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Container-grown plants from commercial nurseries require large amounts of water and nutrients during their production cycle resulting in substantial runoff contaminated with nitrogen and phosphorus. Thus, mitigation of nutrients from exiting runoff water is a serious concern for horticultural concerns. Wight Nurseries of Monrovia Growers, Cairo, Ga., has installed 3.77 ha of planted wetlands to receive direct runoff in excess of recapture needs from a 48.6 ha drainage basin and excess water diverted from adjacent watersheds. Water flows though trench drains between wetland cells and eventually into stilling ponds before it is allowed to exit the property. Water flow through the wetlands ranges from 1.6 million to 2.2 million liters per day. Two years of monitoring data indicates strong seasonal differences in nitrate and nitrite nitrogen removal efficiencies. Nitrogen removal between April and November averaged 93.3% while removal during winter months averaged 44.1%. Nitrite was not found in wetland discharge water samples. Nitrogen as nitrate in discharge water varied from 0.05 ppm to 4.3 ppm, well below drinking water quality standards, and was below 0.6 ppm between June and November except in September during construction activity. Orthophosphate phosphorus removal was highly variable with highest removal during late spring, averaging 33.6%, and some removal during early fall, averaging 13.8%. However, there was a significant net export of phosphorus from the wetlands during winter months and during periods of low vegetative growth. Phosphorus levels ranged between 0.9 and 1.9 ppm. While there is currently no legal water quality standard, these levels are above the generally accepted level of 0.01 ppm for preventing downstream eutrophication.

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Mitigation of offsite movement of nutrients in nursery runoff is a serious concern for commercial nurseries with container-grown plants. Wight Nurseries, Cairo, Ga. has operated 3.77 ha of planted constructed wetlands since 1996 to remediate nutrients from runoff. The wetlands receive drainage from a 48.6 ha nursery production area. Monitoring by nursery staff had suggested net export of nitrogen and phosphorus may occur during spring regeneration. Intensive monitoring was conducted between early March and mid-May 2003. There was no net export of nitrogen during the study. Nitrite nitrogen removal remained at 100% in the 1st stage wetland throughout March but declined in April to 89.6% as loading increased 5-fold. However, the 2nd stage wetland removed 100% of the remaining nitrite. Nitrate removal in the 1st stage wetland was high through early April (97.6%) but low in 2nd stage wetlands (16%) until loading increased 10-fold when efficiency rose to 94.9%. Nitrate removal by the 1st stage declined during mid-April but 2nd stage efficiency remained above 95%. For phosphorus, there was net export during March from both stages. However, during April, the wetlands removed phosphorus although loading tripled during the month. In May, net export of phosphorus from the wetlands recommenced with peak 1st stage export of 130% and 2nd stage uptake declining until mid-May when export began again. Neither water temperature nor rainfall appeared correlated with wetland efficiency. While phosphorus was exported by the wetlands during parts of the study, neither nitrate nor nitrite was exported as spring progressed and decomposition of last year's growth accelerated.

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Substantial quantities of water and nutrients are required for the production of high value nursery and greenhouse crops. As water quality criteria are strengthened locally and nationally, horticultural enterprises will have to meet stricter limits on nutrients in discharge water. This study examined the efficacy of an established vegetated surface-flow constructed wetland to mediate nitrogen (N) and phosphorus (P) in runoff water from a commercial nursery over a period of 38 months. Maximum oxidized nitrogen [nitrate-N (NO3-N) + nitrite-N (NO2-N)] inputs occurred during the spring fertilization period of March through May (11.1 to 29.9 mg·L–1 N) and minimum inputs occurred during winter plant dormancy between December and February (2.8 to 5.2 mg·L–1 N). Nitrogen remediation efficiency averaged 94.7% for March through November sampling dates but declined to a mean of 70.7% between December and February when mean wetland water temperature dropped below 15 °C. Orthophosphate phosphorus (PO4-P) concentrations in nursery runoff showed no dramatic changes over months, seasons, or years. Mean wetland influent orthophosphate concentration ranged from 0.7 to 2.2 mg·L–1 PO4-P with an overall mean of 1.41 mg·L–1 PO4-P for all months sampled. Mean discharge orthophosphate concentration ranged from 0.5 to 2.1 mg·L–1 PO4-P with a mean of 1.45 mg·L–1 PO4-P. Phosphorus remediation efficiency varied widely and there was no correlation with water temperature. This 9.31-acre surface-flow constructed wetland was highly efficient at removing N from nursery runoff from a 120-acre catchment (large container production area), although it failed to consistently lower orthophosphate levels in runoff. This type of constructed wetland is suitable for removing oxidized N forms from nursery runoff and, depending on size, is capable of handling the large volumes of runoff generated by medium to large nursery and greenhouse operations.

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Commercial nurseries utilize large amounts of water and nutrients during the production cycle of container-grown plants. Excess water contaminated with N and P can impact the quality of surface water and groundwater. Earlier work by the authors found that constructed wetlands are highly efficient for removing N at water temperatures above 15 °C. However, PO4 removal was highly variable with uptake coinciding with periods of active plant growth and net export occurring during all other periods. Ornamental plants that remediate nutrients, especially phosphorus, would be very useful in designing constructed wetlands for commercial nurseries and greenhouses, rain gardens, and homeowner buffer strips. A greenhouse study was initiated in 2003 at Clemson Univ.'s Biosystems Research Complex to screen commercially available ornamental plants for their phytoremediation potential. Among others, these included the woody ornamental plants Cornus amomum, Myrica cerifera `Emperor', and Salix integra `Hakura Nishiki' and the semiaquatic herbaceous ornamental plants Canna `Bengal Tiger' and `King Humbert', Colocasia esculenta `Illustris', Rhynchospora colorata, Iris virginica `Full Eclipse, Pontederia cordata `Singapore Pink', and Thalia geniculata `Red Stem'. Plants were grown in pea gravel media kept saturated with one of five concentrations of Hoagland's Solution. Herbaceous and woody ornamental plants were harvested after 8 and 13 weeks, respectively. Water usage and biomass production were measured and nitrogen and phosphorus uptake was assessed. Experiments were replicated twice for each cultivar. Results indicate several species have the potential to be used in phytoremediation systems.

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Container-grown plants require large amounts of water and nutrients during their production cycle. This results in substantial runoff that is contaminated with nitrogen and phosphorus. At our study site, nutrients were delivered through incorporation in the potting media as timed-release prills and through liquid feeding by injection into irrigation water. Mitigation of nutrients in runoff water was dealt with proactively by the container nursery with construction of 3.77 ha of planted wetlands to receive runoff from a 48.6-ha drainage basin and excess water diverted from adjacent watersheds. Water flowed though drains between wetland cells and eventually into stilling ponds before it was allowed to exit the property. Water flow through the wetlands ranged from 1.1 to 3.1 million liters per day over the period. Three years of monitoring data indicate some seasonal differences in nitrogen removal efficiencies. Nitrogen removal between March and November averaged ≥95% while removal during winter (December through February) averaged ≥72%. Nitrogen (as nitrate) varied from 4.28 ppm to ≤0.01 ppm in wetland discharge, well below drinking water quality standards, but occasionally above levels that may cause downstream eutrophication. Orthophosphate phosphorus removal was highly variable with greatest removal occurring during late spring, late fall, and winter. There was a significant net export of phosphorus during some summer months for years 2 and 3. Phosphorus levels in wetland discharge ranged between 0.84 and 2.75 ppm. While there is currently no legal water quality standard for phosphorus, these levels were above the generally accepted level for preventing downstream eutrophication.

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Commercial nurseries use large amounts of water and nutrients during production cycles. Runoff contaminated with N and P can adversely impact surface and groundwater quality. A 3-year monitoring study of nutrient mitigation by a constructed wetland at a container nursery found nitrogen removal was highly efficient. However, orthophosphate-P removal was highly variable. Partial removal occurred during some months, but net export also occurred. P levels in wetland discharge—between 0.84 and 2.75 ppm—were well above the generally accepted level for preventing downstream eutrophication. Therefore, identifying landscape plants that remediate nutrients, especially P, could be useful in improving constructed wetlands. A 2003 greenhouse study screened commercially available landscape plants for their phytoremediation potential. Among the 17 taxa and 19 cultivars examined were woody shrubs, e.g., Cornusamomum, Myricacerifera`Emperor', and Salix integra `Hakura Nishiki'; herbaceous semiaquatics, e.g., Canna(two cultivars), Colocasia esculenta `Illustris', Rhyncospora colorata, Iris`Full Eclipse', Pontederia cordata `Singapore Pink', and Thalia geniculata `Red Stem'; and floating aquatics, e.g., Myriophyllum aquaticum, Eichhornia crassipes, and Pistia stratiotes. Plants were grown in pea gravel media and kept saturated with one of five concentrations of Hoagland's. Herbaceous and woody plants were harvested after 8 and 13 weeks, respectively. Experiments were replicated twice for each cultivar. The nutrient uptake efficiency was determined for each taxon from the total amount of N and P applied and the biomass dry weight and N and P content.

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Commercial nurseries use large amounts of water and nutrients to produce container-grown plants. The large volume of runoff containing nitrogen (N) and phosphorus (P) that leaves nurseries can contaminate surface and groundwater. Subsurface flow-constructed wetlands have been shown to effectively treat agricultural, industrial, and residential wastewater and to be well-suited for growers with limited production space. We investigated the possibility of using commercially available aquatic garden plants in subsurface-constructed wetlands to remove nutrients in a laboratory scale, gravel-based system. Seven popular aquatic garden plants received N and P from Hoagland's nutrient solution every 2 days for 8 weeks. These rates (0.39 to 36.81 mg·L−1 of N and 0.07 to 6.77 mg·L−1 P, respectively) encompassed low to high rates of nutrients found at various points between the discharge and inflow points of other constructed wetland systems currently in use at commercial nurseries. Plant biomass, nutrient recovery, and tissue nutrient concentration and content were measured. Whole plant dry weight positively correlated with total N and P supplied. Louisiana Iris hybrid ‘Full Eclipse’, Canna × generalis Bailey (pro sp.) ‘Bengal Tiger’, Canna × generalis Bailey (pro sp.) ‘Yellow King Humbert’, Colocasia esculenta (L.) Schott ‘Illustris', Peltandra virginica (L.) Schott, and Pontederia cordata L. ‘Singapore Pink’ had the greatest N recovery rates. The P recovery rates were similar for the cannas, Colocasia esculenta ‘Illustris’, Louisiana Iris ‘Full Eclipse’, Pe. virginica, and Po. cordata ‘Singapore Pink’. The potential exists for creating a sustainable nursery and greenhouse production system that incorporates a subsurface-constructed wetland planted with marketable horticultural crops that provide remediation and revenue.

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Intensive production of container-grown nursery and greenhouse crops in soilless substrate may result in significant leaching of nutrients and pesticides. The resulting runoff can escape from production areas and negatively impact surface and ground water. Constructed wetlands (CWs) have been shown to be a simple, low-technology method for treating agricultural, industrial, and municipal wastewater. We investigated the nitrogen (N) and phosphorus (P) removal potential by a vegetated, laboratory-scale subsurface flow (SSF) CW system. Over an 8-week period, five commercially available aquatic garden plants received a range of N and P (0.39 to 36.81 mg·L−1 N and 0.07 to 6.77 mg·L−1 P) that spanned the rates detected in nursery runoff. Whole plant dry weight was positively correlated with N and P supplied. Highest N and P recovery rates were exhibited by Thalia geniculata f. rheumoides Shuey and Oenenathe javanica (Blume) DC. ‘Flamingo’, Phyla lanceolata (Michx.) Greene also had high P recovery rates. The potential exists for using SSF CWs to concomitantly produce aquatic garden plants and attenuate nutrients in a sustainable nursery enterprise.

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