CONSTRUCTED WETLANDS FOR THE LANDSCAPE NURSERY INDUSTRY: NUTRIENT ASSIMILATION AND REMOVAL

Runoff from nursery operations is considered a potential non-point source contamination. Water quality and quantity are quickly becoming important factors that drive management practices at these facilities. Constructed wetland systems (CWS) are a management tool that can be used by nursery operations to improve water quality both for recycling within nursery production areas and for eventual release from nursery production areas into surrounding surface waters. The overall goal of this research was to optimize nutrient removal efficiencies in CWS. To accomplish this goal, I characterized the following: (1) the P sorption and desorption capacity of several substrates; (2) the effect of hydraulic retention time (HRT) and nutrient loading rate on nutrient retention efficiency in surface-flow CWS; (3) P sorption by an industrial mineral aggregate in a secondary, subsurface-flow treatment; (4) the impact of CWS planting style, whether floating mat, rooted plant material, or horticulturally-significant species, on nutrient removal; and (5) brick and industrial mineral aggregate root-bed substrate P sorption capacity under stable nutrient loading rates. The industrial mineral aggregate substrate displayed the greatest P sorption capacity of the substrates screened with a Langmuir Smax of 256.3 mg/kg P sorbed by the coarse aggregate (mesh size 4/20) and 462.9 mg/kg P sorbed by the fine aggregate (mesh size 24/48). Brick substrate (mesh size 4/20) exhibited substantially lower P sorption capacity with a Smax of only 6.79 mg/kg. The coarse aggregate sorbed 76% of the P in solution with exposure concentrations \u3c 100 mg P/L, and so seemed ideally suited as a subsurface flow CWS root-bed substrate. The brick sorbed substantially less P but is also less expensive and, therefore, may be a viable root bed substrate. Nutrient loading rate is very important. High nutrient inflow treatments were not adequately remediated with these experimental-scale systems, whereas the low and medium nutrient inflow treatments were efficiently assimilated. Hydraulic retention time was not a consistent factor influencing nutrient removal efficiency for N or P. The 4-day HRT resulted in consistently less P export from the CWS. Floating and rooted treatments demonstrated highly efficient N and P assimilation, while the horticulturally significant species were not as effective. Brick sorbed P efficiently but it saturated more quickly and did not reduce export concentrations as well as the industrial mineral aggregates, which effectively sorbed P from solution and reduced P exports from the mesocosms. The surface- to subsurface-flow CWS was effective at assimilating and fixing nutrients from simulated nursery runoff