Traditional production of container-grown plants involves the input of water, fertilizers, pesticides, and other agricultural chemicals. Excessive leaching of nutrients and pesticides from containerized crops grown in soilless substrate may occur when production is not managed appropriately (Schoene et al., 2006). The resulting runoff can be discharged from production areas and pollute surface and groundwater. Excess nutrients, notably nitrate–nitrogen (NO3 −N) and soluble reactive phosphorus (PO4 3−, H2PO4 −, H2PO4 2−, and H3PO4−), encourage algal growth and accelerate eutrophication, primarily in freshwater systems. Also, high levels of nitrates in drinking water can cause methemoglobinemia in infants (“Blue Baby Syndrome”). To protect drinking water quality, the U.S. Environmental Protection Agency (EPA) mandates maximum allowable NO3 −N contaminant levels in any discharged water at 10 mg·L−1 (U.S. EPA, 1986). Federal limits on phosphorus (P) concentrations in freshwater have not been set, but the U.S. EPA recommends that total phosphates and total P levels not exceed 0.05 mg·L−1 and 0.1 mg·L−1, respectively (U.S. EPA, 1986). Greenhouse wastewater typically contains 100 mg·L−1 NO3 −N (Wood et al., 1999), whereas nursery runoff levels of NO3 −N range from 0.1 to 135 mg·L−1 (Alexander, 1993; Taylor et al., 2006; Yeager et al., 1993). A range of 0.01 to 20 mg·L−1 P has been reported in nursery runoff (Alexander, 1993; Headley et al., 2001; Taylor et al., 2006).
The future of container nursery irrigation, according to 12 irrigation scientists, growers, and nursery organization directors, will be shaped by increasingly stringent regulations as many provisions of the 1972 Federal Clean Water Act are enforced (Beeson et al., 2004). Environmental concerns and regulatory pressure to reduce nutrient loadings in surface waters have led to the EPA enforcing its Total Maximum Daily Load (TMDL) program for all watersheds and bodies of water (U.S. EPA, 2000). Section 303(d)(1)(C) of the Clean Water Act defines the TMDL as the “level necessary to implement the applicable water quality standards.” U.S. states are mandated to develop an appropriate TMDL for each water body and for each identified pollutant, which involves quantifying the total amount of pollutant loading a water body can receive from point and nonpoint sources and still maintain its designated use and value (e.g., drinking water, fish and wildlife habitat, and recreation). TMDLs of nutrients in agricultural runoff were recently adopted by environmental regulatory agencies in every state (Yeager, 2006). Nutrient-loading criteria for natural waters will eventually be established in every state. Furthermore, several states, including Maryland, Delaware, and California, have enacted nutrient management laws to control the quantity of fertilizer applied and to monitor the concentration of nutrients detected in nursery runoff (Beeson et al., 2004).
To comply with stricter environmental regulations, constructed wetlands have been promoted as a low-cost technology for reducing nutrient levels, pesticides, and other organic contaminants from nursery and greenhouse discharge water (Berghage et al., 1999; Fernandez et al., 1999). Two constructed wetland designs, surface flow and subsurface flow-constructed wetlands, are commonly used to treat agricultural wastewater (Berghage et al., 1999; Scholz and Lee, 2005). The large land area required by typical surface flow-constructed wetlands, which resemble natural wetlands, and the concomitant loss of production area has made them less suitable for greenhouse and nursery water treatment than subsurface flow-constructed wetlands (Berghage et al., 1999).
Subsurface flow-constructed wetlands consist of a lined or impermeable basin filled with a coarse medium having high hydraulic conductivity, typically gravel, and wetland plants (Kadlec and Knight, 1996). They can be operated in flow-through or batch treatment modes with varying hydraulic residence times (Burgoon et al., 1995). Removal or transformation of nitrogen (N) and P occurs through microbial assimilation/transformation, decomposition, plant uptake, adsorption–fixation, sedimentation, and volatilization (Brix and Schierup, 1989).
Plants have both dominant and supporting roles in N and P recovery. Besides the direct assimilation of N and P from wastewater, plant roots and rhizomes support microbial activity and facilitate microbial nitrification in gravel-based constructed wetlands (Gersberg et al., 1986; Huett et al., 2005). Their roots offer colonizing sites and exude carbohydrates, sugars, amino acids, enzymes, and many other compounds (Rovira, 1969). Certain plants oxidize the rhizosphere (Gersberg et al., 1986; Moorhead and Reddy, 1988), which also supports microbial growth and aids in the decomposition of organic matter.
Widely used aquatic emergent plants in subsurface flow-constructed wetland designs include reed canarygrass (Phalaris arundinacea L), common reed [Phragmites australis (Cav.) Trin. ex Steud.], reed mannagrass [Glyceria maxima (Hartman) Holmb.], softstem bulrush [Schoenoplectus tabernaemontani (C. C. Gmel.) Palla], yellow flag (Iris pseudacorus L.), and cattail (Typha spp. L.) (Conley et al., 1991; Hunter et al., 2001). Although the performance of these aforementioned “wetland” plants in wastewater treatment has been well-documented, their widespread use has been tempered by concerns of invasiveness in certain ecosystems and high rates of biomass production and subsequent decomposition, which necessitate harvesting and removal.
Our study investigated a sustainable alternative to traditional wetland plants in constructed wetlands, specifically saleable horticultural plants with remediation potential. Similar to obligate wetland species, aquatic garden plants also thrive in waterlogged environments and offer the potential benefits of phytoremediation and economical value. In addition, they provide aesthetic value to subsurface flow treatment wetlands, which is important to nurseries and greenhouses located in highly populated urban areas (Fraser et al., 2004; Wood et al., 1999). Few studies have examined the survival of aquatic garden plants in subsurface flow-constructed wetlands and their ability to recover nursery runoff rates of N and P (Arnold et al., 1999, 2003; Holt et al., 1999; B. K. Maynard, personal communication). Our objective was to evaluate commercially important species and cultivars of aquatic garden plants in a simple laboratory scale wetland system within the controlled environment of a greenhouse for their ability to grow and recover N and P.
Anonymous 2000 Plant tissue and feed and forage analysis procedures Clemson Agric. Serv. Lab., Clemson Univ Clemson, SC 22 May 2007 <http://www.clemson.edu/agsrvlb/procedures2/photo.htm>
Arnold, M.A., Lesikar, B.J., Kenimer, A.L. & Wilkerson, D.C. 1999 Spring recovery of constructed wetland plants affects nutrient removal from nursery runoff J. Environ. Hort. 17 5 10
Arnold, M.A., Lesikar, B.J., McDonald, G.V., Bryan, D.L. & Gross, A. 2003 Irrigating landscape bedding plants and cut flowers with recycled nursery runoff and constructed wetland treated water J. Environ. Hort. 21 89 98
Barbieri, R. & Esteves, F.A. 1991 The chemical composition of some aquatic macrophyte species and implications for the metabolism of a tropical lacustrine ecosystem—Lobo Reservoir, Sao Paulo, Brazil Hydrobiol. 213 133 140
Barbieri, R., Esteves, F.A. & Reid, J.W. 1984 Contribution of two aquatic macrophytes to the nutrient budget of Lobo Reservoir, Sao Paulo, Brazil Verh. Int. Limnol. 22 1631 1635
Beeson R.C. Jr, Arnold, M.A., Bilderback, T.E., Bolusky, B., Chandler, S., Gramling, H.M., Lea-Cox, J.D., Harris, J.R., Klinger, P.J., Mathers, H.M., Ruter, J.M. & Yeager, T.H. 2004 Strategic vision of container nursery irrigation in the next ten years J. Env. Hort. 22 113 115
Berghage, R.D., MacNeal, E.P., Wheeler, E.F. & Zachritz, W.H. 1999 ‘Green’ water treatment for the green industries: Opportunities for biofiltration of greenhouse and nursery irrigation water and runoff with constructed wetlands HortScience. 34 50 54
Boyd, C.E. 1975 Chemical composition of wetland plants Good R.E., Whigham D.F. & Simpson R.L. Freshwater wetlands: Ecological processes and management potential Academic Press New York
Burgoon, P.S., Reddy, K.R. & DeBusk, T.A. 1995 Performance of subsurface-flow wetlands with batch-load and continuous-flow conditions Water Environ. Res. 67 855 862
Caillet, M., Campbell, J.F., Vaughn, K.C. & Vercher, D. 2000 The Louisiana iris; the taming of a native American wildflower 2nd ed Timber Press Portland, OR
Chambers, R.M. & Fourqurean, J.W. 1991 Alternative criteria for assessing nutrient limitation of a wetland macrophyte [Peltandra virginica (L.) Kunth] Aquat. Bot. 40 305 320
Conley, L.M., Dick, R.I. & Lion, L.W. 1991 An assessment of the root zone method of wastewater treatment Res. J. Wat. Poll. Contr. Fed. 63 239 247
DeBusk, T.A., Dierberg, F.E. & Reddy, K.R. 1995 Use of aquatic and terrestrial plants for removing phosphorus from dairy wastewaters Ecol. Eng. 5 371 390
Fernandez, R.T., Whitwell, T., Riley, M.B. & Bernard, C.R. 1999 Evaluating semiaquatic herbaceous perennials for use in herbicide phytoremediation J. Amer. Soc. Hort. Sci. 124 539 544
Fraser, L.H., Carty, S.M. & Steer, D. 2004 A test of four plant species to reduce total nitrogen and total phosphorus from soil leachate in subsurface wetland microcosms Bio. Tech. 94 185 192
Gersberg, R.M., Elkins, B.V., Lyon, S.R. & Goldman, C.R. 1986 Role of aquatic plants in wastewater treatment by artificial wetlands Water Res. 20 363 368
Greenway, M. & Woolley, A. 1999 Constructed wetlands in Queensland: Performance efficiency and nutrient bioaccumulation Ecol. Eng. 12 39 55
Gustafsson, J.P. 2007 Visual Minteq, ver. 2.52 Dept. of Land and Water Resour. Eng Stockholm 23 May 2007 <http//www.lwr.kth.se/English/OurSoftware/vminteq/>
Headley, T.R., Huett, D.O. & Davison, L. 2001 The removal of nutrients from plant nursery irrigation runoff in subsurface horizontal-flow wetlands Wat. Sci. Tech. 44 77 84
Holt, T.C., Maynard, B.K. & Johnson, W.A. 1999 Nutrient removal by five ornamental wetland plant species grown in treatment-production wetland biofilters HortScience. 34 521 (abstr.)
Huett, D.O., Morris, S.G., Smith, G. & Hunt, N. 2005 Nitrogen and phosphorus removal from plant nursery runoff in vegetated and unvegetated subsurface-flow wetlands Water Res. 39 3259 3272
Hunter, R.G., Combs, D.L. & George, D.B. 2001 Nitrogen, phosphorous, and organic carbon removal in simulated wetland treatment systems Arch. Environ. Contam. Toxicol. 41 274 281
Kingsbury, N. 2006 The new poolside: Cleaned by plants instead of chemicals; natural swimming pools are a fitting choice for gardeners Horticulture 103 54 59
Nyakang'o, J.B. & van Bruggen, J.J.A. 1999 Combination of a well functioning constructed wetland with a pleasing landscape design in Nairobi, Kenya Wat. Sci. Tech. 40 249 256
Romero, J.A., Brix, H. & Comin, F.A. 1999 Interactive effects of N and P on growth, nutrient allocation and NH4 uptake kinetics by Phragmites australis Aquat. Bot. 64 369 380
Schoene, G., Yeager, T. & Haman, D. 2006 Survey of container nursery irrigation practices in west-central Florida: An educational opportunity HortTechnology 16 682 685
Tanner, C.C. 1996 Plants for constructed wetland treatment systems: A comparison of the growth and nutrient uptake of eight emergent species Ecol. Eng. 7 59 83
Tanner, C.C., Clayton, J.S. & Upsdell, M.P. 1995 Effect of loading rate and planting on treatment of dairy farm wastewaters in constructed wetlands. II. Removal of nitrogen and phosphorus Water Res. 29 27 34
Taylor, M.D., White, S.A., Chandler, S.L., Klaine, S.J. & Whitwell, T. 2006 Nutrient management of nursery runoff water using constructed wetland systems HortTechnology 16 610 614
U.S. Environmental Protection Agency (EPA) 1986 Quality criteria for water. EPA Rpt. 440/5-86-001. U.S. EPA Office of Water Regulations and Standards U.S. Gov. Print. Office (PB87-226759) Washington, DC
U.S. EPA 2000 The total maximum daily load (TMDL) program. EPA 841-F-00-009. Office of Water Regulations and Standards U.S. Gov. Print. Office Washington, DC 15 May 2007 <http://www.epa.gov/owow/tmdl/overviewfs.html>
Wood, S.L., Wheeler, E.F., Berghage, R.D. & Graves, R.E. 1999 Temperature effects on wastewater nitrate removal in laboratory-scale constructed wetlands Amer. Soc. of Agr. Eng. 42 185 190
Yeager, T., Wright, R., Fare, D., Gilliam, C., Johnson, J., Bilderback, T. & Zondag, R. 1993 Six state survey of container nitrate nitrogen runoff J. Environ. Hort. 11 206 208