plant sales and reduce nutrient concentration of their farm effluent.
Of the 420 aquaculture producers in the Northeast who utilize either raceways, ponds or recirculating systems and are included in project activities, 15 farmers were estimated to implement aquatic plant culture in their operations reducing nutrient concentration in culture system effluent and increasing farm income through sales of plants. By adding aquatic plant component to their operations, farmers will benefit by: a) wisely utilizing nutrients from aquaculture effluent typically considered a liability, but instead will serve as fertilizer for aquatic plants; b) increase farm diversity by the additional sales of marketable aquatic plants which in turn will; c) increase farm sales and enhance profitability, especially since aquatic plants achieve a greater profit margin than foodfish; d) reduce the off-farm nutrient discharge thereby being more environmentally sustainable; and e) produce plant species that are used for food, ornamentals in water gardens or in mitigation projects in urban or construction areas. Though over 500 individuals were educated directly, and numerous more received publications, only one farmer in West Virginia implemented an aquatic plant system.
Cooperators
Research
For the first objective a market survey of three plant markets (ornamental, restoration and food) was conducted in year one and identified specific plant species with strong demand, current market price and suitability to the growing conditions that exist for the three aquaculture production systems. The second objective consisted of conducting three workshops, one each in Maryland, Delaware and West Virginia to educate farmers on details of the aquatic plant industry, the types of market outlets, how plants can be marketed, what plants offer the greatest desired benefits of growth, nutrient uptake and market value, plant propagation requirement and techniques, possible integration applications with aquaculture systems, and effluent treatment benefits.
The third objective was to conduct production and economic evaluation of three pilot scale research systems integrating aquatic plant culture: trout raceways, recirculating tank system for production of Tilapia and striped bass, and pond system used in baitfish production. Each pilot scale research systems were operated for one plant growing season, which varied depending on the species and its water temperature preference. Plant and fish growth, water quality, treatment effluent nutrient (total phosphorus and total nitrogen) concentration, and cost of operation was monitored and used in the development of an economic analysis presented to farmers at a series of second training workshops. Individual technical support was provided to farmers through one on one farm visits to develop implementation plans and continued through one growing season to monitor and assess project outcomes.
Recirculating Tank Demonstration System:
Brackish water plants, marsh cord grass Spartina alterniflora and swamp hibiscus Hibiscus mochuetos were planted in floating rafts in experimental plant channels and supplied with effluent waters from the recirculating aquaculture operation at University of Maryland’s Aquaculture Restoration and Ecology Laboratory. The system was to be incorporated at a local Tilapia farm, which closed before project implementation. Another collaborator was interested, but restructuring of business goals, prevented implementation. The UM system contains five six-foot fish production tanks, with side-stream effluent flow to the aquatic plant culture channels. Striped bass were stocked as fingerlings for an 8-month growth period, producing ¾-pound fish by project end. The system utilized effluent from the recirculating system and flow through a raft system in a raceway. The experimental plant channels were constructed from treated lumber (2x12’s) and plastic liner. Six (2’ x 3’) will be placed in an 18’L x 3’W x 0.75’D channel where two species of aquatic plants, Spartina alterniflora and Hybiscus mochuetos were grown (See Table and Figure 1). The culture period ran from March through September in year two with biomass being recorded at beginning and end of the project to determine relative growth rates for each aquatic plant species. Initial, two growing season and final plant tissue samples were analyzed for TN and TP to determine nutrient uptake rates. Water quality (e.g. temperature, dissolved oxygen, were measured daily and ammonia, nitrite, pH and carbon dioxide was measured twice weekly.
Raceway culture system:
Plant channels (2’wide x 19’long x 1’deep, 0.61m x 5.79m x 0.3 m) were constructed from plywood and covered with a 45 mil EPDM (Ethylene propylene diene monomer) pond liner. The channels were constructed such that each plywood box consisted of a pair of plant channels. Three boxes, for a total of 6 plant channels, were constructed. A 1” bulkhead fitting, connected to a ball valve formed the inlet; the ball valve permitted control of incoming flow to the channel. A 9” standpipe placed in the socket end of a 2” bulkhead fitting at the end of the channel set the water depth at 9” and conducted water to the drain. Velocities within the plant channels were set at 0.003 L•s (1.35 gal•min).
Floating rafts (2’ x 3’, Maryland Aquatic Nurseries) with twenty four 5” holes were used to support the plant pots. Each channel was filled with 6 rafts that held a total of 144 plants. Hibiscus moscheutos (‘Fireball’ and ‘Moy Grande’) and Iris versicolor (Blueflag Iris) were used. Bareroot plants, purchased from Maryland Aquatic Nurseries, were wrapped with a fibrous inert material to hold them upright and placed in 6” pots that fit the holes in the raft. Rafts were planted 5/11/06.
The aquaponics greenhouse, a 26’ x 48’ double layered plastic house with louvered shutter and exhaust fan and roll-up sides covered with insect netting housed the plant channels. The water source for the plant channels was effluent from a flow-through trout raceway. Water from an artesian spring is supplied via gravity to the headbox of the raceways. During the experiment, the system supported 6000 to 8000 lb of brook trout fed a commercial diet (42% protein, 16% fat) six days a week. A pump placed in the tailbox conveyed the effluent to the aquaponics greenhouse.
Water quality and plant biomass samples were taken at 3 week intervals. Water samples were taken at the end of each channel, the tailbox and at the end of each trout raceway. Samples were analyzed for ammonia (ammonia-selective electrode, 4500-NH3.D), nitrate (cadmium reduction 4500-NO3.E), nitrite (colorimetric, 4500-NO2.B) and phosphate (ascorbic acid, 4500-PO4.E) as described in APHA (1989). In addition, plant tissue samples were tested for total nitrogen (TN) and total phosphorus (TP) to determine nutrient uptake rates with analysis conducted by a private lab.
Presentations were made at the Aquaculture Forum in 2006 and 2008, the annual meeting of the West Virginia Aquaculture Association and WVU College of Agriculture, Forestry, and Consumer Sciences. Trout workshops held at the Reymann Memorial Farm, the facility where the Aquaponics research in flowing water systems was conducted. Tours of the facilities to visitors and for special events like the annual field day. These efforts reached both producers and the general public.
Presentations at the forum generated interest in the workshops. Tours of the aquaponic greenhouse allowed visitors to see how things worked and to receive answers to their questions. It is much more effective to have a demonstration than a presentation.
Aquaponics is a new concept and a new crop for fish producers. They are unfamiliar with horticulture methods and the markets for the products produced. Production and marketing of ornamental plants is a big jump for trout producers serving the recreational and food market. Application of the methods demonstrated will take time for the producers to adopt. Initial work does not describe the range of costs the producer will face. More experience with these systems is necessary. Each flowing water system is unique. Integration of aquaponics into these systems will also be unique.
Pond system:
Un-graded adult baitfish (Fundulus heteroclitus) were stocked into 0.1-ha spawning ponds at between 450 and 500 kg/ha in the early spring. As water temperatures approach 15.5ºC, 50 spawning mats will be added to each brood pond. After eggs are laid, they were stocked directly into 0.05-ha grow-out ponds to reach fry densities of 125,000, 250,000 or 500,000 fry per hectare. Wallace and Waters (2004) estimate that approximately 67% of stocked eggs will hatch successfully, necessitating these ponds be stocked at approximately 185,000, 375,000 or 745,000 eggs/ha. A minimum of three ponds were stocked with baitfish for use in this project. A fourth pond did not have fish and will serve as a control. Fish in ponds were managed as per standard production protocols for the species. Specifically, fish in grow out ponds were monitored weekly and offered a minnow grower feed at 3% of the biomass per day. When water temperatures decline below 15.5ºC, ponds were harvested.
Water from each baitfish grow out pond and the control pond was pumped through one 18’ x 3’ x 2’ plant channel constructed of concrete block and pond liner material, as described previously. Each channel contained six 2’ x 3’ plant rafts and was planted with four species of aquatic plants as determined by the initial market survey Weekly water samples were collected from the inlet and outlet of each plant raceway and analyzed for TN, nitrogen species (ammonia/ammonium, nitrate/nitrite), TP, pH, alkalinity, dissolved oxygen and temperature.
Plants were randomly assigned to either one of the fish ponds or the control pond. Plant biomass was recorded at the beginning and end of the fish growing season (approximately from late March through late September) to determine a relative growth rate. Initial plant size was assessed prior to the placement of plant in the respective pond rafts. In addition, plant tissue samples were tested for total nitrogen (TN) and total phosphorus (TP) to determine nutrient uptake rates.
- Results and Discussion/Milestones
• Aquatic plant market survey identified that 125 ornamental, 270 restoration or mitigation, and 3 food aquatic plants species are marketed in various forms including tubers, bare root, 2 inch plugs, and several container sizes (pint, 4-6 inch and gallon). Prices ranged from $0.27-$3.50 for restoration species, and $2-19.00 for ornamental species.
• Over 360 people attended the 4 workshops and 4 presentations given at aquaculture meetings (see outreach section).
• Over 1,000 people toured the three integrated fish/aquatic plant systems
• It appears that no producers have implemented production of ornamental plants.
We are aware of one WV farmer who has produced salad greens.
Education
Websites:
Project web site: www.hpl.umces.edu/SARE
Abstracts:
• McIntosh, D., E. Markin, D. Wujtewicz and A. Lazur. 2008. Increasing Economic and Environmental Sustainability of Aquaculture Production Through Aquatic Plant Culture. Aquaculture America 2008 Book of Abstracts, Lake Buena Vista, FL, USA.
• Miller, J., K.M. Buzby, K.J. Semmens, A. Lazur, D. McIntosh and T.P. West. 2007. Use of Aquaponics as a Secondary Crop and Effluent Treatment in Ponds, Raceways and Recirculating Tank Systems. Hortscience 42(4):942-943.
Presentations:
• McIntosh, D. 2008. Integrating Aquatic Plant and Finfish Aquaculture. (poster). March 26, 2008. SARE 2008 National Conference, St. Louis, MO.
• McIntosh, D., E. Markin, D. Wujtewicz and A. Lazur. 2008. Increasing Economic and Environmental Sustainability of Aquaculture Production Through Aquatic Plant Culture. (oral). February 12, 2008. Aquaculture America 2008, Lake Buena Vista, FL.
• McIntosh, D. 2008. Increasing Economic and Environmental Sustainability of Aquaculture Systems Through Aquatic Plant Culture. January 9, 2008. DE Ag Week, Harrington, DE.
• Lazur, A., K. Semmens and D. McIntosh. 2006. Increasing Economic and Environmental Sustainability of Aquaculture Systems Through Aquatic Plant Culture. (oral). December 2006. Northeast Aquaculture Conference & Exposition 2006, Groton, CT.
• ASHS 2007 Annual Conference
Sponsored by: American Society for Horticultural Science
Location: Scottsdale, AZ
Date: 16 – 19 July 2007
Poster Title: Use of Aquaponics as a Secondary Crop and Effluent Treatment in Ponds, Raceways and Recirculating Tank Systems.
Authors: Miller*, J., K.M. Buzby, K.J. Semmens, A. Lazur, D. McIntosh and T.P. West
• 2008 Aquaculture Forum
Sponsored by: West Virginia Extension Service and West Virginia Aquaculture Association
Location: Charleson, WV
Date: 19 January 2008
Poster Title: Use of Aquaponics as a Secondary Crop and Effluent Treatment in Ponds, Raceways and Recirculating Tank Systems.
Authors: Miller*, J., K.M. Buzby, K.J. Semmens, A. Lazur, D. McIntosh and T.P. West
• 2009 Aquaculture Forum
Sponsored by: West Virginia Extension Service and West Virginia Aquaculture Association
Location: Moorefield, WV
Date: January 19, 2009
Poster Title: Use of Aquaponics as a Secondary Crop and Effluent Treatment in Ponds, Raceways and Recirculating Tank Systems.
Authors: Miller*, J., K.M. Buzby, K.J. Semmens, A. Lazur, D. McIntosh and T.P. West
Popular Press Articles
• McIntosh, D. and G. Ozbay. 2007. Cleaning Pond Water with Native Aquatic Plants. The Downstate Daily, Sunday July15, 2007.
• McIntosh, D. 2006. Demonstration Project On Integrating Plant Culture With Aquaculture. DSU Aquatic Sciences Newsletter, Spring 2006. >250 hard copies + 50 electronic copies.
• McIntosh, D. 2008. Increasing Economic and Environmental Sustainability of Aquaculture Production Systems Through Aquatic Plant Culture - Project Update. DSU Aquatic Sciences Newsletter, Winter 2008. >250 hard copies + 50 electronic copies.
In addition to the workshops, we sought to introduce the aquaponics concept to growers and the general public at aquaculture meetings. Presentations made at these meetings are posted on the WV Aquaculture Extension web site.
• Culture of Aquatic Plants: Environmental and Economic Opportunities by Andy Lazur, 2006. Aquaculture Forum, January 21, Jackson’s Mill, WV. 97 attendees. Evaluation 32 responses, Score of 4.13 out of a possible 5.
• Integration of Aquatic Plant Culture as a Secondary Crop and Effluent Treatment in Ponds, Raceways and Recirculating Tank Systems by Andy Lazur, Dennis McIntosh and Ken Semmens, Northeast Aquaculture Conference and Exposition. Dec 7, 2006.
• Aquaponics By Todd West and Karen Buzby. 2008 Aquaculture Forum, January 19, Ramada Plaza, Charleston, WV. 74 attendees. Evaluation, 40 responses, 12 producers. Score 4.37 out of a possible 5.
• Reymann Memorial Farm Aquaponics Research and Demonstration facility has about 150 visitors annually.
• Tour of Aquaculture Facility including the Aquaponics Greenhouse as part of the 2009 Aquaculture Forum. January 16, 2009. 15 attendees.
Number of workshops and people attended
• 2008 DSU Aquaculture Research and Demonstration Facility Open House. June 25. 2008. 45 attendees.
• 2007 DSU Aquaculture Research and Demonstration Facility Open House. June 12, 2007. 37 attendees.
• Increasing Economic and Environmental Sustainability of Aquaculture Production Systems Through Aquatic Plant Culture. March 2, 2006. 7 attendees.
Tours/demonstration and number of people contacted including description of people such as farmers, investors, etc...
• The DSU Aquaculture Research and Demonstration Facility is routinely used for tours. Tours typically include an overview of all of the research and demonstration projects being conducted at the Facility and are geared toward the group that has come in. We have provided tours for high school and middle school classes, private individuals, state and national legislatures, and folks from several federal and state agencies. Since the projects’ beginning we have had 511 visitors to the facility.
Number of farmers where technology was implemented in DE and brief description of system:
• None to report at this time, though several groups have expressed an interest in doing so.
Three local high school agriculture programs have received plants from DSU and have incorporated them into their aquaculture programs. All of the schools are using the plants in conjunction with their recirculating aquaculture systems. Polytech high school in Woodside, DE has used the plants provided by this project as a source of propagation material for a created wetland at their school and for a wetland restoration project in conjunction with DNREC (Delaware Department of Natural Resources and Environmental Control).
Additional Project Outcomes
Impacts of Results/Outcomes
Recirculating tank system:
The results of the recirculating tank fish/aquatic plant pilot systems are shown in Tables 4 and 5. Both fish and aquatic plant production were good. Plant growth was especially vigorous and nutrient uptake was approximately twice that of observed uptake in natural marshes. Hibiscus biomass production was 40% greater than Spartina. In addition, it was observed that the potential for taking cuttings from the hibiscus was high, averaging 15 cuttings from each plant and the Spartina plants could have been divided into approximately 6 plants. This capacity to derive multiple plants from one plant after taking up nutrients provides economic potential information.
Specific fish growth results are as follows:
After 138 days of culture, the fish grew from 0.32 lbs. to 1.27 lbs. Survival was 98.5%; growth rate was 3.12 grams/day and feed conversion ratio was 1.35.
Plant gorwth specifics were:
Hibiscus rafts produced 30.17 lbs dry weight; and nitrogen uptake was 0.0198 lbs/square foot; and phosphorus uptake was 0.0027 lbs/square foot.
Raceway System:
Effluent nutrient concentrations were low due to the flow-through nature of the fish culture method and low fish biomass. Nutrient concentrations in the effluent were not measurably reduced by either Hibiscus or Iris (Table 6.).
Iris versicolor significantly produced more biomass over the 15 week production cycle as compared to the other two Hibiscus cultivars evaluated (Fig. 4.). There was no significant difference from the two growing season, 2006 and 2007. Hibiscus ‘Moy Grande’ had a significant growth increase beginning in Week 6 and did not slow during the remainder of the growing season as compared to the other two species which showed slower growth trends. Nutrients were a limiting factor in biomass production and fish effluent nutrient removal. Nutrient deficiencies (nitrogen) were seen in both Hibiscus species with nitrogen deficiencies being more apparent in Hibiscus ‘Moy Grande’. This visual deficiency symptom was verified with Hibiscus ‘Fireball’ having significantly more nitrogen content as compared to Blueflag Iris and Hibiscus ‘Moy Grande’ (Fig. 2). A related species of Hibiscus, H. rosa-sinensis has been reported to have 3.5% total nitrogen content in leaf tissue which is significantly higher than the nitrogen content in both Hibiscus species evaluated in this study. Initial plant nutrient content was not evaluated which makes it difficult to determine amount of actual nutrient uptake during the growing seasons.
Several factors may play a role in the low removal of nutrients from the flow-through raceway effluent. Since the water source to the raceways is an artesian spring, water temperatures average 11°C with little variation throughout the year. Optimum growth of many plants occurs with root zone temperatures between 22 & 35 °C (Bode Stolzfus et al. 1998). Nutrient uptake is less efficient at lower temperatures.
Additionally, nutrient concentrations in the effluent were low, especially with respect to those found in recirculating systems.
Pond integrated system:
Although the changes in nutrient levels between plant channel in-flow and out-flow were not large enough to be statistically significant, there was a clear trend towards a reduction in total phosphorus as affected by plant uptake. Similarly, both the Swamp Hibiscus and the Iris appeared to thrive in the integrated system, increasing in weight by more than 50% and 55%, respectively.
It is important to note that based on preliminary findings of this study, the investigators received another research project: Evaluating restoration and mitigation aquatic plant species and markets to advance the commercialization of the industry. USDA Northeast Regional Aquaculture Center. 2007-2009. This study will further investigate the nutrient uptake potential of twelve aquatic plant species and conduct field evaluations of plant growth and nutrient uptake in stormwater ponds, trout raceways, ponds and a salmon hatchery.
Economic Analysis
Raceway/aquatic plant system:
This project has introduced a new idea to a group of small farmers with limited resources. Finding the optimal way to conduct aquaponics will depend greatly on potential profitability.
Greenhouse 3500.00 3500.00
Pump 500.00 500.00
Plant channels (6)
plywood, screws, glue etc. 456.38
EPDM Liner 421.34
Bulkhead fittings 198.63
Planting supplies
Rafts 871.92
Pots 90.00
Strips 450.00
Mum Mix 39.00
1450.92
S&H 263.07 1713.99
Plants
450 Hibiscus 787.50
450 Iris 787.50 1575.00
S&H 181.46 1756.46
Total Expenditures $8,546.80
Retail Plant Value (Initial plant cost x 3) 1575.00 4725.00
Wholesale Value (Initial plant cost x 2) 1575.00 3150.00
Labor costs are not included in the economic analysis. Labor requirements for this system include establishing the necessary infrastructure (greenhouse, plant channels, plumbing, etc.). The largest annual labor requirement involves preparing and placing the plants into the system. Once the plants are placed into the plant channel, very little labor is required for culturing the plants as compared to conventional ornamental plant production systems. Conventional greenhouse production have high labor requirements for watering by hand or increased infrastructure costs of an automated watering system which is eliminated utilizing this aquaponics flow-through system.
Recirculating tank/aquatic plant system:
Item Cost
Plant channels (6)
plywood, screws, glue etc. 410.00
EPDM Liner 395.00
Bulkhead fittings 278.00
Pump 315.00 $1,398.00
Planting supplies
Rafts 872.00
Pots 90.00
Strips 450.00
Mum Mix 39.00
1451.00
S&H 263.07 $1,714.07
Plants
450 Hibiscus 787.50
450 Spartina 150.00
937.50 $1,087.50
S&H 150.00
Electricity 310.00
Total Expenditures $4,199.57
Retail Plant Value $2,325
Wholesale Value $1,750
Value of cuttings from Hibicsus $4,250.00
Labor was not included in budget, but was estimated at 16 hours for planting, 0.5 hour per day plant maintenance, and 20 hours for plant harvest. An additional 16 hours is estimated for taking and potting cuttings on the hibiscus. The Spartina plants could be divided and sold as smaller plants also. The raceways, rafts, pots and planting strips can be used for at least five years. Taking this into account and depreciating the system costs over five years ($623/year), and the retail value of plants and cuttings, and 112 hours of estimated labor @ $10/hour, the total costs are $3,140.50. Assuming the value of the hibiscus cuttings @$1.00 or $4,800 total (400 plants x 12 cuttings/plant), then a net gain of $1,659.50 is achieved.
It is important to note that the cost of the fish recirculating system is not included in the budget. The assumption is that the plant system is designed to reduce nutrient effluent and serve as a secondary crop. Furthermore, the plant filter system was a pilot scale operation and used to generate initial findings to ascertain potential utility to reduce nutrients and produce aquatic plants using only fish waste. The pilot system is not properly sized to remediate all of the nitrogen from the fish system. A complete analysis of the integrated system would be necessary to assess the biological and economical sustainability of the system, The results of these pilot systems, does demonstrate the utility of using aquatic plants as biofilters and means of generating a secondary crop. However, a number of additional questions arise including: proper species selection and fish culture criteria, water temperature effect on plant growth, water exchange rate in channels, proper sizing of plant to fish ratio, local demand of aquatic plants, and fish producer’s time availability for plant system operation.
Farmer Adoption
Though numerous farmers gained educational material, visited the three fish/plant systems, only one farmer adopted the technology during the study. Other farmers are interested in adopting, but have limited time, funds, and knowledge required to justify the risk of installing a new production system and entering a new market at this time. Adoption of this concept will take time. Researchers, extension agents, and farmers have seen that aquaponics has merit and that more work should be done. It is expected that a variety of plants can be produced and that the impact on water quality will vary with the scale of the system and its design. Interest in using a plant system to extract nutrients appears to be increasingly attractive to farmers. The demonstration systems were very useful in education, but a number of factors appear to have limited farmer implementation. Among these are limited cash flow of small farmers to expand production systems, slow down in economy and demand for fish, and concern over time inputs required to add another crop in their operations. In addition, in the case of Maryland as well as other parts of the northeast, numerous fish culture operations closed during this period due to economic reasons.
Areas needing additional study
The type of plants grown, production strategies, marketing strategies, product volume, and system design all influence profitability of an aquaponic enterprise which is integrated into an existing aquaculture business. It is reasonable to select the best apparent opportunity and scale up production to collect economic data and begin assessing market potential.
Plants utilized in this study were found to be salable at the end of the growing season. Typically this is not a common time of the year to get the highest marketable value for ornamental plants in a retail market. Retail sales of these plants may require the grower to overwinter the plants until the next year for market sale. The fall season could be very desirable for wholesale markets including sales for restoration projects. So further studies on proper plant selection need to be conducted which would include plants that could be salable in the current season such as focusing on fall plant crops such as mums and/or pansies that have high market value at the end of the growing season. Further study needs to be conducted on when to start the growing season to be able to capitalize on spring markets.
Discussions with fish growers interested in incorporating aquaponics into an existing flow-through fish culture system revealed a wide diversity of water quality variables that would impact plant selection and production. Variables included water availability, nutrient content, and water temperature. Recommendations regarding aquaponic system size, suggested plants and expected income generated from such a system are difficult to make currently, as little research has been conducted on aquaponics in flow-through systems.
In the trout raceway system, we observed slight increases in nitrogen levels leaving our plant channels. Anecdotally, it seems as though the plants’ root masses are acting as solids collection unit (i.e. removing suspended solid wastes and phytoplankton from the pond water), resulting is a heavy buildup of organic matter in the plant trays. As a result, we believe that this organic matter is decomposing and in the process leaching additional nutrients into the effluent water. Further study into the case and possible solutions to this problem are needed.
Other observations from the recirculating tank system, show excellent plant growth with plant biomass more than twice that of observed growth in restored marshes. In addition, the plant system as sized showed slightly better nitrogen uptake than the 12 foot tall fluidized bed sand filter that also operated in the system during the study. In comparison with the raceway and pond system, the recirculating tank system exhibited significantly greater plant growth most likely due to the increased nitrogen and phosphorus levels due to much higher feeding rates per volume of water. Water temperatures were also in more favorable ranges for plant growth compared to the trout system.
The concept of integrating aquatic plants with fish culture, or other livestock nutrient sources, is effective in reducing nutrient discharges and can offer farm diversification and secondary economic returns. The big question asked by farmers is seeing more details on properly sizing an integrated fish/plant system so that investment costs and potential returns can be estimated. Larger scale demonstrations of integrated systems would be helpful in increasing farmer adoption.