Phosphorus retention in lab and field-scale subsurface-flow wetlands treating plant nursery runoff |
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Authors: | Sarah A. White Milton D. Taylor Joseph P. Albano Ted Whitwell Stephen J. Klaine |
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Affiliation: | aDepartment of Environmental Horticulture, Clemson University, E-143 Poole Agricultural Center, Clemson, SC 29634-0319, United States;bClemson Institute of Environmental Toxicology, 509 Westinghouse Rd., PO Box 709, Pendleton, SC 29670, United States;cU.S. Department of Agriculture, Agricultural Research Service, U.S. Horticulture Research Laboratory, 2001 South Rock Road, Ft. Pierce, FL 34945, United States |
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Abstract: | Constructed wetland systems built to handle nutrient contaminants are often efficient at removing nitrogen, but ineffective at reducing phosphorus (P) loads. Incorporating a clay-based substrate can enhance P removal in subsurface-flow constructed wetland systems. We evaluated the potential of crushed brick, a recycled building product, and two particle sizes of a palygorskite–bentonite industrial mineral aggregate (calcined clay) to sorb P from simulated nutrient-rich plant nursery effluent. The three substrates were screened for P sorbing behavior using sorption, desorption, and equilibration experiments. We selected one substrate to evaluate in an 8-month field trial to compare field sorption capacity with laboratory sorption capacity. In the laboratory, coarse calcined clay average sorption capacity was 497 mg kg−1 and it sorbed the highest percentage of P supplied (76%), except at exposure concentrations >100 mg L−1 where the increased surface area of fine calcined clay augmented its P sorption capacity. Subsurface-flow mesocosms were filled with coarse calcined clay and exposed to a four and seven day hydraulic retention time treatment. Phosphorus export was reduced by 60 to 74% for both treatments until substrate P-binding sites began to saturate during month seven. During the eight month experiment, the four and seven day treatments fixed 1273 ± 22 mg kg−1 P and 937 ± 16 mg kg−1 P, respectively. Sequential extractions of the P saturated clay indicated that P could desorb slowly over time from various pools within the calcined clay; thus, if the calcined clay were recycled as a soil amendment, most P released would be slowly available for plant uptake and use. This study demonstrated the viability of using coarse calcined clay as a root bed substrate in subsurface-flow treatment wetlands remediating phosphorus from plant nursery runoff. |
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Keywords: | Calcined clay Sorption Desorption Treatment wetlands Agricultural runoff Phosphorus |
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